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Sample records for advanced visible-light astronomical

  1. Advances and prospects in visible light communications

    NASA Astrophysics Data System (ADS)

    Hongda, Chen; Chunhui, Wu; Honglei, Li; Xiongbin, Chen; Zongyu, Gao; Shigang, Cui; Qin, Wang

    2016-01-01

    Visible light communication (VLC) is an emerging technology in optical wireless communication (OWC) that has attracted worldwide research in recent years. VLC can combine communication and illumination together, which could be applied in many application scenarios such as visible light communication local area networks (VLANs), indoor localization, and intelligent lighting. In recent years, pioneering and significant work have been made in the field of VLC. In this paper, an overview of the recent progress in VLC is presented. We also demonstrate our recent experiment results including bidirectional 100 Mbit/s VLAN or Li-Fi system based on OOK modulation without blue filter. The VLC systems that we proposed are good solutions for high-speed VLC application systems with low-cost and low-complexity. VLC technology shows a bright future due to its inherent advantages, shortage of RF spectra and ever increasing popularity of white LEDs. Project supported by the National High Technology Research and Development Program of China (Nos. 2015AA033303, 2013AA013602, 2013AA013603, 2013AA03A104), the National Natural Science Foundation of China (Nos. 61178051, 61321063, 61335010, 61178048, 61275169), and the National Basic Research Program of China (Nos. 2013CB329205, 2011CBA00608).

  2. High security chaotic multiple access scheme for visible light communication systems with advanced encryption standard interleaving

    NASA Astrophysics Data System (ADS)

    Qiu, Junchao; Zhang, Lin; Li, Diyang; Liu, Xingcheng

    2016-06-01

    Chaotic sequences can be applied to realize multiple user access and improve the system security for a visible light communication (VLC) system. However, since the map patterns of chaotic sequences are usually well known, eavesdroppers can possibly derive the key parameters of chaotic sequences and subsequently retrieve the information. We design an advanced encryption standard (AES) interleaving aided multiple user access scheme to enhance the security of a chaotic code division multiple access-based visible light communication (C-CDMA-VLC) system. We propose to spread the information with chaotic sequences, and then the spread information is interleaved by an AES algorithm and transmitted over VLC channels. Since the computation complexity of performing inverse operations to deinterleave the information is high, the eavesdroppers in a high speed VLC system cannot retrieve the information in real time; thus, the system security will be enhanced. Moreover, we build a mathematical model for the AES-aided VLC system and derive the theoretical information leakage to analyze the system security. The simulations are performed over VLC channels, and the results demonstrate the effectiveness and high security of our presented AES interleaving aided chaotic CDMA-VLC system.

  3. Towards advanced study of Active Galactic Nuclei with visible light adaptive optics

    NASA Astrophysics Data System (ADS)

    Ammons, Stephen Mark

    . These observations are meant to develop robust techniques for understanding AGN hosts at high spatial resolution. I present a new technique for constraining intrinsic color gradients in galaxies when a point spread function (PSF) is not well-constrained. Utilizing parametric 2-D fitting routines to compute aperture corrections, this method is more robust to PSF variation than most deconvolution methods. Future adaptive optics instrumentation may deliver the spatial resolution required to resolve circumnuclear starbursting in AGN and faint hosts around bright QSOs at redshifts beyond 1, which may be helpful for testing other predictions of AGN evolution theory. Toward this end, for the second part of my thesis, I describe the use of a laboratory mock-up of the adaptive optics system for a 10-meter telescope to demonstrate diffraction-limited imaging with laser guide stars at visible wavelengths (710 nm). This laser tomographic AO system maintains 24-34% Strehl over a 45" field in R-band. I present new developments in open-loop wavefront sensing and calibration that will be important for laser guide star visible-light AO systems on 8-10 meter class telescopes. These experiments lend credence to development of high-order, visible-light AO instrumentation on 8-10 meter telescopes in the coming decade.

  4. An Advanced Semimetal-Organic Bi Spheres-g-C3N4 Nanohybrid with SPR-Enhanced Visible-Light Photocatalytic Performance for NO Purification.

    PubMed

    Dong, Fan; Zhao, Zaiwang; Sun, Yanjuan; Zhang, Yuxin; Yan, Shuai; Wu, Zhongbiao

    2015-10-20

    To achieve efficient photocatalytic air purification, we constructed an advanced semimetal-organic Bi spheres-g-C3N4 nanohybrid through the in-situ growth of Bi nanospheres on g-C3N4 nanosheets. This Bi-g-C3N4 compound exhibited an exceptionally high and stable visible-light photocatalytic performance for NO removal due to the surface plasmon resonance (SPR) endowed by Bi metal. The SPR property of Bi could conspicuously enhance the visible-light harvesting and the charge separation. The electromagnetic field distribution of Bi spheres involving SPR effect was simulated and reaches its maximum in close proximity to the Bi particle surface. When the Bi metal content was controlled at 25%, the corresponding Bi-g-C3N4 displayed outstanding photocatalytic capability and transcended those of other visible-light photocatalysts. The Bi-g-C3N4 exhibited a high structural stability under repeated photocatalytic runs. A new visible-light-induced SPR-based photocatalysis mechanism with Bi-g-C3N4 was proposed on the basis of the DMPO-ESR spin-trapping. The photoinduced electrons could transfer from g-C3N4 to the Bi metal, as revealed with time-resolved fluorescence spectra. The function of Bi semimetal as a plasmonic cocatalyst for boosting visible light photocatalysis was similar to that of noble metals, which demonstrated a great potential of utilizing the economically feasible Bi element as a substitute for noble metals for the advancement of photocatalysis efficiency.

  5. An Advanced Semimetal-Organic Bi Spheres-g-C3N4 Nanohybrid with SPR-Enhanced Visible-Light Photocatalytic Performance for NO Purification.

    PubMed

    Dong, Fan; Zhao, Zaiwang; Sun, Yanjuan; Zhang, Yuxin; Yan, Shuai; Wu, Zhongbiao

    2015-10-20

    To achieve efficient photocatalytic air purification, we constructed an advanced semimetal-organic Bi spheres-g-C3N4 nanohybrid through the in-situ growth of Bi nanospheres on g-C3N4 nanosheets. This Bi-g-C3N4 compound exhibited an exceptionally high and stable visible-light photocatalytic performance for NO removal due to the surface plasmon resonance (SPR) endowed by Bi metal. The SPR property of Bi could conspicuously enhance the visible-light harvesting and the charge separation. The electromagnetic field distribution of Bi spheres involving SPR effect was simulated and reaches its maximum in close proximity to the Bi particle surface. When the Bi metal content was controlled at 25%, the corresponding Bi-g-C3N4 displayed outstanding photocatalytic capability and transcended those of other visible-light photocatalysts. The Bi-g-C3N4 exhibited a high structural stability under repeated photocatalytic runs. A new visible-light-induced SPR-based photocatalysis mechanism with Bi-g-C3N4 was proposed on the basis of the DMPO-ESR spin-trapping. The photoinduced electrons could transfer from g-C3N4 to the Bi metal, as revealed with time-resolved fluorescence spectra. The function of Bi semimetal as a plasmonic cocatalyst for boosting visible light photocatalysis was similar to that of noble metals, which demonstrated a great potential of utilizing the economically feasible Bi element as a substitute for noble metals for the advancement of photocatalysis efficiency. PMID:26375261

  6. Effects of visible light on the skin.

    PubMed

    Mahmoud, Bassel H; Hexsel, Camile L; Hamzavi, Iltefat H; Lim, Henry W

    2008-01-01

    Electromagnetic radiation has vast and diverse effects on human skin. Although photobiologic studies of sunlight date back to Sir Isaac Newton in 1671, most available studies focus on the UV radiation part of the spectrum. The effects of visible light and infrared radiation have not been, until recently, clearly elucidated. The goal of this review is to highlight the effects of visible light on the skin. As a result of advances in the understanding of skin optics, and comprehensive studies regarding the absorption spectrum of endogenous and exogenous skin chromophores, various biologic effects have been shown to be exerted by visible light radiation including erythema, pigmentation, thermal damage and free radical production. It has also been shown that visible light can induce indirect DNA damage through the generation of reactive oxygen species. Furthermore, a number of photodermatoses have an action spectrum in the visible light range, even though most of the currently available sunscreens offer, if any, weak protection against visible light. Conversely, because of its cutaneous biologic effects, visible light is used for the treatment of a variety of skin diseases and esthetic conditions in the form of lasers, intense pulsed light and photodynamic therapy.

  7. Recent advances in visible-light-responsive photocatalysts for hydrogen production and solar energy conversion--from semiconducting TiO2 to MOF/PCP photocatalysts.

    PubMed

    Horiuchi, Yu; Toyao, Takashi; Takeuchi, Masato; Matsuoka, Masaya; Anpo, Masakazu

    2013-08-28

    The present perspective describes recent advances in visible-light-responsive photocatalysts intended to develop novel and efficient solar energy conversion technologies, including water splitting and photofuel cells. Water splitting is recognized as one of the most promising techniques to convert solar energy as a clean and abundant energy resource into chemical energy in the form of hydrogen. In recent years, increasing concern is directed to not only the development of new photocatalytic materials but also the importance of technologies to produce hydrogen and oxygen separately. Photofuel cells can convert solar energy into electrical energy by decomposing bio-related compounds and livestock waste as fuels. The advances of photocatalysts enabling these solar energy conversion technologies have been going on since the discovery of semiconducting titanium dioxide materials and have extended to organic-inorganic hybrid materials, such as metal-organic frameworks and porous coordination polymers (MOF/PCP).

  8. Visible Light Communication Physical Layer Design for Jist Simulation

    NASA Astrophysics Data System (ADS)

    Tomaš, Boris

    2014-12-01

    Current advances in computer networking consider using visible light spectrum to encode and decode digital data. This approach is relatively non expensive. However, designing appropriate MAC or any other upper layer protocol for Visible Light Communication (VLC) requires appropriate hardware. This paper proposes and implements such hardware simulation (physical layer) that is compatible with existing network stack.

  9. Band engineered epitaxial 3D GaN-InGaN core-shell rod arrays as an advanced photoanode for visible-light-driven water splitting.

    PubMed

    Caccamo, Lorenzo; Hartmann, Jana; Fàbrega, Cristian; Estradé, Sonia; Lilienkamp, Gerhard; Prades, Joan Daniel; Hoffmann, Martin W G; Ledig, Johannes; Wagner, Alexander; Wang, Xue; Lopez-Conesa, Lluis; Peiró, Francesca; Rebled, José Manuel; Wehmann, Hergo-Heinrich; Daum, Winfried; Shen, Hao; Waag, Andreas

    2014-02-26

    3D single-crystalline, well-aligned GaN-InGaN rod arrays are fabricated by selective area growth (SAG) metal-organic vapor phase epitaxy (MOVPE) for visible-light water splitting. Epitaxial InGaN layer grows successfully on 3D GaN rods to minimize defects within the GaN-InGaN heterojunctions. The indium concentration (In ∼ 0.30 ± 0.04) is rather homogeneous in InGaN shells along the radial and longitudinal directions. The growing strategy allows us to tune the band gap of the InGaN layer in order to match the visible absorption with the solar spectrum as well as to align the semiconductor bands close to the water redox potentials to achieve high efficiency. The relation between structure, surface, and photoelectrochemical property of GaN-InGaN is explored by transmission electron microscopy (TEM), electron energy loss spectroscopy (EELS), Auger electron spectroscopy (AES), current-voltage, and open circuit potential (OCP) measurements. The epitaxial GaN-InGaN interface, pseudomorphic InGaN thin films, homogeneous and suitable indium concentration and defined surface orientation are properties demanded for systematic study and efficient photoanodes based on III-nitride heterojunctions. PMID:24517402

  10. How visible light curing came into dentistry.

    PubMed

    Wilson, N H F

    2016-01-01

    The present paper details the history of the introduction of visible light curing into dentistry. This history provides an excellent example of 'out of the box', lateral thinking translation of innovative scientific technology into dentistry. Visible light curing is an important UK contribution to the recent history and current practice of dentistry, with several million visible light curing procedures being carried out globally on a daily basis.

  11. Broadband Visible Light Induced NO Formation

    NASA Astrophysics Data System (ADS)

    Lubart, Rachel; Eichler, Maor; Friedmann, Harry; Savion, N.; Breitbart, Haim; Ankri, Rinat

    2009-06-01

    Nitric oxide formation is a potential mechanism for photobiomodulation because it is synthesized in cells by nitric oxide synthase (NOS), which contains both flavin and heme, and thus absorbs visible light. The purpose of this work was to study broadband visible light induced NO formation in various cells. Cardiac, endothelial, sperm cells and RAW 264.7 macrophages were illuminated with broadband visible light, 40-130 mW/cm2, 2.4-39 J/cm2, and nitric oxide production was quantified by using the Griess reagent. The results showed that visible light illumination increased NO concentration both in sperm and endothelial cells, but not in cardiac cells. Activation of RAW 264.7 macrophages was very small. It thus appears that NO is involved in photobiomodulation, though different light parameters and illumination protocols are needed to induce NO in various cells.

  12. Solar synthesis: prospects in visible light photocatalysis.

    PubMed

    Schultz, Danielle M; Yoon, Tehshik P

    2014-02-28

    Chemists have long aspired to synthesize molecules the way that plants do-using sunlight to facilitate the construction of complex molecular architectures. Nevertheless, the use of visible light in photochemical synthesis is fundamentally challenging because organic molecules tend not to interact with the wavelengths of visible light that are most strongly emitted in the solar spectrum. Recent research has begun to leverage the ability of visible light-absorbing transition metal complexes to catalyze a broad range of synthetically valuable reactions. In this review, we highlight how an understanding of the mechanisms of photocatalytic activation available to these transition metal complexes, and of the general reactivity patterns of the intermediates accessible via visible light photocatalysis, has accelerated the development of this diverse suite of reactions.

  13. Broadband Visible Light Induced NO Formation

    SciTech Connect

    Lubart, Rachel; Eichler, Maor; Friedmann, Harry; Ankri, Rinat; Savion, N.; Breitbart, Haim

    2009-06-19

    Nitric oxide formation is a potential mechanism for photobiomodulation because it is synthesized in cells by nitric oxide synthase (NOS), which contains both flavin and heme, and thus absorbs visible light. The purpose of this work was to study broadband visible light induced NO formation in various cells. Cardiac, endothelial, sperm cells and RAW 264.7 macrophages were illuminated with broadband visible light, 40-130 mW/cm2, 2.4-39 J/cm2, and nitric oxide production was quantified by using the Griess reagent. The results showed that visible light illumination increased NO concentration both in sperm and endothelial cells, but not in cardiac cells. Activation of RAW 264.7 macrophages was very small. It thus appears that NO is involved in photobiomodulation, though different light parameters and illumination protocols are needed to induce NO in various cells.

  14. Recent Advances for LGBT Astronomers in the United States

    NASA Astrophysics Data System (ADS)

    Dixon, William V.; Rigby, Jane; Oppenheimer, Rebecca

    2015-08-01

    The legal environment for lesbian, gay, bisexual, and transgender (LGBT) astronomers in the United States has changed dramatically in recent years. In 2013, the Supreme Court ruled that Section 3 of the Defense of Marriage Act (DOMA), which had barred the federal government from recognizing same-sex marriages, was unconstitutional. This decision particularly affects astronomers, since astronomers in the U.S. are more likely than the general population to be foreign nationals, to have a foreign-born spouse, or to work for the federal government. In 2014, the Attorney General directed the Department of Justice to take the position in litigation that the protection of Title VII of the Civil Rights Act of 1964 extends to claims of discrimination based on an individual’s gender identity, including transgender status. Title VII makes it unlawful for employers to discriminate in the employment of an individual “because of such individual’s... sex,” among other protected characteristics. As of March 2015, more than 70% of the population lives in states that recognize same-sex marriage, and the Supreme Court is expected to rule on the constitutionality of the remaining same-sex marriage bans during the current term. In this poster, we discuss these advances and their implications for the personal and professional lives of LGBT astronomers across the United States.

  15. Catadioptric lenses in Visible Light Communications

    NASA Astrophysics Data System (ADS)

    Garcia-Marquez, J.; Valencia, J. C.; Perez, H.; Topsu, S.

    2015-04-01

    Since few years ago, visible light communications (VLC) have experience an accelerated interest from a research point of view. The beginning of this decade has seen many improvements in VLC at an electronic level. High rates of transmission at low bit error ratios (BER) have been reported. A few numbers of start-ups have initiated activities to offer a variety of applications ranging from indoor geo-localization to internet, but in spite of these advancements, some other problems arise. Long-range transmissions mean a high BER which reduce the number of applications. In this sense, new redesigned optical collectors or in some cases, optical reflectors must be considered to ensure a low BER at higher distance transmissions. Here we also expose a preliminary design of a catadioptric and monolithical lens for a LI-FI receiver with two rotationally symmetrical main piecewise surfaces za and zb. These surfaces are represented in a system of cylindrical coordinates with an anterior surface za with a central and refractive sector surrounded by a peripheral reflective sector and a back piecewise surface zb with a central refractive sector and a reflective sector, both characterized as ideal for capturing light within large acceptance angles.

  16. [VISIBLE LIGHT AND HUMAN SKIN (REVIEW)].

    PubMed

    Tsibadze, A; Chikvaidze, E; Katsitadze, A; Kvachadze, I; Tskhvediani, N; Chikviladze, A

    2015-09-01

    Biological effect of a visible light depends on extend of its property to penetrate into the tissues: the greater is a wavelength the more is an effect of a radiation. An impact of a visible light on the skin is evident by wave and quantum effects. Quanta of a visible radiation carry more energy than infrared radiation, although an influence of such radiation on the skin is produced by the light spectrum on the boarder of the ultraviolet and the infrared rays and is manifested by thermal and chemical effects. It is determined that large doses of a visible light (405-436 nm) can cause skin erythema. At this time, the ratio of generation of free radicals in the skin during an exposure to the ultraviolet and the visible light range from 67-33% respectively. Visible rays of 400-500 nm length of wave cause an increase of the concentration of oxygen's active form and mutation of DNA and proteins in the skin. The urticaria in 4-18% of young people induced by photodermatosis is described. As a result of a direct exposure to sunlight photosensitive eczema is more common in elderly. Special place holds a hereditary disease - porphyria, caused by a visible light. In recent years, dermatologists widely use phototherapy. The method uses polychromatic, non-coherent (wavelength of 515-1200 nm) pulsating beam. During phototherapy/light treatment a patient is being exposed to sunlight or bright artificial light. Sources of visible light are lasers, LEDs and fluorescent lamps which have the full range of a visible light. Phototherapy is used in the treatment of acne vulgaris, seasonal affective disorders, depression, psoriasis, eczema and neurodermities. LED of the red and near infrared range also is characterized by the therapeutic effect. They have an ability to influence cromatophores and enhance ATP synthesis in mitochondria. To speed up the healing of wounds and stimulate hair growth light sources of a weak intensity are used. The light of blue-green spectrum is widely used for

  17. Broadband polygonal invisibility cloak for visible light.

    PubMed

    Chen, Hongsheng; Zheng, Bin

    2012-01-01

    Invisibility cloaks have recently become a topic of considerable interest thanks to the theoretical works of transformation optics and conformal mapping. The design of the cloak involves extreme values of material properties and spatially dependent parameter tensors, which are very difficult to implement. The realization of an isolated invisibility cloak in the visible light, which is an important step towards achieving a fully movable invisibility cloak, has remained elusive. Here, we report the design and experimental demonstration of an isolated polygonal cloak for visible light. The cloak is made of several elements, whose electromagnetic parameters are designed by a linear homogeneous transformation method. Theoretical analysis shows the proposed cloak can be rendered invisible to the rays incident from all the directions. Using natural anisotropic materials, a simplified hexagonal cloak which works for six incident directions is fabricated for experimental demonstration. The performance is validated in a broadband visible spectrum. PMID:22355767

  18. Broadband polygonal invisibility cloak for visible light

    PubMed Central

    Chen, Hongsheng; Zheng, Bin

    2012-01-01

    Invisibility cloaks have recently become a topic of considerable interest thanks to the theoretical works of transformation optics and conformal mapping. The design of the cloak involves extreme values of material properties and spatially dependent parameter tensors, which are very difficult to implement. The realization of an isolated invisibility cloak in the visible light, which is an important step towards achieving a fully movable invisibility cloak, has remained elusive. Here, we report the design and experimental demonstration of an isolated polygonal cloak for visible light. The cloak is made of several elements, whose electromagnetic parameters are designed by a linear homogeneous transformation method. Theoretical analysis shows the proposed cloak can be rendered invisible to the rays incident from all the directions. Using natural anisotropic materials, a simplified hexagonal cloak which works for six incident directions is fabricated for experimental demonstration. The performance is validated in a broadband visible spectrum. PMID:22355767

  19. Wavelength control of visible light laser diodes

    NASA Astrophysics Data System (ADS)

    Goto, N.; Fujii, T.; Nemoto, K.; Suzuki, H.; Nakagawa, K.; Otsu, M.

    1990-04-01

    Wavelength control of visible light laser diodes was studied. By combining an interferometer and a diffraction grating, it became possible to control the wavelength of continuous oscillation in the range of 664 to 673nm, the frequency fine control range being 2GHz. And the spectral linewidth was narrowed to about 44kHz (10 exp minus 7 nm). With the use of a collimator lens, the beam expansion was narrowed to 2mrad. It was confirmed that the pulse output of continuous oscillation visible light laser diodes can be amplified by the YAG laser excitation dye laser. In the case of pulse oscillation, oscillation of 1GHz spectral width was obtained at the wavelength of 0.8 micro m by using an injection synchronization method. In the injection synchronization method, other laser beam is injected in an oscillator and a superior laser beam of synchronized components alone is obtained. As the wavelength control method is now stabilized and satisfies the conditions of narrow band, it has the prospect to be applied to the laser uranium enrichment technology.

  20. Visible-Light-Induced Click Chemistry.

    PubMed

    Mueller, Jan O; Schmidt, Friedrich G; Blinco, James P; Barner-Kowollik, Christopher

    2015-08-24

    A rapid and catalyst-free cycloaddition system for visible-light-induced click chemistry is reported. A readily accessible photoreactive 2H-azirine moiety was designed to absorb light at wavelengths above 400 nm. Irradiation with low-energy light sources thus enables efficient small-molecule synthesis with a diverse range of multiple-bond-containing compounds. Moreover, in order to demonstrate the efficiency of the current approach, quantitative ligation of the photoactivatable chromophore with functional polymeric substrates was performed and full conversion with irradiation times of only 1 min at ambient conditions was achieved. The current report thus presents a highly efficient method for applications involving selective cycloaddition to electron-deficient multiple-bond-containing materials.

  1. Visible-Light-Activated Molecular Switches.

    PubMed

    Bléger, David; Hecht, Stefan

    2015-09-21

    The ability to influence key properties of molecular systems by using light holds much promise for the fields of materials science and life sciences. The cornerstone of such systems is molecules that are able to reversibly photoisomerize between two states, commonly referred to as photoswitches. One serious restriction to the development of functional photodynamic systems is the necessity to trigger switching in at least one direction by UV light, which is often damaging and penetrates only partially through most media. This review provides a summary of the different conceptual strategies for addressing molecular switches in the visible and near-infrared regions of the optical spectrum. Such visible-light-activated molecular switches tremendously extend the scope of photoswitchable systems for future applications and technologies.

  2. Visible light communications with compound spectra

    NASA Astrophysics Data System (ADS)

    Vitasek, Jan; Vasinek, Vladimir; Latal, Jan; Hajek, Lukas

    2016-03-01

    At present the Visible Light Communications (VLC) attract attention of academia and industry thanks to rapid progress in the development of white light emitting diodes (LED). This article deals with the VLC and proposes their new solution, which may help remove some lacks of the current VLC. The substance of the new VLC solution is purposeful suppression of a part of the spectrum by a notch filter and by subsequent reconstruction of the original spectrum. Thus, only a part of the visible spectrum will transmit the information data. This is the main difference in comparison with the current VLC. This might be the way how the crucial parameters of the VLC may be improved.

  3. A carpet cloak for visible light.

    PubMed

    Gharghi, Majid; Gladden, Christopher; Zentgraf, Thomas; Liu, Yongmin; Yin, Xiaobo; Valentine, Jason; Zhang, Xiang

    2011-07-13

    We report an invisibility carpet cloak device, which is capable of making an object undetectable by visible light. The cloak is designed using quasi conformal mapping and is fabricated in a silicon nitride waveguide on a specially developed nanoporous silicon oxide substrate with a very low refractive index (n<1.25). The spatial index variation is realized by etching holes of various sizes in the nitride layer at deep subwavelength scale creating a local effective medium index. The fabricated device demonstrates wideband invisibility throughout the visible spectrum with low loss. This silicon nitride on low index substrate can also be a general scheme for implementation of transformation optical devices at visible frequencies. PMID:21619019

  4. Visible Light Mediated Photoredox Catalytic Arylation Reactions.

    PubMed

    Ghosh, Indrajit; Marzo, Leyre; Das, Amrita; Shaikh, Rizwan; König, Burkhard

    2016-08-16

    Introducing aryl- and heteroaryl moieties into molecular scaffolds are often key steps in the syntheses of natural products, drugs, or functional materials. A variety of cross-coupling methods have been well established, mainly using transition metal mediated reactions between prefunctionalized substrates and arenes or C-H arylations with functionalization in only one coupling partner. Although highly developed, one drawback of the established sp2-sp2 arylations is the required transition metal catalyst, often in combination with specific ligands and additives. Therefore, photoredox mediated arylation methods have been developed as alternative over the past decade. We begin our survey with visible light photo-Meerwein arylation reactions, which allow C-H arylation of heteroarenes, enones, alkenes, and alkynes with organic dyes, such as eosin Y, as the photocatalyst. A good number of examples from different groups illustrate the broad application of the reaction in synthetic transformations. While initially only photo-Meerwein arylation-elimination processes were reported, the reaction was later extended to photo-Meerwein arylation-addition reactions giving access to the photoinduced three component synthesis of amides and esters from alkenes, aryl diazonium salts, nitriles or formamides, respectively. Other substrates with redox-active leaving groups have been explored in photocatalyzed arylation reactions, such as diaryliodonium and triarylsulfonium salts, and arylsulfonyl chlorides. We discus some examples with their scope and limitations. The scope of arylation reagents for photoredox reactions was extended to aryl halides. The challenge here is the extremely negative reduction potential of aryl halides in the initial electron transfer step compared to, e.g., aryl diazonium or diaryliodonium salts. In order to reach reduction potentials over -2.0 V vs SCE two consecutive photoinduced electron transfer steps were used. The intermediary formed colored radical

  5. Visible Light Mediated Photoredox Catalytic Arylation Reactions.

    PubMed

    Ghosh, Indrajit; Marzo, Leyre; Das, Amrita; Shaikh, Rizwan; König, Burkhard

    2016-08-16

    Introducing aryl- and heteroaryl moieties into molecular scaffolds are often key steps in the syntheses of natural products, drugs, or functional materials. A variety of cross-coupling methods have been well established, mainly using transition metal mediated reactions between prefunctionalized substrates and arenes or C-H arylations with functionalization in only one coupling partner. Although highly developed, one drawback of the established sp2-sp2 arylations is the required transition metal catalyst, often in combination with specific ligands and additives. Therefore, photoredox mediated arylation methods have been developed as alternative over the past decade. We begin our survey with visible light photo-Meerwein arylation reactions, which allow C-H arylation of heteroarenes, enones, alkenes, and alkynes with organic dyes, such as eosin Y, as the photocatalyst. A good number of examples from different groups illustrate the broad application of the reaction in synthetic transformations. While initially only photo-Meerwein arylation-elimination processes were reported, the reaction was later extended to photo-Meerwein arylation-addition reactions giving access to the photoinduced three component synthesis of amides and esters from alkenes, aryl diazonium salts, nitriles or formamides, respectively. Other substrates with redox-active leaving groups have been explored in photocatalyzed arylation reactions, such as diaryliodonium and triarylsulfonium salts, and arylsulfonyl chlorides. We discus some examples with their scope and limitations. The scope of arylation reagents for photoredox reactions was extended to aryl halides. The challenge here is the extremely negative reduction potential of aryl halides in the initial electron transfer step compared to, e.g., aryl diazonium or diaryliodonium salts. In order to reach reduction potentials over -2.0 V vs SCE two consecutive photoinduced electron transfer steps were used. The intermediary formed colored radical

  6. Imaging of Biological Tissues by Visible Light CDI

    NASA Astrophysics Data System (ADS)

    Karpov, Dmitry; Dos Santos Rolo, Tomy; Rich, Hannah; Fohtung, Edwin

    Recent advances in the use of synchrotron and X-ray free electron laser (XFEL) based coherent diffraction imaging (CDI) with application to material sciences and medicine proved the technique to be efficient in recovering information about the samples encoded in the phase domain. The current state-of-the-art algorithms of reconstruction are transferable to optical frequencies, which makes laser sources a reasonable milestone both in technique development and applications. Here we present first results from table-top laser CDI system for imaging of biological tissues and reconstruction algorithms development and discuss approaches that are complimenting the data quality improvement that is applicable to visible light frequencies due to it's properties. We demonstrate applicability of the developed methodology to a wide class of soft bio-matter and condensed matter systems. This project is funded by DOD-AFOSR under Award No FA9550-14-1-0363 and the LANSCE Professorship at LANL.

  7. Optical bidirectional beacon based visible light communications.

    PubMed

    Tiwari, Samrat Vikramaditya; Sewaiwar, Atul; Chung, Yeon Ho

    2015-10-01

    In an indoor bidirectional visible light communications (VLC), a line-of-sight (LOS) transmission plays a major role in obtaining adequate performance of a VLC system. Signals are often obstructed in the LOS transmission path, causing an effect called optical shadowing. In the absence of LOS, the performance of the VLC system degrades significantly and, in particular, at uplink transmission this degradation becomes severe due to design constraints and limited power at uplink devices. In this paper, a novel concept and design of an optical bidirectional beacon (OBB) is presented as an efficient model to counter the performance degradation in a non-line-of-sight (NLOS) VLC system. OBB is an independent operating bidirectional transceiver unit installed on walls, composed of red, green, and blue (RGB) light emitting diodes (LEDs), photodetectors (PDs) and color filters. OBB improves the coverage area in the form of providing additional or alternate paths for transmission and enhances the performance of the VLC system in terms of bit error rate (BER). To verify the effectiveness of the proposed system, simulations were carried out under optical shadowing conditions at various locations in an indoor environment. The simulation results and analysis show that the implementation of OBB improves the performance of the VLC system significantly, especially when the LOS bidirectional transmission paths are completely or partially obstructed.

  8. Bright visible light emission from graphene

    NASA Astrophysics Data System (ADS)

    Kim, Young Duck; Kim, Hakseong; Cho, Yujin; Ryoo, Ji Hoon; Park, Cheol-Hwan; Kim, Pilkwang; Kim, Yong Seung; Lee, Sunwoo; Li, Yilei; Park, Seung-Nam; Shim Yoo, Yong; Yoon, Duhee; Dorgan, Vincent E.; Pop, Eric; Heinz, Tony F.; Hone, James; Chun, Seung-Hyun; Cheong, Hyeonsik; Lee, Sang Wook; Bae, Myung-Ho; Park, Yun Daniel

    2015-08-01

    Graphene and related two-dimensional materials are promising candidates for atomically thin, flexible and transparent optoelectronics. In particular, the strong light-matter interaction in graphene has allowed for the development of state-of-the-art photodetectors, optical modulators and plasmonic devices. In addition, electrically biased graphene on SiO2 substrates can be used as a low-efficiency emitter in the mid-infrared range. However, emission in the visible range has remained elusive. Here, we report the observation of bright visible light emission from electrically biased suspended graphene devices. In these devices, heat transport is greatly reduced. Hot electrons (˜2,800 K) therefore become spatially localized at the centre of the graphene layer, resulting in a 1,000-fold enhancement in thermal radiation efficiency. Moreover, strong optical interference between the suspended graphene and substrate can be used to tune the emission spectrum. We also demonstrate the scalability of this technique by realizing arrays of chemical-vapour-deposited graphene light emitters. These results pave the way towards the realization of commercially viable large-scale, atomically thin, flexible and transparent light emitters and displays with low operation voltage and graphene-based on-chip ultrafast optical communications.

  9. Bright visible light emission from graphene.

    PubMed

    Kim, Young Duck; Kim, Hakseong; Cho, Yujin; Ryoo, Ji Hoon; Park, Cheol-Hwan; Kim, Pilkwang; Kim, Yong Seung; Lee, Sunwoo; Li, Yilei; Park, Seung-Nam; Yoo, Yong Shim; Yoon, Duhee; Dorgan, Vincent E; Pop, Eric; Heinz, Tony F; Hone, James; Chun, Seung-Hyun; Cheong, Hyeonsik; Lee, Sang Wook; Bae, Myung-Ho; Park, Yun Daniel

    2015-08-01

    Graphene and related two-dimensional materials are promising candidates for atomically thin, flexible and transparent optoelectronics. In particular, the strong light-matter interaction in graphene has allowed for the development of state-of-the-art photodetectors, optical modulators and plasmonic devices. In addition, electrically biased graphene on SiO2 substrates can be used as a low-efficiency emitter in the mid-infrared range. However, emission in the visible range has remained elusive. Here, we report the observation of bright visible light emission from electrically biased suspended graphene devices. In these devices, heat transport is greatly reduced. Hot electrons (∼2,800 K) therefore become spatially localized at the centre of the graphene layer, resulting in a 1,000-fold enhancement in thermal radiation efficiency. Moreover, strong optical interference between the suspended graphene and substrate can be used to tune the emission spectrum. We also demonstrate the scalability of this technique by realizing arrays of chemical-vapour-deposited graphene light emitters. These results pave the way towards the realization of commercially viable large-scale, atomically thin, flexible and transparent light emitters and displays with low operation voltage and graphene-based on-chip ultrafast optical communications.

  10. Measuring scintillation light using Visible Light

    NASA Astrophysics Data System (ADS)

    Chavarria, Alvaro

    2006-11-01

    A new search for the neutron electric dipole moment (EDM) using ultra cold neutrons proposes an improvement on the neutron EDM by two orders of magnitude over the current limit (to 10-28 e*cm). Detection of scintillation light in superfluid ^4He is at the heart of this experiment. One possible scheme to detect this light is to use wavelength-shifting fibers in the superfluid ^4He to collect the scintillation light and transport it out of the measuring cell. The fiber terminates in a visible light photon counter (VLPC). VLPCs are doped, silicon based, solid state photomultipliers with high quantum efficiency (up to 80%) and high gain ( 40000 electrons per converted photon). Moreover, they are insensitive to magnetic fields and operate at temperatures of 6.5K. A test setup has been assembled at Duke University using acrylic cells wrapped in wavelength-shifting fibers that terminate on VLPCs. This setup is being used to evaluate the feasibility of this light detection scheme. The results obtained in multiple experiments done over the past summer (2006) and the current status of the project will be presented at the conference.Reference:A New Search for the Neutron Electric Dipole Moment, funding pre-proposal by the EDM collaboration; R. Golub and S. Lamoreaux, Phys. Rep. 237, 1 (1994).

  11. Japanese Virtual Observatory (JVO) as an advanced astronomical research environment

    NASA Astrophysics Data System (ADS)

    Shirasaki, Yuji; Tanaka, Masahiro; Kawanomoto, Satoshi; Honda, Satoshi; Ohishi, Masatoshi; Mizumoto, Yoshihiko; Yasuda, Naoki; Masunaga, Yoshifumi; Ishihara, Yasuhide; Tsutsumi, Jumpei; Nakamoto, Hiroyuki; Kobayashi, Yuusuke; Sakamoto, Michito

    2006-06-01

    We present the design and implementation of the Japanese Virtual Observatory (JVO) system. JVO is a portal site to various kinds of astronomical resources distributed all over the world. We have developed five components for constructing the portal: (1) registry, (2) data service, (3) workflow system, (4) data analysis service (5) portal GUI. Registry services are used for publishing and searching data services in the VO, and they are constructed using an OAI-PMH metadata harvesting protocol and a SOAP web service protocol so that VO standard architecture is applied. Data services are developed based on the Astronomical Data Query Language (ADQL) which is an international VO standard and an extension of the standard SQL. The toolkit for building the ADQL-based service is released to the public on the JVO web site. The toolkit also provides the protocol translation from a Simple Image Access Protocol (SIAP) to ADQL protocol, so that both the VO standard service can be constructed using our toolkit. In order to federate the distributed databases and analysis services, we have designed a workflow language which is described in XML and developed execution system of the workflow. We have succeeded to connect to a hundred of data resources of the world as of April 2006. We have applied this system to the study of QSO environment by federating a QSO database, a Subaru Suprim-Cam database, and some analysis services such a SExtractor and HyperZ web services. These experiences are described is this paper.

  12. Integrating visible light 3D scanning into the everyday world

    NASA Astrophysics Data System (ADS)

    Straub, Jeremy

    2015-05-01

    Visible light 3D scanning offers the potential to non-invasively and nearly non-perceptibly incorporate 3D imaging into the everyday world. This paper considers the various possible uses of visible light 3D scanning technology. It discusses multiple possible usage scenarios including in hospitals, security perimeter settings and retail environments. The paper presents a framework for assessing the efficacy of visible light 3D scanning for a given application (and compares this to other scanning approaches such as those using blue light or lasers). It also discusses ethical and legal considerations relevant to real-world use and concludes by presenting a decision making framework.

  13. The Development of Visible-Light Photoredox Catalysis in Flow

    PubMed Central

    Garlets, Zachary J.; Nguyen, John D.

    2014-01-01

    Visible-light photoredox catalysis has recently emerged as a viable alternative for radical reactions otherwise carried out with tin and boron reagents. It has been recognized that by merging photoredox catalysis with flow chemistry, slow reaction times, lower yields, and safety concerns may be obviated. While flow reactors have been successfully applied to reactions carried out with UV light, only recent developments have demonstrated the same potential of flow reactors for the improvement of visible-light-mediated reactions. This review examines the initial and continuing development of visible-light-mediated photoredox flow chemistry by exemplifying the benefits of flow chemistry compared with conventional batch techniques. PMID:25484447

  14. Lethal effects of short-wavelength visible light on insects

    NASA Astrophysics Data System (ADS)

    Hori, Masatoshi; Shibuya, Kazuki; Sato, Mitsunari; Saito, Yoshino

    2014-12-01

    We investigated the lethal effects of visible light on insects by using light-emitting diodes (LEDs). The toxic effects of ultraviolet (UV) light, particularly shortwave (i.e., UVB and UVC) light, on organisms are well known. However, the effects of irradiation with visible light remain unclear, although shorter wavelengths are known to be more lethal. Irradiation with visible light is not thought to cause mortality in complex animals including insects. Here, however, we found that irradiation with short-wavelength visible (blue) light killed eggs, larvae, pupae, and adults of Drosophila melanogaster. Blue light was also lethal to mosquitoes and flour beetles, but the effective wavelength at which mortality occurred differed among the insect species. Our findings suggest that highly toxic wavelengths of visible light are species-specific in insects, and that shorter wavelengths are not always more toxic. For some animals, such as insects, blue light is more harmful than UV light.

  15. Indoor optical wireless communication by ultraviolet and visible light

    NASA Astrophysics Data System (ADS)

    Cui, Kaiyun; Chen, Gang; He, Qunfeng; Xu, Zhengyuan

    2009-08-01

    Visible light communication in conjunction with solid state lighting has become an emerging area of interest to achieve lighting and wireless communication simultaneously in an indoor environment. It is anticipated to be a low cost supplement to existing wireless communication technologies. Most existing work has primarily focused on a unidirectional downlink using visible light spectra. The appropriate choice of an uplink to achieve bidirectional communication is a big challenge. In this paper, candidate options of the uplink are compared in terms of device performance, light safety, background interference, and path loss. In visible light communication, white light emitting diodes as optical transmitters are also characterized in terms of impulse response and electrical spectrum. A digital preequalization idea to increase their bandwidth is proposed. Performance of the downlink visible light communication system is also experimentally studied in order to demonstrate the feasibility of the proposed design.

  16. Visible Light Responsive Catalyst for Air Water Purification Project

    NASA Technical Reports Server (NTRS)

    Wheeler, Raymond M.

    2014-01-01

    Investigate and develop viable approaches to render the normally UV-activated TIO2 catalyst visible light responsive (VLR) and achieve high and sustaining catalytic activity under the visible region of the solar spectrum.

  17. Lethal effects of short-wavelength visible light on insects.

    PubMed

    Hori, Masatoshi; Shibuya, Kazuki; Sato, Mitsunari; Saito, Yoshino

    2014-12-09

    We investigated the lethal effects of visible light on insects by using light-emitting diodes (LEDs). The toxic effects of ultraviolet (UV) light, particularly shortwave (i.e., UVB and UVC) light, on organisms are well known. However, the effects of irradiation with visible light remain unclear, although shorter wavelengths are known to be more lethal. Irradiation with visible light is not thought to cause mortality in complex animals including insects. Here, however, we found that irradiation with short-wavelength visible (blue) light killed eggs, larvae, pupae, and adults of Drosophila melanogaster. Blue light was also lethal to mosquitoes and flour beetles, but the effective wavelength at which mortality occurred differed among the insect species. Our findings suggest that highly toxic wavelengths of visible light are species-specific in insects, and that shorter wavelengths are not always more toxic. For some animals, such as insects, blue light is more harmful than UV light.

  18. A titanium and visible light-polymerized resin obturator.

    PubMed

    Rilo, Benito; da Silva, José Luis; Martinez-Insua, Arturo; Santana, Urbano

    2002-04-01

    Obturator prostheses are typically large, and their weight and size are often important design factors. This article describes the fabrication of an obturator prosthesis with a titanium framework and visible light-polymerized denture base resin. It is speculated that these low-density materials may produce prostheses lighter than similar ones made with conventional materials. An added advantage is that visible light-polymerizing resins facilitate relining. PMID:12011852

  19. Visible Light Sensitization of Vinyl Azides by Transition Metal Photocatalysis

    PubMed Central

    Farney, Elliot P.; Yoon, Tehshik P.

    2014-01-01

    Irradiation of vinyl and aryl azides with visible light in the presence of Ru photocatalysts results in the formation of reactive nitrenes, which can undergo a variety of C–N bond-forming reactions. The ability to use low-energy visible light instead of UV in the photochemical activation of azides avoids competitive photodecomposition processes that have long been a significant limitation on the synthetic utility of these reactions. PMID:24281908

  20. A titanium and visible light-polymerized resin obturator.

    PubMed

    Rilo, Benito; da Silva, José Luis; Martinez-Insua, Arturo; Santana, Urbano

    2002-04-01

    Obturator prostheses are typically large, and their weight and size are often important design factors. This article describes the fabrication of an obturator prosthesis with a titanium framework and visible light-polymerized denture base resin. It is speculated that these low-density materials may produce prostheses lighter than similar ones made with conventional materials. An added advantage is that visible light-polymerizing resins facilitate relining.

  1. Visible light alters yeast metabolic rhythms by inhibiting respiration.

    PubMed

    Robertson, James Brian; Davis, Chris R; Johnson, Carl Hirschie

    2013-12-24

    Exposure of cells to visible light in nature or in fluorescence microscopy often is considered to be relatively innocuous. However, using the yeast respiratory oscillation (YRO) as a sensitive measurement of metabolism, we find that non-UV visible light has a significant impact on yeast metabolism. Blue/green wavelengths of visible light shorten the period and dampen the amplitude of the YRO, which is an ultradian rhythm of cell metabolism and transcription. The wavelengths of light that have the greatest effect coincide with the peak absorption regions of cytochromes. Moreover, treating yeast with the electron transport inhibitor sodium azide has similar effects on the YRO as visible light. Because impairment of respiration by light would change several state variables believed to play vital roles in the YRO (e.g., oxygen tension and ATP levels), we tested oxygen's role in YRO stability and found that externally induced oxygen depletion can reset the phase of the oscillation, demonstrating that respiratory capacity plays a role in the oscillation's period and phase. Light-induced damage to the cytochromes also produces reactive oxygen species that up-regulate the oxidative stress response gene TRX2 that is involved in pathways that enable sustained growth in bright visible light. Therefore, visible light can modulate cellular rhythmicity and metabolism through unexpectedly photosensitive pathways.

  2. Water splitting on semiconductor catalysts under visible-light irradiation.

    PubMed

    Navarro Yerga, Rufino M; Alvarez Galván, M Consuelo; del Valle, F; Villoria de la Mano, José A; Fierro, José L G

    2009-01-01

    Sustainable hydrogen production is a key target for the development of alternative, future energy systems that will provide a clean and affordable energy supply. The Sun is a source of silent and precious energy that is distributed fairly all over the Earth daily. However, its tremendous potential as a clean, safe, and economical energy source cannot be exploited unless the energy is accumulated or converted into more useful forms. The conversion of solar energy into hydrogen via the water-splitting process, assisted by photo-semiconductor catalysts, is one of the most promising technologies for the future because large quantities of hydrogen can potentially be generated in a clean and sustainable manner. This Minireview provides an overview of the principles, approaches, and research progress on solar hydrogen production via the water-splitting reaction on photo-semiconductor catalysts. It presents a survey of the advances made over the last decades in the development of catalysts for photochemical water splitting under visible-light irradiation. The Minireview also analyzes the energy requirements and main factors that determine the activity of photocatalysts in the conversion of water into hydrogen and oxygen using sunlight. Remarkable progress has been made since the pioneering work by Fujishima and Honda in 1972, but he development of photocatalysts with improved efficiencies for hydrogen production from water using solar energy still faces major challenges. Research strategies and approaches adopted in the search for active and efficient photocatalysts, for example through new materials and synthesis methods, are presented and analyzed.

  3. Robotic visible-light laser adaptive optics

    NASA Astrophysics Data System (ADS)

    Baranec, Christoph; Riddle, Reed; Law, Nicholas; Ramaprakash, A. N.; Tendulkar, Shriharsh; Bui, Khanh; Burse, Mahesh; Chordia, Pravin; Das, Hillol; Dekany, Richard; Kulkarni, Shrinivas; Punnadi, Sujit

    2013-12-01

    Robo-AO is the first autonomous laser adaptive optics system and science instrument operating on sky. With minimal human oversight, the system robotically executes large scale surveys, monitors long-term astrophysical dynamics and characterizes newly discovered transients, all at the visible diffraction limit. The adaptive optics setup time, from the end of the telescope slew to the beginning of an observation, is a mere ~50-60 s, enabling over 200 observations per night. The first of many envisioned systems has finished 58 nights of science observing at the Palomar Observatory 60-inch (1.5 m) telescope, with over 6,400 robotic observations executed thus far. The system will be augmented in late 2013 with a low-noise wide field infrared camera, which doubles as a tip-tilt sensor, to widen the spectral bandwidth of observations and increase available sky coverage while also enabling deeper visible imaging using adaptive-optics sharpened infrared tip-tilt guide sources. Techniques applicable to larger telescope systems will also be tested: the infrared camera will be used to demonstrate advanced multiple region-of-interest tip-tilt guiding methods, and a visitor instrument port will be used for evaluation of other instrumentation, e.g. single-mode and photonic fibers to feed compact spectrographs.

  4. Visible light metasurfaces based on gallium nitride high contrast gratings

    NASA Astrophysics Data System (ADS)

    Wang, Zhenhai; He, Shumin; Liu, Qifa; Wang, Wei

    2016-05-01

    We propose visible-light metasurfaces (VLMs) capable of serving as lens and beam deflecting element based on gallium nitride (GaN) high contrast gratings (HCGs). By precisely manipulating the wavefront of the transmitted light, we theoretically demonstrate an HCG focusing lens with transmissivity of 86.3%, and a VLM with beam deflection angle of 6.09° and transmissivity as high as 91.4%. The proposed all-dielectric metasurfaces are promising for GaN-based visible light-emitting diodes (LEDs), which would be robust and versatile for controlling the output light propagation and polarization, as well as enhancing the extraction efficiency of the LEDs.

  5. In Vivo Visible Light-Triggered Drug Release From an Implanted Depot

    PubMed Central

    Carling, Carl-Johan; Viger, Mathieu L.; Huu, Viet Anh Nguyen; Garcia, Arnold V.; Almutairi, Adah

    2014-01-01

    Controlling chemistry in space and time has offered scientists and engineers powerful tools for research and technology. For example, on-demand photo-triggered activation of neurotransmitters has revolutionized neuroscience. Non-invasive control of the availability of bioactive molecules in living organisms will undoubtedly lead to major advances; however, this requires the development of photosystems that efficiently respond to regions of the electromagnetic spectrum that innocuously penetrate tissue. To this end, we have developed a polymer that photochemically degrades upon absorption of one photon of visible light and demonstrated its potential for medical applications. Particles formulated from this polymer release molecular cargo in vitro and in vivo upon irradiation with blue visible light through a photoexpansile swelling mechanism. PMID:25598962

  6. Developing Tools for Undergraduate Spectroscopy: An Inexpensive Visible Light Spectrometer

    ERIC Educational Resources Information Center

    Vanderveen, Jesse R.; Martin, Brian; Ooms, Kristopher J.

    2013-01-01

    The design and implementation of an inexpensive, high-resolution Littrow-type visible light spectrometer is presented. The instrument is built from low-cost materials and interfaced with the program RSpec for real-time spectral analysis, making it useful for classroom and laboratory exercises. Using a diffraction grating ruled at 1200 lines/mm and…

  7. Co doped ZnO nanowires as visible light photocatalysts

    NASA Astrophysics Data System (ADS)

    Šutka, Andris; Käämbre, Tanel; Pärna, Rainer; Juhnevica, Inna; Maiorov, Mihael; Joost, Urmas; Kisand, Vambola

    2016-06-01

    High aspect ratio cobalt doped ZnO nanowires showing strong photocatalytic activity and moderate ferromagnetic behaviour were successfully synthesized using a solvothermal method and characterized by scanning electron microscopy (SEM), X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS), X-ray absorption spectroscopy (XAS), vibrating sample magnetometry (VSM) and UV-visible absorption spectroscopy. The photocatalytic activities evaluated for visible light driven degradation of an aqueous methylene orange (MO) solution were higher than for Co doped ZnO nanoparticles at the same doping level and synthesized by the same synthesis route. The rate constant for MO visible light photocatalytic degradation was 1.9·10-3 min-1 in case of nanoparticles and 4.2·10-3 min-1 in case of nanowires. We observe strongly enhanced visible light photocatalytic activity for moderate Co doping levels, with an optimum at a composition of Zn0.95Co0.05O. The enhanced photocatalytic activities of Co doped ZnO nanowires were attributed to the combined effects of enhanced visible light absorption at the Co sites in ZnO nanowires, and improved separation efficiency of photogenerated charge carriers at optimal Co doping.

  8. Improved spring model-based collaborative indoor visible light positioning

    NASA Astrophysics Data System (ADS)

    Luo, Zhijie; Zhang, WeiNan; Zhou, GuoFu

    2016-06-01

    Gaining accuracy with indoor positioning of individuals is important as many location-based services rely on the user's current position to provide them with useful services. Many researchers have studied indoor positioning techniques based on WiFi and Bluetooth. However, they have disadvantages such as low accuracy or high cost. In this paper, we propose an indoor positioning system in which visible light radiated from light-emitting diodes is used to locate the position of receivers. Compared with existing methods using light-emitting diode light, we present a high-precision and simple implementation collaborative indoor visible light positioning system based on an improved spring model. We first estimate coordinate position information using the visible light positioning system, and then use the spring model to correct positioning errors. The system can be employed easily because it does not require additional sensors and the occlusion problem of visible light would be alleviated. We also describe simulation experiments, which confirm the feasibility of our proposed method.

  9. Established Designs For Advanced Ground Based Astronomical Telescopes In The 1-meter To 4-meter Domain

    NASA Astrophysics Data System (ADS)

    Hull, Anthony B.; Barentine, J.; Legters, S.

    2012-01-01

    The same technology and analytic approaches that led to cost-effective unmitigated successes for the spaceborne Kepler and WISE telescopes are now being applied to meter-class to 4-meter-class ground telescopes, providing affordable solutions to ground astronomy, with advanced features as needed for the application. The range of optical and mechanical performance standards and features that can be supplied for ground astronomy shall be described. Both classical RC designs, as well as unobscured designs are well represented in the IOS design library, allowing heritage designs for both night time and day time operations, the latter even in the proximity of the sun. In addition to discussing this library of mature features, we will also describe a process for working with astronomers early in the definition process to provide the best-value solution. Solutions can include remote operation and astronomical data acquisition and transmission.

  10. Conducting polymer nanostructures for photocatalysis under visible light

    NASA Astrophysics Data System (ADS)

    Ghosh, Srabanti; Kouamé, Natalie A.; Ramos, Laurence; Remita, Samy; Dazzi, Alexandre; Deniset-Besseau, Ariane; Beaunier, Patricia; Goubard, Fabrice; Aubert, Pierre-Henri; Remita, Hynd

    2015-05-01

    Visible-light-responsive photocatalysts can directly harvest energy from solar light, offering a desirable way to solve energy and environment issues. Here, we show that one-dimensional poly(diphenylbutadiyne) nanostructures synthesized by photopolymerization using a soft templating approach have high photocatalytic activity under visible light without the assistance of sacrificial reagents or precious metal co-catalysts. These polymer nanostructures are very stable even after repeated cycling. Transmission electron microscopy and nanoscale infrared characterizations reveal that the morphology and structure of the polymer nanostructures remain unchanged after many photocatalytic cycles. These stable and cheap polymer nanofibres are easy to process and can be reused without appreciable loss of activity. Our findings may help the development of semiconducting-based polymers for applications in self-cleaning surfaces, hydrogen generation and photovoltaics.

  11. Controlled release of fragrant molecules with visible light.

    PubMed

    Wang, Zhuozhi; Johns, Valentine K; Liao, Yi

    2014-11-01

    Controlled release of odorous molecules is the key to digital scent technology which will add another dimension to electronics. Photorelease is a cold mechanism that promises better temporal and spatial control than thermal release. Herein we report a novel material composed of an acid-sensitive polymer carrying a fragrant aldehyde and a reversible metastable-state photoacid. It releases the fragrant molecule under visible light, and stops releasing it after the light is turned off. A metastable-state photoacid with a fast reverse-reaction rate was developed to quickly stop the release after irradiation. Both the carrier polymer and the photoacid can be reused after all the fragrant molecules have been released. The material combines the advantages of visible-light activity, fast on/off rate, easy preparation, and recyclability, and thus is promising for digital scent technology. PMID:25284277

  12. Heterogeneous visible light photocatalysis for selective organic transformations.

    PubMed

    Lang, Xianjun; Chen, Xiaodong; Zhao, Jincai

    2014-01-01

    The future development of chemistry entails environmentally friendly and energy sustainable alternatives for organic transformations. Visible light photocatalysis can address these challenges, as reflected by recent intensive scientific endeavours to this end. This review covers state-of-the-art accomplishments in visible-light-induced selective organic transformations by heterogeneous photocatalysis. The discussion comprises three sections based on the photocatalyst type: metal oxides such as TiO2, Nb2O5 and ZnO; plasmonic photocatalysts like nanostructured Au, Ag or Cu supported on metal oxides; and polymeric graphitic carbon nitride. Finally, recent strides in bridging the gap between photocatalysis and other areas of catalysis will be highlighted with the aim of overcoming the existing limitations of photocatalysis by developing more creative synthetic methodologies.

  13. Hydrogen generation under visible light using nitrogen doped titania anodes

    SciTech Connect

    Lin, H.; Rumaiz, A.; Schulz, M.; Huang, C.P.; Sha, S. I.

    2010-06-16

    Hydrogen is among several energy sources that will be needed to replace the quickly diminishing fossil fuels. Free hydrogen is not available naturally on earth and the current processes require a fossil fuel, methane, to generate hydrogen. Electrochemical splitting of water on titania proposed by Fujishima suffers from low efficiency. The efficiency could be enhanced if full sun spectrum can be utilized. Using pulsed laser deposition technique we synthesized nitrogen doped titanium dioxide (TiO{sub 2-x}N{sub x}) thin films with improved visible light sensitivity. The photoactivity was found to be N concentration dependent. Hydrogen evolution was observed under visible light irradiation (wavelength > 390 nm) without the presence of any organic electron donor.

  14. Emission of Visible Light by Hot Dense Metals

    SciTech Connect

    More, R.M.; Goto, M.; Graziani, F.; Ni, P.A.; Yoneda, H.

    2009-12-01

    We consider the emission of visible light by hot metal surfaces having uniform and non-uniform temperature distributions and by small droplets of liquid metal. The calculations employ a nonlocal transport theory for light emission, using the Kubo formula to relate microscopic current fluctuations to the dielectric function of the material. We describe a related algorithm for calculating radiation emission in particle simulation of hot fusion plasmas.

  15. Hexaarylbiimidazoles as Visible Light Thiol–Ene Photoinitiators

    PubMed Central

    Clarkson, Brian H.; Scott, Timothy F.

    2015-01-01

    Objectives The aim of this study is to determine if hexaarylbiimidazoles (HABIs) are efficient, visible light-active photoinitiators for thiol–ene systems. We hypothesize that, owing to the reactivity of lophyl radicals with thiols and the necessarily high concentration of thiol in thiol–ene formulations, HABIs will effectively initiate thiol–ene polymerization upon visible light irradiation. Methods UV-vis absorption spectra of photoinitiator solutions were obtained using UV-vis spectroscopy, while EPR spectroscopy was used to confirm radical species generation upon HABI photolysis. Functional group conversions during photopolymerization were monitored using FTIR spectroscopy, and thermomechanical properties were determined using dynamic mechanical analysis. Results The HABI derivatives investigated exhibit less absorptivity than camphorquinone at 469 nm; however, they afford increased sensitivity at this wavelength when compared with bis(2,4,6-trimethylbenzoyl)-phenylphosphineoxide. Photolysis of the investigated HABIs affords lophyl radicals. Affixing hydroxyhexyl functional groups to the HABI core significantly improved solubility. Thiol–ene resins formulated with HABI photoinitiators polymerized rapidly upon irradiation with 469 nm. The glass transition temperatures of the thiol–ene resin formulated with a bis(hydroxyhexyl)-functionalized HABI and photopolymerized at room and body temperature were 49.5±0.5°C and 52.2±0.1°C, respectively. Significance Although thiol–enes show promise as continuous phases for composite dental restorative materials, they show poor reactivity with the conventional camphorquinone/tertiary amine photoinitiation system. Conversely, despite their relatively low visible light absorptivity, HABI photoinitiators afford rapid thiol–ene photopolymerization rates. Moreover, minor structural modifications suggest pathways for improved HABI solubility and visible light absorption. PMID:26119702

  16. Trifluoromethylation of alkenes by visible light photoredox catalysis.

    PubMed

    Iqbal, Naeem; Choi, Sungkyu; Kim, Eunjin; Cho, Eun Jin

    2012-12-21

    A method for trifluoromethylation of alkenes has been developed employing visible light photoredox catalysis with CF(3)I, Ru(Phen)(3)Cl(2), and DBU. This process works especially well for terminal alkenes to give alkenyl-CF(3) products with only E-stereochemistry. The mild reaction conditions enable the trifluoromethylation of a range of alkenes that bear various functional groups. PMID:23167602

  17. Rhenium complexes with visible-light-induced anticancer activity.

    PubMed

    Kastl, Anja; Dieckmann, Sandra; Wähler, Kathrin; Völker, Timo; Kastl, Lena; Merkel, Anna Lena; Vultur, Adina; Shannan, Batool; Harms, Klaus; Ocker, Matthias; Parak, Wolfgang J; Herlyn, Meenhard; Meggers, Eric

    2013-06-01

    Shedding light on the matter: Rhenium(I) indolato complexes with highly potent visible-light-triggered antiproliferative activity (complex 1: EC50 light=0.1 μM vs EC50 dark=100 μM) in 2D- and 3D-organized cancer cells are reported and can be traced back to an efficient generation of singlet oxygen, causing rapid morphological changes and an induction of apoptosis.

  18. A possible mechanism for visible-light-induced skin rejuvenation

    NASA Astrophysics Data System (ADS)

    Longo, Leonardo; Lubart, Rachel; Friedman, Harry; Lavie, R.

    2004-09-01

    In recent years there has been intensive research in the field of non-ablative skin rejuvenation. This comes as a response to the desire for a simple method of treating rhytids caused by aging, UV exposure and acne scars. In numerous studies intense visible light pulsed systems (20-30J/cm2) are used. The mechanism of action was supposed to be a selective heat induced denaturalization of dermal collagen that leads to subsequent reactive synthesis. In this study we suggest a different mechanism for photorejuvenation based on light induced Reactive Oxygen Species (ROS) formation. We irradiated collagen in-vitro with a broad band of visible light, 400-800 nm, 12-22J/cm2, and used the spin trapping coupled with electron paramagnetic resonance (EPR) spectroscopy to detect ROS. In vivo, we used dose 30 J in average (35 for acnis scars, 25 for wrinkles and redness). Irradiated collagen results in hydroxyl and methyl radicals formation. We propose, as a new concept, that visible light at the intensity used for skin rejuvenation, 20-30J/cm2, produces high amounts of ROS which destroy old collagen fibers encouraging the formation of new ones. On the other hand at inner depths of the skin, where the light intensity is much weaker, low amounts of ROS are formed which are well known to stimulate fibroblast proliferation.

  19. Hybrid bilayer plasmonic metasurface efficiently manipulates visible light

    PubMed Central

    Qin, Fei; Ding, Lu; Zhang, Lei; Monticone, Francesco; Chum, Chan Choy; Deng, Jie; Mei, Shengtao; Li, Ying; Teng, Jinghua; Hong, Minghui; Zhang, Shuang; Alù, Andrea; Qiu, Cheng-Wei

    2016-01-01

    Metasurfaces operating in the cross-polarization scheme have shown an interesting degree of control over the wavefront of transmitted light. Nevertheless, their inherently low efficiency in visible light raises certain concerns for practical applications. Without sacrificing the ultrathin flat design, we propose a bilayer plasmonic metasurface operating at visible frequencies, obtained by coupling a nanoantenna-based metasurface with its complementary Babinet-inverted copy. By breaking the radiation symmetry because of the finite, yet small, thickness of the proposed structure and benefitting from properly tailored intra- and interlayer couplings, such coupled bilayer metasurface experimentally yields a conversion efficiency of 17%, significantly larger than that of earlier single-layer designs, as well as an extinction ratio larger than 0 dB, meaning that anomalous refraction dominates the transmission response. Our finding shows that metallic metasurface can counterintuitively manipulate the visible light as efficiently as dielectric metasurface (~20% in conversion efficiency in Lin et al.’s study), although the metal’s ohmic loss is much higher than dielectrics. Our hybrid bilayer design, still being ultrathin (~λ/6), is found to obey generalized Snell’s law even in the presence of strong couplings. It is capable of efficiently manipulating visible light over a broad bandwidth and can be realized with a facile one-step nanofabrication process. PMID:26767195

  20. Fungal photobiology: visible light as a signal for stress, space and time

    PubMed Central

    Fuller, Kevin K.; Loros, Jennifer J.; Dunlap, Jay C.

    2014-01-01

    Visible light is an important source of energy and information for much of life on this planet. Though fungi are neither photosynthetic nor capable of observing adjacent objects, it is estimated that the majority of fungal species display some form of light response, ranging from developmental decision making to metabolic reprogramming to pathogenesis. As such, advances in our understanding of fungal photobiology will likely reach the broad fields impacted by these organisms, including agriculture, industry and medicine. In this review, we will first describe the mechanisms by which fungi sense light and then discuss the selective advantages likely imparted by their ability to do so. PMID:25323429

  1. Fungal photobiology: visible light as a signal for stress, space and time.

    PubMed

    Fuller, Kevin K; Loros, Jennifer J; Dunlap, Jay C

    2015-08-01

    Visible light is an important source of energy and information for much of life on this planet. Though fungi are neither photosynthetic nor capable of observing adjacent objects, it is estimated that the majority of fungal species display some form of light response, ranging from developmental decision-making to metabolic reprogramming to pathogenesis. As such, advances in our understanding of fungal photobiology will likely reach the broad fields impacted by these organisms, including agriculture, industry and medicine. In this review, we will first describe the mechanisms by which fungi sense light and then discuss the selective advantages likely imparted by their ability to do so.

  2. Asymmetric photoredox transition-metal catalysis activated by visible light

    NASA Astrophysics Data System (ADS)

    Huo, Haohua; Shen, Xiaodong; Wang, Chuanyong; Zhang, Lilu; Röse, Philipp; Chen, Liang-An; Harms, Klaus; Marsch, Michael; Hilt, Gerhard; Meggers, Eric

    2014-11-01

    Asymmetric catalysis is seen as one of the most economical strategies to satisfy the growing demand for enantiomerically pure small molecules in the fine chemical and pharmaceutical industries. And visible light has been recognized as an environmentally friendly and sustainable form of energy for triggering chemical transformations and catalytic chemical processes. For these reasons, visible-light-driven catalytic asymmetric chemistry is a subject of enormous current interest. Photoredox catalysis provides the opportunity to generate highly reactive radical ion intermediates with often unusual or unconventional reactivities under surprisingly mild reaction conditions. In such systems, photoactivated sensitizers initiate a single electron transfer from (or to) a closed-shell organic molecule to produce radical cations or radical anions whose reactivities are then exploited for interesting or unusual chemical transformations. However, the high reactivity of photoexcited substrates, intermediate radical ions or radicals, and the low activation barriers for follow-up reactions provide significant hurdles for the development of efficient catalytic photochemical processes that work under stereochemical control and provide chiral molecules in an asymmetric fashion. Here we report a highly efficient asymmetric catalyst that uses visible light for the necessary molecular activation, thereby combining asymmetric catalysis and photocatalysis. We show that a chiral iridium complex can serve as a sensitizer for photoredox catalysis and at the same time provide very effective asymmetric induction for the enantioselective alkylation of 2-acyl imidazoles. This new asymmetric photoredox catalyst, in which the metal centre simultaneously serves as the exclusive source of chirality, the catalytically active Lewis acid centre, and the photoredox centre, offers new opportunities for the `green' synthesis of non-racemic chiral molecules.

  3. Wireless visible light communication technology using optical beamforming

    NASA Astrophysics Data System (ADS)

    Kim, Sung-Man; Kim, Seong-Min

    2013-10-01

    We propose and demonstrate a new wireless visible light communication (VLC) technology using optical beamforming to improve signal-to-noise ratio (SNR) and transmission distance. Optical beamforming is a technology that can focus light-emitting diode (LED) light on a desired target device. Our experimental results show that SNR can be improved by 12 dB and transmission distance can be almost doubled by using optical beamforming. We can also control the modulation depth of the optical beamforming if we want to use the LED light as illumination at the same time. We also propose an algorithm to direct the beam to the target device automatically.

  4. Visible Light Communication System Using an Organic Bulk Heterojunction Photodetector

    PubMed Central

    Arredondo, Belén; Romero, Beatriz; Pena, José Manuel Sánchez; Fernández-Pacheco, Agustín; Alonso, Eduardo; Vergaz, Ricardo; de Dios, Cristina

    2013-01-01

    A visible light communication (VLC) system using an organic bulk heterojunction photodetector (OPD) is presented. The system has been successfully proven indoors with an audio signal. The emitter consists of three commercial high-power white LEDs connected in parallel. The receiver is based on an organic photodetector having as active layer a blend of poly(3-hexylthiophene) (P3HT) and phenyl C61-butyric acid methyl ester (PCBM). The OPD is opto-electrically characterized, showing a responsivity of 0.18 A/W and a modulation response of 790 kHz at −6 V. PMID:24036584

  5. Performance Analysis of Visible Light Communication Using CMOS Sensors

    PubMed Central

    Do, Trong-Hop; Yoo, Myungsik

    2016-01-01

    This paper elucidates the fundamentals of visible light communication systems that use the rolling shutter mechanism of CMOS sensors. All related information involving different subjects, such as photometry, camera operation, photography and image processing, are studied in tandem to explain the system. Then, the system performance is analyzed with respect to signal quality and data rate. To this end, a measure of signal quality, the signal to interference plus noise ratio (SINR), is formulated. Finally, a simulation is conducted to verify the analysis. PMID:26938535

  6. Organocatalyzed atom transfer radical polymerization driven by visible light.

    PubMed

    Theriot, Jordan C; Lim, Chern-Hooi; Yang, Haishen; Ryan, Matthew D; Musgrave, Charles B; Miyake, Garret M

    2016-05-27

    Atom transfer radical polymerization (ATRP) has become one of the most implemented methods for polymer synthesis, owing to impressive control over polymer composition and associated properties. However, contamination of the polymer by the metal catalyst remains a major limitation. Organic ATRP photoredox catalysts have been sought to address this difficult challenge but have not achieved the precision performance of metal catalysts. Here, we introduce diaryl dihydrophenazines, identified through computationally directed discovery, as a class of strongly reducing photoredox catalysts. These catalysts achieve high initiator efficiencies through activation by visible light to synthesize polymers with tunable molecular weights and low dispersities.

  7. Location-adaptive transmission for indoor visible light communication

    NASA Astrophysics Data System (ADS)

    Wang, Chun-yue; Wang, Lang; Chi, Xue-fen

    2016-01-01

    A location-adaptive transmission scheme for indoor visible light communication (VLC) system is proposed in this paper. In this scheme, the symbol error rate ( SER) of less than 10-3 should be guaranteed. And the scheme is realized by the variable multilevel pulse-position modulation (MPPM), where the transmitters adaptively adjust the number of time slots n in the MPPM symbol according to the position of the receiver. The purpose of our scheme is to achieve the best data rate in the indoor different locations. The results show that the location-adaptive transmission scheme based on the variable MPPM is superior in the indoor VLC system.

  8. A Spinel Oxynitride with Visible-Light Photocatalytic Activity

    SciTech Connect

    Boppana, V.; Doren, D; Lobo, R

    2010-01-01

    Spinel zinc gallium oxynitride photocatalysts are prepared by the sol-gel method, at 550 C. In these materials, of base composition ZnGa{sub 2}O{sub 4} (octahedral Ga), reaction with ammonia leads to ZnGa{sub 2}O{sub x}N{sub y}, with a dramatic reduction of the bandgap to 2.7 eV, with just 1.3% N and no loss of Zn. At 850 C this phase is converted into wurzite (tetrahedral Ga). The novel oxynitrides also show visible-light photocatalytic activity towards the degradation of methylene blue.

  9. Nanosecond high-power dense microplasma switch for visible light

    SciTech Connect

    Bataller, A. Koulakis, J.; Pree, S.; Putterman, S.

    2014-12-01

    Spark discharges in high-pressure gas are known to emit a broadband spectrum during the first 10 s of nanoseconds. We present calibrated spectra of high-pressure discharges in xenon and show that the resulting plasma is optically thick. Laser transmission data show that such a body is opaque to visible light, as expected from Kirchoff's law of thermal radiation. Nanosecond framing images of the spark absorbing high-power laser light are presented. The sparks are ideal candidates for nanosecond, high-power laser switches.

  10. Nanosecond high-power dense microplasma switch for visible light

    NASA Astrophysics Data System (ADS)

    Bataller, A.; Koulakis, J.; Pree, S.; Putterman, S.

    2014-12-01

    Spark discharges in high-pressure gas are known to emit a broadband spectrum during the first 10 s of nanoseconds. We present calibrated spectra of high-pressure discharges in xenon and show that the resulting plasma is optically thick. Laser transmission data show that such a body is opaque to visible light, as expected from Kirchoff's law of thermal radiation. Nanosecond framing images of the spark absorbing high-power laser light are presented. The sparks are ideal candidates for nanosecond, high-power laser switches.

  11. Resource allocation for multichannel broadcasting visible light communication

    NASA Astrophysics Data System (ADS)

    Le, Nam-Tuan; Jang, Yeong Min

    2015-11-01

    Visible light communication (VLC), which offers the possibility of using light sources for both illumination and data communications simultaneously, will be a promising incorporation technique with lighting applications. However, it still remains some challenges especially coverage because of field-of-view limitation. In this paper, we focus on this issue by suggesting a resource allocation scheme for VLC broadcasting system. By using frame synchronization and a network calculus QoS approximation, as well as diversity technology, the proposed VLC architecture and QoS resource allocation for the multichannel-broadcasting MAC (medium access control) protocol can solve the coverage limitation problem and the link switching problem of exhibition service.

  12. Asynchronous indoor positioning system based on visible light communications

    NASA Astrophysics Data System (ADS)

    Zhang, Weizhi; Chowdhury, M. I. Sakib; Kavehrad, Mohsen

    2014-04-01

    Indoor positioning has become an attractive research topic within the past two decades. However, no satisfying solution has been found with consideration of both accuracy and system complexity. Recently, research on visible light communications (VLC) offer new opportunities in realizing accurate indoor positioning with relatively simple system configuration. An indoor positioning system based on VLC technology is introduced, with no synchronization requirement on the transmitters. Simulation results show that, with over 95% confidence, the target receiver can be located with an accuracy of 5.9 cm, assuming indirect sunlight exposure and proper installation of light-emitting diode bulbs.

  13. Bactericidal mechanisms of Au@TNBs under visible light irradiation.

    PubMed

    Guo, Lingqiao; Shan, Chao; Liang, Jialiang; Ni, Jinren; Tong, Meiping

    2015-04-01

    Au@TNBs nanocomposites were synthesized by depositing Au nanoparticles onto the surfaces of TiO2 nanobelts (TNBs). The disinfection activities of Au@TNBs on model cell type, Gram-negative Escherichia coli (E. coli), were examined under visible light irradiation conditions. Au@TNBs exhibited stronger bactericidal properties toward E. coli than those of TNBs and Au NPs under visible light irradiation. The bactericidal mechanisms of Au@TNBs under light conditions were explored, specifically, the specific active species controlling the inactivation of bacteria were determined. Active species (H2O2, diffusing ∙OH, ∙O2-, 1O2, and e-) generated by Au@TNBs were found to play important roles on the inactivation of bacteria. Moreover, the concentrations of H2O2, ·OH, ·O2-, and 1O2 generated in the antimicrobial system were estimated. Without the presence of active species, the direct contact of Au@TNBs with bacterial cells was found to have no bactericidal effect. The reusability of Au@TNBs were also determined. Au@TNBs exhibited strong antibacterial activity toward E. coli even in five consecutively reused cycles. This study indicated that the fabricated Au@TNBs could be potentially utilized to inactivate bacteria in water.

  14. Visible light powered self-disinfecting coatings for influenza viruses

    NASA Astrophysics Data System (ADS)

    Weng, Ding; Qi, Hangfei; Wu, Ting-Ting; Yan, Ming; Sun, Ren; Lu, Yunfeng

    2012-04-01

    Influenza A viruses, the pathogens responsible for the recent swine flu outbreak and many historical pandemics, remain a threat to the public health. We report herein the fabrication of self-disinfecting surfaces from photoactive building nanocrystals, which can inactivate influenza viruses rapidly, spontaneously and continuously under visible light illumination.Influenza A viruses, the pathogens responsible for the recent swine flu outbreak and many historical pandemics, remain a threat to the public health. We report herein the fabrication of self-disinfecting surfaces from photoactive building nanocrystals, which can inactivate influenza viruses rapidly, spontaneously and continuously under visible light illumination. Electronic supplementary information (ESI) available: XRD, UV-Vis absorbance, TEM, AFM of as-prepared nanocrystals and as-fabricated self-disinfecting surfaces, disinfection of influenza A virus by TiO2 (P25) with UV irradiation as reference control, photoinactivation of influenza A virus envelope proteins and photoinactivation of trypsin. See DOI: 10.1039/c2nr30388d

  15. Strongly Coupled Nafion Molecules and Ordered Porous CdS Networks for Enhanced Visible-Light Photoelectrochemical Hydrogen Evolution.

    PubMed

    Zheng, Xue-Li; Song, Ji-Peng; Ling, Tao; Hu, Zhen Peng; Yin, Peng-Fei; Davey, Kenneth; Du, Xi-Wen; Qiao, Shi-Zhang

    2016-06-01

    Strongly coupled Nafion molecules and ordered porous CdS networks are fabricated for visible-light photoelectrochemical (PEC) hydrogen evolution. The Nafion layer coating shifts the band position of CdS upward and accelerates charge transfer in the photoelectrode/electrolyte interface. It is highly expected that the strong coupling effect between organic and inorganic materials will provide new routes to advance PEC water splitting. PMID:27038367

  16. Strongly Coupled Nafion Molecules and Ordered Porous CdS Networks for Enhanced Visible-Light Photoelectrochemical Hydrogen Evolution.

    PubMed

    Zheng, Xue-Li; Song, Ji-Peng; Ling, Tao; Hu, Zhen Peng; Yin, Peng-Fei; Davey, Kenneth; Du, Xi-Wen; Qiao, Shi-Zhang

    2016-06-01

    Strongly coupled Nafion molecules and ordered porous CdS networks are fabricated for visible-light photoelectrochemical (PEC) hydrogen evolution. The Nafion layer coating shifts the band position of CdS upward and accelerates charge transfer in the photoelectrode/electrolyte interface. It is highly expected that the strong coupling effect between organic and inorganic materials will provide new routes to advance PEC water splitting.

  17. Visible-light-accelerated oxygen vacancy migration in strontium titanate

    PubMed Central

    Li, Y.; Lei, Y.; Shen, B. G.; Sun, J. R.

    2015-01-01

    Strontium titanate is a model transition metal oxide that exhibits versatile properties of special interest for both fundamental and applied researches. There is evidence that most of the attractive properties of SrTiO3 are closely associated with oxygen vacancies. Tuning the kinetics of oxygen vacancies is then highly desired. Here we reported on a dramatic tuning of the electro-migration of oxygen vacancies by visible light illumination. It is found that, through depressing activation energy for vacancy diffusion, light illumination remarkably accelerates oxygen vacancies even at room temperature. This effect provides a feasible approach towards the modulation of the anionic processes. The principle proved here can be extended to other perovskite oxides, finding a wide application in oxide electronics. PMID:26420376

  18. Performance of indoor optical femtocell by visible light communication

    NASA Astrophysics Data System (ADS)

    Cui, Kaiyun; Quan, Jinguo; Xu, Zhengyuan

    2013-07-01

    Femotocell has been proposed and deployed to improve the indoor coverage and capacity of a cellular network. One big challenge in its deployment is the interference between the macrocell and femtocell cellular networks. In this paper we propose a new physical layer for the implementation of indoor femtocells - optical femtocells by LED-based visible light communication. A general system structure of the indoor optical femtocell network is first introduced. A combined wavelength division and code division multiple access scheme is proposed to differentiate cells and multiple users within a cell. This scheme coupled with directional beaming characteristics of the LEDs helps to mitigate intercell interference and intracell inference. The communication performance adopting the dimming compatible variable-PPM modulation suggested by the IEEE standard is analyzed. Monte-Carlo simulation is then carried out to reveal the system performance numerically under typical system settings and effects of various parameters.

  19. Theory of Visible Light Emission from Scanning Tunneling Microscope

    NASA Astrophysics Data System (ADS)

    Uehara, Yoichi; Kimura, Yuichi; Ushioda, Sukekatsu; Takeuchi, Koichiro

    1992-08-01

    The mechanism for visible light emission from the scanning tunneling microscope (STM) has been investigated theoretically by adapting a theory for light emitting tunnel junctions (LETJ). From the analysis of the calculated results and available experimental data, the following picture emerges. The tunneling current first excites localized surface plasmons (LSP) that are localized in a region of a few tens of Angstroms between the STM tip-front and the sample surface. Some of them decay into surface plasmon polaritons (SPP) that propagate along the sample surface. There are two channels of light emission: one is direct emission from LSP and the other is emission through SPP. The relative branching ratio between these two channels depends on the experimental configuration. The effect of sample surface roughness is very small and negligible.

  20. Visible light photocatalysis as a greener approach to photochemical synthesis

    NASA Astrophysics Data System (ADS)

    Yoon, Tehshik P.; Ischay, Michael A.; Du, Juana

    2010-07-01

    Light can be considered an ideal reagent for environmentally friendly, 'green' chemical synthesis; unlike many conventional reagents, light is non-toxic, generates no waste, and can be obtained from renewable sources. Nevertheless, the need for high-energy ultraviolet radiation in most organic photochemical processes has limited both the practicality and environmental benefits of photochemical synthesis on industrially relevant scales. This Perspective describes recent approaches to the use of metal polypyridyl photocatalysts in synthetic organic transformations. Given the remarkable photophysical properties of these complexes, these new transformations, which use Ru(bpy)32+ and related photocatalysts, can be conducted using almost any source of visible light, including both store-bought fluorescent light bulbs and ambient sunlight. Transition metal photocatalysis thus represents a promising strategy towards the development of practical, scalable industrial processes with great environmental benefits.

  1. A Reversible Photoacid Functioning in PBS Buffer under Visible Light.

    PubMed

    Abeyrathna, Nawodi; Liao, Yi

    2015-09-01

    A metastable-state photoacid that can reversibly release a proton in PBS buffer (pH = 7.4) under visible light is reported. The design is based on the dual acid-base property and tautomerization of indazole. The quantum yield was as high as 0.73, and moderate light intensity (10(2) μmol·m(2)·s(-1)) is sufficient for the photoreaction. Reversible pH change of 1.7 units was demonstrated using a 0.1 mM aqueous solution. This type of photoacid is promising for control of proton-transfer processes in physiological conditions and may find applications in biomedical areas.

  2. Visible light responsive systems based on metastable-state photoacids

    NASA Astrophysics Data System (ADS)

    Liao, Yi

    2015-09-01

    Proton transfer is one of the most fundamental processes in nature. Metastable-state photoacids can reversibly generate a large proton concentration under visible light with moderate intensity. which provides a general approach to control various proton transfer processes. Several applications of mPAHs have been demonstrated recently including control of acid-catalyzed reactions, volume-change of hydrogels, polymer conductivity, bacteria killing, odorant release, and color change of materials. They have also been utilized to control supramolecular assemblies, molecular switches, microbial fuel cells and cationic sensors. In this talk, the mechanism, structure design, and applications of metastable-state photoacids are introduced. Recent development of different types of metastable-state photoacids is presented. Challenges and future work are also discussed.

  3. An integrated PIN-array receiver for visible light communication

    NASA Astrophysics Data System (ADS)

    Li, Jie-Hui; Huang, Xing-Xing; Ji, Xin-Ming; Chi, Nan; Shi, Jian-Yang

    2015-10-01

    This paper first designs and demonstrates an integrated receiver for a visible light communication (VLC) system based on RGB LED and an array of silicon PIN diode detectors. The system uses a maximal ratio combining (MRC) algorithm to enhance system performance. The novel integrated PIN diode array design yields a high date rate of 1.2 Gbit s-1 by 16QAM-OFDM based on a commercially available RGB LED in a VLC system with bit error rate under a 7% pre-forward-error-correction (FEC) threshold of 3.8 × 10-3 after 30 cm free-space transmission. The results show that the use of integrated antennas in VLC systems will become a trend in the future.

  4. CO2 SEQUESTRATION AND RECYCLE BY PHOTOCATALYSIS WITH VISIBLE LIGHT

    SciTech Connect

    Steven S.C. Chuang

    2001-10-01

    Visible light-photocatalysis could provide a cost-effective route to recycle CO{sub 2} to useful chemicals or fuels. Development of an effective catalyst for the photocatalytic synthesis requires (i) the knowledge of the surface band gap and its relation to the surface structure, (ii) the reactivity of adsorbates and their reaction pathways, and (iii) the ability to manipulate the actives site for adsorption, surface reaction, and electron transfer. The objective of this research is to study the photo-catalytic activity of TiO{sub 2}-base catalyst. A series of TiO{sub 2}-supported metal catalysts were prepared for determining the activity and selectivity for the synthesis of methane and methanol. 0.5 wt% Cu/SrTiO{sub 3} was found to be the most active and selective catalyst for methanol synthesis. The activity of the catalyst decreased in the order: Ti silsesquioxane > Cu/SrTiO{sub 3} > Pt/TiO{sub 2} > Cu/TiO{sub 2} > TiO{sub 2} > Rh/TiO{sub 2}. To further increase the number of site for the reaction, we propose to prepare monolayer and multiplayer TiOx on high surface area mesoporous oxides. These catalysts will be used for in situ IR study in the Phase II research project to determine the reactivity of adsorbates. Identification of active adsorbates and sites will allow incorporation of acid/basic sites to alter the nature of CO{sub 2} and H{sub 2}O adsorbates and with Pt/Cu sites to direct reaction pathways of surface intermediates, enhancing the overall activity and selectivity for methanol and hydrocarbon synthesis. The overall goal of this research is to provide a greater predictive capability for the design of visible light-photosynthesis catalysts by a deeper understanding of the reaction kinetics and mechanism as well as by better control of the coordination/chemical environment of active sites.

  5. Photocatalytic activities of various pentavalent bismuthates under visible light irradiation

    SciTech Connect

    Takei, Takahiro; Haramoto, Rie; Dong, Qiang; Kumada, Nobuhiro; Yonesaki, Yoshinori; Kinomura, Nobukazu; Mano, Takayuki; Nishimoto, Shunsuke; Kameshima, Yoshikazu; Miyake, Michihiro

    2011-08-15

    LiBiO{sub 3}, NaBiO{sub 3}, MgBi{sub 2}O{sub 6}, KBiO{sub 3}, ZnBi{sub 2}O{sub 6}, SrBi{sub 2}O{sub 6}, AgBiO{sub 3}, BaBi{sub 2}O{sub 6} and PbBi{sub 2}O{sub 6} were synthesized by various processes such as hydrothermal treatment, heating and so on. These materials were examined for their photocatalytic activities in the decolorization of methylene blue and decomposition of phenol under visible light irradiation. For methylene blue decolorization, the presence of KBiO{sub 3} resulted in complete decoloration within 5 min. For phenol decomposition, NaBiO{sub 3} showed the highest activity, while LiBiO{sub 3}, SrBi{sub 2}O{sub 6} and BaBi{sub 2}O{sub 6} possessed almost comparable decomposition rates. Their decomposition rates were apparently higher than that by anatase (P25) under UV irradiation. - Graphical abstract: Nine pentavalent bismuthates were synthesized and were examined for their photocatalytic activities by decomposition of phenol under visible light irradiation. NaBiO{sub 3}, LiBiO{sub 3}, SrBi{sub 2}O{sub 6} and BaBi{sub 2}O{sub 6} indicated faster decomposition rate than that of anatase (P25) under UV-vis light irradiation. Highlights: > KBiO{sub 3} decolorize methylene blue aqueous solution immediately within 5 min. > NaBiO{sub 3}, LiBiO{sub 3}, SrBi{sub 2}O{sub 6} and BaBi{sub 2}O{sub 6} indicated high decomposition rate of phenol. > The d electron of Zn, Ag and Pb form broad conduction band. > The broad conduction band poses to diminish photocatalytic activity.

  6. Functional inactivation of lymphocytes by methylene blue with visible light.

    PubMed

    Zhang, Bo; Cheng, Zhenzhen; Mo, Qin; Wang, Li; Wang, Xun; Wu, Xiaofei; Jia, Yao; Huang, Yuwen

    2015-10-01

    Transfusion of allogeneic white blood cells (WBCs) may cause adverse reactions in immunocompromised recipients, including transfusion-associated graft-versus-host disease (TA-GVHD), which is often fatal and incurable. In this study, the in vitro effect of methylene blue with visible light (MB + L) treatment on lymphocyte proliferation and cytokine production was measured to investigate whether MB + L can be used to prevent immune reactions that result from transfused lymphocytes. WBCs and 3 μM of MB were mixed and transferred into medical PVC bags, which were then exposed to visible light. Gamma irradiation was conducted as a parallel positive control. The cells without treatment were used as untreated group. All the groups were tested for the ability of cell proliferation and cytokine production upon stimulation. After incubation with mitogen phytohemagglutinin (PHA) or plate-bound anti-CD3 plus anti-CD28, the proliferation of MB + L/gamma-irradiation treated lymphocytes was significantly inhibited (P < 0.01) as compared to the untreated ones; the proliferation inhibitive rate of the MB + L group was even higher than that of gamma-irradiated cells (73.77% ± 28.75% vs. 44.72% ± 38.20%). MB + L treated cells incubated up to 7 days with PHA also showed no significant proliferation. The levels of TNF-α, IFN-γ, IL-6, IL-8, IL-10 and IL-1β present in the supernatant of MB + L treated lymphocytes upon stimulation were significantly lower than those of untreated lymphocytes. These results demonstrated that MB + L treatment functionally and irreversibly inactivated lymphocytes by inhibiting lymphocyte proliferation and the production of cytokines. MB + L treatment might be a promising method for the prevention of adverse immune responses caused by WBCs. PMID:26295729

  7. Enhanced thermal stability under DC electrical conductivity retention and visible light activity of Ag/TiO₂@polyaniline nanocomposite film.

    PubMed

    Ansari, Mohd Omaish; Khan, Mohammad Mansoob; Ansari, Sajid Ali; Raju, Kati; Lee, Jintae; Cho, Moo Hwan

    2014-06-11

    The development of organic-inorganic photoactive materials has resulted in significant advancements in heterogeneous visible light photocatalysis. This paper reports the synthesis of visible light-active Ag/TiO2@Pani nanocomposite film via a simple biogenic-chemical route. Electrically conducting Ag/TiO2@Pani nanocomposites were prepared by incorporating Ag/TiO2 in N-methyl-2-pyrrolidone solution of polyaniline (Pani), followed by the preparation of Ag/TiO2@Pani nanocomposite film using solution casting technique. The synthesized Ag/TiO2@Pani nanocomposite was confirmed by UV-visible spectroscopy, photoluminescence spectroscopy, scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and thermogravimetric analysis. The Ag/TiO2@Pani nanocomposite film showed superior activity towards the photodegradation of methylene blue under visible light compared to Pani film, even after repeated use. Studies on the thermoelectrical behavior by DC electrical conductivity retention under cyclic aging techniques showed that the Ag/TiO2@Pani nanocomposite film possessed a high combination of electrical conductivity and thermal stability. Because of its better thermoelectric performance and photodegradation properties, such materials might be a suitable advancement in the field of smart materials in near future.

  8. VISION: A Six-Telescope Fiber-Fed Visible Light Beam Combiner for the Navy Precision Optical Interferometer

    NASA Astrophysics Data System (ADS)

    Garcia, Eugenio; Muterspaugh, Matthew W.; van Belle, Gerard; Monnier, John D.; Stassun, Keivan; Ghasempour, Askari; Swihart, Samuel

    2016-01-01

    Visible-light long baseline interferometry holds the promise of advancing a number of important applications in fundamental astronomy, including the direct measurement of the angular diameters and oblateness of stars, and the direct measurement of the orbits of binary and multiple star systems. To advance, the field of visible-light interferometry requires development of instruments capable of combining more than just two or three beams at once. The Visible Imaging System for Interferometric Observations at NPOI (VISION) is a new visible light beam combiner for the Navy Precision Optical Interferometer (NPOI) that uses single-mode fibers to coherently combine light from up to six telescopes simultaneously with an image-plane combination scheme. It features a photometric camera for calibrations, and spatial filtering from single-mode fibers with two Andor Ixon electron multiplying CCDs. Here we present the VISION system, results of laboratory tests, and results of commissioning on-sky observations. We determine a new set of corrections to the power spectrum and bispectrum when using an electron-multipying CCD to measure visibility and closure phase, by taking into account non-Gaussian statistics and read noise, as required by our post-processing pipeline. We verify our post-processing pipeline via new on-sky observations of the O-type supergiant binary Zeta Orionis A, obtaining a flux ratio, position angle and separation in good agreement with expectations from the previously published orbit.

  9. A cryogenic dichroic mirror for separating visible light from wideband infrared

    NASA Astrophysics Data System (ADS)

    Enya, K.; Fujishiro, N.; Haze, K.; Kotani, T.; Kaneda, H.; Oyabu, S.; Ishihara, D.; Oseki, S.

    2014-08-01

    We present the design, fabrication and test results for a dichroic mirror, which was primarily developed for the SPICA Coronagraph Instrument (SCI), but is potentially useful for various types of astronomical instrument. The dichroic mirror is designed to reflect near- and mid-infrared but to transmit visible light. Two designs, one with 3 layers and one with 5 layers on BK7 glass substrates, are presented. The 3-layer design, consisting of Ag and ZnS, is simpler, and the 5-layer design, consisting of Ag and TiO2 is expected to have better performance. Tape tests, evaluation of the surface figure, and measurements of the reflectivity and transmittance were carried out at ambient temperature in air. The reflectivity obtained from measurements made on mirrors with 5 layers were < 80 % for wavelengths, λ, from 1.2 to 22 μm and < 90 % for λ from 1.8 to 20 μm. The transmittance obtained from measurements made on mirrors with 5 layers were < 70 % for λ between 0.4 and 0.8 μm. Optical ghosting is estimated to be smaller than 10-4 at λ < 1.5 μm. A protective coating for preventing corrosion was applied and its influence on the reflectivity and transmittance evaluated. A study examining the trade-offs imposed by various configurations for obtaining a telescope pointing correction signal was also undertaken.

  10. Visible Light Induces Melanogenesis in Human Skin through a Photoadaptive Response.

    PubMed

    Randhawa, Manpreet; Seo, InSeok; Liebel, Frank; Southall, Michael D; Kollias, Nikiforos; Ruvolo, Eduardo

    2015-01-01

    Visible light (400-700 nm) lies outside of the spectral range of what photobiologists define as deleterious radiation and as a result few studies have studied the effects of visible light range of wavelengths on skin. This oversight is important considering that during outdoors activities skin is exposed to the full solar spectrum, including visible light, and to multiple exposures at different times and doses. Although the contribution of the UV component of sunlight to skin damage has been established, few studies have examined the effects of non-UV solar radiation on skin physiology in terms of inflammation, and limited information is available regarding the role of visible light on pigmentation. The purpose of this study was to determine the effect of visible light on the pro-pigmentation pathways and melanin formation in skin. Exposure to visible light in ex-vivo and clinical studies demonstrated an induction of pigmentation in skin by visible light. Results showed that a single exposure to visible light induced very little pigmentation whereas multiple exposures with visible light resulted in darker and sustained pigmentation. These findings have potential implications on the management of photo-aggravated pigmentary disorders, the proper use of sunscreens, and the treatment of depigmented lesions.

  11. Long-range visible light communication system based on LED collimating lens

    NASA Astrophysics Data System (ADS)

    Chen, Yingcong; Wen, Shangsheng; Wu, Yuxiang; Ren, Yuanyuan; Guan, Weipeng; Zhou, Yunlin

    2016-10-01

    An advanced visible light communication (VLC) system is proposed for long-range VLC, such as marine communication. The design of the system is conducted into two parts. Firstly, we design and optimize a collimating lens for the optical antenna by using Taguchi method. The lighting effects and optical power of the receiving end in different distances are simulated by TracePro software. Then, the long-range VLC channel is reconstructed by integrating the influence of the atmospheric attenuation and frequency response. The performance of the OOK coding VLC system is tested by Matlab software. The results show that: the emitting angle of the optimized collimating lens is 1.7°. By using 1 W LED and collimating lens as an optical antenna, the system can achieve a data rate of 210 Mbit/s at a bit error rate of 10-3 in 90 m.

  12. Performance study for indoor visible light communication systems

    NASA Astrophysics Data System (ADS)

    Gao, Shuo

    The field of Optical Wireless Communications (OWC) has seen rapid development during the recent years. This growing popularity is due to several characteristics of considerable importance to consumer electronics products, such as large bandwidth that is also not having spectrum regulations imposed, low cost, and license free operation. As a branch of OWC, visible light communication (VLC) systems have their own unique advantages, with several new technologies, products and patents having been developed during since the end of last century. In this research, a VLC system for indoor application is proposed. In this work, we focus on reducing cost, and for that, we had to make appropriate selection of system's components, e.g. modulation, coding, filtering. Our objective was to achieve acceptable bit error rate (BER) performance for indoor use, with a low cost system. Through our research we met this objective. Our designs were evaluated through computer simulations. The acquired results proved the suitability of the proposed schemes and the performance's degree of dependency on several parameters such as distance, incidence angle and irradiance angle. A software tool was created allowing easy assessment of the communication system. It is using a user friendly GUI through which the user enters the system's parameters and the system outputs the corresponding BER value.

  13. Studies on microleakage associated with visible light cured dental composites.

    PubMed

    Krishnan, V K; Bindhu, D B; Manjusha, K

    1996-04-01

    The objective of this investigation was twofold: 1) to determine the extent of microleakage associated with two visible light cured dental composites, one of which is an indigenously developed light cure composite (chitra light cure system) compared with a commercially available control material (Prisma APH light cure system), and 2) to study the effect of using bonding agents upon the above phenomena. The bonding agents used along with the above composites during restoration were chitra bonding agent system containing chitra primer/chitra resin and a control (Probond) which was purchased commercially. A comparison of microleakage in freshly restored human premolar teeth by silver nitrate staining technique was made during the above study. Cavities were restored with both composites with and without bonding agents, stored in 50 percent silver nitrate, and sections were cut after developing. The microtomed sections were observed under the optical light microscope and scanning electron microscope. Results indicate that bonding agents are mandatory for effective bonding at the tooth/resin interface and subsequent reduction in marginal leakage. Chitra bonding agent showed excellent adhesive bonding characteristics at the dentine/composite interface with minimal marginal leakage compared to the control bonding system. The chitra light cure composite material also showed lower shrinkage characteristics compared to Prisma APH composite. PMID:8859406

  14. Distributed user-centric scheduling for visible light communication networks.

    PubMed

    Chen, Lingjiao; Wang, Jiaheng; Zhou, Jiantao; Ng, Derrick Wing Kwan; Schober, Robert; Zhao, Chunming

    2016-07-11

    Visible light communication (VLC) networks, consisting of multiple light-emitting diodes (LEDs) acting as optical access points (APs), can provide low-cost high-rate data transmission to multiple users simultaneously in indoor environments. However, the performance of VLC networks is severely limited by the interference between different users. In this paper, we establish a distributed user-centric scheduling framework based on stable marriage theory, and propose a novel decentralized scheduling method to manage interference by forming flexible amorphous cells for all users. The proposed scheduling method has provable low computational complexity and requires only the exchange of a few 1-bit messages between the APs and the users but not the feedback of the channel state information of the entire network. We further show that the proposed method can achieve both user-wise and system-wise optimality as well as a certain level of fairness. Simulation results indicate that our decentralized user-centric scheduling method outperforms existing centralized approaches in terms of throughput, fairness, and computational complexity.

  15. Mobile health-monitoring system through visible light communication.

    PubMed

    Tan, Yee-Yong; Chung, Wan-Young

    2014-01-01

    Promising development in the light emitting diode (LED) technology has spurred the interest to adapt LED for both illumination and data transmission. This has fostered the growth of interest in visible light communication (VLC), with on-going research to utilize VLC in various applications. This paper presents a mobile-health monitoring system, where healthcare information such as biomedical signals and patient information are transmitted via the LED lighting. A small and portable receiver module is designed and developed to be attached to the mobile device, providing a seamless monitoring environment. Three different healthcare information including ECG, PPG signals and HL7 text information is transmitted simultaneously, using a single channel VLC. This allows for a more precise and accurate monitoring and diagnosis. The data packet size is carefully designed, to transmit information in a minimal packet error rate. A comprehensive monitoring application is designed and developed through the use of a tablet computer in our study. Monitoring and evaluation such as heart rate and arterial blood pressure measurement can be performed concurrently. Real-time monitoring is demonstrated through experiment, where non-hazardous transmission method can be implemented alongside a portable device for better and safer healthcare service.

  16. Toward user mobility for OFDM-based visible light communications.

    PubMed

    Hong, Yang; Chen, Lian-Kuan

    2016-08-15

    We propose and experimentally demonstrate a mobile visible light communications (mobi-VLC) transmission system. The impact of user mobility on the performance of the mobi-VLC system is characterized, and we propose the use of the channel-independent orthogonal circulant matrix transform (OCT) precoding to combat the packet loss performance degradation induced by mobility. A mobile user terminal is used to detect the signal from a blue laser placed at 1 m away from the moving track. Various moving speeds (20, 40, 60, and 80  cm/s) and lateral moving distances (30, 40, and 50 cm) of the user terminal are investigated. The effectiveness of the OCT precoding is evaluated by the comparison with the conventional orthogonal frequency division multiplexing (OFDM) scheme and the adaptive-loaded discrete multi-tone (DMT) scheme. Experimental results show that the system performance degrades with the increase in user mobility speed and in moving distance. Furthermore, the OCT precoding provides performance improvement that is superior over that of conventional OFDM schemes, and it exhibits lower packet loss rate than that of adaptive-loaded DMT. No packet loss for 300  Mb/s transmission is achieved with a 30 cm lateral moving distance at 20  cm/s. PMID:27519083

  17. Measuring scintillation light using Visible Light Photon Counters (VLPC)

    NASA Astrophysics Data System (ADS)

    Chavarria, Alvaro

    2006-10-01

    A new search for the neutron electric dipole moment (EDM) using ultra cold neutrons proposes an improvement on the neutron EDM by two orders of magnitude over the current limit (to 10-28 e*cm). Detection of scintillation light in superfluid ^4He is at the heart of this experiment.One possible scheme to detect this light is to use wavelength-shifting fibers in the superfluid ^4He to collect the scintillation light and transport it out of the measuring cell. The fiber terminates in a visible light photon counter (VLPC). VLPCs are doped, silicon based, solid state photomultipliers with high quantum efficiency (up to 80%) and high gain ( 40000 electrons per converted photon). Moreover, they are insensitive to magnetic fields and operate at temperatures of 6.5K.A test setup has been assembled at Duke University using acrylic cells wrapped in wavelength-shifting fibers that terminate on VLPCs. This setup is being used to evaluate the feasibility of this light detection scheme. The results obtained in multiple experiments done over the past summer (2006) and the current status of the project will be presented at the conference.Reference:A New Search for the Neutron Electric Dipole Moment, funding pre-proposal by the EDM collaboration; R. Golub and S. Lamoreaux, Phys. Rep. 237, 1 (1994).

  18. Distributed user-centric scheduling for visible light communication networks.

    PubMed

    Chen, Lingjiao; Wang, Jiaheng; Zhou, Jiantao; Ng, Derrick Wing Kwan; Schober, Robert; Zhao, Chunming

    2016-07-11

    Visible light communication (VLC) networks, consisting of multiple light-emitting diodes (LEDs) acting as optical access points (APs), can provide low-cost high-rate data transmission to multiple users simultaneously in indoor environments. However, the performance of VLC networks is severely limited by the interference between different users. In this paper, we establish a distributed user-centric scheduling framework based on stable marriage theory, and propose a novel decentralized scheduling method to manage interference by forming flexible amorphous cells for all users. The proposed scheduling method has provable low computational complexity and requires only the exchange of a few 1-bit messages between the APs and the users but not the feedback of the channel state information of the entire network. We further show that the proposed method can achieve both user-wise and system-wise optimality as well as a certain level of fairness. Simulation results indicate that our decentralized user-centric scheduling method outperforms existing centralized approaches in terms of throughput, fairness, and computational complexity. PMID:27410830

  19. Astronomical data fusion tool based on PostgreSQL

    NASA Astrophysics Data System (ADS)

    Han, Bo; Zhang, Yan-Xia; Zhong, Shou-Bo; Zhao, Yong-Heng

    2016-11-01

    With the application of advanced astronomical technologies, equipments and methods all over the world, astronomical observations cover the range from radio, infrared, visible light, ultraviolet, X-ray and gamma-ray bands, and enter into the era of full wavelength astronomy. How to effectively integrate data from different ground- and space-based observation equipments, different observers, different bands and different observation times, requires data fusion technology. In this paper we introduce a cross-match tool that is developed in the Python language, is based on the PostgreSQL database and uses Q3C as the core index, facilitating the cross-match work of massive astronomical data. It provides four different cross-match functions, namely: (I) cross-match of the custom error range; (II) cross-match of catalog errors; (III) cross-match based on the elliptic error range; (IV) cross-match of the nearest neighbor algorithm. The resulting cross-matched set provides a good foundation for subsequent data mining and statistics based on multiwavelength data. The most advantageous aspect of this tool is a user-oriented tool applied locally by users. By means of this tool, users can easily create their own databases, manage their own data and cross-match databases according to their requirements. In addition, this tool is also able to transfer data from one database into another database. More importantly, it is easy to get started with the tool and it can be used by astronomers without writing any code.

  20. Exploration of Visible-Light Photocatalysis in Heterocycle Synthesis and Functionalization: Reaction Design and Beyond.

    PubMed

    Chen, Jia-Rong; Hu, Xiao-Qiang; Lu, Liang-Qiu; Xiao, Wen-Jing

    2016-09-20

    Visible-light photocatalysis has recently received increasing attention from chemists because of its wide application in organic synthesis and its significance for sustainable chemistry. This catalytic strategy enables the generation of various reactive species, frequently without stoichiometric activation reagents under mild reaction conditions. Manipulation of these reactive intermediates can result in numerous synthetically useful bond formations in a controllable manner. In this Account, we describe our recent advances in the rational design and strategic application of photocatalysis in the synthesis of various synthetically and biologically important heterocycles. Our main research efforts toward this goal can be classified into four categories: formal cycloaddition and cyclization reactions, radical-mediated olefin functionalization/cyclization cascades, photocatalytic generation and cyclization of N-centered radicals, and photocatalytic functionalization of heterocycles by visible-light-induced dual catalysis. Inspired by the wide application of tertiary amines as reductive additives in photoredox catalysis, we exploited a series of readily accessible or rationally designed tertiary amines with reactive sites in a range of photocatalytic formal cycloaddition and cyclization reactions, providing efficient access to diverse nitrogen heterocycles. Employing various photogenerated radical species, we further developed a series of radical-mediated olefin functionalization/cyclization cascade reactions to successfully assemble various five- and six-membered heterocycles. We have also achieved for the first time the direct catalytic conversion of recalcitrant N-H bonds into neutral N-centered radicals through a visible-light-photocatalytic oxidative deprotonation electron transfer. Using this generic strategy, we have devised several types of radical cyclizations of unsaturated hydrazones, leading to the construction of diversely functionalized pyrazoline and

  1. The efficient photocatalytic degradation of methyl tert-butyl ether under Pd/ZnO and visible light irradiation.

    PubMed

    Seddigi, Zaki S; Ahmed, Saleh A; Bumajdad, Ali; Danish, Ekram Y; Shawky, Ahmed M; Gondal, Mohammed A; Soylak, Mustafa

    2015-01-01

    Methyl tert-butyl ether is a commonly used fuel oxygenate that is present in gasoline. It was introduced to eliminate the use of leaded gasoline and to improve the octane quality because it aids in the complete combustion of fuel by supplying oxygen during the combustion process. Over the past decade, the use of MTBE has increased tremendously worldwide. For obvious reasons relating to accidental spillage, MTBE started to appear as an environmental and human health threat because of its nonbiodegradable nature and carcinogenic potential, respectively. In this work, MTBE was degraded with the help of an advanced oxidation process through the use of zinc oxide as a photocatalyst in the presence of visible light. A mixture of 200 mg of zinc oxide in 350 mL of 50 ppm MTBE aqueous solution was irradiated with visible light for a given time. The complete degradation of MTBE was recorded, and approximately 99% photocatalytic degradation of 100 ppm MTBE solution was observed. Additionally, the photoactivity of 1% Pd-doped ZnO was tested under similar conditions to understand the effect of Pd doping on ZnO. Our results obtained under visible light irradiation are very promising, and they could be further explored for the degradation of several nondegradable environmental pollutants.

  2. Revolutionary visible and infrared sensor detectors for the most advanced astronomical AO systems

    NASA Astrophysics Data System (ADS)

    Feautrier, Philippe; Gach, Jean-Luc; Guieu, Sylvain; Downing, Mark; Jorden, Paul; Rothman, Johan; de Borniol, Eric D.; Balard, Philippe; Stadler, Eric; Guillaume, Christian; Boutolleau, David; Coussement, Jérome; Kolb, Johann; Hubin, Norbert; Derelle, Sophie; Robert, Clélia; Tanchon, Julien; Trollier, Thierry; Ravex, Alain; Zins, Gérard; Kern, Pierre; Moulin, Thibaut; Rochat, Sylvain; Delpoulbé, Alain; Lebouqun, Jean-Baptiste

    2014-07-01

    We report in this paper decisive advance on the detector development for the astronomical applications that require very fast operation. Since the CCD220 and OCAM2 major success, new detector developments started in Europe either for visible and IR wavelengths. Funded by ESO and the FP7 Opticon European network, the NGSD CMOS device is fully dedicated to Natural and Laser Guide Star AO for the E-ELT with strong ESO involvement. The NGSD will be a 880x840 pixels CMOS detector with a readout noise of 3 e (goal 1e) at 700 Hz frame rate and providing digital outputs. A camera development, based on this CMOS device and also funded by the Opticon European network, is ongoing. Another major AO wavefront sensing detector development concerns IR detectors based on Avalanche Photodiode (e- APD) arrays within the RAPID project. Developed by the SOFRADIR and CEA/LETI manufacturers, the latter offers a 320x255 8 outputs 30 microns IR array, sensitive from 0.4 to 3 microns, with less than 2 e readout noise at 1600 fps. A rectangular window can also be programmed to speed up even more the frame rate when the full frame readout is not required. The high QE response, in the range of 70%, is almost flat over this wavelength range. Advanced packaging with miniature cryostat using pulse tube cryocoolers was developed in the frame of this programme in order to allow use on this detector in any type of environment. The characterization results of this device are presented here. Readout noise as low as 1.7 e at 1600 fps has been measured with a 3 microns wavelength cut-off chip and a multiplication gain of 14 obtained with a limited photodiode polarization of 8V. This device also exhibits excellent linearity, lower than 1%. The pulse tube cooling allows smart and easy cooling down to 55 K. Vibrations investigations using centroiding and FFT measurements were performed proving that the miniature pulse tube does not induce measurable vibrations to the optical bench, allowing use of this

  3. Visible light response, electrical transport, and amorphization in compressed organolead iodine perovskites

    NASA Astrophysics Data System (ADS)

    Ou, Tianji; Yan, Jiejuan; Xiao, Chuanhai; Shen, Wenshu; Liu, Cailong; Liu, Xizhe; Han, Yonghao; Ma, Yanzhang; Gao, Chunxiao

    2016-06-01

    Recent scientific advances on organic-inorganic hybrid perovskites are mainly focused on the improvement of power conversion efficiency. So far, how compression tunes their electronic and structural properties remains less understood. By combining in situ photocurrent, impedance spectroscopy, and X-ray diffraction (XRD) measurements, we have studied the electrical transport and structural properties of compressed CH3NH3PbI3 (MAPbI3) nanorods. The visible light response of MAPbI3 remains robust below 3 GPa while it is suppressed when it becomes amorphous. Pressure-induced electrical transport properties of MAPbI3 including resistance, relaxation frequency, and relative permittivity have been investigated under pressure up to 8.5 GPa by in situ impedance spectroscopy measurements. These results indicate that the discontinuous changes of these physical parameters occur around the structural phase transition pressure. The XRD studies of MAPbI3 under high pressure up to 20.9 GPa show that a phase transformation below 0.7 GPa, could be attributed to the tilting and distortion of PbI6 octahedra. And pressure-induced amorphization is reversible at a low density amorphous state but irreversible at a relatively higher density state. Furthermore, the MAPbI3 nanorods crush into nanopieces around 0.9 GPa which helps us to explain why the mixed phase of tetragonal and orthorhombic was observed at 0.5 GPa. The pressure modulated changes of electrical transport and visible light response properties open up a new approach for exploring CH3NH3PbI3-based photo-electronic applications.Recent scientific advances on organic-inorganic hybrid perovskites are mainly focused on the improvement of power conversion efficiency. So far, how compression tunes their electronic and structural properties remains less understood. By combining in situ photocurrent, impedance spectroscopy, and X-ray diffraction (XRD) measurements, we have studied the electrical transport and structural properties of

  4. Fluorescence enhancement in visible light: dielectric or noble metal?

    PubMed

    Sun, S; Wu, L; Bai, P; Png, C E

    2016-07-28

    A high permittivity dielectric gives the impression of outperforming plasmonic noble metal in visible light fluorescence enhancement primarily because of its small loss. Nonetheless, the performances of these two platforms in various situations remain obscure due to the different optical confinement mechanisms as well as the complexity in the fluorescence enhancement process. This study presents a comprehensive comparison between these two platforms based on nanoparticles (NPs) to evaluate their capability and applicability in fluorescence enhancement by taking into account the fluorescence excitation rate, the quantum yield, the fluorophore wavelengths and Stokes shifts as well as the far field intensity. In a low permittivity sensing medium (e.g. air), the dielectric NP can achieve comparable or higher fluorescence enhancement than the metal NP due to its decent NP-enhanced excitation rate and larger quantum yield. In a relatively high permittivity sensing medium (e.g. water), however, there is a significant decrement of the excitation rate of the dielectric NP as the permittivity contrast decreases, leading to a smaller fluorescence enhancement compared to the metallic counterpart. Combining the fluorescence enhancement and the far field intensity studies, we further conclude that for both dielectric and plasmonic NPs, the optimal situation occurs when the fluorescence excitation wavelength, the fluorescence emission wavelength and the electric-dipole-mode of the dielectric NP (or the plasmonic resonance of the metal NP) are the same and all fall in the low conductivity region of the NP material. We also find that the electric-dipole-mode of the dielectric NP performs better than the magnetic-dipole-mode for fluorescence enhancement applications because only the electric-dipole-mode can be strongly excited by the routinely used fluorescent dyes and quantum dots, which behave as electric dipoles by nature.

  5. Fluorescence enhancement in visible light: dielectric or noble metal?

    PubMed

    Sun, S; Wu, L; Bai, P; Png, C E

    2016-07-28

    A high permittivity dielectric gives the impression of outperforming plasmonic noble metal in visible light fluorescence enhancement primarily because of its small loss. Nonetheless, the performances of these two platforms in various situations remain obscure due to the different optical confinement mechanisms as well as the complexity in the fluorescence enhancement process. This study presents a comprehensive comparison between these two platforms based on nanoparticles (NPs) to evaluate their capability and applicability in fluorescence enhancement by taking into account the fluorescence excitation rate, the quantum yield, the fluorophore wavelengths and Stokes shifts as well as the far field intensity. In a low permittivity sensing medium (e.g. air), the dielectric NP can achieve comparable or higher fluorescence enhancement than the metal NP due to its decent NP-enhanced excitation rate and larger quantum yield. In a relatively high permittivity sensing medium (e.g. water), however, there is a significant decrement of the excitation rate of the dielectric NP as the permittivity contrast decreases, leading to a smaller fluorescence enhancement compared to the metallic counterpart. Combining the fluorescence enhancement and the far field intensity studies, we further conclude that for both dielectric and plasmonic NPs, the optimal situation occurs when the fluorescence excitation wavelength, the fluorescence emission wavelength and the electric-dipole-mode of the dielectric NP (or the plasmonic resonance of the metal NP) are the same and all fall in the low conductivity region of the NP material. We also find that the electric-dipole-mode of the dielectric NP performs better than the magnetic-dipole-mode for fluorescence enhancement applications because only the electric-dipole-mode can be strongly excited by the routinely used fluorescent dyes and quantum dots, which behave as electric dipoles by nature. PMID:27374052

  6. Isotope effects in photo dissociation of ozone with visible light

    NASA Astrophysics Data System (ADS)

    Früchtl, Marion; Janssen, Christof; Röckmann, Thomas

    2014-05-01

    Ozone (O3) plays a key role for many chemical oxidation processes in the Earth's atmosphere. In these chemical reactions, ozone can transfer oxygen to other trace gases. This is particularly interesting, since O3 has a very peculiar isotope composition. Following the mass dependent fractionation equation δ17O = 0.52 * δ18O, most fractionation processes depend directly on mass. However, O3 shows an offset to the mass dependent fractionation line. Processes, which show such anomalies, are termed mass independent fractionations (MIF). A very well studied example for a chemical reaction that leads to mass independent fractionation is the O3 formation reaction. To what degree O3 destruction reactions need to be considered in order to understand the isotope composition of atmospheric O3 is still not fully understood and an open question within scientific community. We set up new experiments to investigate the isotope effect resulting from photo dissociation of O3 in the Chappuis band (R1). Initial O3 is produced by an electric discharge. After photolysis O3 is collected in a cold trap at the triple point temperature of nitrogen (63K). O3 is then converted to O2 in order to measure the oxygen isotopes of O3 using isotope ratio mass spectrometry. To isolate O3 photo dissociation (R1) from O3 decomposition (R2) and secondary O3 formation (R3), we use varying amounts of carbon monoxide (CO) as O atom quencher (R4). In this way we suppress the O + O3 reaction (R3) and determine the isotope fractionation in R1 and R2 separately. We present first results on the isotope effects in O3 photo dissociation with visible light in the presence of different bath gases. Results are interpreted based on chemical kinetics modeling. (R1) O3 + hυ → O (3P) + O2 (R2) O3 + O (3P) → 2 O2 (R3) O + O2 + M → O3 + M (R4) O (3P) + CO + M → CO2 + M

  7. Visible light water splitting using dye-sensitized oxide semiconductors.

    PubMed

    Youngblood, W Justin; Lee, Seung-Hyun Anna; Maeda, Kazuhiko; Mallouk, Thomas E

    2009-12-21

    Researchers are intensively investigating photochemical water splitting as a means of converting solar to chemical energy in the form of fuels. Hydrogen is a key solar fuel because it can be used directly in combustion engines or fuel cells, or combined catalytically with CO(2) to make carbon containing fuels. Different approaches to solar water splitting include semiconductor particles as photocatalysts and photoelectrodes, molecular donor-acceptor systems linked to catalysts for hydrogen and oxygen evolution, and photovoltaic cells coupled directly or indirectly to electrocatalysts. Despite several decades of research, solar hydrogen generation is efficient only in systems that use expensive photovoltaic cells to power water electrolysis. Direct photocatalytic water splitting is a challenging problem because the reaction is thermodynamically uphill. Light absorption results in the formation of energetic charge-separated states in both molecular donor-acceptor systems and semiconductor particles. Unfortunately, energetically favorable charge recombination reactions tend to be much faster than the slow multielectron processes of water oxidation and reduction. Consequently, visible light water splitting has only recently been achieved in semiconductor-based photocatalytic systems and remains an inefficient process. This Account describes our approach to two problems in solar water splitting: the organization of molecules into assemblies that promote long-lived charge separation, and catalysis of the electrolysis reactions, in particular the four-electron oxidation of water. The building blocks of our artificial photosynthetic systems are wide band gap semiconductor particles, photosensitizer and electron relay molecules, and nanoparticle catalysts. We intercalate layered metal oxide semiconductors with metal nanoparticles. These intercalation compounds, when sensitized with [Ru(bpy)(3)](2+) derivatives, catalyze the photoproduction of hydrogen from sacrificial

  8. Ag/AgBr/TiO2 visible light photocatalyst for destruction of azodyes and bacteria.

    PubMed

    Hu, Chun; Lan, Yongqing; Qu, Jiuhui; Hu, Xuexiang; Wang, Aimin

    2006-03-01

    Ag/AgBr/TiO2 was prepared by the deposition-precipitation method and was found to be a novel visible light driven photocatalyst. The catalyst showed high efficiency for the degradation of nonbiodegradable azodyes and the killing of Escherichia coli under visible light irradiation (lambda>420 nm). The catalyst activity was maintained effectively after successive cyclic experiments under UV or visible light irradiation without the destruction of AgBr. On the basis of the characterization of X-ray diffraction, X-ray photoelectron spectroscopy, and Auger electron spectroscopy, the surface Ag species mainly exist as Ag0 in the structure of all samples before and after reaction, and Ag0 species scavenged hVB+ and then trapped eCB- in the process of photocatalytic reaction, inhibiting the decomposition of AgBr. The studies of ESR and H2O2 formation revealed that *OH and O2*- were formed in visible light irradiated aqueous Ag/AgBr/TiO2 suspension, while there was no reactive oxygen species in the visible light irradiated Ag0/TiO2 system. The results indicate that AgBr is the main photoactive species for the destruction of azodyes and bacteria under visible light. In addition, the bactericidal efficiency and killing mechanism of Ag/AgBr/TiO2 under visible light irradiation are illustrated and discussed. PMID:16509698

  9. World-wide deployment of Robo-AO visible-light robotic laser adaptive optics systems

    NASA Astrophysics Data System (ADS)

    Baranec, Christoph; Riddle, Reed; Law, Nicholas Michael; Lu, Jessica R.; Tonry, John; Tully, R. Brent; Wright, Shelley; Kulkarni, Shrinivas; Severson, Scott; Choi, Philip; Ramaprakash, A.; Chun, Mark; Connelley, Mike; Tokunaga, Alan; Hall, Donald

    2015-08-01

    In the next few years, several modest-sized telescopes around the world will be upgraded with autonomous laser adaptive optics systems based on the Robo-AO prototype deployed at the Palomar Observatory 1.5-m telescope. The prototype commenced scientific operations in June 2012 and more than 19,000 observations have since been performed at the ~0.12" visible-light diffraction limit. We are planning to move the prototype system to the 2.1-m telescope at Kitt Peak for a 3-year deployment which will serve a consortium of users including Caltech, the University of Hawai`i, IUCAA, NCU and institutions in China. Additionally, 2 months per year will be made available to the US astronomical community.New Robo-AO systems are in various stages of development: a clone by IUCAA for the 2-m IGO telescope in India; a natural guide star variant, KAPAO, by Pomona College at the 1-m Table Mountain telescope in California; and second generation Robo-AO systems are planned for the 3-m IRTF and 2.2-m University of Hawai'i telescopes on Maunakea, Hawai`i. The latter will exploit Maunakea's excellent observing conditions to provide higher Strehl ratios, sharper imaging, ~0.07", and correction to lambda = 400 nm. An additional infrared integral-field spectrograph will be fed by the UH 2.2-m Robo-AO system to quickly classify transients, such as supernovae and asteroids, discovered by the ATLAS system in Hawai`i.

  10. Reduction of aryl halides by consecutive visible light-induced electron transfer processes.

    PubMed

    Ghosh, Indrajit; Ghosh, Tamal; Bardagi, Javier I; König, Burkhard

    2014-11-01

    Biological photosynthesis uses the energy of several visible light photons for the challenging oxidation of water, whereas chemical photocatalysis typically involves only single-photon excitation. Perylene bisimide is reduced by visible light photoinduced electron transfer (PET) to its stable and colored radical anion. We report here that subsequent excitation of the radical anion accumulates sufficient energy for the reduction of stable aryl chlorides giving aryl radicals, which were trapped by hydrogen atom donors or used in carbon-carbon bond formation. This consecutive PET (conPET) overcomes the current energetic limitation of visible light photoredox catalysis and allows the photocatalytic conversion of less reactive chemical bonds in organic synthesis.

  11. Vision: A Six-telescope Fiber-fed Visible Light Beam Combiner for the Navy Precision Optical Interferometer

    NASA Astrophysics Data System (ADS)

    Garcia, Eugenio V.; Muterspaugh, Matthew W.; van Belle, Gerard; Monnier, John D.; Stassun, Keivan G.; Ghasempour, Askari; Clark, James H.; Zavala, R. T.; Benson, James A.; Hutter, Donald J.; Schmitt, Henrique R.; Baines, Ellyn K.; Jorgensen, Anders M.; Strosahl, Susan G.; Sanborn, Jason; Zawicki, Stephen J.; Sakosky, Michael F.; Swihart, Samuel

    2016-05-01

    Visible-light long baseline interferometry holds the promise of advancing a number of important applications in fundamental astronomy, including the direct measurement of the angular diameters and oblateness of stars, and the direct measurement of the orbits of binary and multiple star systems. To advance, the field of visible-light interferometry requires development of instruments capable of combining light from 15 baselines (6 telescopes) simultaneously. The Visible Imaging System for Interferometric Observations at NPOI (VISION) is a new visible light beam combiner for the Navy Precision Optical Interferometer (NPOI) that uses single-mode fibers to coherently combine light from up to six telescopes simultaneously with an image-plane combination scheme. It features a photometric camera for calibrations and spatial filtering from single-mode fibers with two Andor Ixon electron multiplying CCDs. This paper presents the VISION system, results of laboratory tests, and results of commissioning on-sky observations. A new set of corrections have been determined for the power spectrum and bispectrum by taking into account non-Gaussian statistics and read noise present in electron-multipying CCDs to enable measurement of visibilities and closure phases in the VISION post-processing pipeline. The post-processing pipeline has been verified via new on-sky observations of the O-type supergiant binary ζ Orionis A, obtaining a flux ratio of 2.18+/- 0.13 with a position angle of 223.°9 ± 1.°0 and separation 40.6+/- 1.8 mas over 570-750 nm, in good agreement with expectations from the previously published orbit.

  12. Vision: A Six-telescope Fiber-fed Visible Light Beam Combiner for the Navy Precision Optical Interferometer

    NASA Astrophysics Data System (ADS)

    Garcia, Eugenio V.; Muterspaugh, Matthew W.; van Belle, Gerard; Monnier, John D.; Stassun, Keivan G.; Ghasempour, Askari; Clark, James H.; Zavala, R. T.; Benson, James A.; Hutter, Donald J.; Schmitt, Henrique R.; Baines, Ellyn K.; Jorgensen, Anders M.; Strosahl, Susan G.; Sanborn, Jason; Zawicki, Stephen J.; Sakosky, Michael F.; Swihart, Samuel

    2016-05-01

    Visible-light long baseline interferometry holds the promise of advancing a number of important applications in fundamental astronomy, including the direct measurement of the angular diameters and oblateness of stars, and the direct measurement of the orbits of binary and multiple star systems. To advance, the field of visible-light interferometry requires development of instruments capable of combining light from 15 baselines (6 telescopes) simultaneously. The Visible Imaging System for Interferometric Observations at NPOI (VISION) is a new visible light beam combiner for the Navy Precision Optical Interferometer (NPOI) that uses single-mode fibers to coherently combine light from up to six telescopes simultaneously with an image-plane combination scheme. It features a photometric camera for calibrations and spatial filtering from single-mode fibers with two Andor Ixon electron multiplying CCDs. This paper presents the VISION system, results of laboratory tests, and results of commissioning on-sky observations. A new set of corrections have been determined for the power spectrum and bispectrum by taking into account non-Gaussian statistics and read noise present in electron-multipying CCDs to enable measurement of visibilities and closure phases in the VISION post-processing pipeline. The post-processing pipeline has been verified via new on-sky observations of the O-type supergiant binary ζ Orionis A, obtaining a flux ratio of 2.18+/- 0.13 with a position angle of 223.°9 ± 1.°0 and separation 40.6+/- 1.8 mas over 570–750 nm, in good agreement with expectations from the previously published orbit.

  13. Sustainable Strategy Utilizing Biomass: Visible-Light-Mediated Synthesis of γ-Valerolactone

    EPA Science Inventory

    A novel sustainable approach to valued γ-valerolactone is described that exploits visible light mediated conversion of biomass-derived levulinic acid using a bimetallic catalyst on graphitic carbon nitride, AgPd@g-C3N4.

  14. Nanostructure sensitization of transition metal oxides for visible-light photocatalysis

    PubMed Central

    Chen, Hongjun

    2014-01-01

    Summary To better utilize the sunlight for efficient solar energy conversion, the research on visible-light active photocatalysts has recently attracted a lot of interest. The photosensitization of transition metal oxides is a promising approach for achieving effective visible-light photocatalysis. This review article primarily discusses the recent progress in the realm of a variety of nanostructured photosensitizers such as quantum dots, plasmonic metal nanostructures, and carbon nanostructures for coupling with wide-bandgap transition metal oxides to design better visible-light active photocatalysts. The underlying mechanisms of the composite photocatalysts, e.g., the light-induced charge separation and the subsequent visible-light photocatalytic reaction processes in environmental remediation and solar fuel generation fields, are also introduced. A brief outlook on the nanostructure photosensitization is also given. PMID:24991507

  15. Phase-dependent photocatalytic H2 evolution of copper zinc tin sulfide under visible light.

    PubMed

    Chang, Zhi-Xian; Zhou, Wen-Hui; Kou, Dong-Xing; Zhou, Zheng-Ji; Wu, Si-Xin

    2014-10-28

    CZTS exhibited apparently phase-dependent photocatalytic H2 evolution under visible light. Possible factors for the phase-dependent photocatalytic activity of CZTS were discussed in detail. PMID:25205452

  16. TiO{sub 2}-coated carbon nanotubes: A redshift enhanced photocatalysis at visible light

    SciTech Connect

    Lu, S.-Y.; Tang, C.-W.; Lin, Y.-H.; Kuo, H.-F.; Lai, Y.-C.; Ouyang Hao; Hsu, W.-K.; Tsai, M.-Y.

    2010-06-07

    Annealing of carbon nanotubes coated with thin and uniform TiO{sub 2} results in carbon diffusion into oxygen lattices and doping induced redshift is evident by an efficient photocatalysis at visible light. The underlying mechanism is discussed.

  17. Evaluation techniques for x-ray mirrors and systems using visible light

    SciTech Connect

    Takacs, P.Z.; Colbert, J.

    1985-09-01

    Severely diffraction-broadened visible light images from grazing incidence optical systems are measured and analyzed using a diffraction integral model to predict slope errors and image quality at XUV wavelengths.

  18. Visible Light and pH Responsive Polymer-Coated Mesoporous Silica Nanohybrids for Controlled Release.

    PubMed

    Wang, Guojie; Dong, Jie; Yuan, Tingting; Zhang, Juchen; Wang, Lei; Wang, Hao

    2016-07-01

    A visible light and pH responsive anticancer drug delivery system based on polymer-coated mesoporous silica nanoparticles (MSNs) has been developed. Perylene-functionalized poly(dimethylaminoethyl methacrylates) sensitive to visible light and pH are electrostatically attached on the surface of MSNs to seal the nanopores. Stimulation of visible light and acid can unseal the nanopores to induce controlled drug release from the MSNs. More interestingly, the release can be enhanced under the combined stimulation of the dual-stimuli. The synergistic effect of visible light and acid stimulation on the efficient release of anticancer drugs from the nanohybrids endows the system with great potential for cancer therapy. PMID:26938147

  19. Microcrystalline sodium tungsten bronze nanowire bundles as efficient visible light-responsive photocatalysts.

    PubMed

    Wang, Lei; Zhan, Jinhua; Fan, Weiliu; Cui, Guanwei; Sun, Honggang; Zhuo, Linhai; Zhao, Xian; Tang, Bo

    2010-12-14

    Microcrystalline sodium tungsten bronze nanowire bundles were obtained via a facile hydrothermal synthesis, and were applied in water purification as visible-light-driven photocatalysts for the first time.

  20. Self-Assembled PDINH Supramolecular System for Photocatalysis under Visible Light.

    PubMed

    Liu, Di; Wang, Jun; Bai, Xiaojuan; Zong, Ruilong; Zhu, Yongfa

    2016-09-01

    A self-assembled perylene-3,4,9,10-tetracarboxylic diimide(PDINH) supramolecular system consisting of all-organic PDINH molecule building blocks through non-covalent interactions works as a visible light photocatalyst with high activity.

  1. Visible light photoreduction of CO.sub.2 using heterostructured catalysts

    DOEpatents

    Matranga, Christopher; Thompson, Robert L; Wang, Congjun

    2015-03-24

    The method provides for use of sensitized photocatalyst for the photocatalytic reduction of CO.sub.2 under visible light illumination. The photosensitized catalyst is comprised of a wide band gap semiconductor material, a transition metal co-catalyst, and a semiconductor sensitizer. The semiconductor sensitizer is photoexcited by visible light and forms a Type II band alignment with the wide band gap semiconductor material. The wide band gap semiconductor material and the semiconductor sensitizer may be a plurality of particles, and the particle diameters may be selected to accomplish desired band widths and optimize charge injection under visible light illumination by utilizing quantum size effects. In a particular embodiment, CO.sub.2 is reduced under visible light illumination using a CdSe/Pt/TiO2 sensitized photocatalyst with H.sub.2O as a hydrogen source.

  2. Photo-oxidation of polymer-like amorphous hydrogenated carbon under visible light illumination

    SciTech Connect

    Baxamusa, Salmaan; Laurence, Ted; Worthington, Matthew; Ehrmann, Paul

    2015-11-10

    Amorphous hydrogenated carbon (a-C:H), a polymer-like network typically synthesized by plasma chemical vapor deposition, has long been understood to exhibit optical absorption of visible light (λ > 400 nm). In this report we explain that this absorption is accompanied by rapid photo-oxidation (within minutes) that behaves in most respects like classic polymer photo-oxidation with the exception that it occurs under visible light illumination rather than ultraviolet illumination.

  3. Scalable Synthesis of Piperazines Enabled by Visible-Light Irradiation and Aluminum Organometallics

    PubMed Central

    Suárez-Pantiga, Samuel; Colas, Kilian; Johansson, Magnus J; Mendoza, Abraham

    2015-01-01

    The development of more active C–H oxidation catalysts has inspired a rapid, scalable, and stereoselective assembly of multifunctional piperazines through a [3+3] coupling of azomethine ylides. A combination of visible-light irradiation and aluminum organometallics is essential to promote this transformation, which introduces visible-light photochemistry of main-group organometallics and sets the basis for new and promising catalysts. PMID:26337253

  4. Transition metal-modified zinc oxides for UV and visible light photocatalysis.

    PubMed

    Bloh, J Z; Dillert, R; Bahnemann, D W

    2012-11-01

    In order to use photocatalysis with solar light, finding more active and especially visible light active photocatalysts is a very important challenge. Also, studies of these photocatalysts should employ a standardized test procedure so that their results can be accurately compared and evaluated with one another. A systematic study of transition metal-modified zinc oxide was conducted to determine whether they are suitable as visible light photocatalysts. The photocatalytic activity of ZnO modified with eight different transition metals (Cu, Co, Fe, Mn, Ni, Ru, Ti, Zr) in three different concentrations (0.01, 0.1, and 1 at.%) was investigated under irradiation with UV as well as with visible light. The employed activity test is the gas-phase degradation of acetaldehyde as described by the ISO standard 22197-2. The results suggest that the UV activity can be improved with almost any modification element and that there exists an optimal modification ratio at about 0.1 at.%. Additionally, Mn- and Ru-modified ZnO display visible light activity. Especially the Ru-modified ZnO is highly active and surpasses the visible light activity of all studied titania standards. These findings suggest that modified zinc oxides may be a viable alternative to titanium dioxide-based catalysts for visible light photocatalysis. Eventually, possible underlying mechanisms are proposed and discussed.

  5. Highly Transparent, Visible-Light Photodetector Based on Oxide Semiconductors and Quantum Dots.

    PubMed

    Shin, Seung Won; Lee, Kwang-Ho; Park, Jin-Seong; Kang, Seong Jun

    2015-09-01

    Highly transparent phototransistors that can detect visible light have been fabricated by combining indium-gallium-zinc oxide (IGZO) and quantum dots (QDs). A wide-band-gap IGZO film was used as a transparent semiconducting channel, while small-band-gap QDs were adopted to absorb and convert visible light to an electrical signal. Typical IGZO thin-film transistors (TFTs) did not show a photocurrent with illumination of visible light. However, IGZO TFTs decorated with QDs showed enhanced photocurrent upon exposure to visible light. The device showed a responsivity of 1.35×10(4) A/W and an external quantum efficiency of 2.59×10(4) under illumination by a 635 nm laser. The origin of the increased photocurrent in the visible light was the small band gap of the QDs combined with the transparent IGZO films. Therefore, transparent phototransistors based on IGZO and QDs were fabricated and characterized in detail. The result is relevant for the development of highly transparent photodetectors that can detect visible light. PMID:26293387

  6. Highly Transparent, Visible-Light Photodetector Based on Oxide Semiconductors and Quantum Dots.

    PubMed

    Shin, Seung Won; Lee, Kwang-Ho; Park, Jin-Seong; Kang, Seong Jun

    2015-09-01

    Highly transparent phototransistors that can detect visible light have been fabricated by combining indium-gallium-zinc oxide (IGZO) and quantum dots (QDs). A wide-band-gap IGZO film was used as a transparent semiconducting channel, while small-band-gap QDs were adopted to absorb and convert visible light to an electrical signal. Typical IGZO thin-film transistors (TFTs) did not show a photocurrent with illumination of visible light. However, IGZO TFTs decorated with QDs showed enhanced photocurrent upon exposure to visible light. The device showed a responsivity of 1.35×10(4) A/W and an external quantum efficiency of 2.59×10(4) under illumination by a 635 nm laser. The origin of the increased photocurrent in the visible light was the small band gap of the QDs combined with the transparent IGZO films. Therefore, transparent phototransistors based on IGZO and QDs were fabricated and characterized in detail. The result is relevant for the development of highly transparent photodetectors that can detect visible light.

  7. N Doping to ZnO Nanorods for Photoelectrochemical Water Splitting under Visible Light: Engineered Impurity Distribution and Terraced Band Structure

    PubMed Central

    Wang, Meng; Ren, Feng; Zhou, Jigang; Cai, Guangxu; Cai, Li; Hu, Yongfeng; Wang, Dongniu; Liu, Yichao; Guo, Liejin; Shen, Shaohua

    2015-01-01

    Solution-based ZnO nanorod arrays (NRAs) were modified with controlled N doping by an advanced ion implantation method, and were subsequently utilized as photoanodes for photoelectrochemical (PEC) water splitting under visible light irradiation. A gradient distribution of N dopants along the vertical direction of ZnO nanorods was realized. N doped ZnO NRAs displayed a markedly enhanced visible-light-driven PEC photocurrent density of ~160 μA/cm2 at 1.1 V vs. saturated calomel electrode (SCE), which was about 2 orders of magnitude higher than pristine ZnO NRAs. The gradiently distributed N dopants not only extended the optical absorption edges to visible light region, but also introduced terraced band structure. As a consequence, N gradient-doped ZnO NRAs can not only utilize the visible light irradiation but also efficiently drive photo-induced electron and hole transfer via the terraced band structure. The superior potential of ion implantation technique for creating gradient dopants distribution in host semiconductors will provide novel insights into doped photoelectrode materials for solar water splitting. PMID:26262752

  8. N Doping to ZnO Nanorods for Photoelectrochemical Water Splitting under Visible Light: Engineered Impurity Distribution and Terraced Band Structure.

    PubMed

    Wang, Meng; Ren, Feng; Zhou, Jigang; Cai, Guangxu; Cai, Li; Hu, Yongfeng; Wang, Dongniu; Liu, Yichao; Guo, Liejin; Shen, Shaohua

    2015-01-01

    Solution-based ZnO nanorod arrays (NRAs) were modified with controlled N doping by an advanced ion implantation method, and were subsequently utilized as photoanodes for photoelectrochemical (PEC) water splitting under visible light irradiation. A gradient distribution of N dopants along the vertical direction of ZnO nanorods was realized. N doped ZnO NRAs displayed a markedly enhanced visible-light-driven PEC photocurrent density of ~160 μA/cm(2) at 1.1 V vs. saturated calomel electrode (SCE), which was about 2 orders of magnitude higher than pristine ZnO NRAs. The gradiently distributed N dopants not only extended the optical absorption edges to visible light region, but also introduced terraced band structure. As a consequence, N gradient-doped ZnO NRAs can not only utilize the visible light irradiation but also efficiently drive photo-induced electron and hole transfer via the terraced band structure. The superior potential of ion implantation technique for creating gradient dopants distribution in host semiconductors will provide novel insights into doped photoelectrode materials for solar water splitting. PMID:26262752

  9. Self-assembly based plasmonic arrays tuned by atomic layer deposition for extreme visible light absorption.

    PubMed

    Hägglund, Carl; Zeltzer, Gabriel; Ruiz, Ricardo; Thomann, Isabell; Lee, Han-Bo-Ram; Brongersma, Mark L; Bent, Stacey F

    2013-07-10

    Achieving complete absorption of visible light with a minimal amount of material is highly desirable for many applications, including solar energy conversion to fuel and electricity, where benefits in conversion efficiency and economy can be obtained. On a fundamental level, it is of great interest to explore whether the ultimate limits in light absorption per unit volume can be achieved by capitalizing on the advances in metamaterial science and nanosynthesis. Here, we combine block copolymer lithography and atomic layer deposition to tune the effective optical properties of a plasmonic array at the atomic scale. Critical coupling to the resulting nanocomposite layer is accomplished through guidance by a simple analytical model and measurements by spectroscopic ellipsometry. Thereby, a maximized absorption of light exceeding 99% is accomplished, of which up to about 93% occurs in a volume-equivalent thickness of gold of only 1.6 nm. This corresponds to a record effective absorption coefficient of 1.7 × 10(7) cm(-1) in the visible region, far exceeding those of solid metals, graphene, dye monolayers, and thin film solar cell materials. It is more than a factor of 2 higher than that previously obtained using a critically coupled dye J-aggregate, with a peak width exceeding the latter by 1 order of magnitude. These results thereby substantially push the limits for light harvesting in ultrathin, nanoengineered systems. PMID:23805835

  10. Self-assembly based plasmonic arrays tuned by atomic layer deposition for extreme visible light absorption.

    PubMed

    Hägglund, Carl; Zeltzer, Gabriel; Ruiz, Ricardo; Thomann, Isabell; Lee, Han-Bo-Ram; Brongersma, Mark L; Bent, Stacey F

    2013-07-10

    Achieving complete absorption of visible light with a minimal amount of material is highly desirable for many applications, including solar energy conversion to fuel and electricity, where benefits in conversion efficiency and economy can be obtained. On a fundamental level, it is of great interest to explore whether the ultimate limits in light absorption per unit volume can be achieved by capitalizing on the advances in metamaterial science and nanosynthesis. Here, we combine block copolymer lithography and atomic layer deposition to tune the effective optical properties of a plasmonic array at the atomic scale. Critical coupling to the resulting nanocomposite layer is accomplished through guidance by a simple analytical model and measurements by spectroscopic ellipsometry. Thereby, a maximized absorption of light exceeding 99% is accomplished, of which up to about 93% occurs in a volume-equivalent thickness of gold of only 1.6 nm. This corresponds to a record effective absorption coefficient of 1.7 × 10(7) cm(-1) in the visible region, far exceeding those of solid metals, graphene, dye monolayers, and thin film solar cell materials. It is more than a factor of 2 higher than that previously obtained using a critically coupled dye J-aggregate, with a peak width exceeding the latter by 1 order of magnitude. These results thereby substantially push the limits for light harvesting in ultrathin, nanoengineered systems.

  11. Advances in a study of sky quality for astronomical observations in Colombia

    NASA Astrophysics Data System (ADS)

    González-Díaz, D.; Pinzón, G.

    2015-10-01

    The aim of this study is to determine the sky quality in Colombia for astronomical observations in the optic. About 10,000 images in infrared (6.7 mu m and 10.7 mu m) were analyzed from the GOES meteorological satellites in three night times taken during a period of five years (2008 to 2014). A novel methodology was followed to determine how clear or covered was the sky in a given image. Meteorological data also were used from the weather stations network of the national meteorological institute, IDEAM. A correlation between threshold temperature and altitude was found for a historical data series of about 30 years. The results of the average percentage of nights with clear skies per year or clear sky fraction (CSF) were validated with the reports on the number of hours of astronomical observation from the logbooks of Llano del Hato Observatory in Merida-Venezuela, obtaining a cumulative percentage difference during the five years less than 10%. Annual cloud covering was computed over the whole country and it was classified the nights as clear or usable based on the definition of a quality factor.

  12. Improving the Visible Light Photoactivity of Supported Fullerene Photocatalysts through the Use of [C₇₀] Fullerene.

    PubMed

    Moor, Kyle J; Valle, Dhyan C; Li, Chuanhao; Kim, Jae-Hong

    2015-05-19

    We herein present the first instance of employing [C₇₀] fullerene for photocatalytic ¹O₂ production in water, through covalent immobilization onto a mesoporous silica support via nucelophilic amine addition directly to fullerene's cage. This attachment approach prevents the aggregation of individual fullerene molecules in water, thus allowing fullerene to retain its photoactivity, yet is much less complex than other techniques commonly pursued to create such supported-fullerene materials, which typically rely on water-soluble fullerene derivatives and elaborate immobilization methods. The solid-supported C₇₀ material exhibits significantly improved aqueous visible-light photoactivity compared to previous C₆₀- and C₆₀-derivative-based supported fullerene materials. Further, this material rapidly inactivates MS2 bacteriophage under sunlight illumination, oxidizes various organic contaminants, and does not appear to be significantly fouled by natural organic matter (NOM), highlighting the potential of these materials in real-world applications. Collectively, the ease of preparation and significantly enhanced visible-light photoactivity of these materials advance fullerene-based technologies for water treatment.

  13. Visible light photocatalytic activity of TiO2 nanoparticles hybridized by conjugated derivative of polybutadiene

    NASA Astrophysics Data System (ADS)

    Liu, Guoquan; Liu, Longchen; Song, Jinran; Liang, Jiudi; Luo, Qingzhi; Wang, Desong

    2014-05-01

    A series of conjugated polymer/TiO2 (CP/TiO2) nanocomposites were prepared from TiO2 and commercial polybutadiene. The as-prepared CP/TiO2 nanocomposites were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier-transform infrared spectroscopy (FTIR), Raman Spectroscopy, UV-vis diffuse reflectance spectroscopy (UV-vis DRS), and X-ray photoelectron spectroscopy (XPS). The photocatalytic activities of CP/TiO2 nanocomposites were investigated by monitoring the degradation of methyl orange aqueous solution under visible light irradiation. The effects of preparation conditions (such as the mass ratio of PB to TiO2 in suspensions for PB/TiO2 preparation, heat-treatment temperature and time) of CP/TiO2 nanocomposites on their visible light photocatalytic activity were investigated. The results show that the CP/TiO2 nanocomposites have excellent visible light photocatalytic activity. As the content of conjugated polymer on the TiO2 surface, heat-treatment temperature and time increase, the visible light photocatalytic activity increases at first and then decreases. The visible light photocatalytic mechanism of the CP/TiO2 nanocomposites has been discussed.

  14. Photodamage to the oxygen evolving complex of photosystem II by visible light.

    PubMed

    Zavafer, Alonso; Cheah, Mun Hon; Hillier, Warwick; Chow, Wah Soon; Takahashi, Shunichi

    2015-11-12

    Light damages photosynthetic machinery, primarily photosystem II (PSII), and it results in photoinhibition. A new photodamage model, the two-step photodamage model, suggests that photodamage to PSII initially occurs at the oxygen evolving complex (OEC) by light energy absorbed by manganese and that the PSII reaction center is subsequently damaged by light energy absorbed by photosynthetic pigments due to the limitation of electrons to the PSII reaction center. However, it is still uncertain whether this model is applicable to photodamage to PSII under visible light as manganese absorbs visible light only weakly. In the present study, we identified the initial site of photodamage to PSII upon illumination of visible light using PSII membrane fragments isolated from spinach leaves. When PSII samples were exposed to visible light in the presence of an exogenous electron acceptor, both PSII total activity and the PSII reaction centre activity declined due to photodamage. The supplemental addition of an electron donor to the PSII reaction centre alleviated the decline of the reaction centre activity but not the PSII total activity upon the light exposure. Our results demonstrate that visible light damages OEC prior to photodamage to the PSII reaction center, consistent with two-step photodamage model.

  15. Experimental Verification of n=0 Structures for Visible Light

    NASA Astrophysics Data System (ADS)

    Vesseur, Ernst Jan R.; Coenen, Toon; Caglayan, Humeyra; Engheta, Nader; Polman, Albert

    2013-01-01

    We fabricate and characterize a metal-dielectric nanostructure with an effective refractive index n=0 in the visible spectral range. Light is excited in the material at deep subwavelength resolution by a 30-keV electron beam. From the measured spatially and angle-resolved emission patterns, a vanishing phase advance, corresponding to an effective ɛ=0 and n=0, is directly observed at the cutoff frequency. The wavelength at which this condition is observed can be tuned over the entire visible or near-infrared spectral range by varying the waveguide width. This n=0 plasmonic nanostructure may serve as a new building block in nanoscale optical integrated circuits and to control spontaneous emission as experimentally demonstrated by the strongly enhanced radiative optical density of states over the entire n=0 structure.

  16. Dual-polarity plasmonic metalens for visible light.

    PubMed

    Chen, Xianzhong; Huang, Lingling; Mühlenbernd, Holger; Li, Guixin; Bai, Benfeng; Tan, Qiaofeng; Jin, Guofan; Qiu, Cheng-Wei; Zhang, Shuang; Zentgraf, Thomas

    2012-01-01

    Surface topography and refractive index profile dictate the deterministic functionality of a lens. The polarity of most lenses reported so far, that is, either positive (convex) or negative (concave), depends on the curvatures of the interfaces. Here we experimentally demonstrate a counter-intuitive dual-polarity flat lens based on helicity-dependent phase discontinuities for circularly polarized light. Specifically, by controlling the helicity of the input light, the positive and negative polarity are interchangeable in one identical flat lens. Helicity-controllable real and virtual focal planes, as well as magnified and demagnified imaging, are observed on the same plasmonic lens at visible and near-infrared wavelengths. The plasmonic metalens with dual polarity may empower advanced research and applications in helicity-dependent focusing and imaging devices, angular-momentum-based quantum information processing and integrated nano-optoelectronics.

  17. Dual-polarity plasmonic metalens for visible light

    NASA Astrophysics Data System (ADS)

    Chen, Xianzhong; Huang, Lingling; Mühlenbernd, Holger; Li, Guixin; Bai, Benfeng; Tan, Qiaofeng; Jin, Guofan; Qiu, Cheng-Wei; Zhang, Shuang; Zentgraf, Thomas

    2012-11-01

    Surface topography and refractive index profile dictate the deterministic functionality of a lens. The polarity of most lenses reported so far, that is, either positive (convex) or negative (concave), depends on the curvatures of the interfaces. Here we experimentally demonstrate a counter-intuitive dual-polarity flat lens based on helicity-dependent phase discontinuities for circularly polarized light. Specifically, by controlling the helicity of the input light, the positive and negative polarity are interchangeable in one identical flat lens. Helicity-controllable real and virtual focal planes, as well as magnified and demagnified imaging, are observed on the same plasmonic lens at visible and near-infrared wavelengths. The plasmonic metalens with dual polarity may empower advanced research and applications in helicity-dependent focusing and imaging devices, angular-momentum-based quantum information processing and integrated nano-optoelectronics.

  18. Dual-polarity plasmonic metalens for visible light

    PubMed Central

    Chen, Xianzhong; Huang, Lingling; Mühlenbernd, Holger; Li, Guixin; Bai, Benfeng; Tan, Qiaofeng; Jin, Guofan; Qiu, Cheng-Wei; Zhang, Shuang; Zentgraf, Thomas

    2012-01-01

    Surface topography and refractive index profile dictate the deterministic functionality of a lens. The polarity of most lenses reported so far, that is, either positive (convex) or negative (concave), depends on the curvatures of the interfaces. Here we experimentally demonstrate a counter-intuitive dual-polarity flat lens based on helicity-dependent phase discontinuities for circularly polarized light. Specifically, by controlling the helicity of the input light, the positive and negative polarity are interchangeable in one identical flat lens. Helicity-controllable real and virtual focal planes, as well as magnified and demagnified imaging, are observed on the same plasmonic lens at visible and near-infrared wavelengths. The plasmonic metalens with dual polarity may empower advanced research and applications in helicity-dependent focusing and imaging devices, angular-momentum-based quantum information processing and integrated nano-optoelectronics. PMID:23149743

  19. Sb(2)O(3) nanobelt networks for excellent visible-light-range photodetectors.

    PubMed

    Li, L; Zhang, Y X; Fang, X S; Zhai, T Y; Liao, M Y; Wang, H Q; Li, G H; Koide, Y; Bando, Y; Golberg, D

    2011-04-22

    Excellent photoconductive properties have been found in Sb(2)O(3) nanobelts synthesized by a surfactant-assisted solvothermal method. Visible-light photodetectors have been designed from Sb(2)O(3) nanobelt networks using micrometer-wide gold wires as masks. Photodetectors show high sensitivity to visible light, high stability, and reproducibility. Fast response and decay times (<0.3 s) are comparable or even better than these parameters in many other metal oxide nanoscale photodetectors. The dominant mechanism of excellent photoconductivity is attributed to the barrier height modulations in the nanobelt-to-nanobelt contact regions. These results demonstrate that Sb(2)O(3) nanobelt networks can indeed serve as high-performance photodetectors in the visible light range.

  20. Enhanced visible-light activity of titania via confinement inside carbon nanotubes.

    PubMed

    Chen, Wei; Fan, Zhongli; Zhang, Bei; Ma, Guijun; Takanabe, Kazuhiro; Zhang, Xixiang; Lai, Zhiping

    2011-09-28

    Titania confined inside carbon nanotubes (CNTs) was synthesized using a restrained hydrolysis method. Raman spectra and magnetic measurements using a SQUID magnetometer suggested the formation of remarkable oxygen vacancies over the encapsulated TiO(2) in comparison with nanoparticles dispersed on the outer surface of CNTs, extending the photoresponse of TiO(2) from the UV to the visible-light region. The CNT-confined TiO(2) exhibited improved visible-light activity in the degradation of methylene blue (MB) relative to the outside titania and commercial P25, which is attributed to the modification of the electronic structure of TiO(2) induced by the unique confinement inside CNTs. These results provide further insight into the effect of confinement within CNTs, and the composites are expected to be promising for applications in visible-light photocatalysis.

  1. Photoinduced reactions between Pb3O4 and organic dyes in aqueous solution under visible light.

    PubMed

    Zhou, Yangen; Long, Jinlin; Gu, Quan; Lin, Huaxiang; Lin, Huan; Wang, Xuxu

    2012-12-01

    Pb(3)O(4) could react with organic dyes in aqueous solution under visible light irradiation, in which Pb(3)O(4) was transformed into Pb(3)(CO(3))(2)(OH)(2) along with oxidation of the organic dyes. Cu(2+) has considerable effect on the reaction. In the presence of Cu(2+), MO (20 ppm) and RhB (10(-5) mol L(-1)) were completely degraded under visible light within 6 and 20 min, respectively, while both Pb(3)O(4) and Cu(2+) keep almost stable during photodegradation. The mechanisms of the reactions with and without Cu(2+) ions were studied. The photochemical system of Pb(3)O(4) cooperating with Cu(2+) ions is probably used for the treatment of organic pollutants in water under visible light.

  2. Visible light inactivation of bacteria and fungi by modified titanium dioxide.

    PubMed

    Mitoraj, Dariusz; Jańczyk, Agnieszka; Strus, Magdalena; Kisch, Horst; Stochel, Grazyna; Heczko, Piotr B; Macyk, Wojciech

    2007-06-01

    Visible light induced photocatalytic inactivation of bacteria (Escherichia coli, Staphylococcus aureus, Enterococcus faecalis) and fungi (Candida albicans, Aspergillus niger) was tested. Carbon-doped titanium dioxide and TiO2 modified with platinum(IV) chloride complexes were used as suspension or immobilised at the surface of plastic plates. A biocidal effect was observed under visible light irradiation in the case of E. coli in the presence of both photocatalysts. The platinum(IV) modified titania exhibited a higher inactivation effect, also in the absence of light. The mechanism of visible light induced photoinactivation is briefly discussed. The observed detrimental effect of photocatalysts on various microorganism groups decreases in the order: E. coli > S. aureus approximately E. faecalis>C. albicans approximately A. niger. This sequence results most probably from differences in cell wall or cell membrane structures in these microorganisms and is not related to the ability of catalase production. PMID:17549266

  3. Low-level visible light (LLVL) irradiation promotes proliferation of mesenchymal stem cells.

    PubMed

    Lipovsky, Anat; Oron, Uri; Gedanken, Aharon; Lubart, Rachel

    2013-07-01

    Low-level visible light irradiation was found to stimulate proliferation potential of various types of cells in vitro. Stem cells in general are of significance for implantation in regenerative medicine. The aim of the present study was to investigate the effect of low-level light irradiation on the proliferation of mesenchymal stem cells (MSCs). MSCs were isolated from the bone marrow, and light irradiation was applied at energy densities of 2.4, 4.8, and 7.2 J/cm(2). Illumination of the MSCs resulted in almost twofold increase in cell number as compared to controls. Elevated reactive oxygen species and nitric oxide production was also observed in MSCs cultures following illumination with broadband visible light. The present study clearly demonstrates the ability of broadband visible light illumination to promote proliferation of MSCs in vitro. These results may have an important impact on wound healing.

  4. Melanin photosensitization and the effect of visible light on epithelial cells.

    PubMed

    Chiarelli-Neto, Orlando; Ferreira, Alan Silva; Martins, Waleska Kerllen; Pavani, Christiane; Severino, Divinomar; Faião-Flores, Fernanda; Maria-Engler, Silvya Stuchi; Aliprandini, Eduardo; Martinez, Glaucia R; Di Mascio, Paolo; Medeiros, Marisa H G; Baptista, Maurício S

    2014-01-01

    Protecting human skin from sun exposure is a complex issue that involves unclear aspects of the interaction between light and tissue. A persistent misconception is that visible light is safe for the skin, although several lines of evidence suggest otherwise. Here, we show that visible light can damage melanocytes through melanin photosensitization and singlet oxygen (1O2) generation, thus decreasing cell viability, increasing membrane permeability, and causing both DNA photo-oxidation and necro-apoptotic cell death. UVA (355 nm) and visible (532 nm) light photosensitize 1O2 with similar yields, and pheomelanin is more efficient than eumelanin at generating 1O2 and resisting photobleaching. Although melanin can protect against the cellular damage induced by UVB, exposure to visible light leads to pre-mutagenic DNA lesions (i.e., Fpg- and Endo III-sensitive modifications); these DNA lesions may be mutagenic and may cause photoaging, as well as other health problems, such as skin cancer.

  5. Automatic illumination compensation device based on a photoelectrochemical biofuel cell driven by visible light.

    PubMed

    Yu, You; Han, Yanchao; Xu, Miao; Zhang, Lingling; Dong, Shaojun

    2016-04-28

    Inverted illumination compensation is important in energy-saving projects, artificial photosynthesis and some forms of agriculture, such as hydroponics. However, only a few illumination adjustments based on self-powered biodetectors that quantitatively detect the intensity of visible light have been reported. We constructed an automatic illumination compensation device based on a photoelectrochemical biofuel cell (PBFC) driven by visible light. The PBFC consisted of a glucose dehydrogenase modified bioanode and a p-type semiconductor cuprous oxide photocathode. The PBFC had a high power output of 161.4 μW cm(-2) and an open circuit potential that responded rapidly to visible light. It adjusted the amount of illumination inversely irrespective of how the external illumination was changed. This rational design of utilizing PBFCs provides new insights into automatic light adjustable devices and may be of benefit to intelligent applications. PMID:27076202

  6. Indoor anti-occlusion visible light positioning systems based on particle filtering

    NASA Astrophysics Data System (ADS)

    Jiang, Meng; Huang, Zhitong; Li, Jianfeng; Zhang, Ruqi; Ji, Yuefeng

    2015-04-01

    As one of the most popular categories of mobile services, a rapid growth of indoor location-based services has been witnessed over the past decades. Indoor positioning methods based on Wi-Fi, radio-frequency identification or Bluetooth are widely commercialized; however, they have disadvantages such as low accuracy or high cost. An emerging method using visible light is under research recently. The existed visible light positioning (VLP) schemes using carrier allocation, time allocation and multiple receivers all have limitations. This paper presents a novel mechanism using particle filtering in VLP system. By this method no additional devices are needed and the occlusion problem in visible light would be alleviated which will effectively enhance the flexibility for indoor positioning.

  7. Laser-Modified Black Titanium Oxide Nanospheres and Their Photocatalytic Activities under Visible Light.

    PubMed

    Chen, Xing; Zhao, Dongxu; Liu, Kewei; Wang, Chunrui; Liu, Lei; Li, Binghui; Zhang, Zhenzhong; Shen, Dezhen

    2015-07-29

    A facile pulse laser ablation approach for preparing black titanium oxide nanospheres, which could be used as photocatalysts under visible light, is proposed. The black titanium oxide nanospheres are prepared by pulsed-laser irradiation of pure titanium oxide in suspended aqueous solution. The crystalline phases, morphology, and optical properties of the obtained nanospheres are characterized by means of X-ray diffraction (XRD), field-emission scanning electron microscopy (SEM), transmission electron microscopy (TEM), selected area electron diffraction (SAED), X-ray photoelectron spectroscopy (XPS), and UV-vis-NIR diffuse reflectance spectroscopy. It is shown that high-energy laser ablation of titanium oxide suspended solution benefited the formation of Ti(3+) species and surface disorder on the surface of the titanium oxide nanospheres. The laser-modified black titanium oxide nanospheres could absorb the full spectrum of visible light, thus exhibiting good photocatalytic performance under visible light.

  8. Three-visible-light wave combiner based on photonic crystal waveguides.

    PubMed

    Liu, Dingwen; Sun, Yiling; Ouyang, Zhengbiao

    2014-07-20

    We present a three-visible-light wave combiner based on two-dimensional photonic crystal waveguides whose widths are not integral multiples of the lattice period. The proposed device consists of two cascaded directional couplers. It combines three visible light waves with different wavelengths from three input ports into a single output port. As an example, a combiner for combining light waves of 635, 532, and 488 nm, which are commonly used as the three primary colors in laser display systems, is designed and demonstrated through the finite-difference time-domain method. The results show that the proposed device can perform efficient synthesis for three visible light waves with transmittance exceeding 89% for each wavelength and high ability in preventing the backward coupling of waves from different waveguides. The method for designing the combiner is useful for designing other waveguide couplers based on photonic crystals made of dispersion materials.

  9. Melanin Photosensitization and the Effect of Visible Light on Epithelial Cells

    PubMed Central

    Chiarelli-Neto, Orlando; Ferreira, Alan Silva; Martins, Waleska Kerllen; Pavani, Christiane; Severino, Divinomar; Faião-Flores, Fernanda; Maria-Engler, Silvya Stuchi; Aliprandini, Eduardo; Martinez, Glaucia R.; Di Mascio, Paolo; Medeiros, Marisa H. G.; Baptista, Maurício S.

    2014-01-01

    Protecting human skin from sun exposure is a complex issue that involves unclear aspects of the interaction between light and tissue. A persistent misconception is that visible light is safe for the skin, although several lines of evidence suggest otherwise. Here, we show that visible light can damage melanocytes through melanin photosensitization and singlet oxygen (1O2) generation, thus decreasing cell viability, increasing membrane permeability, and causing both DNA photo-oxidation and necro-apoptotic cell death. UVA (355 nm) and visible (532 nm) light photosensitize 1O2 with similar yields, and pheomelanin is more efficient than eumelanin at generating 1O2 and resisting photobleaching. Although melanin can protect against the cellular damage induced by UVB, exposure to visible light leads to pre-mutagenic DNA lesions (i.e., Fpg- and Endo III-sensitive modifications); these DNA lesions may be mutagenic and may cause photoaging, as well as other health problems, such as skin cancer. PMID:25405352

  10. Efficient ZnO-based visible-light-driven photocatalyst for antibacterial applications.

    PubMed

    Kumar, Raju; Anandan, Srinivasan; Hembram, Kaliyan; Rao, Tata Narasinga

    2014-08-13

    Herein, we report the development of a ZnO-based visible-light-driven photocatalyst by interfacial charge transfer process for the inactivation of pathogens under visible-light illumination. Surface modification by a cocatalyst on ZnO, prepared by flame spray pyrolysis process is carried out to induce the visible-light absorption in ZnO. Optical studies showed that surface modification of Cu(2+) induces the visible-light absorption in ZnO by interfacial charge transfer between ZnO and surface Cu(2+) ions upon light irradiation. The photocatalytic efficiency of pure and modified ZnO is evaluated for the inactivation of pathogens and the decomposition of methylene blue under visible-light illumination. The antibacterial activity of Cu(2+)-ZnO is several orders higher than pure ZnO and commercial Degussa-P25 and comparable with Cu(2+)-TiO2. Cu(2+)-ZnO nanorods show better photocatalytic activity than Cu(2+)-ZnO nanosphere, which is attributed to high surface area to volume ratio of former than later. The holes generated in the valence band and the Cu(1+) species generated during the interfacial charge transfer process may attribute for the inactivation of bacteria, whereas the strong oxidation power of hole is responsible for the decomposition of methylene blue. Besides the advantage of Cu(2+)-modified ZnO for visible-light-assisted photocatalytic applications, the method (FSP) used for the synthesis of ZnO in the present study is attractive for commercial application because the process has potential for the production of large quantities (2-3 kg/h) of semiconductors. PMID:25029041

  11. Automatic illumination compensation device based on a photoelectrochemical biofuel cell driven by visible light

    NASA Astrophysics Data System (ADS)

    Yu, You; Han, Yanchao; Xu, Miao; Zhang, Lingling; Dong, Shaojun

    2016-04-01

    Inverted illumination compensation is important in energy-saving projects, artificial photosynthesis and some forms of agriculture, such as hydroponics. However, only a few illumination adjustments based on self-powered biodetectors that quantitatively detect the intensity of visible light have been reported. We constructed an automatic illumination compensation device based on a photoelectrochemical biofuel cell (PBFC) driven by visible light. The PBFC consisted of a glucose dehydrogenase modified bioanode and a p-type semiconductor cuprous oxide photocathode. The PBFC had a high power output of 161.4 μW cm-2 and an open circuit potential that responded rapidly to visible light. It adjusted the amount of illumination inversely irrespective of how the external illumination was changed. This rational design of utilizing PBFCs provides new insights into automatic light adjustable devices and may be of benefit to intelligent applications.Inverted illumination compensation is important in energy-saving projects, artificial photosynthesis and some forms of agriculture, such as hydroponics. However, only a few illumination adjustments based on self-powered biodetectors that quantitatively detect the intensity of visible light have been reported. We constructed an automatic illumination compensation device based on a photoelectrochemical biofuel cell (PBFC) driven by visible light. The PBFC consisted of a glucose dehydrogenase modified bioanode and a p-type semiconductor cuprous oxide photocathode. The PBFC had a high power output of 161.4 μW cm-2 and an open circuit potential that responded rapidly to visible light. It adjusted the amount of illumination inversely irrespective of how the external illumination was changed. This rational design of utilizing PBFCs provides new insights into automatic light adjustable devices and may be of benefit to intelligent applications. Electronic supplementary information (ESI) available. See DOI: 10.1039/c6nr00759g

  12. The chemistry of amine radical cations produced by visible light photoredox catalysis

    PubMed Central

    Hu, Jie; Wang, Jiang; Nguyen, Theresa H

    2013-01-01

    Summary Amine radical cations are highly useful reactive intermediates in amine synthesis. They have displayed several modes of reactivity leading to some highly sought-after synthetic intermediates including iminium ions, α-amino radicals, and distonic ions. One appealing method to access amine radical cations is through one-electron oxidation of the corresponding amines under visible light photoredox conditions. This approach and subsequent chemistries are emerging as a powerful tool in amine synthesis. This article reviews synthetic applications of amine radical cations produced by visible light photocatalysis. PMID:24204409

  13. Water-plasma-assisted synthesis of black titania spheres with efficient visible-light photocatalytic activity.

    PubMed

    Panomsuwan, Gasidit; Watthanaphanit, Anyarat; Ishizaki, Takahiro; Saito, Nagahiro

    2015-06-01

    Black titania spheres (H-TiO2-x) were synthesized via a simple green method assisted by water plasma at a low temperature and atmospheric pressure. The in situ production of highly energetic hydroxyl and hydrogen species from water plasma are the prominent factors in the oxidation and hydrogenation reactions during the formation of H-TiO2-x, respectively. The visible-light photocatalytic activity toward the dye degradation of H-TiO2-x can be attributed to the synergistic effect of large-surface area, visible-light absorption and the existence of oxygen vacancies and Ti(3+) sites. PMID:25946395

  14. Water-plasma-assisted synthesis of black titania spheres with efficient visible-light photocatalytic activity.

    PubMed

    Panomsuwan, Gasidit; Watthanaphanit, Anyarat; Ishizaki, Takahiro; Saito, Nagahiro

    2015-06-01

    Black titania spheres (H-TiO2-x) were synthesized via a simple green method assisted by water plasma at a low temperature and atmospheric pressure. The in situ production of highly energetic hydroxyl and hydrogen species from water plasma are the prominent factors in the oxidation and hydrogenation reactions during the formation of H-TiO2-x, respectively. The visible-light photocatalytic activity toward the dye degradation of H-TiO2-x can be attributed to the synergistic effect of large-surface area, visible-light absorption and the existence of oxygen vacancies and Ti(3+) sites.

  15. Strong visible light emission from well-aligned multiwalled carbon nanotube films under infrared laser irradiation

    SciTech Connect

    Zhang Yong; Gong Tao; Liu Wenjin; Zhang Xianfeng; Chang Jianguo; Wang Kunlin; Wu Dehai

    2005-10-24

    We report strong and brilliant visible light emission from well-aligned multiwalled carbon nanotube (AMWNT) films under infrared (IR) laser irradiation with wavelength at 1.06 and 10.6 {mu}m, respectively. The AMWNT film shows a high durability against laser irradiation and achieved a conversion from IR laser to visible light. It is a good candidate for optical converter. Light emission spectra versus different wavelengths and various powers were found to have similar line shapes. It could be explained as combination of laser-induced photoluminescence and resistive heating.

  16. Nitrogen-sensitized dual phase titanate/titania for visible-light driven phenol degradation

    SciTech Connect

    Cheng, Yu Hua; Subramaniam, Vishnu P.; Gong, Dangguo; Tang, Yuxin; Highfield, James; Pehkonen, Simo O.; Pichat, Pierre; Chen, Zhong

    2012-12-15

    A dual-phase material (DP-160) comprising hydrated titanate (H{sub 2}Ti{sub 3}O{sub 7}{center_dot}xH{sub 2}O) and anatase (TiO{sub 2}) was synthesized in a low-temperature one-pot process in the presence of triethylamine (TEA) as the N-source. The unique structure exhibits strong visible light absorption. The chromophore is linked to Ti-N bonds derived from both surface sensitization and sub-surface (bulk) doping. From transmission electron microscope (TEM) and textural studies by N{sub 2} physisorption, the composite exists as mesoporous particles with a grain size of {approx}20 nm and mean pore diameter of 3.5 nm, responsible for the high surface area ({approx}180 m{sup 2}/g). DP-160 demonstrated photocatalytic activity in the degradation of phenol under visible light ({lambda}>420 nm). The activity of the composite was further enhanced by a small addition (0.001 M) of H{sub 2}O{sub 2}, which also gave rise to some visible light activity in the control samples. This effect is believed to be associated with the surface peroxo-titanate complex. GC-MS analyses showed that the intermediate products of phenol degradation induced by visible light irradiation of DP-160 did not differ from those obtained by UV (band-gap) irradiation of TiO{sub 2}. The overall performance of the composite is attributed to efficient excitation via inter-band states (due to N-doping), surface sensitization, improved adsorptive properties of aromatic compounds due to the N-carbonaceous overlayer, and the presence of heterojunctions that are known to promote directional charge transfer in other mixed-phase titanias like Degussa P25. - graphical abstract: Nitrogen-sensitized dual phase titanate/titania photocatalyst showing extended visible light absorption and efficient photocatalytic degradation of phenol. Highlights: Black-Right-Pointing-Pointer Low temperature one-pot synthesis of visible light active dual phase photocatalyst. Black-Right-Pointing-Pointer The dual phase consists of

  17. Iron(III)-oxo centers on TiO{sub 2} for visible light photocatalysis.

    SciTech Connect

    Libera, J. A.; Elam, J. W.; Sather, N. F.; Rajh, T.; Dimitrijevic, N. M.

    2009-01-01

    Isolated iron(III)-oxo clusters were synthesized onto TiO{sub 2} using atomic layer deposition. The Fe{sub x}O{sub y}/TiO{sub 2} nanocomposites have unique properties that enable not only absorption of visible light, but efficient photocatalysis as demonstrated by methylene blue degradation. The localization of photogenerated electrons in core TiO{sub 2} nanocrystallites upon visible light excitation demonstrates coupling of conduction bands of mixed oxides. The redox properties of photogenerated charges in nanocomposites were studied using in situ electron paramagnetic resonance spectroscopy.

  18. Patterning of silver nanoparticles on visible light-sensitive Mn-doped lithium niobate photogalvanic crystals

    SciTech Connect

    Liu Xiaoyan; Ohuchi, Fumio; Hatano, Hideki; Takekawa, Shunji; Kitamura, Kenji

    2011-08-01

    Visible light-induced polarization-dependent photochemical deposition of silver nanoparticles (AgNPs) has been demonstrated using Mn-doped congruent LiNbO{sub 3} (CLN) single crystals. Mn-doped CLN has a strong absorption over a wide region of the visible spectrum that allowed effective visible light irradiation for photochemical deposition. The AgNPs deposition on Mn-doped CLN was compared with that on non-doped congruent LiNbO{sub 3}, and together these further confirmed that the photochemical deposition on LiNbO{sub 3} is caused by the strong photogalvanic effect.

  19. Photocatalytic water treatment over WO 3 under visible light irradiation combined with ozonation

    NASA Astrophysics Data System (ADS)

    Nishimoto, Shunsuke; Mano, Takayuki; Kameshima, Yoshikazu; Miyake, Michihiro

    2010-11-01

    Photocatalytic water treatment over bare WO 3 under visible light irradiation combined with ozonation (O 3/vis/WO 3) was investigated using an aqueous phenol solution as model wastewater. The O 3/vis/WO 3 treatment exhibited a much higher total organic carbon removal than ozonation alone. Bare WO 3 was found to function as an active visible-light-responsive photocatalyst for decomposition of organic compounds in the presence of ozone, which readily reacts with photoexcited electrons in the conduction band of WO 3.

  20. Characterization of internal geometry / covered surface defects with a visible light sensing system

    NASA Astrophysics Data System (ADS)

    Straub, Jeremy

    2016-05-01

    Previous work has used visible light scanning to detect and characterize defects in 3D printed objects. This paper focuses on assessing the internal structures and external surfaces (that will be later hidden) of complex objects. These features make in-process defect detection far more important than it would be with an object that can be fully assessed with a post-completion scan, as it is required both for in-process correction and end-product quality assurance. This paper presents work on the use of a multi-camera visible light 3D scanning system to identify defects with printed objects' interior and covered / obscured exterior surfaces.

  1. High bandwidth based on a tapped delay line equalization in visible light communications

    NASA Astrophysics Data System (ADS)

    Zhang, Minglun; Guo, Xujing; Zhu, Hetian; Wang, Chao; Bai, Xiaonan; Zhai, Xiangwen

    2015-08-01

    In the visible light communication, the white LED bandwidth severely limits the transmission rate of information. This paper presents an analog pre-equalization technology to compensate for the bandwidth of white LED. The technology not only can debug according to the actual channel changing, but also avoid the high costs of using FPGA technology. The pre-equalization technology is implemented by an analog circuit of tapped-delay-line, in the circuit we select an appropriate delay line and a digital to analog converter. In our LED visible light communication system, we can achieve a bandwidth of 150MHz which was proved theoretically in the paper.

  2. A visible-light-promoted aerobic metal-free C-3 thiocyanation of indoles.

    PubMed

    Fan, Weigang; Yang, Qi; Xu, Fengshan; Li, Pixu

    2014-11-01

    A simple and efficient visible-light-promoted method for the C-3 thiocyanation of indoles has been developed. The transformation uses Rose Bengal as the photocatalyst and air as the terminal oxidant. The reaction is mild, high-yielding, and environmentally benign.

  3. Antibacterial property of Ag nanoparticle-impregnated N-doped titania films under visible light

    NASA Astrophysics Data System (ADS)

    Wong, Ming-Show; Chen, Chun-Wei; Hsieh, Chia-Chun; Hung, Shih-Che; Sun, Der-Shan; Chang, Hsin-Hou

    2015-07-01

    Photocatalysts produce free radicals upon receiving light energy; thus, they possess antibacterial properties. Silver (Ag) is an antibacterial material that disrupts bacterial physiology. Our previous study reported that the high antibacterial property of silver nanoparticles on the surfaces of visible light-responsive nitrogen-doped TiO2 photocatalysts [TiO2(N)] could be further enhanced by visible light illumination. However, the major limitation of this Ag-TiO2 composite material is its durability; the antibacterial property decreased markedly after repeated use. To overcome this limitation, we developed TiO2(N)/Ag/TiO2(N) sandwich films in which the silver is embedded between two TiO2(N) layers. Various characteristics, including silver and nitrogen amounts, were examined in the composite materials. Various analyses, including electron microscopy, energy dispersive spectroscopy, X-ray diffraction, and ultraviolet-visible absorption spectrum and methylene blue degradation rate analyses, were performed. The antibacterial properties of the composite materials were investigated. Here we revealed that the antibacterial durability of these thin films is substantially improved in both the dark and visible light, by which bacteria, such as Escherichia coli, Streptococcus pyogenes, Staphylococcus aureus, and Acinetobacter baumannii, could be efficiently eliminated. This study demonstrated a feasible approach to improve the visible-light responsiveness and durability of antibacterial materials that contain silver nanoparticles impregnated in TiO2(N) films.

  4. Visible-light-mediated chan-lam coupling reactions of aryl boronic acids and aniline derivatives.

    PubMed

    Yoo, Woo-Jin; Tsukamoto, Tatsuhiro; Kobayashi, Shū

    2015-05-26

    The copper(II)-catalyzed aerobic oxidative coupling reaction between aryl boronic acids and aniline derivatives was found to be improved significantly under visible-light-mediated photoredox catalysis. The substrate scope of this oxidative Chan-Lam reaction was thus expanded to include electron-deficient aryl boronic acids as viable starting materials.

  5. Layered double hydroxides as highly efficient photocatalysts for visible light oxygen generation from water.

    PubMed

    Gomes Silva, Cláudia; Bouizi, Younès; Fornés, Vicente; García, Hermenegildo

    2009-09-30

    Oxygen generation through photocatalytic water splitting under visible light irradiation is a challenging process. In this work we have synthesized a series of Zn/Ti, Zn/Ce, and Zn/Cr layered double hydroxides (LDH) at different Zn/metal atomic ratio (from 4:2 to 4:0.25) and tested them for the visible light photocatalytic oxygen generation. The most active material was found to be (Zn/Cr)LDH with an atomic ratio of 4:2 that exhibits two absorption bands in the visible region at lambda(max) of 410 and 570 nm. It was found that the efficiency of these chromium layered double oxides for oxygen generation increases asymptotically with the Cr content. Using iron oxalate as chemical actinometer we have determined that the apparent quantum yields for oxygen generation (Phi apparent = 4 x mol oxygen/mol incident photons) are of 60.9% and 12.2% at 410 and 570 nm, respectively. These quantum yields are among the highest values ever determined with visible light for solid materials in the absence of light harvesting dye. The overall efficiency of (Zn/Cr)LDH for visible light oxygen generation was found to be 1.6 times higher than that of WO(3) under the same conditions.

  6. Antibacterial property of Ag nanoparticle-impregnated N-doped titania films under visible light

    PubMed Central

    Wong, Ming-Show; Chen, Chun-Wei; Hsieh, Chia-Chun; Hung, Shih-Che; Sun, Der-Shan; Chang, Hsin-Hou

    2015-01-01

    Photocatalysts produce free radicals upon receiving light energy; thus, they possess antibacterial properties. Silver (Ag) is an antibacterial material that disrupts bacterial physiology. Our previous study reported that the high antibacterial property of silver nanoparticles on the surfaces of visible light-responsive nitrogen-doped TiO2 photocatalysts [TiO2(N)] could be further enhanced by visible light illumination. However, the major limitation of this Ag-TiO2 composite material is its durability; the antibacterial property decreased markedly after repeated use. To overcome this limitation, we developed TiO2(N)/Ag/TiO2(N) sandwich films in which the silver is embedded between two TiO2(N) layers. Various characteristics, including silver and nitrogen amounts, were examined in the composite materials. Various analyses, including electron microscopy, energy dispersive spectroscopy, X-ray diffraction, and ultraviolet–visible absorption spectrum and methylene blue degradation rate analyses, were performed. The antibacterial properties of the composite materials were investigated. Here we revealed that the antibacterial durability of these thin films is substantially improved in both the dark and visible light, by which bacteria, such as Escherichia coli, Streptococcus pyogenes, Staphylococcus aureus, and Acinetobacter baumannii, could be efficiently eliminated. This study demonstrated a feasible approach to improve the visible-light responsiveness and durability of antibacterial materials that contain silver nanoparticles impregnated in TiO2(N) films. PMID:26156001

  7. Polymer nanoparticles for controlled release stimulated by visible light and pH.

    PubMed

    Dong, Jie; Zhang, Ruichen; Wu, Hao; Zhan, Xiaowei; Yang, Huai; Zhu, Siquan; Wang, Guojie

    2014-07-01

    Polymer nanoparticles are prepared by self-assembly of visible light and pH sensitive perylene-functionalized copolymers which are synthesized by quaternization between 1-(bromomethyl)perylene and the dimethylaminoethyl units of poly(dimethylaminoethyl methacrylate) (PDMAEMA). The perylene-containing polymethacrylate segments afford the system visible light responsiveness and the unquaternized PDMAEMA segments afford the system pH responsiveness. The self-assembled nanoparticles exhibit a unique dual stimuli response. They can be photocleaved under visible light irradiation, shrunken to smaller nanoparticles at high pH, and swollen at low pH. The structural change endows the nanoparticle with great potential as a sensitive nanocarrier for controlled release of Nile Red and lysozyme under this stimulation. The visible light responsiveness and synergistic effect on the release of loaded molecules with the dual stimulation may obviate the need for harsh conditions such as UV light or extreme pH stimulation, rendering the system more applicable under mild conditions. PMID:24719021

  8. Effects of ultraviolet radiation, visible light, and infrared radiation on erythema and pigmentation: a review.

    PubMed

    Sklar, Lindsay R; Almutawa, Fahad; Lim, Henry W; Hamzavi, Iltefat

    2013-01-01

    The effects of ultraviolet radiation, visible light, and infrared radiation on cutaneous erythema, immediate pigment darkening, persistent pigment darkening, and delayed tanning are affected by a variety of factors. Some of these factors include the depth of cutaneous penetration of the specific wavelength, the individual skin type, and the absorption spectra of the different chromophores in the skin. UVB is an effective spectrum to induce erythema, which is followed by delayed tanning. UVA induces immediate pigment darkening, persistent pigment darkening, and delayed tanning. At high doses, UVA (primarily UVA2) can also induce erythema in individuals with skin types I-II. Visible light has been shown to induce erythema and a tanning response in dark skin, but not in fair skinned individuals. Infrared radiation produces erythema, which is probably a thermal effect. In this article we reviewed the available literature on the effects of ultraviolet radiation, visible light, and infrared radiation on the skin in regards to erythema and pigmentation. Much remains to be learned on the cutaneous effects of visible light and infrared radiation.

  9. Gain dispersion in Visible Light Photon Counters as a function of counting rate

    SciTech Connect

    Bross, A.; Buscher, V.; Estrada, J.; Ginther, G.; Molina, J.; /Rio de Janeiro State U.

    2005-03-01

    We present measurements of light signals using Visible Light Photon Counters (VLPC), that indicate an increase in gain dispersion as the counting rate increases. We show that this dispersion can be understood on the basis of a recent observation of localized field reduction in VLPCs at high input rates.

  10. Antibacterial property of Ag nanoparticle-impregnated N-doped titania films under visible light.

    PubMed

    Wong, Ming-Show; Chen, Chun-Wei; Hsieh, Chia-Chun; Hung, Shih-Che; Sun, Der-Shan; Chang, Hsin-Hou

    2015-07-09

    Photocatalysts produce free radicals upon receiving light energy; thus, they possess antibacterial properties. Silver (Ag) is an antibacterial material that disrupts bacterial physiology. Our previous study reported that the high antibacterial property of silver nanoparticles on the surfaces of visible light-responsive nitrogen-doped TiO2 photocatalysts [TiO2(N)] could be further enhanced by visible light illumination. However, the major limitation of this Ag-TiO2 composite material is its durability; the antibacterial property decreased markedly after repeated use. To overcome this limitation, we developed TiO2(N)/Ag/TiO2(N) sandwich films in which the silver is embedded between two TiO2(N) layers. Various characteristics, including silver and nitrogen amounts, were examined in the composite materials. Various analyses, including electron microscopy, energy dispersive spectroscopy, X-ray diffraction, and ultraviolet-visible absorption spectrum and methylene blue degradation rate analyses, were performed. The antibacterial properties of the composite materials were investigated. Here we revealed that the antibacterial durability of these thin films is substantially improved in both the dark and visible light, by which bacteria, such as Escherichia coli, Streptococcus pyogenes, Staphylococcus aureus, and Acinetobacter baumannii, could be efficiently eliminated. This study demonstrated a feasible approach to improve the visible-light responsiveness and durability of antibacterial materials that contain silver nanoparticles impregnated in TiO2(N) films.

  11. Visible-light Induced Reduction of Graphene Oxide Using Plasmonic Nanoparticle.

    PubMed

    Kumar, Dinesh; Lee, Ah-Reum; Kaur, Sandeep; Lim, Dong-Kwon

    2015-09-22

    Present work demonstrates the simple, chemical free, fast, and energy efficient method to produce reduced graphene oxide (r-GO) solution at RT using visible light irradiation with plasmonic nanoparticles. The plasmonic nanoparticle is used to improve the reduction efficiency of GO. It only takes 30 min at RT by illuminating the solutions with Xe-lamp, the r-GO solutions can be obtained by completely removing gold nanoparticles through simple centrifugation step. The spherical gold nanoparticles (AuNPs) as compared to the other nanostructures is the most suitable plasmonic nanostructure for r-GO preparation. The reduced graphene oxide prepared using visible light and AuNPs was equally qualitative as chemically reduced graphene oxide, which was supported by various analytical techniques such as UV-Vis spectroscopy, Raman spectroscopy, powder XRD and XPS. The reduced graphene oxide prepared with visible light shows excellent quenching properties over the fluorescent molecules modified on ssDNA and excellent fluorescence recovery for target DNA detection. The r-GO prepared by recycled AuNPs is found to be of same quality with that of chemically reduced r-GO. The use of visible light with plasmonic nanoparticle demonstrates the good alternative method for r-GO synthesis.

  12. Visible light induced photobleaching of methylene blue over melamine-doped TiO2 nanocatalyst

    EPA Science Inventory

    TiO2 doping with N-rich melamine produced a stable, active and visible light sentisized nanocatalyst that showed a remarkable efficiency towards the photobleaching of a model compound – methylene blue (MB) in aqueous solution. The photobleaching followed a mixed reaction order ki...

  13. Visible light photon counters (VLPCs) for high rate tracking medical imaging and particle astrophysics

    SciTech Connect

    Atac, M.

    1998-02-01

    This paper is on the operation principles of the Visible Light Photon Counters (VLPCs), application to high luminosity-high multiplicity tracking for High Energy Charged Particle Physics, and application to Medical Imaging and Particle Astrophysics. The VLPCs as Solid State Photomultipliers (SSPMS) with high quantum efficiency can detect down to single photons very efficiently with excellent time resolution and high avalanche gains.

  14. Regioselective 2,2,2-Trifluoroethylation of Imidazopyridines by Visible Light Photoredox Catalysis.

    PubMed

    Zhu, Mei; Han, Xin; Fu, Weijun; Wang, Zhiqiang; Ji, Baoming; Hao, Xin-Qi; Song, Mao-Ping; Xu, Chen

    2016-08-19

    A visible-light-induced C-3 selective trifluoroethylation of imidazoheterocycles using 1,1,1-trifluoro-2-iodoethane as trifluoroethyl radical sources was developed. The methodology enables the introduction of a trifluoroethyl group in a fast and efficient reaction under mild conditions with excellent regioselectivities and high functional group tolerance. PMID:27328667

  15. Visible-Light-Induced Bactericidal Activity of Titanium Dioxide Co-doped with Nitrogen and Silver

    PubMed Central

    Wu, Pinggui; Xie, Rongcai; Imlay, Kari; Shang, Jian-Ku

    2011-01-01

    Titanium dioxide nanoparticles co-doped with nitrogen and silver (Ag2O/TiON) were synthesized by the sol-gel process and found to be an effective visible light driven photocatalyst. The catalyst showed strong bactericidal activity against Escherichia coli (E. coli) under visible light irradiation (λ> 400 nm). In x-ray photoelectron spectroscopy and x-ray diffraction characterization of the samples, the as-added Ag species mainly exist as Ag2O. Spin trapping EPR study showed Ag addition greatly enhanced the production of hydroxyl radicals (•OH) under visible light irradiation. The results indicate that the Ag2O species trapped eCB− in the process of Ag2O/TiON photocatalytic reaction, thus inhibiting the recombination of eCB− and hVB+ in agreement with the stronger photocatalytic bactericidal activity of Ag2O/TiON. The killing mechanism of Ag2O/TiON under visible light irradiation is shown to be related to oxidative damages in the forms of cell wall thinning and cell disconfiguration. PMID:20726520

  16. Visible-Light-Driven Photocatalytic Initiation of Radical Thiol-Ene Reactions Using Bismuth Oxide.

    PubMed

    Fadeyi, Olugbeminiyi O; Mousseau, James J; Feng, Yiqing; Allais, Christophe; Nuhant, Philippe; Chen, Ming Z; Pierce, Betsy; Robinson, Ralph

    2015-12-01

    A nontoxic and inexpensive photocatalytic initiation of anti-Markovnikov hydrothiolation of olefins using visible light is reported. This method is characterized by low catalyst loading, thereby enabling a mild and selective method for radical initiation in thiol-ene reactions between a wide scope of olefins and thiols. PMID:26572219

  17. Phototoxic effect of visible light on Porphyromonas gingivalis and Fusobacterium nucleatum: an in vitro study.

    PubMed

    Feuerstein, Osnat; Persman, Nir; Weiss, Ervin I

    2004-01-01

    The antibacterial effect of visible light irradiation combined with photosensitizers has been reported. The objective of this was to test the effect of visible light irradiation without photosensitizers on the viability of oral microorganisms. Strains of Porphyromonas gingivalis, Fusobacterium nucleatum, Streptococcus mutans and Streptococcus faecalis in suspension or grown on agar were exposed to visible light at wavelengths of 400-500 nm. These wavelengths are used to photopolymerize composite resins widely used for dental restoration. Three photocuring light sources, quartz-tungsten-halogen lamp, light-emitting diode and plasma-arc, at power densities between 260 and 1300 mW/cm2 were used for up to 3 min. Bacterial samples were also exposed to a near-infrared diode laser (wavelength, 830 nm), using identical irradiation parameters for comparison. The results show that blue light sources exert a phototoxic effect on P. gingivalis and F. nucleatum. The minimal inhibitory dose for P. gingivalis and F. nucleatum was 16-62 J/cm2, a value significantly lower than that for S. mutans and S. faecalis (159-212 J/cm2). Near-infrared diode laser irradiation did not affect any of the bacteria tested. Our results suggest that visible light sources without exogenous photosensitizers have a phototoxic effect mainly on Gram-negative periodontal pathogens. PMID:15623322

  18. Selective Breaking of Hydrogen Bonds of Layered Carbon Nitride for Visible Light Photocatalysis.

    PubMed

    Kang, Yuyang; Yang, Yongqiang; Yin, Li-Chang; Kang, Xiangdong; Wang, Lianzhou; Liu, Gang; Cheng, Hui-Ming

    2016-08-01

    Selective breaking of the hydrogen bonds of graphitic carbon nitride can introduce favorable features, including increased band tails close to the band edges and the creation of abundant pores. These features can simultaneously improve the three basic processes of photocatalysis. As a consequence, the photocatalytic hydrogen-generation activity of carbon nitride under visible light is drastically increased by tens of times.

  19. Visible-Light-Sensitive Photocatalysts: Nanocluster-Grafted Titanium Dioxide for Indoor Environmental Remediation.

    PubMed

    Miyauchi, Masahiro; Irie, Hiroshi; Liu, Min; Qiu, Xiaoqing; Yu, Huogen; Sunada, Kayano; Hashimoto, Kazuhito

    2016-01-01

    Photocatalytic degradation of organic compounds requires photoexcited holes with strong oxidative power in the valence band (VB) of semiconductors. Although numerous types of doped semiconductors, such as nitrogen-doped TiO2, have been studied as visible-light-sensitive photocatalysts, the quantum yields of these materials were very low because of the limited oxidation power of holes in the nitrogen level above the VB. Recently, we developed visible-light-sensitive Cu(II) and Fe(III) nanocluster-grafted TiO2 using a facile impregnation method and demonstrated that visible-light absorption occurs at the interface between the nanoclusters and TiO2, as electrons in the VB of TiO2 are excited to the nanoclusters under visible-light irradiation. In addition, photogenerated holes in the VB of TiO2 efficiently oxidize organic contaminants, and the excited electrons that accumulate in nanoclusters facilitate the multielectron reduction of oxygen. Notably, Cu(II) and Fe(III) nanocluster-grafted TiO2 photocatalyst has the highest quantum yield among reported photocatalysts and has antiviral, self-cleaning, and air purification properties under illumination by indoor light fixtures equipped with white fluorescent bulbs or white light-emitting diodes. PMID:26654353

  20. Intermolecular C-H Quaternary Alkylation of Aniline Derivatives Induced by Visible-Light Photoredox Catalysis.

    PubMed

    Cheng, Jie; Deng, Xia; Wang, Guoqiang; Li, Ying; Cheng, Xu; Li, Guigen

    2016-09-16

    The intermolecular direct C-H alkylation of aniline derivatives with α-bromo ketones to build a quaternary carbon center was reported with a visible-light catalysis procedure. The reaction covers a variety of functional groups with good to excellent yields. A regioselectivity favoring the ortho position for the amine group was observed and investigated with Fukui indices and spectral methods.

  1. Synthesis of novel photocatalytic RGO-InVO{sub 4} nanocomposites with visible light photoactivity

    SciTech Connect

    Shen, Jianfeng; Li, Xianfu; Huang, Weishi; Li, Na; Ye, Mingxin

    2013-09-01

    Graphical abstract: A facile method for preparation of reduced graphene oxide (RGO) sheets supported indium vanadate (InVO{sub 4}) photocatalysts is reported. The visible light response and adsorption ability of RGO-InVO{sub 4} nanocomposites is greatly improved, which can effectively remove methyl orange and Cr (VI) from water. - Highlights: • Supramolecular photocatalyst of RGO-InVO{sub 4} was achieved. • Reduction of GO and preparation of RGO-InVO{sub 4} was simultaneous. • The prepared RGO-InVO{sub 4} shows high photocatalytic activity and adsorption capacity under visible light. • In situ growth of uniform InVO{sub 4} particles on RGO sheets is facile and efficient - Abstract: In this study, we report a facile method for preparation of reduced graphene oxide (RGO) sheets supported indium vanadate (InVO{sub 4}) photocatalysts. A wide range of characterization techniques, such as Fourier transform infrared spectroscopy, Raman spectroscopy, X-ray diffraction, Thermogravimetric analysis and Transmission electron microscopy were applied to characterize the obtained composites. The results indicated that the composites consist of uniformly dispersed InVO{sub 4} nanocrystals on RGO sheets. Visible light responses of RGO-InVO{sub 4} nanocomposites are greatly improved as compared with the bulk InVO{sub 4}. The as-prepared RGO-InVO{sub 4} nanocomposites can effectively remove methyl orange and Cr (VI) from water under visible light irradiation, which can be used as novel photocatalysts for environmental protection.

  2. Development and Progress in Enabling the Photocatalyst Ti02 Visible-Light-Active

    NASA Technical Reports Server (NTRS)

    Levine, Lanfang H.; Coutts, Janelle L.; Clausen, Christian A.

    2011-01-01

    Photocatalytic oxidation (PCO) of organic contaminants is a promising air and water quality management approach which offers energy and cost savings compared to thermal catalytic oxidation (TCO). The most widely used photocatalyst, anatase TiO2, has a wide band gap (3.2 eV) and is activated by UV photons. Since solar radiation consists of less than 4% UV, but contains 45% visible light, catalysts capable of utilizing these visible photons need to be developed to make peo approaches more efficient, economical, and safe. Researchers have attempted various approaches to enable TiO2 to be visible-light-active with varied degrees of success'. Strategies attempted thus far fall into three categories based on their electrochemical' mechanisms: 1) narrowing the band gap of TiO2 by implantation of transition metal elements or nonmetal elements such as N, S, and C, 2) modifying electron-transfer processes during PCO by adsorbing sensitizing dyes, and 3) employing light-induced interfacial electron transfer in the heteronanojunction systems consisting of narrow band gap semiconductors represented by metal sulfides and TiO2. There are diverse technical approaches to implement each of these strategies. This paper presents a review of these approaches and results of the photocatalytic activity and photonic efficiency of the end .products under visible light. Although resulting visible-light-active (VLA) photocatalysts show promise, there is often no comparison with unmodified TiO2 under UV. In a limited number of studies where such comparison was provided, the UV-induced catalytic activity of bare TiO2 is much greater than the visible-light-induced catalytic activity of the VLA catalyst. Furthermore, VLA-catalysts have much lower quantum efficiency compared to the approx.50% quantum efficiency of UV-catalysts. This stresses the need for continuing research in this area.

  3. Visible light Cr(VI) reduction and organic chemical oxidation by TiO2 photocatalysis.

    PubMed

    Sun, Bo; Reddy, Ettireddy P; Smirniotis, Panagiotis G

    2005-08-15

    Here we report the simultaneous Cr(VI) reduction and 4-chlorophenol (4-CP) oxidation in water under visible light (wavelength > 400 nm) using commercial Degussa P25 TiO2. This remarkable observation was attributed to a synergistic effect among TiO2, Cr(VI), and 4-CP. It is well known that TiO2 alone cannot remove either 4-CP or Cr(VI) efficiently under visible light. Moreover, the interaction between Cr(VI) and 4-CP is minimal if not negligible. However, we found that the combination of TiO2, Cr(VI), and 4-CP together can enable efficient Cr(VI) reduction and 4-CP oxidation under visible light. The specific roles of the three ingredients in the synergistic system were studied parametrically. It was found that optimal concentrations of Cr(VI) and TiO2 exist for the Cr(VI) reduction and 4-CP oxidation. Cr(VI) was compared experimentally with other metals such as Cu(ll), Fe(lll), Mn(IV), Ce(IV), and V(V). Among all these metal ions, only Cr(VI) promotes the photocatalytic oxidation of 4-CP. The amount of 4-CP removed was directly related to the initial concentration of Cr(VI). The system was also tested with four other chemicals (aniline, salicylic acid, formic acid, and diethyl phosphoramidate). We found that the same phenomenon occurred for organics containing acid and/or phenolic groups. Cr(VI) was reduced at the same time as the organic chemicals being oxidized during photoreaction under visible light. The synergistic effect was also found with pure anatase TiO2 and rutile TiO2. This study demonstrates a possible economical way for environmental cleanup under visible light.

  4. [TiO2-Induced Photodegradation of Levofloxacin by Visible Light and Its Mechanism].

    PubMed

    Guo, Hong-sheng; Liu, Ya-nan; Qiao, Qi; Wei, Hong; Dong, Cheng-xing; Xue, Jie; Li, Ke-bin

    2015-05-01

    Levofloxacin is an emerging pollutant. Single levofloxacin and TiO2 have no visible-light activity. However, photodegradation of levofloxacin dramatically enhanced in the presence of TiO2 under visible light irradiation. Considering this finding, he photodegradation of levofloxacin over TiO2 was investigated under visible light irradiation. Effects of TiO2 dosage, levofloxacin concentration, and solution pH on levofloxacin photodegradation were examined by monitoring its concentration decay with time. The results showed that levofloxacin photodegradation fitted the Langmuir-Hinshelwood kinetic model. Solution pH, TiO2 dose, and levofloxacin concentration had significant effects on the photodegradation rates. In addition, batch adsorption experiments revealed that adsorption of levofloxacin on TiO2 conformed to the pseudo-second-order kinetics and the Langmuir isotherm. DRS spectrum of levofloxacin-adsorbed TiO2 suggested that a surface complex was formed between levofloxacin and TiO2. Addition of radical scavengers and N2-degassing affecting levofloxacin photodegradation indicated that the superoxide ion radical was mainly active species. UV-Vis spectra of a deaerated TiO2 and levofloxacin suspensions further confirmed that the electron injection into TiO2 conduction band took place under visible light irradiation. Based on these results, a charge-transfer mechanism initiated by photoexcitation of TiO2/ levofloxacin surface complex was proposed for levofloxacin photocatalytic degradation over TiO2 under visible light. This study indicates that the charge-transfer-complex-mediated photocatalytic technique has promising applications in the removal of colorless organic pollutants.

  5. Property Characterization and Photocatalytic Activity Evaluation of BiGdO₃ Nanoparticles under Visible Light Irradiation.

    PubMed

    Luan, Jingfei; Shen, Yue; Zhang, Lingyan; Guo, Ningbin

    2016-01-01

    BiGdO₃ nanoparticles were prepared by a solid-state reaction method and applied in photocatalytic degradation of dyes in this study. BiGdO₃ was characterized by X-ray powder diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, Brunauer-Emmett-Teller, UV-Vis diffuse reflectance spectroscopy and transmission electron microscopy. The results showed that BiGdO₃ crystallized well with the fluorite-type structure, a face-centered cubic crystal system and a space group Fm3m 225. The lattice parameter of BiGdO₃ was 5.465 angstrom. The band gap of BiGdO₃ was estimated to be 2.25 eV. BiGdO₃ showed a strong optical absorption during the visible light region. Moreover, the photocatalytic activity of BiGdO₃ was evaluated by photocatalytic degradation of direct dyes in aqueous solution under visible light irradiation. BiGdO₃ demonstrated excellent photocatalytic activity in degrading Direct Orange 26 (DO-26) or Direct Red 23 (DR-23) under visible light irradiation. The photocatalytic degradation of DO-26 or DR-23 followed the first-order reaction kinetics, and the first-order rate constant was 0.0046 or 0.0023 min(-1) with BiGdO₃ as catalyst. The degradation intermediates of DO-26 were observed and the possible photocatalytic degradation pathway of DO-26 under visible light irradiation was provided. The effect of various operational parameters on the photocatalytic activity and the stability of BiGdO₃ particles were also discussed in detail. BiGdO₃/(visible light) photocatalysis system was confirmed to be suitable for textile industry wastewater treatment. PMID:27618018

  6. Nitrogen-modified nano-titania: True phase composition, microstructure and visible-light induced photocatalytic NOx abatement

    NASA Astrophysics Data System (ADS)

    Tobaldi, D. M.; Pullar, R. C.; Gualtieri, A. F.; Otero-Irurueta, G.; Singh, M. K.; Seabra, M. P.; Labrincha, J. A.

    2015-11-01

    Titanium dioxide (TiO2) is a popular photocatalyst used for many environmental and anti-pollution applications, but it normally operates under UV light, exploiting ∼5% of the solar spectrum. Nitrification of titania to form N-doped TiO2 has been explored as a way to increase its photocatalytic activity under visible light, and anionic doping is a promising method to enable TiO2 to harvest visible-light by changing its photo-absorption properties. In this paper, we explore the insertion of nitrogen into the TiO2 lattice using our green sol-gel nanosynthesis method, used to create 10 nm TiO2 NPs. Two parallel routes were studied to produce nitrogen-modified TiO2 nanoparticles (NPs), using HNO3+NH3 (acid-precipitated base-peptised) and NH4OH (totally base catalysed) as nitrogen sources. These NPs were thermally treated between 450 and 800 °C. Their true phase composition (crystalline and amorphous phases), as well as their micro-/nanostructure (crystalline domain shape, size and size distribution, edge and screw dislocation density) was fully characterised through advanced X-ray methods (Rietveld-reference intensity ratio, RIR, and whole powder pattern modelling, WPPM). As pollutants, nitrogen oxides (NOx) are of particular concern for human health, so the photocatalytic activity of the NPs was assessed by monitoring NOx abatement, using both solar and white-light (indoor artificial lighting), simulating outdoor and indoor environments, respectively. Results showed that the onset of the anatase-to-rutile phase transformation (ART) occurred at temperatures above 450 °C, and NPs heated to 450 °C possessed excellent photocatalytic activity (PCA) under visible white-light (indoor artificial lighting), with a PCA double than that of the standard P25 TiO2 NPs. However, higher thermal treatment temperatures were found to be detrimental for visible-light photocatalytic activity, due to the effects of four simultaneous occurrences: (i) loss of OH groups and water adsorbed

  7. High performance Au-Cu alloy for enhanced visible-light water splitting driven by coinage metals.

    PubMed

    Liu, Mingyang; Zhou, Wei; Wang, Ting; Wang, Defa; Liu, Lequan; Ye, Jinhua

    2016-03-28

    A Au-Cu alloy strategy is, for the first time, demonstrated to be effective in enhancing visible-light photocatalytic H2 evolution via promoting metal interband transitions. Au3Cu/SrTiO3, in which oxidation of Cu was successfully restrained, showed the highest visible-light H2 evolution activity.

  8. Highly Active TiO2-Based Visible-Light Photocatalyst with Nonmetal Doping and Plasmonic Metal Decoration

    SciTech Connect

    Zhang, Qiao; Lima, Diana Q.; Chi, Miaofang; Yin, Yadong

    2011-01-01

    A sandwich-structured photocatalyst shows an excellent performance in degradation reactions of a number of organic compounds under UV, visible light, and direct sunlight (see picture). The catalyst was synthesized by a combination of nonmetal doping and plasmonic metal decoration of TiO2 nanocrystals, which improves visible-light activity and enhances light harvesting and charge separation, respectively.

  9. High performance Au-Cu alloy for enhanced visible-light water splitting driven by coinage metals.

    PubMed

    Liu, Mingyang; Zhou, Wei; Wang, Ting; Wang, Defa; Liu, Lequan; Ye, Jinhua

    2016-03-28

    A Au-Cu alloy strategy is, for the first time, demonstrated to be effective in enhancing visible-light photocatalytic H2 evolution via promoting metal interband transitions. Au3Cu/SrTiO3, in which oxidation of Cu was successfully restrained, showed the highest visible-light H2 evolution activity. PMID:26952932

  10. An Amorphous Carbon Nitride Photocatalyst with Greatly Extended Visible-Light-Responsive Range for Photocatalytic Hydrogen Generation.

    PubMed

    Kang, Yuyang; Yang, Yongqiang; Yin, Li-Chang; Kang, Xiangdong; Liu, Gang; Cheng, Hui-Ming

    2015-08-19

    Amorphous carbon nitride (ACN) with a bandgap of 1.90 eV shows an order of magnitude higher photocatalytic activity in hydrogen evolution under visible light than partially crystalline graphitic carbon nitride with a bandgap of 2.82 eV. ACN is photocatalytically active under visible light at a wavelength beyond 600 nm.

  11. Ag-loaded TiO2/reduced graphene oxide nanocomposites for enhanced visible-light photocatalytic activity

    NASA Astrophysics Data System (ADS)

    Vasilaki, E.; Georgaki, I.; Vernardou, D.; Vamvakaki, M.; Katsarakis, N.

    2015-10-01

    In this work, Ag nanoparticles were loaded by chemical reduction onto TiO2 P25 under different loadings ranging from 1 up to 4 wt% and hydrothermally deposited on reduced graphene oxide sheets. Chemical reduction was determined to be an effective preparation approach for Ag attachment to titania, leading to the formation of small silver nanoparticles with an average diameter of 4.2 nm. The photocatalytic performance of the hybrid nanocomposite materials was evaluated via methylene blue (MB) dye removal under visible-light irradiation. The rate of dye decolorization was found to depend on the metal loading, showing an increase till a threshold value of 3 wt%, above which the rate drops. Next, the as prepared sample of TiO2/Ag of better photocatalytic response, i.e., at a 3 wt% loading value, was hydrothermally deposited on a platform of reduced graphene oxide (rGO) of tunable content (mass ratio). TiO2/Ag/rGO coupled nanocomposite presented significantly enhanced photocatalytic activity compared to the TiO2/Ag, TiO2/rGO composites and bare P25 titania semiconductor photocatalysts. In particular, after 45 min of irradiation almost complete decolorization of the dye was observed for the TiO2/Ag/rGO nanocatalyst, while the respective removal efficiency was 92% for TiO2/Ag, 93% for TiO2/rGO and only 80% for the bare TiO2 nanoparticles. This simple step by step preparation strategy allows for optimum exploitation of the advanced properties of metal plasmonic effect and reduced graphene oxide as the critical host for boosting the overall photocatalytic activity towards visible-light.

  12. Carbon quantum dots with photo-generated proton property as efficient visible light controlled acid catalyst

    NASA Astrophysics Data System (ADS)

    Li, Haitao; Liu, Ruihua; Kong, Weiqian; Liu, Juan; Liu, Yang; Zhou, Lei; Zhang, Xing; Lee, Shuit-Tong; Kang, Zhenhui

    2013-12-01

    Developing light-driven acid catalyst will be very meaningful for the controlled-acid catalytic processes towards a green chemical industry. Here, based on scanning electrochemical microscopy (SECM) and ΔpH testing, we demonstrate that the 5-10 nm carbon quantum dots (CQDs) synthesized by electrochemical ablation of graphite have strong light-induced proton properties under visible light in solution, which can be used as an acid catalyst. The 5-10 nm CQDs' catalytic activity is strongly dependent on the illumination intensity and the temperature of the reaction system. As an effective visible light driven and controlled acid-catalyst, 5-10 nm CQDs can catalyze a series of organic reactions (esterification, Beckmann rearrangement and aldol condensation) with high conversion (34.7-46.2%, respectively) in water solution under visible light, while the 1-4 nm CQDs and 10-2000 nm graphite do not have such excellent catalytic activity. The use of 5-10 nm CQDs as a light responsive and controllable photocatalyst is truly a novel application of carbon-based nanomaterials, which may significantly push research in the current catalytic industry, environmental pollution and energy issues.Developing light-driven acid catalyst will be very meaningful for the controlled-acid catalytic processes towards a green chemical industry. Here, based on scanning electrochemical microscopy (SECM) and ΔpH testing, we demonstrate that the 5-10 nm carbon quantum dots (CQDs) synthesized by electrochemical ablation of graphite have strong light-induced proton properties under visible light in solution, which can be used as an acid catalyst. The 5-10 nm CQDs' catalytic activity is strongly dependent on the illumination intensity and the temperature of the reaction system. As an effective visible light driven and controlled acid-catalyst, 5-10 nm CQDs can catalyze a series of organic reactions (esterification, Beckmann rearrangement and aldol condensation) with high conversion (34

  13. Visible-Light-Triggered Drug Release from TiO2 Nanotube Arrays: A Controllable Antibacterial Platform.

    PubMed

    Xu, Jingwen; Zhou, Xuemei; Gao, Zhida; Song, Yan-Yan; Schmuki, Patrik

    2016-01-11

    In this work, we use a double-layered stack of TiO2 nanotubes (TiNTs) to construct a visible-light-triggered drug delivery system. The key for visible light drug release is a hydrophobic cap on the nanotubes containing Au nanoparticles (AuNPs). The AuNPs allow for a photocatalytic scission of the hydrophobic chain under visible light. To demonstrate this principle, we loaded ampicillin (AMP) into the lower part of the TiO2 nanotube stack, triggered visible-light-induced release, and carried out antibacterial studies. The release from the platform becomes most controllable if the drug is silane-grafted in the hydrophilic bottom layer for drug storage. Thus, visible light photocatalysis can also determine the release kinetics of the active drug from the nanotube wall.

  14. Statistically Optimal Approximations of Astronomical Signals: Implications to Classification and Advanced Study of Variable Stars

    NASA Astrophysics Data System (ADS)

    Andronov, I. L.; Chinarova, L. L.; Kudashkina, L. S.; Marsakova, V. I.; Tkachenko, M. G.

    2016-06-01

    We have elaborated a set of new algorithms and programs for advanced time series analysis of (generally) multi-component multi-channel observations with irregularly spaced times of observations, which is a common case for large photometric surveys. Previous self-review on these methods for periodogram, scalegram, wavelet, autocorrelation analysis as well as on "running" or "sub-interval" local approximations were self-reviewed in (2003ASPC..292..391A). For an approximation of the phase light curves of nearly-periodic pulsating stars, we use a Trigonometric Polynomial (TP) fit of the statistically optimal degree and initial period improvement using differential corrections (1994OAP.....7...49A). For the determination of parameters of "characteristic points" (minima, maxima, crossings of some constant value etc.) we use a set of methods self-reviewed in 2005ASPC..335...37A, Results of the analysis of the catalogs compiled using these programs are presented in 2014AASP....4....3A. For more complicated signals, we use "phenomenological approximations" with "special shapes" based on functions defined on sub-intervals rather on the complete interval. E. g. for the Algol-type stars we developed the NAV ("New Algol Variable") algorithm (2012Ap.....55..536A, 2012arXiv1212.6707A, 2015JASS...32..127A), which was compared to common methods of Trigonometric Polynomial Fit (TP) or local Algebraic Polynomial (A) fit of a fixed or (alternately) statistically optimal degree. The method allows determine the minimal set of parameters required for the "General Catalogue of Variable Stars", as well as an extended set of phenomenological and astrophysical parameters which may be used for the classification. Totally more that 1900 variable stars were studied in our group using these methods in a frame of the "Inter-Longitude Astronomy" campaign (2010OAP....23....8A) and the "Ukrainian Virtual Observatory" project (2012KPCB...28...85V).

  15. Astronomical observatories

    NASA Technical Reports Server (NTRS)

    Ponomarev, D. N.

    1983-01-01

    The layout and equipment of astronomical observatories, the oldest scientific institutions of human society are discussed. The example of leading observatories of the USSR allows the reader to familiarize himself with both their modern counterparts, as well as the goals and problems on which astronomers are presently working.

  16. Impact of different visible light spectra on oxygen absorption and surface discoloration of bologna sausage.

    PubMed

    Böhner, Nadine; Rieblinger, Klaus

    2016-11-01

    The objective of this study was to evaluate the influence of several visible light spectra in various intensities on the oxygen absorption and surface color of sliced bologna. Sausage samples were stored in a gastight model packaging system and illuminated at 5°C with six single-colored LEDs covering the main part of the visible light spectrum. The initial oxygen level was set at 0.5% in order to simulate common residual oxygen amounts in conventional packaging. The oxygen absorption and the discoloration measured as changes in CIE a*-value were dependent from the applied light intensity. The color stability of bologna was differently affected by light of various wavelengths. The results show that the use of suitable LEDs with specific spectra for display illumination can help to reduce the light induced deterioration of cured sausages in retail markets. PMID:27343458

  17. Synthesis of visible light-activated TiO 2 photocatalyst via surface organic modification

    NASA Astrophysics Data System (ADS)

    Jiang, Dong; Xu, Yao; Hou, Bo; Wu, Dong; Sun, Yuhan

    2007-05-01

    A visible light-activated TiO 2 photocatalyst was successfully synthesized by the surface organic modification to sol-gel-hydrothermal synthesized TiO 2. The surface hydroxyls of TiO 2 nanoparticles reacted with the active -NCO groups of tolylene diisocyanate (TDI) to form a surface complex that was confirmed by the FT-IR and XPS spectra. Due to the existence of surface complex, the absorption edge of as-prepared TDI-modified TiO 2 nanomaterial extended well into visible region. Compared with unmodified TiO 2 and Degussa P25, the TDI-modified TiO 2 photocatalysts showed higher activity for the photocatalytic degradation of methylene blue under visible light irradiation.

  18. Accelerated gas-liquid visible light photoredox catalysis with continuous-flow photochemical microreactors.

    PubMed

    Straathof, Natan J W; Su, Yuanhai; Hessel, Volker; Noël, Timothy

    2016-01-01

    In this protocol, we describe the construction and use of an operationally simple photochemical microreactor for gas-liquid photoredox catalysis using visible light. The general procedure includes details on how to set up the microreactor appropriately with inlets for gaseous reagents and organic starting materials, and it includes examples of how to use it to achieve continuous-flow preparation of disulfides or trifluoromethylated heterocycles and thiols. The reported photomicroreactors are modular, inexpensive and can be prepared rapidly from commercially available parts within 1 h even by nonspecialists. Interestingly, typical reaction times of gas-liquid visible light photocatalytic reactions performed in microflow are lower (in the minute range) than comparable reactions performed as a batch process (in the hour range). This can be attributed to the improved irradiation efficiency of the reaction mixture and the enhanced gas-liquid mass transfer in the segmented gas-liquid flow regime. PMID:26633128

  19. Photodynamic Approach for Teratoma-Free Pluripotent Stem Cell Therapy Using CDy1 and Visible Light

    PubMed Central

    2016-01-01

    Pluripotent stem cells (PSC) are promising resources for regeneration therapy, but teratoma formation is one of the critical problems for safe clinical application. After differentiation, the precise detection and subsequent elimination of undifferentiated PSC is essential for teratoma-free stem cell therapy, but a practical procedure is yet to be developed. CDy1, a PSC specific fluorescent probe, was investigated for the generation of reactive oxygen species (ROS) and demonstrated to induce selective death of PSC upon visible light irradiation. Importantly, the CDy1 and/or light irradiation did not negatively affect differentiated endothelial cells. The photodynamic treatment of PSC with CDy1 and visible light irradiation confirmed the inhibition of teratoma formation in mice, and suggests a promising new approach to safe PSC-based cell therapy. PMID:27725957

  20. Superhydrophilicity-assisted preparation of transparent and visible light activated N-doped titania film.

    PubMed

    Xu, Qing Chi; Wellia, Diana V; Amal, Rose; Liao, Dai Wei; Loo, Say Chye Joachim; Tan, Timothy Thatt Yang

    2010-07-01

    A novel and environmental friendly method was developed to prepare transparent, uniform, crack-free and visible light activated nitrogen doped (N-doped) titania thin films without the use of organic Ti precursors and organic solvents. The N-doped titania films were prepared from heating aqueous peroxotitanate thin films deposited uniformly on superhydrophilic uncoated glass substrates. The pure glass substrates were superhydrophilic after being heated at 500 degrees C for 1 h. Nitrogen concentrations in the titania films were adjusted by changing the amount of ammonia solution. The optimal photocatalytic activity of the N-doped titania films was about 14 times higher than that of a commercial self-cleaning glass under the same visible light illumination. The current reported preparative technique is generally applicable for the preparation of other thin films.

  1. Versatile Micropatterning of Plasmonic Nanostructures by Visible Light Induced Electroless Silver Plating on Gold Nanoseeds.

    PubMed

    Yoshikawa, Hiroyuki; Hironou, Asami; Shen, ZhengJun; Tamiya, Eiichi

    2016-09-14

    A versatile fabrication technique for plasmonic silver (Ag) nanostructures that uses visible light exposure for micropatterning and plasmon resonance tuning is presented. The surface of a glass substrate modified with gold (Au) nanoseeds by a thermal dewetting process was used as a Ag plating platform. When a solution containing silver nitrate and sodium citrate was dropped on the Au nanoseeds under visible light exposure, the plasmon-mediated reduction of Ag ions was induced on the Au nanoseeds to form Ag nanostructures. The plasmon resonance spectra of Ag nanostructures were examined by an absorption spectral measurement and a finite-difference time-domain (FDTD) simulation. Some examples of Ag nanostructure patterning were demonstrated by means of light exposure through a photomask, direct writing with a focused laser beam, and the interference between two laser beams. Surface enhanced Raman spectroscopy (SERS) of 4-aminothiophenol (4-ATP) was conducted with fabricated Ag nanostructures.

  2. Vehicle-mounted real-time digital voice communication system based on visible light communication

    NASA Astrophysics Data System (ADS)

    Yan, Qiurong; Gu, Xiuxiu; Chen, Du; Wang, Hui; Huang, Hua; Chen, Xuxin; Cao, Qingshan; Liu, Hongqing

    2015-11-01

    Based on the phenomenon that more and more cars use LED for lighting and the current rise of visible light communication technology, this paper proposes a vehicle real-time voice communication system with high reliability on the basis of visible light communication for verification. The paper introduces the design of digital audio collection and output module, On-Off Keying (OOK) modulation and demodulation, Reed-Solomon encoding and decoding module, array LEDs emission and the module of PIN receiving signals. The LED lamp frequency response, communication distance, error rate and other parameters are tested and calibrated. The digital audio real-time communication system's receiving speed is 500Kbps when the communication distance is 3.9 meters.

  3. An adaptive scaling and biasing scheme for OFDM-based visible light communication systems.

    PubMed

    Wang, Zhaocheng; Wang, Qi; Chen, Sheng; Hanzo, Lajos

    2014-05-19

    Orthogonal frequency-division multiplexing (OFDM) has been widely used in visible light communication systems to achieve high-rate data transmission. Due to the nonlinear transfer characteristics of light emitting diodes (LEDs) and owing the high peak-to-average-power ratio of OFDM signals, the transmitted signal has to be scaled and biased before modulating the LEDs. In this contribution, an adaptive scaling and biasing scheme is proposed for OFDM-based visible light communication systems, which fully exploits the dynamic range of the LEDs and improves the achievable system performance. Specifically, the proposed scheme calculates near-optimal scaling and biasing factors for each specific OFDM symbol according to the distribution of the signals, which strikes an attractive trade-off between the effective signal power and the clipping-distortion power. Our simulation results demonstrate that the proposed scheme significantly improves the performance without changing the LED's emitted power, while maintaining the same receiver structure. PMID:24921387

  4. Accelerated gas-liquid visible light photoredox catalysis with continuous-flow photochemical microreactors.

    PubMed

    Straathof, Natan J W; Su, Yuanhai; Hessel, Volker; Noël, Timothy

    2016-01-01

    In this protocol, we describe the construction and use of an operationally simple photochemical microreactor for gas-liquid photoredox catalysis using visible light. The general procedure includes details on how to set up the microreactor appropriately with inlets for gaseous reagents and organic starting materials, and it includes examples of how to use it to achieve continuous-flow preparation of disulfides or trifluoromethylated heterocycles and thiols. The reported photomicroreactors are modular, inexpensive and can be prepared rapidly from commercially available parts within 1 h even by nonspecialists. Interestingly, typical reaction times of gas-liquid visible light photocatalytic reactions performed in microflow are lower (in the minute range) than comparable reactions performed as a batch process (in the hour range). This can be attributed to the improved irradiation efficiency of the reaction mixture and the enhanced gas-liquid mass transfer in the segmented gas-liquid flow regime.

  5. Measurement of temperature generated by visible-light-cure lamps in an in vitro model.

    PubMed

    Goodis, H E; White, J M; Andrews, J; Watanabe, L G

    1989-07-01

    The dental pulp is vulnerable to cavity preparation and restoration procedures. This vulnerability may be a result of the temperature rise generated by those procedures. When visible-light-cure lamps are used to place composite restorations, they cause the temperature in the pulp to rise. This study measured the temperature rise recorded when six visible-light-cure lamps were tested for 20- and 60-second exposure times. They were also tested in conjunction with an air current passed along the face of the lens in order to lower the temperature. Analysis of the data indicates that the lamps do cause a temperature rise within the pulp chamber--a higher rise the longer the lamp is used. Dentin thickness is important, and air lowers the temperature generated.

  6. Study of Visible Light Reactive Photocatalyst TIO2 Prepared with Thiourea

    NASA Astrophysics Data System (ADS)

    Murai, Kei-Ichiro; Endo, Kazuki; Nakagawa, Taisuke; Yamahata, Akiko; Moriga, Toshihiro

    Visible light reactive N-doped TiO2 samples were prepared with thiourea in the sol-gel method. They had the single anatase-type crystal structure. N-doped TiO2 synthesized with thiourea (T-TiO2) had a higher catalytic activity than that synthesized with urea (U-TiO2). The S2p peak observed on the surface of T-TiO2 was assigned to S6+ by XPS measurement. It was estimated that sulfuric acid species exist on the surface of T-TiO2. However, it was concluded that sulfuric acid species do not have the catalytic activity directly, but depress the crystallinity, the decrease of specific surface area and the decrease of visible light absorption.

  7. BODIPY star-shaped molecules as solid state colour converters for visible light communications

    NASA Astrophysics Data System (ADS)

    Vithanage, D. A.; Manousiadis, P. P.; Sajjad, M. T.; Rajbhandari, S.; Chun, H.; Orofino, C.; Cortizo-Lacalle, D.; Kanibolotsky, A. L.; Faulkner, G.; Findlay, N. J.; O'Brien, D. C.; Skabara, P. J.; Samuel, I. D. W.; Turnbull, G. A.

    2016-07-01

    In this paper, we study a family of solid-state, organic semiconductors for visible light communications. The star-shaped molecules have a boron-dipyrromethene (BODIPY) core with a range of side arm lengths which control the photophysical properties. The molecules emit red light with photoluminescence quantum yields ranging from 22% to 56%. Thin films of the most promising BODIPY molecules were used as a red colour converter for visible light communications. The film enabled colour conversion with a modulation bandwidth of 73 MHz, which is 16 times higher than that of a typical phosphor used in LED lighting systems. A data rate of 370 Mbit/s was demonstrated using On-Off keying modulation in a free space link with a distance of ˜15 cm.

  8. Visible light assisted degradation of organic dye using Ag3PO4

    NASA Astrophysics Data System (ADS)

    Dhanabal, R.; Velmathi, S.; Bose, A. Chandra

    2015-06-01

    The study of visible light photodegradation of organic dye Methylene Blue (MB) have been investigated using silver phosphate (Ag3PO4) as a photocatalyst which is good efficient material for photocatalytic reaction. The simple ion-exchange method is used to prepare Ag3PO4. The structure of the material have been confirmed using X-ray diffraction which shows cubic structure of Ag3PO4. The functional group of the Ag3PO4 has been verified by Fourier transform infrared spectroscopy. The bandgap of Ag3PO4 is calculated using kubelka-munk function from the ultra violet-visible diffuse reflectance spectroscopy, the absorption of Ag3PO4 starts from 470 nm. Under simulated visible light irradiation, Ag3PO4 catalyst exhibits good catalytic ability for degrading MB dye.

  9. [Development of low-concentration hydrogen peroxide whitening agent using visible light-responsive titania photocatalyst].

    PubMed

    Arai, Hiroshi

    2010-06-01

    Although highly concentrated hydrogen peroxide (HP) has been used to bleach vital discolored teeth during office whitening, low-concentration HP was recognized to have insufficient whitening ability. We demonstrated that using a visible light-responsive titania photocatalyst (VLRTP) and a vis-Nd : YAG laser, 3 wt% HP-bleached oxytetracycline (OTC)-stained teeth models were more efficient than 30 wt% HP. The stained samples were prepared by soaking synthetic hydroxyapatite ceramic disks in OTC aqueous solutions. Color images of the OTC-stained models before and after whitening were taken with a conventional flatbed scanner and calibrated using a photocell colorimeter. By VLRTP treatment with vis-Nd : YAG laser irradiation, the lightness value (L*) significantly increased and the yellowness index (b*) significantly approached zero. This suggests that a diluted HP agent with VLRTP can more efficiently decolorize stained teeth by visible light irradiation.

  10. Dye-sensitized polyoxometalate for visible-light-driven photoelectrochemical cells.

    PubMed

    Gao, Junkuo; Miao, Jianwei; Li, Yongxin; Ganguly, Rakesh; Zhao, Yang; Lev, Ovadia; Liu, Bin; Zhang, Qichun

    2015-08-28

    A simple and facile one-step method for the synthesis of an organic dye-functionalized polyoxometalate (POM) hybrid with visible-light photo-response was reported. The POM hybrid was fully characterized via single crystal XRD, powder XRD, FTIR and elemental analysis. The reaction of the organic dye with inorganic salts gave the dye-functionalized POM (MoBB3), in which the POM cluster was formed in situ. The electronic absorption peak of this hybrid was successfully extended beyond 680 nm. Photoelectrochemical measurement indicated that MoBB3 was photoresponsive under visible-light illumination, suggesting that it is an n-type (electron conductive) semiconducting material. This result might offer a method for the design of novel organic dye-functionalized POMs for photoelectric applications.

  11. Versatile Micropatterning of Plasmonic Nanostructures by Visible Light Induced Electroless Silver Plating on Gold Nanoseeds.

    PubMed

    Yoshikawa, Hiroyuki; Hironou, Asami; Shen, ZhengJun; Tamiya, Eiichi

    2016-09-14

    A versatile fabrication technique for plasmonic silver (Ag) nanostructures that uses visible light exposure for micropatterning and plasmon resonance tuning is presented. The surface of a glass substrate modified with gold (Au) nanoseeds by a thermal dewetting process was used as a Ag plating platform. When a solution containing silver nitrate and sodium citrate was dropped on the Au nanoseeds under visible light exposure, the plasmon-mediated reduction of Ag ions was induced on the Au nanoseeds to form Ag nanostructures. The plasmon resonance spectra of Ag nanostructures were examined by an absorption spectral measurement and a finite-difference time-domain (FDTD) simulation. Some examples of Ag nanostructure patterning were demonstrated by means of light exposure through a photomask, direct writing with a focused laser beam, and the interference between two laser beams. Surface enhanced Raman spectroscopy (SERS) of 4-aminothiophenol (4-ATP) was conducted with fabricated Ag nanostructures. PMID:27564976

  12. Ti-O-O coordination bond caused visible light photocatalytic property of layered titanium oxide

    PubMed Central

    Kong, Xingang; Zeng, Chaobin; Wang, Xing; Huang, Jianfeng; Li, Cuiyan; Fei, Jie; Li, Jiayin; Feng, Qi

    2016-01-01

    The layered titanium oxide is a useful and unique precursor for the facile and rapid preparation of the peroxide layered titanium oxide H1.07Ti1.73O4·nH2O (HTO) crystal with enhanced visible light photoactivity. The H2O2 molecules as peroxide chemicals rapidly enter into the interlayers of HTO crystal, and coordinate with Ti within TiO6 octahedron to form a mass of Ti-O-O coordination bond in the interlayers. The introduction of these Ti-O-O coordination bonds result in lowering the band gap of HTO, and promoting the separation efficiency of the photo induced electron–hole pairs. Meanwhile, the photocatalytic investigation indicates that such peroxide HTO crystal has the enhanced photocatalytic performance for RhB degradation and water splitting to generate oxygen under visible light irradiating. PMID:27350285

  13. Construction of carbon nanodots/tungsten trioxide and their visible-light sensitive photocatalytic activity.

    PubMed

    Yan, Fanyong; Kong, Depeng; Fu, Yang; Ye, Qianghua; Wang, Yinyin; Chen, Li

    2016-03-15

    Herein we designed a simple and effective method for synthesizing carbon nanodots/tungsten trioxide nanocomposite with high photocatalytic activity. The as-prepared carbon nanodots/ tungsten trioxide has strong photoabsorption under visible light irradiation. Then, carbon nanodots/tungsten trioxide was successfully applied to the degradation of methylene blue. The photodegradation efficiency of methylene blue can be reached as high as 100% after 0.5 h visible light illumination. In addition, carbon nanodots/tungsten trioxide could also be used to degrade rhodamine B and methyl orange. Most importantly, the photocatalytic activity of carbon nanodots/tungsten trioxide did not exhibit obvious changes after five cycles. The results indicate that carbon nanodots/tungsten trioxide has potential applications in the degradation of organic pollutants in industrial waste water.

  14. Visible-light-driven hydrogen production in a dye sensitized polyoxometalate system without noble metals

    NASA Astrophysics Data System (ADS)

    Liu, Xing; Li, Yuexiang; Peng, Shaoqin; Lai, Hua; Yi, Zhengji

    2016-05-01

    In this work, a noble-metal-free homogeneous system was constructed in one step with Keggin-type polyoxometalate (POM) SiW12O404- as a catalyst, Eosin Y as a photosensitizer, and triethanolamine (TEOA) as a sacrificial electron donor for water splitting to produce hydrogen under visible-light irradiation. A two-electron reduced heteropoly blue SiW12O406- is produced by photosensitization under visible-light irradiation. The effect of various component concentrations and POMs with different central atoms (PW12O403-, GeW12O404-, etc.) on hydrogen production was discussed. This simple system made of earth-abundant elements is expected to contribute toward the development of functional and efficient artificial photosynthetic system.

  15. Ti-O-O coordination bond caused visible light photocatalytic property of layered titanium oxide

    NASA Astrophysics Data System (ADS)

    Kong, Xingang; Zeng, Chaobin; Wang, Xing; Huang, Jianfeng; Li, Cuiyan; Fei, Jie; Li, Jiayin; Feng, Qi

    2016-06-01

    The layered titanium oxide is a useful and unique precursor for the facile and rapid preparation of the peroxide layered titanium oxide H1.07Ti1.73O4·nH2O (HTO) crystal with enhanced visible light photoactivity. The H2O2 molecules as peroxide chemicals rapidly enter into the interlayers of HTO crystal, and coordinate with Ti within TiO6 octahedron to form a mass of Ti-O-O coordination bond in the interlayers. The introduction of these Ti-O-O coordination bonds result in lowering the band gap of HTO, and promoting the separation efficiency of the photo induced electron–hole pairs. Meanwhile, the photocatalytic investigation indicates that such peroxide HTO crystal has the enhanced photocatalytic performance for RhB degradation and water splitting to generate oxygen under visible light irradiating.

  16. Impact of different visible light spectra on oxygen absorption and surface discoloration of bologna sausage.

    PubMed

    Böhner, Nadine; Rieblinger, Klaus

    2016-11-01

    The objective of this study was to evaluate the influence of several visible light spectra in various intensities on the oxygen absorption and surface color of sliced bologna. Sausage samples were stored in a gastight model packaging system and illuminated at 5°C with six single-colored LEDs covering the main part of the visible light spectrum. The initial oxygen level was set at 0.5% in order to simulate common residual oxygen amounts in conventional packaging. The oxygen absorption and the discoloration measured as changes in CIE a*-value were dependent from the applied light intensity. The color stability of bologna was differently affected by light of various wavelengths. The results show that the use of suitable LEDs with specific spectra for display illumination can help to reduce the light induced deterioration of cured sausages in retail markets.

  17. Effect of interferences on indoor visible light car-to-car communication systems

    NASA Astrophysics Data System (ADS)

    Kim, Jong-Young; Park, Bong-Seok; Choi, Hyun-Sik; Kim, So Eun; Moon, Inkyu; Lee, Chung Ghiu

    2016-04-01

    We report the effect of interferences on visible light car-to-car communication system. The interferences from floor reflections and fluorescent lamps are taken into account for indoor car-to-car visible light communication (VLC) systems. The system is composed of a white LED lamp as a VLC transmitter and a photo-receiver with an appropriate optical filter as a VLC receiver. The signal power distribution patterns are measured and analyzed at a transmission distance, considering the positions of the transmitter and receiver. Generally, the light from fluorescent lamps in indoor environment affects the DC level of the received signal power, which is more significant at higher receiver positions. The measurements show that the indoor VLC communication performance can be varied depending on floor reflections. Also, the fluorescent ceiling illuminations affect the DC level change of the received VLC signal waveforms.

  18. Batch and Flow Synthesis of Disulfides by Visible-Light-Induced TiO2 Photocatalysis.

    PubMed

    Bottecchia, Cecilia; Erdmann, Nico; Tijssen, Patricia M A; Milroy, Lech-Gustav; Brunsveld, Luc; Hessel, Volker; Noël, Timothy

    2016-07-21

    A mild and practical method for the preparation of disulfides through visible-light-induced photocatalytic aerobic oxidation of thiols has been developed. The method involves the use of TiO2 as a heterogeneous photocatalyst. The catalyst's high stability and recyclability makes this method highly practical. The reaction can be substantially accelerated in a continuous-flow packed-bed reactor, which enables a safe and reliable scale-up of the reaction conditions. The batch and flow protocol described herein can be applied to a diverse set of thiol substrates for the preparation of homo- and hetero-dimerized disulfides. Furthermore, biocompatible reaction conditions (i.e., room temperature, visible light, neutral buffer solution, and no additional base) have been developed, which permits the rapid and chemoselective modification of densely functionalized peptide substrates without recourse to complex purification steps.

  19. Dye-sensitized polyoxometalate for visible-light-driven photoelectrochemical cells.

    PubMed

    Gao, Junkuo; Miao, Jianwei; Li, Yongxin; Ganguly, Rakesh; Zhao, Yang; Lev, Ovadia; Liu, Bin; Zhang, Qichun

    2015-08-28

    A simple and facile one-step method for the synthesis of an organic dye-functionalized polyoxometalate (POM) hybrid with visible-light photo-response was reported. The POM hybrid was fully characterized via single crystal XRD, powder XRD, FTIR and elemental analysis. The reaction of the organic dye with inorganic salts gave the dye-functionalized POM (MoBB3), in which the POM cluster was formed in situ. The electronic absorption peak of this hybrid was successfully extended beyond 680 nm. Photoelectrochemical measurement indicated that MoBB3 was photoresponsive under visible-light illumination, suggesting that it is an n-type (electron conductive) semiconducting material. This result might offer a method for the design of novel organic dye-functionalized POMs for photoelectric applications. PMID:26200796

  20. Decoding mobile-phone image sensor rolling shutter effect for visible light communications

    NASA Astrophysics Data System (ADS)

    Liu, Yang

    2016-01-01

    Optical wireless communication (OWC) using visible lights, also known as visible light communication (VLC), has attracted significant attention recently. As the traditional OWC and VLC receivers (Rxs) are based on PIN photo-diode or avalanche photo-diode, deploying the complementary metal-oxide-semiconductor (CMOS) image sensor as the VLC Rx is attractive since nowadays nearly every person has a smart phone with embedded CMOS image sensor. However, deploying the CMOS image sensor as the VLC Rx is challenging. In this work, we propose and demonstrate two simple contrast ratio (CR) enhancement schemes to improve the contrast of the rolling shutter pattern. Then we describe their processing algorithms one by one. The experimental results show that both the proposed CR enhancement schemes can significantly mitigate the high-intensity fluctuations of the rolling shutter pattern and improve the bit-error-rate performance.

  1. Oxygen deficient ZnO1-x nanosheets with high visible light photocatalytic activity

    NASA Astrophysics Data System (ADS)

    Guo, Hong-Li; Zhu, Qing; Wu, Xi-Lin; Jiang, Yi-Fan; Xie, Xiao; Xu, An-Wu

    2015-04-01

    Zinc oxide is one of the most important wide-band-gap (3.2 eV) materials with versatile properties, however, it can not be excited by visible light. In this work, we have developed an exquisite and simple way to prepare oxygen-deficient ZnO1-x nanosheets with a gray-colored appearance and excellent visible light photocatalytic activity. Detailed analysis based on UV-Vis absorption spectra, X-band electron paramagnetic resonance (EPR) spectra, and photoluminescence (PL) spectra confirms the existence of oxygen vacancies in ZnO1-x. The incorporation of oxygen defects could effectively extend the light absorption of ZnO1-x into the visible-light region due to the fact that the energy of the localized state is located in the forbidden gap. Thus, our obtained ZnO1-x shows a higher photodegradation of methyl orange (MO) compared to defect-free ZnO under visible light illumination. Additionally, the high content of &z.rad;OH radicals with a strong photo-oxidation capability over the ZnO1-x nanosheets significantly contributes to the improvement in the photocatalytic performance. Our oxygen deficient ZnO1-x sample shows a very high photocatalytic activity for the degradation of MO even after 5 cycles without any obvious decline. The results demonstrate that defect engineering is a powerful tool to enhance the optoelectronic and photocatalytic performances of nanomaterials.Zinc oxide is one of the most important wide-band-gap (3.2 eV) materials with versatile properties, however, it can not be excited by visible light. In this work, we have developed an exquisite and simple way to prepare oxygen-deficient ZnO1-x nanosheets with a gray-colored appearance and excellent visible light photocatalytic activity. Detailed analysis based on UV-Vis absorption spectra, X-band electron paramagnetic resonance (EPR) spectra, and photoluminescence (PL) spectra confirms the existence of oxygen vacancies in ZnO1-x. The incorporation of oxygen defects could effectively extend the light

  2. Synthesis of nanoplate bismuth oxychloride—a visible light active material

    NASA Astrophysics Data System (ADS)

    Tripathi, Gagan Kant; Saini, K. K.; Kurchania, Rajnish

    2015-10-01

    We have synthesized bismuth oxychloride (BiOCl) by wet chemical route. Characterization of the synthesized samples has been carried out using XRD, SEM with EDAX, HRTEM, FT-IR, Raman Spectroscopy, PL and UV. XRD and SEM analysis confirms crystallite size varying from 20-40 nm. FTIR spectrum indicates that the prepared material is highly pure and there is no water molecule present. Raman and photoluminescence spectrum of the bismuth oxychloridenanoplate demonstrated strong blue light emission which brings them in a special class of materials which work under visible light exposure. UV-Vis spectroscopy shows very less charge carriers transit time under visible light thus confirming excellent photocatalytic properties of material.

  3. Facile synthesis and enhanced visible-light photocatalysis of graphitic carbon nitride composite semiconductors.

    PubMed

    Li, Huiquan; Liu, Yuxing; Gao, Xing; Fu, Cong; Wang, Xinchen

    2015-04-13

    The semiconductor heterojunction has been an effective architecture to enhance photocatalytic activity by promoting photogenerated charge separation. Here, graphitic carbon nitride (CN) and B-modified graphitic carbon nitride (CNB) composite semiconductors were fabricated by a facile calcination process using cheap, sustainable, and easily available sodium tetraphenylboron and urea as precursors. The synthetic CN-CNB-25 semiconductor with a suitable CNB content showed the highest visible-light activity. Its degradation ratio for methyl orange and phenol was more than twice that of CN and CNB and its H2 evolution rate was ∼3.4 and ∼1.8 times higher than that of CN and CNB, respectively. It also displayed excellent stability and reusability. The enhanced activity of CN-CNB-25 was attributed predominantly to the efficient separation of photoinduced electrons and holes. This paper describes a visible-light-responsive CN composite semiconductor with great potential in environmental and energy applications.

  4. Self-Sensitized Carbon Nitride Microspheres for Long-Lasting Visible-Light-Driven Hydrogen Generation.

    PubMed

    Gu, Quan; Gao, Ziwei; Xue, Can

    2016-07-01

    A new type of metal-free photocatalyst is reported having a microsphere core of oxygen-containing carbon nitride and self-sensitized surfaces by covalently linked polymeric triazine dyes. These self-sensitized carbon nitride microspheres exhibit high visible-light activities in photocatalytic H2 generation with excellent stability for more than 100 h reaction. Comparing to the traditional g-C3 N4 with activities terminated at 450 nm, the polymeric triazine dyes on the carbon nitride microsphere surface allow for effective wide-range visible-light harvesting and extend the H2 generation activities up to 600 nm. It is believed that this new type of highly stable self-sensitized metal-free structure opens a new direction of future development of low-cost photocatalysts for efficient and long-term solar fuels production.

  5. Reduced graphene oxide and Ag wrapped TiO2 photocatalyst for enhanced visible light photocatalysis

    NASA Astrophysics Data System (ADS)

    Leong, Kah Hon; Sim, Lan Ching; Bahnemann, Detlef; Jang, Min; Ibrahim, Shaliza; Saravanan, Pichiah

    2015-10-01

    A well-organised reduced graphene oxide (RGO) and silver (Ag) wrapped TiO2 nano-hybrid was successfully achieved through a facile and easy route. The inherent characteristics of the synthesized RGO-Ag/TiO2 were revealed through crystalline phase, morphology, chemical composition, Raman scattering, UV-visible absorption, and photoluminescence analyses. The adopted synthesis route significantly controlled the uniform formation of silver nanoparticles and contributed for the absorption of light in the visible spectrum through localized surface plasmon resonance effects. The wrapped RGO nanosheets triggered the electron mobility and promoted visible light shift towards red spectrum. The accomplishment of synergised effect of RGO and Ag well degraded Bisphenol A under visible light irradiation with a removal efficiency of 61.9%.

  6. Tuning laccase catalytic activity with phosphate functionalized carbon dots by visible light.

    PubMed

    Li, Hao; Guo, Sijie; Li, Chuanxi; Huang, Hui; Liu, Yang; Kang, Zhenhui

    2015-05-13

    The phosphate functionalized carbon dots (PCDs) with high biocompatibility and low toxicity can be used as efficient additives for the construction of laccase/PCDs hybrids catalyst. A series of experiments indicated that the activity of laccase/PCDs was higher than that of free laccase (increased by 47.7%). When laccase/PCDs hybrids catalyst was irradiated with visible light (laccase/PCDs-Light), its activity was higher than that of laccase/PCDs hybrids without light irradiation (increased by 92.1%). In the present system, the T1 Cu in laccase was combined with the phosphate group on PCDs, which can increase binding capacity of laccase/PCDs hybrids and substrate. Further, the visible light irradiation increased the donating and accepting electronic capability of the laccase/PCDs hybrids, improving their catalytic activity.

  7. Batch and Flow Synthesis of Disulfides by Visible-Light-Induced TiO2 Photocatalysis.

    PubMed

    Bottecchia, Cecilia; Erdmann, Nico; Tijssen, Patricia M A; Milroy, Lech-Gustav; Brunsveld, Luc; Hessel, Volker; Noël, Timothy

    2016-07-21

    A mild and practical method for the preparation of disulfides through visible-light-induced photocatalytic aerobic oxidation of thiols has been developed. The method involves the use of TiO2 as a heterogeneous photocatalyst. The catalyst's high stability and recyclability makes this method highly practical. The reaction can be substantially accelerated in a continuous-flow packed-bed reactor, which enables a safe and reliable scale-up of the reaction conditions. The batch and flow protocol described herein can be applied to a diverse set of thiol substrates for the preparation of homo- and hetero-dimerized disulfides. Furthermore, biocompatible reaction conditions (i.e., room temperature, visible light, neutral buffer solution, and no additional base) have been developed, which permits the rapid and chemoselective modification of densely functionalized peptide substrates without recourse to complex purification steps. PMID:27329945

  8. Blind Astronomers

    NASA Astrophysics Data System (ADS)

    Hockey, Thomas A.

    2011-01-01

    The phrase "blind astronomer” is used as an allegorical oxymoron. However, there were and are blind astronomers. What of famous blind astronomers? First, it must be stated that these astronomers were not martyrs to their craft. It is a myth that astronomers blind themselves by observing the Sun. As early as France's William of Saint-Cloud (circa 1290) astronomers knew that staring at the Sun was ill-advised and avoided it. Galileo Galilei did not invent the astronomical telescope and then proceed to blind himself with one. Galileo observed the Sun near sunrise and sunset or through projection. More than two decades later he became blind, as many septuagenarians do, unrelated to their profession. Even Isaac Newton temporarily blinded himself, staring at the reflection of the Sun when he was a twentysomething. But permanent Sun-induced blindness? No, it did not happen. For instance, it was a stroke that left Scotland's James Gregory (1638-1675) blind. (You will remember the Gregorian telescope.) However, he died days later. Thus, blindness little interfered with his occupation. English Abbot Richard of Wallingford (circa 1291 - circa 1335) wrote astronomical works and designed astronomical instruments. He was also blind in one eye. Yet as he further suffered from leprosy, his blindness seems the lesser of Richard's maladies. Perhaps the most famous professionally active, blind astronomer (or almost blind astronomer) is Dominique-Francois Arago (1786-1853), director until his death of the powerful nineteenth-century Paris Observatory. I will share other _ some poignant _ examples such as: William Campbell, whose blindness drove him to suicide; Leonhard Euler, astronomy's Beethoven, who did nearly half of his life's work while almost totally blind; and Edwin Frost, who "observed” a total solar eclipse while completely sightless.

  9. Control of the Metal-Insulator Transition at Complex Oxide Heterointerfaces through Visible Light.

    PubMed

    Lin, Jheng-Cyuan; Tra, Vu Thanh; Tsai, Dung-Sheng; Lin, Tai-Te; Huang, Po-Cheng; Hsu, Wei-Lun; Wu, Hui Jun; Huang, Rong; Van Chien, Nguyen; Yoshida, Ryuji; Lin, Jiunn-Yuan; Ikuhara, Yuichi; Chiu, Ya-Ping; Gwo, Shangjr; Tsai, Din Ping; He, Jr-Hau; Chu, Ying-Hao

    2016-01-27

    The coupling of the localized surface plasmon resonance of Au nanoparticles is utilized to deliver a visible-light stimulus to control conduction at the LaAlO3 /SrTiO3 interface. A giant photoresponse and the controllable metal-insulator transition are characterized at this heterointerface. This study paves a new route to optical control of the functionality at the heterointerfaces.

  10. Intermolecular C-H Quaternary Alkylation of Aniline Derivatives Induced by Visible-Light Photoredox Catalysis.

    PubMed

    Cheng, Jie; Deng, Xia; Wang, Guoqiang; Li, Ying; Cheng, Xu; Li, Guigen

    2016-09-16

    The intermolecular direct C-H alkylation of aniline derivatives with α-bromo ketones to build a quaternary carbon center was reported with a visible-light catalysis procedure. The reaction covers a variety of functional groups with good to excellent yields. A regioselectivity favoring the ortho position for the amine group was observed and investigated with Fukui indices and spectral methods. PMID:27571116

  11. Enhanced visible light photocatalytic performance of polyaniline modified mesoporous single crystal TiO2 microsphere

    NASA Astrophysics Data System (ADS)

    Deng, Yaocheng; Tang, Lin; Zeng, Guangming; Dong, Haoran; Yan, Ming; Wang, Jingjing; Hu, Wei; Wang, Jiajia; Zhou, Yaoyu; Tang, Jing

    2016-11-01

    Polyaniline (PANI) modified mesoporous single crystal TiO2 microsphere (PANI/MS-TiO2) with excellent photocatalytic activity was successfully prepared by a simple method of solution evaporation and chemisorption. The X-ray diffraction characterization demonstrated that the whole MS-TiO2 kept the crystal type of anatase. The nitrogen adsorption-desorption characterization coupled with scanning electron microscopy indicated that the MS-TiO2 possessed a unique mesoporous structure with high specific surface area, which resulted in the increased load of PANI on the surface of MS-TiO2 and multiple light reflection in the photocatalyst. The UV-vis diffuse reflectance spectra confirmed that PANI/MS-TiO2 presented more absorption ability in the visible light range than that of the pristine MS-TiO2. The transient photocurrent responses and electrochemical impedance spectroscopy (EIS) indicated the high photo responses and fast photogenerated charge separation efficiency of PANI/MS-TiO2. The photocatalytic activity of the PANI/MS-TiO2 was evaluated by the photodegradation of RhB and MB under visible light irradiation. MS-TiO2 photocatalyst with different molar ration of PANI had been prepared, and the results showed that the optimal photocatalyst (PANI/MS-TiO2 (1:40)) exhibited the highest photocatalytic efficiency which is nearly three times as great as that of pristine MS-TiO2 for the degradation of the RhB and MB under visible light irradiation. The remarkable performance of the PANI/MS-TiO2 under visible light was attributed to its mesoporous single crystal structure with large surface, conductivity, as well as the synergistic effect between PANI and MS-TiO2.

  12. N-Iodosuccinimide-Promoted Hofmann-Löffler Reactions of Sulfonimides under Visible Light.

    PubMed

    O'Broin, Calvin Q; Fernández, Patricia; Martínez, Claudio; Muñiz, Kilian

    2016-02-01

    Conditions for an attractive and productive protocol for the position-selective intramolecular C-H amination of aliphatic groups (Hofmann-Löffler reaction) are reported employing sulfonimides as nitrogen sources. N-Iodosuccinimide is the only required promoter for this transformation, which is conveniently initiated by visible light. The overall transformation provides pyrrolidines under mild and selective conditions as demonstrated for 17 different substrates.

  13. Controlled trifluoromethylation reactions of alkynes through visible-light photoredox catalysis.

    PubMed

    Iqbal, Naeem; Jung, Jaehun; Park, Sehyun; Cho, Eun Jin

    2014-01-01

    The control of a reaction that can form multiple products is a highly attractive and challenging concept in synthetic chemistry. A set of valuable CF3 -containing molecules, namely trifluoromethylated alkenyl iodides, alkenes, and alkynes, were selectively generated from alkynes and CF3 I by environmentally benign and efficient visible-light photoredox catalysis. Subtle differences in the combination of catalyst, base, and solvent enabled the control of reactivity and selectivity for the reaction between an alkyne and CF3 I.

  14. [Degrading anticancer drugs in the medical environment using a visible light-driven photocatalyst].

    PubMed

    Sato, Junya; Kikuchi, Satomi; Kudo, Kenzo

    2014-01-01

      Occupational exposure to anticancer drugs is recognized as a risk for healthcare workers. Reducing anticancer drugs in the environment is important to prevent the exposure of individuals to anticancer drugs. However, there are currently no effective degrading agents for all anticancer drugs used in clinical settings. We previously reported the resolution of an anticancer drug with the use of a photocatalyst (TiO2), which acts by absorbing ultraviolet light to degrade organic compounds. In this study, we evaluated anticancer drug degradation using a visible light-driven photocatalyst (Cu/WO3). Anticancer drugs [cyclophosphamide (CPA), paclitaxel (PTX), methotrexate (MTX), irinotecan (CPT-11), cytarabine (Ara-C), and 5-fluorouracil (5-FU)], were experimentally deposited on a stainless steel plate. The visible light-driven photocatalytic agent (0.075% Cu/WO3 solution) was sprayed onto the plate, and the plate was then left under a fluorescent lamp for 12 h. The anticancer drugs remaining on the plate were assayed by high-performance liquid chromatography (HPLC). CPA, PTX, MTX, CPT-11, Ara-C, and 5-FU were found to be degraded by up to 37.7%, >99.0%, 57.1%, 54.6%, 69.5%, and 36.3%, respectively. The visible light-driven photocatalyst was therefore confirmed to degrade anticancer drugs under a fluorescent lamp. The ability of the visible light-driven photocatalyst to degrade multiple chemotherapeutic agents without the need for altering the light source could make it a useful tool for reducing anticancer drug pollution in clinical settings.

  15. Photoinduced Cleavage of N–N Bonds of Aromatic Hydrazines and Hydrazides by Visible Light

    PubMed Central

    Zhu, Mingzhao

    2012-01-01

    A photocatalytic system involving [Ru(bpyrz)3](PF6)2·2H2O, visible light, and air has been developed for cleavage of the N–N bonds of hydrazines and hydrazides. This catalytic system is generally effective for N,N-disubstituted hydrazine and hydrazide derivatives, including arylhydrazides, N-alkyl-N-arylhydrazines, and N,N-diarylhydrazines. The utility of this cleavage reaction has been demonstrated by synthesizing a variety of secondary aromatic amines. PMID:23543799

  16. Local Measurement of Flap Oxygen Saturation: An Application of Visible Light Spectroscopy.

    PubMed

    Nasseri, Nassim; Kleiser, Stefan; Reidt, Sascha; Wolf, Martin

    2016-01-01

    The aim was to develop and test a new device (OxyVLS) to measure tissue oxygen saturation by visible light spectroscopy independently of the optical pathlength and scattering. Its local applicability provides the possibility of real time application in flap reconstruction surgery. We tested OxyVLS in a liquid phantom with optical properties similar to human tissue. Our results were in good agreement with a conventional near infrared spectroscopy device.

  17. Organic Photocatalytic Cyclization of Polyenes: A Visible-Light-Mediated Radical Cascade Approach.

    PubMed

    Yang, Zhongbo; Li, Han; Zhang, Long; Zhang, Ming-Tian; Cheng, Jin-Pei; Luo, Sanzhong

    2015-10-12

    A visible-light-mediated, organic photocatalytic stereoselective radical cascade cyclization of polyprenoids is described. The desired cascade cyclization products are achieved in good yields and high stereoselectivities with eosin Y as photocatalyst in hexafluoro-2-propanol. The catalyst system is also suitable for 1,3-dicarbonyl compounds, which require only catalytic amounts of LiBr to promote the formation of the corresponding enols.

  18. Visible-Light-Promoted Oxidative [4 + 2] Cycloadditions of Aryl Silyl Enol Ethers.

    PubMed

    Yang, Bo; Lu, Zhan

    2016-08-19

    Visible-light-promoted oxidative [4 + 2] cycloadditions of ε,3-unsaturated silyl enol ethers have been developed to efficiently and diastereoselectively construct polycyclic skeletons under mild conditions. The diastereoselectivities were dependent on the stereoconfiguration of silyl enol ether, substitutions on the link, as well as electric properties of substitutions on aryl rings. The intermediates could be trapped by TEMPO, oxygen or methanol. Mechanistic studies indicated the reaction was initiated by one-electron oxidation of the silyl enol ether. PMID:27391768

  19. The Uranyl Cation as a Visible-Light Photocatalyst for C(sp(3) )-H Fluorination.

    PubMed

    West, Julian G; Bedell, T Aaron; Sorensen, Erik J

    2016-07-25

    The fluorination of unactivated C(sp(3) )-H bonds remains a desirable and challenging transformation for pharmaceutical, agricultural, and materials scientists. Previous methods for this transformation have used bench-stable fluorine atom sources; however, many still rely on the use of UV-active photocatalysts for the requisite high-energy hydrogen atom abstraction event. Uranyl nitrate hexahydrate is described as a convenient, hydrogen atom abstraction catalyst that can mediate fluorinations of certain alkanes upon activation with visible light. PMID:27320442

  20. Fast visible light photoelectric switch based on ultralong single crystalline V₂O₅ nanobelt.

    PubMed

    Lu, Jianing; Hu, Ming; Tian, Ye; Guo, Chuanfei; Wang, Chuang; Guo, Shengming; Liu, Qian

    2012-03-26

    A photoelectric switch with fast response to visible light (<200 μs), suitable photosensitivity and excellent repeatability is proposed based on the ultralong single crystalline V₂O₅ nanobelt, which are synthesized by chemical vapor deposition and its photoconductive mechanism can well be explained by small polaron hopping theory. Our results reveal that the switch has a great potential in next generation photodetectors and light-wave communications.

  1. Significantly Enhanced Visible Light Photoelectrochemical Activity in TiO₂ Nanowire Arrays by Nitrogen Implantation.

    PubMed

    Wang, Gongming; Xiao, Xiangheng; Li, Wenqing; Lin, Zhaoyang; Zhao, Zipeng; Chen, Chi; Wang, Chen; Li, Yongjia; Huang, Xiaoqing; Miao, Ling; Jiang, Changzhong; Huang, Yu; Duan, Xiangfeng

    2015-07-01

    Titanium oxide (TiO2) represents one of most widely studied materials for photoelectrochemical (PEC) water splitting but is severely limited by its poor efficiency in the visible light range. Here, we report a significant enhancement of visible light photoactivity in nitrogen-implanted TiO2 (N-TiO2) nanowire arrays. Our systematic studies show that a post-implantation thermal annealing treatment can selectively enrich the substitutional nitrogen dopants, which is essential for activating the nitrogen implanted TiO2 to achieve greatly enhanced visible light photoactivity. An incident photon to electron conversion efficiency (IPCE) of ∼10% is achieved at 450 nm in N-TiO2 without any other cocatalyst, far exceeding that in pristine TiO2 nanowires (∼0.2%). The integration of oxygen evolution reaction (OER) cocatalyst with N-TiO2 can further increase the IPCE at 450 nm to ∼17% and deliver an unprecedented overall photocurrent density of 1.9 mA/cm(2), by integrating the IPCE spectrum with standard AM 1.5G solar spectrum. Systematic photoelectrochemical and electrochemical studies demonstrated that the enhanced PEC performance can be attributed to the significantly improved visible light absorption and more efficient charge separation. Our studies demonstrate the implantation approach can be used to reliably dope TiO2 to achieve the best performed N-TiO2 photoelectrodes to date and may be extended to fundamentally modify other semiconductor materials for PEC water splitting.

  2. Functionally Diverse Nucleophilic Trapping of Iminium Intermediates Generated Utilizing Visible Light

    PubMed Central

    Freeman, David B.; Furst, Laura; Condie, Allison G.

    2011-01-01

    Our previous studies into visible light-mediated aza-Henry reactions demonstrated that molecular oxygen played a vital role in catalyst turnover as well as the production of base to facilitate the nucleophilic addition of nitroalkanes. Herein, improved conditions for the generation of iminium ions from tetrahydroisoquinolines that allow for versatile nucleophilic trapping are reported. The new conditions provide access to a diverse range of functionality under mild, anaerobic reaction conditions as well as mechanistic insights into the photoredox cycle. PMID:22148974

  3. Volume-scalable high-brightness three-dimensional visible light source

    SciTech Connect

    Subramania, Ganapathi; Fischer, Arthur J; Wang, George T; Li, Qiming

    2014-02-18

    A volume-scalable, high-brightness, electrically driven visible light source comprises a three-dimensional photonic crystal (3DPC) comprising one or more direct bandgap semiconductors. The improved light emission performance of the invention is achieved based on the enhancement of radiative emission of light emitters placed inside a 3DPC due to the strong modification of the photonic density-of-states engendered by the 3DPC.

  4. The high frequency characteristics of laser reflection and visible light during solid state disk laser welding

    NASA Astrophysics Data System (ADS)

    Gao, Xiangdong; You, Deyong; Katayama, Seiji

    2015-07-01

    Optical properties are related to weld quality during laser welding. Visible light radiation generated from optical-induced plasma and laser reflection is considered a key element reflecting weld quality. An in-depth analysis of the high-frequency component of optical signals is conducted. A combination of a photoelectric sensor and an optical filter helped to obtain visible light reflection and laser reflection in the welding process. Two groups of optical signals were sampled at a high sampling rate (250 kHz) using an oscilloscope. Frequencies in the ranges 1-10 kHz and 10-125 kHz were investigated respectively. Experimental results showed that there was an obvious correlation between the high-frequency signal and the laser power, while the high-frequency signal was not sensitive to changes in welding speed. In particular, when the defocus position was changed, only a high frequency of the visible light signal was observed, while the high frequency of the laser reflection signal remained unchanged. The basic correlation between optical features and welding status during the laser welding process is specified, which helps to provide a new research focus for investigating the stability of welding status.

  5. Visible-Light Photoexcited Electron Dynamics of Scandium Endohedral Metallofullerenes: The Cage Symmetry and Substituent Effects.

    PubMed

    Wu, Bo; Hu, Jiahua; Cui, Peng; Jiang, Li; Chen, Zongwei; Zhang, Qun; Wang, Chunru; Luo, Yi

    2015-07-15

    Endohedral metallofullerenes (EMFs) have become an important class of molecular materials for optoelectronic applications. The performance of EMFs is known to be dependent on their symmetries and characters of the substituents, but the underlying electron dynamics remain unclear. Here we report a systematic study on several scandium EMFs and representative derivatives to examine the cage symmetry and substituent effects on their photoexcited electron dynamics using ultrafast transient absorption spectroscopy. Our attention is focused on the visible-light (530 nm as a demonstration) photoexcited electron dynamics, which is of broad interest to visible-light solar energy harvesting but is considered to be quite complicated as the visible-light photons would promote the system to a high-lying energy region where dense manifolds of electronic states locate. Our ultrafast spectroscopy study enables a full mapping of the photoinduced deactivation channels involved and reveals that the long-lived triplet exciton plays a decisive role in controlling the photoexcited electron dynamics under certain conditions. More importantly, it is found that the opening of the triplet channels is highly correlated to the fullerene cage symmetry as well as the electronic character of the substituents.

  6. Visible-light sensitized luminescent europium(III)-β-diketonate complexes: bioprobes for cellular imaging.

    PubMed

    Reddy, M L P; Divya, V; Pavithran, Rani

    2013-11-21

    Visible-light sensitized luminescent europium(III) molecular materials are of considerable importance because their outstanding photophysical properties make them well suited as labels in fluorescence-based bioassays and low-voltage driven pure red-emitters in optoelectronic technology. One challenge in this field is development of visible-light sensitizing ligands that can form highly emissive europium(III) complexes with sufficient stability and aqueous solubility for practical applications. Indeed, some of the recent reports have demonstrated that the excitation-window can be shifted to longer-wavelengths in europium(III)-β-diketonate complexes by appropriate molecular engineering and suitably expanded π-conjugation in the complex molecules. In this review, attention is focused on the latest innovations in the syntheses and photophysical properties of visible-light sensitized europium(III)-β-diketonate complexes and their application as bioprobes for cellular imaging. Furthermore, luminescent nanomaterials derived from long-wavelength sensitized europium(III)-β-diketonate complexes and their application in life sciences are also highlighted.

  7. Visible-light electroluminescence in Mn-doped GaAs light-emitting diodes

    NASA Astrophysics Data System (ADS)

    Maruo, Daiki; Hai, Pham Nam; Tanaka, Masaaki

    2015-03-01

    We demonstrate visible-light electroluminescence (EL) due to d- d transitions in GaAs:Mn based LEDs. We design p+-n junctions with a p+ GaAs:Mn layer, in which at a reverse bias voltage (-3 to -6 V), an intense electric field builds up in the depletion layers of the p+-n junctions. Holes are injected to the depletion layer by Zener tunneling from the conduction band or by diffusion of minority holes from the valence band of the n-type layer. These holes are accelerated by the intense electric field in the depletion layer, and excite the d electrons of Mn in the p+ GaAs:Mn layer by impact excitations. We observe visible-light emission at E1 = 1.89 eV and E2 = 2.16 eV, which are exactly the same as the 4T1-->6A1 and 4A2-->4T1 transition energy of Mn. The threshold voltage for observation of visible-light EL is -4 V, corresponding to -(E1 +E2) / e. This indicates that the impact excitation is most effective for the one step excitation from the ground state 6A1 to the highest excited state 4A2 .

  8. Synthesis of supported silver nano-spheres on zinc oxide nanorods for visible light photocatalytic applications

    SciTech Connect

    Saoud, Khaled; Alsoubaihi, Rola; Bensalah, Nasr; Bora, Tanujjal; Bertino, Massimo; Dutta, Joydeep

    2015-03-15

    Highlights: • Synthesis of supported Ag NPs on ZnO nanorods using open vessel microwave reactor. • Use of the Ag/ZnO NPs as an efficient visible light photocatalyst. • Complete degradation of methylene blue in 1 h with 0.5 g/L Ag/ZnO NPs. - Abstract: We report the synthesis of silver (Ag) nano-spheres (NS) supported on zinc oxide (ZnO) nanorods through two step mechanism, using open vessel microwave reactor. Direct reduction of ZnO from zinc nitrates was followed by deposition precipitation of the silver on the ZnO nanorods. The supported Ag/ZnO nanoparticles were then characterized by electron microscopy, X-ray diffraction, FTIR, photoluminescence and UV–vis spectroscopy. The visible light photocatalytic activity of Ag/ZnO system was investigated using a test contaminant, methylene blue (MB). Almost complete removal of MB in about 60 min for doses higher than 0.5 g/L of the Ag/ZnO photocatalyst was achieved. This significant improvement in the photocatalytic efficiency of Ag/ZnO photocatalyst under visible light irradiation can be attributed to the presence of Ag nanoparticles on the ZnO nanoparticles which greatly enhances absorption in the visible range of solar spectrum enabled by surface plasmon resonance effect from Ag nanoparticles.

  9. Visible-Light Photoexcited Electron Dynamics of Scandium Endohedral Metallofullerenes: The Cage Symmetry and Substituent Effects.

    PubMed

    Wu, Bo; Hu, Jiahua; Cui, Peng; Jiang, Li; Chen, Zongwei; Zhang, Qun; Wang, Chunru; Luo, Yi

    2015-07-15

    Endohedral metallofullerenes (EMFs) have become an important class of molecular materials for optoelectronic applications. The performance of EMFs is known to be dependent on their symmetries and characters of the substituents, but the underlying electron dynamics remain unclear. Here we report a systematic study on several scandium EMFs and representative derivatives to examine the cage symmetry and substituent effects on their photoexcited electron dynamics using ultrafast transient absorption spectroscopy. Our attention is focused on the visible-light (530 nm as a demonstration) photoexcited electron dynamics, which is of broad interest to visible-light solar energy harvesting but is considered to be quite complicated as the visible-light photons would promote the system to a high-lying energy region where dense manifolds of electronic states locate. Our ultrafast spectroscopy study enables a full mapping of the photoinduced deactivation channels involved and reveals that the long-lived triplet exciton plays a decisive role in controlling the photoexcited electron dynamics under certain conditions. More importantly, it is found that the opening of the triplet channels is highly correlated to the fullerene cage symmetry as well as the electronic character of the substituents. PMID:26097975

  10. Investigation of optical intensity in indoor visible light communication with different LEDs array

    NASA Astrophysics Data System (ADS)

    Chen, Hsi-Chao; Liou, Cheng-Jyun; Chou, Yang; Siao, Syuan-Ruei; Liu, I.-Ju; Lai, Wei-Cheng

    2014-09-01

    The purpose of this study was look for the optimized design of light source array applied in indoor lighting combined with visible light communication. The design of different light source arrays: circle, radiation, and rectangle were simulated and experimental for lighting, and then actually be used in visible light communication. The simulation results showed the rectangle array has the largest illumination flux than other arrays. And its total flux was 2662.3 lm; maximum illumination was 338 lx, and the effective illumination area of above 200 lx with a cover area of 2090 mm2. The measurement results also exhibited the rectangle array has the largest illumination flux than other arrays. Its total luminous flux is 2538.95 lm, and the effective illumination area of above 200 lx with a cover area of 2078 mm2. The measurement and simulation results have the same trend and the curve similarity was more than 99% by normalized cross correlation. Finally, combined with the signal transfer analysis of visible light communication, a measurement system was built with the input signal frequency of 1k Hz and the transmission distance of 1.8m. The receive waveform of rectangle array was best in the transport of free space to other arrays and the divergence angle could reaches to 85°.

  11. Black lead molybdate nanoparticles: Facile synthesis and photocatalytic properties responding to visible light

    NASA Astrophysics Data System (ADS)

    Du, Weimin; Liu, Lixin; Zhou, Keke; Ma, Xiaodan; Hao, Yaming; Qian, Xuefeng

    2015-02-01

    Black lead molybdate (PbMoO4) nanoparticles were first synthesized by the glycol-solvothermal method. Phase, morphology, crystal lattice, and specific surface of products were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and Brunauer-Emmett-Teller nitrogen adsorption-desorption, respectively. Results revealed that the as-synthesized PbMoO4 nanoparticles are the scheelite-type tetragonal structure with 30-50 nm in size. Also, glycol played a dual function in present synthetic system: solvent and surface modification agent. Optical properties reveal glycol-modification on the surface of PbMoO4 nanoparticles can generate new energy level between the original conduction band and valence band, leading to better absorption of visible light and the black appearance. Photocatalytic experimental results demonstrate that black PbMoO4 nanoparticles synthesized in glycol medium have pretty visible-light-responsive photocatalytic degradation performance on methylene blue and phenol solution. Reaction mechanism investigations show that the excellent photocatalytic activities of black PbMoO4 nanoparticles derive from the novel energy band structure, smaller size, and larger specific surface area. Hence one can see that black PbMoO4 nanoparticles are a type of visible-light-responsive photocatalysts with excellent photocatalytic activities and potentially applied prospects in dye wastewater treatment and environmental protection. Meanwhile, the present work provides an innovative strategy for adjusting the energy band structure of wide band-gap semiconductors.

  12. PbO-modified TiO2 thin films: a route to visible light photocatalysts.

    PubMed

    Bhachu, Davinder S; Sathasivam, Sanjayan; Carmalt, Claire J; Parkin, Ivan P

    2014-01-21

    PbO clusters were deposited onto polycrystalline titanium dioxide (anatase) films on glass substrates by aerosol-assisted chemical vapor deposition (AACVD). The as-deposited PbO/TiO2 films were then tested for visible light photocatalysis. This was monitored by the photodegradation of stearic acid under visible light conditions. PbO/TiO2 composite films were able to degrade stearic acid at a rate of 2.28 × 10(15) molecules cm(-2) h(-1), which is 2 orders of magnitude greater than what has previously been reported. The PbO/TiO2 composite film demonstrated UVA degradation of resazurin redox dye, with the formal quantum yield (FQY) and formal quantum efficiency (FQE) exceeding that of a TiO2 film grown under the same conditions and Pilkington Activ, a commercially available self-cleaning glass. This work correlates with computational studies that predicted PbO nanoclusters on TiO2 form active visible light photocatalysts through new electronic states through PbO/TiO2 interfacial bonds resulting in new electronic states above the valence band maximum in TiO2, shifting the valence band upward as well as more efficient electron/hole separation with hole localization on PbO particles and electron on the TiO2 surface.

  13. Efficient visible-light photocatalytic performance of cuprous oxide porous nanosheet arrays

    SciTech Connect

    Li, Xianghua; Wang, Jianqiang; Cao, Minhua

    2015-10-15

    Graphical Abstract: We demonstrated a facile and efficient process for fabricating Cu{sub 2}O porous nanosheet arrays on Cu mesh. Benefiting from the 1D array structure and porous structure, the as-prepared Cu{sub 2}O sample exhibited significantly improved photocatalytic activity for methyl orange degradation under visible light irradiation. - Highlights: • Cu{sub 2}O porous nanosheet arrays on Cu mesh were synthesized via the facile and efficient process. • The Cu{sub 2}O sample exhibited the 1D array structure and porous nanosheet morphology. • The as-prepared Cu{sub 2}O porous nanosheet arrays exhibited significantly improved photocatalytic activity. - Abstract: One-dimensional nanostructures are of great interest for a wide range of applications. In this work, we demonstrated the fabrication of visible-light-responsive Cu{sub 2}O porous nanosheet arrays. The synthesis involved the growth of Cu(OH){sub 2} nanosheet arrays on Cu mesh by solution-based corrosion and thermal transformation of Cu(OH){sub 2} nanosheet to Cu{sub 2}O porous nanosheets on Cu mesh. Benefiting from the one dimensional array structure and porous structure, the as-prepared Cu{sub 2}O porous nanosheet arrays exhibited significantly improved photocatalytic activity for methyl orange degradation under visible light irradiation.

  14. Indoor visible light communication: modeling and analysis of multi-state modulation

    NASA Astrophysics Data System (ADS)

    Koudelka, Petr; Latal, Jan; Siska, Petr; Vitasek, Jan; Liner, Andrej; Martinek, Radek; Vasinek, Vladimir

    2014-10-01

    The new dynamic direction of wireless networks development is based on the idea of networks utilizing the optical radiation in the visible spectrum VLC (Visible Light Communications). The impulse of this development direction was improvement in the semiconductor lighting technologies, namely the white power LEDs (Light Emitting Diode). These types of wireless networks are denoted as the optical wireless networks for indoor spaces utilizing optical radiation in the visible spectrum. The paper deals with the issue of deployment of multi-state modulations into the indoor visible light communications in LOS (Line of Sight) configuration. The first part of the paper focuses on design of modulation element (SMD LED matrix 3 × 3) and problems connected to deployment of multi-state modulation M-QAM (subcarrier intensity modulation) through this modulation element into the indoor visible light communications (MER). The second part deals with the irradiation distribution in dark room in comparison with real room during used multi-state modulation scheme in both simulation and real measurement.

  15. Turn on the lights: leveraging visible light for communications and positioning

    NASA Astrophysics Data System (ADS)

    Hranilovic, Steve

    2015-01-01

    The need for ubiquitous broadband connectivity is continually growing, however, radio spectrum is increasingly scarce and limited by interference. In addition, the energy efficiency of many radio transmitters is low and most input energy is converted to heat. A widely overlooked resource for positioning and broadband access is optical wireless communication reusing existing illumination installations. As many of the 14 billion incandescent bulbs in use worldwide are converted to energy efficient LED lighting, a unique opportunity exists to augment them with visible light communications (VLC) and visible light positioning (VLP). VLC- and VLP- enabled LED lighting is not only energy efficient but enables a host of new use cases such as location-aware ubiquitous high-speed wireless communication links. This talk presents the recent work of the Free-space Optical Communication Algorithms Laboratory (FOCAL) at McMaster University in Hamilton, Canada in developing novel signaling and indoor localization techniques using illumination devices. Developments in the signaling design for VLC systems will be presented along with several prototype VLC communication systems. Novel approaches to the integration of VLC networks with power line communications (PLC) are discussed. The role of visible light communications and ranging for automotive safety will also be highlighted. Several approaches to indoor positioning using illumination devices and simple smartphone-based receivers will be presented. Finally, a vision for VLC and VLP technologies will be presented along with our ongoing research directions.

  16. Growth of Au capped GeO2 nanowires for visible-light photodetection

    NASA Astrophysics Data System (ADS)

    Ghosh, Arnab; Guha, Puspendu; Mukherjee, Subhrajit; Bar, Rajshekhar; Ray, Samit K.; Satyam, Parlapalli V.

    2016-09-01

    A single step process to grow Au capped oxygen deficient GeO2 crystalline nanowires via generation of growth species through the metal induced surface decomposition of Ge substrate is reported. Without the external source supply, the growth of the Au-GeO2 nanowires on the Ge substrate is addressed with possible mechanism. Despite high band gap, application of GeO2 as a possible new material for visible light photodetection is presented. The as-grown samples were found to have a photo-response of ≥102 with 17% external quantum efficiency at -2.0 V applied bias upon visible-light illumination (λ = 540 nm, 0.2 mW/cm2). This visible-light detection can be attributed to the oxygen vacancy related defect states as well as localized surface plasmon resonance induced absorption and subsequent hot electron injection from Au to conduction band of GeO2. The photodetection performance of the devices has been understood by the proposed energy band diagrams. In addition, ≈4 times enhancement in the efficiency has been achieved by further decoration of the Au nanoparticles on the as-grown nanowire surfaces.

  17. Electronic Reconstruction of α-Ag2WO4 Nanorods for Visible-Light Photocatalysis.

    PubMed

    Lin, Zhaoyong; Li, Jiling; Zheng, Zhaoqiang; Yan, Jiahao; Liu, Pu; Wang, Chengxin; Yang, Guowei

    2015-07-28

    α-Ag2WO4 (AWO) has been studied extensively due to its H2 evolution and organic pollution degradation ability under the irradiation of UV light. However, the band gap of AWO is theoretically calculated to be 3.55 eV, resulting in its sluggish reaction to visible light. Herein, we demonstrated that, by using the electronic reconstruction of AWO nanorods upon a unique process of laser irradiation in liquid, these nanorods performed good visible-light photocatalytic organics degradation and H2 evolution. Using commercial AWO powders as the starting materials, we achieved the electronic reconstruction of AWO by a recrystallization of the starting powders upon laser irradiation in liquid and synthesized AWO nanorods. Due to the weak bond energy of AWO and the far from thermodynamic equilibrium process created by laser irradiation in liquid, abundant cluster distortions, especially [WO6] cluster distortions, are introduced into the crystal lattice, the defect density increases by a factor of 2.75, and uneven intermediate energy levels are inset into the band gap, resulting in a 0.44 eV decrease of the band gap, which modified the AWO itself by electronic reconstruction to be sensitive to visible light without the addition of others. Further, the first-principles calculation was carried out to clarify the electronic reconstruction of AWO, and the theoretical results confirmed the deduction based on the experimental measurements.

  18. Efficient chemical and visible-light-driven water oxidation using nickel complexes and salts as precatalysts.

    PubMed

    Chen, Gui; Chen, Lingjing; Ng, Siu-Mui; Lau, Tai-Chu

    2014-01-01

    Chemical and visible-light-driven water oxidation catalyzed by a number of Ni complexes and salts have been investigated at pH 7-9 in borate buffer. For chemical oxidation, [Ru(bpy)3](3+) (bpy = 2,2'-bipyridine) was used as the oxidant, with turnover numbers (TONs) >65 and a maximum turnover frequency (TOFmax) >0.9 s(-1). Notably, simple Ni salts such as Ni(NO3 )2 are more active than Ni complexes that bear multidentate N-donor ligands. The Ni complexes and salts are also active catalysts for visible-light-driven water oxidation that uses [Ru(bpy)3](2+) as the photosensitizer and S2 O8 (2-) as the sacrificial oxidant; a TON>1200 was obtained at pH 8.5 by using Ni(NO3)2 as the catalyst. Dynamic light scattering measurements revealed the formation of nanoparticles in chemical and visible-light-driven water oxidation by the Ni catalysts. These nanoparticles aggregated during water oxidation to form submicron particles that were isolated and shown to be partially reduced β-NiOOH by various techniques, which include SEM, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, XRD, and IR spectroscopy. These results suggest that the Ni complexes and salts act as precatalysts that decompose under oxidative conditions to form an active nickel oxide catalyst. The nature of this active oxide catalyst is discussed.

  19. Visible-light-induced instability in amorphous metal-oxide based TFTs for transparent electronics

    SciTech Connect

    Ha, Tae-Jun

    2014-10-15

    We investigate the origin of visible-light-induced instability in amorphous metal-oxide based thin film transistors (oxide-TFTs) for transparent electronics by exploring the shift in threshold voltage (V{sub th}). A large hysteresis window in amorphous indium-gallium-zinc-oxide (a-IGZO) TFTs possessing large optical band-gap (≈3 eV) was observed in a visible-light illuminated condition whereas no hysteresis window was shown in a dark measuring condition. We also report the instability caused by photo irradiation and prolonged gate bias stress in oxide-TFTs. Larger V{sub th} shift was observed after photo-induced stress combined with a negative gate bias than the sum of that after only illumination stress and only negative gate bias stress. Such results can be explained by trapped charges at the interface of semiconductor/dielectric and/or in the gate dielectric which play a role in a screen effect on the electric field applied by gate voltage, for which we propose that the localized-states-assisted transitions by visible-light absorption can be responsible.

  20. The study of visible light active bismuth modified nitrogen doped titanium dioxide photocatlysts: Role of bismuth

    NASA Astrophysics Data System (ADS)

    Bagwasi, Segomotso; Niu, Yuxiao; Nasir, Muhammad; Tian, Baozhu; Zhang, Jinlong

    2013-01-01

    Bismuth modified nitrogen doped TiO2 nanoparticles have been successfully prepared by two steps synthesis route which includes hydrothermal and impregnation hydrolysis method. Samples were characterized using X-ray diffraction (XRD), N2 physical adsorption, Transmission electron microscopy (TEM), UV-vis diffuse reflectance spectroscopy (UV-vis DRS), Fourier Transmission Infrared (FTIR), Raman, X-ray photoelectron spectroscopy (XPS) and photoluminescence spectroscopy (PLS) technologies. The preparatory method afforded the production of well crystallized spherical Bi modified N-doped TiO2 nanoparticles with varied amounts of Bi content. XRD analysis results reveal that Bi exists as rare metastable Bi20TiO32 which started to surface at Bi loading content of 7 mol% in relation to Ti ions. All Bi modified N-TiO2 samples exhibited higher photocatalytic activity toward degradation of 2,4-DCP over N-TiO2 under visible light irradiation. The sample with 10% composition of the Bi20TiO32 exhibited the highest activity. The superior photocatalytic performance of 10%Bi/N-TiO2 is attributed to high visible light absorption as well as effective charge carrier separation. Therefore, the role of Bi species in the N-TiO2 is improvement of visible light harvesting and facilitation of charge carrier separation hence alleviating electron-hole recombination.

  1. Visible-light active conducting polymer nanostructures with superior photocatalytic activity

    PubMed Central

    Ghosh, Srabanti; Kouame, Natalie Amoin; Remita, Samy; Ramos, Laurence; Goubard, Fabrice; Aubert, Pierre-Henri; Dazzi, Alexandre; Deniset-Besseau, Ariane; Remita, Hynd

    2015-01-01

    The development of visible-light responsive photocatalysts would permit more efficient use of solar energy, and thus would bring sustainable solutions to many environmental issues. Conductive polymers appear as a new class of very active photocatalysts under visible light. Among them poly(3,4-ethylenedioxythiophene) (PEDOT) is one of the most promising conjugated polymer with a wide range of applications. PEDOT nanostructures synthesized in soft templates via chemical oxidative polymerization demonstrate unprecedented photocatalytic activities for water treatment without the assistance of sacrificial reagents or noble metal co-catalysts and turn out to be better than TiO2 as benchmark catalyst. The PEDOT nanostructures exhibit a narrow band gap (E = 1.69 eV) and are characterized by excellent ability to absorb light in visible and near infrared region. The novel PEDOT-based photocatalysts are very stable with cycling and can be reused without appreciable loss of activity. Interestingly, hollow micrometric vesicular structures of PEDOT are not effective photocatalysts as compared to nanometric spindles suggesting size and shape dependent photocatalytic properties. The visible-light active photocatalytic properties of the polymer nanostructures present promising applications in solar light harvesting and broader fields. PMID:26657168

  2. PbO-modified TiO2 thin films: a route to visible light photocatalysts.

    PubMed

    Bhachu, Davinder S; Sathasivam, Sanjayan; Carmalt, Claire J; Parkin, Ivan P

    2014-01-21

    PbO clusters were deposited onto polycrystalline titanium dioxide (anatase) films on glass substrates by aerosol-assisted chemical vapor deposition (AACVD). The as-deposited PbO/TiO2 films were then tested for visible light photocatalysis. This was monitored by the photodegradation of stearic acid under visible light conditions. PbO/TiO2 composite films were able to degrade stearic acid at a rate of 2.28 × 10(15) molecules cm(-2) h(-1), which is 2 orders of magnitude greater than what has previously been reported. The PbO/TiO2 composite film demonstrated UVA degradation of resazurin redox dye, with the formal quantum yield (FQY) and formal quantum efficiency (FQE) exceeding that of a TiO2 film grown under the same conditions and Pilkington Activ, a commercially available self-cleaning glass. This work correlates with computational studies that predicted PbO nanoclusters on TiO2 form active visible light photocatalysts through new electronic states through PbO/TiO2 interfacial bonds resulting in new electronic states above the valence band maximum in TiO2, shifting the valence band upward as well as more efficient electron/hole separation with hole localization on PbO particles and electron on the TiO2 surface. PMID:24354409

  3. Visible-light-induced degradation of rhodamine B by nanosized Bi2WO6.

    PubMed

    Fu, Hongbo; Pan, Chengshi; Yao, Wenqing; Zhu, Yongfa

    2005-12-01

    Visible-light-induced photodegradation of rhodamine B over nanosized Bi2WO6 has been observed. Bi2WO6 exhibited a high photoactivity to photodegrade rhodamine B in the central pH solution under visible irradiation (lambda > 420 nm). After five recycles for the photodegradation of rhodamine B, the catalyst did not exhibit any significant loss of activity, confirming the photocatalyst is essentially stable. The total organic carbon measurement displayed that a high degree of mineralization was achieved in the present photochemical system. The results of density functional theory calculation illuminated that the visible-light absorption band in the Bi2WO6 catalyst is attributed to the band transition from the hybrid orbitals of Bi6s and O2p to the W5d orbitals. The Bi2WO6-assisted photocatalytic degradation of rhodamine occurs via two competitive processes: a photocatalytic process and a photosensitized process. The transformation of rhodamine is mainly via the photocatalytic process. Kinetic studies by using electron spin resonance and the radical scavenger technologies suggest that *OH is not the dominant photooxidant. Direct hole transfers and O2*- could take part in Bi2WO6 photocatalysis. This study provided a possible treatment approach for organic pollutants by using visible light in aqueous ecosystems.

  4. A dye-sensitized visible light photocatalyst-Bi24O31Cl10

    PubMed Central

    Wang, Liang; Shang, Jun; Hao, Weichang; Jiang, Shiqi; Huang, Shiheng; Wang, Tianmin; Sun, Ziqi; Du, Yi; Dou, Shixue; Xie, Tengfeng; Wang, Dejun; Wang, Jiaou

    2014-01-01

    The p-block semiconductors are regarded as a new family of visible-light photocatalysts because of their dispersive and anisotropic band structures as well as high chemical stability. The bismuth oxide halides belong to this family and have band structures and dispersion relations that can be engineered by modulating the stoichiometry of the halogen elements. Herein, we have developed a new visible-light photocatalyst Bi24O31Cl10 by band engineering, which shows high dye-sensitized photocatalytic activity. Density functional theory calculations reveal that the p-block elements determine the nature of the dispersive electronic structures and narrow band gap in Bi24O31Cl10. Bi24O31Cl10 exhibits excellent visible-light photocatalytic activity towards the degradation of Rhodamine B, which is promoted by dye sensitization due to compatible energy levels and high electronic mobility. In addition, Bi24O31Cl10 is also a suitable photoanode material for dye-sensitized solar cells and shows power conversion efficiency of 1.5%. PMID:25488704

  5. CdS-graphene Nanocomposite for Efficient Visible-light-driven Photocatalytic and Photoelectrochemical Applications.

    PubMed

    Khan, Mohammad Ehtisham; Khan, Mohammad Mansoob; Cho, Moo Hwan

    2016-11-15

    This paper reports cadmium sulphide nanoparticles-(CdS NPs)-graphene nanocomposite (CdS-Graphene), prepared by a simple method, in which CdS NPs were anchored/decorated successfully onto graphene sheets. The as-synthesized nanocomposite was characterized using standard characterization techniques. A combination of CdS NPs with the optimal amount of two-dimensional graphene sheets had a profound influence on the properties of the resulting hybrid nanocomposite, such as enhanced optical, photocatalytic, and photo-electronic properties. The photocatalytic degradation ability of the CdS-Graphene nanocomposite was evaluated by degrading different types of dyes in the dark and under visible light irradiation. Furthermore, the photoelectrode performance of the nanocomposite was evaluated by different electrochemical techniques. The results showed that the CdS-Graphene nanocomposite can serve as an efficient visible-light-driven photocatalyst as well as photoelectrochemical performance for optoelectronic applications. The significantly enhanced photocatalytic and photoelectrochemical performance of the CdS-Graphene nanocomposite was attributed to the synergistic effects of the enhanced light absorption behaviour and high electron conductivity of the CdS NPs and graphene sheets, which facilitates charge separation and lengthens the lifetime of photogenerated electron-hole pairs by reducing the recombination rate. The as-synthesized narrow band gap CdS-Graphene nanocomposite can be used for wide range of visible light-induced photocatalytic and photoelectrochemical based applications. PMID:27505275

  6. Photocatalysis using zero-valent nano-copper for degrading methyl orange under visible light irradiation

    NASA Astrophysics Data System (ADS)

    Liú, Dan; Wang, Guoqiang; Liŭ, Dan; Lin, Junhong; He, Yingqiao; Li, Xiangru; Li, Ziheng

    2016-03-01

    As one of zero-valent transition metals, nano-copper was synthesized by a simple chemical reduction route and its photocatalytic activity was appraised by the degradation rate of methyl orange (MO) in aqueous solution under irradiation of a three-band fluorescent lamp. The results showed that nano-copper possessed visible-light photocatalytic activity. The finite-difference time-domain (FDTD) method was used to simulate the electric field distribution of nano-copper. From the results of simulation, it found that there was an enhancement electric field in course of light absorption on the surface of nano-copper, different morphology resulted in a diverse electric field distribution. Enhancement electric field intensity decided the visible-light photocatalytic activity of nano-copper. So the activity was affected by the morphology of nano-copper, as the size reduced and surface roughness increased, could be enhanced. It did be worth noting that the nanoscale of copper played the fatal decisive role for whether copper has the ability to degrade MO. So As-prepared nano-copper may be a novel visible-light photocatalytic material to treat organic pollution.

  7. Tungsten trioxide as a visible light photocatalyst for volatile organic carbon removal.

    PubMed

    Wicaksana, Yossy; Liu, Sanly; Scott, Jason; Amal, Rose

    2014-10-31

    Tungsten trioxide (WO3) has been demonstrated to possess visible light photoactivity and presents a means of overcoming the UV-light dependence of photocatalysts, such as titanium dioxide. In this study, WO3 nanostructures have been synthesised by a hydrothermal method using sodium tungstate (Na2WO4·2H2O), sulphate precursors and pH as structure-directing agents and parameters, respectively. By altering the concentration of the sulphate precursors and pH, it was shown that different morphologies and phases of WO3 can be achieved. The effect of the morphology of the final WO3 product on the visible light photoactivity of ethylene degradation in the gas phase was investigated. In addition, platinum (Pt) was photodeposited on the WO3 structures with various morphologies to enhance the photocatalytic properties. It was found that the photocatalytic properties of the WO3 samples greatly depend on their morphology, chemical composition and surface modification. WO3 with a cuboid morphology exhibited the highest visible light photoactivity compared to other morphologies, while adding Pt to the surface improved the performance of certain WO3 structures.

  8. A dye-sensitized visible light photocatalyst-Bi24O31Cl10.

    PubMed

    Wang, Liang; Shang, Jun; Hao, Weichang; Jiang, Shiqi; Huang, Shiheng; Wang, Tianmin; Sun, Ziqi; Du, Yi; Dou, Shixue; Xie, Tengfeng; Wang, Dejun; Wang, Jiaou

    2014-01-01

    The p-block semiconductors are regarded as a new family of visible-light photocatalysts because of their dispersive and anisotropic band structures as well as high chemical stability. The bismuth oxide halides belong to this family and have band structures and dispersion relations that can be engineered by modulating the stoichiometry of the halogen elements. Herein, we have developed a new visible-light photocatalyst Bi24O31Cl10 by band engineering, which shows high dye-sensitized photocatalytic activity. Density functional theory calculations reveal that the p-block elements determine the nature of the dispersive electronic structures and narrow band gap in Bi24O31Cl10. Bi24O31Cl10 exhibits excellent visible-light photocatalytic activity towards the degradation of Rhodamine B, which is promoted by dye sensitization due to compatible energy levels and high electronic mobility. In addition, Bi24O31Cl10 is also a suitable photoanode material for dye-sensitized solar cells and shows power conversion efficiency of 1.5%. PMID:25488704

  9. Far Ultraviolet and Visible Light Scatter Measurements for CVD Silicon Carbide Mirrors for SOHO

    NASA Technical Reports Server (NTRS)

    Leviton, Douglas B.; Gardner, Larry D.

    1998-01-01

    Chemically-vapor-deposited (CVD) silicon carbide (SiC) has become a popular mirror material for spaceborne solar instrumentation for the vacuum ultraviolet wavelength range due to its appreciable broadband reflectance and favorable thermal and opto-mechanical properties. Scatter from surfaces of mirrors operating in this wavelength range can destroy otherwise good image contrast especially for extended targets such as the sun. While visible light scatter measurements are relatively easy to conduct, far ultraviolet (FUV) scatter measurements are not so easy. Visible light (633 nm) scatter measurements were performed on CVD SiC telescope mirrors (from the same vendor) for two instruments on the Solar and Heliospheric Observatory (SOHO) -- Ultraviolet Coronagraph Spectrometer (UVCS) and Solar Ultraviolet Measurement of Emitted Radiation (SUMER). Additionally, extensive FUV scatter measurements were made for SUMER telescope mirrors. We attempt to correlate the results for those visible light scatter measurements and to explore the usefulness of visible scatter measurements to predictions of FUV scatter for this important material.

  10. Graphene oxide modified TiO2 nanotube arrays: enhanced visible light photoelectrochemical properties

    SciTech Connect

    Song, Peng; Zhang, Xiaoyan; Sun, Mingxuan; Cui, Xiaoli; Lin, Yuehe

    2012-01-01

    Novel nanocomposite films based on graphene oxide (GO) and TiO2 nanotube arrays were synthesized by assembling GO on the surface of self-organized TiO2 nanotube arrays through a simple assembling method. The composite films were characterized with field emission scanning electron microscopy, X-ray diffraction, Raman spectroscopy, and UV-vis diffuse reflectance spectroscopy. Photoelectrochemical properties of the composite nanotube arrays were investigated under visible light illumination. Remarkably enhanced visible light photoelectrochemical response was observed for the GO decorated TiO2 nanotube composite electrode compared with pristine TiO2 nanotube arrays. Sensitizing effect of GO on the photoelectrochemical response of TiO2 nanotube arrays was demonstrated and about 15 times enhanced maximum photoconversion efficiency was obtained with the presence of GO. Enhanced photocatalytic activity of TiO2 nanotube arrays towards degradation of methyl blue was also demonstrated after modification of GO. The results presented here demonstrate GO to be efficient for the improvement of utilization of visible light for TiO2 nanotube arrays.

  11. Graphene oxide modified TiO2 nanotube arrays: enhanced visible light photoelectrochemical properties

    NASA Astrophysics Data System (ADS)

    Song, Peng; Zhang, Xiaoyan; Sun, Mingxuan; Cui, Xiaoli; Lin, Yuehe

    2012-02-01

    Novel nanocomposite films, based on graphene oxide (GO) and TiO2 nanotube arrays, were synthesized by assembling GO on the surface of self-organized TiO2 nanotube arrays through a simple impregnation method. The composite films were characterized with field emission scanning electron microscopy, X-ray diffraction, Raman spectroscopy and UV-vis diffuse reflectance spectroscopy. The photoelectrochemical properties of the composite nanotube arrays were investigated under visible light illumination. Remarkably enhanced visible light photoelectrochemical response was observed for the GO decorated TiO2 nanotube composite electrode compared with pristine TiO2 nanotube arrays. The sensitizing effect of GO on the photoelectrochemical response of the TiO2 nanotube arrays was demonstrated and about 15 times enhanced maximum photoconversion efficiency was obtained with the presence of GO. An enhanced photocatalytic activity of the TiO2 nanotube arrays towards the degradation of methyl blue was also demonstrated after modification with GO. The results presented here demonstrate GO to be efficient for the improved utilization of visible light for TiO2 nanotube arrays.

  12. Graphene oxide modified TiO2 nanotube arrays: enhanced visible light photoelectrochemical properties.

    PubMed

    Song, Peng; Zhang, Xiaoyan; Sun, Mingxuan; Cui, Xiaoli; Lin, Yuehe

    2012-03-01

    Novel nanocomposite films, based on graphene oxide (GO) and TiO(2) nanotube arrays, were synthesized by assembling GO on the surface of self-organized TiO(2) nanotube arrays through a simple impregnation method. The composite films were characterized with field emission scanning electron microscopy, X-ray diffraction, Raman spectroscopy and UV-vis diffuse reflectance spectroscopy. The photoelectrochemical properties of the composite nanotube arrays were investigated under visible light illumination. Remarkably enhanced visible light photoelectrochemical response was observed for the GO decorated TiO(2) nanotube composite electrode compared with pristine TiO(2) nanotube arrays. The sensitizing effect of GO on the photoelectrochemical response of the TiO(2) nanotube arrays was demonstrated and about 15 times enhanced maximum photoconversion efficiency was obtained with the presence of GO. An enhanced photocatalytic activity of the TiO(2) nanotube arrays towards the degradation of methyl blue was also demonstrated after modification with GO. The results presented here demonstrate GO to be efficient for the improved utilization of visible light for TiO(2) nanotube arrays. PMID:22297577

  13. Merging Visible Light Photoredox Catalysis with Metal Catalyzed C-H Activations: On the Role of Oxygen and Superoxide Ions as Oxidants.

    PubMed

    Fabry, David C; Rueping, Magnus

    2016-09-20

    The development of efficient catalytic systems for direct aromatic C-H bond functionalization is a long-desired goal of chemists, because these protocols provide environmental friendly and waste-reducing alternatives to classical methodologies for C-C and C-heteroatom bond formation. A key challenge for these transformations is the reoxidation of the in situ generated metal hydride or low-valent metal complexes of the primary catalytic bond forming cycle. To complete the catalytic cycle and to regenerate the C-H activation catalyst, (super)stoichiometric amounts of Cu(II) or Ag(I) salts have often been applied. Recently, "greener" approaches have been developed by applying molecular oxygen in combination with Cu(II) salts, internal oxidants that are cleaved during the reaction, or solvents or additives enabling the metal hydride reoxidation. All these approaches improved the environmental friendliness but have not overcome the obstacles associated with the overall limited functional group and substrate tolerance. Hence, catalytic processes that do not feature the unfavorable aspects described above and provide products in a streamlined as well as economically and ecologically advantageous manner would be desirable. In this context, we decided to examine visible light photoredox catalysis as a new alternative to conventionally applied regeneration/oxidation procedures. This Account summarizes our recent advances in this expanding area and will highlight the new concept of merging distinct redox catalytic processes for C-H functionalizations through the application of visible light photoredox catalysis. Photoredox catalysis can be considered as catalytic electron-donating or -accepting processes, making use of visible-light absorbing homogeneous and heterogeneous metal-based catalysts, as well as organic dye sensitizers or polymers. As a consequence, photoredox catalysis is, in principle, an ideal tool for the recycling of any given metal catalyst via a coupled

  14. Merging Visible Light Photoredox Catalysis with Metal Catalyzed C-H Activations: On the Role of Oxygen and Superoxide Ions as Oxidants.

    PubMed

    Fabry, David C; Rueping, Magnus

    2016-09-20

    The development of efficient catalytic systems for direct aromatic C-H bond functionalization is a long-desired goal of chemists, because these protocols provide environmental friendly and waste-reducing alternatives to classical methodologies for C-C and C-heteroatom bond formation. A key challenge for these transformations is the reoxidation of the in situ generated metal hydride or low-valent metal complexes of the primary catalytic bond forming cycle. To complete the catalytic cycle and to regenerate the C-H activation catalyst, (super)stoichiometric amounts of Cu(II) or Ag(I) salts have often been applied. Recently, "greener" approaches have been developed by applying molecular oxygen in combination with Cu(II) salts, internal oxidants that are cleaved during the reaction, or solvents or additives enabling the metal hydride reoxidation. All these approaches improved the environmental friendliness but have not overcome the obstacles associated with the overall limited functional group and substrate tolerance. Hence, catalytic processes that do not feature the unfavorable aspects described above and provide products in a streamlined as well as economically and ecologically advantageous manner would be desirable. In this context, we decided to examine visible light photoredox catalysis as a new alternative to conventionally applied regeneration/oxidation procedures. This Account summarizes our recent advances in this expanding area and will highlight the new concept of merging distinct redox catalytic processes for C-H functionalizations through the application of visible light photoredox catalysis. Photoredox catalysis can be considered as catalytic electron-donating or -accepting processes, making use of visible-light absorbing homogeneous and heterogeneous metal-based catalysts, as well as organic dye sensitizers or polymers. As a consequence, photoredox catalysis is, in principle, an ideal tool for the recycling of any given metal catalyst via a coupled

  15. Merging Visible Light Photoredox Catalysis with Metal Catalyzed C–H Activations: On the Role of Oxygen and Superoxide Ions as Oxidants

    PubMed Central

    2016-01-01

    Conspectus The development of efficient catalytic systems for direct aromatic C–H bond functionalization is a long-desired goal of chemists, because these protocols provide environmental friendly and waste-reducing alternatives to classical methodologies for C–C and C–heteroatom bond formation. A key challenge for these transformations is the reoxidation of the in situ generated metal hydride or low-valent metal complexes of the primary catalytic bond forming cycle. To complete the catalytic cycle and to regenerate the C–H activation catalyst, (super)stoichiometric amounts of Cu(II) or Ag(I) salts have often been applied. Recently, “greener” approaches have been developed by applying molecular oxygen in combination with Cu(II) salts, internal oxidants that are cleaved during the reaction, or solvents or additives enabling the metal hydride reoxidation. All these approaches improved the environmental friendliness but have not overcome the obstacles associated with the overall limited functional group and substrate tolerance. Hence, catalytic processes that do not feature the unfavorable aspects described above and provide products in a streamlined as well as economically and ecologically advantageous manner would be desirable. In this context, we decided to examine visible light photoredox catalysis as a new alternative to conventionally applied regeneration/oxidation procedures. This Account summarizes our recent advances in this expanding area and will highlight the new concept of merging distinct redox catalytic processes for C–H functionalizations through the application of visible light photoredox catalysis. Photoredox catalysis can be considered as catalytic electron-donating or -accepting processes, making use of visible-light absorbing homogeneous and heterogeneous metal-based catalysts, as well as organic dye sensitizers or polymers. As a consequence, photoredox catalysis is, in principle, an ideal tool for the recycling of any given metal

  16. Increased visible-light photocatalytic activity of TiO2 via band gap manipulation

    NASA Astrophysics Data System (ADS)

    Pennington, Ashley Marie

    Hydrogen gas is a clean burning fuel that has potential applications in stationary and mobile power generation and energy storage, but is commercially produced from non-renewable fossil natural gas. Using renewable biomass as the hydrocarbon feed instead could provide sustainable and carbon-neutral hydrogen. We focus on photocatalytic oxidation and reforming of methanol over modified titanium dioxide (TiO2) nanoparticles to produce hydrogen gas. Methanol is used as a model for biomass sugars. By using a photocatalyst, we aim to circumvent the high energy cost of carrying out endothermic reactions at commercial scale. TiO2 is a semiconductor metal oxide of particular interest in photocatalysis due to its photoactivity under ultraviolet illumination and its stability under catalytic reaction conditions. However, TiO2 primarily absorbs ultraviolet light, with little absorption of visible light. While an effective band gap for absorbance of photons from visible light is 1.7 eV, TiO2 polymorphs rutile and anatase, have band gaps of 3.03 eV and 3.20 eV respectively, which indicate ultraviolet light. As most of incident solar radiation is visible light, we hypothesize that decreasing the band gap of TiO2 will increase the efficiency of TiO2 as a visible-light active photocatalyst. We propose to modify the band gap of TiO2 by manipulating the catalyst structure and composition via metal nanoparticle deposition and heteroatom doping in order to more efficiently utilize solar radiation. Of the metal-modified Degussa P25 TiO2 samples (P25), the copper and nickel modified samples, 1%Cu/P25 and 1%Ni/P25 yielded the lowest band gap of 3.05 eV each. A difference of 0.22 eV from the unmodified P25. Under visible light illumination 1%Ni/P25 and 1%Pt/P25 had the highest conversion of methanol of 9.9% and 9.6%, respectively.

  17. Visible light may directly induce nuclear DNA damage triggering the death pathway in RGC-5 cells

    PubMed Central

    Fan, Bin; Ma, Tong-Hui

    2011-01-01

    Purpose Visible light has been previously demonstrated to induce retinal ganglion cell (RGC)-5 cell death through the mitochondrial pathway. The present study was designed to determine whether visible light might also directly trigger the death pathway by damaging nuclear DNA. Methods RGC-5 cells were exposed to various intensities and durations of visible light exposure. Cell viability and death were monitored with the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay and propidium iodide staining. Nuclear DNA damage caused by light was determined with the plasmid assay, genome DNA assay, and in situ terminal deoxynucleotidyl transferase dUTP nick end labeling. The subsequent activation of nuclear enzyme poly(ADP-ribose) polymerase-1 (PARP-1) was measured with western blot, and PARP-1’s role in the death pathway was assessed by using specific inhibitors. Poly (ADP-ribose) glycohydrolase and apoptosis-inducing factor (AIF) inhibitors were used to show their influence on light-induced cell death. Calcium influx was examined with the fura-2 assay and calcium channel blocker. Results We found that visible light induced RGC-5 cell death in a time- and intensity-dependent manner. After the light intensity was increased to 2,600 lx, activation of the death pathway in RGC-5 cells was clearly observed by detecting double-strand DNA breaks and nuclear DNA damage in vitro. Nuclear enzyme PARP-1 was promptly activated after exposure to 2,600 lx of light for 2 days, and specific inhibitors of PARP-1 had significant neuroprotective effects. The poly(ADP-ribose) glycohydrolase inhibitor tannic acid and AIF inhibitor N-phenylmaleimide partially protected RGC-5 cells from light injury. A massive calcium influx was detected after 2 days of light exposure, and a calcium channel blocker partially protected cells against light injury. Conclusions These results suggest that visible light exposure may directly cause nuclear DNA damage, which consequently activates

  18. Indium oxide thin film as potential photoanodes for corrosion protection of stainless steel under visible light

    SciTech Connect

    Zhang, Yan; Yu, Jianqiang; Sun, Kai; Zhu, Yukun; Bu, Yuyu; Chen, Zhuoyuan

    2014-05-01

    Graphical abstract: If the conduction band potential of In{sub 2}O{sub 3} is more negative than the corrosion potential of stainless steel, photo-induced electrons will be transferred from In{sub 2}O{sub 3} to the steel, thus shifting the potential of the steel into a corrosion immunity region and preventing the steel from the corrosion. - Highlights: • Indium oxide performed novel application under visible light. • Indium oxide by sol–gel method behaved better photoelectrochemical properties. • Electrons were transferred to stainless steel from indium oxide once light on. - Abstract: This paper reports the photoelectrochemical cathodic protection of 304 stainless steel by In{sub 2}O{sub 3} thin-film under visible-light. The films were fabricated with In{sub 2}O{sub 3} powders, synthesized by both sol–gel (In{sub 2}O{sub 3}-sg) and solid-state (In{sub 2}O{sub 3}-ss) processes. The photo-induced open circuit potential and the photo-to-current efficiency measurements suggested that In{sub 2}O{sub 3} could be a promising candidate material for photoelectrochemical cathodic protection of metallic alloys under visible light. Moreover, the polarization curve experimental results indicated that In{sub 2}O{sub 3}-sg thin-film can mitigate the corrosion potential of 304 stainless steel to much more negative values with a higher photocurrent density than the In{sub 2}O{sub 3}-ss film under visible-light illumination. All the results demonstrated that the In{sub 2}O{sub 3}-sg thin-film provides a better photoelectrochemical cathodic protection for 304 stainless steel than In{sub 2}O{sub 3}-ss thin-film under visible-light illumination. The higher photoelectrochemical efficiency is possibly due to the uniform thin films produced with the smaller particle size of In{sub 2}O{sub 3}-sg, which facilitates the transfer of the photo-induced electrons from bulk to the surface and suppresses the charge recombination of the electrons and holes.

  19. Women Astronomers.

    ERIC Educational Resources Information Center

    Warner, Deborah Jean

    1979-01-01

    Traces the role of women in the scientific community in the United States since the mid-nineteenth century. Specific concern is directed towards the education and career opportunities of female astronomers. (MA)

  20. Visible Light Generation and Its Influence on Supercontinuum in Chalcogenide As2S3 Microstructured Optical Fiber

    NASA Astrophysics Data System (ADS)

    Gao, Weiqing; Liao, Meisong; Yan, Xin; Kito, Chihiro; Kohoutek, Tomas; Suzuki, Takenobu; El-Amraoui, Mohammed; Jules, Jean-Charles; Gadret, Grégory; Désévédavy, Frédéric; Smektala, Frédéric; Ohishi, Yasutake

    2011-10-01

    We demonstrate visible light generation in chalcogenide As2S3 microstructured optical fiber. The generated visible light causes irreversible damage to the fiber core because of the high absorption coefficient of chalcogenide glasses in the visible band. The SCs (supercontinua) are measured in both untapered and tapered As2S3 fibers, no wider SC is obtained in the tapered one. The SC growth is prevented by the visible light generation since the damage to the fiber core decreases the fiber transmission substantially. This effect can be avoided by designing the fiber to enable the pump source to work in single-mode operation.

  1. Metal free earth abundant elemental red phosphorus: a new class of visible light photocatalyst and photoelectrode materials.

    PubMed

    Ansari, Sajid Ali; Ansari, Mohammad Shahnawaze; Cho, Moo Hwan

    2016-02-01

    Developing a high-performance photocatalyst and a photoelectrode with enhanced visible light harvesting properties is essential for practical visible light photocatalytic applications. Noble metal-free, highly visible light-active, elemental red phosphorus (RP) was prepared by a facile mechanical ball milling method, which is a reproducible, low cost and controllable synthesis process. The synthesis used inexpensive and abundant raw materials because most RP hybrids are based on expensive noble-metals. The novel milled RP showed significantly enhanced photocatalytic and photoelectrochemical performances with a lower charge transfer resistance compared to commercial RP under wide visible photoirradiation, making it a feasible alternative for photocatalytic applications. PMID:26765211

  2. Dendritic Au/TiO2 nanorod arrays for visible-light driven photoelectrochemical water splitting

    NASA Astrophysics Data System (ADS)

    Su, Fengli; Wang, Tuo; Lv, Rui; Zhang, Jijie; Zhang, Peng; Lu, Jianwei; Gong, Jinlong

    2013-09-01

    This paper describes the synthesis of TiO2 branched nanorod arrays (TiO2 BNRs) with plasmonic Au nanoparticles attached on the surface. Such Au/TiO2 BNR composites exhibit high photocatalytic activity in photoelectrochemical (PEC) water splitting. The unique structure of Au/TiO2 BNRs shows enhanced activity with a photocurrent of 0.125 mA cm-2 under visible light (>=420 nm) and 2.32 +/- 0.1 mA cm-2 under AM 1.5 G illumination (100 mW cm-2). The obtained photocurrent is comparable to the highest value ever reported. Furthermore, the Au/TiO2 BNRs achieve the highest efficiency of ~1.27% at a low bias of 0.50 V vs. RHE, indicating elevated charge separation and transportation efficiencies. The high PEC performance is mainly due to the plasmonic effect of Au nanoparticles, which enhances the visible light absorption, together with the large surface area, efficient charge separation and high carrier mobility of the TiO2 BNRs. The carrier density of Au/TiO2 BNRs is nearly 6 times higher than the pristine TiO2 BNRs as calculated by the Mott-Schottky plot. Based on the analysis by UV-Vis spectroscopy, electrochemical impedance spectroscopy, and photoluminescence, a mechanism was proposed to explain the high activity of Au/TiO2 BNRs in PEC water splitting. The capability of synthesizing highly visible light active Au/TiO2 BNR based photocatalysts is useful for solar conversion applications, such as PEC water splitting, dye-sensitized solar cells and photovoltaic devices.This paper describes the synthesis of TiO2 branched nanorod arrays (TiO2 BNRs) with plasmonic Au nanoparticles attached on the surface. Such Au/TiO2 BNR composites exhibit high photocatalytic activity in photoelectrochemical (PEC) water splitting. The unique structure of Au/TiO2 BNRs shows enhanced activity with a photocurrent of 0.125 mA cm-2 under visible light (>=420 nm) and 2.32 +/- 0.1 mA cm-2 under AM 1.5 G illumination (100 mW cm-2). The obtained photocurrent is comparable to the highest value ever

  3. Photocatalytic oxidation of organic dyes with visible-light-driven codoped TiO2 photocatalysts

    NASA Astrophysics Data System (ADS)

    Zhang, Dongfang; Zeng, Fanbin

    2011-06-01

    A novel copper (II) and zinc (II) codoped TiO2 photocatalyst was synthesized by a modified sol-gel method using titanium (IV) isopropoxide, Zn(NO3)2 · 6H2O and copper(Il) nitrate as precursors. The samples were characterized by X-ray diffraction (XRD), diffuse reflectance spectroscopy (DRS) and photo-luminescence spectra (PL). The XRD results showed undoped and Zn, Cu-codoped TiO2 nanoparticles mainly including anatase phase and a tiny amount of Zn- and Cu-oxides exist in the mixed system, which is attributed to the decomposition of copper and zinc nitrates in the TiO2 gel to form CuO and ZnO and randomly dispersed on the TiO2 surface. On the basis of the optical characterization results, we found that the codoping of copper (II) and zinc (II) resulted a red shift of adsorption and lower recombination probability between electrons and holes, which were the reasons for high photocatalytic activity of Zn, Cu-codoped TiO2 nanoparticles under visible light (λ > 400 nm). The photocatalytic activity of samples was tested for degradation of methyl orange (MO) in solutions. The results indicated that the visible-light driven capability of the codoped catalyst were much higher than that of the pure TiO2 catalyst under visible irradiation. Because of the synergetic effect of copper (II) and zinc (II) element, the Zn, Cu-codoped TiO2 catalyst will show higher quantum yield and enhance absorption of visible light. In the end, a key mechanism was proposed in order to account for the enhanced activity.

  4. Facile fabrication of visible light induced Bi2O3 nanorod using conventional heat treatment method

    NASA Astrophysics Data System (ADS)

    Raza, Waseem; Khan, Azam; Alam, Umair; Muneer, M.; Bahnemann, D.

    2016-03-01

    In this paper, a new Bi2O3 based photocatalyst doped with varying concentration of Nb and Mn metal ion was fabricated by conventional heat treatment method and their photocatalytic activity was investigated. The prepared material was characterized by X-ray diffraction (XRD), UV-Visible Spectroscopy, Fourier transform infrared (FTIR) and Scanning Electron Microscopic (SEM) techniques. The XRD analysis of synthesized photocatalyst was found to exhibit characteristic peaks of well crystallized monoclinic α-Bi2O3. The XRD pattern of pure and metal doped Bi2O3 were found to more or less similar. The crystallite size of doped materials were smaller than pure Bi2O3 and size decreases with increasing dopant concentration from 0.5 to 2.0% for Nb & 1.0-3.0% for Mn and remains almost constant at higher dopant concentration. The SEM analysis clearly indicate the formation of nanorod like morphologies. The UV-Vis absorption spectra of synthesized nanorods revealed that the absorption edge shift towards longer wavelength on doping with Nb and Mn metal ions which is beneficial for absorbing more visible light in the solar spectrum. The prepared doped Bi2O3 nanorod showed the excellent photocatalytic activity for degradation of selected organic pollutants, such as Methylene Blue (MB) and Rodaamime B (RhB) under visible light source. The higher activity of doped Bi2O3 nanorod may be attributed to absorption of more visible light leading to generation of higher photogenerated electron hole pairs and efficient separation of photoinduced charge carrier to inhibit the recombination rate.

  5. Aerosol impacts on visible light extinction in the atmosphere of Mexico City.

    PubMed

    Eidels-Dubovoi, Silvia

    2002-03-27

    Eleven diurnal aerosol visible light absorption and scattering patterns were obtained from measurements done with an aethalometer and an integrating nephelometer during 28 February-10 March 1997 at two different sites in the Mexico City basin. Both measurement sites, the Merced site affected by regional and urban-scale aerosol and the Pedregal site dominated by regional-scale aerosol, showed a variety of diurnal light absorption and scattering patterns. For the majority of the 11 studied days, the highest absorption peaks appeared in the early morning, 07.00-09.30 h while those of scattering appeared later, 09.30-11.00 h. The earlier absorption peaks could be attributed to the elevated elemental carbon vehicular emissions during the heavy traffic hours whereas the later scattering peaks could be attributed to secondary aerosols formed photochemically in the atmosphere. During the period examined, the Pedregal site exhibited on the average a lower aerosol scattering and a higher aerosol absorption contribution to the total aerosol visible light extinction and a better visibility than that of the Merced site. Hence, the impact of aerosol absorption on the visibility degradation due to aerosols was greater at the less hazy Pedregal site. The overall 11-day aerosol visibility average of 20.9 km found at La Merced site, was only 9.4 km lower than that of 30.3 km found at the Pedregal site. This small aerosol visibility difference, of the order of the standard deviation, led to the conclusion that besides the regional-scale aerosol impact, the urban-scale aerosol impact on aerosol visible light extinction is very similar at La Merced and Pedregal sites.

  6. Facile synthesis of phosphorus doped graphitic carbon nitride polymers with enhanced visible-light photocatalytic activity

    SciTech Connect

    Zhang, Ligang; Chen, Xiufang; Guan, Jing; Jiang, Yijun; Hou, Tonggang; Mu, Xindong

    2013-09-01

    Graphical abstract: - Highlights: • P-doped g-C{sub 3}N{sub 4} has been prepared by a one-pot green synthetic approach. • The incorporation of P resulted in favorable textural and electronic properties. • Doping with P enhanced the visible-light photocatalytic activity of g-C{sub 3}N{sub 4}. • A postannealing treatment further enhanced the activity of P-doped g-C{sub 3}N{sub 4}. • Photogenerated holes were the main species responsible for the activity. - Abstract: Phosphorus-doped carbon nitride materials were prepared by a one-pot green synthetic approach using dicyandiamide monomer and a phosphorus containing ionic liquid as precursors. The as-prepared materials were subjected to several characterizations and investigated as metal-free photocatalysts for the degradation of organic pollutants (dyes like Rhodamine B, Methyl orange) in aqueous solution under visible light. Results revealed that phosphorus-doped carbon nitride have a higher photocatalytic activity for decomposing Rhodamine B and Methyl orange in aqueous solution than undoped g-C{sub 3}N{sub 4}, which was attributed to the favorable textural, optical and electronic properties caused by doping with phosphorus heteroatoms into carbon nitride host. A facile postannealing treatment further improved the activity of the photocatalytic system, due to the higher surface area and smaller structural size in the postcalcined catalysts. The phosphorus-doped carbon nitride showed high visible-light photocatalytic activity, making them promising materials for a wide range of potential applications in photochemistry.

  7. Visible-light system for detecting doxorubicin contamination on skin and surfaces.

    PubMed

    Van Raalte, J; Rice, C; Moss, C E

    1990-05-01

    A portable system that uses fluorescence stimulated by visible light to identify doxorubicin contamination on skin and surfaces was studied. When activated by violet-blue light in the 465-nm range, doxorubicin fluoresces, emitting orange-red light in the 580-nm range. The light source to stimulate fluorescence was a slide projector with a filter to selectively pass short-wave (blue) visible light. Fluorescence was both observed visually with viewing spectacles and photographed. Solutions of doxorubicin in sterile 0.9% sodium chloride injection were prepared in nine standard concentrations ranging from 2 to 0.001 mg/mL. Droplets of each admixture were placed on stainless steel, laboratory coat cloth, pieces of latex examination glove, bench-top absorbent padding, and other materials on which antineoplastics might spill or leak. These materials then were stored for up to eight weeks and photographed weekly. The relative ability of water, household bleach, hydrogen peroxide solution, and soap solution to deactivate doxorubicin was also measured. Finally, this system was used to inspect the antineoplastic-drug preparation and administration areas of three outpatient cancer clinics for doxorubicin contamination. Doxorubicin fluorescence was easily detectable with viewing spectacles when a slide projector was used as the light source. The photographic method was sensitive for doxorubicin concentrations from 2.0 to 0.001 mg/mL. Immersion of study materials in bleach for one minute eliminated detectable fluorescence. Doxorubicin contamination is detectable for at least eight weeks in the ambient environment. Probable doxorubicin contamination was detected in two of the three clinics surveyed. A safe, portable system that uses fluorescence stimulated by visible light is a sensitive method for detecting doxorubicin on skin and surfaces.

  8. Antimicrobial materials for water disinfection based on visible-light photocatalysts

    NASA Astrophysics Data System (ADS)

    Wu, Pinggui

    Since the discovery of photocatalytic water-splitting on TiO2 in 1972, enormous effort has been devoted to the study of TiO2. Since the optical properties of TiO2 and e--h + recombination are essential to the photon-driven applications, these two areas have drawn tremendous research attention in the past few years. But there is no single optimal system to date that has visible-light activity, high photo-efficiency and easy recovery. In this study, chemical co-doping approach was adopted to achieve desirable properties of TiO2-based photocatalyst. Nitrogen and metal ions selected from the transition metal or the rare earth element group were incorporated into TiO2 to induce a red-shift to the visible-light absorption regime and to enhance photocatalytic activity. The anion and cation co-doped TiO2 was made into various forms, including thin film, fiber, and foam that circumvent the problems associated with catalyst recovery. Chemical composition, structure, microstructure, optical, and photocatalytic properties were investigated to characterize each type of the materials. Electronic structure calculation and electron paramagnetic resonance spectroscopy were conducted to understand the role of nitrogen and metal ions. The photocatalytic property of these visible-light-active photocatalysts were studied in the inactivation of bacteria and bacterial spores in water. Fast killing rate was obtained for the inactivation of E. coli, P. aeruginosa, S. aureus and B. subtilis endospores. The results of mechanistic study provided evidence of oxidative damages, and indicated that hydroxyl radicals are one of the key killing species. Atomic force microscopy and electron microscopy showed that the cell walls were attacked by photocatalytic inactivation. The potential application of the photocatalyst in water disinfection was demonstrated by flow-through tests.

  9. Continuous flow α-trifluoromethylation of ketones by metal-free visible light photoredox catalysis.

    PubMed

    Cantillo, David; de Frutos, Oscar; Rincón, Juan A; Mateos, Carlos; Kappe, C Oliver

    2014-02-01

    A continuous-flow, two-step procedure for the preparation of α-CF3-substituted carbonyl compounds has been developed. The carbonyl substrates were converted in situ into the corresponding silyl enol ethers, mixed with the CF3 radical source, and then irradiated with visible light using a flow reactor based on transparent tubing and a household compact fluorescent lamp. The continuous protocol uses Eosin Y as an inexpensive photoredox catalyst and requires only 20 min to complete the two reaction steps.

  10. Ferrocene-modified carbon nitride for direct oxidation of benzene to phenol with visible light.

    PubMed

    Ye, Xiangju; Cui, Yanjuan; Wang, Xinchen

    2014-03-01

    Ferrocene moieties were heterogenized onto carbon nitride polymers by a covalent -C=N- linkage bridging the two conjugation systems, enabling the merging of the redox function of ferrocene with carbon nitride photocatalysis to construct a heterogeneous Photo-Fenton system for green organocatalysis at neutral conditions. The synergistic donor-acceptor interaction between the carbon nitride matrix and ferrocene group, improved exciton splitting, and coupled photocatalytic performance allowed the direct synthesis of phenol from benzene in the presence of H2 O2 under visible light irradiation. This innovative modification method will offer an avenue to construct functionalized two-dimensional polymers useful also for other green synthesis processes using solar irradiation.

  11. Controllable Chemoselectivity in Visible-Light Photoredox Catalysis: Four Diverse Aerobic Radical Cascade Reactions.

    PubMed

    Liu, Xinfei; Ye, Xinyi; Bureš, Filip; Liu, Hongjun; Jiang, Zhiyong

    2015-09-21

    Reported is the controllable selectivity syntheses of four distinct products from the same starting materials by visible-light photoredox catalysis. By employing a dicyanopyrazine-derived chromophore (DPZ) as photoredox catalyst, an aerobic radical mechanism has been developed, and allows the reactions of N-tetrahydroisoquinolines (THIQs) with N-itaconimides to through four different pathways, including addition-cyclization, addition-elimination, addition-coupling, and addition-protonation, with satisfactory chemoselectivity. The current strategy provide straightforward access to four different but valuable N-heterocyclic adducts in moderate to excellent yields.

  12. Visible Light-Induced Carbonylation Reactions with Organic Dyes as the Photosensitizers.

    PubMed

    Peng, Jin-Bao; Qi, Xinxin; Wu, Xiao-Feng

    2016-09-01

    Dyes can CO do it: Organic dyes and pigments are usually applied in textile dyeing, which can be dated back to the Neolithic period. Interestingly, the possibility to use organic dyes as photoredox catalysts has also been noticed by organic chemists and applied in organic synthesis. Carbonylation reactions as a powerful procedure in carbonyl-containing compound preparation have also been studied. In this manuscript, the recent achievements in using organic dyes as visible-light sensitizers in carbonylation chemistry are summarized and discussed.

  13. Environmental remediation and superhydrophilicity of ultrafine antibacterial tungsten oxide-based nanofibers under visible light source

    NASA Astrophysics Data System (ADS)

    Srisitthiratkul, Chutima; Yaipimai, Wittaya; Intasanta, Varol

    2012-10-01

    Fabrication of nanosilver-decorated WO3 nanofibers was successfully performed. First, deposition of nanosilver onto electrospun WO3 nanofibers' surface was done via photoreduction of silver ion under visible or UV light. The resulting hybrid nanofibers not only revealed antibacterial characteristics but also maintained their photocatalytic performance towards methylene blue decomposition. Unexpectedly, the nanofibrous layers prepared from these nanofibers showed superhydrophilicity under a visible light source. The nanofibers might be advantageous in environmental and hygienic nanofiltration under natural light sources, where the self-cleaning characteristics could be valuable in maintenance processes.

  14. Comparison of thresholding schemes for visible light communication using mobile-phone image sensor.

    PubMed

    Liu, Yang; Chow, Chi-Wai; Liang, Kevin; Chen, Hung-Yu; Hsu, Chin-Wei; Chen, Chung-Yen; Chen, Shih-Hao

    2016-02-01

    Based on the rolling shutter effect of the complementary metal-oxide-semiconductor (CMOS) image sensor, bright and dark fringes can be observed in each received frame. By demodulating the bright and dark fringes, the visible light communication (VLC) data logic can be retrieved. However, demodulating the bright and dark fringes is challenging as there is a high data fluctuation and large extinction ratio (ER) variation in each frame due. Hence proper thresholding scheme is needed. In this work, we propose and compare experimentally three thresholding schemes; including third-order polynomial curve fitting, iterative scheme and quick adaptive scheme. The evaluation of these three thresholding schemes is performed.

  15. Visible-light sensitization of boron-doped nanocrystalline diamond through non-covalent surface modification.

    PubMed

    Krysova, Hana; Vlckova-Zivcova, Zuzana; Barton, Jan; Petrak, Vaclav; Nesladek, Milos; Cigler, Petr; Kavan, Ladislav

    2015-01-14

    A novel simple and versatile synthetic strategy is developed for the surface modification of boron-doped diamond. In a two-step procedure, polyethyleneimine is adsorbed on the hydrogenated diamond surface and subsequently modified with a model light-harvesting donor-π-bridge-acceptor molecule (coded P1). The sensitized diamond exhibits stable cathodic photocurrents under visible-light illumination in aqueous electrolyte solution with dimethylviologen serving as an electron mediator. In spite of the simplicity of the surface sensitization protocol, the photoelectrochemical performance is similar to or better than that of other sensitized diamond electrodes which were reported in previous studies (2008-2014). PMID:25418375

  16. Photocatalytic Ohmic layered nanocomposite for efficient utilization of visible light photons

    SciTech Connect

    Kim, Hyun Gyu; Jeong, Euh Duck; Borse, Pramod H.; Jeon, Seongho; Yong, Kijung; Lee, Jae Sung; Li Wei; Oh, Se H.

    2006-08-07

    The WO{sub 3}/W/PbBi{sub 2}Nb{sub 1.9}Ti{sub 0.1}O{sub 9} photocatalyst was fabricated by depositing the tungsten clusters over the p-type perovskite base material with the chemical vapor deposition method, and later partly oxidizing the surfaces of these clusters to obtain n-type WO{sub 3} overlayers and W metal layer as an Ohmic junction. This NCPC showed unprecedented high activity for the photocatalytic oxidation of water, photocurrent generation, and acetaldehyde decomposition under visible light irradiation ({lambda}{>=}420 nm)

  17. Catalytic Access to Alkyl Bromides, Chlorides and Iodides via Visible Light-Promoted Decarboxylative Halogenation.

    PubMed

    Candish, Lisa; Standley, Eric A; Gómez-Suárez, Adrián; Mukherjee, Satobhisha; Glorius, Frank

    2016-07-11

    Herein is reported the catalytic, visible light-promoted, decarboxylative halogenation (bromination, chlorination, and iodination) of aliphatic carboxylic acids. This operationally-simple reaction tolerates a range of functional groups, proceeds at room temperature, and is redox neutral. By employing an iridium photocatalyst in concert with a halogen atom source, the use of stoichiometric metals such as silver, mercury, thallium, and lead can be circumvented. This reaction grants access to valuable synthetic building blocks from the large pool of cheap, readily available carboxylic acids. PMID:27191347

  18. Aromatic Monochlorination Photosensitized by DDQ with Hydrogen Chloride under Visible-Light Irradiation.

    PubMed

    Ohkubo, Kei; Fujimoto, Atsushi; Fukuzumi, Shunichi

    2016-04-01

    Photochlorination of aromatic substrates by hydrogen chloride with 2,3-dichloro-5,6-cyano-p-benzoquinone (DDQ) occurs efficiently to produce the corresponding monochlorinated products selectively under visible-light irradiation. The yields for the chlorination of phenol were 70 % and 18 % for p- and o-chlorophenol, respectively, without formation of further chlorinated products. The photoinduced chlorination is initiated by electron transfer from Cl(-) to the triplet excited state of DDQ. The radical intermediates involved in the photochemical reaction have been detected by time-resolved transient absorption measurements.

  19. Continuous flow α-trifluoromethylation of ketones by metal-free visible light photoredox catalysis.

    PubMed

    Cantillo, David; de Frutos, Oscar; Rincón, Juan A; Mateos, Carlos; Kappe, C Oliver

    2014-02-01

    A continuous-flow, two-step procedure for the preparation of α-CF3-substituted carbonyl compounds has been developed. The carbonyl substrates were converted in situ into the corresponding silyl enol ethers, mixed with the CF3 radical source, and then irradiated with visible light using a flow reactor based on transparent tubing and a household compact fluorescent lamp. The continuous protocol uses Eosin Y as an inexpensive photoredox catalyst and requires only 20 min to complete the two reaction steps. PMID:24432711

  20. Visible light-promoted metal-free sp(3)-C-H fluorination.

    PubMed

    Xia, Ji-Bao; Zhu, Chen; Chen, Chuo

    2014-10-11

    Photoexcited acetophenone can catalyze the fluorination of unactivated C(sp(3))-H groups. While acetophenone, a colorless oil, only has a trace amount of absorption in the visible light region, its photoexcitation can be achieved by irradiation with light generated by a household compact fluorescent lamp (CFL). This operational simple method provides improved substrate scope for the direct incorporation of a fluorine atom into simple organic molecules. CFL-irradiation can also be used to promote certain classic UV-promoted photoreactions of colorless monoarylketones and enones/enals. PMID:25143256

  1. Fountain code-based error control scheme for dimmable visible light communication systems

    NASA Astrophysics Data System (ADS)

    Feng, Lifang; Hu, Rose Qingyang; Wang, Jianping; Xu, Peng

    2015-07-01

    In this paper, a novel error control scheme using Fountain codes is proposed in on-off keying (OOK) based visible light communications (VLC) systems. By using Fountain codes, feedback information is needed to be sent back to the transmitter only when transmitted messages are successfully recovered. Therefore improved transmission efficiency, reduced protocol complexity and relative little wireless link-layer delay are gained. By employing scrambling techniques and complementing symbols, the least complemented symbols are needed to support arbitrary dimming target values, and the value of entropy of encoded message are increased.

  2. Visible Light-Induced Carbonylation Reactions with Organic Dyes as the Photosensitizers.

    PubMed

    Peng, Jin-Bao; Qi, Xinxin; Wu, Xiao-Feng

    2016-09-01

    Dyes can CO do it: Organic dyes and pigments are usually applied in textile dyeing, which can be dated back to the Neolithic period. Interestingly, the possibility to use organic dyes as photoredox catalysts has also been noticed by organic chemists and applied in organic synthesis. Carbonylation reactions as a powerful procedure in carbonyl-containing compound preparation have also been studied. In this manuscript, the recent achievements in using organic dyes as visible-light sensitizers in carbonylation chemistry are summarized and discussed. PMID:27488198

  3. Synthesis of highly functionalized polycyclic quinoxaline derivatives using visible-light photoredox catalysis.

    PubMed

    He, Zhi; Bae, Minwoo; Wu, Jie; Jamison, Timothy F

    2014-12-22

    A mild and facile method for preparing highly functionalized pyrrolo[1,2-a]quinoxalines and other nitrogen-rich heterocycles, each containing a quinoxaline core or an analogue thereof, has been developed. The novel method features a visible-light-induced decarboxylative radical coupling of ortho-substituted arylisocyanides and radicals generated from phenyliodine(III) dicarboxylate reagents and exhibits excellent functional group compatibility. A wide range of quinoxaline heterocycles have been prepared. Finally, a telescoped preparation of these polycyclic compounds by integration of the in-line isocyanide formation and photochemical cyclization has been established in a three-step continuous-flow system.

  4. Visible Light Initiated Hantzsch Synthesis of 2,5-Diaryl-Substituted Pyrroles at Ambient Conditions.

    PubMed

    Lei, Tao; Liu, Wen-Qiang; Li, Jian; Huang, Mao-Yong; Yang, Bing; Meng, Qing-Yuan; Chen, Bin; Tung, Chen-Ho; Wu, Li-Zhu

    2016-05-20

    Irradiation of a mixture of enamines and α-bromo ketones, with a catalytic amount of Ir(ppy)3 by visible light (λ = 450 nm), enables the production of various 2,5-diaryl-substituted pyrroles in good to excellent yields. The key intermediates in this reaction have been identified as alkyl radicals, generated from single-electron transfer from the photoexcited Ir(ppy)3* to α-bromo ketones, which subsequently react with a broad range of enamines to undergo the Hantzsch reaction rapidly at ambient conditions. PMID:27199225

  5. Is it effective to harvest visible light by decreasing the band gap of photocatalytic materials?

    SciTech Connect

    Fu Ning; Tang Xinhu; Li Dongyang

    2012-02-27

    In situ variations in the electron work function and photo-current of TiO{sub 2} nanotubes demonstrate that long-wavelength illumination only has a minor effect on the excitation of electrons in the nanotubes after being exposed to short-wavelength light or when the short-wavelength light coexisted, indicating that the solar spectrum may not be utilized as efficiently as expected by extending the absorption spectrum of the photocatalytic material to visible light range with decreased band gaps.

  6. Radio and visible light observations of matter ejected from the sun

    NASA Technical Reports Server (NTRS)

    Wagner, W. J.; Hildner, E.; House, L. L.; Sawyer, C.; Sheridan, K. V.; Dulk, G. A.

    1981-01-01

    An initial set of visible light and radio observations of a coronal transient made with the Coronagraph/Polarimeter experiment on SMM and the radioheliograph at Culgoora, Australia is presented. It is noted that an enormous loop-shaped transient observed on April 7, 1980, exhibited bright material having whiplike, nonradial motions, as well as moving and stationary radio sources. The data make it possible to establish that a moving type IV radio source was located on or very close to the fast-moving loop. The thermal, kinetic, and magnetic energies in the transient are estimated and, for the first time, compared with the radiative energy of the associated flare.

  7. QPSK modulation for AC-power-signal-biased visible light communication system

    NASA Astrophysics Data System (ADS)

    Liu, Yu-Feng; Yeh, Chien-Hung; Chow, Chi-Wai; Liu, Yang

    2013-01-01

    With the integration of light emitting diode (LED), visible light communication (VLC) can provide wireless communication link using the lightning system. Due to the consideration of power efficiency, AC-LED has the design of reducing energy waste with alternating current from the power outlet. In this work, we propose an AC-power-signalbiased system that provides communication on both DC-LED and AC-LED. The bias circuit is designed to combine ACpower signal and the message signal with QPSK format. This driving scheme needs no AC-to-DC converters and it is suitable for driving AC LED. Synchronization is completed to avoid threshold effect of LED.

  8. Conjugated Microporous Poly(Benzochalcogenadiazole)s for Photocatalytic Oxidative Coupling of Amines under Visible Light.

    PubMed

    Wang, Zi Jun; Garth, Kim; Ghasimi, Saman; Landfester, Katharina; Zhang, Kai A I

    2015-10-26

    Metal-free visible-light photocatalysts offer a clean, sustainable solution to many pressing environmental issues. Herein, we present a molecular design strategy to fine-tune the valence and conduction band levels of a series of conjugated microporous polymer networks based on poly(benzochalcogenadiazole) for heterogeneous photocatalysis. Enhanced photocatalytic efficiency was observed by altering the chalcogene moieties in the electron-accepting benzochalcogenadiazole unit of the polymer backbone structure. Photooxidative coupling of benzylamines was chosen as a model reaction. This design strategy leading to enhanced efficiency could potentially improve a wide range of photoredox reactions.

  9. Spin-Selective Generation of Triplet Nitrenes: Olefin Aziridination through Visible-Light Photosensitization of Azidoformates.

    PubMed

    Scholz, Spencer O; Farney, Elliot P; Kim, Sangyun; Bates, Desiree M; Yoon, Tehshik P

    2016-02-01

    Azidoformates are interesting potential nitrene precursors, but their direct photochemical activation can result in competitive formation of aziridination and allylic amination products. Herein, we show that visible-light-activated transition-metal complexes can be triplet sensitizers that selectively produce aziridines through the spin-selective photogeneration of triplet nitrenes from azidoformates. This approach enables the aziridination of a wide range of alkenes and the formal oxyamination of enol ethers using the alkene as the limiting reagent. Preparative-scale aziridinations can be easily achieved under continuous-flow conditions.

  10. The effects of narrowbands of visible light upon some skin disorders: a review.

    PubMed

    Greaves, A J

    2016-08-01

    This review article focuses on clinical studies published in the fields of (i) photorejuvenation and anti-ageing, (ii) oily or acne-prone skin and related imperfections, (iii) skin pigmentation and lightening, (iv) dandruff and other Malassezia-related skin disorders and (v) prevention and reversal of hair loss using non-thermal, non-ablative devices (principally light-emitting diodes). It mainly focuses on clinical proof of performance and also on in vitro studies that support the clinical findings. The mode of action of narrowbands of visible light upon the skin is only briefly discussed since their biological effects have been previously reviewed. PMID:26708128

  11. Visible light nitrogen dioxide spectrophotometer intercomparison: Mount Kobau, British Columbia, July 28 to August 10, 1991

    NASA Technical Reports Server (NTRS)

    Mcelroy, C. T.; Elokhov, A. S.; Elansky, N.; Frank, H.; Johnston, P.; Kerr, J. B.

    1994-01-01

    Under the auspices of the World Meteorological Organization, Environment Canada hosted an international comparison of visible light spectrophotometers at Mt. Kobau, British Columbia in August of 1991. Instruments from four countries were involved. The intercomparison results have indicated that some significant differences exist in the responses of the various instruments, and have provided a basis for the comparison of the historical data sets which currently exist as a result of the independent researches carried out in the past in the former Soviet Union, New Zealand, and Canada.

  12. Carbon nitride for the selective oxidation of aromatic alcohols in water under visible light.

    PubMed

    Long, Baihua; Ding, Zhengxin; Wang, Xinchen

    2013-11-01

    The selective oxidation of aromatic alcohols in water is achieved by using a carbon nitride (CN) catalyst, dioxygen, and visible light. The unique electronic structure of CN avoids the direct formation of hydroxyl radicals, which typically cause the total oxidation of organics. The chemical stability of CN allows several chemical protocols for photoredox catalysis in water, as exemplified by cooperative catalysis involving Brønsted acids. This leads to a new, green pathway for diverse organic transformations using sunlight and water. PMID:24039175

  13. Group III-nitride nanowire structures for photocatalytic hydrogen evolution under visible light irradiation

    SciTech Connect

    Chowdhury, Faqrul A.; Mi, Zetian Kibria, Md G.; Trudeau, Michel L.

    2015-10-01

    The performance of photochemical water splitting over the emerging nanostructured photocatalysts is often constrained by their surface electronic properties, which can lead to imbalance in redox reactions, reduced efficiency, and poor stability. We have investigated the impact of surface charge properties on the photocatalytic activity of InGaN nanowires. By optimizing the surface charge properties through controlled p-type dopant (Mg) incorporation, we have demonstrated an apparent quantum efficiency of ∼17.1% and ∼12.3% for InGaN nanowire arrays under visible light irradiation (400 nm–490 nm) in aqueous methanol and in the overall neutral-pH water splitting reaction, respectively.

  14. Visible-Light-Promoted Trifluoromethylthiolation of Styrenes by Dual Photoredox/Halide Catalysis.

    PubMed

    Honeker, Roman; Garza-Sanchez, R Aleyda; Hopkinson, Matthew N; Glorius, Frank

    2016-03-18

    Herein, we report a new visible-light-promoted strategy to access radical trifluoromethylthiolation reactions by combining halide and photoredox catalysis. This approach allows for the synthesis of vinyl-SCF3 compounds of relevance in pharmaceutical chemistry directly from alkenes under mild conditions with irradiation from household light sources. Furthermore, alkyl-SCF3-containing cyclic ketone and oxindole derivatives can be accessed by radical-polar crossover semi-pinacol and cyclization processes. Inexpensive halide salts play a crucial role in activating the trifluoromethylthiolating reagent towards photoredox catalysis and aid the formation of the SCF3 radical.

  15. Visible light activated photocatalytic behaviour of rare earth modified commercial TiO{sub 2}

    SciTech Connect

    Tobaldi, D.M.; Seabra, M.P.; Labrincha, J.A.

    2014-02-01

    Highlights: • RE gave more surface hydroxyl groups attached to the photocatalyst's surface. • RE gave the modified and fired samples a high specific surface area. • Photocatalytic activity was assessed in gas–solid phase under visible-light exposure. • Thermal treated RE-TiO{sub 2}s showed a superior visible-light photocatalytic activity. • La-TiO{sub 2} was the best performing photocatalyst. - Abstract: A commercial TiO{sub 2} nanopowder, Degussa P25, was modified with several rare earth (RE) elements in order to extend its photocatalytic activity into the visible range. The mixtures were prepared via solid-state reaction of the precursor oxides, and thermally treated at high temperature (900 and 1000 °C), with the aim of investigating the photocatalytic activity of the thermally treated samples. This thermal treatment was chosen for a prospective application as a surface layer in materials that need to be processed at high temperatures. The photocatalytic activity (PCA) of the samples was assessed in gas–solid phase – monitoring the degradation of isopropanol (IPA) – under visible-light irradiation. Results showed that the addition of the REs lanthanum, europium and yttrium to TiO{sub 2} greatly improved its photocatalytic activity, despite the thermal treatment, because of the presence of more surface hydroxyl groups attached to the photocatalyst's surface, together with a higher specific surface area (SSA) of the modified and thermally treated samples, with regard to the unmodified and thermally treated Degussa P25. The samples doped with La, Eu and Y all had excellent PCA under visible-light irradiation, even higher than the untreated Degussa P25 reference sample, despite their thermal treatment at 900 °C, with lanthanum producing the best results (i.e. the La-, Eu- and Y-TiO{sub 2} samples, thermally treated at 900 °C, had, respectively, a PCA equal to 26, 27 and 18 ppm h{sup −1} – in terms of acetone formation – versus 15 ppm h

  16. Research on illuminance distribution of LED spherical arrays for indoor visible light communication

    NASA Astrophysics Data System (ADS)

    Li, Yankun; Yang, Aiying; Sun, Yu-nan; Wu, Yongsheng; Wang, Yu; Hou, Yifei

    2013-12-01

    Illuminance distribution of LED spherical arrays is studied by theoretical analysis and simulation. The optimal layout of the LED spherical array is founded by changing the angle, the ball radius, and the power of different LED. The uniformity of illumination of the LED spherical array is verified, which is better than LED planar array. In addition, the illuminance distribution of indoor ground surface illuminated by LED spherical array with different parameters and the related curves are obtained. The LED spherical array mentioned in this paper can be useful in the application of indoor visible light communication.

  17. Clinical applications of visible light-cured resin in maxillofacial prosthetics. Part I: Denture base and reline material.

    PubMed

    Shifman, A

    1990-11-01

    A visible light-cured resin system enables the dentist to accomplish chairside relining of removable prosthesis. The material is pliable and can be initially cured in the mouth with the regular hand-held visible light. A special unit is needed to completely cure the material, which thereafter is comparable in quality to heat-polymerized acrylic resin. The value of this system for the practice of maxillofacial prosthetics is demonstrated by the ease of relining of various devices and obturator prostheses.

  18. A copper(II)-ethylenediamine modified polyoxoniobate with photocatalytic H2 evolution activity under visible light irradiation.

    PubMed

    Wang, Zhen-Li; Tan, Hua-Qiao; Chen, Wei-Lin; Li, Yang-Guang; Wang, En-Bo

    2012-09-01

    A new dimer polyoxoniobate [Cu(en)(2)](11)K(4)Na(2)[KNb(24)O(72)H(9)](2)·120H(2)O (1) has been synthesized and systematically characterized. Visible light photocatalytic H(2) evolution activity was researched with 1 as the visible-light photosensitizer and catalyst, cobaloximes [Co(III)(dmgH)(2)pyCl] as the co-catalysts, and triethylamine (TEA) as the sacrificial electron donor. PMID:22763602

  19. Visible light active, nano-architectured metal oxide photo-catalysts for solar fuel applications

    NASA Astrophysics Data System (ADS)

    LaTempa, Thomas Joseph, Jr.

    Large-scale implementation of renewable energy sources such as solar requires the development of an efficient energy capture, conversion and storage scheme. Harnessing solar energy to create storable fuels, i.e., solar fuels, provides a unique strategy to meet this objective. In this regard, hydrogen generation through water photoelectrolysis and methane generation via the photocatalytic conversion of carbon dioxide and water vapor are investigated. The primary motivation of this work lies in the development of efficient, low cost materials for solar fuel applications. Metal oxide semiconductors such as n-type titanium dioxide (TiO 2) have generated significant interest in the scientific community due to their low cost, stability and high photocatalytic activity under band gap illumination. The implementation of nano-structured materials has significantly enhanced the conversion efficiency obtained with TiO2 in applications such as water photoelectrolysis. Despite these advancements, TiO2 has an inherently poor photoresponse due its wide band gap (3.0-3.2 eV), which accounts for ≈ 5% of the solar spectrum energy. Therefore, the primary objective of this work is to develop materials with a photocatalytic activity approaching that of TiO2, while shifting the photo-response to harness the visible light portion of the solar spectrum. Two differing approaches are evaluated in this work to meet this objective. Hematite (alpha-Fe2O3) has a band gap ≈ 2.2 eV, well suited for capturing solar energy, but suffers from intrinsically poor electrical characteristics. To overcome these limitations, iron oxide nanotubes were developed using a temperature controlled anodization technique. This provides greater control over the film morphology to create high aspect ratio nano-structures approximately 1-4 mum in length, sufficient to harness solar energy, with a wall thickness approaching 10 nm to improve the electrical characteristics for photocatalytic application. The

  20. Synthetic Utilization of α-Aminoalkyl Radicals and Related Species in Visible Light Photoredox Catalysis.

    PubMed

    Nakajima, Kazunari; Miyake, Yoshihiro; Nishibayashi, Yoshiaki

    2016-09-20

    Single electron oxidation of amines provides an efficient way to access synthetically useful α-aminoalkyl radicals as reactive intermediates. After the single electron oxidation of amines, fragmentation of the resulting radical cations proceeds to give the α-aminoalkyl radicals along with generation of a proton. In the synthetic utilization of the α-aminoalkyl radicals, precise control of single electron transfer is essential, because further oxidation of the α-aminoalkyl radicals occurs more easily than the starting amines and the α-aminoalkyl radicals are converted into the corresponding iminium ions. As a result, photoinduced single electron transfer is quite attractive in the synthetic utilization of the α-aminoalkyl radicals. Recently, visible light-photoredox catalysis using transition metal-polypyridyl complexes and other dyes as catalysts has attracted considerable attention, where useful molecular transformations can be achieved through the single electron transfer process between the excited catalysts and substrates. In this context, MacMillan et al. ( Science 2011, 334 , 1114 , DOI: 10.1126/science.1213920 ) reported an aromatic substitution reaction of cyanoarenes with amines, where α-aminoalkyl radicals work as key reactive intermediates. Pandey and Reiser et al. ( Org. Lett. 2012 , 14 , 672 , DOI: 10.1021/ol202857t ) and our group ( Nishibayashi et al. J. Am. Chem. Soc. 2012 , 134 , 3338 , DOI: 10.1021/ja211770y ) independently reported reactions of amines with α,β-unsaturated carbonyl compounds, where addition of α-aminoalkyl radicals to alkenes is a key step. After these earliest examples, nowadays, a variety of transformations using the α-aminoalkyl radicals as reactive intermediates have been reported by many groups. The α-aminoalkyl radicals are usually produced from amines by single electron oxidation and the subsequent deprotonation of the C-H bond adjacent to the nitrogen atom. In addition, the α-aminoalkyl radicals are also

  1. Synthetic Utilization of α-Aminoalkyl Radicals and Related Species in Visible Light Photoredox Catalysis.

    PubMed

    Nakajima, Kazunari; Miyake, Yoshihiro; Nishibayashi, Yoshiaki

    2016-09-20

    Single electron oxidation of amines provides an efficient way to access synthetically useful α-aminoalkyl radicals as reactive intermediates. After the single electron oxidation of amines, fragmentation of the resulting radical cations proceeds to give the α-aminoalkyl radicals along with generation of a proton. In the synthetic utilization of the α-aminoalkyl radicals, precise control of single electron transfer is essential, because further oxidation of the α-aminoalkyl radicals occurs more easily than the starting amines and the α-aminoalkyl radicals are converted into the corresponding iminium ions. As a result, photoinduced single electron transfer is quite attractive in the synthetic utilization of the α-aminoalkyl radicals. Recently, visible light-photoredox catalysis using transition metal-polypyridyl complexes and other dyes as catalysts has attracted considerable attention, where useful molecular transformations can be achieved through the single electron transfer process between the excited catalysts and substrates. In this context, MacMillan et al. ( Science 2011, 334 , 1114 , DOI: 10.1126/science.1213920 ) reported an aromatic substitution reaction of cyanoarenes with amines, where α-aminoalkyl radicals work as key reactive intermediates. Pandey and Reiser et al. ( Org. Lett. 2012 , 14 , 672 , DOI: 10.1021/ol202857t ) and our group ( Nishibayashi et al. J. Am. Chem. Soc. 2012 , 134 , 3338 , DOI: 10.1021/ja211770y ) independently reported reactions of amines with α,β-unsaturated carbonyl compounds, where addition of α-aminoalkyl radicals to alkenes is a key step. After these earliest examples, nowadays, a variety of transformations using the α-aminoalkyl radicals as reactive intermediates have been reported by many groups. The α-aminoalkyl radicals are usually produced from amines by single electron oxidation and the subsequent deprotonation of the C-H bond adjacent to the nitrogen atom. In addition, the α-aminoalkyl radicals are also

  2. Observatory Sponsoring Astronomical Image Contest

    NASA Astrophysics Data System (ADS)

    2005-05-01

    Forget the headphones you saw in the Warner Brothers thriller Contact, as well as the guttural throbs emanating from loudspeakers at the Very Large Array in that 1997 movie. In real life, radio telescopes aren't used for "listening" to anything - just like visible-light telescopes, they are used primarily to make images of astronomical objects. Now, the National Radio Astronomy Observatory (NRAO) wants to encourage astronomers to use radio-telescope data to make truly compelling images, and is offering cash prizes to winners of a new image contest. Radio Galaxy Fornax A Radio Galaxy Fornax A Radio-optical composite image of giant elliptical galaxy NGC 1316, showing the galaxy (center), a smaller companion galaxy being cannibalized by NGC 1316, and the resulting "lobes" (orange) of radio emission caused by jets of particles spewed from the core of the giant galaxy Click on image for more detail and images CREDIT: Fomalont et al., NRAO/AUI/NSF "Astronomy is a very visual science, and our radio telescopes are capable of producing excellent images. We're sponsoring this contest to encourage astronomers to make the extra effort to turn good images into truly spectacular ones," said NRAO Director Fred K.Y. Lo. The contest, offering a grand prize of $1,000, was announced at the American Astronomical Society's meeting in Minneapolis, Minnesota. The image contest is part of a broader NRAO effort to make radio astronomical data and images easily accessible and widely available to scientists, students, teachers, the general public, news media and science-education professionals. That effort includes an expanded image gallery on the observatory's Web site. "We're not only adding new radio-astronomy images to our online gallery, but we're also improving the organization and accessibility of the images," said Mark Adams, head of education and public outreach (EPO) at NRAO. "Our long-term goal is to make the NRAO Image Gallery an international resource for radio astronomy imagery

  3. Astronomical Polarimetry

    NASA Astrophysics Data System (ADS)

    Tinbergen, Jaap

    1996-09-01

    This handy volume provides a clear, comprehensive and concise introduction to astronomical polarimetry at all wavelengths. Starting from first principles and a simple physical picture of polarized radiation, the author introduces the reader to all the key topics, including Stokes parameters, applications of polarimetry in astronomy, polarization algebra, polarization errors and calibration methods, and a selection of instruments (from radio to X-ray). The author rounds off the book with a number of useful case studies, a collection of exercises, an extensive list of further reading and an informative index. This review of all aspects of astronomical polarization provides both an essential introduction for graduate students, and a valuable reference for practicing astronomers.

  4. Astronomical kaleidoscope

    NASA Astrophysics Data System (ADS)

    Gaina, Alex

    2005-10-01

    The entry contains two Moon eclipses (a picture of a total eclipse and a photo of a penumbral one), photographs of monuments of few greatest astronomers: Nikolay Kopernik, Tiho Brahe and Johannes Kepler, a photo from the JENAM-1995 (Catania, Sicily) as well as photographs of few astronomers related with Moldova and Romania: V. Grigorevskii, N. Donitch, V.Nadolschi, D. Mangeron, two nice clocks in Prague, as well as a map of the Sanctuary in Orheiul -Vechi (Bessarabia) with an supposed ancient calendar.

  5. Bare Cd1-xZnxS ZB/WZ Heterophase Nanojunctions for Visible Light Photocatalytic Hydrogen Production with High Efficiency.

    PubMed

    Du, Hong; Liang, Kuang; Yuan, Cheng-Zong; Guo, Hong-Li; Zhou, Xiao; Jiang, Yi-Fan; Xu, An-Wu

    2016-09-21

    In this work, we report the synthesis of Cd1-xZnxS zinc blende/wurtzite (ZB/WZ) heterophase nanojunctions with highly efficient charge separation by a solvothermal method in a mixed solution of diethylenetriamine (DETA) and distilled water. l-Cysteine was selected as a sulfur source and a protecting ligand for stabilization of the ZB/WZ homojunction. The optimal ternary chalcogenide Cd0.7Zn0.3S elongated nanocrystals (NCs) without any cocatalyst loading show very high visible light photocatalytic activity with H2 production efficiency of 3.13 mmol h(-1) and an apparent quantum efficiency of 65.7% at 420 nm. This is one of the best visible light photocatalysts ever reported for photocatalytic hydrogen production without any cocatalysts. The charge separation efficiency, having a critical role in enhancing photocatalytic activity for hydrogen production, was significantly improved. Highly efficient charge separation with a prolonged carrier lifetime is driven by the internal electrostatic field originating from the type-II staggered band alignment at the ZB/WZ junctions, as confirmed by steady and time-resolved photoluminescence spectra. Further, the strong binding between the l-cysteine ligand and Cd1-xZnxS elongated nanocrystals protects and stabilizes NCs; the l-cysteine ligand at the interface could trap holes from Cd1-xZnxS NCs, while photogenerated electrons transfer to Cd1-xZnxS catalytic sites for proton reduction. Our results demonstrate that Cd1-xZnxS ZB/WZ heterophase junctions stabilized by l-cysteine molecules can effectively separate charge carriers and achieve highly visible light photocatalytic hydrogen production. The present study provides a new insight into the design and fabrication of advanced materials with homojunction structures for photocatalytic applications and optoelectronic devices. PMID:27598838

  6. Bare Cd1-xZnxS ZB/WZ Heterophase Nanojunctions for Visible Light Photocatalytic Hydrogen Production with High Efficiency.

    PubMed

    Du, Hong; Liang, Kuang; Yuan, Cheng-Zong; Guo, Hong-Li; Zhou, Xiao; Jiang, Yi-Fan; Xu, An-Wu

    2016-09-21

    In this work, we report the synthesis of Cd1-xZnxS zinc blende/wurtzite (ZB/WZ) heterophase nanojunctions with highly efficient charge separation by a solvothermal method in a mixed solution of diethylenetriamine (DETA) and distilled water. l-Cysteine was selected as a sulfur source and a protecting ligand for stabilization of the ZB/WZ homojunction. The optimal ternary chalcogenide Cd0.7Zn0.3S elongated nanocrystals (NCs) without any cocatalyst loading show very high visible light photocatalytic activity with H2 production efficiency of 3.13 mmol h(-1) and an apparent quantum efficiency of 65.7% at 420 nm. This is one of the best visible light photocatalysts ever reported for photocatalytic hydrogen production without any cocatalysts. The charge separation efficiency, having a critical role in enhancing photocatalytic activity for hydrogen production, was significantly improved. Highly efficient charge separation with a prolonged carrier lifetime is driven by the internal electrostatic field originating from the type-II staggered band alignment at the ZB/WZ junctions, as confirmed by steady and time-resolved photoluminescence spectra. Further, the strong binding between the l-cysteine ligand and Cd1-xZnxS elongated nanocrystals protects and stabilizes NCs; the l-cysteine ligand at the interface could trap holes from Cd1-xZnxS NCs, while photogenerated electrons transfer to Cd1-xZnxS catalytic sites for proton reduction. Our results demonstrate that Cd1-xZnxS ZB/WZ heterophase junctions stabilized by l-cysteine molecules can effectively separate charge carriers and achieve highly visible light photocatalytic hydrogen production. The present study provides a new insight into the design and fabrication of advanced materials with homojunction structures for photocatalytic applications and optoelectronic devices.

  7. An orthophosphate semiconductor with photooxidation properties under visible-light irradiation.

    PubMed

    Yi, Zhiguo; Ye, Jinhua; Kikugawa, Naoki; Kako, Tetsuya; Ouyang, Shuxin; Stuart-Williams, Hilary; Yang, Hui; Cao, Junyu; Luo, Wenjun; Li, Zhaosheng; Liu, Yun; Withers, Ray L

    2010-07-01

    The search for active semiconductor photocatalysts that directly split water under visible-light irradiation remains one of the most challenging tasks for solar-energy utilization. Over the past 30 years, the search for such materials has focused mainly on metal-ion substitution as in In(1-x)Ni(x)TaO(4) and (V-,Fe- or Mn-)TiO(2) (refs 7,8), non-metal-ion substitution as in TiO(2-x)N(x) and Sm(2)Ti(2)O(5)S(2) (refs 9,10) or solid-solution fabrication as in (Ga(1-x)Zn(x))(N(1-x)O(x)) and ZnS-CuInS(2)-AgInS(2) (refs 11,12). Here we report a new use of Ag(3)PO(4) semiconductor, which can harness visible light to oxidize water as well as decompose organic contaminants in aqueous solution. This suggests its potential as a photofunctional material for both water splitting and waste-water cleaning. More generally, it suggests the incorporation of p block elements and alkali or alkaline earth ions into a simple oxide of narrow bandgap as a strategy to design new photoelectrodes or photocatalysts.

  8. Visible-Light Induced Self-Powered Sensing Platform Based on a Photofuel Cell.

    PubMed

    Yan, Kai; Yang, Yaohua; Okoth, Otieno Kevin; Cheng, Ling; Zhang, Jingdong

    2016-06-21

    A self-powered sensing system possesses the capacity of harvesting energy from the environment and has no requirement for external electrical power supply during the chemical sensing of analytes. Herein, we design an enzyme-free self-powered sensing platform based on a photofuel cell (PFC) driven by visible-light, using glucose as a model analyte. The fabricated PFC consists of a Ni(OH)2/CdS/TiO2 photoanode and a hemin-graphene (HG) nanocomposite coated cathode in separated chambers. Under visible-light irradiation, glucose in the anodic chamber is facilely oxidized on Ni(OH)2/CdS/TiO2 while H2O2 in the cathodic chamber is catalytically reduced by HG, which generates a certain cell output sensitive to the variation of glucose concentration. Thus, a PFC based self-powered sensor is realized for glucose detection. Compared to the existing enzymatic self-powered glucose sensors, our proposed PFC based strategy exhibits much lower detection concentration. Moreover, it avoids the limitation of conventional enzyme immobilized electrodes and has the potential to develop high-performance self-powered sensors with broader analyte species. PMID:27237828

  9. Fe ion-implanted TiO2 thin film for efficient visible-light photocatalysis

    NASA Astrophysics Data System (ADS)

    Impellizzeri, G.; Scuderi, V.; Romano, L.; Sberna, P. M.; Arcadipane, E.; Sanz, R.; Scuderi, M.; Nicotra, G.; Bayle, M.; Carles, R.; Simone, F.; Privitera, V.

    2014-11-01

    This work shows the application of metal ion-implantation to realize an efficient second-generation TiO2 photocatalyst. High fluence Fe+ ions were implanted into thin TiO2 films and subsequently annealed up to 550 °C. The ion-implantation process modified the TiO2 pure film, locally lowering its band-gap energy from 3.2 eV to 1.6-1.9 eV, making the material sensitive to visible light. The measured optical band-gap of 1.6-1.9 eV was associated with the presence of effective energy levels in the energy band structure of the titanium dioxide, due to implantation-induced defects. An accurate structural characterization was performed by Rutherford backscattering spectrometry, transmission electron microscopy, Raman spectroscopy, X-ray diffraction, and UV/VIS spectroscopy. The synthesized materials revealed a remarkable photocatalytic efficiency in the degradation of organic compounds in water under visible light irradiation, without the help of any thermal treatments. The photocatalytic activity has been correlated with the amount of defects induced by the ion-implantation process, clarifying the operative physical mechanism. These results can be fruitfully applied for environmental applications of TiO2.

  10. Organic Polymer Dots as Photocatalysts for Visible Light-Driven Hydrogen Generation.

    PubMed

    Wang, Lei; Fernández-Terán, Ricardo; Zhang, Lei; Fernandes, Daniel L A; Tian, Lei; Chen, Hong; Tian, Haining

    2016-09-26

    For the first time, organic semiconducting polymer dots (Pdots) based on poly[(9,9'-dioctylfluorenyl-2,7-diyl)-co-(1,4-benzo-{2,1',3} thiadiazole)] (PFBT) and polystyrene grafting with carboxyl-group-functionalized ethylene oxide (PS-PEG-COOH) are introduced as a photocatalyst towards visible-light-driven hydrogen generation in a completely organic solvent-free system. With these organic Pdots as the photocatalyst, an impressive initial rate constant of 8.3 mmol h(-1)  g(-1) was obtained for visible-light-driven hydrogen production, which is 5-orders of magnitude higher than that of pristine PFBT polymer under the same catalytic conditions. Detailed kinetics studies suggest that the productive electron transfer quench of the excited state of Pdots by an electron donor is about 40 %. More importantly, we also found that the Pdots can tolerate oxygen during catalysis, which is crucial for further application of this material for light-driven water splitting. PMID:27604393

  11. Superior visible light hydrogen evolution of Janus bilayer junctions via atomic-level charge flow steering.

    PubMed

    Li, Jie; Zhan, Guangming; Yu, Ying; Zhang, Lizhi

    2016-01-01

    Although photocatalytic hydrogen evolution (PHE) is ideal for solar-to-fuel conversion, it remains challenging to construct a highly efficient PHE system by steering the charge flow in a precise manner. Here we tackle this challenge by assembling 1T MoS2 monolayers selectively and chemically onto (Bi12O17) end-faces of Bi12O17Cl2 monolayers to craft two-dimensional (2D) Janus (Cl2)-(Bi12O17)-(MoS2) bilayer junctions, a new 2D motif different from van der Waals heterostructure. Electrons and holes from visible light-irradiated Bi12O17Cl2 are directionally separated by the internal electric field to (Bi12O17) and (Cl2) end-faces, respectively. The separated electrons can further migrate to MoS2 via Bi-S bonds formed between (Bi12O17) and MoS2 monolayers. This atomic-level directional charge separation endows the Janus bilayers with ultralong carrier lifetime of 3,446 ns and hence a superior visible-light PHE rate of 33 mmol h(-1) g(-1). Our delineated Janus bilayer junctions on the basis of the oriented assembly of monolayers presents a new design concept to effectively steer the charge flow for PHE. PMID:27157679

  12. Band-engineered SrTiO{sub 3} nanowires for visible light photocatalysis

    SciTech Connect

    Fu, Q.; He, T.; Li, J. L.; Yang, G. W.

    2012-11-15

    We have theoretically investigated the structural, electronic, and optical properties of perovskite SrTiO{sub 3} nanowires for use in visible light photocatalytic applications using pseudopotential density-functional theory calculations. The electronic structure calculations show that the band gap is modified in the SrTiO{sub 3} nanowires compared with that of the bulk. For TiO{sub 2}-terminated nanowires, the mid-band states induced by the combination of oxygen and strontium atoms on the surface lead to a shift in the valence band toward the conduction band without interference from the edge of the conduction band, which reduces the band gap. On the contrary, the electronic states induced by the combination of oxygen and strontium atoms on the surface of SrO-terminated nanowires lead to a shift in the conduction band toward the valence band. The calculated optical results indicate that the absorption edge of the nanowires shift towards the red-light region. These theoretical results suggest that perovskite SrTiO{sub 3} nanowires are promising candidates for use in visible light photocatalytic processes such as solar-assisted water splitting reactions.

  13. Synthesis and photocatalytic activity of perovskite niobium oxynitrides with wide visible-light absorption bands.

    PubMed

    Siritanaratkul, Bhavin; Maeda, Kazuhiko; Hisatomi, Takashi; Domen, Kazunari

    2011-01-17

    Photocatalytic activities of perovskite-type niobium oxynitrides (CaNbO₂N, SrNbO₂N, BaNbO₂N, and LaNbON₂) were examined for hydrogen and oxygen evolution from water under visible-light irradiation. These niobium oxynitrides were prepared by heating the corresponding oxide precursors, which were synthesized using the polymerized complex method, for 15 h under a flow of ammonia. They possess visible-light absorption bands between 600-750 nm, depending on the A-site cations in the structures. The oxynitride CaNbO₂N, was found to be active for hydrogen and oxygen evolution from methanol and aqueous AgNO₃, respectively, even under irradiation by light at long wavelengths (λ<560 nm). The nitridation temperature dependence of CaNbO₂N was investigated and 1023 K was found to be the optimal temperature. At lower temperatures, the oxynitride phase is not adequately produced, whereas higher temperatures produce more reduced niobium species (e. g., Nb³(+) and Nb⁴(+)), which can act as electron-hole recombination centers, resulting in a decrease in activity.

  14. Analysis of optical transmission by 400-500 nm visible light into aesthetic dental biomaterials.

    PubMed

    Watts, D C; Cash, A J

    1994-04-01

    The penetration of visible light into dental biomaterials is an essential factor in photoinitiation of setting reactions and in the optical aspects of dental aesthetics. Light of visible blue wavelengths, 400-500 nm, has been applied at normal angles to 0.2-5.0 mm sections of human dentine and representative ceramic, polymerceramic composites and hybrid glass-polyalkenoate materials. The integrated optical transmission has been determined for each material section. The data have been converted to absorbance values and analysed to check for mathematical conformity to the Beer-Lambert Law. It is found that conformity (typically, P < 0.01) to the linear Beer-Lambert Law is only attained by making a substantial correction for the intensity of light reflected from the surface of aesthetic biomaterials. This is otherwise expressed by distinguishing between true and apparent absorbance. From linear regression of apparent absorbance with section thickness, the intercept depends upon the logarithm of the surface-reflection ratio. This factor ranges from 30% to 90% in the materials investigated. It follows that there is a high degree of inefficiency in the transmission of visible light into and through aesthetic biomaterials for the purposes of photoactivation using existing technology. Means by which this limitation and inefficiency may be reduced are discussed. While the reflectivity of aesthetic biomaterials has been perceived by dental practitioners, the magnitude of this effect and its implications in connection with light-cured materials have not been analysed and emphasized hitherto. PMID:8195476

  15. Stable quantum dot photoelectrolysis cell for unassisted visible light solar water splitting.

    PubMed

    Yang, Hong Bin; Miao, Jianwei; Hung, Sung-Fu; Huo, Fengwei; Chen, Hao Ming; Liu, Bin

    2014-10-28

    Sunlight is an ideal source of energy, and converting sunlight into chemical fuels, mimicking what nature does, has attracted significant attention in the past decade. In terms of solar energy conversion into chemical fuels, solar water splitting for hydrogen production is one of the most attractive renewable energy technologies, and this achievement would satisfy our increasing demand for carbon-neutral sustainable energy. Here, we report corrosion-resistant, nanocomposite photoelectrodes for spontaneous overall solar water splitting, consisting of a CdS quantum dot (QD) modified TiO2 photoanode and a CdSe QD modified NiO photocathode, where cadmium chalcogenide QDs are protected by a ZnS passivation layer and gas evolution cocatalysts. The optimized device exhibited a maximum efficiency of 0.17%, comparable to that of natural photosynthesis with excellent photostability under visible light illumination. Our device shows spontaneous overall water splitting in a nonsacrificial environment under visible light illumination (λ > 400 nm) through mimicking nature's "Z-scheme" process. The results here also provide a conceptual layout to improve the efficiency of solar-to-fuel conversion, which is solely based on facile, scalable solution-phase techniques.

  16. Plasmonic nanostructures to enhance catalytic performance of zeolites under visible light

    PubMed Central

    Zhang, Xingguang; Ke, Xuebin; Du, Aijun; Zhu, Huaiyong

    2014-01-01

    Light absorption efficiency of heterogeneous catalysts has restricted their photocatalytic capability for commercially important organic synthesis. Here, we report a way of harvesting visible light efficiently to boost zeolite catalysis by means of plasmonic gold nanoparticles (Au-NPs) supported on zeolites. Zeolites possess strong Brønsted acids and polarized electric fields created by extra-framework cations. The polarized electric fields can be further intensified by the electric near-field enhancement of Au-NPs, which results from the localized surface plasmon resonance (LSPR) upon visible light irradiation. The acetalization reaction was selected as a showcase performed on MZSM-5 and Au/MZSM-5 (M = H+, Na+, Ca2+, or La3+). The density functional theory (DFT) calculations confirmed that the intensified polarized electric fields played a critical role in stretching the C = O bond of the reactants of benzaldehyde to enlarge their molecular polarities, thus allowing reactants to be activated more efficiently by catalytic centers so as to boost the reaction rates. This discovery should evoke intensive research interest on plasmonic metals and diverse zeolites with an aim to take advantage of sunlight for plasmonic devices, molecular electronics, energy storage, and catalysis. PMID:24448225

  17. A new class of homogeneous visible-light photocatalysts: molecular cerium vanadium oxide clusters.

    PubMed

    Seliverstov, Andrey; Streb, Carsten

    2014-07-28

    The first systematic access to molecular cerium vanadium oxides is presented. A family of structurally related, di-cerium-functionalized vanadium oxide clusters and their use as visible-light-driven photooxidation catalysts is reported. Comparative analyses show that photocatalytic activity is controlled by the cluster architecture. Increased photoreactivity of the cerium vanadium oxides in the visible range compared with nonfunctionalized vanadates is observed. Based on the recent discovery of the first molecular cerium vanadate cluster, (nBu4 N)2 [(Ce(dmso)3 )2 V12 O33 Cl]⋅2 DMSO (1), two new di-cerium-containing vanadium oxide clusters [(Ce(dmso)4 )2 V11 O30 Cl]⋅DMSO (2) and [(Ce(nmp)4 )2 V12 O32 Cl]⋅NMP⋅Me2 CO (3; NMP=N-methyl-2-pyrrolidone) were obtained by using a novel fragmentation and reassembly route. Pentagonal building units {(V)M5 } (M=V, Ce) reminiscent of "Müller-type" pentagons are observed in 2 and 3. Compounds 1-3 feature high visible-light photooxidative activity, and quantum efficiencies >10 % for indigo photooxidation are observed. Photocatalytic performance increases in the order 1<3<2. Mechanistic studies show that the irradiation wavelength and the presence of oxygen strongly affect photoreactivity. Initial findings suggest that the photooxidation mechanism proceeds by intermediate formation of hydroxyl radicals. The findings open new avenues for the bottom-up design of sunlight-driven photocatalysts.

  18. Visible light photoinitiation of mesenchymal stem cell-laden bioresponsive hydrogels.

    PubMed

    Bahney, C S; Lujan, T J; Hsu, C W; Bottlang, M; West, J L; Johnstone, B

    2011-07-15

    Biological activity can be added to synthetic scaffolds by incorporating functional peptide sequences that provide enzyme-mediated degradation sites, facilitate cellular adhesion or stimulate signaling pathways. Poly(ethylene glycol) diacrylate is a popular synthetic base for tissue engineering scaffolds because it creates a hydrophilic environment that can be chemically manipulated to add this biological functionality. Furthermore, the acrylate groups allow for encapsulation of cells using photopolymerization under physiological conditions. One complication with the addition of these peptides is that aromatic amino acids absorb light at 285 nm and compete with the ultraviolet (UV)-sensitive photoinitiators such as IrgacureTM 2959 (I2959), the most commonly used initiator for cytocompatible photoencapsulation of cells into synthetic scaffolds. In this study we define non-toxic conditions for photoencapsulation of human mesenchymal stem cells (hMSC) in PEGDA scaffolds using a visible light photoinitiator system composed of eosin Y, triethanolamine and 1-vinyl-2-pyrrolidinone. This visible light photoinitiator produced hydrogel scaffolds with an increased viability of encapsulated hMSCs and a more tightly crosslinked network in one-third the time of UV polymerization with I2959.

  19. Light-concentrating plasmonic Au superstructures with significantly visible-light-enhanced catalytic performance.

    PubMed

    Yang, Jinhu; Li, Ying; Zu, Lianhai; Tong, Lianming; Liu, Guanglei; Qin, Yao; Shi, Donglu

    2015-04-22

    Noble metals are well-known for their surface plasmon resonance effect that enables strong light absorption typically in the visible regions for gold and silver. However, unlike semiconductors, noble metals are commonly considered incapable of catalyzing reactions via photogenerated electron-hole pairs due to their continuous energy band structures. So far, photonically activated catalytic system based on pure noble metal nanostructures has seldom been reported. Here, we report the development of three different novel plasmonic Au superstructures comprised of Au nanoparticles, multiple-twinned nanoparticles and nanoworms assembling on the surfaces of SiO2 nanospheres respectively via a well-designed synthetic strategy. It is found that these novel Au superstructures show enhanced broadband visible-light absorption due to the plasmon resonance coupling within the superstructures, and thus can effectively focus the energy of photon fluxes to generate much more excited hot electrons and holes for promoting catalytic reactions. Accordingly, these Au superstructures exhibit significantly visible-light-enhanced catalytic efficiency (up to ∼264% enhancement) for the commercial reaction of p-nitrophenol reduction. PMID:25840556

  20. Recognizing Banknote Fitness with a Visible Light One Dimensional Line Image Sensor

    PubMed Central

    Pham, Tuyen Danh; Park, Young Ho; Kwon, Seung Yong; Nguyen, Dat Tien; Vokhidov, Husan; Park, Kang Ryoung; Jeong, Dae Sik; Yoon, Sungsoo

    2015-01-01

    In general, dirty banknotes that have creases or soiled surfaces should be replaced by new banknotes, whereas clean banknotes should be recirculated. Therefore, the accurate classification of banknote fitness when sorting paper currency is an important and challenging task. Most previous research has focused on sensors that used visible, infrared, and ultraviolet light. Furthermore, there was little previous research on the fitness classification for Indian paper currency. Therefore, we propose a new method for classifying the fitness of Indian banknotes, with a one-dimensional line image sensor that uses only visible light. The fitness of banknotes is usually determined by various factors such as soiling, creases, and tears, etc. although we just consider banknote soiling in our research. This research is novel in the following four ways: first, there has been little research conducted on fitness classification for the Indian Rupee using visible-light images. Second, the classification is conducted based on the features extracted from the regions of interest (ROIs), which contain little texture. Third, 1-level discrete wavelet transformation (DWT) is used to extract the features for discriminating between fit and unfit banknotes. Fourth, the optimal DWT features that represent the fitness and unfitness of banknotes are selected based on linear regression analysis with ground-truth data measured by densitometer. In addition, the selected features are used as the inputs to a support vector machine (SVM) for the final classification of banknote fitness. Experimental results showed that our method outperforms other methods. PMID:26343654

  1. Reversible dissolution/formation of polymer nanoparticles controlled by visible light

    NASA Astrophysics Data System (ADS)

    Wang, Zhuozhi; Liao, Yi

    2016-07-01

    Noncovalent crosslinking between polyvinyl pyridine and a copolymer of acrylic acid led to the formation of a polymer nanoparticle. In the presence of a metastable-state photoacid, reversible dissolution and formation of the nanoparticle can be controlled by visible light. Photo-induced proton transfer from the photoacid to the polymers broke the hydrogen bonding and ionic bonding and led to the dissolution of the nanoparticle. Cycles of dissolution and formation were controlled by turning on and off irradiation, and were demonstrated by the transmittance change.Noncovalent crosslinking between polyvinyl pyridine and a copolymer of acrylic acid led to the formation of a polymer nanoparticle. In the presence of a metastable-state photoacid, reversible dissolution and formation of the nanoparticle can be controlled by visible light. Photo-induced proton transfer from the photoacid to the polymers broke the hydrogen bonding and ionic bonding and led to the dissolution of the nanoparticle. Cycles of dissolution and formation were controlled by turning on and off irradiation, and were demonstrated by the transmittance change. Electronic supplementary information (ESI) available. See DOI: 10.1039/c6nr02163h

  2. Superior visible light hydrogen evolution of Janus bilayer junctions via atomic-level charge flow steering

    NASA Astrophysics Data System (ADS)

    Li, Jie; Zhan, Guangming; Yu, Ying; Zhang, Lizhi

    2016-05-01

    Although photocatalytic hydrogen evolution (PHE) is ideal for solar-to-fuel conversion, it remains challenging to construct a highly efficient PHE system by steering the charge flow in a precise manner. Here we tackle this challenge by assembling 1T MoS2 monolayers selectively and chemically onto (Bi12O17) end-faces of Bi12O17Cl2 monolayers to craft two-dimensional (2D) Janus (Cl2)-(Bi12O17)-(MoS2) bilayer junctions, a new 2D motif different from van der Waals heterostructure. Electrons and holes from visible light-irradiated Bi12O17Cl2 are directionally separated by the internal electric field to (Bi12O17) and (Cl2) end-faces, respectively. The separated electrons can further migrate to MoS2 via Bi-S bonds formed between (Bi12O17) and MoS2 monolayers. This atomic-level directional charge separation endows the Janus bilayers with ultralong carrier lifetime of 3,446 ns and hence a superior visible-light PHE rate of 33 mmol h-1 g-1. Our delineated Janus bilayer junctions on the basis of the oriented assembly of monolayers presents a new design concept to effectively steer the charge flow for PHE.

  3. Zinc oxide nanorod mediated visible light photoinactivation of model microbes in water

    NASA Astrophysics Data System (ADS)

    Sapkota, Ajaya; Anceno, Alfredo J.; Baruah, Sunandan; Shipin, Oleg V.; Dutta, Joydeep

    2011-05-01

    The inactivation of model microbes in aqueous matrix by visible light photocatalysis as mediated by ZnO nanorods was investigated. ZnO nanorods were grown on glass substrate following a hydrothermal route and employed in the inactivation of gram-negative Escherichia coli and gram-positive Bacillus subtilis in MilliQ water. The concentration of Zn2 + ions in the aqueous matrix, bacterial cell membrane damage, and DNA degradation at post-exposure were also studied. The inactivation efficiencies for both organisms under light conditions were about two times higher than under dark conditions across the cell concentrations assayed. Anomalies in supernatant Zn2 + concentration were observed under both conditions as compared to control treatments, while cell membrane damage and DNA degradation were observed only under light conditions. Inactivation under dark conditions was hence attributed to the bactericidal effect of Zn2 + ions, while inactivation under light conditions was due to the combined effects of Zn2 + ions and photocatalytically mediated electron injection. The reduction of pathogenic bacterial densities by the photocatalytically active ZnO nanorods in the presence of visible light implies potential ex situ application in water decontamination at ambient conditions under sunlight.

  4. VISIBLE LIGHT PHOTOINITIATION OF MESENCHYMAL STEM CELL-LADEN BIORESPONSIVE HYDROGELS

    PubMed Central

    Bahney, C.S.; Lujan, T.J.; Hsu, C.W.; Bottlang, M.; West, J.L.; Johnstone, B.

    2016-01-01

    Biological activity can be added to synthetic scaffolds by incorporating functional peptide sequences that provide enzyme-mediated degradation sites, facilitate cellular adhesion or stimulate signaling pathways. Poly(ethylene glycol) diacrylate is a popular synthetic base for tissue engineering scaffolds because it creates a hydrophilic environment that can be chemically manipulated to add this biological functionality. Furthermore, the acrylate groups allow for encapsulation of cells using photopolymerization under physiological conditions. One complication with the addition of these peptides is that aromatic amino acids absorb light at 285nm and compete with the ultraviolet (UV)-sensitive photoinitiators such as Irgacure™ 2959 (I2959), the most commonly used initiator for cytocompatible photoencapsulation of cells into synthetic scaffolds. In this study we define non-toxic conditions for photoencapsulation of human mesenchymal stem cells (hMSC) in PEGDA scaffolds using a visible light photoinitiator system composed of eosin Y, triethanolamine and 1-vinyl-2-pyrrolidinone. This visible light photoinitiator produced hydrogel scaffolds with an increased viability of encapsulated hMSCs and a more tightly crosslinked network in one-third the time of UV polymerization with I2959. PMID:21761391

  5. Superior visible light hydrogen evolution of Janus bilayer junctions via atomic-level charge flow steering

    PubMed Central

    Li, Jie; Zhan, Guangming; Yu, Ying; Zhang, Lizhi

    2016-01-01

    Although photocatalytic hydrogen evolution (PHE) is ideal for solar-to-fuel conversion, it remains challenging to construct a highly efficient PHE system by steering the charge flow in a precise manner. Here we tackle this challenge by assembling 1T MoS2 monolayers selectively and chemically onto (Bi12O17) end-faces of Bi12O17Cl2 monolayers to craft two-dimensional (2D) Janus (Cl2)-(Bi12O17)-(MoS2) bilayer junctions, a new 2D motif different from van der Waals heterostructure. Electrons and holes from visible light-irradiated Bi12O17Cl2 are directionally separated by the internal electric field to (Bi12O17) and (Cl2) end-faces, respectively. The separated electrons can further migrate to MoS2 via Bi–S bonds formed between (Bi12O17) and MoS2 monolayers. This atomic-level directional charge separation endows the Janus bilayers with ultralong carrier lifetime of 3,446 ns and hence a superior visible-light PHE rate of 33 mmol h−1 g−1. Our delineated Janus bilayer junctions on the basis of the oriented assembly of monolayers presents a new design concept to effectively steer the charge flow for PHE. PMID:27157679

  6. Ab initio study of TaON, an active photocatalyst under visible light irradiation.

    PubMed

    Reshak, A H

    2014-06-14

    Tantalum oxynitride has been studied as an active photocatalyst under visible light, using a full potential linearized augmented plane wave method within the framework of density functional theory. The electronic and optical properties of TaON are calculated using local density approximation (LDA), generalized gradient approximation (GGA), Engel-Vosko generalized gradient approximation (EVGGA) and the modified Becke-Johnson (mBJ) potential approximation to describe the exchange-correlation potential. The calculated band gap value obtained by the mBJ approximation approach (2.5 eV) is very close to the experimental result (2.5 eV). We found that hybridization among the Ta-d, O-p and N-p states results in the formation of a covalent bond between Ta-N and Ta-O. The calculated optical properties confirm that the TaON is an active photocatalyst under visible light irradiation. TaON has a high dielectric constant and the components show anisotropy in the energy range between 3.0 eV and 10.0 eV. A high refractive index of 2.47 at 632.8 nm is obtained which shows better agreement with the experimental value (2.5 at 632.8 nm) than previous results.

  7. Silver bromide in montmorillonite as visible light-driven photocatalyst and the role of montmorillonite

    NASA Astrophysics Data System (ADS)

    Sohrabnezhad, Sh.; Pourahmad, A.; Razavi, M.

    2016-09-01

    In this study, novel plasmonic photocatalyst, Ag/AgBr-montmorillonite (MMT) nanocomposite, was prepared by dispersion method and light irradiation. The structure, composition and optical properties of such material was investigated by transmission electron microscopy, UV-visible diffuse reflectance spectroscopy, X-ray diffraction and Fourier transform infrared spectroscopy. The powder X-ray diffraction showed intercalation of Ag/AgBr nanoparticles into the clay interlayer space. The results showed that the prepared sample has a similar phase composition. However, their photocatalytic activity varied significantly. The photocatalytic testing result showed that the Ag/AgBr-MMT nanocomposite was more efficient photocatalyst in the discoloration of methylene blue under visible light illumination. The Ag/AgBr-MMT nanocomposite in pH = 2 and under visible light degraded 92 % of dye at the irradiation time of 20 min. MMT as matrix showed excellent role in separation efficiency of electron-hole pairs. The mechanism of separation of the photogenerated electrons and holes at the Ag/AgBr-MMT nanocomposite was discussed.

  8. Fullerene C70 decorated TiO2 nanowires for visible-light-responsive photocatalyst

    NASA Astrophysics Data System (ADS)

    Cho, Er-Chieh; Ciou, Jing-Hao; Zheng, Jia-Huei; Pan, Job; Hsiao, Yu-Sheng; Lee, Kuen-Chan; Huang, Jen-Hsien

    2015-11-01

    In this study, we have synthesized C60 and C70-modified TiO2 nanowire (NW) through interfacial chemical bonding. The results indicate that the fullerenes (C60 and C70 derivatives) can act as sinks for photogenerated electrons in TiO2, while the fullerene/TiO2 is illuminated under ultraviolet (UV) light. Therefore, in comparison to the pure TiO2 NWs, the modified TiO2 NWs display a higher photocatalytic activity under UV irradiation. Moreover, the fullerenes also can function as a sensitizer to TiO2 which expand the utilization of solar light from UV to visible light. The results reveal that the C70/TiO2 NWs show a significant photocatalytic activity for degradation of methylene blue (MB) in visible light region. To better understand the mechanism responsible for the effect of fullerenes on the photocatalytic properties of TiO2, the electron only devices and photoelectrochemical cells based on fullerenes/TiO2 are also fabricated and evaluated.

  9. Microwave-assisted synthesis of bismuth oxybromochloride nanoflakes for visible light photodegradation of pollutants

    NASA Astrophysics Data System (ADS)

    Bijanzad, Keyvan; Tadjarodi, Azadeh; Moghaddasi Khiavi, Mohammad; Akhavan, Omid

    2015-10-01

    BiOBrxCl1-x (0Visible light-assisted photocatalytic studies showed that the degradation efficiency of the as-prepared BiOBrxCl1-x for (100 mL of 10 mg L-1) Rhodamine B (RhB), Natural Red 4 (N-Red) dye solutions was 98.14% and for the colorless organic pentachlorophenol (PCP) solution was 91.09% over 150 min. The possible mechanisms involved in the visible light photodegradation of the pollutants by BiOBrxCl1-x photocatalyst were also discussed.

  10. Recognizing Banknote Fitness with a Visible Light One Dimensional Line Image Sensor.

    PubMed

    Pham, Tuyen Danh; Park, Young Ho; Kwon, Seung Yong; Nguyen, Dat Tien; Vokhidov, Husan; Park, Kang Ryoung; Jeong, Dae Sik; Yoon, Sungsoo

    2015-08-27

    In general, dirty banknotes that have creases or soiled surfaces should be replaced by new banknotes, whereas clean banknotes should be recirculated. Therefore, the accurate classification of banknote fitness when sorting paper currency is an important and challenging task. Most previous research has focused on sensors that used visible, infrared, and ultraviolet light. Furthermore, there was little previous research on the fitness classification for Indian paper currency. Therefore, we propose a new method for classifying the fitness of Indian banknotes, with a one-dimensional line image sensor that uses only visible light. The fitness of banknotes is usually determined by various factors such as soiling, creases, and tears, etc. although we just consider banknote soiling in our research. This research is novel in the following four ways: first, there has been little research conducted on fitness classification for the Indian Rupee using visible-light images. Second, the classification is conducted based on the features extracted from the regions of interest (ROIs), which contain little texture. Third, 1-level discrete wavelet transformation (DWT) is used to extract the features for discriminating between fit and unfit banknotes. Fourth, the optimal DWT features that represent the fitness and unfitness of banknotes are selected based on linear regression analysis with ground-truth data measured by densitometer. In addition, the selected features are used as the inputs to a support vector machine (SVM) for the final classification of banknote fitness. Experimental results showed that our method outperforms other methods.

  11. Preparation and visible light photocatalytic activity of N-doped titania.

    PubMed

    Hu, Yulong; Liu, Hongfang; Chen, Weiran; Chen, Debin; Yin, Jiwei; Guo, Xingpeng

    2010-03-01

    N-doped titania powders were prepared with titanium tetraisopropoxide (TTIP) as the titanium source and urea as the nitrogen source by the sol-gel method. The samples were characterized using X-ray diffraction (XRD), diffuse reflectance spectrum (DRS), X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM). The XRD and TEM results indicated that urea played an important role in controlling the size and aggregation process of titania nanoparticles. As an appropriate amount of urea was added into the titania sol, the size of the particles decreased. However, the excess urea reduced the dispersion of the particles and resulted in the aggregation. At the same time, the size of particle increased, and the size distribution broadened. The XPS and DRS results showed that the nitrogen was incorporated into titania lattice successfully, which brought about the redshift of the absorption edge and induced the photocatalytic activity in the visible light region. The photocatalytic experiments showed that the N-doped titania nanoparticles could effectively photodegrade methyl orange (MO) aqueous solution under visible light irradiation. The photocatalytic activity increased with the increase of the nitrogen doping level in the titania lattice, but decreased with the increase of the particle size and the organic surface residues caused by excess urea. PMID:20355662

  12. Importance of Plasmonic Heating on Visible Light Driven Photocatalysis of Gold Nanoparticle Decorated Zinc Oxide Nanorods

    NASA Astrophysics Data System (ADS)

    Bora, Tanujjal; Zoepfl, David; Dutta, Joydeep

    2016-05-01

    Herein we explore the role of localized plasmonic heat generated by resonantly excited gold (Au) NPs on visible light driven photocatalysis process. Au NPs are deposited on the surface of vertically aligned zinc oxide nanorods (ZnO NRs). The localized heat generated by Au NPs under 532 nm continuous laser excitation (SPR excitation) was experimentally probed using Raman spectroscopy by following the phonon modes of ZnO. Under the resonant excitation the temperature at the surface of the Au-ZnO NRs reaches up to about 300 °C, resulting in almost 6 times higher apparent quantum yield (AQY) for photocatalytic degradation of methylene blue (MB) compared to the bare ZnO NRs. Under solar light irradiation the Au-ZnO NRs demonstrated visible light photocatalytic activity twice that of what was achieved with bare ZnO NRs, while significantly reduced the activation energy required for the photocatalytic reactions allowing the reactions to occur at a faster rate.

  13. Visible-Light-Driven Water Oxidation by a Molecular Manganese Vanadium Oxide Cluster.

    PubMed

    Schwarz, Benjamin; Forster, Johannes; Goetz, McKenna K; Yücel, Duygu; Berger, Claudia; Jacob, Timo; Streb, Carsten

    2016-05-17

    Photosynthetic water oxidation in plants occurs at an inorganic calcium manganese oxo cluster, which is known as the oxygen evolving complex (OEC), in photosystem II. Herein, we report a synthetic OEC model based on a molecular manganese vanadium oxide cluster, [Mn4 V4 O17 (OAc)3 ](3-) . The compound is based on a [Mn4 O4 ](6+) cubane core, which catalyzes the homogeneous, visible-light-driven oxidation of water to molecular oxygen and is stabilized by a tripodal [V4 O13 ](6-) polyoxovanadate and three acetate ligands. When combined with the photosensitizer [Ru(bpy)3 ](2+) and the oxidant persulfate, visible-light-driven water oxidation with turnover numbers of approximately 1150 and turnover frequencies of about 1.75 s(-1) is observed. Electrochemical, mass-spectrometric, and spectroscopic studies provide insight into the cluster stability and reactivity. This compound could serve as a model for the molecular structure and reactivity of the OEC and for heterogeneous metal oxide water-oxidation catalysts.

  14. Synthesis, characterization and application of iodine modified titanium dioxide in phototcatalytical reactions under visible light irradiation

    NASA Astrophysics Data System (ADS)

    Bagwasi, Segomotso; Tian, Baozhu; Chen, Feng; Zhang, Jinlong

    2012-02-01

    Iodine doped titanium dioxide has been successfully prepared by simple hydrolysis of tetrabutyl titanate in the presence of iodic acid. The adopted method allowed for the production of spherical iodine doped titaniun dioxide nanoparticles with varied amount of iodine content. Analysis by X-ray diffraction, Raman, transmission electron microscopy as well as UV-vis DRS revealed that titanium dioxide nanostructures were doped with iodine which existed in two different valence states I5+ and I-. The iodine in the form of I5+ is believed to have doped into the lattice whereas I- was well dispersed on the surface of TiO2 probably as iodine adducts hence rendering it to be highly absorbing in visible light region. The I-TiO2 exhibited improved photocatalytic activity toward degradation of acid orange 7 (AO7), methyl orange (MO) and 2,4-dichlorophenol (2,4-DCP) under visible light over the pristine TiO2 prepared by the same method. High catalytic properties are attributed to iodine doping which led to high specific surface area, absorption in visible region as well as alleviation of charge carrier recombination. The most probable route undertaken in the degradation of AO7 is through indirect oxidation by the hydroxyl radicals.

  15. Nonmetal species in the carbon modified TiO2 and its visible light photocatalytic activity

    NASA Astrophysics Data System (ADS)

    Shi, Yanfen; Chen, Feng; Zhang, Jinlong

    2013-01-01

    A carbon modified TiO2 (CT) was synthesized by hydrolyzing titanium tetrachloride with diethylamine and calcination at 400 °C. CT was then handled with a NaOH aqueous solution elution and a subsequent re-assembling treatment. X-ray diffraction (XRD), transmission electron microscopy (TEM), nitrogen adsorption-desorption analysis, X-ray photoelectron spectroscopy (XPS), thermogravimetric and differential thermal analysis (TG-DTA), chemical oxygen demand (COD) and UV-vis diffuse reflectance spectroscopy (DRS) were then used to assess the changes of CT during the whole process. It is revealed that carbon in the CT should mostly be presented as surface deposited organic matters but not likely doped into the TiO2 lattice. CT exhibits obvious visible absorption and high photocatalytic activity for the degradation of 2,4-dichlorophenol (DCP) under visible light irradiation. Meanwhile, CT photocatalyst possesses excellent stability and reusability. NaOH solution elution washes off a large amount of surface deposited organics and worsens the visible absorbance and photocatalytic activity of CT, which can be well recovered by the re-assembling treatment. The re-assembled photocatalyst, CTSL, exhibits exhibits a very similar photocataytic activity with CT for degradation of DCP under the visible light irradiation, but is much higher than that of CTS.

  16. Synthesis and visible light photocatalytic properties of iron oxide-silver orthophosphate composites

    NASA Astrophysics Data System (ADS)

    Febiyanto, Eliani, Irma Vania; Riapanitra, Anung; Sulaeman, U.

    2016-04-01

    The iron oxide-silver orthophosphate composites were successfully synthesized by co-precipitation method using Fe(NO3)3.9H2O, AgNO3, and Na2HPO4.12 H2O, followed by calcination at 500°C for 5 hours. The Fe/Ag mole ratios of iron oxide-silver orthophosphate composites were designed at 0, 0.1, 0.2, 0.3 and 0.4. The samples were characterized using X-ray Diffraction, Diffuse Reflectance Spectroscopy, Scanning Electron Microscopy and Specific Surface Area. The photocatalytic activities were evaluated using Rhodamine B degradation under visible light irradiation. The iron oxide-silver orthophosphate composite with the Fe/Ag mole ratio of 0.2 exhibited higher photocatalytic activity compared to the pure Ag3PO4 under visible light irradiation. The enhanced photocatalytic activity could be attributed to the effective separation of hole (+) and electron pairs in the iron oxide-silver orthophosphate composite.

  17. Visible light carrier generation in co-doped epitaxial titanate films

    SciTech Connect

    Comes, Ryan B. Kaspar, Tiffany C.; Chambers, Scott A.; Smolin, Sergey Y.; Baxter, Jason B.; Gao, Ran; Apgar, Brent A.; Martin, Lane W.; Bowden, Mark E.

    2015-03-02

    Perovskite titanates such as SrTiO{sub 3} (STO) exhibit a wide range of important functional properties, including ferroelectricity and excellent photocatalytic performance. The wide optical band gap of titanates limits their use in these applications; however, making them ill-suited for integration into solar energy harvesting technologies. Our recent work has shown that by doping STO with equal concentrations of La and Cr, we can enhance visible light absorption in epitaxial thin films while avoiding any compensating defects. In this work, we explore the optical properties of photoexcited carriers in these films. Using spectroscopic ellipsometry, we show that the Cr{sup 3+} dopants, which produce electronic states immediately above the top of the O 2p valence band in STO reduce the direct band gap of the material from 3.75 eV to 2.4–2.7 eV depending on doping levels. Transient reflectance spectroscopy measurements are in agreement with the observations from ellipsometry and confirm that optically generated carriers are present for longer than 2 ns. Finally, through photoelectrochemical methylene blue degradation measurements, we show that these co-doped films exhibit enhanced visible light photocatalysis when compared to pure STO.

  18. Surface photoelectric and visible light driven photocatalytic properties of zinc antimonate-based photocatalysts

    SciTech Connect

    Wu, Shaojun; Li, Guoqiang; Zhang, Yang; Zhang, Weifeng

    2013-03-15

    Highlights: ► N-doped and pristine ZnSb{sub 2}O{sub 6} photocatalysts were synthesized by a facile method. ► N-doped ZnSb{sub 2}O{sub 6} shows a significant enhanced visible light photocatalytic activity. ► The N-doped ZnSb{sub 2}O{sub 6} shows the reduced surface photovoltage signals. - Abstract: The N-doped and pristine ZnSb{sub 2}O{sub 6} photocatalysts were synthesized by a facile method. The samples were characterized by X-ray diffraction (XRD), UV–vis spectroscopy, surface photovoltage spectroscopy and scanning electron microscopy. The photocatalytic activities of the prepared samples were evaluated from the degradation of rhodamine B (RhB) under full arc and visible light irradiation of Xe lamp. The XRD and UV–vis results indicated that the N-doping did not change the crystal structure, but decrease the band gap in comparison with the pristine one. The N-doped ZnSb{sub 2}O{sub 6} shows the reduced surface photovoltage signals and the significantly enhanced photocatalytic activity under two irradiation conditions.

  19. Hierarchical Bi based nanobundles: an excellent photocatalyst for visible-light degradation of Rhodamine B dye.

    PubMed

    Gao, Fangfang; Zhao, Yan; Li, Yawen; Wu, Gongjuan; Lu, Yan; Song, Yuehong; Huang, Zhifang; Li, Na; Zhao, Jingzhe

    2015-06-15

    Hierarchical Bi based nanobundles were self-assembled via an aqueous reduction approach using hydrazine hydrate as reductive agent, and were used as photocatalysts for the degradation of Rhodamine B (RhB) under visible light. PVP molecules were designed as inducing agent to construct the Bi based nanobundles. The as-obtained samples were characterized by X-ray diffraction (XRD), energy dispersive X-ray (EDX), thermogravimetric-differential thermal analyzer (TG-DTA), infrared spectroscopy (IR) and field emission scanning electron microscopy (FESEM) to get clear information of the crystals. A possible formation mechanism for the interesting architectures was proposed in the paper. The Bi based nanobundles exhibited excellent photocatalytic activity and good cycling performance towards photodegradation of RhB under visible light. The pH-sensitive degradation can reach 96% in degradation rate after 90 min, which indicates potential applications of the Bi based nanobundles on the degradation of organic pollutants. Degradation mechanism is proposed on the combination of Bi and BiOCl crystals.

  20. Enhanced visible light photocatalytic activity of Bi2WO6 via modification with polypyrrole

    NASA Astrophysics Data System (ADS)

    Duan, Fang; Zhang, Qianhong; Shi, Dongjian; Chen, Mingqing

    2013-03-01

    Enhanced visible light photocatalytic activity of Bi2WO6 photocatalyst modified with different amounts of polypyrrole (PPy) was synthesized by 'in situ' deposition oxidative polymerization of pyrrole. The as-prepared PPy/Bi2WO6 composites were characterized by X-ray powder diffraction (XRD), field emission scanning electron microscopy (FE-SEM), Fourier transform infrared (FT-IR) spectra, X-ray photoelectron spectroscopy (XPS) and UV-vis diffuse absorption spectra. The photocatalytic activities of the PPy/Bi2WO6 samples were determined by photocatalytic degradation of rhodamine-B (RhB) and methylene blue (MB) in aqueous solution under visible light irradiation. The results indicated that the existence of PPy did not affect the crystal structure and the morphology of Bi2WO6 photocatalyst, but showed great influences on the photocatalytic activity of Bi2WO6. Besides, an optimal content of PPy on the surface of Bi2WO6 photocatalyst with the highest photocatalytic ability was discovered, and the obtained PPy/Bi2WO6 photocatalysts showed high stability and did not photocorrode during the photocatalytic process. The possible mechanism of enhanced photocatalytic activities of PPy/Bi2WO6 samples was also discussed in this work.

  1. Visible-light-driven photocatalytic and chemical sensing properties of SnS2 nanoflakes.

    PubMed

    Umar, Ahmad; Akhtar, M S; Dar, G N; Abaker, M; Al-Hajry, A; Baskoutas, S

    2013-09-30

    This work demonstrated the successful and facile large-scale synthesis and characterizations of SnS2 nanoflakes. The detailed morphological studies revealed that the synthesized products were nanoflakes and were grown in large quantity. The XRD pattern and detailed compositional studies confirmed that the synthesized SnS2 nanoflakes were well-crystalline and possessing hexagonal SnS2 phase. The synthesized SnS2 nanoflakes were used as efficient photocatalysts for photocatalytic degradation and effective electron mediators for the fabrication of chemical sensor. The photocatalytic properties of SnS2 nanoflakes towards the photocatalytic degradation of Rhodamine B dye under visible light irradiation showed reasonably good degradation of ~61%. Moreover, the as-synthesized SnS2 nanoflakes were used as efficient electron mediators for the fabrication of nitroaniline chemical sensor by simple I-V technique. Very high-sensitivity of ~ 505.82±0.02 mAcm(-2).(mole/L)(-1) and experimental detection limit of ~15×10(-6) (mole/L) in a short response time of ~10.0 s with LDR in the range of 15.6×10(-6)-0.5×10(-3) mole L(-1) were observed for the fabricated nitroaniline chemical sensor. The observed results indicated that the SnS2 nanoflakes can efficiently be used as visible-light-driven photocatalysts and the fabrication of ultra-high sensitive chemical sensors.

  2. Hydrothermal Synthesis of BiFeO3 Nanoparticles for Visible Light Photocatalytic Applications.

    PubMed

    Niu, Feng; Gao, Tong; Zhang, Ning; Chen, Zhi; Huang, Qiaoli; Qin, Laishun; Sun, Xingguo; Huang, Yuexiang

    2015-12-01

    Bismuth ferrite is a promising material for visible light response photocatalytic applications due to its narrow band gap. In this work, single crystalline BiFeO3 nanoparticles were prepared by a modified hydrothermal process. The effects of hydrothermal temperature, reaction time and precursor xerogel amoumt on the as-prepared BiFeO3 particle size and morphology were investigated by XRD, TEM and HRTEM. The XRD analysis reveals that single crystalline BiFeO3 particles can be obtained when the hydrothermal temperature is kept below 220 degrees C. TEM observation showed that the as-formed BFO particles are in a square or rectangle-like shape and that the particle size is increased with increasing hydrothermal temperature. The hydrothermal reaction time and the amount of xerogel could also influence the as-formed BFO particle morphology and size. The band gap of the as-prepared BFO nanoparticles was identified by UV-vis diffuse reflectance spectrum. The measurement of photodegradation of methyl orange dye in an aqueous solution revealed that the as-prepared BFO nanoparticles exhibit photocatalytic activity under visible light irradiation.

  3. Hydrothermal synthesis of cerium titanate nanorods and its application in visible light photocatalysis

    SciTech Connect

    Pei, L.Z. Liu, H.D.; Lin, N.; Yu, H.Y.

    2015-01-15

    Highlights: • Cerium titanate nanorods have been synthesized by a simple hydrothermal process. • The size of the cerium titanate nanorods can be controlled by growth conditions. • Cerium titanate nanorods exhibit good photocatalytic activities for methyl blue. - Abstract: Cerium titanate nanorods have been prepared via a hydrothermal process using sodium dodecyl sulfate (SDS) as the surfactant. The cerium titanate nanorods have been analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution TEM (HRTEM), and ultraviolet–visible (UV–vis) diffuse reflectance spectrum. XRD shows that the nanorods are composed of CeTi{sub 21}O{sub 38} phase. Electron microscopy observations indicate that the nanorods have good single crystalline nature. The diameter and length of the nanorods are about 50–200 nm and 1–2 μm, respectively. Cerium titanate nanorods have a band gap of 2.65 eV. The photocatalytic activities of the nanorods have been investigated by degrading methylene blue (MB) under visible light irradiation. MB solution with the concentration of 10 mg L{sup −1} can be degraded totally with the irradiation time increasing to 240 min. Cerium titanate nanorods exhibit great potential in photocatalytic degradation of MB under visible light irradiation.

  4. Importance of Plasmonic Heating on Visible Light Driven Photocatalysis of Gold Nanoparticle Decorated Zinc Oxide Nanorods

    PubMed Central

    Bora, Tanujjal; Zoepfl, David; Dutta, Joydeep

    2016-01-01

    Herein we explore the role of localized plasmonic heat generated by resonantly excited gold (Au) NPs on visible light driven photocatalysis process. Au NPs are deposited on the surface of vertically aligned zinc oxide nanorods (ZnO NRs). The localized heat generated by Au NPs under 532 nm continuous laser excitation (SPR excitation) was experimentally probed using Raman spectroscopy by following the phonon modes of ZnO. Under the resonant excitation the temperature at the surface of the Au-ZnO NRs reaches up to about 300 °C, resulting in almost 6 times higher apparent quantum yield (AQY) for photocatalytic degradation of methylene blue (MB) compared to the bare ZnO NRs. Under solar light irradiation the Au-ZnO NRs demonstrated visible light photocatalytic activity twice that of what was achieved with bare ZnO NRs, while significantly reduced the activation energy required for the photocatalytic reactions allowing the reactions to occur at a faster rate. PMID:27242172

  5. Microwave hydrothermal synthesis of AgInS{sub 2} with visible light photocatalytic activity

    SciTech Connect

    Zhang, Wenjuan; Li, Danzhen; Chen, Zhixin; Sun, Meng; Li, Wenjuan; Lin, Qiang; Fu, Xianzhi

    2011-07-15

    Highlights: {yields} AgInS{sub 2} nanoparticles were synthesized by a microwave hydrothermal method. {yields} This method involves no organic solvents, catalysts, or surfactants. {yields} AgInS{sub 2} showed higher activity for photocatalytic degradation MO than TiO{sub 2-x}N{sub x}. {yields} Holes, O{sub 2}{center_dot}{sup -}, and H{sub 2}O{sub 2} played an important role in the photocatalytic process. -- Abstract: AgInS{sub 2} nanoparticles with superior visible light photocatalytic activity were successfully synthesized by a microwave hydrothermal method. This method is a highly efficient and rapid route that involves no organic solvents, catalysts, or surfactants. The photocatalytic activity of AgInS{sub 2} nanoparticles was investigated through the degradation of dyes under visible light irradiation. Compared with TiO{sub 2-x}N{sub x}, AgInS{sub 2} has exhibited a superior activity for photocatalytic degradation MO under the same condition. The experiment results showed that superoxide radicals (O{sub 2}{center_dot}{sup -}), hydrogen peroxides (H{sub 2}O{sub 2}) and holes (h{sup +}) were the mainly active species for the degradation of organic pollutants over AgInS{sub 2}. Through the determination of flat band potential, the energy band structure of the sample was obtained. A possible mechanism for the degradation of organic pollutant over AgInS{sub 2} was proposed.

  6. Visible light assisted degradation of organic dye using Ag{sub 3}PO{sub 4}

    SciTech Connect

    Dhanabal, R.; Bose, A. Chandra; Velmathi, S.

    2015-06-24

    The study of visible light photodegradation of organic dye Methylene Blue (MB) have been investigated using silver phosphate (Ag{sub 3}PO{sub 4}) as a photocatalyst which is good efficient material for photocatalytic reaction. The simple ion-exchange method is used to prepare Ag{sub 3}PO{sub 4}. The structure of the material have been confirmed using X-ray diffraction which shows cubic structure of Ag{sub 3}PO{sub 4}. The functional group of the Ag{sub 3}PO{sub 4} has been verified by Fourier transform infrared spectroscopy. The bandgap of Ag{sub 3}PO{sub 4} is calculated using kubelka-munk function from the ultra violet-visible diffuse reflectance spectroscopy, the absorption of Ag{sub 3}PO{sub 4} starts from 470 nm. Under simulated visible light irradiation, Ag{sub 3}PO{sub 4} catalyst exhibits good catalytic ability for degrading MB dye.

  7. Activation of peroxymonosulfate by BiVO4 under visible light for degradation of Rhodamine B

    NASA Astrophysics Data System (ADS)

    Liu, Yang; Guo, Hongguang; Zhang, Yongli; Tang, Weihong; Cheng, Xin; Liu, Hongwei

    2016-06-01

    A photocatalytic system involving visible light and BiVO4 (Vis/BiVO4) in the presence of peroxymonosulfate (PMS) has been developed to oxidize the target pollutant Rhodamine B (RhB) in aqueous solution. It was found that PMS could enhance the photocatalytic efficiency of BiVO4 and could be activated to promote the removal of RhB with sulfate radicals, hydroxyl radicals and superoxide radicals. Critical impacting factors in the Vis/BiVO4/PMS system were investigated concerning the influence of PMS concentration, solution pH, catalyst dosage, initial concentration of RhB and the presence of anions (Cl- and CO32-). In addition, by using isopropanol, tert-butanol, 1,4-benzoquinone and ethylenediamine tetraacetic acid disodium salt as probe compounds, the main active species were demonstrated including radSO4-, radOH and radO2- in the system, and a detail photocatalytic mechanism for the Vis/BiVO4/PMS system was proposed. Finally, up to 10 intermediate products of RhB were identified by GC/MS, included benzenoid organic compounds, organic acids and three nitrogenous organic compounds. This study provides a feasible way to degrade organic pollutants in wastewater using BiVO4 with PMS under visible light.

  8. Visible-light emission at room temperature in Mn-doped Si light-emitting diodes

    NASA Astrophysics Data System (ADS)

    Hai, Pham Nam; Maruo, Daiki; Anh, Le Duc; Tanaka, Masaaki

    2016-03-01

    We demonstrate Si-based light-emitting diodes that continuously emit reddish-yellow visible light at room temperature by utilizing optical transitions between the p-d hybrid orbitals of Mn atoms doped in Si. Our light-emitting diodes show clear visible-light electroluminescence with two peaks at E1=1.75 and E2=2.30 eV , corresponding to optical transitions between p-d hybrid orbitals of Mn atoms. The electrons at the p-d hybrid orbitals of Mn in Si are excited by hot holes that are accelerated by an intensive electric field in the depletion layer of reverse biased Si p -n junctions containing a Mn-doped Si (Si:Mn) layer. The observed two peaks at E1=1.75 and E2=2.30 eV are redshifted and blueshifted by 0.14 eV, respectively, from those of GaAs:Mn or ZnS:Mn. Our observations are consistent with the p -d hybridized electronic structure of Mn atoms doped in Si as predicted by first-principles calculations.

  9. Visible-Light-Driven Water Oxidation by a Molecular Manganese Vanadium Oxide Cluster.

    PubMed

    Schwarz, Benjamin; Forster, Johannes; Goetz, McKenna K; Yücel, Duygu; Berger, Claudia; Jacob, Timo; Streb, Carsten

    2016-05-17

    Photosynthetic water oxidation in plants occurs at an inorganic calcium manganese oxo cluster, which is known as the oxygen evolving complex (OEC), in photosystem II. Herein, we report a synthetic OEC model based on a molecular manganese vanadium oxide cluster, [Mn4 V4 O17 (OAc)3 ](3-) . The compound is based on a [Mn4 O4 ](6+) cubane core, which catalyzes the homogeneous, visible-light-driven oxidation of water to molecular oxygen and is stabilized by a tripodal [V4 O13 ](6-) polyoxovanadate and three acetate ligands. When combined with the photosensitizer [Ru(bpy)3 ](2+) and the oxidant persulfate, visible-light-driven water oxidation with turnover numbers of approximately 1150 and turnover frequencies of about 1.75 s(-1) is observed. Electrochemical, mass-spectrometric, and spectroscopic studies provide insight into the cluster stability and reactivity. This compound could serve as a model for the molecular structure and reactivity of the OEC and for heterogeneous metal oxide water-oxidation catalysts. PMID:27062440

  10. Three-visible-light wave combiner based on photonic crystal microcavities.

    PubMed

    Zhou, Xiaoyi; Liu, Dingwen; Sun, Yiling; Ouyang, Zhengbiao

    2015-08-01

    We propose a three-visible-light wave combiner based on two-dimensional square-lattice photonic crystal (PhC) microcavities. A coupled-cavity waveguide is introduced to reduce the insertion losses for the three waves in the combiner. The transmission characteristic of light waves in PhCs with point defects is analyzed. As an example, a combiner for combining light waves of 488, 532, and 635 nm, which are commonly used as the three primary colors in laser display systems, is designed and demonstrated through the finite-difference time-domain method. The three visible light waves of 488, 532, and 635 nm are output at the same output port with transmittances of 97.6%, 98.1%, and 90.0%, respectively. The results show that the proposed device can perform efficient synthesis and the designing method can be applied in building other combiners based on PhCs made of dispersion materials.

  11. Maximum likelihood estimation of vehicle position for outdoor image sensor-based visible light positioning system

    NASA Astrophysics Data System (ADS)

    Zhao, Xiang; Lin, Jiming

    2016-04-01

    Image sensor-based visible light positioning can be applied not only to indoor environments but also to outdoor environments. To determine the performance bounds of the positioning accuracy from the view of statistical optimization for an outdoor image sensor-based visible light positioning system, we analyze and derive the maximum likelihood estimation and corresponding Cramér-Rao lower bounds of vehicle position, under the condition that the observation values of the light-emitting diode (LED) imaging points are affected by white Gaussian noise. For typical parameters of an LED traffic light and in-vehicle camera image sensor, simulation results show that accurate estimates are available, with positioning error generally less than 0.1 m at a communication distance of 30 m between the LED array transmitter and the camera receiver. With the communication distance being constant, the positioning accuracy depends on the number of LEDs used, the focal length of the lens, the pixel size, and the frame rate of the camera receiver.

  12. Photodegradation of aniline by goethite doped with boron under ultraviolet and visible light irradiation

    SciTech Connect

    Liu, Guanglong; Liao, Shuijiao; Zhu, Duanwei; Liu, Linghua; Cheng, Dongsheng; Zhou, Huaidong

    2011-08-15

    Highlights: {yields} Goethite modified by boron was prepared by sol-gel method in presence of boron acid at the low temperature. {yields} B-goethite has slight red shift in the band gap transition beside their stronger light absorption compared with pristine goethite. {yields} The results showed that semiconductor photocatalytic reaction mechanism should exist in the process of aniline degradation with goethite and B-goethite as photocatalyst. -- Abstract: In the present study, goethite and goethite doped with boron (B-goethite) were employed to detect the presence or absence of semiconductor photocatalytic reaction mechanism in the reaction systems. B-goethite was prepared by sol-gel method in presence of boron acid in order to improve its photocatalystic efficiency under the ultraviolet and visible light irradiation. The optical properties of goethite and B-goethite were characterized by ultraviolet and visible absorption spectra and the result indicated that B-goethite has slight red shift in the band gap transition beside their stronger light absorption compared with pristine goethite. Degradation of aniline was investigated in presence of goethite and B-goethite in aqueous solution. It was found that the B-goethite photocatalyst exhibited enhanced ultraviolet and visible light photocatalytic activity in degradation of aniline compared with the pristine goethite. The photocatalytic degradation mechanism of B-goethite was discussed.

  13. Plasmonic nanostructures to enhance catalytic performance of zeolites under visible light

    NASA Astrophysics Data System (ADS)

    Zhang, Xingguang; Ke, Xuebin; Du, Aijun; Zhu, Huaiyong

    2014-01-01

    Light absorption efficiency of heterogeneous catalysts has restricted their photocatalytic capability for commercially important organic synthesis. Here, we report a way of harvesting visible light efficiently to boost zeolite catalysis by means of plasmonic gold nanoparticles (Au-NPs) supported on zeolites. Zeolites possess strong Brønsted acids and polarized electric fields created by extra-framework cations. The polarized electric fields can be further intensified by the electric near-field enhancement of Au-NPs, which results from the localized surface plasmon resonance (LSPR) upon visible light irradiation. The acetalization reaction was selected as a showcase performed on MZSM-5 and Au/MZSM-5 (M = H+, Na+, Ca2+, or La3+). The density functional theory (DFT) calculations confirmed that the intensified polarized electric fields played a critical role in stretching the C = O bond of the reactants of benzaldehyde to enlarge their molecular polarities, thus allowing reactants to be activated more efficiently by catalytic centers so as to boost the reaction rates. This discovery should evoke intensive research interest on plasmonic metals and diverse zeolites with an aim to take advantage of sunlight for plasmonic devices, molecular electronics, energy storage, and catalysis.

  14. Paper-Based Analytical Devices Relying on Visible-Light-Enhanced Glucose/Air Biofuel Cells.

    PubMed

    Wu, Kaiqing; Zhang, Yan; Wang, Yanhu; Ge, Shenguang; Yan, Mei; Yu, Jinghua; Song, Xianrang

    2015-11-01

    A strategy that combines visible-light-enhanced biofuel cells (BFCs) and electrochemical immunosensor into paper-based analytical devices was proposed for sensitive detection of the carbohydrate antigen 15-3 (CA15-3). The gold nanoparticle modified paper electrode with large surface area and good conductibility was applied as an effective matrix for primary antibodies. The glucose dehydrogenase (GDH) modified gold-silver bimetallic nanoparticles were used as bioanodic biocatalyst and signal magnification label. Poly(terthiophene) (pTTh), a photoresponsive conducting polymer, served as catalyst in cathode for the reduction of oxygen upon illumination by visible light. In the bioanode, electrons were generated through the oxidation of glucose catalyzed by GDH. The amount of electrons is determined by the amount of GDH, which finally depended on the amount of CA15-3. In the cathode, electrons from the bioanode could combine with the generated holes in the HOMO energy level of cathode catalysts pTTh. Meanwhile, the high energy level photoexcited electrons were generated in the LUMO energy level and involved in the oxygen reduction reaction, finally resulting in an increasing current and a decreasing overpotential. According to the current signal, simple and efficient detection of CA15-3 was achieved.

  15. Microfluidic reactors for visible-light photocatalytic water purification assisted with thermolysis

    PubMed Central

    Wang, Ning; Tan, Furui; Wan, Li; Wu, Mengchun

    2014-01-01

    Photocatalytic water purification using visible light is under intense research in the hope to use sunlight efficiently, but the conventional bulk reactors are slow and complicated. This paper presents an integrated microfluidic planar reactor for visible-light photocatalysis with the merits of fine flow control, short reaction time, small sample volume, and long photocatalyst durability. One additional feature is that it enables one to use both the light and the heat energy of the light source simultaneously. The reactor consists of a BiVO4-coated glass as the substrate, a blank glass slide as the cover, and a UV-curable adhesive layer as the spacer and sealant. A blue light emitting diode panel (footprint 10 mm × 10 mm) is mounted on the microreactor to provide uniform irradiation over the whole reactor chamber, ensuring optimal utilization of the photons and easy adjustments of the light intensity and the reaction temperature. This microreactor may provide a versatile platform for studying the photocatalysis under combined conditions such as different temperatures, different light intensities, and different flow rates. Moreover, the microreactor demonstrates significant photodegradation with a reaction time of about 10 s, much shorter than typically a few hours using the bulk reactors, showing its potential as a rapid kit for characterization of photocatalyst performance. PMID:25584117

  16. Efficient Visible-Light Photocatalytic Properties in Low-Temperature Bi-Nb-O System Photocatalysts

    NASA Astrophysics Data System (ADS)

    Zhai, Haifa; Shang, Shuying; Zheng, Liuyang; Li, Panpan; Li, Haiqin; Luo, Hongying; Kong, Jizhou

    2016-08-01

    Low-temperature Bi-Nb-O system photocatalysts were prepared by a citrate method using homemade water-soluble niobium precursors. The structures, morphologies, and optical properties of Bi-Nb-O system photocatalysts with different compositions were investigated deeply. All the Bi-Nb-O powders exhibit appreciably much higher photocatalytic efficiency of photo-degradation of methyl violet (MV), especially for Bi-Nb-O photocatalysts sintered at 750 °C (BNO750), only 1.5 h to completely decompose MV, and the obtained first-order rate constant ( k) is 1.94/h. A larger degradation rate of Bi-Nb-O photocatalysts sintered at 550 °C (BNO550) can be attributed to the synergistic effect between β-BiNbO4 and Bi5Nb3O15. Bi5Nb3O15 with small particle size on β-BiNbO4 surface can effectively short the diffuse length of electron. BNO750 exhibits the best photocatalytic properties under visible-light irradiation, which can be attributed to its better crystallinity and the synergistic effect between β-BiNbO4 and α-BiNbO4. The small amount of α-BiNbO4 loading on surface of β-BiNbO4 can effectively improve the electron and hole segregation and migration. Holes are the main active species of Bi-Nb-O system photocatalysts in aqueous solution under visible-light irradiation.

  17. [BiOBr promoted the photocatalytic degradation of beta-cypermethrin under visible light].

    PubMed

    Peng, Yi-Zhu; Zhao, Xiao-Rong; Jia, Man-Ke; Zhou, Wei; Huang, Ying-Ping

    2014-05-01

    As a visible light photocatalyst, bismuth oxide bromide (BiOBr) was used to catalyze the degradation of beta-cypermethrin (beta-CP). The photocatalytic degradation of beta-CP was studied with gas chromatography. The effects of pH and catalyst dose on the photocatalytic degradation efficiency were discussed. The oxidization and mineralization of beta-CP were detected by chemical oxygen demand (COD) analyzer. The results showed that beta-CP could be effectively degraded under visible light irradiation using BiOBr as the catalyst. At given experimental conditions, the degradation rate of beta-CP reached 94. 68% after 10 h and the COD removal rate reached 67. 99% after 36 h. With the increase of catalyst dose and pH value, the degradation rate was improved. The photocatalytic oxidation species was determined by peroxidase method and terephthalic acid fluorescence method. These results suggested that the photocatalytic degradation process mainly referred to hydroxyl radical ( OH) mechanism. PMID:25055669

  18. Visible light photooxidative performance of a high-nuclearity molecular bismuth vanadium oxide cluster.

    PubMed

    Tucher, Johannes; Streb, Carsten

    2014-01-01

    The visible light photooxidative performance of a new high-nuclearity molecular bismuth vanadium oxide cluster, H3[{Bi(dmso)3}4V13O40], is reported. Photocatalytic activity studies show faster reaction kinetics under anaerobic conditions, suggesting an oxygen-dependent quenching of the photoexcited cluster species. Further mechanistic analysis shows that the reaction proceeds via the intermediate formation of hydroxyl radicals which act as oxidant. Trapping experiments using ethanol as a hydroxyl radical scavenger show significantly decreased photocatalytic substrate oxidation in the presence of EtOH. Photocatalytic performance analyses using monochromatic visible light irradiation show that the quantum efficiency Φ for indigo photooxidation is strongly dependent on the irradiation wavelength, with higher quantum efficiencies being observed at shorter wavelengths (Φ395nm ca. 15%). Recycling tests show that the compound can be employed as homogeneous photooxidation catalyst multiple times without loss of catalytic activity. High turnover numbers (TON ca. 1200) and turnover frequencies up to TOF ca. 3.44 min(-1) are observed, illustrating the practical applicability of the cluster species. PMID:24991508

  19. Visible Light Active Cu2+/TiO2 Nanocatalyst for Degradation of Dichlorvos

    NASA Astrophysics Data System (ADS)

    Segne, Teshome Abdo; Tirukkovalluri, Siva Rao; Challapalli, Subrahmanyam

    2012-10-01

    The advantage of doping of TiO2 with copper has been utilized for enhanced degradation of pesticide under visible light irradiation. The sol-gel method has been undertaken for the synthesis of copper-doped TiO2 by varying the dopant loadings from 0.25 wt.% to 1.0 wt.% of Cu2+. The doped samples were characterized by UV-Visible Diffuse Reflectance Spectroscopy (DRS), N2 adsorption-desorption (BET), X-ray Diffraction (XRD), X-ray Photoelectron Spectroscopy (XPS), Scanning Electron Microscopy (SEM), and Energy Dispersive Spectrometry (EDS). The photocatalytic activity of the catalyst was tested by degradation of dichlorvos under visible light illumination. The results found that 0.75 wt.% of Cu2+ doped nanocatalysts have better photo catalytic activity than the rest of percentages doped, undoped TiO2 and Degussa P25. The reduction of band gap was estimated and the influence of the process parameters on photo catalytic activity of the catalyst has been explained.

  20. Enhanced visible light photocatalytic inactivation of Escherichia coli using silver nanoparticles as photocatalyst.

    PubMed

    Tahir, Kamran; Nazir, Sadia; Li, Baoshan; Khan, Arif Ullah; Khan, Zia Ul Haq; Ahmad, Aftab; Khan, Qudrat Ullah; Zhao, Yunchen

    2015-12-01

    The silver nanoparticles (AgNPs) were green synthesized using Cirsium arvense plant extract as a reducing and stabilizing agent, with superior photo inactivation activity against Escherichia coli (E. coli). The synthesized AgNPs had crystalline structure and were characterized by UV-vis spectroscopy, XRD, HRTEM, SEM, EDX and FT-IR. The formation of nanoparticles was observed at different pH and different plant extract concentrations and it was found that at higher pH (pH>6) and at lower concentration (10 mL), the reducing and stabilizing efficiency of plant extract was increased. The synthesized AgNPs had small size (<15 nm) and spherical shape. The AgNPs were evaluated for antibacterial activity against E. coli. Before transferring it to antibacterial activity, it was placed under visible light for 120 min. The same experiment was performed in dark as a control medium. The photo irradiated AgNPs were observed to be more effective against E. coli. The results showed, that the diameter of zone of inhibition of visible light irradiated AgNPs against E. coli was 23 (±0.5)mm and in dark was 11 (±0.4)mm.

  1. Importance of Plasmonic Heating on Visible Light Driven Photocatalysis of Gold Nanoparticle Decorated Zinc Oxide Nanorods.

    PubMed

    Bora, Tanujjal; Zoepfl, David; Dutta, Joydeep

    2016-01-01

    Herein we explore the role of localized plasmonic heat generated by resonantly excited gold (Au) NPs on visible light driven photocatalysis process. Au NPs are deposited on the surface of vertically aligned zinc oxide nanorods (ZnO NRs). The localized heat generated by Au NPs under 532 nm continuous laser excitation (SPR excitation) was experimentally probed using Raman spectroscopy by following the phonon modes of ZnO. Under the resonant excitation the temperature at the surface of the Au-ZnO NRs reaches up to about 300 °C, resulting in almost 6 times higher apparent quantum yield (AQY) for photocatalytic degradation of methylene blue (MB) compared to the bare ZnO NRs. Under solar light irradiation the Au-ZnO NRs demonstrated visible light photocatalytic activity twice that of what was achieved with bare ZnO NRs, while significantly reduced the activation energy required for the photocatalytic reactions allowing the reactions to occur at a faster rate. PMID:27242172

  2. Ag/TiO{sub 2} nanofiber heterostructures: Highly enhanced photocatalysts under visible light

    SciTech Connect

    Wang Yuan; Liu Lixin; Xu Liang; Meng Chuanmin; Zhu Wenjun

    2013-05-07

    Photocatalysis of TiO{sub 2} has recently drawn considerable attention, while the photoefficiency of TiO{sub 2} is limited by its large band-gap energy and usually fast electron-hole recombination. Here, we present an unconventional heterostructure of Ag nanoparticles modified TiO{sub 2} nanofibers synthesized by one-step electrospinning process, to improve the photoefficiency of TiO{sub 2} host. The efficient promotion of the visible light photocatalysis of Ag/TiO{sub 2} nanofiber heterostructures can be ascribed to the electronic excitation of Ag nanoparticles under visible light and the transfer of the electrons to TiO{sub 2} conduction band, which deeply depends on the number of Ag/TiO{sub 2} junctions and the height of Schottky barrier. The Ag/Ti molar ratio can be easily controlled by the electrospinning process and the Ag/TiO{sub 2} nanofibers with Ag/Ti molar ratio of 0.05 exhibit the highest photocatalytic activity. Simultaneously, the Ag/TiO{sub 2} nanofiber heterostructures show excellent photocatalytic stability.

  3. Visible light carrier generation in co-doped epitaxial titanate films

    SciTech Connect

    Comes, Ryan B.; Smolin, Sergey Y.; Kaspar, Tiffany C.; Gao, Ran; Apgar, Brent A.; Martin, Lane W.; Bowden, Mark E.; Baxter, Jason; Chambers, Scott A.

    2015-03-02

    Perovskite titanates such as SrTiO3 (STO) exhibit a wide range of important functional properties, including high electron mobility, ferroelectricity—which may be valuable in photovoltaic applications—and excellent photocatalytic performance. The wide optical band gap of titanates limits their use in these applications, however, making them ill-suited for integration into solar energy harvesting technologies. Our recent work has shown that by doping STO with equal concentrations of La and Cr we can enhance visible light absorption in epitaxial thin films while avoiding any compensating defects. In this work, we explore the optical properties of photoexcited carriers in these films. Using spectroscopic ellipsometry, we show that the Cr3+ dopants, which produce electronic states immediately above the top of the O 2p valence band in STO reduce the direct band gap of the material from 3.75 eV to between 2.4 and 2.7 eV depending on doping levels. Transient reflectance measurements confirm that optically generated carriers have a recombination lifetime comparable to that of STO and are in agreement with the observations from ellipsometry. Finally, through photoelectrochemical yield measurements, we show that these co-doped films exhibit enhanced visible light photocatalysis when compared to pure STO.

  4. Visible-Light-Induced Effects of Au Nanoparticle on Laccase Catalytic Activity.

    PubMed

    Guo, Sijie; Li, Hao; Liu, Juan; Yang, Yanmei; Kong, Weiqian; Qiao, Shi; Huang, Hui; Liu, Yang; Kang, Zhenhui

    2015-09-23

    A deep understanding of the interaction between the nanoparticle and enzyme is important for biocatalyst design. Here, we report the in situ synthesis of laccase-Au NP (laccase-Au) hybrids and its catalytic activity modulation by visible light. In the present hybrid system, the activity of laccase was significantly improved (increased by 91.2% vs free laccase) by Au NPs. With a short time visible light illumination (λ > 420 nm, within 3 min), the activity of laccase-Au hybrids decreased by 8.1% (vs laccase-Au hybrid without light), which can be restored to its initial one when the illumination is removed. However, after a long time illumination (λ > 420 nm, over 10 min), the catalytic activity of laccase-Au hybrids consecutively decreases and is not reversible even after removing the illumination. Our experiments also suggested that the local surface plasma resonance effect of Au NPs causes the structure change of laccase and local high temperature near the Au NPs. Those changes eventually affect the transportation of electrons in laccase, which further results in the declined activity of laccase.

  5. Novel visible-light AgBr/Ag₃PO₄ hybrids photocatalysts with surface plasma resonance effects

    SciTech Connect

    Wang, Yunfang Li, Xiuli; Wang, Yawen; Fan, Caimei

    2013-06-01

    Three kinds of AgBr/Ag₃PO₄ hybrids were synthesised via an anion-exchange precipitation method and characterised by XRD, XPS, SEM, EDS, and UV–vis. The results showed that AgBr/Ag₃PO₄ hybrids displayed much higher photocatalytic activities than single Ag₃PO₄ or AgBr under visible light (λ>420 nm), and ·OH and h⁺ were the major active species during the degradation process. Considering interstitial ions Agᵢ⁺ on lattice gap of AgBr are easy to become sliver particle, we deduced the possible photocatalytic mechanism could be ascribed to the synergistic effects of the appropriate valence band position of Ag₃PO₄ and AgBr, surface plasmon resonance effect of Ag⁰, reactive radical species Br⁰, and the Ag vacancy on the surface of catalysts. - Graphical abstract: The optical absorption and structural morphology of the as-prepared AgBr@Ag₃PO₄ photocatalyst using an anion-exchange precipitation method are conductive to the photocatalytic degradation of organics in water. Highlights: • Novel AgBr/Ag₃PO₄ hybrids are synthesised by a facile method. •AgBr/Ag₃PO₄ hybrids show excellent photocatalytic activities under visible light. • Interstitial ions are in favour of the formation of Ag particle. • Surface plasmon resonance effect plays a key factor for light absorption. • The photocatalytic mechanism for AgBr/Ag₃PO₄ hybrids is studied.

  6. Photovoltaic powered ultraviolet and visible light-emitting diodes for sustainable point-of-use disinfection of drinking waters.

    PubMed

    Lui, Gough Yumu; Roser, David; Corkish, Richard; Ashbolt, Nicholas; Jagals, Paul; Stuetz, Richard

    2014-09-15

    For many decades, populations in rural and remote developing regions will be unable to access centralised piped potable water supplies, and indeed, decentralised options may be more sustainable. Accordingly, improved household point-of-use (POU) disinfection technologies are urgently needed. Compared to alternatives, ultraviolet (UV) light disinfection is very attractive because of its efficacy against all pathogen groups and minimal operational consumables. Though mercury arc lamp technology is very efficient, it requires frequent lamp replacement, involves a toxic heavy metal, and their quartz envelopes and sleeves are expensive, fragile and require regular cleaning. An emerging alternative is semiconductor-based units where UV light emitting diodes (UV-LEDs) are powered by photovoltaics (PV). Our review charts the development of these two technologies, their current status, and challenges to their integration and POU application. It explores the themes of UV-C-LEDs, non-UV-C LED technology (e.g. UV-A, visible light, Advanced Oxidation), PV power supplies, PV/LED integration and POU suitability. While UV-C LED technology should mature in the next 10 years, research is also needed to address other unresolved barriers to in situ application as well as emerging research opportunities especially UV-A, photocatalyst/photosensitiser use and pulsed emission options. PMID:24946032

  7. Improving the modulation bandwidth of LED by CdSe/ZnS quantum dots for visible light communication.

    PubMed

    Xiao, Xiangtian; Tang, Haodong; Zhang, Tianqi; Chen, Wei; Chen, Wanli; Wu, Dan; Wang, Rui; Wang, Kai

    2016-09-19

    Visible light communication (VLC) is an advanced and high-efficiency wireless communication technology. As one of the most important light sources in VLC, conventional white light emitting diode (WLED) based on Y3Al5O12:Ce3+ (YAG:Ce) phosphor limits the system transmitting rate severely due to its narrow modulation bandwidth. Considering the short fluorescent lifetime of quantum dots (QDs), QD-LEDs with wide modulation bandwidths were designed here to improve the transmitting rate of VLC. CdSe/ZnS core/shell QDs and related luminescent microspheres (LMS) were implemented as light conversion materials for the QD-LEDs. Compared with conventional phosphor WLED, the proposed QD-LED and QD-WLED reached maximum improvement on modulation bandwidth at 74.19% and 67.75% respectively. Furthermore, mathematical modeling of smearing was analyzed to establish the relationship between fluorescent lifetime and modulation bandwidth. Our findings will provide an effective solution of white LEDs for high speed VLC. PMID:27661896

  8. Improving the modulation bandwidth of LED by CdSe/ZnS quantum dots for visible light communication.

    PubMed

    Xiao, Xiangtian; Tang, Haodong; Zhang, Tianqi; Chen, Wei; Chen, Wanli; Wu, Dan; Wang, Rui; Wang, Kai

    2016-09-19

    Visible light communication (VLC) is an advanced and high-efficiency wireless communication technology. As one of the most important light sources in VLC, conventional white light emitting diode (WLED) based on Y3Al5O12:Ce3+ (YAG:Ce) phosphor limits the system transmitting rate severely due to its narrow modulation bandwidth. Considering the short fluorescent lifetime of quantum dots (QDs), QD-LEDs with wide modulation bandwidths were designed here to improve the transmitting rate of VLC. CdSe/ZnS core/shell QDs and related luminescent microspheres (LMS) were implemented as light conversion materials for the QD-LEDs. Compared with conventional phosphor WLED, the proposed QD-LED and QD-WLED reached maximum improvement on modulation bandwidth at 74.19% and 67.75% respectively. Furthermore, mathematical modeling of smearing was analyzed to establish the relationship between fluorescent lifetime and modulation bandwidth. Our findings will provide an effective solution of white LEDs for high speed VLC.

  9. Photovoltaic powered ultraviolet and visible light-emitting diodes for sustainable point-of-use disinfection of drinking waters.

    PubMed

    Lui, Gough Yumu; Roser, David; Corkish, Richard; Ashbolt, Nicholas; Jagals, Paul; Stuetz, Richard

    2014-09-15

    For many decades, populations in rural and remote developing regions will be unable to access centralised piped potable water supplies, and indeed, decentralised options may be more sustainable. Accordingly, improved household point-of-use (POU) disinfection technologies are urgently needed. Compared to alternatives, ultraviolet (UV) light disinfection is very attractive because of its efficacy against all pathogen groups and minimal operational consumables. Though mercury arc lamp technology is very efficient, it requires frequent lamp replacement, involves a toxic heavy metal, and their quartz envelopes and sleeves are expensive, fragile and require regular cleaning. An emerging alternative is semiconductor-based units where UV light emitting diodes (UV-LEDs) are powered by photovoltaics (PV). Our review charts the development of these two technologies, their current status, and challenges to their integration and POU application. It explores the themes of UV-C-LEDs, non-UV-C LED technology (e.g. UV-A, visible light, Advanced Oxidation), PV power supplies, PV/LED integration and POU suitability. While UV-C LED technology should mature in the next 10 years, research is also needed to address other unresolved barriers to in situ application as well as emerging research opportunities especially UV-A, photocatalyst/photosensitiser use and pulsed emission options.

  10. Astronomical Ecosystems

    NASA Astrophysics Data System (ADS)

    Neuenschwander, D. E.; Finkenbinder, L. R.

    2004-05-01

    Just as quetzals and jaguars require specific ecological habitats to survive, so too must planets occupy a tightly constrained astronomical habitat to support life as we know it. With this theme in mind we relate the transferable features of our elementary astronomy course, "The Astronomical Basis of Life on Earth." Over the last five years, in a team-taught course that features a spring break field trip to Costa Rica, we have introduced astronomy through "astronomical ecosystems," emphasizing astronomical constraints on the prospects for life on Earth. Life requires energy, chemical elements, and long timescales, and we emphasize how cosmological, astrophysical, and geological realities, through stabilities and catastrophes, create and eliminate niches for biological life. The linkage between astronomy and biology gets immediate and personal: for example, studies in solar energy production are followed by hikes in the forest to examine the light-gathering strategies of photosynthetic organisms; a lesson on tides is conducted while standing up to our necks in one on a Pacific beach. Further linkages between astronomy and the human timescale concerns of biological diversity, cultural diversity, and environmental sustainability are natural and direct. Our experience of teaching "astronomy as habitat" strongly influences our "Astronomy 101" course in Oklahoma as well. This "inverted astrobiology" seems to transform our student's outlook, from the universe being something "out there" into something "we're in!" We thank the SNU Science Alumni support group "The Catalysts," and the SNU Quetzal Education and Research Center, San Gerardo de Dota, Costa Rica, for their support.

  11. ViewSpace: A model for advancing public understanding of astronomical research through museum-based multimedia

    NASA Astrophysics Data System (ADS)

    Stoke, J. M.

    2002-05-01

    The Office of Public Outreach (OPO) of the Space Telescope Science Institute (STScI) has developed a unique multimedia presentation product that orchestrates images, digital video animations, music and interpretive text to provide a frequently-updated astronomy display suitable for mini-theater environments in museum-based exhibit galleries and planetarium lobbies (that may be, otherwise, seldom updated). "ViewSpace" utilizes the scientific expertise of STScI astronomers and puts Hubble discoveries into publically-accessible contexts. The program, which is offered at no charge to the museum and planetarium community in the United States, has been received with strong enthusiasm by the informal science education community. Future aspirations include higher-definition and immersive presentation formats, multi-lingual text display, an audible description track for the visually impaired, an associated interactive kiosk, and correlated education guides. Astronomers with interesting science stories to tell are invited to participate in the development of a ViewSpace segment.

  12. Efficient photocatalytic degradation of organic pollutants by magnetically recoverable nitrogen-doped TiO2 nanocomposite photocatalysts under visible light irradiation.

    PubMed

    Hamzezadeh-Nakhjavani, Sahar; Tavakoli, Omid; Akhlaghi, Seyed Parham; Salehi, Zeinab; Esmailnejad-Ahranjani, Parvaneh; Arpanaei, Ayyoob

    2015-12-01

    Preparation of novel nanocomposite particles (NCPs) with high visible-light-driven photocatalytic activity and possessing recovery potential after advanced oxidation process (AOP) is much desired. In this study, pure anatase phase titania (TiO2) nanoparticles (NPs) as well as three types of NCPs including nitrogen-doped titania (TiO2-N), titania-coated magnetic silica (Fe3O4 cluster@SiO2@TiO2 (FST)), and a novel magnetically recoverable TiO2 nanocomposite photocatalyst containing nitrogen element (Fe3O4 cluster@SiO2@TiO2-N (FST-N)) were successfully synthesized via a sol-gel process. The photocatalysts were characterized by X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, field emission scanning electron microscopy (FE-SEM) with an energy-dispersive X-ray (EDX) spectroscopy analysis, X-ray photoelectron spectroscopy (XPS), UV-vis diffuse reflectance spectroscopy (DRS), and vibrating sample magnetometer (VSM). The photocatalytic activity of as-prepared samples was further investigated and compared with each other by degradation of phenol, as a model for the organic pollutants, in deionized (DI) water under visible light irradiation. The TiO2-N (55 ± 1.5%) and FST-N (46 ± 1.5%) samples exhibited efficient photocatalytic activity in terms of phenol degradation under visible light irradiation, while undoped samples were almost inactive under same operating conditions. Moreover, the effects of key operational parameters, the optimum sample calcination temperature, and reusability of FST-N NCPs were evaluated. Under optimum conditions (calcination temperature of 400 °C and near-neutral reaction medium), the obtained results revealed efficient degradation of phenol for FST-N NCPs under visible light irradiation (46 ± 1.5%), high yield magnetic separation and efficient reusability of FST-N NCPs (88.88% of its initial value) over 10 times reuse.

  13. Efficient photocatalytic degradation of organic pollutants by magnetically recoverable nitrogen-doped TiO2 nanocomposite photocatalysts under visible light irradiation.

    PubMed

    Hamzezadeh-Nakhjavani, Sahar; Tavakoli, Omid; Akhlaghi, Seyed Parham; Salehi, Zeinab; Esmailnejad-Ahranjani, Parvaneh; Arpanaei, Ayyoob

    2015-12-01

    Preparation of novel nanocomposite particles (NCPs) with high visible-light-driven photocatalytic activity and possessing recovery potential after advanced oxidation process (AOP) is much desired. In this study, pure anatase phase titania (TiO2) nanoparticles (NPs) as well as three types of NCPs including nitrogen-doped titania (TiO2-N), titania-coated magnetic silica (Fe3O4 cluster@SiO2@TiO2 (FST)), and a novel magnetically recoverable TiO2 nanocomposite photocatalyst containing nitrogen element (Fe3O4 cluster@SiO2@TiO2-N (FST-N)) were successfully synthesized via a sol-gel process. The photocatalysts were characterized by X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, field emission scanning electron microscopy (FE-SEM) with an energy-dispersive X-ray (EDX) spectroscopy analysis, X-ray photoelectron spectroscopy (XPS), UV-vis diffuse reflectance spectroscopy (DRS), and vibrating sample magnetometer (VSM). The photocatalytic activity of as-prepared samples was further investigated and compared with each other by degradation of phenol, as a model for the organic pollutants, in deionized (DI) water under visible light irradiation. The TiO2-N (55 ± 1.5%) and FST-N (46 ± 1.5%) samples exhibited efficient photocatalytic activity in terms of phenol degradation under visible light irradiation, while undoped samples were almost inactive under same operating conditions. Moreover, the effects of key operational parameters, the optimum sample calcination temperature, and reusability of FST-N NCPs were evaluated. Under optimum conditions (calcination temperature of 400 °C and near-neutral reaction medium), the obtained results revealed efficient degradation of phenol for FST-N NCPs under visible light irradiation (46 ± 1.5%), high yield magnetic separation and efficient reusability of FST-N NCPs (88.88% of its initial value) over 10 times reuse. PMID:26206125

  14. TiO{sub 2}/carbon nanotube hybrid nanostructures: Solvothermal synthesis and their visible light photocatalytic activity

    SciTech Connect

    Tian Lihong; Ye Liqun; Deng Kejian; Zan Ling

    2011-06-15

    MWCNT/TiO{sub 2} hybrid nanostructures were prepared via solvothermal synthesis and sol-gel method with benzyl alcohol as a surfactant. As-prepared hybrid materials were characterized by X-ray diffraction, transmission electron microscopy, UV-vis diffuse reflectance spectra and X-ray photoelectron spectroscopy. The results showed that MWCNTs were uniformly decorated with anatase nanocrystals in solvothermal condition, but MWCNTs were embedded in a majority of TiO{sub 2} nanoparticles by sol-gel method. When the weight ratio of MWCNTs to TiO{sub 2} was 20%, MWCNT/TiO{sub 2} hybrid nanostructures prepared by solvothermal synthesis exhibited higher visible-light-driven photocatalytic activity than that prepared by sol-gel method. Post-annealing of MWCNT/TiO{sub 2} nanostructures at 400 deg. C resulted in the formation of the carbonaceous Ti-C bonds on the interface between TiO{sub 2} and MWCNTs, which enhanced the photoabsorbance of the hybrid materials in the visible light region and improved the visible-light degradation efficiency of methylene blue. - Graphical abstract: MWCNT/TiO{sub 2} nanostructures have been prepared by solvothermal method, which exhibited higher visible-light-driven photocatalytic activity than that prepared by sol-gel method. The carbonaceous Ti-C bonds on the interface between TiO{sub 2} and MWCNTs enhanced the photoabsorbance of the hybrid materials in the visible light region. Highlights: > Anatase TiO{sub 2} nanoparticles were anchored on CNTs surface uniformly via solvothermal method {yields} The morphology facilitated the electron transfer between CNTs and TiO{sub 2} {yields} Ti-C bonds extended the absorption of MWCNT/TiO{sub 2} to the whole visible light region. > The hybrid nanostructures showed enhanced visible-light induced photocatalytic activity.

  15. Simultaneously promoting charge separation and photoabsorption of BiOX (X = Cl, Br) for efficient visible-light photocatalysis and photosensitization by compositing low-cost biochar

    NASA Astrophysics Data System (ADS)

    Li, Min; Huang, Hongwei; Yu, Shixin; Tian, Na; Dong, Fan; Du, Xin; Zhang, Yihe

    2016-11-01

    Exploration of novel and efficient composite photocatalysts is of great significance for advancing the practical application of photocatalysis. BiOX (X = Cl, Br) is a kind of promising photocatalysts, but the charge separation efficiency and photoabsorption need to be ameliorated. In this work, we first employ a low-cost and easily accessable carbon material biochar to modify BiOX (X = Cl, Br) and develop biochar/BiOX (X = Cl, Br) composite photocatalysts via a facile in-situ deposition method. The as-prepared composites are detailedly characterized by SEM, SEM-mapping, TEM, XRD and XPS, and DRS result demonstrates that the visible-light absorption of BiOX (X = Cl, Br) catalysts can be exceedingly enhanced by biochar. The biochar/BiOX (X = Cl, Br) composites are found to unfold remarkably enhanced visible-light-driven photocatalytic activity toward degradation of MO and photocurrent generation. The strengthened photocatalytic performance mainly stems from the profoundly improved charge separation and delivery efficiency, as evidenced by the electrochemical impedance spectra (EIS), photoluminescence (PL), and time-resolved PL decay spectra. Additionally, the biochar exerts importance in enhancing the two different types of photochemical reactions of BiOBr and BiOCl, in which the photocatalytic mechanisms are found to be photocatalysis and photosensitization process, respectively. The present work may open up a new avenue for framing economic and efficient photocatalytic materials and new composite materials for photoelectric application.

  16. Survival of Escherichia coli exposed to visible light in seawater: analysis of rpoS-dependent effects.

    PubMed

    Gourmelon, M; Touati, D; Pommepuy, M; Cormier, M

    1997-11-01

    We investigated the effect of visible light on Escherichia coli in seawater microcosms. Escherichia coli lost its ability to form colonies in marine environments when exposed to artificial continuous visible light. Survival of illuminated bacteria during the stationary phase was drastically reduced in the absence of the sigma factor (RpoS or KatF) that regulates numerous genes induced in this phase. In the stationary phase, double catalase mutants katE katG and mutants defective in the protein Dps (both catalase and Dps are involved in resistance to hydrogen peroxide (H2O2)), were more sensitive to light. In the exponenital phase, a mutation in oxyR, the regulatory gene of the adaptive response to H2O2, increased sensitivity to light, further suggesting that deleterious effects might be associated with H2O2 production. However, in the stationary phase, the katE katG dps mutant was considerably more resistant to visible light than the rpoS mutant, suggesting rpoS-dependent protection against deleterious effects other than those related to H2O2. The deleterious action of visible light was less important when the salinity decreased. In freshwater, rpoS and katE katG dps mutants did not show a drastic difference in sensitivity to light suggesting that osmolarity sensitizes E. coli to those deleterious effects of visible light that are unrelated to H2O2.

  17. Reduced graphene oxide-silver nanoparticle composite as visible light photocatalyst for degradation of colorless endocrine disruptors.

    PubMed

    Bhunia, Susanta Kumar; Jana, Nikhil R

    2014-11-26

    Sunlight-induced degradation of organic pollutants is an ideal approach for environmental pollution control and wastewater treatment. Although a variety of photocatalysts have been designed toward this goal, efficient degradation of colorless organic pollutants by visible light is a challenging issue. Here, we show that a reduced graphene oxide (rGO)-based composite with silver nanoparticle (rGO-Ag) can act as an efficient visible-light photocatalyst for the degradation of colorless organic pollutants. We have developed a simple, large-scale synthesis method for rGO-Ag and used it for the degradation of three well-known endocrine disruptors (phenol, bisphenol A, and atrazine) under UV and visible light. It is found that photocatalytic efficiency by rGO-Ag under visible light is significantly higher compared to that of rGO or silver nanoparticles. It is proposed that Ag nanoparticles offer visible-light-induced excitation of silver plasmons, and conductive rGO offers efficient charge separation and thus induces oxidative degradation of the organic pollutant. This approach can be extended for sunlight-induced degradation of different organic pollutants.

  18. A design of Si-based nanoplasmonic structure as an antenna and reception amplifier for visible light communication

    SciTech Connect

    Yan, J. H.; Lin, Z. Y.; Liu, P.; Yang, G. W.

    2014-10-21

    Visible light communication has been widely investigated due to its larger bandwidth and higher bit rate, and it can combine with the indoor illumination system that makes it more convenient to carry out. Receiving and processing the visible light signal on chip request for nanophotonics devices performing well. However, conventional optical device cannot be used for light-on-chip integration at subwavelength dimensions due to the diffraction limit. Herein, we propose a design of Si-based nanoplasmonic structure as an antenna and reception amplifier for visible light communication based on the interaction between Si nanoparticle and Au nanorod. This device integrates the unique scattering property of high-refractive index dielectric Si nanoparticles, whose scattering spectrum is dependent on the particle size, with the localized surface plasmon resonance of Au nanorod. We calculated the spectra collected by plane detector and near field distribution of nanostructure, and theoretically demonstrate that the proposed device can act as good receiver, amplifier and superlens during the visible light signal receiving and processing. Besides, unlike some other designs of nanoantenna devices focused less on how to detect the signals, our hybrid nanoantenna can realize the transfer between the scattering source and the detector effectively by Au nanorod waveguides. These findings suggest that the designed nanoplasmonic structure is expected to be used in on-chip nanophotonics as antenna, spectral splitter and demultiplexer for visible light communication.

  19. Role of carbon in titania as visible-light photocatalyst prepared by flat-flame chemical vapor condensation method

    SciTech Connect

    Chen, Y. J.; Wu, J. M.; Lin, C. S.; Jhan, G. Y.; Wong, M. S.; Ke, S.-C.; Lo, H. H.

    2009-07-15

    In this article, the authors report that titania nanopowders synthesized by low-pressure flat-flame metal-organic chemical vapor condensation show visible-light photocatalytic ability. Using acetylene and oxygen as fuel and oxidizer for the flame, the titanium isopropoxide was decomposed and oxidized, and the nanoparticles of titania were formed. From the methylene blue decomposition study they found that the powder synthesized under low precursor feed rate possesses high photocatalytic efficiency under illumination of visible light. The visible-light absorption is resort to the presence of carbon since no other chemical elements were found associated with titania. The presence of carbon species is coincident with the presence of visible-light absorption and carbon is in the form of C-C bond. It also suggests that carbon species are associated with catalytic site on anatase surface so that carriers generated by photon absorption by the carbon species can transfer quickly onto catalytic sites and perform the subsequent catalytic reactions. A possibly unreported mechanism of visible-light TiO{sub 2} photocatalysis induced by carbon doping is identified.

  20. Photocatalytic degradation of Orange G on nitrogen-doped TiO2 catalysts under visible light and sunlight irradiation.

    PubMed

    Sun, Jianhui; Qiao, Liping; Sun, Shengpeng; Wang, Guoliang

    2008-06-30

    In this paper, the degradation of an azo dye Orange G (OG) on nitrogen-doped TiO2 photocatalysts has been investigated under visible light and sunlight irradiation. Under visible light irradiation, the doped TiO2 nanocatalysts demonstrated higher activity than the commercial Dugussa P25 TiO2, allowing more efficient utilization of solar light, while under sunlight, P25 showed higher photocatalytic activity. According to the X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and UV-vis spectra analyses, it was found that both the nanosized anatase structure and the appearance of new absorption band in the visible region caused by nitrogen doping were responsible for the significant enhancement of OG degradation under visible light. In addition, the photosensitized oxidation mechanism originated from OG itself was also considered contributing to the higher visible-light-induced degradation efficiency. The effect of the initial pH of the solution and the dosage of hydrogen peroxide under different light sources was also investigated. Under visible light and sunlight, the optimal solution pH was both 2.0, while the optimal dosage of H2O2 was 5.0 and 15.0 mmol/l, respectively.

  1. Astronomical photometry

    NASA Astrophysics Data System (ADS)

    Henden, Arne A.; Kaitchuck, Ronald H.

    A handbook of astronomical photometry is presented in a format amenable to both professional and amateur use. The fundamental equipment, procedures, theory, and applications of photometry are described. Photometric systems such as the UBV, M-K, and Stromgren classification methods are explained, together with statistical treatments of photometric data. Data reduction techniques and applications in air-mass calculations, the determination of first-order extinction, and for computing zero-point values are defined. Baseline standards such as solar, universal,and sidereal time, and dating methods are provided. Instructions for constructing photometer heads are given, and the operational principles and techniques for using pulse-counting and dc electronics are explored. Finally, observational techniques and applications of photoelectric photometry are suggested and targets are indicated. A review is also offered of the theoretical basis and computational tools involved in the science of astronomical photometry.

  2. Thickness-dependent photocatalytic performance of graphite oxide for degrading organic pollutants under visible light.

    PubMed

    Oh, Junghoon; Chang, Yun Hee; Kim, Yong-Hyun; Park, Sungjin

    2016-04-28

    Photocatalysts use sustainable solar light energy to trigger various catalytic reactions. Metal-free nanomaterials have been suggested as cost-effective and environmentally friendly photocatalysts. In this work, we propose thickness-controlled graphite oxide (GO) as a metal-free photocatalyst, which is produced by exfoliating thick GO particles via stirring and sonication. All GO samples exhibit photocatalytic activity for degrading an organic pollutant, rhodamine B under visible light, and the thickest sample shows the best catalytic performance. UV-vis-NIR diffuse reflectance absorption spectra indicate that thicker GO samples absorb more vis-NIR light than thinner ones. Density-functional theory calculations show that GO has a much smaller band gap than that of single-layer graphene oxide, and thus suggest that the largely-reduced band gap is responsible for this trend of light absorption. PMID:27040040

  3. Visible-light electroluminescence in Mn-doped GaAs light-emitting diodes

    NASA Astrophysics Data System (ADS)

    Nam Hai, Pham; Maruo, Daiki; Tanaka, Masaaki

    2014-03-01

    We observed visible-light electroluminescence (EL) due to d-d transitions in light-emitting diodes with Mn-doped GaAs layers (here, referred to as GaAs:Mn). Besides the band-gap emission of GaAs, the EL spectra show two peaks at 1.89 eV and 2.16 eV, which are exactly the same as 4A2(4F) → 4T1(4G) and 4T1(4G) → 6A1(6S) transitions of Mn atoms doped in ZnS. The temperature dependence and the current-density dependence are consistent with the characteristics of d-d transitions. We explain the observed EL spectra by the p-d hybridized orbitals of the Mn d electrons in GaAs.

  4. Orthogonal frequency-division multiplexing access (OFDMA) based wireless visible light communication (VLC) system

    NASA Astrophysics Data System (ADS)

    Sung, Jiun-Yu; Yeh, Chien-Hung; Chow, Chi-Wai; Lin, Wan-Feng; Liu, Yang

    2015-11-01

    An orthogonal frequency-division multiplexing access (OFDMA) based visible light communication (VLC) system is proposed in this paper. The architecture of the proposed system is divided into several VLC cells, which is defined in this paper. The deployment and upgrade of the system involve only simple combination of the VLC cells. Hence it is economically advantageous. To guarantee smooth communication, nearly equal data rate is provided at every location within the system with no concern on the system scale. The user location monitor strategy is also discussed to solve the region division issues. The characteristics of the proposed system are analyzed in detail in this paper. A one-dimensional experiment was demonstrated with 13.6 Mb/s data rate.

  5. Dimming-discrete-multi-tone (DMT) for simultaneous color control and high speed visible light communication.

    PubMed

    Sung, Jiun-Yu; Chow, Chi-Wai; Yeh, Chien-Hung

    2014-04-01

    Visible light communication (VLC) using LEDs has attracted significant attention recently for the future secure, license-free and electromagnetic-interference (EMI)-free optical wireless communication. Dimming technique in LED lamp is advantageous for energy efficiency. Color control can be performed in the red-green-blue (RGB) LEDs by using dimming technique. It is highly desirable to employ dimming technique to provide simultaneous color and dimming control and high speed VLC. Here, we proposed and demonstrated a LED dimming control using dimming-discrete-multi-tone (DMT) modulation. High speed DMT-based VLC with simultaneous color and dimming control is demonstrated for the first time to the best of our knowledge. Demonstration and analyses for several modulation conditions and transmission distances are performed, for instance, demonstrating the data rate of 103.5 Mb/s (using RGB LED) with fast Fourier transform (FFT) size of 512.

  6. Generation of photocurrent by visible-light irradiation of conjugated dawson polyoxophosphovanadotungstate-porphyrin copolymers.

    PubMed

    Azcarate, Iban; Huo, Zhaohui; Farha, Rana; Goldmann, Michel; Xu, Hualong; Hasenknopf, Bernold; Lacôte, Emmanuel; Ruhlmann, Laurent

    2015-05-26

    Four hybrid polyoxometalate-porphyrin copolymer films were obtained by the electrooxidation of zinc octaethylporphyrin in the presence of four different Dawson-type polyoxometalates bearing two pyridyl groups (POM(py)2) with various spacers. The POM monomers were designed around 1,3,5-trisubstituted benzene rings. Two of the substituents of the benzene ring are linked to the pyridyl groups, and the third is connected to the POM subunit. The four monomers vary in the relative positions of the nitrogen atoms of the pyridine rings or in the distance from the carbonyl group. The monomers were fully characterized by (1)H, (31)P, and (13)C NMR spectroscopy, electrospray mass spectrometry, IR and UV/Vis spectroscopy, and electrochemistry. The copolymers were characterized by UV/Vis spectroscopy, X-ray photoelectron spectroscopy, electrochemistry, and AFM. Their photovoltaic performance under visible light irradiation was investigated by photocurrent transient measurements under visible illumination. PMID:25900250

  7. Visible Light Image-Based Method for Sugar Content Classification of Citrus.

    PubMed

    Wang, Xuefeng; Wu, Chunyan; Hirafuji, Masayuki

    2016-01-01

    Visible light imaging of citrus fruit from Mie Prefecture of Japan was performed to determine whether an algorithm could be developed to predict the sugar content. This nondestructive classification showed that the accurate segmentation of different images can be realized by a correlation analysis based on the threshold value of the coefficient of determination. There is an obvious correlation between the sugar content of citrus fruit and certain parameters of the color images. The selected image parameters were connected by addition algorithm. The sugar content of citrus fruit can be predicted by the dummy variable method. The results showed that the small but orange citrus fruits often have a high sugar content. The study shows that it is possible to predict the sugar content of citrus fruit and to perform a classification of the sugar content using light in the visible spectrum and without the need for an additional light source.

  8. Selective Release of Aromatic Heterocycles from Ruthenium Tris(2-pyridylmethyl)amine with Visible Light

    PubMed Central

    Li, Ao; White, Jessica K.; Arora, Karan; Herroon, Mackenzie K.; Martin, Philip D.; Schlegel, H. Bernhard; Podgorski, Izabela; Turro, Claudia; Kodanko, Jeremy J.

    2016-01-01

    Three complexes of the general formula [Ru(TPA)L2](PF6)2 [TPA = tris(2-pyridylmethyl)amine], where L = pyridine (1), nicotinamide (2), and imidazole (3), were prepared and characterized spectroscopically. X-ray crystallographic data were obtained for 1 and 3. Complexes 1–3 show strong absorption in the visible region and selective release of heterocycles upon irradiation with visible light. Time-dependent density functional theory calculations are consistent with the presence of singlet metal-to-ligand charge-transfer bands in the visible region in 1–3. Caged heterocycles 1–3 are highly stable in solution in the dark, including in cell growth media. Cell viability data show no signs of toxicity of 1–3 against PC-3 cells at concentrations up to 100 μM under light and dark conditions, consistent with Ru(TPA) acting as a nontoxic and effective photocaging group for aromatic heterocycles. PMID:26670781

  9. I-TiO2/PVC film with highly photocatalytic antibacterial activity under visible light.

    PubMed

    Deng, Weihua; Ning, Shangbo; Lin, Qianying; Zhang, Hualei; Zhou, Tanghua; Lin, Huaxiang; Long, Jinlin; Lin, Qun; Wang, Xuxu

    2016-08-01

    Iodine-modified TiO2(I-TiO2) film were coated on medical-grade PVC material by impregnation-deposition method and subsequently characterized by XRD, SEM, TEM, AFM, DRS and XPS. The photocatalytic anti-bacterial activity of I-TiO2/PVC was investigated both by in vitro anti-bacterial experiments and by clinical study. The results revealed that I-TiO2/PVC exhibit excellent photocatalytic antibacterial activity, which can destroy the propagation of the Escherichia coli and cause the deactivation and death of most E. coli bacteria within 30min visible light illumination. Clinical study on animals showed that I-TiO2 coated on PVC decrease the formation of biofilm on PVC surface in the mechanical ventilation. Furthermore, I-TiO2/PVC can effectively reduce inflammation of tracheal tissue of bam suckling pig and prevents the occurrence of VAP.

  10. Engaging unactivated alkyl, alkenyl and aryl iodides in visible-light-mediated free radical reactions.

    PubMed

    Nguyen, John D; D'Amato, Erica M; Narayanam, Jagan M R; Stephenson, Corey R J

    2012-10-01

    Radical reactions are a powerful class of chemical transformations. However, the formation of radical species to initiate these reactions has often required the use of stoichiometric amounts of toxic reagents, such as tributyltin hydride. Recently, the use of visible-light-mediated photoredox catalysis to generate radical species has become popular, but the scope of these radical precursors has been limited. Here, we describe the identification of reaction conditions under which photocatalysts such as fac-Ir(ppy)3 can be utilized to form radicals from unactivated alkyl, alkenyl and aryl iodides. The generated radicals undergo reduction via hydrogen atom abstraction or reductive cyclization. The reaction protocol utilizes only inexpensive reagents, occurs under mild reaction conditions, and shows exceptional functional group tolerance. Reaction efficiency is maintained upon scale-up and decreased catalyst loading, and the reaction time can be significantly shortened when the reaction is performed in a flow reactor.

  11. (Gold core)@(ceria shell) nanostructures for plasmon-enhanced catalytic reactions under visible light.

    PubMed

    Li, Benxia; Gu, Ting; Ming, Tian; Wang, Junxin; Wang, Peng; Wang, Jianfang; Yu, Jimmy C

    2014-08-26

    Driving catalytic reactions with sunlight is an excellent example of sustainable chemistry. A prerequisite of solar-driven catalytic reactions is the development of photocatalysts with high solar-harvesting efficiencies and catalytic activities. Herein, we describe a general approach for uniformly coating ceria on monometallic and bimetallic nanocrystals through heterogeneous nucleation and growth. The method allows for control of the shape, size, and type of the metal core as well as the thickness of the ceria shell. The plasmon shifts of the Au@CeO2 nanostructures resulting from the switching between Ce(IV) and Ce(III) are observed. The selective oxidation of benzyl alcohol to benzaldehyde, one of the fundamental reactions for organic synthesis, performed under both broad-band and monochromatic light, demonstrates the visible-light-driven catalytic activity and reveals the synergistic effect on the enhanced catalysis of the Au@CeO2 nanostructures.

  12. Constraints on drivers for visible light communications emitters based on energy efficiency.

    PubMed

    Del Campo-Jimenez, Guillermo; Perez-Jimenez, Rafael; Lopez-Hernandez, Francisco Jose

    2016-05-01

    In this work we analyze the energy efficiency constraints on drivers for Visible light communication (VLC) emitters. This is the main reason why LED is becoming the main source of illumination. We study the effect of the waveform shape and the modulation techniques on the overall energy efficiency of an LED lamp. For a similar level of illumination, we calculate the emitter energy efficiency ratio η (PLED/PTOTAL) for different signals. We compare switched and sinusoidal signals and analyze the effect of both OOK and OFDM modulation techniques depending on the power supply adjustment, level of illumination and signal amplitude distortion. Switched and OOK signals present higher energy efficiency behaviors (0.86≤η≤0.95) than sinusoidal and OFDM signals (0.53≤η≤0.79). PMID:27137609

  13. Anodic titanium oxide as immobilized photocatalyst in UV or visible light devices.

    PubMed

    Diamanti, M V; Ormellese, M; Marin, E; Lanzutti, A; Mele, A; Pedeferri, M P

    2011-02-28

    Titanium anodizing can be a powerful technique to generate photoactive oxides, strongly adherent to the metallic substrate, and to modify their chemical composition by inducing doping effects. This work investigates the photocatalytic behavior of differently obtained anodic TiO(2) films under UV and visible light irradiation, so as to define the best treatment for wastewaters purifiers. Anodizing was performed in H(3)PO(4) and H(2)SO(4) mixtures or in fluoride containing electrolytes. Morphology, elemental composition and crystal structure of the anodic films were characterized by XDR, GDOES and SEM. When amorphous oxides were obtained, an annealing treatment was used to promote the formation of anatase crystals. Annealing was also performed in nitrogen atmosphere to induce nitrogen doping. The photocatalytic efficiency of anatase-enriched TiO(2) was investigated in rhodamine B photodegradation. Doping was induced not only by annealing but also directly by anodizing, and generated photoactivity in both the UV and Vis components of light.

  14. Visible light communications for the implementation of internet-of-things

    NASA Astrophysics Data System (ADS)

    Chen, Chia-Wei; Wang, Wei-Chung; Wu, Jhao-Ting; Chen, Hung-Yu; Liang, Kevin; Wei, Liang-Yu; Hsu, Yung; Hsu, Chin-Wei; Chow, Chi-Wai; Yeh, Chien-Hung; Liu, Yang; Hsieh, Hsiang-Chin; Chen, Yen-Ting

    2016-06-01

    It is predicted that the number of internet-of-things (IoT) devices will be >28 billion in 2020. Due to the shortage of the conventional radio-frequency spectrum, using visible light communication (VLC) for IoT can be promising. IoT networks may only require very low-data rate communication for transmitting sensing or identity information. The implementation of a VLC link on existing computer communication standards and interfaces is important. Among the standards, universal asynchronous receiver/transmitter (UART) is very popular. We propose and demonstrate a VLC-over-UART system. Bit error rate analysis is performed. Different components and modules used in the proposed VLC-over-UART system are discussed. Then, we also demonstrate a real-time simultaneous temperature, humidity, and illuminance monitoring using the proposed VLC link.

  15. Broadband visible-light absorber via hybridization of propagating surface plasmon.

    PubMed

    Cong, Jiawei; Zhou, Zhiqiang; Yun, Binfeng; Lv, Liu; Yao, Hongbing; Fu, Yonghong; Ren, Naifei

    2016-05-01

    We demonstrate a broadband visible-light absorber based on excitation of multiple propagating surface plasmon (PSP) resonances. The simple structure is constructed of continuous gold/silica multi-layers covered by a one-dimensional gold grating. The broadening of bandwidth arises from the inter-layer hybridization and spectral superposition of PSPs, which is predicted with the analytical coupled oscillator model and validated using the RCWA simulation. The average absorption increases with the number of gold/silica pairs and exceeds 95% over the whole visible spectrum when only five pairs are included. Moreover, results show that the absorption can be further enhanced by grading the thickness of silica layers. The presented design might enable promising applications in the fields of photovoltaic cells and thermal emitters, owing to its advantages of wideband, near-unity absorption and simple fabrication simultaneously. PMID:27128050

  16. Visible-light-responsive ZnCuO nanoparticles: benign photodynamic killers of infectious protozoans

    PubMed Central

    Nadhman, Akhtar; Nazir, Samina; Khan, Malik Ihsanullah; Ayub, Attiya; Muhammad, Bakhtiar; Khan, Momin; Shams, Dilawar Farhan; Yasinzai, Masoom

    2015-01-01

    Human beings suffer from several infectious agents such as viruses, bacteria, and protozoans. Recently, there has been a great interest in developing biocompatible nanostructures to deal with infectious agents. This study investigated benign ZnCuO nanostructures that were visible-light-responsive due to the resident copper in the lattice. The nanostructures were synthesized through a size-controlled hot-injection process, which was adaptable to the surface ligation processes. The nanostructures were then characterized through transmission electron microscopy, X-ray diffraction, diffused reflectance spectroscopy, Rutherford backscattering, and photoluminescence analysis to measure crystallite nature, size, luminescence, composition, and band-gap analyses. Antiprotozoal efficiency of the current nanoparticles revealed the photodynamic killing of Leishmania protozoan, thus acting as efficient metal-based photosensitizers. The crystalline nanoparticles showed good biocompatibility when tested for macrophage toxicity and in hemolysis assays. The study opens a wide avenue for using toxic material in resident nontoxic forms as an effective antiprotozoal treatment. PMID:26604755

  17. UV-modulated one-dimensional photonic-crystal resonator for visible lights

    SciTech Connect

    Yang, S. Y.; Yang, P. H.; Liao, C. D.; Chieh, J. J.; Chen, Y. P.; Horng, H. E.; Hong, Chin-Yih; Yang, H. C.

    2006-12-04

    The one-dimensional photonic-crystal (A/SiO{sub 2}){sub 6}/ZnO/(SiO{sub 2}/A){sub 6} resonators at visible lights are fabricated and characterized, where A may be ZnO or indium tin oxide. Owing to the absorption of ultraviolet (UV) light by the ZnO layers, the refractive index of ZnO layers is changed temporally. This fact led to a temporary shifting of the forbidden band and the resonant mode of the resonator under UV irradiation. Besides, via adjusting the thickness of the ZnO defect layer, the resonant wavelength is manipulated. These experimental data show good consistence with simulated results.

  18. Selective hydrothermally synthesis of hexagonal WS2 platelets and their photocatalytic performance under visible light irradiation

    NASA Astrophysics Data System (ADS)

    Vattikuti, S. V. Prabhakar; Byon, Chan; Chitturi, Veerendra

    2016-06-01

    Hexagonal WS2 platelets have been synthesized via simple hydrothermal synthesis method. The hexagonal WS2 is formed by the oriented attachment (OA)-self-assembly (SA). The thickness of the WS2 platelets was between ∼20 and 100 nm. The specific surface area of these platelets is 94.63 m2 g-1. The hexagonal WS2 platelets exhibited excellent photocatalytic activity compared to irregular WS2 platelets for the degradation of rhodamine B (RhB) under visible light irradiation. This work paves the method for designing hexagonal shaped WS2 platelets with great potential for a wide spectrum of applications in photocatalysis. Moreover, this synthetic procedure may open up an opportunity to tailor the morphologies of the other nanomaterials especially transition metal sulfides.

  19. An in-Depth Survey of Visible Light Communication Based Positioning Systems

    PubMed Central

    Do, Trong-Hop; Yoo, Myungsik

    2016-01-01

    While visible light communication (VLC) has become the candidate for the wireless technology of the 21st century due to its inherent advantages, VLC based positioning also has a great chance of becoming the standard approach to positioning. Within the last few years, many studies on VLC based positioning have been published, but there are not many survey works in this field. In this paper, an in-depth survey of VLC based positioning systems is provided. More than 100 papers ranging from pioneering papers to the state-of-the-art in the field were collected and classified based on the positioning algorithms, the types of receivers, and the multiplexing techniques. In addition, current issues and research trends in VLC based positioning are discussed. PMID:27187395

  20. Optimized pre-equalization for gigabit polarization division multiplexed visible light communication

    NASA Astrophysics Data System (ADS)

    Kwon, Do-Hoon; Kim, Sung-Jin; Yang, Se-Hoon; Han, Sang-Kook

    2015-07-01

    We experimentally demonstrated a gigabit visible light communication system employing polarization division multiplexing and adaptive modulation optical-discrete multitones by using a phosphor-based white light-emitting diode. An optimized pre-equalization circuit was used to prevent clipping of the baseband signal, which exceeded the linear operating range of the LED, and to control the power distribution of each subcarrier in order to obtain an efficient bit-loading profile. Using this technique, we achieved 1.025 and 1.016 Gbps transmissions for each polarization channel and a total of 2.041 Gbps transmissions were experimentally verified. In each transmission, bit error rate performances were below the forward error correction limit.

  1. Novel self-growth photocatalytic rod-like heterojunction for hydrogen production under visible light

    NASA Astrophysics Data System (ADS)

    Liu, Xiaobin; Que, Wenxiu; Xing, Yonglei; Yin, Xingtian; He, Yucheng; Javed, H. M. Asif

    2015-06-01

    Novel H3ONb3O8-CuNb3O8 (HN-CN) semiconductors with a configuration of rod-like heterojunction were formed through analogous self-growth process, including ion-exchange and crystal structure transition processes. A p-type CuNb3O8 nano-semiconductor was grown on a layer structured rod-like KNb3O8 crystal and the as-prepared HN-CN sample showed a broad absorption range (~800 nm). Especially, the HN-CN sample exhibited an improved photocatalytic activity for hydrogen production, and a model was proposed to explain the improvement in photocatalytic activity. Current study may provide a new way for the preparation of the p-n heterojunction with high performance under visible light.

  2. Solvothermal synthesis of designed nonstoichiometric strontium titanate for efficient visible-light photocatalysis

    SciTech Connect

    Sulaeman, Uyi; Yin, Shu; Sato, Tsugio

    2010-09-06

    SrTiO{sub 3} powders with various Sr/Ti atomic ratios were synthesized by microwave-assisted solvothermal reactions of SrCl{sub 2} and Ti(OC{sub 3}H{sub 7}){sub 4} in KOH aqueous solutions. The nanoparticles of perovskite type SrTiO{sub 3} structure with the particle size of 30-40 nm were synthesized. The photocatalytic activity was determined by deNO{sub x} ability using light emitting diode lamps of various wavelengths such as 627 nm (red), 530 nm (green), 445 nm (blue), and 390 nm (UV). The photocatalytic activity significantly changed depending on the Sr/Ti atomic ratio, i.e., the strontium rich sample (Sr/Ti atomic ratio>1) showed excellent visible light responsive photocatalytic activity for the oxidative destruction of NO.

  3. Visible-Light-Driven Selective Photocatalytic Hydrogenation of Cinnamaldehyde over Au/SiC Catalysts.

    PubMed

    Hao, Cai-Hong; Guo, Xiao-Ning; Pan, Yung-Tin; Chen, Shuai; Jiao, Zhi-Feng; Yang, Hong; Guo, Xiang-Yun

    2016-08-01

    Highly selective hydrogenation of cinnamaldehyde to cinnamyl alcohol with 2-propanol was achieved using SiC-supported Au nanoparticles as photocatalyst. The hydrogenation reached a turnover frequency as high as 487 h(-1) with 100% selectivity for the production of alcohol under visible light irradiation at 20 °C. This high performance is attributed to a synergistic effect of localized surface plasmon resonance of Au NPs and charge transfer across the SiC/Au interface. The charged metal surface facilitates the oxidation of 2-propanol to form acetone, while the electron and steric effects at the interface favor the preferred end-adsorption of α,β-unsaturated aldehydes for their selective conversion to unsaturated alcohols. We show that this Au/SiC photocatalyst is capable of hydrogenating a large variety of α,β-unsaturated aldehydes to their corresponding unsaturated alcohols with high conversion and selectivity. PMID:27403658

  4. Imaging hemodynamic response after ischemic stroke in mouse cortex using visible-light optical coherence tomography

    PubMed Central

    Chen, Siyu; Liu, Qi; Shu, Xiao; Soetikno, Brian; Tong, Shanbao; Zhang, Hao F.

    2016-01-01

    Visible-light optical coherence tomography (Vis-OCT) is an emerging technology that can image hemodynamic response in microvasculature. Vis-OCT can retrieve blood oxygen saturation (sO2) mapping using intrinsic optical absorption contrast while providing high-resolution anatomical vascular structures at the same time. To improve the accuracy of Vis-OCT oximetry on vessels embedded in highly scattering medium, i.e., brain cortex, we developed and formulated a novel dual-depth sampling and normalization strategy that allowed us to minimize the detrimental effect of ubiquitous tissue scattering. We applied our newly developed approach to monitor the hemodynamic response in mouse cortex after focal photothrombosis. We observed vessel dilatation, which was negatively correlated with the original vessel diameter, in the penumbra region. The sO2 of vessels in the penumbra region also dropped below normal range after focal ischemia.

  5. Enantioselective Visible-Light-Induced Radical-Addition Reactions to 3-Alkylidene Indolin-2-ones.

    PubMed

    Lenhart, Dominik; Bauer, Andreas; Pöthig, Alexander; Bach, Thorsten

    2016-05-01

    The title compounds underwent a facile and high-yielding addition reaction (19 examples, 66-99% yield) with various N-(trimethylsilyl)methyl-substituted amines upon irradiation with visible light and catalysis by a metal complex. If the alkylidene substituent is non-symmetric and if the reaction is performed in the presence of a chiral hydrogen-bonding template, products are obtained with significant enantioselectivity (58-72% ee) as a mixture of diastereoisomers. Mechanistic studies suggest a closed catalytic cycle for the photoactive metal complex. However, the silyl transfer from the amine occurs not only to the product, but also to the substrate, and interferes with the desired chirality transfer.

  6. Visible-Light-Responsive Catalyst Development for Volatile Organic Carbon Remediation Project

    NASA Technical Reports Server (NTRS)

    Zeitlin, Nancy; Hintze, Paul E.; Coutts, Janelle

    2015-01-01

    Photocatalysis is a process in which light energy is used to 'activate' oxidation/reduction reactions. Unmodified titanium dioxide (TiO2), a common photocatalyst, requires high-energy UV light for activation due to its large band gap (3.2 eV). Modification of TiO2 can reduce this band gap, leading to visible-light-responsive (VLR) photocatalysts. These catalysts can utilize solar and/or visible wavelength LED lamps as an activation source, replacing mercury-containing UV lamps, to create a "greener," more energy-efficient means for air and water revitalization. Recently, KSC developed several VLR catalysts that, on preliminary evaluation, possessed high catalytic activity within the visible spectrum; these samples out-performed existing commercial VLR catalysts.

  7. Visible light photoactivity of Polypropylene coated Nano-TiO2 for dyes degradation in water.

    PubMed

    Giovannetti, R; Amato, C A D'; Zannotti, M; Rommozzi, E; Gunnella, R; Minicucci, M; Di Cicco, A

    2015-12-02

    The use of Polypropylene as support material for nano-TiO2 photocatalyst in the photodegradation of Alizarin Red S in water solutions under the action of visible light was investigated. The optimization of TiO2 pastes preparation using two commercial TiO2, Aeroxide P-25 and Anatase, was performed and a green low-cost dip-coating procedure was developed. Scanning electron microscopy, Atomic Force Microscopy and X-Ray Diffraction analysis were used in order to obtain morphological and structural information of as-prepared TiO2 on support material. Equilibrium and kinetics aspects in the adsorption and successive photodegradation of Alizarin Red S, as reference dye, are described using polypropylene-TiO2 films in the Visible/TiO2/water reactor showing efficient dyes degradation.

  8. Conversion of visible light to electrical energy - Stable cadmium selenide photoelectrodes in aqueous electrolytes

    NASA Technical Reports Server (NTRS)

    Wrighton, M. S.; Ellis, A. B.; Kaiser, S. W.

    1977-01-01

    Stabilization of n-type CdSe to photoanodic dissolution is reported. The stabilization is accomplished by the competitive oxidation of S(--) or S(n)(--) at the CdSe photoanode in an electrochemical cell. Such stabilized cells are shown to sustain the conversion of low energy (not less than 1.7 eV) visible light to electricity with good efficiency and no deterioration of the CdSe photoelectrode or of the electrolyte. The electrolyte undergoes no net chemical change because the oxidation occurring at the photoelectrode is reversed at the cathode. Conversion of monochromatic light at 633 nm to electricity is shown to be up to approximately 9% efficient with output potentials of approximately 0.4 V. Conversion of solar energy to electricity is estimated to be approximately 2% efficient.

  9. Constraints on drivers for visible light communications emitters based on energy efficiency.

    PubMed

    Del Campo-Jimenez, Guillermo; Perez-Jimenez, Rafael; Lopez-Hernandez, Francisco Jose

    2016-05-01

    In this work we analyze the energy efficiency constraints on drivers for Visible light communication (VLC) emitters. This is the main reason why LED is becoming the main source of illumination. We study the effect of the waveform shape and the modulation techniques on the overall energy efficiency of an LED lamp. For a similar level of illumination, we calculate the emitter energy efficiency ratio η (PLED/PTOTAL) for different signals. We compare switched and sinusoidal signals and analyze the effect of both OOK and OFDM modulation techniques depending on the power supply adjustment, level of illumination and signal amplitude distortion. Switched and OOK signals present higher energy efficiency behaviors (0.86≤η≤0.95) than sinusoidal and OFDM signals (0.53≤η≤0.79).

  10. Visible Light-Induced Photoredox Construction of Trifluoromethylated Quaternary Carbon Centers from Trifluoromethylated Tertiary Bromides.

    PubMed

    Huan, Feng; Chen, Qing-Yun; Guo, Yong

    2016-08-19

    A mild, operationally simple, visible light-induced photoredox method for constructing novel trifluoromethylated quaternary carbon centers from trifluoromethylated tertiary bromides has been developed. Using this method, a wide range of alkenes were successfully bifunctionalized to γ-butyrolactams. As for electron-rich alkenes, reactions catalyzed by Ir(dF(CF3)ppy)2(dtbbpy)(PF6) were kinetic processes with high yields and short times. For styrenes, reactions catalyzed by Ir(ppy)2(dtbbpy)(PF6) were thermodynamic processes with moderate yields and prolonged reaction times. For aliphatic alkenes, the reactions were neither thermodynamic nor kinetic and fac-Ir(ppy)3 was used as catalyst. Thus, reactions were not as efficient as electron-rich alkenes. The atom-transfer radical addition reactions of trifluoromethylated tertiary bromides with alkynes were also achieved. The configuration of products we separated was E type only. Some of the products exhibited bactericidal activity.

  11. Enhanced visible light emission from Co 2+ doped ZnS nanoparticles

    NASA Astrophysics Data System (ADS)

    Sarkar, R.; Tiwary, C. S.; Kumbhakar, P.; Mitra, A. K.

    2009-11-01

    ZnS nanoparticles with Co 2+ doping have been prepared at room temperature through a soft chemical route, namely the chemical co-precipitation method. The nanostructures of the prepared nanoparticles have been analyzed using X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), selected-area electron diffraction (SAED), and UV-vis spectrophotometer. The sizes of as prepared nanoparticles are found to be in 1-4 nm range. Room-temperature photoluminescence (PL) spectrum of the undoped sample exhibits emission in the blue region with multiple peaks under UV excitation. On the other hand, in the Co 2+ doped ZnS samples enhanced visible light emissions with emission intensities of ~35 times larger than that of the undoped sample are observed under the same UV excitation wavelength of 280 nm.

  12. Polarization-independent and high-efficiency dielectric metasurfaces for visible light.

    PubMed

    Li, Qi-Tong; Dong, Fengliang; Wang, Bong; Gan, Fengyuan; Chen, Jianjun; Song, Zhiwei; Xu, Lixua; Chu, Weiguo; Xiao, Yun-Feng; Gong, Qihuang; Li, Yan

    2016-07-25

    Dielectric metasurfaces are capable of completely manipulating the phase, amplitude, and polarization of light with high spatial resolutions. The emerging design based on high-index and low-loss dielectrics has led to the realization of novel metasurfaces with high transmissions, but these devices usually operate at the limited bandwidth, and are sensitive to the incident polarization. Here, we report the realization of the polarization-independent and high-efficiency silicon metasurfaces spanning the visible wavelengths about 200 nm. The fabricated computer-generated meta-holograms exhibit a 90% diffraction efficiency, which are verified by gradient metasurfaces with measured efficiencies up to 93% at 670 nm, and exceeding 75% at the wavelengths from 600 to 800 nm for the two orthogonally polarized incidences. These dielectric metasurfaces effectively decouple the phase modulation from the polarization states and frequencies for visible light, which hold great potential for novel flat optical devices operating over a broad spectrum. PMID:27464084

  13. Mesoporous Au/TiO2 nanocomposite microspheres for visible-light photocatalysis.

    PubMed

    Wang, Guannan; Wang, Xiaofei; Liu, Junfeng; Sun, Xiaoming

    2012-04-23

    Mesoporous Au/TiO(2) nanocomposite microspheres have been synthesized by using a microemulsion-based bottom-up self-assembly (EBS) process starting from monodisperse gold and titania nanocrystals as building blocks. The microspheres had large surface areas (above 270 m(2) g(-1)) and open mesopores (about 5 nm), which led to the adsorption-driven concentration of organic molecules in the vicinity of the microspheres. Au nanoparticles, which were stably confined within the microspheres, enhanced the absorption over the broad UV/Vis/NIR spectroscopic range, owing to their strong surface plasmon resonance (SPR); as a result, the Au nanoparticles promoted the visible-light photo-induced degradation of organic compounds.

  14. Visible light photoactivity of Polypropylene coated Nano-TiO2 for dyes degradation in water

    PubMed Central

    Giovannetti, R.; Amato, C. A. D’; Zannotti, M.; Rommozzi, E.; Gunnella, R.; Minicucci, M.; Di Cicco, A.

    2015-01-01

    The use of Polypropylene as support material for nano-TiO2 photocatalyst in the photodegradation of Alizarin Red S in water solutions under the action of visible light was investigated. The optimization of TiO2 pastes preparation using two commercial TiO2, Aeroxide P-25 and Anatase, was performed and a green low-cost dip-coating procedure was developed. Scanning electron microscopy, Atomic Force Microscopy and X-Ray Diffraction analysis were used in order to obtain morphological and structural information of as-prepared TiO2 on support material. Equilibrium and kinetics aspects in the adsorption and successive photodegradation of Alizarin Red S, as reference dye, are described using polypropylene-TiO2 films in the Visible/TiO2/water reactor showing efficient dyes degradation. PMID:26627118

  15. Printable photonic crystals with high refractive index for applications in visible light.

    PubMed

    Calafiore, Giuseppe; Fillot, Quentin; Dhuey, Scott; Sassolini, Simone; Salvadori, Filippo; Mejia, Camilo A; Munechika, Keiko; Peroz, Christophe; Cabrini, Stefano; Piña-Hernandez, Carlos

    2016-03-18

    Nanoimprint lithography (NIL) of functional high-refractive index materials has proved to be a powerful candidate for the inexpensive manufacturing of high-resolution photonic devices. In this paper, we demonstrate the fabrication of printable photonic crystals (PhCs) with high refractive index working in the visible wavelengths. The PhCs are replicated on a titanium dioxide-based high-refractive index hybrid material by reverse NIL with almost zero shrinkage and high-fidelity reproducibility between mold and printed devices. The optical responses of the imprinted PhCs compare very well with those fabricated by conventional nanofabrication methods. This study opens the road for a low-cost manufacturing of PhCs and other nanophotonic devices for applications in visible light.

  16. Synthesis of Bi2WO6 Microspheres with Visible-Light Photocatalytic Properties

    NASA Astrophysics Data System (ADS)

    Wan, Gengping; Wang, Guizhen

    2013-12-01

    Bi2WO6 microspheres constructed from nanosheets have been synthesized by a controllable solvothermal route in a large scale. The structure characterizations of the microspheres were investigated in detail by means of X-ray diffraction (XRD), scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM). On the basis of XRD analysis and SEM observation of the products at different reaction time periods, a growth mechanism of Bi2WO6 microspheres was proposed. UV-Visible diffuse reflectance (DR) spectrum of the prepared Bi2WO6 microspheres demonstrates that they have absorption in the visible light region. The photocatalytic activity of Bi2WO6 microspheres toward Rhodamine-B (RhB) degradation was investigated and the as-prepared products exhibited good photocatalytic activity in degradation of RhB under 300 W Xe lamp light irradiation.

  17. Visible Light-Induced Photoredox Construction of Trifluoromethylated Quaternary Carbon Centers from Trifluoromethylated Tertiary Bromides.

    PubMed

    Huan, Feng; Chen, Qing-Yun; Guo, Yong

    2016-08-19

    A mild, operationally simple, visible light-induced photoredox method for constructing novel trifluoromethylated quaternary carbon centers from trifluoromethylated tertiary bromides has been developed. Using this method, a wide range of alkenes were successfully bifunctionalized to γ-butyrolactams. As for electron-rich alkenes, reactions catalyzed by Ir(dF(CF3)ppy)2(dtbbpy)(PF6) were kinetic processes with high yields and short times. For styrenes, reactions catalyzed by Ir(ppy)2(dtbbpy)(PF6) were thermodynamic processes with moderate yields and prolonged reaction times. For aliphatic alkenes, the reactions were neither thermodynamic nor kinetic and fac-Ir(ppy)3 was used as catalyst. Thus, reactions were not as efficient as electron-rich alkenes. The atom-transfer radical addition reactions of trifluoromethylated tertiary bromides with alkynes were also achieved. The configuration of products we separated was E type only. Some of the products exhibited bactericidal activity. PMID:27438228

  18. Cu-doped TiO(2) nanoparticles for photocatalytic disinfection of bacteria under visible light.

    PubMed

    Karunakaran, C; Abiramasundari, G; Gomathisankar, P; Manikandan, G; Anandi, V

    2010-12-01

    Two percent Cu-doped TiO(2) nanoparticles were prepared by a modified ammonia-evaporation-induced synthetic method, calcined at 450°C, and characterized by powder X-ray diffraction, energy dispersive X-ray analysis, ESR spectroscopy, scanning electron microscopy, UV-visible diffuse reflectance spectrum, photoluminescence spectroscopy, and electrochemical impedance spectroscopy. Doping shifts the optical absorption edge to the visible region but increases the charge-transfer resistance and decreases the capacitance. Under visible light, the composite nanoparticles very efficiently catalyze the disinfection of Escherichia coli. The prepared oxide is selective in photocatalysis; under UV light, its photocatalytic activity to degrade sunset yellow, rhodamine B, and methylene blue dyes is less than that of the undoped one. PMID:20832079

  19. Broadband visible-light absorber via hybridization of propagating surface plasmon.

    PubMed

    Cong, Jiawei; Zhou, Zhiqiang; Yun, Binfeng; Lv, Liu; Yao, Hongbing; Fu, Yonghong; Ren, Naifei

    2016-05-01

    We demonstrate a broadband visible-light absorber based on excitation of multiple propagating surface plasmon (PSP) resonances. The simple structure is constructed of continuous gold/silica multi-layers covered by a one-dimensional gold grating. The broadening of bandwidth arises from the inter-layer hybridization and spectral superposition of PSPs, which is predicted with the analytical coupled oscillator model and validated using the RCWA simulation. The average absorption increases with the number of gold/silica pairs and exceeds 95% over the whole visible spectrum when only five pairs are included. Moreover, results show that the absorption can be further enhanced by grading the thickness of silica layers. The presented design might enable promising applications in the fields of photovoltaic cells and thermal emitters, owing to its advantages of wideband, near-unity absorption and simple fabrication simultaneously.

  20. Polarization-independent and high-efficiency dielectric metasurfaces for visible light.

    PubMed

    Li, Qi-Tong; Dong, Fengliang; Wang, Bong; Gan, Fengyuan; Chen, Jianjun; Song, Zhiwei; Xu, Lixua; Chu, Weiguo; Xiao, Yun-Feng; Gong, Qihuang; Li, Yan

    2016-07-25

    Dielectric metasurfaces are capable of completely manipulating the phase, amplitude, and polarization of light with high spatial resolutions. The emerging design based on high-index and low-loss dielectrics has led to the realization of novel metasurfaces with high transmissions, but these devices usually operate at the limited bandwidth, and are sensitive to the incident polarization. Here, we report the realization of the polarization-independent and high-efficiency silicon metasurfaces spanning the visible wavelengths about 200 nm. The fabricated computer-generated meta-holograms exhibit a 90% diffraction efficiency, which are verified by gradient metasurfaces with measured efficiencies up to 93% at 670 nm, and exceeding 75% at the wavelengths from 600 to 800 nm for the two orthogonally polarized incidences. These dielectric metasurfaces effectively decouple the phase modulation from the polarization states and frequencies for visible light, which hold great potential for novel flat optical devices operating over a broad spectrum.

  1. A review of iron species for visible-light photocatalytic water purification.

    PubMed

    Jack, Russell S; Ayoko, Godwin A; Adebajo, Moses O; Frost, Ray L

    2015-05-01

    Iron species are one of the least toxic and least expensive substances that are photocatalytic in the visible region of the spectrum. Therefore, this article focuses on iron-based photocatalysts sensitive to visible light. Photo-Fenton reactions are considered with respect to those assisted by and involve the in situ production of H₂O₂. The possible role that photoactive iron species play by interacting with natural organic matter in water purification in the natural environment is considered. The review also considered photosensitization by phthalocyanines and the potential role that layered double hydroxides may have not only as catalyst supports but also as photosensitizers themselves. Finally, photocatalytic disinfection of water is discussed, and the desirability of standardized metrics and experimental conditions to assist in the comparative evaluation of photocatalysts is highlighted.

  2. Novel GQD-PVP-CdS composite with enhanced visible-light-driven photocatalytic properties

    NASA Astrophysics Data System (ADS)

    Fan, Tao; Li, Yinle; Shen, Jianfeng; Ye, Mingxin

    2016-03-01

    A facile one-step hydrothermal method to synthesize graphene quantum dots (GQDs)-polyvinyl pyrrolidone (PVP)-CdS nanocomposite was reported. The nanocomposite was thoroughly characterized with X-ray diffraction, transmission electron microscopy, scanning electron microscopy, Fourier-transform infrared spectroscopy, Raman spectroscopy, X-ray photoelectron spectroscopy and ultraviolet-visible spectroscopy. The results confirmed the formation of GQD-PVP-CdS composite with a uniform size (5-10 nm) and a relatively low band gap (Eg = 2.23 eV). Moreover, the as-prepared composite exhibited enhanced photocatalytic activity toward the degradation of organic contaminants, with 92.3% of methyl orange (10 mg/L) removed after 3 hours of visible light illumination. This enhancement in photocatalytic activity was postulated to be attributed to the upconversion property of GQDs and a more efficient charge distribution between GQDs and CdS particles.

  3. Covalent Triazine-Based Frameworks as Visible Light Photocatalysts for the Splitting of Water.

    PubMed

    Bi, Jinhong; Fang, Wei; Li, Liuyi; Wang, Jinyun; Liang, Shijing; He, Yunhui; Liu, Minghua; Wu, Ling

    2015-10-01

    Covalent triazine-based frameworks (CTFs) with a graphene-like layered morphology have been controllably synthesized by the trifluoromethanesulfonic acid-catalyzed nitrile trimerization reactions at room temperature via selecting different monomers. Platinum nanoparticles are well dispersed in CTF-T1, which is ascribed to the synergistic effects of the coordination of triazine moieties and the nanoscale confinement effect of CTFs. CTF-T1 exhibits excellent photocatalytic activity and stability for H2 evolution in the presence of platinum under visible light irradiation (λ ≥ 420 nm). The activity and stability of CTF-T1 are comparable to those of g-C3 N4 . Importantly, as a result of the tailorable electronic and spatial structures of CTFs that can be achieved through the judicial selection of monomers, CTFs not only show great potential as organic semiconductor for photocatalysis but also may provide a molecular-level understanding of the inherent heterogeneous photocatalysis.

  4. Visible-light-driven CO2 reduction with carbon nitride: enhancing the activity of ruthenium catalysts.

    PubMed

    Kuriki, Ryo; Sekizawa, Keita; Ishitani, Osamu; Maeda, Kazuhiko

    2015-02-16

    A heterogeneous photocatalyst system that consists of a ruthenium complex and carbon nitride (C3N4), which act as the catalytic and light-harvesting units, respectively, was developed for the reduction of CO2 into formic acid. Promoting the injection of electrons from C3N4 into the ruthenium unit as well as strengthening the electronic interactions between the two units enhanced its activity. The use of a suitable solvent further improved the performance, resulting in a turnover number of greater than 1000 and an apparent quantum yield of 5.7% at 400 nm. These are the best values that have been reported for heterogeneous photocatalysts for CO2 reduction under visible-light irradiation to date.

  5. Visible light communication using mobile-phone camera with data rate higher than frame rate.

    PubMed

    Chow, Chi-Wai; Chen, Chung-Yen; Chen, Shih-Hao

    2015-10-01

    Complementary Metal-Oxide-Semiconductor (CMOS) image sensors are widely used in mobile-phone and cameras. Hence, it is attractive if these image sensors can be used as the visible light communication (VLC) receivers (Rxs). However, using these CMOS image sensors are challenging. In this work, we propose and demonstrate a VLC link using mobile-phone camera with data rate higher than frame rate of the CMOS image sensor. We first discuss and analyze the features of using CMOS image sensor as VLC Rx, including the rolling shutter effect, overlapping of exposure time of each row of pixels, frame-to-frame processing time gap, and also the image sensor "blooming" effect. Then, we describe the procedure of synchronization and demodulation. This includes file format conversion, grayscale conversion, column matrix selection avoiding blooming, polynomial fitting for threshold location. Finally, the evaluation of bit-error-rate (BER) is performed satisfying the forward error correction (FEC) limit.

  6. Visible light photoreactivity from Carbon nitride bandgap states in Nb and Ti oxides

    NASA Astrophysics Data System (ADS)

    Lee, Hosik; Ohno, Takahisa; Icnsee Team

    2011-03-01

    Lamellar niobic and titanic solid acids (HNb3O8 , H2Ti4O9) are photocatalysts which can be used for environmental cleanup application and hydrogen production through water splitting. To increase their efficiency, bandgap adjustment which can induce visible light reactivity in addition to ultraviolet light has been one of hot issue in this kinds of photo-catalytic materials. Nitrogen-doping was one of the direction and its microscopic structures are disputed in this decade. In this work, we calculate the layered niobic and titanic solid acids structure and bandgap. Bandgap reduction by carbon nitride absorption are observed computationally. It is originated from localized nitrogen state which is consistent with previous experiments.

  7. Broadband visible light source based on AllnGaN light emitting diodes

    DOEpatents

    Crawford, Mary H.; Nelson, Jeffrey S.

    2003-12-16

    A visible light source device is described based on a light emitting diode and a nanocluster-based film. The light emitting diode utilizes a semiconductor quantum well structure between n-type and p-type semiconductor materials on the top surface a substrate such as sapphire. The nanocluster-based film is deposited on the bottom surface of the substrate and can be derived from a solution of MoS.sub.2, MoSe.sub.2, WS.sub.2, and WSe.sub.2 particles of size greater than approximately 2 nm in diameter and less than approximately 15 nm in diameter, having an absorption wavelength greater than approximately 300 nm and less than approximately 650 nm.

  8. Visible light photoactivity of Polypropylene coated Nano-TiO2 for dyes degradation in water

    NASA Astrophysics Data System (ADS)

    Giovannetti, R.; Amato, C. A. D.'; Zannotti, M.; Rommozzi, E.; Gunnella, R.; Minicucci, M.; di Cicco, A.

    2015-12-01

    The use of Polypropylene as support material for nano-TiO2 photocatalyst in the photodegradation of Alizarin Red S in water solutions under the action of visible light was investigated. The optimization of TiO2 pastes preparation using two commercial TiO2, Aeroxide P-25 and Anatase, was performed and a green low-cost dip-coating procedure was developed. Scanning electron microscopy, Atomic Force Microscopy and X-Ray Diffraction analysis were used in order to obtain morphological and structural information of as-prepared TiO2 on support material. Equilibrium and kinetics aspects in the adsorption and successive photodegradation of Alizarin Red S, as reference dye, are described using polypropylene-TiO2 films in the Visible/TiO2/water reactor showing efficient dyes degradation.

  9. Visible Light Photocatalysis via CdS/ TiO 2 Nanocomposite Materials

    DOE PAGES

    Srinivasan, Sesha S.; Wade, Jeremy; Stefanakos, Elias K.

    2006-01-01

    Nmore » anostructured colloidal semiconductors with heterogeneous photocatalytic behavior have drawn considerable attention over the past few years. This is due to their large surface area, high redox potential of the photogenerated charge carriers, and selective reduction/oxidation of different classes of organic compounds. In the present paper, we have carried out a systematic synthesis of nanostructured CdS- TiO 2 via reverse micelle process. The structural and microstructural characterizations of the as-prepared CdS- TiO 2 nanocomposites are determined using XRD and SEM-EDS techniques. The visible light assisted photocatalytic performance is monitored by means of degradation of phenol in water suspension.« less

  10. A linear receiver for visible light communication systems with phase modulated OFDM

    NASA Astrophysics Data System (ADS)

    Xie, Gui-Teng; Yu, Hong-Yi; Zhu, Yi-Jun; Ji, Xin-Sheng

    2016-07-01

    In the orthogonal frequency-division multiplexing (OFDM) systems for visible light communication (VLC), the peak-to-average power ratio (PAPR) of OFDM signals is the primary concern of high-speed data transmission. In order to get low PAPR signals and reduce the influence of nonlinearity of the light-emitting diode (LED), a phase modulated OFDM (PM-OFDM) system is developed and a linear receiver is presented. Unlike the conventional angle detection receiver implemented by arctangent calculator, the linear receiver has lower computation complexity and is immune to the threshold effect. Simulation results indicate that the proposed PM-OFDM obtains significant performance gains over DC-biased optical OFDM (DCO-OFDM) and precoded OFDM.

  11. Massive MIMO-OFDM indoor visible light communication system downlink architecture design

    NASA Astrophysics Data System (ADS)

    Lang, Tian; Li, Zening; Chen, Gang

    2014-10-01

    Multiple-input multiple-output (MIMO) technique is now used in most new broadband communication system, and orthogonal frequency division multiplexing (OFDM) is also utilized within current 4th generation (4G) of mobile telecommunication technology. With MIMO and OFDM combined, visible light communication (VLC) system's diversity gain is increase, yet system capacity for dispersive channels is also enhanced. Moreover, with the emerging massive MIMO-OFDM VLC system, there are significant advantages than smaller systems' such as channel hardening, further increasing of energy efficiency (EE) and spectral efficiency (SE) based on law of large number. This paper addresses one of the major technological challenges, system architecture design, which was solved by semispherical beehive structure (SBS) receiver and so that diversity gain can be identified and applied in Massive MIMO VLC system. Simulation results shows that the proposed design clearly presents a spatial diversity over conventional VLC systems.

  12. Carrier dynamics of a visible-light-responsive Ta3N5 photoanode for water oxidation.

    PubMed

    Ziani, Ahmed; Nurlaela, Ela; Dhawale, Dattatray S; Silva, Diego Alves; Alarousu, Erkki; Mohammed, Omar F; Takanabe, Kazuhiro

    2015-01-28

    The physicochemical properties of a tantalum nitride (Ta3N5) photoanode were investigated in detail to understand the fundamental aspects associated with the photoelectrochemical (PEC) water oxidation. The Ta3N5 thin films were synthesized using DC magnetron sputtering followed by annealing in air and nitridation under ammonia (NH3). A polycrystalline structure with a dense morphology of the monoclinic Ta3N5 films was obtained. A relatively low absorption coefficient (10(4) to 10(5) cm(-1)) in the visible light range was measured for Ta3N5, consistent with the nature of the indirect band-gap. Ultra-fast spectroscopic measurements revealed that the Ta3N5 with different thicknesses films possess low transport properties and fast carrier recombination (<10 ps). These critical kinetic properties of Ta3N5 as a photoanode may necessitate high overpotentials to achieve appreciable photocurrents for water oxidation (onset ∼0.6 V vs. RHE).

  13. Visible Light Image-Based Method for Sugar Content Classification of Citrus

    PubMed Central

    Wang, Xuefeng; Wu, Chunyan; Hirafuji, Masayuki

    2016-01-01

    Visible light imaging of citrus fruit from Mie Prefecture of Japan was performed to determine whether an algorithm could be developed to predict the sugar content. This nondestructive classification showed that the accurate segmentation of different images can be realized by a correlation analysis based on the threshold value of the coefficient of determination. There is an obvious correlation between the sugar content of citrus fruit and certain parameters of the color images. The selected image parameters were connected by addition algorithm. The sugar content of citrus fruit can be predicted by the dummy variable method. The results showed that the small but orange citrus fruits often have a high sugar content. The study shows that it is possible to predict the sugar content of citrus fruit and to perform a classification of the sugar content using light in the visible spectrum and without the need for an additional light source. PMID:26811935

  14. Imaging hemodynamic response after ischemic stroke in mouse cortex using visible-light optical coherence tomography

    PubMed Central

    Chen, Siyu; Liu, Qi; Shu, Xiao; Soetikno, Brian; Tong, Shanbao; Zhang, Hao F.

    2016-01-01

    Visible-light optical coherence tomography (Vis-OCT) is an emerging technology that can image hemodynamic response in microvasculature. Vis-OCT can retrieve blood oxygen saturation (sO2) mapping using intrinsic optical absorption contrast while providing high-resolution anatomical vascular structures at the same time. To improve the accuracy of Vis-OCT oximetry on vessels embedded in highly scattering medium, i.e., brain cortex, we developed and formulated a novel dual-depth sampling and normalization strategy that allowed us to minimize the detrimental effect of ubiquitous tissue scattering. We applied our newly developed approach to monitor the hemodynamic response in mouse cortex after focal photothrombosis. We observed vessel dilatation, which was negatively correlated with the original vessel diameter, in the penumbra region. The sO2 of vessels in the penumbra region also dropped below normal range after focal ischemia. PMID:27699105

  15. RGB visible light communication using mobile-phone camera and multi-input multi-output.

    PubMed

    Liang, Kevin; Chow, Chi-Wai; Liu, Yang

    2016-05-01

    Red, green, blue (RGB) light-emitting-diodes (LEDs) are used to increase the visible light communication (VLC) transmission capacity via wavelength-division-multiplexing (WDM), and the color image sensor in mobile phone is used to separate different color signals via a color filter array. However, due to the wide optical bandwidths of the color filters, there is a high spectral overlap among different channels, and a high inter-channel interference (ICI) happens. Here, we propose and demonstrate an RGB VLC transmission using CMOS image sensor with multi-input multi-output (MIMO) technique to mitigate the ICI and retrieve the three independent color channels in the rolling shutter pattern. Data pattern extinction-ratio (ER) enhancement and thresholding are deployed.

  16. Astronomical instruments.

    NASA Astrophysics Data System (ADS)

    Rai, R. N.

    Indian astronomers have devised a number of instruments and the most important of these is the armillary sphere. The earliest armillary spheres were very simple instruments. Ptolemy in his Almagest enumerates at least three. The simplest of all was the equinoctial armilla. They had also the solstitial armilla which was a double ring, erected in the plane of the meridian with a rotating inner circle. This was used to measure the solar altitude.

  17. Astronomical superhighways

    NASA Astrophysics Data System (ADS)

    Leach, D. C.

    1995-08-01

    The expansion of data supply has been prolific over the past decade. Publishers of text are only just beginning to consider what the aim of their publications should be in the light of competition from computer databases. Increasingly sources of data are becoming linked into a global network. The modem has revolutionised the way many astronomers interact with the outside world and each other. Access to data sources world wide can now be undertaken with a simple telephone call and a desktop computer.

  18. Toxicity of Chlorophyllin against Lymnaea acuminata at Different Wavelengths of Visible Light.

    PubMed

    Chaturvedi, Divya; Singh, Vinay Kumar

    2016-08-01

    Fasciolosis is a water and food-borne disease caused by the liver fluke Fasciola hepatica and Fasciola gigantica. This disease is widespread in different parts of the world. Lymnaeidae and Planorbidae snails are the intermediate hosts of these flukes. Snail population management is a good tool to control fasciolosis because gastropods represent the weakest link in the life-cycle of trematodes. Chlorophyll can be extracted from any green plant. Chlorophyllin was prepared from spinach in 100% ethanol by using different types of chemicals. The chlorophyll obtained from spinach was transformed into water-soluble chlorophyllin. In the present paper, toxicity of chlorophyllin against the snail Lymnaea acuminata was time and concentration dependent. The toxicity of extracted and pure chlorophyllin at continuous 4 h exposure of sunlight was highest with lethal concentration (LC50) of 331.01 mg/L and 2.60 mg/L, respectively, than discontinuous exposure of sunlight up to 8 h with LC50 of 357.04 mg/L and 4.94 mg/L, respectively. Toxicity of extracted chlorophyllin was noted in the presence of different monochromatic visible lights. The highest toxicity was noted in yellow light (96 h, LC50 392.77 mg/L) and the lowest in green light (96 h, LC50 833.02 mg/L). Chlorophyllin in combination with solar radiation or different wavelength of monochromatic visible lights may become a latent remedy against the snail L. acuminata. It was demonstrated that chlorophyllin was more toxic in sunlight. Chlorophyllin is ecologically safe and more economical than synthetic molluscicides which have the potential to control the incidence of fasciolosis in developing countries. PMID:27688849

  19. Visible light degradation of Orange II using xCuyOz/TiO2 heterojunctions.

    PubMed

    Helaïli, N; Bessekhouad, Y; Bouguelia, A; Trari, M

    2009-08-30

    Cu(2)O/TiO(2), Cu/Cu(2)O/TiO(2) and Cu/Cu(2)O/CuO/TiO(2) heterojunctions were prepared and studied for their potential application as photocatalysts able to induce high performance under visible light. Orange II was used as a representative dye molecule. The effect of the amount and composition of the photosensitizers toward the activation of TiO(2) was studied. In each case, the global mechanism of Inter Particle Electrons Injection (IPEI) was discussed. The highest photocatalytic activity was observed for the system Cu/Cu(2)O/CuO (MB2 catalyst) under visible light (t(1/2)=24 min, k=159.7 x 10(-3)min(-1)) and for the heterojunction cascade Cu/Cu(2)O/CuO/TiO(2) (MB2 (50%)/TiO(2)) under UV-vis light (t(1/2)=4 min, k=1342 x 10(-3)min(-1)). In the last case, the high performance was attributed firstly to the electromotive forces developed under this configuration in which CuO energy bands mediate the electrons transfer from Cu(2)O to TiO(2). The formation of monobloc sensitizers also accounts for the decrease of the probability of the charges lost. It was demonstrated that "Cu(2)O/CuO" governs the capability of the heterojunction cascade and Cu does not play a significant role regardless of the heterojunction cascade efficiency. The electrical energy consumption per order of magnitude for photocatalytic degradation of Orange II was investigated for some representative catalytic systems. Visible/MB2 and UV/vis MB2 (50%)/TiO(2) exhibited respectively 0.340 and 0.05 kW hm(-3) demonstrating the high efficiency of the systems. PMID:19307056

  20. Toxicity of Chlorophyllin against Lymnaea acuminata at Different Wavelengths of Visible Light.

    PubMed

    Chaturvedi, Divya; Singh, Vinay Kumar

    2016-08-01

    Fasciolosis is a water and food-borne disease caused by the liver fluke Fasciola hepatica and Fasciola gigantica. This disease is widespread in different parts of the world. Lymnaeidae and Planorbidae snails are the intermediate hosts of these flukes. Snail population management is a good tool to control fasciolosis because gastropods represent the weakest link in the life-cycle of trematodes. Chlorophyll can be extracted from any green plant. Chlorophyllin was prepared from spinach in 100% ethanol by using different types of chemicals. The chlorophyll obtained from spinach was transformed into water-soluble chlorophyllin. In the present paper, toxicity of chlorophyllin against the snail Lymnaea acuminata was time and concentration dependent. The toxicity of extracted and pure chlorophyllin at continuous 4 h exposure of sunlight was highest with lethal concentration (LC50) of 331.01 mg/L and 2.60 mg/L, respectively, than discontinuous exposure of sunlight up to 8 h with LC50 of 357.04 mg/L and 4.94 mg/L, respectively. Toxicity of extracted chlorophyllin was noted in the presence of different monochromatic visible lights. The highest toxicity was noted in yellow light (96 h, LC50 392.77 mg/L) and the lowest in green light (96 h, LC50 833.02 mg/L). Chlorophyllin in combination with solar radiation or different wavelength of monochromatic visible lights may become a latent remedy against the snail L. acuminata. It was demonstrated that chlorophyllin was more toxic in sunlight. Chlorophyllin is ecologically safe and more economical than synthetic molluscicides which have the potential to control the incidence of fasciolosis in developing countries.

  1. Toxicity of Chlorophyllin against Lymnaea acuminata at Different Wavelengths of Visible Light

    PubMed Central

    Chaturvedi, Divya; Singh, Vinay Kumar

    2016-01-01

    Fasciolosis is a water and food-borne disease caused by the liver fluke Fasciola hepatica and Fasciola gigantica. This disease is widespread in different parts of the world. Lymnaeidae and Planorbidae snails are the intermediate hosts of these flukes. Snail population management is a good tool to control fasciolosis because gastropods represent the weakest link in the life-cycle of trematodes. Chlorophyll can be extracted from any green plant. Chlorophyllin was prepared from spinach in 100% ethanol by using different types of chemicals. The chlorophyll obtained from spinach was transformed into water-soluble chlorophyllin. In the present paper, toxicity of chlorophyllin against the snail Lymnaea acuminata was time and concentration dependent. The toxicity of extracted and pure chlorophyllin at continuous 4 h exposure of sunlight was highest with lethal concentration (LC50) of 331.01 mg/L and 2.60 mg/L, respectively, than discontinuous exposure of sunlight up to 8 h with LC50 of 357.04 mg/L and 4.94 mg/L, respectively. Toxicity of extracted chlorophyllin was noted in the presence of different monochromatic visible lights. The highest toxicity was noted in yellow light (96 h, LC50 392.77 mg/L) and the lowest in green light (96 h, LC50 833.02 mg/L). Chlorophyllin in combination with solar radiation or different wavelength of monochromatic visible lights may become a latent remedy against the snail L. acuminata. It was demonstrated that chlorophyllin was more toxic in sunlight. Chlorophyllin is ecologically safe and more economical than synthetic molluscicides which have the potential to control the incidence of fasciolosis in developing countries. PMID:27688849

  2. Bismuth titanate pyrochlore microspheres: Directed synthesis and their visible light photocatalytic activity

    SciTech Connect

    Hou, Jungang; Jiao, Shuqiang; Zhu, Hongmin; Kumar, R.V.

    2011-01-15

    Bismuth titanates, Bi{sub 2}Ti{sub 2}O{sub 7} (BIT), with well-defined spherical structures were synthesized by a facile hydrothermal process without the use of any surfactant or template. XRD and SEM studies have shown that spheres could be fabricated in high yields by simply manipulating the concentrations of hydroxide ions. In this case, hydroxide ions seem to play a pivotal role in controlling the formation of seeds and growth rates of the BIT particles. On the basis of structural analysis of samples obtained at different concentrations of OH{sup -}, we also proposed a plausible mechanism to account for the formation of these distinctive morphologies under different conditions. The as-prepared BIT microspheres with good stability exhibited higher photocatalytic activities in the degradation of Rhodamine B (RhB) under visible light irradiation than that in commercial P25 TiO{sub 2}. Furthermore, the enhanced photocatalytic performance for RhB degradation was also investigated with assistance of a small amount of H{sub 2}O{sub 2}. -- Graphical abstract: Bismuth titanate pyrochlore microspheres were synthesized by a facile hydrothermal process without the use of any surfactant or template, and the effects of concentration of OH{sup -} on the diameter of microspheres, growth mechanism and photocatalytic properties were investigated. Display Omitted Research Highlights: Bismuth titanate pyrochlore microspheres with different diameters were synthesized by a facile hydrothermal process without the use of any surfactant or template. The BIT microspheres with good stability exhibited higher photocatalytic activities in the degradation of RhB under visible light irradiation than that in commercial P25 TiO{sub 2}. Further enhanced photocatalytic activity for RhB degradation was ascribed to the assistance of a small amount of H{sub 2}O{sub 2}.

  3. Quantum dots/silica/polymer nanocomposite films with high visible light transmission and UV shielding properties

    NASA Astrophysics Data System (ADS)

    Mumin, Md Abdul; Xu, William Z.; Charpentier, Paul A.

    2015-08-01

    The dispersion of light-absorbing inorganic nanomaterials in transparent plastics such as poly(ethylene-co-vinyl acetate) (PEVA) is of enormous current interest in emerging solar materials, including photovoltaic (PV) modules and commercial greenhouse films. Nanocrystalline semiconductor or quantum dots (QDs) have the potential to absorb UV light and selectively emit visible light, which can control plant growth in greenhouses or enhance PV panel efficiencies. This work provides a new and simple approach for loading mesoporous silica-encapsulated QDs into PEVA. Highly luminescent CdS and CdS-ZnS core-shell QDs with 5 nm size were synthesized using a modified facile approach based on pyrolysis of the single-molecule precursors and capping the CdS QDs with a thin layer of ZnS. To make both the bare and core-shell structure QDs more resistant against photochemical reactions, a mesoporous silica layer was grown on the QDs through a reverse microemulsion technique based on hydrophobic interactions. By careful experimental tuning, this encapsulation technique enhanced the quantum yield (˜65%) and photostability compared to the bare QDs. Both the encapsulated bare and core-shell QDs were then melt-mixed with EVA pellets using a mini twin-screw extruder and pressed into thin films with controlled thickness. The results demonstrated for the first time that mesoporous silica not only enhanced the quantum yield and photostability of the QDs but also improved the compatibility and dispersibility of QDs throughout the PEVA films. The novel light selective films show high visible light transmission (˜90%) and decreased UV transmission (˜75%).

  4. Efficient Visible-Light Photocatalytic Properties in Low-Temperature Bi-Nb-O System Photocatalysts.

    PubMed

    Zhai, Haifa; Shang, Shuying; Zheng, Liuyang; Li, Panpan; Li, Haiqin; Luo, Hongying; Kong, Jizhou

    2016-12-01

    Low-temperature Bi-Nb-O system photocatalysts were prepared by a citrate method using homemade water-soluble niobium precursors. The structures, morphologies, and optical properties of Bi-Nb-O system photocatalysts with different compositions were investigated deeply. All the Bi-Nb-O powders exhibit appreciably much higher photocatalytic efficiency of photo-degradation of methyl violet (MV), especially for Bi-Nb-O photocatalysts sintered at 750 °C (BNO750), only 1.5 h to completely decompose MV, and the obtained first-order rate constant (k) is 1.94/h. A larger degradation rate of Bi-Nb-O photocatalysts sintered at 550 °C (BNO550) can be attributed to the synergistic effect between β-BiNbO4 and Bi5Nb3O15. Bi5Nb3O15 with small particle size on β-BiNbO4 surface can effectively short the diffuse length of electron. BNO750 exhibits the best photocatalytic properties under visible-light irradiation, which can be attributed to its better crystallinity and the synergistic effect between β-BiNbO4 and α-BiNbO4. The small amount of α-BiNbO4 loading on surface of β-BiNbO4 can effectively improve the electron and hole segregation and migration. Holes are the main active species of Bi-Nb-O system photocatalysts in aqueous solution under visible-light irradiation. PMID:27576523

  5. Toxicity of Chlorophyllin against Lymnaea acuminata at Different Wavelengths of Visible Light

    PubMed Central

    Chaturvedi, Divya; Singh, Vinay Kumar

    2016-01-01

    Fasciolosis is a water and food-borne disease caused by the liver fluke Fasciola hepatica and Fasciola gigantica. This disease is widespread in different parts of the world. Lymnaeidae and Planorbidae snails are the intermediate hosts of these flukes. Snail population management is a good tool to control fasciolosis because gastropods represent the weakest link in the life-cycle of trematodes. Chlorophyll can be extracted from any green plant. Chlorophyllin was prepared from spinach in 100% ethanol by using different types of chemicals. The chlorophyll obtained from spinach was transformed into water-soluble chlorophyllin. In the present paper, toxicity of chlorophyllin against the snail Lymnaea acuminata was time and concentration dependent. The toxicity of extracted and pure chlorophyllin at continuous 4 h exposure of sunlight was highest with lethal concentration (LC50) of 331.01 mg/L and 2.60 mg/L, respectively, than discontinuous exposure of sunlight up to 8 h with LC50 of 357.04 mg/L and 4.94 mg/L, respectively. Toxicity of extracted chlorophyllin was noted in the presence of different monochromatic visible lights. The highest toxicity was noted in yellow light (96 h, LC50 392.77 mg/L) and the lowest in green light (96 h, LC50 833.02 mg/L). Chlorophyllin in combination with solar radiation or different wavelength of monochromatic visible lights may become a latent remedy against the snail L. acuminata. It was demonstrated that chlorophyllin was more toxic in sunlight. Chlorophyllin is ecologically safe and more economical than synthetic molluscicides which have the potential to control the incidence of fasciolosis in developing countries.

  6. Vitamin B2 in nanoscopic environments under visible light: photosensitized antioxidant or phototoxic drug?

    PubMed

    Chaudhuri, Siddhi; Batabyal, Subrata; Polley, Nabarun; Pal, Samir Kumar

    2014-06-01

    Vitamin B2 has been studied as a conventional antioxidant (in the dark) since its discovery in 1926. The effect of visible light on vitamin B2-containing food has a long history of scientific investigation. Although photodegradation of the vitamin producing several photoproducts is evident in certain experimental conditions, phototoxicity revealing an additional oxidative stress in the medium is also clear from some reports. Here we report the photosensitized antioxidant effect of the vitamin, which is found to be greater than 2 orders of magnitude more efficient than that in the dark condition. The photoinduced antioxidant property is apparently paradoxical compared to the reported phototoxic effect of the vitamin. Our present study unravels a unified picture underlying the difference in character of vitamin B2 under visible light irradiation. UV-vis absorption and fluorescence studies in a number of physiologically relevant nanoscopic environments (micelles and reverse micelles) reveal the antioxidant activity to a well-known oxidative stress marker 2,2-diphenyl-1-picrylhydrazyl (DPPH) as well as a phototoxicity effect resulting in self-degradation of the vitamin. Picosecond-resolved Förster resonance energy transfer (FRET) from the vitamin to the marker DPPH in the biomimetic environments clearly reveals the role of proximity of an oxidizing agent in the photoinduced effect of the vitamin. Our systematic and detailed studies unravel a simple picture of the mechanistic pathway of the photosensitized vitamin in the physiologically important environments leading to the antioxidant/phototoxicity effect of the vitamin. The excited vitamin transfers its electron to the oxidizing agent in proximity for the antioxidant effect, but otherwise it employs oxygen to generate reactive oxygen species (ROS), resulting in phototoxicity/self-degradation.

  7. Efficient Visible-Light Photocatalytic Properties in Low-Temperature Bi-Nb-O System Photocatalysts.

    PubMed

    Zhai, Haifa; Shang, Shuying; Zheng, Liuyang; Li, Panpan; Li, Haiqin; Luo, Hongying; Kong, Jizhou

    2016-12-01

    Low-temperature Bi-Nb-O system photocatalysts were prepared by a citrate method using homemade water-soluble niobium precursors. The structures, morphologies, and optical properties of Bi-Nb-O system photocatalysts with different compositions were investigated deeply. All the Bi-Nb-O powders exhibit appreciably much higher photocatalytic efficiency of photo-degradation of methyl violet (MV), especially for Bi-Nb-O photocatalysts sintered at 750 °C (BNO750), only 1.5 h to completely decompose MV, and the obtained first-order rate constant (k) is 1.94/h. A larger degradation rate of Bi-Nb-O photocatalysts sintered at 550 °C (BNO550) can be attributed to the synergistic effect between β-BiNbO4 and Bi5Nb3O15. Bi5Nb3O15 with small particle size on β-BiNbO4 surface can effectively short the diffuse length of electron. BNO750 exhibits the best photocatalytic properties under visible-light irradiation, which can be attributed to its better crystallinity and the synergistic effect between β-BiNbO4 and α-BiNbO4. The small amount of α-BiNbO4 loading on surface of β-BiNbO4 can effectively improve the electron and hole segregation and migration. Holes are the main active species of Bi-Nb-O system photocatalysts in aqueous solution under visible-light irradiation.

  8. Quantum dots/silica/polymer nanocomposite films with high visible light transmission and UV shielding properties.

    PubMed

    Mumin, Md Abdul; Xu, William Z; Charpentier, Paul A

    2015-08-01

    The dispersion of light-absorbing inorganic nanomaterials in transparent plastics such as poly(ethylene-co-vinyl acetate) (PEVA) is of enormous current interest in emerging solar materials, including photovoltaic (PV) modules and commercial greenhouse films. Nanocrystalline semiconductor or quantum dots (QDs) have the potential to absorb UV light and selectively emit visible light, which can control plant growth in greenhouses or enhance PV panel efficiencies. This work provides a new and simple approach for loading mesoporous silica-encapsulated QDs into PEVA. Highly luminescent CdS and CdS-ZnS core-shell QDs with 5 nm size were synthesized using a modified facile approach based on pyrolysis of the single-molecule precursors and capping the CdS QDs with a thin layer of ZnS. To make both the bare and core-shell structure QDs more resistant against photochemical reactions, a mesoporous silica layer was grown on the QDs through a reverse microemulsion technique based on hydrophobic interactions. By careful experimental tuning, this encapsulation technique enhanced the quantum yield (∼65%) and photostability compared to the bare QDs. Both the encapsulated bare and core-shell QDs were then melt-mixed with EVA pellets using a mini twin-screw extruder and pressed into thin films with controlled thickness. The results demonstrated for the first time that mesoporous silica not only enhanced the quantum yield and photostability of the QDs but also improved the compatibility and dispersibility of QDs throughout the PEVA films. The novel light selective films show high visible light transmission (∼90%) and decreased UV transmission (∼75%). PMID:26177824

  9. Vitamin B2 in nanoscopic environments under visible light: photosensitized antioxidant or phototoxic drug?

    PubMed

    Chaudhuri, Siddhi; Batabyal, Subrata; Polley, Nabarun; Pal, Samir Kumar

    2014-06-01

    Vitamin B2 has been studied as a conventional antioxidant (in the dark) since its discovery in 1926. The effect of visible light on vitamin B2-containing food has a long history of scientific investigation. Although photodegradation of the vitamin producing several photoproducts is evident in certain experimental conditions, phototoxicity revealing an additional oxidative stress in the medium is also clear from some reports. Here we report the photosensitized antioxidant effect of the vitamin, which is found to be greater than 2 orders of magnitude more efficient than that in the dark condition. The photoinduced antioxidant property is apparently paradoxical compared to the reported phototoxic effect of the vitamin. Our present study unravels a unified picture underlying the difference in character of vitamin B2 under visible light irradiation. UV-vis absorption and fluorescence studies in a number of physiologically relevant nanoscopic environments (micelles and reverse micelles) reveal the antioxidant activity to a well-known oxidative stress marker 2,2-diphenyl-1-picrylhydrazyl (DPPH) as well as a phototoxicity effect resulting in self-degradation of the vitamin. Picosecond-resolved Förster resonance energy transfer (FRET) from the vitamin to the marker DPPH in the biomimetic environments clearly reveals the role of proximity of an oxidizing agent in the photoinduced effect of the vitamin. Our systematic and detailed studies unravel a simple picture of the mechanistic pathway of the photosensitized vitamin in the physiologically important environments leading to the antioxidant/phototoxicity effect of the vitamin. The excited vitamin transfers its electron to the oxidizing agent in proximity for the antioxidant effect, but otherwise it employs oxygen to generate reactive oxygen species (ROS), resulting in phototoxicity/self-degradation. PMID:24814086

  10. Quantum dots/silica/polymer nanocomposite films with high visible light transmission and UV shielding properties.

    PubMed

    Mumin, Md Abdul; Xu, William Z; Charpentier, Paul A

    2015-08-01

    The dispersion of light-absorbing inorganic nanomaterials in transparent plastics such as poly(ethylene-co-vinyl acetate) (PEVA) is of enormous current interest in emerging solar materials, including photovoltaic (PV) modules and commercial greenhouse films. Nanocrystalline semiconductor or quantum dots (QDs) have the potential to absorb UV light and selectively emit visible light, which can control plant growth in greenhouses or enhance PV panel efficiencies. This work provides a new and simple approach for loading mesoporous silica-encapsulated QDs into PEVA. Highly luminescent CdS and CdS-ZnS core-shell QDs with 5 nm size were synthesized using a modified facile approach based on pyrolysis of the single-molecule precursors and capping the CdS QDs with a thin layer of ZnS. To make both the bare and core-shell structure QDs more resistant against photochemical reactions, a mesoporous silica layer was grown on the QDs through a reverse microemulsion technique based on hydrophobic interactions. By careful experimental tuning, this encapsulation technique enhanced the quantum yield (∼65%) and photostability compared to the bare QDs. Both the encapsulated bare and core-shell QDs were then melt-mixed with EVA pellets using a mini twin-screw extruder and pressed into thin films with controlled thickness. The results demonstrated for the first time that mesoporous silica not only enhanced the quantum yield and photostability of the QDs but also improved the compatibility and dispersibility of QDs throughout the PEVA films. The novel light selective films show high visible light transmission (∼90%) and decreased UV transmission (∼75%).

  11. An enhancing effect of visible light and UV radiation on phenolic compounds and various antioxidants in broad bean seedlings

    PubMed Central

    Hasaneen, Mohammed Naguib Abdel-Ghany; Abdel-Aziz, Heba Mahmoud Mohammed

    2010-01-01

    Exposure of dark- or ambient visible light-grown broad bean seedlings to low (LL) and high (HL) visible light intensities, UV-A or UV-C, either alone or in combination, induced significant increases in total phenolic compounds as well as in anthocyanins content, throughout the germination period, as compared with the respective levels in control seedlings. In general, as compared with control levels, exposure of both dark- or light-grown broad bean seedlings to LL, HL, UV-A or UV-C, induced significant increases in the contents of non-enzymatic antioxidants (total ascorbate; ASA-DASA and total glutathione; GSSG-GSH) and enzymatic antioxidant activities (superoxide dismutase; SOD, catalase; CAT, ascorbate peroxidase; APO and glutathione reductase; GR). The obtained results are discussed in relation to induced mechanisms of protection and repair from the inevitable exposure to damaging visible light and UV radiation. PMID:20505357

  12. Degradation of organic dyes via bismuth silver oxide initiated direct oxidation coupled with sodium bismuthate based visible light photocatalysis.

    PubMed

    Yu, Kai; Yang, Shaogui; Liu, Cun; Chen, Hongzhe; Li, Hui; Sun, Cheng; Boyd, Stephen A

    2012-07-01

    Organic dye degradation was achieved via direct oxidation by bismuth silver oxide coupled with visible light photocatalysis by sodium bismuthate. Crystal violet dye decomposition by each reagent proceeded via two distinct pathways, each involving different active oxygen species. A comparison of each treatment method alone and in combination demonstrated that using the combined methods in sequence achieved a higher degree of degradation, and especially mineralization, than that obtained using either method alone. In the combined process direct oxidation acts as a pretreatment to rapidly bleach the dye solution which substantially facilitates subsequent visible light photocatalytic processes. The integrated sequential direct oxidation and visible light photocatalysis are complementary manifesting a > 100% increase in TOC removal, compared to either isolated method. The combined process is proposed as a novel and effective technology based on one primary material, sodium bismuthate, for treating wastewaters contaminated by high concentrations of organic dyes.

  13. Silver Phosphate Based Plasmonic Photocatalyst: Highly Active Visible-Light Photocatalytic Property and Photosensitized Degradation of Pollutants

    NASA Astrophysics Data System (ADS)

    Lei, Yongqian; Wang, Guanhua; Guo, Pengran; Song, Huacan

    2012-11-01

    A stable silver phosphate based plasmonic photocatalyst (Ag-Ag3PO4) was successfully fabricated, which can drive catalytic reaction under low-intensity visible light. The synthesized plasmonic photocatalyst shows high performance and stability on the photodegradation of RhB under visible-light irradiation, and represents obviously enhanced photocatalytic activity than the pure Ag3PO4 sample. The photosensitization process was carried out in the photodegradation of 2,4-DCP and RhB mixture, of which the photocatalyst shows the enhancement activity for 2,4-DCP while weaker for RhB. The investigation is likely to open up a new sight for the preparation of high efficient and stable plasmonic photocatalysts which utilizes visible light.

  14. Enhanced Visible-Light Photocatalytic Activity of C/Ce-Codoped ZnO Nanoellipsoids Synthesized by Hydrothermal Method

    NASA Astrophysics Data System (ADS)

    Ha, Luu Thi Viet; Dai, Luu Minh; Nhiem, Dao Ngoc; Van Cuong, Nguyen

    2016-08-01

    C/Ce-codoped ZnO nanomaterial has been synthesized by a hydrothermal method and its physical properties and characterization investigated using thermogravimetric and differential thermal analysis (TG-DTA), x-ray diffraction (XRD) analysis, Fourier-transform infrared (FTIR) spectroscopy, energy-dispersive x-ray (EDX) spectroscopy, UV-Vis diffuse reflectance spectroscopy, and scanning electron microscopy (SEM). The photocatalytic activity of the nanomaterial was examined using methylene blue as organic dye under visible-light source. The results show that the C/Ce-codoped ZnO nanomaterial exhibited higher photocatalytic activity under visible-light irradiation compared with undoped ZnO, Ce-doped ZnO or C-doped ZnO nanomaterials. Such enhancement of the photocatalytic activity of C/Ce-codoped ZnO under visible-light irradiation suggests that these nanoparticles might have good applications in optoelectronics and wastewater treatment.

  15. Facet-selective photodeposition of gold nanoparticles on faceted ZnO crystals for visible light photocatalysis.

    PubMed

    Wang, Xuewen; Wang, Wuyou; Miao, Yuanquan; Feng, Gang; Zhang, Rongbin

    2016-08-01

    Hexagonal prism-like ZnO crystals dominated with polar facets were synthesized using a hydrothermal method. The Gold (Au) nanoparticles were selectively photodeposited on the polar surfaces of faceted ZnO crystals as a result of anisotropic photocatalytic activities of the polar and nonpolar facets. The size of Au nanoparticles uniformly dispersed on the polar facets increased with increasing Au-loading amount. These Au-loaded ZnO crystals showed an additional visible light absorption band from 400nm to 800nm. The 0.1wt% Au-loaded ZnO crystals with visible light absorption peak at approximately 690nm exhibited the highest photocatalytic activity under visible light irradiation.

  16. Facet-selective photodeposition of gold nanoparticles on faceted ZnO crystals for visible light photocatalysis.

    PubMed

    Wang, Xuewen; Wang, Wuyou; Miao, Yuanquan; Feng, Gang; Zhang, Rongbin

    2016-08-01

    Hexagonal prism-like ZnO crystals dominated with polar facets were synthesized using a hydrothermal method. The Gold (Au) nanoparticles were selectively photodeposited on the polar surfaces of faceted ZnO crystals as a result of anisotropic photocatalytic activities of the polar and nonpolar facets. The size of Au nanoparticles uniformly dispersed on the polar facets increased with increasing Au-loading amount. These Au-loaded ZnO crystals showed an additional visible light absorption band from 400nm to 800nm. The 0.1wt% Au-loaded ZnO crystals with visible light absorption peak at approximately 690nm exhibited the highest photocatalytic activity under visible light irradiation. PMID:27156091

  17. Preparation of mesoporous CdS-containing TiO{sub 2} film and enhanced visible light photocatalytic property

    SciTech Connect

    Zhu, Yanmei; Wang, Renliang Zhang, Wenping; Ge, Haiyan; Wang, Xiaopeng; Li, Li

    2015-01-15

    Highlights: • Well-dispersed distribution of CdS nanoparticles inside of TiO{sub 2} mesoporous structures was fabricated. • The sensitization of CdS nanoparticles significantly extends the response of TiO{sub 2} mesoporous film in the visible region. • An improved visible light photocatalytic activity was observed by the CdS–MTF. - Abstract: Mesoporous TiO{sub 2} films containing CdS nanocrystals were successfully fabricated by a two-step process of successive ionic layer adsorption and reaction (SILAR) technique and a solvothermal method followed by annealing. The distribution of CdS nanoparticles in the inner structures of the TiO{sub 2} mesoporous films is confirmed by field emission scanning electron microscope. The CdS modification of the mesoporous films results in an increase in the visible light adsorption, and exhibits more excellent photocatalytic degradation of methyl orange (MO) under visible light irradiation.

  18. Modification of Wide-Band-Gap Oxide Semiconductors with Cobalt Hydroxide Nanoclusters for Visible-Light Water Oxidation.

    PubMed

    Maeda, Kazuhiko; Ishimaki, Koki; Tokunaga, Yuki; Lu, Daling; Eguchi, Miharu

    2016-07-11

    Cobalt-based compounds, such as cobalt(II) hydroxide, are known to be good catalysts for water oxidation. Herein, we report that such cobalt species can also activate wide-band-gap semiconductors towards visible-light water oxidation. Rutile TiO2 powder, a well-known wide-band-gap semiconductor, was capable of harvesting visible light with wavelengths of up to 850 nm, and thus catalyzed water oxidation to produce molecular oxygen, when decorated with cobalt(II) hydroxide nanoclusters. To the best of our knowledge, this system constitutes the first example that a particulate photocatalytic material that is capable of water oxidation upon excitation by visible light can also operate at such long wavelengths, even when it is based on earth-abundant elements only. PMID:27225394

  19. Synthesis and photocatalytic activity of mesoporous cerium doped TiO{sub 2} as visible light sensitive photocatalyst

    SciTech Connect

    Aman, Noor; Satapathy, P.K.; Mishra, T.; Mahato, M.; Das, N.N.

    2012-02-15

    Graphical abstract: Cerium doped titania having optimum 5 wt% of cerium can decompose methylene blue and reduce selenium (IV) efficiently under visible light. Highlights: Black-Right-Pointing-Pointer Effect of cerium doping on the surface properties and visible light mediated photocatalytic reaction is studied. Black-Right-Pointing-Pointer Cerium doping increases the anatase phase stability, surface area (up to 137 m{sup 2}/g) and visible light absorption. Black-Right-Pointing-Pointer Importance of Ce{sup 3+}/Ce{sup 4+}, oxygen vacancy, surface area and crystallinity is correlated with improved catalytic activity. Black-Right-Pointing-Pointer Material with 5 wt% Ce is found to be most active photocatalyst for methylene blue decomposition and Se (IV) reduction. -- Abstract: Cerium doped titania materials were synthesized varying the cerium concentration from 0 to 10 wt%. Materials are characterised by XRD, TEM, XPS and N{sub 2} adsorption desorption method. Surface area and visible light absorption substantially increases and crystallite size decreases with the increasing cerium content. Cerium doping stabilizes the anatase phase and surface area even at 600 Degree-Sign C calcination. Photocatalytic activity towards methylene blue decomposition and selenium (IV) reduction is found to increase with the cerium content up to 5 wt% and then decreases. Materials calcined at 600 Degree-Sign C shows better activity than that calcined at 400 Degree-Sign C, even though surface area decreases. Anatase crystallinity mostly decides the photocatalytic activity rather than only surface area. It can be concluded that the optimum visible light absorption and oxygen vacancy with 5% cerium doping enhances the photocatalytic activity. In addition photocatalytic performance is found to depend on the presence of Ce{sup 4+}/Ce{sup 3+} rather than only visible light absorption.

  20. Visible-light-promoted iminyl-radical formation from acyl oximes: a unified approach to pyridines, quinolines, and phenanthridines.

    PubMed

    Jiang, Heng; An, Xiaode; Tong, Kun; Zheng, Tianyi; Zhang, Yan; Yu, Shouyun

    2015-03-23

    A unified strategy involving visible-light-induced iminyl-radical formation has been established for the construction of pyridines, quinolines, and phenanthridines from acyl oximes. With fac-[Ir(ppy)3 ] as a photoredox catalyst, the acyl oximes were converted by 1 e(-) reduction into iminyl radical intermediates, which then underwent intramolecular homolytic aromatic substitution (HAS) to give the N-containing arenes. These reactions proceeded with a broad range of substrates at room temperature in high yield. This strategy of visible-light-induced iminyl-radical formation was successfully applied to a five-step concise synthesis of benzo[c]phenanthridine alkaloids.

  1. All-silicon Michelson instrument on chip: Distance and surface profile measurement and prospects for visible light spectrometry

    SciTech Connect

    Malak, M.; Marty, F.; Bourouina, T.; Nouira, H.; Vailleau, G.

    2013-04-08

    A miniature Michelson interferometer is analyzed theoretically and experimentally. The fabricated micro-interferometer is incorporated at the tip of a monolithic silicon probe to achieve contactless distance measurements and surface profilometry. For infrared operation, two approaches are studied, based on the use of monochromatic light and wavelength sweep, respectively. A theoretical model is devised to depict the system characteristics taking into account Gaussian beam divergence and light spot size. Furthermore, preliminary results using visible light demonstrate operation of the probe as a visible light spectrometer, despite silicon absorbance, thanks to the micrometer thickness involved in the beam splitter.

  2. Photochemical Synthesis of Complex Carbazoles: Evaluation of Electronic Effects in Both UV- and Visible-Light Methods in Continuous Flow.

    PubMed

    Hernandez-Perez, Augusto C; Caron, Antoine; Collins, Shawn K

    2015-11-01

    An evaluation of both a visible-light- and UV-light-mediated synthesis of carbazoles from various triarylamines with differing electronic properties under continuous-flow conditions has been conducted. In general, triarylamines bearing electron-rich groups tend to produce higher yields than triarylamines possessing electron-withdrawing groups. The incorporation of nitrogen-based heterocycles, as well as halogen-containing arenes in carbazole skeletons, was well tolerated, and often synthetically useful complementarity was observed between the UV-light and visible-light (photoredox) methods.

  3. A visible-light-driven composite photocatalyst of TiO2 nanotube arrays and graphene quantum dots.

    PubMed

    Chan, Donald K L; Cheung, Po Ling; Yu, Jimmy C

    2014-01-01

    TiO2 nanotube arrays are well-known efficient UV-driven photocatalysts. The incorporation of graphene quantum dots could extend the photo-response of the nanotubes to the visible-light range. Graphene quantum dot-sensitized TiO2 nanotube arrays were synthesized by covalently coupling these two materials. The product was characterized by Fourier-transform infrared spectrometry (FTIR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), thermogravimetric analysis (TGA) and UV-vis absorption spectroscopy. The product exhibited high photocatalytic performance in the photodegradation of methylene blue and enhanced photocurrent under visible light irradiation. PMID:24991506

  4. Visible-light-responsive multielectron redox catalysis of lacunary polyoxometalates induced by substrate coordination to their lacuna.

    PubMed

    Suzuki, Kosuke; Jeong, Jinu; Yamaguchi, Kazuya; Mizuno, Noritaka

    2015-01-01

    We describe herein the efficient visible-light-responsive polyoxometalate-based multielectron photoredox catalysis induced by in situ coordination of alcohols to the lacuna of TBA4 H4 [γ-SiW10 O36 ] (I, TBA=tetra-n-butylammonium). The coordination of alcohols to the lacuna of I generated a new highest occupied molecular orbital as the electron donor level and enabled the visible-light-responsive multielectron transfer from alcohols to I, which could be utilized for aerobic alcohol oxidation and one-pot synthesis of N-arylimines starting from nitroarenes and primary alcohols.

  5. Ancient Chinese Astronomical Technologies

    NASA Astrophysics Data System (ADS)

    Walsh, Jennifer Robin

    2004-05-01

    I am interested in the astronomical advances of the Ancient Chinese in measuring the solar day. Their development of gnomon & ruler, sundial, and water clock apparatuses enabled Chinese astronomers to measure the annual solar orbit and solar day more precisely than their contemporaries. I have built one of each of these devices to use in collecting data from Olympia, Washington. I will measure the solar day in the Pacific Northwest following the methodology of the ancient Chinese. I will compare with my data, the available historical Chinese astronomical records and current records from the United States Naval Observatory Master Clock. I seek to understand how ancient Chinese investigations into solar patterns enabled them to make accurate predictions about the movement of the celestial sphere and planets, and to develop analytic tests of their theories. Mayall, R. Newton; Sundials: their construction and use. Dover Publications 2000 North, John; The Norton History of Astronomy and Cosmology W.W. Norton& Co. 1995 Zhentao Xu, David W. Pankenier, Yaotiao Jiang; East Asian archaeoastronomy : historical records of astronomical observations of China, Japan and Korea Published on behalf of the Earth Space Institute by Gordon and Breach Science Publishers, c2000

  6. Oxygen vacancies and intense luminescence in manganese loaded Zno microflowers for visible light water splitting

    NASA Astrophysics Data System (ADS)

    Sambandam, Balaji; Michael, Robin Jude Vimal; Manoharan, Periakaruppan T.

    2015-08-01

    ZnO nanorods and Mn/ZnO microflowers with nano-sized petals exhibit singly ionized oxygen vacancies, V+O. This is strongly supported by a green photoluminescence emission at 2.22 eV and an EPR g value of 1.953, both of which are suppressed greatly after annealing in an oxygen atmosphere. A strong red emission observed during exposure to X-rays reveals the presence of F+ centres as a consequence of the V+O. Mn/ZnO displayed enhanced H2 generation with visible light exposure, when compared to pure ZnO and annealed Mn/ZnO in the visible region, which directly correlated with the oxygen vacancy concentration. There is an interesting correlation between the intensities of the EPR lines at the g-value of 1.953 due to the oxygen vacancies, the intensity of light emitted from the exposure to X-rays, the intensity of the photoluminescence due to oxygen vacancies and the quantity of H2 produced by the photocatalytic effect when comparing the three different nanomaterials, viz. pure ZnO, Mn/ZnO before and after annealing, all having been made exactly by the same methodologies.ZnO nanorods and Mn/ZnO microflowers with nano-sized petals exhibit singly ionized oxygen vacancies, V+O. This is strongly supported by a green photoluminescence emission at 2.22 eV and an EPR g value of 1.953, both of which are suppressed greatly after annealing in an oxygen atmosphere. A strong red emission observed during exposure to X-rays reveals the presence of F+ centres as a consequence of the V+O. Mn/ZnO displayed enhanced H2 generation with visible light exposure, when compared to pure ZnO and annealed Mn/ZnO in the visible region, which directly correlated with the oxygen vacancy concentration. There is an interesting correlation between the intensities of the EPR lines at the g-value of 1.953 due to the oxygen vacancies, the intensity of light emitted from the exposure to X-rays, the intensity of the photoluminescence due to oxygen vacancies and the quantity of H2 produced by the

  7. Preparation and functionalization of a visible-light-excited europium complex-modified luminescent protein for cell imaging applications.

    PubMed

    Tian, Lu; Dai, Zhichao; Ye, Zhiqiang; Song, Bo; Yuan, Jingli

    2014-03-01

    Lanthanide complex-based luminescent bioprobes have shown great utility in a variety of time-resolved luminescence bioassays, but these bioprobes often require UV excitation and suffer from problems related to bioaffinity and biocompatibility for in vivo applications. In this work, a new visible-light-excited europium(III) complex with the maximum excitation wavelength over 400 nm, BHHBB-Eu(3+)-BPT {BHHBB: 1,2-bis[4'-(1'',1'',1'',2'',2'',3'',3''-heptafluoro-4'',6''-hexanedion-6''-yl)-benzyl]-benzene; BPT: 2-(N,N-diethylanilin-4-yl)-4,6-bis(pyrazol-1-yl)-1,3,5-triazine}, has been synthesized for the preparation of an artificial luminescent protein that can be used as a visible-light-excited luminescent bioprobe for cell imaging. By encapsulating BHHBB-Eu(3+)-BPT into apoferritin with a simple dissociation-reassembly method, the luminescent protein, Eu@AFt, with a maximum excitation peak at 420 nm and a long luminescence lifetime of 365 μs was fabricated and successfully used for visible-light-excited time-resolved luminescence cell imaging. Moreover, by conjugating a mitochondria-targeting molecule, (5-N-succinimidoxy-5-oxopentyl)-triphenylphosphonium bromide (SPTPP), onto the surface of Eu@AFt, a mitochondria-specifically-tracking luminescent probe, Eu@AFt-SPTPP, was further prepared and used for visible-light-excited confocal luminescence microscopy imaging to visualize the mitochondria of living cells.

  8. Visible light photocatalytic activity induced by Rh(III) modification on the surface of BiOCl

    NASA Astrophysics Data System (ADS)

    Hu, Jinli; Wu, Xin; Huang, Caijin; Fan, Wenjie; Qiu, Xiaoqing

    2016-11-01

    Using impregnation technique, a small amount of Rh(III) clusters has been grafted on the BiOCl microflowers. The samples are characterized by X-ray diffraction, scanning electron microscopy coupled with high energy distribution X-ray, transmission electron microscopy, X-ray photoelectron spectroscopy, and UV-vis diffuse reflectance spectroscopy. The photocatalytic activities are investigated by the decomposition of gaseous acetaldehyde under irradiation of visible light. The bare BiOCl microflowers exhibit the limited visible light photocatalytic activity because of its wide band gap. After surface modification of Rh(III) clusters, the Rh(III)-BiOCl samples show an enhanced photocatalytic activity for the decomposition gaseous acetaldehyde under visible light irradiation. It is found that the Rh(III) clusters play an important role for the visible light absorption, probably through the electron transfer between Rh(III) clusters and the BiOCl, as well as the redox reaction centers for the multi-electron reduction of O2.

  9. Photoorganocatalysed and visible light photoredox catalysed trifluoromethylation of olefins and (hetero)aromatics in batch and continuous flow.

    PubMed

    Lefebvre, Quentin; Hoffmann, Norbert; Rueping, Magnus

    2016-02-11

    Trifluoromethylation of olefins and (hetero)aromatics with sodium triflinate as CF3 source and readily accessible benzophenone derivatives as photosensitisers has been developed in batch and flow. The use of an iridium-based photocatalyst enables the trifluoromethylation to proceed under visible light irradiation.

  10. Magnetosomes extracted from Magnetospirillum magneticum strain AMB-1 showed enhanced peroxidase-like activity under visible-light irradiation.

    PubMed

    Li, Kefeng; Chen, Chuanfang; Chen, Changyou; Wang, Yuzhan; Wei, Zhao; Pan, Weidong; Song, Tao

    2015-05-01

    Magnetosomes are intracellular structures produced by magnetotactic bacteria and are magnetic nanoparticles surrounded by a lipid bilayer membrane. Magnetosomes reportedly possess intrinsic enzyme mimetic activity similar to that found in horseradish peroxidase (HRP) and can scavenge reactive oxygen species depending on peroxidase activity. Our previous study has demonstrated the phototaxis characteristics of Magnetospirillum magneticum strain AMB-1 cells, but the mechanism is not well understood. Therefore, we studied the relationship between visible-light irradiation and peroxidase-like activity of magnetosomes extracted from M. magneticum strain AMB-1. We then compared this characteristic with that of HRP, iron ions, and naked magnetosomes using 3,3',5,5'-tetramethylbenzidine as a peroxidase substrate in the presence of H2O2. Results showed that HRP and iron ions had different activities from those of magnetosomes and naked magnetosomes when exposed to visible-light irradiation. Magnetosomes and naked magnetosomes had enhanced peroxidase-like activities under visible-light irradiation, but magnetosomes showed less affinity toward substrates than naked magnetosomes under visible-light irradiation. These results suggested that the peroxidase-like activity of magnetosomes may follow an ordered ternary mechanism rather than a ping-pong mechanism. This finding may provide new insight into the function of magnetosomes in the phototaxis in magnetotactic bacteria.

  11. Visible-Light-Induced Activity Control of Peroxidase Bound to Fe-Doped Titanate Nanosheets with Nanometric Lateral Dimensions.

    PubMed

    Kamada, Kai; Ito, Daiki; Soh, Nobuaki

    2015-10-21

    Catalytic performance of horseradish peroxidase (HRP) electrostatically adsorbed on nanometric and semiconducting Fe-doped titanate (FT) nanosheets was successfully manipulated by visible light illumination. A colloidal solution of FT with a narrow band gap corresponding to a visible light region was fabricated through a hydrolysis reaction of metals sources. HRP could be easily bound to the FT at pH = 4 through an electrostatic interaction between them, and the formed HRP-FT was utilized for the visible-light-driven enzymatic reaction. Under exposure to visible light with enough energy for band gap excitation of the FT, catalytic activity of HRP-FT was dramatically enhanced as compared with free (unbound) HRP and was simply adjusted by light intensity. In addition, wavelength dependence of an enzymatic reaction rate was analogous to an optical absorption spectrum of the FT. These results substantiated an expected reaction mechanism in which the photoenzymatic reaction was initiated by band gap excitation of FT followed by transferring holes generated in the valence band of irradiated FT to HRP. The excited HRP oxidized substrates (amplex ultrared: AUR) accompanied by two-electron reduction to regenerate the resting state. In addition, the catalytic activity was clearly switched by turning on and off the light source.

  12. Difunctionalization of Alkenes via the Visible-Light-Induced Trifluoromethylarylation/1,4-Aryl Shift/Desulfonylation Cascade Reactions.

    PubMed

    Zheng, Lewei; Yang, Chao; Xu, ZhaoZhong; Gao, Fei; Xia, Wujiong

    2015-06-01

    A novel visible-light-induced trifluoromethylarylation/1,4-aryl shift/desulfonylation cascade reaction using CF3SO2Cl as CF3 source was described. The protocol provides an efficient approach for the synthesis of α-aryl-β-trifluoromethyl amides and/or CF3-containing oxindoles as well as the isoquinolinediones under benign conditions.

  13. Fabrication and visible-light photocatalytic activity of novel Ag/TiO2-xNx nanocatalyst

    EPA Science Inventory

    The efforts of the scientific community are directed towards the preparation of photocatalysts that are active under solar or artificial visible light irradiation. TiO2 is one of the most 15 widely used photocatalyst that is employed in self-cleaning coatings, photocatalytic proc...

  14. Visible-light-promoted chloramination of olefins with N-chlorosulfonamide as both nitrogen and chlorine sources.

    PubMed

    Qin, Qixue; Ren, Daan; Yu, Shouyun

    2015-11-01

    A visible-light-promoted chloramination of olefins is reported. N-Chlorosulfonamides serve as both nitrogen and chlorine sources. These reactions provide a simple, efficient, regioselective, and atom-economical method for the preparation of vicinal haloamine derivatives under mild reaction conditions. A variety of olefins were tolerated, and chloramination products were obtained in good yields.

  15. In vivo ratiometric Zn2+ imaging in zebrafish larvae using a new visible light excitable fluorescent sensor.

    PubMed

    Liu, Zhipeng; Zhang, Changli; Chen, Yuncong; Qian, Fang; Bai, Yang; He, Weijiang; Guo, Zijian

    2014-02-01

    A visible light excitable ratiometric Zn(2+) sensor was developed by integrating a Zn(2+) chelator as the ICT donor of the fluorophore sulfamoylbenzoxadiazole, which displays the Zn(2+)-induced hypsochromic emission shift (40 nm) and favors the in vivo ratiometric Zn(2+) imaging in zebrafish larvae.

  16. Visible-light-driven photodegradation of sulfamethoxazole and methylene blue by Cu2O/rGO photocatalysts.

    PubMed

    Liu, Shou-Heng; Wei, Yu-Shao; Lu, Jun-Sheng

    2016-07-01

    The cuprous oxide-reduced graphene oxide (Cu2O/rGO-x) composites were prepared via a simple wet-chemical method by using CuSO4·5H2O and graphene oxide as precursors and ascorbic acid as a reducing agent, respectively. These Cu2O/rGO-x were employed as photocatalysts for degrading emerging contaminants and organic dye pollutants (i.e., sulfamethoxazole (SMX) and methylene blue (MB)) under visible light. A variety of different spectroscopic and analytical techniques, such as X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, Raman scattering spectroscopy and UV-Visible spectroscopy were used to characterize the physical properties of photocatalysts. In the photodegrading experiments, it can be found that the Cu2O/rGO-80 photocatalyst has the superior visible-light response of ca. 50% removal efficiency of SMX within 120 min and 100% removal efficiency of MB within 40 min. These observations may be attributed the well-dispersed and visible-light-responsive Cu2O nanoparticles are supported on the surface of rGO sheets that can enhance absorption of visible light during photocatalysis. PMID:27043377

  17. The visible light degradation activity and the photocatalytic mechanism of tetra(4-carboxyphenyl) porphyrin sensitized TiO{sub 2}

    SciTech Connect

    Wang, Huigang; Zhou, Dongmei; Wu, Zhangzhu; Wan, Junmin; Zheng, Xuming; Yu, Lihong; Phillips, David Lee

    2014-09-15

    Highlights: • Tetra(4-carboxyphenyl) porphyrin were chemically sensitized on TiO{sub 2}. • S2–S0 fluorescence intensity is enhanced and lifetime prolonged noticeably by TiO{sub 2}. • The TCPP-TiO{sub 2} exhibits better photoactivity under visible light than that of TiO{sub 2}. • The electronic relaxation dynamics is presented, catalytic mechanism is discussed. • Adsorption and photo degradation of MB were systematically investigated. - Abstract: Tetra(4-carboxyphenyl) porphyrin(TCPP) were chemically sensitized on TiO{sub 2} to act as visible light antenna and to modify the photoresponse properties of TiO{sub 2} particles, their properties of photo-generated holes and electrons were studied by transient absorption spectroscopes. The time-correlated single-photon counting (TCSPC) technique revealed that the S2–S0 fluorescence intensity of TCPP is enhanced noticeably by TiO{sub 2}, and the lifetime prolonged. Adsorption and photo degradation of methylene blue (MB) over TCPP-TiO{sub 2} were systematically investigated. Moreover the overall picture of electronic relaxation dynamics for TCPP-TiO{sub 2} is presented, and the detailed short-time dynamics for visible-light induced catalytic mechanism was discussed. The development of the porphyrin-based photocatalyst provides an alternative approach in harnessing solar visible light and show promising prospect for the treatment of dye pollutants from wastewaters in future industrial application.

  18. Preparation N-F-codoped TiO{sub 2} nanorod array by liquid phase deposition as visible light photocatalyst

    SciTech Connect

    Lv, Yan; Fu, Zhengping; Yang, Beifang; Xu, Jiao; Wu, Min; Zhu, Changqiong; Zhao, Yongxun

    2011-03-15

    Research highlights: {yields} The formation of N, F-codoped TiO{sub 2} nanorod arrays via the LPD. {yields} Calcination temperature greatly effects the incorporation of N and F into TiO{sub 2}. {yields} TNRAs calcined at 450 {sup o}C showed highest visible light photocatalytic activity. {yields} A synergetic effect of 1D nanorod arrays and appropriate amount of N and F codoping. -- Abstract: An efficient method for the preparation of N-F-codoped visible light active TiO{sub 2} nanorod arrays is reported. In the process, simultaneous nitrogen and fluorine doped TiO{sub 2} nanorod arrays on the glass substrates were achieved by liquid phase deposition method using ZnO nanorod arrays as templates with different calcination temperature. The as-prepared samples were characterized by Raman spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and UV-vis absorption spectra measurements. It was found that calcination temperature is an important factor influencing the microstructure and the amount of N and F in TiO{sub 2} nanorod arrays samples. The visible light photocatalytic properties were investigated using methylene blue (MB) dye as a model system. The results showed that N-F-codoped TiO{sub 2} nanorod arrays sample calcined at 450 {sup o}C demonstrated the best visible light activity in all samples, much higher than that of TiO{sub 2} nanoparticles and P25 particles films.

  19. Synthesis of N-doped TiO2 Using Guanidine Nitrate: An Excellent Visible Light Photocatalyst

    EPA Science Inventory

    An excellent visible light active nitrogen-rich TiO2 photocatalyst have been synthesized by using guanidine nitrate as the doping material. The catalytic efficiency of the catalyst has been demonstrated by the decomposition of the dye, methyl orange (MO), and the pollutant, 2,4 d...

  20. Flower-like CdSe ultrathin nanosheet assemblies for enhanced visible-light-driven photocatalytic H2 production.

    PubMed

    Peng, Yong; Shang, Lu; Bian, Tong; Zhao, Yufei; Zhou, Chao; Yu, Huijun; Wu, Li-Zhu; Tung, Chen-Ho; Zhang, Tierui

    2015-03-18

    Flower-like CdSe architectures composed of ultrathin nanosheets were prepared via a facile solvothermal method. A relationship was established between the solvothermal temperature and the product structure, and thus the photocatalytic activity. When compared with well-studied CdSe quantum dots, the ultrathin nanosheet assemblies exhibited a better photocatalytic H2 evolution activity under visible light irradiation.