Semiconductor Particulate Systems Research Articles

Photodegradation of phenol in a polymer-modified TiO2 semiconductor particulate system under the irradiation of visible light

Preparation methods and photocatalytic activity of the photocatalyst nanometer TiO2/poly-(fluorene-co-thiophene) (PFT) were studied under GaI3 lamp irradiation in the present research. The degradation rate of phenol using the target photocatalyst was much higher than it was using TiO2/rhodamine B. Diffuse reflectance spectra showed that the absorbance range of TiO2/PFT was expanded from 387nm (TiO2) to about 500nm, and fluorescent emission spectra showed that the spectral shape of TiO2/PFT was identical with that of pure PFT. The fluorescent quantum efficiency of TiO2/PFT was estimated at 3.8% while that of PFT film was about 14.7%, which indicated that electrons transferred from the PFT into the conduction band of TiO2.

Photoassisted detoxification of organic pollutants on the surface modified TiO 2 semiconductor particulate system

Photoassisted decomposition of phenol, chlorophenol and trichloroethylene in waste water has been achieved on the surface of TiO 2 semiconductor modified with 8-hydroxyquinoline (HOQ) by using visible light. After 5 h of irradiation with a 50 W tungsten lamp, over 70–80% degradation of pollutants is achieved. A working mechanism involving excitation of surface bound dye, followed by charge injection into the TiO 2 conduction band is proposed.

Photocatalytic reduction of hydrazine to ammonia catalysed by [Ru III(edta)(H 2O)] − complex in a Pt/TiO 2 semiconductor particulate system

Illumination of aqueous suspensions of Pt/TiO 2 semiconductor photocatalyst in the presence of [Ru III(edta)(H 2O)] − resulted in the reduction of hydrazine to ammonia. A working mechanism involving the formation of a [Ru III(edta)(N 2H 5)] species (adsorbed onto TiO 2 surface) which undergoes two-electron transfer reduction followed by cleavage of the N–N bond of coordinated hydrazine has been suggested.

An overview on semiconductor particulate systems for photoproduction of hydrogen

Hydrogen production from aqueous solutions using semiconductor particles as photocatalysts has been reviewed highlighting the experimental techniques and mechanistic aspects. Several factors which influence the hydrogen production efficiency of semiconductor particles have been critically analysed with specific examples from literature. Photocatalytic efficiencies of individual semiconductors such as, CdS, TiO 2, WO 3 have also been assessed with reference to hydrogen production in the presence and absence of loaded metals, electrondonors/acceptors and hole scavengers. The main focus of this overview is to provide literature-based information on hydrogen production reactions using semiconductor particles in the presence of light energy.

Synthesis and characteristics of mixed ligand Ru(III) complexes with EDTA—polypyridyl, and Pt/TiO 2/RuO 2 semiconductor particulate system modified by the complexes

The mixed ligand complexes K[Ru III(EDTA)(bipy)] ( 1) and K[Ru III(EDTA)( o-Phen)] ( 2) (EDTA, ethylenediaminetetraacetate; bipy, bipyridine; o-Phen, o-phenanthroline) were synthesized and characterized by physicochemical methods. Their redox and photophysical properties were studied. The kinetic and equilibrium data for the formation of these mixed ligand complexes are reported. Surface modification of a TiO 2 semiconductor was CO 2 was achieved at an energy lower than the band gap energy of TiO 2.

Photofixation of carbon dioxide in semiconductor particulate and microbial systems

Photocatalytic reduction of CO2 to HCOOH and HCHO was carried out in a Pt/CdS/RuO2 semiconductor particulate system using [RuIII(EDTA-H)H2O] complex as catalyst. Upon illumination at 505 nm (band gap energy of CdS), the system produced HCOOH and HCHO at rates equal to 3.05 × l0−2 Mh−1 and 2.0 × 10−2 M h−1, respectively. Trace amounts of CH2OH, CH4 and CO were also detected in the reaction vessel. Photobiological conversion of CO2 to formic acid was achieved by usingHalobacterium halobium MMT22 in aqueous solution at a rate equal to 0.45 M h−1. A one-and-half-fold increase in the rate of formation of formic acid was observed when the photobiological reduction of CO2 was performed in the presence of L-ascorbic acid as electron-donating agent and [RuIII(bipy)3]2+ as photosensitizer.

Photocatalytic reduction of N2 to NH 3 sensitized by the [RuIII-ethylenediaminetetraacetate-2,2′-bipyridyl]− complex in a Pt-TiO2 semiconductor particulate system

The complex K[RuIII(EDTA)(bipy)] (where EDTA denotes ethylenediaminetetraacetate, and bipy denotes 2,2′-bipyridyl) was synthesized and characterized. The photophysical properties of this complex were studied and its application as photosensitizer in the photoreduction of N2 to NH3 in a Pt-TiO2 semiconductor particulate system is reported.

Photo-oxidation of saturated hydrocarbons through H 2O as a source of O 2 catalysed by [Ru III(EDTA—H)Cl] − complex in a Pt/TiO 2/RuO 2 semiconductor particulate system

Photo-oxidation of cyclohexane and adamantane was carried out in a semiconductor particulate system containing Pt/TiO 2/RuO 2 semiconductor powder, [Ru III(EDTA—H)Cl] − ( 1) complex as catalyst, and the substrate (cyclohexane, adamantane) in water-dioxane medium. Illumination of the system at 390 nm (energy equivalent to the band-gap energy of TiO 2) produces cyclohexanol and 1-adamantanol at rates of 1.92 × 10 −6 mol h −1 and 1.33 × 10 −6 mol h −1, respectively. Trace amounts of cyclohexanone, 2-adamantanol, and 2-adamantanone were also detected in the reaction system. In the absence of complex 1 the reaction gives negligible amounts of oxidation products. A mechanism involving oxygen-atom transfer from the photogenerated [Ru v(EDTA)(O)] − ( 2) complex to the substrates has been proposed for the photo-oxidation reaction.

Photosensitized reduction of N 2 by Ru II(bipy) 32+ adsorbed on the surface of Pt/TiO 2/RuO 2 semiconductor particulate system containing Ru III-EDTA complex and L-ascorbic acid

Photocatalytic reduction of N 2 to NH 3 was carried out in a surface-modified semiconductor particulate system containing Pt/TiO 2/RuO 2 semiconductor powder, K[Ru III(EDTA-H)Cl]-(EDTA-H = anion of ethylenediaminetetracetic acid) complex as a catalyst and L-ascorbic acid as a sacrificial electron donor. The surface of the Pt/TiO 2/RuO 2 semiconductor was modified by adsorbing photoactive Ru II(bipy) 3 2+ complex. Illumination of the system containing N 2, surface-modified semiconductor, Ru III-EDTA complex and ascorbic acid at the photoexcitation energy of Ru II(bipy) 3 2+ (510 nm) produces appreciable amounts of NH 3 with a turnover rate of 1.13 mol NH 3 per mol Ru III-EDTA complex per hour. An improvement in the rate of ammonia formation (1.67 mol h −1 per mol Ru III-EDTA complex) was observed when the same system was illuminated at the band gap energy of TiO 2 (390 nm). A suitable mechanism involving the formation of an intermediate dinitrogen complex of ruthenium(II), (Ru II(EDTA)N 2 −) was proposed for the photoreduction of N 2 to NH 3.

Photoelectrochemistry in semiconductor particulate systems. 17. Photosensitization of large-bandgap semiconductors: charge injection from triplet excited thionine into zinc oxide colloids

The kinetics and mechanism of a diffusion-controlled interfacial charge transfer between excited triplet thionine and ZnO colloids in ethanol have been elucidated with laser flash photolysis. The singlet excited state of thionine, which has a lifetime of 450 ps in ethanol, did not participate in the charge injection process. However, the triplet excited state of thionine was quenched by ZnO colloids. The triplet lifetime ({tau}{sub T}) decreased from 88 to 15 {mu}s with increasing ZnO colloid concentration. The maximum charge injection efficiency ({theta}{sub TH{center_dot}}2+) which was measured from the yield of dye cation radical was 0.1. The increase in the rate constant for reverse electron transfer (k{sub r}) at high ZnO concentration resulted in a small decrease in charge-transfer efficiency. The dependence of {tau}{sub T}, {theta}{sub TH{center_dot}}2+, and k{sub r} on the concentration of ZnO is described. 49 refs., 9 figs.

Stepwise reduction of coordinated dinitrogen to ammonia via diazinido and hydrazido intermediates on a visible light irradiated Pt/CdS · Ag 2S/RuO 2 particulate system suspended in an aqueous solution of K[Ru(EDTA-H)Cl]2H 2O

We report the photocatalytic fixation of coordinated dinitrogen to ammonia in aqueous solution under ambient conditions (30 °C and 1 atm N 2) in the presence of the modified semiconductor particulate system Pt/CdS · Ag 2S/RuO 2 catalysed by K[Ru(EDTA-H)Cl]2H 2O. Doping of the photon absorber CdS with Ag 2S (0.05 wt.% relative to the weight of CdS) leads to an enhanced rate of production of NH 3 at 505 nm. The reaction shows a first-order dependence on the catalyst concentration. The quantum yields of the product were obtained at five monochromatic absorption lines between 450 and 550 nm. Illumination of the system with 505–525 nm light gives the highest quantum yield of 0.35. A mechanism is proposed for the formation of NH 3 which involves the in situ formation of a dinitrogen complex of ruthenium(II). The —NN bond in this complex appears to undergo stepwise reduction to NH 3 via diazinido and hydrazido intermediates which were characterized by the nuclear magnetic resonance (NMR) spectra of the solution from the reaction cell. The estimated deuterium kinetic isotope effect is 1.77 indicating a hydrogen atom transfer in the rate-determining step. The source of the nitrogen atom in NH 3 is dinitrogen as confirmed by 15N 2 studies. Photo-oxidation of H 2O to oxygen is confirmed by performing studies in H 2 18O (10%) enriched medium.

Photocatalytic hydrogen production with semiconductor particulate systems: An effort to enhance the efficiency

Abstract Hydrogen production in visible light (λ = 437 nm) with the following semiconductor particulate systems, Ag(I)/WO3, Fe(III)/WO3 and Cr(III)/WO3 and mixed semiconductors, WO3 -CdS and WO3 -Pt/CdS, has been investigated in the presence of an electron relay, methylviologen, MV2+. The efficiency of WO3-CdS mixed photocatalyst is found to be less than that of CdS alone. However, Pt loaded CdS powders mixed with WO3 powders (WO3-Pt/CdS) exhibited a notable enhancement in the photocatalytic activity. The effect of sintering temperature on the efficiency of WO3 showed that the sample sintered at 800°C was with higher efficiency than that sintered at 300°C. Similarly, loading of WO3 with Ag(I), Fe(III) and Cr(III) by high temperature (800°C) sintering enhanced the quantum yields when compared to those sintered at 300°C. Simultaneous use of the electron relay (MV2+) and a hole scavenger (oxalic acid) for water splitting reaction in the presence of Ag(I)/WO3 is found to be less efficient compared to that observed in the presence of MV2+ or oxalic acid alone, which might be due to the interaction of CO2 molecules formed, with methylviologen radical cations.

ChemInform Abstract: Photoelectrochemistry in Semiconductor Particulate Systems. Part 16. Photophysical and Photochemical Aspects of Coupled Semiconductors. Charge‐Transfer Processes in Colloidal CdS‐TiO2 and CdS‐AgI Systems.

AbstractTEM, emission measurements, and picosecond transient absorption spectroscopy are used to study the mechanism and kinetics of the charge injection from excited CdS into the large bandgap semiconductors AgI and TiO2 in the mixed semiconductor colloids.

Photocatalytic hydrogenation of cyclohexene through H 2O as a source of H 2 by Pt/CdS/RuO 2 semiconductor particulate system catalysed by K[Ru(H—EDTA)Cl]2H 2O

Hydrogenation of cyclohexene in aqueous ethanolic solutions (80:20 ethanol-water) of K[Ru(H—EDTA)Cl]2H 2O occurs during illumination of a semiconducting Pt/CdS/RuO 2 particulate system under ambient conditions. Cyclohexane is formed at a rate equal to 23μ1h −1 (turnover rate = 8.5 mol cyclohexane per mol catalyst per hour) and a total of 7–8% of cyclohexene is hydrogenated in about 12 h irradiation time. A mechanism for the hydro-genation of cyclohexene is proposed incorporating metal-alkene and mixed metal-alkene-hydride intermediates. The formation of these intermediates is amply supported by spectroscopic studies of photolysed reaction mixture. Hydrogen for the hydrogenation of cyclohexene is obtained by the photosplitting of H 2O.

Colloidal semiconductors as photocatalysts for solar energy conversion

Considerable attention has been drawn in recent years to develop ultrafine semiconductor particles which exhibit excellent photocatalytic properties. Size quantization effects, nonlinear optical properties and enhanced photoredox properties make quantized colloidal semiconductors potentially useful in the design of photoelectrochemical systems. Photochemical and photophysical processes that directly influence the photocatalytic properties of the semiconductor colloids and the factors that limit the charge transfer at the semiconductor/electrolyte interface are discussed here. Applications of semiconductor particulate systems in the conversion and storage of solar energy are also described.

Photoelectrochemistry in semiconductor particulate systems. 13. Surface modification of cadmium sulfide semiconductor colloids with diethyldithiocarbamate

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTPhotoelectrochemistry in semiconductor particulate systems. 13. Surface modification of cadmium sulfide semiconductor colloids with diethyldithiocarbamatePrashant V. Kamat and Nada M. DimitrijevicCite this: J. Phys. Chem. 1989, 93, 10, 4259–4263Publication Date (Print):May 1, 1989Publication History Published online1 May 2002Published inissue 1 May 1989https://doi.org/10.1021/j100347a069RIGHTS & PERMISSIONSArticle Views248Altmetric-Citations42LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (628 KB) Get e-Alerts

Utilization of the Semiconductor Particle as a Microphotoelectrochemical Cell: Electrochemical Evidence for Interparticle Electron Transfer and Application to Photocatalysis

Illuminated semiconductor particulate systems mimic the properties of photoelectrochemical cells; electron/hole pair separation and the rapid movement of the photogenerated charge carriers to the particle surface form anodic and cathodic sites at which efficient redox chemistry can take place. It is shown that chemical etching of well‐defined spherical (2–20 μm) particles changes the nature of the surface (SEM) and bears on the efficiency of the photocatalytic cleavage of in aqueous alkaline media. Coupling and semiconductor results in interparticle electron transfer (IPET) and significantly improves the rate of production; this electron transfer process was probed photocatalytically and by photoelectrochemical techniques.

Photophysical and photochemical primary events in semiconductor particulate systems. Colloidal CdS with methylviologen

The photogenerated electron/hole pairs in excited CdS, produced by irradiation (355 nm) from a Nd:YAG mode-locked laser, yield a luminescence which decays in ≤ 30 ps. Time-resolved change-in-absorbance spectra of CdS in the presence of methylviologen MV 2+ (degassed) show formation of MV + and its dimer (MV +) 2 (λ max ∼ 530 nm) in ∼ 1 ns.

Design of semiconductor photoelectrochemical systems for solar energy conversion

Abstract : The principles and applications of semiconductor electrodes in photoelectrochemical (PEC) cells for carrying out useful chemical reactions are described. The factors in the design of efficient and stable systems and semiconductor particulate systems constructed on the basis of PEC cell principles are discussed. (Author)