Showing papers in "Journal of Photochemistry and Photobiology A-chemistry in 2004"

Conversion of sunlight to electric power by nanocrystalline dye-sensitized solar cells

Abstract: The dye-sensitized solar cell (DSC) provides a technically and economically credible alternative concept to present day p–n junction photovoltaic devices. In contrast to the conventional silicon systems, where the semiconductor assumes both the task of light absorption and charge carrier transport the two functions are separated here. Light is absorbed by a sensitizer, which is anchored to the surface of a wide band gap oxide semiconductor. Charge separation takes place at the interface via photo-induced electron injection from the dye into the conduction band of the solid. Carriers are transported in the conduction band of the semiconductor to the charge collector. The use of sensitizers having a broad absorption band in conjunction with oxide films of nanocrystalline morphology permits to harvest a large fraction of sunlight. Nearly quantitative conversion of incident photon into electric current is achieved over a large spectral range extending from the UV to the near IR region. Overall solar (standard AM 1.5) to current conversion efficiencies of 10.6% have been reached. New electrolytes based on ionic liquids have been developed that show excellent stability both under prolonged light soaking and high temperature stress. There are good prospects to produce these cells at lower cost than conventional devices. Here we present the current state of the field, and discuss the importance of mastering the interface of the mesoporous films by assisting the self-assembly of the sensitizer at the surface of the oxide nanocrystals.

Photocatalytic degradation of azo dye acid red 14 in water on ZnO as an alternative catalyst to TiO2

Abstract: The degradation of acid red 14 (AR14), commonly used as a textile dye, can be photocatalysed by ZnO. Using advanced oxidation processes (AOPs), zinc oxide appears to be a suitable alternative to TiO2 for water treatment. In this study, a detailed investigation of photocatalytic degradation of acid red 14 is presented. Photodegradation efficiency was small when the photolysis was carried out in the absence of ZnO and it was also negligible in the absence of UV light. The semi-log plot of dye concentration versus time was linear, suggesting first order reaction (K=0.0548 min−1). The effects of some parameters such as pH, amount of photocatalyst, hydrogen peroxide and ethanol concentration were also examined. The addition of proper amount of hydrogen peroxide improved the decolorization, while the excess hydrogen peroxide could quenched the formation of hydroxyl radicals ( OH). As our results indicated that ethanol inhibited the photodegradation of dye, we concluded from the inhibitive effect of ethanol that hydroxyl radicals played a significant role in the photodegradation of dye. This should not undermine direct oxidation caused by positive holes.

Bi2S3/TiO2 and CdS/TiO2 heterojunctions as an available configuration for photocatalytic degradation of organic pollutant

Abstract: Bi2S3/TiO2 and CdS/TiO2 heterojunctions were prepared by direct mixture of both constituents and by precipitation of the sensitizer with commercial TiO2 at different concentrations. UV-Vis spectroscopy analysis showed that the junctions-based Bi2S3 and CdS are able to absorb a large part of visible light (respectively up to 800 and 600 nm). This fact was confirmed by photocatalytic experiment performed under visible light. A part of charge recombination that can take place when both semiconductors are excited was observed when photocatalytic experiment was performed under UV-Vis illumination. Orange II, 4-hydroxybenzoique acid (4-HBZ) and benzamide (BZ) were used as pollutants. Photoactivity of the junctions was found to be strongly dependent on the substrate. The different phenomena taking place in each case are discussed.

Comparison of Ag deposition effects on the photocatalytic activity of nanoparticulate TiO2 under visible and UV light irradiation

Abstract: We investigated the photocatalytic degradation of rhodamine B (RB) dye in the aqueous suspensions of TiO2 (∼17 nm) and Ag-deposited TiO2 nanoparticles under visible and UV light irradiation in order to evaluate and distinguish various effects of the Ag deposition on the TiO2 photocatalytic activity. The TiO2 and Ag–TiO2 photocatalysts were characterized by XRD, TEM, XPS, UV-visible absorption and photon correlation spectroscopy. For comparison, the RB photodegradation was carried out in Degussa P25 TiO2 and Ag-deposited P25 suspensions under the same condition. In the RB/Ag–TiO2 system, Ag deposits significantly enhanced the RB photodegradation under visible light irradiation whereas the RB photodegradation under UV irradiation was slightly enhanced. The significant enhancement in the Ag–TiO2 photoactivity under visible light irradiation can be ascribed to simultaneous effects of Ag deposits by both acting as electron traps and enhancing the RB adsorption on the Ag–TiO2 surface. © 2004 Elsevier B.V. All rights reserved.

A visible-light response vanadium-doped titania nanocatalyst by sol–gel method

Abstract: A series of vanadium-doped TiO 2 catalysts were synthesized by two modified sol–gel methods. V-doped TiO 2 was found to be mainly preserved its anatase phase after calcination at 400 °C. The TEM micrographs showed the sizes of primary particles were in the range of 6–20 nm. The increase of vanadium doping promoted the particle growth, and enhanced “red-shift” in the UV-Vis absorption spectra. The XPS (X-ray photoelectron spectroscopy) could not detect vanadium indicating negligible vanadium on the surface of catalysts, furthermore, there were also no peak of vanadium oxide in the XRD patterns. XAS (X-ray absorption spectroscopy) analysis indicating V 4+ instead of V 5+ implied that vanadium either substituted Ti 4+ site or embedded in the vacancy of TiO 2 structure. Therefore, vanadium was concluded to be highly dispersed inside the TiO 2 structure. The photocatalytic activity was evaluated by the degradation of crystal violet (CV) and methylene blue (MB) under visible light irradiation. The degradation rate of CV and MB on V-doped TiO 2 were higher than those of pure TiO 2 . As the results, V-doped TiO 2 possessed better absorption ability of visible light.

I−/I3− redox reaction behavior on poly(3,4-ethylenedioxythiophene) counter electrode in dye-sensitized solar cells

Abstract: I−/I3− redox reaction behaviors on chemically polymerized p-toluenesulfonate doped poly(3,4-ethylenedioxythiophene) (PEDOT-TsO) and sputtered-Pt electrode were characterized to compare its performance as the counter electrode in dye sensitized solar cells (DSCs). Adsorption of iodide species at the PEDOT surface, as well as Pt surface was little affected the redox reaction at the low concentration of redox couple. The PEDOT-TsO film had porous structure and charge transfer resistance of the PEDOT-TsO electrode decreased with the thickness. Photovoltaic performance of DSCs with PEDOT-TsO counter electrode (CE) also improved with the thickness of PEDOT-TsO when ionic liquid was used for the electrolyte. The use of porous PEDOT-TsO counter electrode that has low cost, simplified fabrication process and sufficient catalytic activity could enhance the potential of the DSCs for practical use.

H2 evolution from an aqueous methanol solution on SrTiO3 photocatalysts codoped with chromium and tantalum ions under visible light irradiation

Abstract: SrTiO 3 photocatalysts doped with chromium ions showed photocatalytic activities for H 2 evolution from an aqueous methanol solution under visible light irradiation However, it had a long induction period Codoping of niobium or tantalum ions with chromium ions shortened the induction period, and increased the photocatalytic activities in respect of the H 2 evolution The photocatalytic activities of chromium- and chromium/tantalum-doped SrTiO 3 were improved when they were pretreated at 773 K in the hydrogen reduction atmosphere Codoping of tantalum ions suppressed the formation of Cr 6+ ions and oxygen defects which would work as nonradiative recombination centers between photogenerated electrons and holes, resulting in the shortening of induction periods and the improvement of photocatalytic activities

High performance dye-sensitized solar cells using ionic liquids as their electrolytes

Abstract: Room temperature ionic liquids have been used as electrolytes to investigate the performance and the characteristics in dye-sensitized solar cells (DSSCs). The ionic liquids used are 1-ethyl-3-methylimidazolium bis(trifluoromethane sulfonyl)imide (EMImTFSI), 1-ethyl-3-methylimidazolium tetrafluoroborate (EMImBF4), 1-butyl-3-methylimidazolium hexafluorophosphate (BMImPF6), 1-ethyl-3-methylimidazolium dicyanamide (EMImDCA), and 1-butylpyridinium bis(trifluoromethane sulfonyl)imide (BPTFSI), in which 1-ethyl-3-methylimidazolium iodide (EMImI) and I2 are dissolved as a redox couple. The structure and the property greatly influence the DSSC performances. Especially, the photocurrents are affected by the ionic conductivity (viscosity) and charge transport by the exchange reaction between the iodide/tri-iodide redox couple. EMImDCA is specific in terms of enhancement of the open-circuit voltages. The photo-energy conversion efficiency of DSSCs with EMImDCA under 100 mW cm−2 can be optimized up to 5.5%, when [I−] + [I3−] = 2 M and [I−]:[I2]=10:1 with the addition of 4-t-butylpyridine and LiI.

The study on the interaction between human serum albumin and a new reagent with antitumour activity by spectrophotometric methods

Abstract: In this work, the binding of 2-hydroxy-3-nitro-9-fluorenone (HNF; a new reagent with antitumour activity) to human serum albumin (HSA) was investigated by fluorescence spectroscopy combined with UV-Vis absorption, circular dichroism (CD), and Fourier transform infrared (FT-IR) spectrophotometric techniques under simulative physiological conditions for the first time. A strong fluorescence quenching reaction of HNF to HSA was observed and the quenching mechanism was suggested as static quenching according to the Stern–Volmer (S–V) equation. The binding constants of HNF with HSA at 300, 310 and 320 K were calculated as 6.08×10 5 , 3.80×10 5 and 2.79×10 5 M −1 , respectively, and corresponding numbers of binding sites ( n ) were 1.1, 1.0 and 1.0. Experimental results observed showed that the binding of HNF to HSA induced conformational change of HSA. The quantitative analysis data of CD spectra from that of the α-helix 60.3% in free HSA to 56.5% in the HNF–HSA complex further confirmed that the secondary structure of the protein was modified by HNF. The thermodynamic parameters, standard enthalpy change (Δ H °) and the standard entropy change (Δ S °), were obtained to be −31.10 kJ mol −1 and 6.87 J mol −1 K −1 , respectively, which indicated that a hydrophobic force played a major role in the interaction of HNF with HSA. All these experimental results and theoretical data clarified that HNF could bind to HSA and be effectively transported and eliminated in body, which could be a useful guideline for further drug design.

Enhanced photocatalytic performance of nanosized coupled ZnO/SnO2 photocatalysts for methyl orange degradation

Abstract: Nanosized coupled ZnO/SnO2 photocatalysts with different Sn contents were prepared using the coprecipitation method, and characterized by X-ray diffraction, specific surface area and UV-Vis diffuse reflectance spectroscopy. The phases, mean grain sizes and band gap energy of the coupled ZnO/SnO2 photocatalysts varied with the Sn contents and the calcination temperatures. The photocatalytic activities of the coupled ZnO/SnO2 photocatalysts, evaluated using the photodegradation of methyl orange as a probe reaction, were also found to be related to the calcination temperatures and the Sn contents. The photocatalytic activities of the coupled ZnO/SnO2 photocatalysts decreased with the increasing calcination temperatures. The maximum photocatalytic activity of the coupled ZnO/SnO2 photocatalyst, which is about 1.3 times the photocatalytic activity of ZnO and 21.3 times that of SnO2, was observed with a Sn content of 33.3 mol% under calcination at 500 °C for 10 h. The enhancement of the photocatalytic activity might arise from the hetero-junctions ZnO/SnO2 in the coupled oxides. The photo-stability of the ZnO/SnO2 photocatalyst was also studied.

Optimization of solar photocatalytic degradation conditions of bisphenol A in water using titanium dioxide

Abstract: The photocatalytic degradation conditions of 4,4′-isopropylidenediphenol (bisphenol A, BPA), a representative endocrine disruptor, in water using titanium dioxide were optimized under sunlight illumination. The effect of various factors, such as photocatalyst dosage, initial substrate concentration, temperature, pH and light intensity, on the photocatalytic degradation of bisphenol A was investigated. The final degradation product was carbon dioxide, and the stoichiometric formation of CO2 from aqueous bisphenol A solution was observed as the complete mineralization. The solar photocatalytic degradation treatment is simple, easy handling and cheap. Therefore, since the artificial lamp devices, for example Hg–Xe lamp, are particularly expensive in the local and nonexclusive areas, the proposed technique appears to be a very suitable method for the treatment of wastewater including bisphenol A in those areas.

Improved dye-sensitized solar cells using ionic nanocomposite gel electrolytes

Abstract: In this study, an effect of addition of nanoparticles into a dye-sensitized solar cells (DSCs) ionic liquid electrolyte was explored. Carbon nanotubes, other carbon nanoparticles and titanium dioxide nanoparticles were dispersed individually into a 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMIm-TFSI) ionic liquid electrolyte by grinding. It was centrifuged to form an ionic nanocomposite gel electrolyte. The dispersion of nanoparticles resulted in a substantial increase in their viscosity. Their electric conductivity increased as well. Notable effects were obtained in photocurrent density and voltage measurements of the DSC assembled with them. Energy conversion efficiency of them was significantly improved and increased compared with a DSC using a bare ionic liquid electrolyte.

Long-term stability testing of dye-sensitized solar cells

Abstract: This study comprises the behavior of dye-sensitized nanocrystalline TiO 2 solar cells (nc-DSC) under various testing conditions regarding accelerated aging. nc-DSCs are potentially vulnerable to various kinds of degradation. The cell performance is seriously decreased upon heat treatments, despite the fact that leakage of the electrolyte liquid is effectively prevented. Even when cells are stored in the dark at elevated temperatures, apparently side reactions occur, resulting in cell degradation. Since elevated temperatures are hard to exclude under normal operation conditions, this is the most critical criterion regarding long-term stability. The nc-DSC should be modified in such a way that it is not sensitive to elevated temperatures, representative for outdoor conditions. The emphasis of this paper is on the long-term stability of nc-DSCs at high temperature. nc-DSCs have been subjected to various aging tests. A cyclic test comprising thermal stress in the dark (85 °C) alternated by full sun illumination under milder conditions reveals a recovery process occurring in degraded cells. A combination of 85 °C and full sun illumination leads to a significant decrease of the cell performance.

Solar photocatalytic disinfection of a group of bacteria and fungi aqueous suspensions with TiO2, ZnO and Sahara desert dust

Abstract: This photocatalytic method was aimed to destroy bacteria, to prevent fungi in some industrial products and to create desirable hygienic medium under solar irradiation. The efficiencies of disinfection with the photoactive metal oxides and the Sahara desert dust was investigated. We have studied photocatalytic disinfection of two-groups of microorganisms which are known as bacteria and fungus in pathogenic-organisms: Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus, Saccharomyces cerevisiae, Candida albicans, Aspergillius niger . Aqueous suspension of the microorganisms (1.10 5 cfu/ml), in the presence of TiO 2 , ZnO and Sahara desert dust were irradiated with a 400 W sodium lamp for various time periods in order to simulate solar radiation. Minimum catalyst concentration was used as 0.01 mg/ml. Sahara desert dust that contain some photoactive/inactive metal oxides (ZnO, Fe 2 O 3 , etc.) and some organics, is known as fertilizer of bioactivities in nature. In accordance with, no microbicidal effect of Sahara dust. Efficient microbicidal effects of TiO 2 and ZnO were detected under sodium light irradiations. Except for A. niger , all selected bacteria and fungus were disinfected in a short period by using 400 W sodium lamp in the presence of photocatalysts. Three strains of bacteria were destroyed in 40 min, two strains of fungi were also destroyed in 120 min at the same conditions. Photocatalytical method is an advantageous and an alternative one in comparison with former literatures.

Degradation of bisphenol A in water by the photo-Fenton reaction

Abstract: The photodegradation of bisphenol A (BPA), a representative endocrine disrupting chemical, was carried out in the presence of the Fenton reagent. The degradation rate was strongly influenced by the pH, and initial concentrations of H2O2 and Fe(II). An initial BPA concentration of 10 mg l−1 was completely degraded after 9 min under the optimum conditions. This reaction was found to follow the first order kinetics law. The formation of CO2 as a result of mineralization of BPA was observed during the photo-Fenton process. The degree of BPA conversion to CO2 was more than 90% under UV irradiation for 36 h. The decomposition of BPA during the photo-Fenton treatment gave six kinds of intermediate products, such as phenol, p-hydroquinone, etc. The degradation mechanism of BPA was proposed on the base of the evidence of the identified intermediates. Based on these results, the photo-Fenton reaction could be useful technology for the treatment of wastewater containing BPA.

Kinetic modeling of photocatalytic degradation of Acid Red 27 in UV/TiO2 process

Abstract: The photocatalytic degradation of Acid Red 27 (AR27) was investigated using UV radiation in the presence of TiO2-P25 as a function of initial concentration of AR27 ([AR27]0), oxygen concentration ([O2]), TiO2-P25 amount, light intensity (Ia), pH and temperature. The activation energy of the photocatalytic degradation of AR27 was 8.24 kJ mol−1. The photocatalytic degradation rate follows pseudo-first order kinetic with respect to the AR27 concentration. The following rate of decolorization was achieved by kinetic modeling: r AR 27 =5.294 I a exp −8247 RT 0.79 O 2 1+0.79 O 2 4.23 AR 27 1+4.23 AR 27 0 The calculated results obtained from above equation were in good agreement with experimental data. This model predicts the concentration of AR27 during the photodegradation process at different temperatures, light intensities, AR27 and oxygen concentrations.

Two-photon absorption cross-sections of common photoinitiators

Abstract: Recent interests in and applications of two-photon absorption (2PA) induced photopolymerization have afforded advanced opportunities to perform three-dimensionally resolved polymerization, resulting in intricate microfabrication and imaging. Many of the reported 2PA-induced polymerizations make use of commercially available photoinitiators, and a key parameter to consider is the two-photon absorption cross-section (δ) of the initiator. To date, there has been no comprehensive investigation of two-photon absorptivity of commercial photoinitiators, though a few studies presenting novel photoinitiators for two-photon polymerization have appeared. Herein, we report the 2PA properties of common, commercially available photoinitiators typically utilized in conventional radiation curing science and technologies, and often used in 2PA-based polymerizations. Z-scan and white-light continuum (WLC) pump–probe techniques were utilized to obtain two-photon absorption cross-sections ( δ). The results for most compounds were found to yield good agreement between the two methods. Most of the photoinitiators studied possess low δ, except Irgacure OXE01, indicating a need for the development of new photoinitiators with improved properties optimized for 2PA applications. A compound prepared in our laboratories exhibits high 2PA and was useful as a two-photon free-radical photoinitiator. © 2004 Elsevier B.V. All rights reserved.

Effect of alkaline-doped TiO2 on photocatalytic efficiency

Abstract: Alkaline (Li, Na, K) modified titanium dioxide nanoparticles were prepared by sol–gel route and by impregnation technology. XRD analysis showed that the crystallinity level of catalysts is largely dependent on both the nature and the concentration of alkaline. Indeed, the best crystallinity is obtained for Li-doped TiO2 and is lowest for K-doped TiO2. In general, it was found that the anatase phase is stabilised by the alkaline. pH of zero charge has been found to be in the range 6.6–7.9. Depending on the alkaline concentration, the charge compensation may occur at the surface of the catalyst in acidic and basic environment. For photocatalytic test, Malachite green oxalate, 4-hydroxybenzoic acid and benzamide were used as representative organic pollutants. The catalysts prepared by the impregnation technique were found more efficient than those prepared by sol–gel route, for a given alkaline concentration. When applied to the Malachite green degradation, the best results were obtained for 5% Li-doped TiO2 prepared by impregnation technique. Whatever the alkaline used, and at low concentration, our results show that the efficiency of the catalysts, when prepared by impregnation technique, is better than that of TiO2-P25. Therefore, at low concentration, alkaline doped-TiO2 can be considered as promising materials for organic pollutants degradation.

Effect of doping mode on the photocatalytic activities of Mo/TiO2

Abstract: The thin films of photocatalyst, TiO2 doped by Mo6+ in different forms, were prepared by sol–gel method. The photocatalysts were characterized by X-ray diffraction (XRD), UV-Vis transmittance spectra and electrochemical impedance spectroscopy, and the photocatalytic activity was characterized by photocatalytic degradation of aqueous methyl orange under UV radiation. The results showed that the TiO2 doped by Mo6+ extend absorption edge and interfacial charge transfer resistance decrease. The photocatalytic activity of TiO2 doped by Mo6+ in bottom is much better than that of pure TiO2, those doped in surface, or those doped uniformly. The activity of TiO2 doped by Mo6+ in bottom mode at optimal concentration, 1 at.%, increased nearly two times than pure TiO2. The effects of doping modes on the photocatalytic activities were discussed in the terms of separateness of charge carriers that there maybe form barrier of carrier in bottom doping mode and then restraining the (e−–h+) pair recombination.

Photocatalysis in microreactors

Abstract: A photocatalytic microreactor with immobilized titanium dioxide as photocatalyst and illuminated by UV-A light emitting diodes was constructed and tested for the degradation of the model substance 4-chlorophenol. The microreactor consisted of 19 channels with a cross-section of approximately 200 μm ×300 μm. Intrinsic kinetic parameters of the reaction could be determined and mass-transfer limitations for the employed operating conditions could be excluded by calculating appropriate Damkohler numbers. Photonic efficiencies for the degradation of 4-chlorophenol are provided. The illuminated specific surface of the microstructured reactor surpasses that of conventional photocatalytic reactors by a factor of 4–400.

New ultraviolet absorption cross-sections of BrO at atmospheric temperatures measured by time-windowing Fourier transform spectroscopy

Abstract: The UV absorption cross-section spectra of the atmospherically important radical BrO have been determined using the recently developed technique of time-windowing Fourier transform spectroscopy (TW-FTS). The absorption spectra of the A 2 Π 3/2 – X 2 Π 3/2 band system were recorded in the flash photolysis of a gaseous mixture of Br2 and O3. The bromine-photosensitized decomposition of O3 was observed at five different temperatures between 203 and 298 K. The absolute UV absorption cross-section was determined from the time-dependent observation of reactant and product absorptions and by a kinetic analysis of the BrO behavior. The integrated UV absorption cross-section of BrO was, within the accuracy of the measurements, constant over the temperature range studied, as expected from spectroscopic considerations. For the (7, 0) vibrational band at 29 540 cm−1 (338.5 nm), the peak absorption cross-sections were determined to be 2.19±0.23 at 298 K, 2.23±0.23 at 273 K, 2.52±0.26 at 243 K, 2.75±0.29 at 223 K, and 3.03±0.31 at 203 K (all in units ×10−17 cm2 per molecule, at a spectral resolution of 3.8 cm−1, with error intervals of 2σ). Further, vibrational constants and the dissociation limit for the electronic state A 2 Π 3/2 were derived. The A←X dissociation energy was determined to be D 0 =35 240±160 cm−1 or 421.6±1.9 kJ/mol.

Photodegradation of dye pollutants on silica gel supported TiO2 particles under visible light irradiation

Abstract: In this paper, silica gel supported titanium dioxide particles (TiO2/SiO2) prepared by acid-catalyzed sol–gel method was as photocatalyst in the degradation of acid orange 7 (AO7) in water under visible light irradiation. The particles were characterized by X-ray diffraction, BET specific surface area determination, and point of zero charge measurement. The supported catalyst had large surface area, high thermal stability and good sedimentation ability. The photodegradation rate of AO7 under visible light irradiation depended strongly on adsorption capacity of the catalyst, and the photoactivity of the supported catalyst was much higher than that of the pure titanium dioxides. The photodegradation rate of AO7 using 31% TiO2/SiO2 particles was faster than that using P-25 and TiO2 (Shanghai) as photocatalyst by 2.3 and 12.3 times, respectively. The effect of the calcination temperature and the TiO2 loading on the photoactivity of TiO2/SiO2 particles was also discussed.

Light-driven oxygen scavenging by titania/polymer nanocomposite films

Abstract: We demonstrate that UV illumination of nanocrystalline TiO2 films in the presence of excess organic hole scavengers can result in the deoxygenation of a closed environment. The kinetics of deoxygenation are investigated under continuous UV illumination as a function of film preparation and hole scavenger employed. Optimum deoxygenation is observed using methanol as a hole scavenger, although efficient deoxygenation is also observed for a range of different polymer/TiO2 nanocomposite films deposited on glass and plastic substrates. Transient absorption spectroscopy is used to probe the kinetics of the deoxygenation reaction, focusing on the kinetics of the reduction of oxygen by photogenerated TiO2 electrons. Under aerobic conditions, this oxygen reduction reaction is observed to exhibit first order kinetics with a rate constant of 70 s−1, more than one order of magnitude faster than alternative reaction pathways for the photogenerated electrons. These observations are discussed in terms of the Langmuir–Hinshelwood equation for photocatalytic action.

Photodegradation of rhodamine B in water assisted by titania films prepared through a novel procedure

Abstract: Well-crystallized anatase thin films were prepared through direct oxidation of metallic titanium with 30 mass% hydrogen peroxide solution at 80 ◦ C for 5 h, followed by soaking in distilled water at 80 ◦ C for 3 days The photodegradation of a dye solution, rhodamine B (RB), assisted by such deposited anatase films was studied It was found that the well-crystallized anatase thin films induced complete degradation of RB in water with an initial concentration of less than 002 mM after 4–5 h of illumination under a 450 W high-pressure mercury lamp The RB decayed directly to colorless end products of water and mineral acids However, when the photocatalytic activity of the anatase films decreased after several repeated uses, an N-de-ethylation process producing rhodamine as an intermediate was evident during the photocatalytic degradation of RB © 2004 Elsevier BV All rights reserved

Synthesis of visible-light-active nanosize rutile titania photocatalyst by low temperature dissolution–reprecipitation process

Abstract: Titania nanocrystals were prepared by a “low temperature dissolution–reprecipitation process” (LTDRP) in liquid media. The crystallization of amorphous precursor could proceed at low temperature around room temperature, which was much lower than those of conventional calcination and hydrothermal reactions. The thermodynamically stable rutile formed at low temperature below 70 °C, while the metastable anatase formed at higher temperature. The phase composition, microstructure, morphology, and specific surface area of titania changed significantly depending on the reprecipitation temperatures. Needle-like rutile titania and spherical anatase titania crystals with high specific surface areas were prepared. Well-crystallized needle-like nanosize rutile crystals possessed higher photocatalytic activities than those of anatase crystals under visible light irradiation of wavelength >400 and/or >510 nm.

Low temperature preparation of mesoporous TiO2 films for efficient dye-sensitized photoelectrode by chemical vapor deposition combined with UV light irradiation

Abstract: A new method for fabricating plastic film-based mesoporous TiO2 electrodes for efficient dye-sensitized solar cells is described. TiO2 nanocrystalline layers electrophoretically deposited on indium-tin-oxide (ITO)-coated polyethylene terephthalate (PET) film was post-treated with chemical vapor deposition (CVD) of Ti alkoxide followed by UV light irradiation at temperatures below 110 °C. UV-assisted CVD treatment drastically enhanced dye-sensitized photocurrent and improved photovoltage up to 750 mV. A film electrode bearing Ru complex (Ru 535-bis TBA) dye-sensitized TiO2 on ITO–PET yielded solar energy conversion efficiency of 3.8%.

Preparation and characterization of ZnO/TiO2, SO42-/ZnO/TiO2 photocatalyst and their photocatalysis

Abstract: A novel binary oxide photocatalyst ZnO/TiO 2 was prepared by a new modified sol–gel method using citric acid as a complex reagent and its photocatalytic activity was investigated. The factors, such as the ratio of amount of doped zinc ion, the precursors, and the calcination temperature on the activities of ZnO/TiO 2 photocatalyst, were investigated. SO 4 2− /ZnO/TiO 2 was prepared by sulfating the dry gels of ZnO/TiO 2 with H 2 SO 4 solution. It was showed that the addition of ZnO could enhance the activity significantly, and sulfating ZnO/TiO 2 with sulfuric acid resulted to dramatic enhancement, the degradation ratio of methyl orange could be up to 71.9%, compared with 55% of degradation of ZnO/TiO 2 catalyst.

Titanium dioxide sol–gel deposited over glass and its application as a photocatalyst for water decontamination

Abstract: Photocatalytic degradation of water pollutants using TiO 2 and solar light has been proposed as an effective alternative of treatment. Usually, TiO 2 as a finely divided powder is added to polluted water forming a suspension, which is then irradiated under sunlight to conduct photochemical reactions. Although the literature frequently points out the minor efficiency of immobilized systems, it is desirable to look for a fixed catalyst to avoid wastes of time and materials during separation of the powder at the end of the treatment. This paper presents results that show the use of anatase thin films as an efficient form of deposited TiO 2 for the photocatalytic degradation of 4-chlorophenol, a priority pollutant commonly used as a model in photocatalysis, and for carbaryl, a carbamic pesticide. The thin films were deposited over small cylindrical pieces of glass, using a sol–gel technique, the average thickness being 600 nm, and having a band gap of 3.28 eV. The anatase TiO 2 -covered glasses were used to fill a cylindrical photoreactor located at the focus of a parabolic solar collector able to concentrate up to 41 suns. Results show that the films are an effective catalyst in photodegradation, under solar irradiation, and conduct to similar values as those for TiO 2 in suspension. The photoefficiency obtained is similar to that obtained using powder suspension. These results compel us to the continued pursuit of TiO 2 immobilization.

Photo-catalytic reduction of carbon dioxide to methane using TiO2 as suspension in water

Abstract: Photo-catalytic reduction of CO 2 to methane was studied in CO 2 -saturated aqueous solution in presence of TiO 2 photo-catalyst (0.1%, w/v) as a suspension using 350 nm light. CO 2 methanation rate was very much enhanced in the presence of 2-propanol as a hole scavenger. In addition to CO 2 reduction, photo-catalytic reduction of methanol in N 2 -purged system was also tried but no methane was generated in presence of TiO 2 without 2-propanol. The yield of methane was quite low even in presence of 2-propanol in this system. In the methanol photolysis CO 2 was found to be the main product with a yield of 60×10 −8 mol to 200×10 −8 mol . This shows that the generation of CH 4 from CO 2 does not proceed via methanol as an intermediate under these conditions. In the aerated system also, methane was produced during photolysis of TiO 2 suspension in presence of 2-propanol and its yield was comparable to that in CO 2 -saturated system. This suggests that surface-adsorbed as well as in situ generated CO 2 are equally responsible for methane formation through photo-reduction in presence of TiO 2 . In the aerated system, 45 μmol CO 2 was produced by photo-degradation of 2-propanol. In O 2 -saturated system, the methane yield was lower as compared to that in aerated system whereas CO 2 yield was higher. Overall, the yield of methane was quite high if extrapolated to per gram of TiO 2 .