Showing papers on "Photocatalysis published in 2001"
TL;DR: Film and powders of TiO2-x Nx have revealed an improvement over titanium dioxide (TiO2) under visible light in optical absorption and photocatalytic activity such as photodegradations of methylene blue and gaseous acetaldehyde and hydrophilicity of the film surface.
Abstract: To use solar irradiation or interior lighting efficiently, we sought a photocatalyst with high reactivity under visible light. Films and powders of TiO 2- x N x have revealed an improvement over titanium dioxide (TiO 2 ) under visible light (wavelength 2 has proven to be indispensable for band-gap narrowing and photocatalytic activity, as assessed by first-principles calculations and x-ray photoemission spectroscopy.
11,402 citations
TL;DR: In this article, the TiO2/UV photocatalytic degradation of methylene blue (MB) has been investigated in aqueous heterogeneous suspensions, and it has been shown that the degradation pathway can be determined by a careful identification of intermediate products, in particular aromatics, whose successive hydroxylations lead to the aromatic ring opening.
Abstract: The TiO2/UV photocatalytic degradation of methylene blue (MB) has been investigated in aqueous heterogeneous suspensions. In addition to a prompt removal of the color, TiO2/UV-based photocatalysis was simultaneously able to oxidize the dye, with an almost complete mineralization of carbon and of nitrogen and sulfur heteroatoms into CO2 ,N H4 + ,N O3 − and SO4 2− , respectively. A detailed degradation pathway has been determined by a careful identification of intermediate products, in particular aromatics, whose successive hydroxylations lead to the aromatic ring opening. These results suggest that TiO2/UV photocatalysis may be envisaged as a method for treatment of diluted waste waters in textile industries. © 2001 Elsevier Science B.V. All rights reserved.
2,359 citations
TL;DR: Experimental results clearly indicated that the initiation stage of the photooxidation of CdSe nanocrystals was not caused by the chemical oxidation of the system kept in air under dark conditions or the hydrolysis of the cadmium-thiol bonds on the surface of the nanocrystal, both of which were magnitudes slower than the photocatalytic oxidization of the surface ligands if they occurred at all.
Abstract: The photochemical instability of CdSe nanocrystals coated by hydrophilic thiols was studied nondestructively and systematically in water. The results revealed that the photochemical instability of the nanocrystals actually included three distinguishable processes, namely the photocatalytic oxidation of the thiol ligands on the surface of nanocrystals, the photooxidation of the nanocrystals, and the precipitation of the nanocrystals. At first, the thiol ligands on the surface of a nanocrystal were gradually photocatalytically oxidized using the CdSe nanocrystal core as the photocatalyst. This photocatalytic oxidation process was observed as a zero-order reaction in terms of the concentration of the free thiols in the solution. The photogenerated holes in a nanocrystal were trapped onto the thiol ligands bound on the surface of the nanocrystal, which initiated the photooxidation of the ligands and protected the nanocrystal from any photooxidation. After nearly all of the thiol ligands on the surface of the ...
1,079 citations
TL;DR: In this article, the photocatalytic activity of tetragonal BiVO4 for O2 evolution from an aqueous AgNO3 solution under visible light irradiation was negligible.
Abstract: BiVO4 powder with scheelite structure was obtained by hydrolyzing a nitric acid solution of Bi(NO3)3 and Na3VO4 with bases (Na2CO3 and NaHCO3) at room temperature. Tetragonal BiVO4 of a high-temperature form was obtained after 4.5 h of preparation time while monoclinic BiVO4 was done after 46 h. Although the structure and the band gap of tetragonal BiVO4 with scheelite structure were similar to those of monoclinic BiVO4, the photocatalytic activity of the tetragonal BiVO4 for O2 evolution from an aqueous AgNO3 solution under visible light irradiation was negligible. In contrast, the monoclinic BiVO4 showed high photocatalytic activity. Distortion of a Bi−O polyhedron by a 6s2 lone pair of Bi3+ plays an important role for high photocatalytic activity of the monoclinic BiVO4 under visible light irradiation.
947 citations
TL;DR: In this article, a new photocatalyst (WOx-TiO2) powder was prepared by a sol-gel method by extending light absorption of the TiO2-based photocatalysts toward the visible light range and eliminating the rapid recombination of excited electrons/holes during photoreaction.
Abstract: With an attempt to extend light absorption of the TiO2-based photocatalysts toward the visible light range and eliminate the rapid recombination of excited electrons/holes during photoreaction, new photocatalyst (WOx-TiO2) powder was prepared by a sol–gel method. The photooxidation efficiency of WOx-TiO2 catalyst was also evaluated by conducting a set of experiments to photodegrade methylene blue (MB) in aqueous solution. The photocatalytic activity of WOx-TiO2 was examined by X-ray diffraction (XRD), UV–VIS absorption spectra, X-ray photoelectron emission spectroscopy (XPS), photoluminescence spectra (PL), surface photovoltage spectra (SPS) and electron-field-induced surface photovoltage spectra (EFISPS). The experiments demonstrated that the MB in aqueous solution was successfully photodegraded using WOx-TiO2 under visible light irradiation. It was found that an optimal WOx dosage of 3% in WOx-TiO2 achieved the highest rate of MB photodegradation in this experimental condition. It has been confirmed that WOx-TiO2 could be excited by visible light (E
672 citations
TL;DR: In this paper, a new type of photocatalysts (Au/Au3+-TiO2) powder was prepared by a photoreduction/sol−gel process.
Abstract: With an attempt to extend light absorption of TiO2-based photocatalyst toward the visible light range and eliminate the rapid recombination of excited electrons/holes during photoreaction, a new type of photocatalysts (Au/Au3+-TiO2) powder was prepared by a photoreduction/sol−gel process. The crystal phase composition, surface structure, and light absorption of the new photocatalysts were comprehensively examined by X-ray differential detection (XRD), UV−visible absorption spectra, X-ray photoelectron emission spectroscopy (XPS), and photoluminescence (PL) spectra. The photooxidation efficiencies of the photocatalysts were also evaluated in the photodegradation of methylene blue (MB) in aqueous solutions under visible light irradiation from a high-pressure sodium lamp (λ > 400 nm). The results of PL analyses in this study indicated that the gold/gold ion-doping on the surface of TiO2 could eliminate the electron/holes recombination and also increase the light absorption in the visible range. The analytica...
643 citations
TL;DR: The reduction of Cr(VI) in aqueous solution by UV/TiO2 reduction process was studied under various solution pH values, TiO2 dosages, light intensities, dissolved oxygen levels and other operating conditions to determine the reduction rates by photocatalytic-induced elections.
594 citations
TL;DR: In this paper, the degradation of 2-phenylphenol (OPP) can be photocatalysed by TiO 2 and ZnO, and a mechanism is proposed for the photocatalytic transformation of OPP.
Abstract: The degradation of 2-phenylphenol (OPP), commonly used as fungicide, can be photocatalysed by TiO 2 and ZnO. The latter is a little more efficient but cannot be used in acidic solution. In both cases, the main identified photoproducts are hydroquinone (HQ), p -benzoquinone (BQ), phenylhydroquinone (PHQ), phenylbenzoquinone (PBQ), 2,2′- and 2,3-dihydroxybiphenyls (2,2′- and 2,3-BPh(OH) 2 ). The observed minor formation of 2-hydroxydibenzofuran is due to the photocyclisation of PBQ. The influence of various parameters is considered. The phototransformation of OPP is slightly favoured by increasing pH. It is enhanced by the addition of small amounts of H 2 O 2 , but it is inhibited by high concentrations of chloride, sulphate or nitrate. From the inhibiting effect of alcohols, it is deduced that the main degradation pathway involves hydroxyl radicals, but a direct oxidation by positive holes h + is probably not negligible. The observed slow photodegradation of ZnO in unbuffered solution is attributed to an electrochemical process. A mechanism is proposed for the photocatalytic transformation of OPP.
572 citations
TL;DR: In this article, aqueous TiO2 dispersions under UV illumination was examined to assess the influence of temperature, pH, concentration of dissolved oxygen (DOC), initial concentration of MB, and light intensity on the kinetics of decomposition.
Abstract: Methylene blue (MB) is a representative of a class of dyestuffs resistant to biodegradation Its decomposition was examined in aqueous TiO2 dispersions under UV illumination to assess the influence of temperature, pH, concentration of dissolved oxygen (DOC), initial concentration of MB, and light intensity on the kinetics of decomposition Hypsochromic effects (ie blue shifts of spectral bands) resulting from N-demethylation of the dimethylamino group in MB occurs concomitantly with oxidative degradation The maximum quantity of MB adsorbed on TiO2, and the kinetics of degradation of MB and of total organic carbon (TOC) removal were also measured at constant pH 4 Photobleaching of MB solutions takes place at low DOCs and is caused by a reversible reductive process involving photogenerated electrons on TiO2 The rate of degradation of MB remains fairly constant regardless of whether the dispersion was purged with oxygen prior to irradiation or with air during the light irradiation period The photocatalytic process depends on light intensity, but not on the total light energy absorbed The photoreaction followed pseudo-first-order kinetics even at high MB concentrations (03 mM) The temperature dependence of the photodegradation kinetics was assessed (E a =89 kJ/mol ) , as well as the relative photonic efficiency, ξr, relative to phenol (048)
541 citations
TL;DR: In this article, a modified sol-gel process using different alkoxide precursors was used to obtain carbon-containing catalysts with large surface areas, capable to photodegrade p-chlorophenol (4CP) with visible light (λ>400nm).
Abstract: Photocatalysts based on titanium dioxide have been prepared by a modified sol–gel process using different alkoxide precursors. Depending on the precursor and the calcination temperature of the gels, carbon-containing catalysts with large surface areas, capable to photodegrade p-chlorophenol (4CP) with visible light (λ>400 nm), have been obtained. Photodegradation and mineralisation were confirmed by HPLC and TOC measurements. The catalysts were characterised by physisorption of argon, elemental analysis, EPR, UV/VIS, X-ray powder diffraction (XRD), FT-IR and high-resolution transmission electron microscopy (HRTEM). A highly condensed, carbonaceous species formed during calcination is responsible for the photosensitisation. When used as a photoelectrode, the appearance of a photocurrent indicated the semiconductor nature of these novel materials. The catalysts exhibit a surprisingly good long-time stability despite of the carbonaceous nature of the sensitising species. It is also shown, that commercially available TiO2 can be photosensitised by impregnation with suitable alcohols followed by pyrolysis.
509 citations
TL;DR: In this paper, the authors highlight the advances that have been made and identify some of the gaps in our current knowledge of these materials and discuss size quantization effects and semiconductor quantum dots.
Abstract: A diverse array of semiconductor-based composite materials have been prepared, characterized, and utilized in many applications ranging from photocatalysis, photovoltaic cells, photoelectrochromic displays, and light-emitting devices to sensors. The composite architectures (nanoarchitectures in many cases) are equally diverse. In this review, we highlight the advances that have been made and identify some of the gaps in our current knowledge of these materials. Size quantization effects and semiconductor quantum dots are also discussed.
TL;DR: In this paper, a detailed degradation pathway has been determined by careful identification of intermediate products, in particular, carboxylic acids, whose decarboxylation by photo-Kolbe reactions constitutes the main source of CO2 evolution.
TL;DR: In this paper, the role of the gold layer in promoting the photocatalytic charge transfer has been probed using thiocyanate oxidation at a rate constant of 1.25 × 109 s-1.
Abstract: Semiconductor/metal composite nanoparticles have been synthesized by chemically reducing HAuCl4 on the surface of preformed TiO2 nanoparticles. These gold-capped TiO2 nanoparticles (particle diameter 10−40 nm) were stable in acidic (pH 2−4) aqueous solutions. At low [TiO2]:[Au] ratio (<1:1), these composite nanoparticles are bigger in size (20−40 nm) and readily undergo aggregation. The TiO2/Au nanoparticles with TiO2:Au ratio ≥1:10 were relatively stable to 532 nm laser irradiation. On the other hand 532 nm laser pulse excitation of aggregated nanoparticles ([TiO2]:[Au] ≤ 1:1) led to morphological changes as they fused to produce large-size particles. Laser-induced melting/fusion was confirmed from the growth in the particle size as well as the disappearance of the aggregation absorption band. The process of melting and fusion occurred with an apparent rate constant of 1.25 × 109 s-1. The role of the gold layer in promoting the photocatalytic charge transfer has been probed using thiocyanate oxidation at...
TL;DR: In this paper, physical adsorption and photocatalytic reduction of eight environmentally significant metal ions in TiO2 suspensions of Degussa P25 and Hombikat UV100 were investigated.
TL;DR: A novel method for preparing highly photoactive nano-sized TiO2 photocatalysts with anatase and brookite phases has been developed by hydrolysis of titanium tetraisoproproxide in pure water or a 1:1 EtOH-H2O solution under ultrasonic irradiation.
TL;DR: In this article, a transparent TiO2 nanometer thin film with high photocatalytic activity was prepared on soda-lime glass substrates via the sol-gel method using the TiO 2 sol solution.
TL;DR: In this paper, thermal and hydrothermal treatments have been applied to an amorphous TiO2 precursor for obtaining nanosized TiO 2 particles (P11t and P11h, respectively) of different photocatalytic properties.
TL;DR: In this article, the surface properties of ZnO ultrafine particles were studied using TEM, XRD, BET, SPS, EPR, IR, and XPS.
TL;DR: In this article, a high performance photocatalytic TiO2 thin film was successfully obtained by reactive DC magnetron sputtering, which was deposited onto SiO2-coated glass at a substrate temperature of 220°C using a titanium metal target.
TL;DR: In this paper, the effect of particle size and phase composition of those TiO2 nanoparticles on photocatalytic properties such as decomposition of methylene blue, bacteria and ammonia gas were investigated.
Abstract: Titanium dioxide (TiO2) nanoparticles were prepared by the oxidation of titanium tetrachloride (TiCl4) in a diffusion flame reactor. The average diameter of particles was 15–30 nm and mass fraction of anatase ranged from 40% to 80%. Effects of particle size and phase composition of those TiO2 nanoparticles on photocatalytic properties such as decomposition of methylene blue, bacteria and ammonia gas were investigated. The degree of decomposition of methylene blue by the TiO2 nanoparticles under the illumination of the black light was directly proportional to the anatase mass fraction, but inversely to the particle size. The decomposition of bacteria and ammonia gas by the TiO2 nanoparticles under the illumination of the fluorescent light showed the same trend as in the case of the methylene blue.
TL;DR: It was proven that adsorption of dye molecules onto the support material is essential for the processes to be effective and even if their mechanisms differ during the early stages, photocatalysis and photosensitization lead to very similar ultimate breakdown products.
TL;DR: The study showed that the photo-Fenton process, (a mixture of hydrogen peroxide and ferrous or ferric ion), was the most effective treatment process under acidic conditions and produced a higher rate of degradation of p-chlorophenol at a very short radiation time.
TL;DR: In this paper, it was shown that anatase TiO2 dissolves into an HF solution more easily than rutileTiO2, and this property was confirmed by X-ray diffraction patterns and diffuse reflection spectra.
Abstract: We have found that anatase TiO2 dissolves into an HF solution more easily than rutile TiO2. Using this property, we succeeded in isolating pure rutile particles from TiO2 powder consisting of rutile and anatase phases by the HF treatment. The isolation of pure rutile particles was confirmed by X-ray diffraction patterns and diffuse reflection spectra. The rutile particle showed much lower photocatalytic activity than the original powder, if compared for the oxidation of 2-propanol in aqueous solution using dissolved oxygen as the electron acceptor. On the other hand, when Fe(III) ions were used as the electron acceptor for oxidation of 2-propanol and water, the activity scarcely changed after the HF treatment. These results indicate that rutile TiO2 has poor activity for the reduction of oxygen, and the presence of a small amount of an anatase component is crucial for an efficient photocatalytic reaction on TiO2 particles using oxygen as the electron acceptor.
TL;DR: The photocatalytic degradation of p-chlorophenoxyacetic acid has been investigated in oxygenated aqueous suspensions of lanthanide oxide-doped TiO2 photocatalyst and complete mineralization was achieved.
Abstract: The photocatalytic degradation of p-chlorophenoxyacetic acid has been investigated in oxygenated aqueous suspensions of lanthanide oxide-doped TiO2 photocatalysts. Complete mineralization was achieved. The enhanced degradation is attributed to the formation of Lewis acid-base complex between the lanthanide ion and the substrate.
TL;DR: In this paper, electron spin resonance spectroscopy (ESR), Fourier transform infrared (FTIR), and monitoring of pyridine (py) and boric acid trimethyl ester (BATE) adsorption for determining surface acidity and basicity, respectively, were used to carry out further characterization of mixed ZnO/TiO2 polycrystalline solids prepared by different methods.
Abstract: Electron spin resonance spectroscopy (ESR), Fourier transform infrared spectroscopy (FTIR), and monitoring of pyridine (py) and boric acid trimethyl ester (BATE) adsorption for determining surface acidity and basicity, respectively, were used to carry out further characterization of mixed ZnO/TiO2 polycrystalline solids prepared by different methods. Moreover, the powders were tested in a batch photoreactor for a probe reaction, i.e., 4-nitrophenol photodegradation in aqueous medium. ESR results indicated the presence of signals attributable to Zn+ species in ZnO/TiO2 (anatase) solids, while in ZnO/TiO2 (rutile) samples the presence of zinc induced only the formation of signals probably due to Ti3+ centers. FT-IR spectra showed no significant differences of the surface hydroxylation degree of the various photocatalysts, whereas the surface acidic properties generally decrease by increasing the amount of ZnO. Coupling of ZnO and TiO2 semiconducting powders was not so beneficial, as expected on the basis of...
TL;DR: In this study, a photocatalytic decolorization system equipped with immobilized TiO2 and illuminated by solar light was used to remove the color of wastewater and showed potential application for decoloring organic dyes in wastewater.
TL;DR: In this paper, reduction treatment using low-temperature hydrogen plasma with elevated temperatures was applied on anatase TiO2 powder of ST-01 without causing a phase transition to rutile.
Abstract: In order to realize a visible (vis)-light-active TiO2 photocatalyst, reduction treatment using low-temperature hydrogen plasma with elevated temperatures was applied on anatase TiO2 powder of ST-01 without causing a phase transition to rutile. According to plasma-heat treatment, oxygen was evacuated from ST-01 particles and the colored ST-01, ivory to beige, was obtained. XPS results showed non-stoichiometric, expressed as TiO2−x
} and x was increased with the increase of treating time. Plasma-heat treated ST-01 showed new ESR signal at g = 2.003 assigned to electrons trapped at the oxygen-defect site. This signal was strengthened when vis-light illumination was applied. Results of vis-light activity tests, evaluated by photocatalytic oxidation of benzoic acid in liquid phase and 2-propanol in gas phase using vis-light illumination (>406 nm), showed excellent activity while low ST-01 showed almost no activity on both tests.
TL;DR: In this paper, the photocatalytic degradation of polyvinyl chloride (PVC) and TiO2 composite films was investigated under the ambient air in order to assess the feasibility of developing photodegradable polymers.
Abstract: The solid-phase photocatalytic degradation of poly(vinyl chloride) (PVC)–TiO2 composite films was investigated under the ambient air in order to assess the feasibility of developing photodegradable polymers. The photodegradation of the composite films was compared with that of pure PVC films through performing weight loss monitoring, scanning electron microscopic (SEM) analysis, gel permeation chromatography (GPC), FT-IR and UV–VIS spectroscopy, and X-ray photoelectron spectroscopy (XPS). TiO2-embedded PVC showed highly enhanced photodegradation. Irradiating the composite film for 300 h under air reduced its average molecular weight by two-thirds and weight by 27% while the irradiation under nitrogen atmosphere induced little degradation. The photocatalytic degradation of the composite film accompanied the increase in the FT-IR carbonyl peak intensity, the evolution of CO2 and H2O, and the whitening due to the visible light scattering from growing cavities. XPS analysis of the composite film showed that the surface concentration of oxygen increased while that of chlorine decreased with irradiation. The SEM images of the irradiated composite films showed the development of cavities around the imbedded TiO2 particles and implied that active oxygen species which were photogenerated on TiO2 surface desorb and diffuse across a few micrometers to react with the polymer matrix.
TL;DR: In this paper, the average diameter of agglomerated MoO3/TiO2 particles in aqueous solution is only 85−110 nm, which is about one-fifth to one-fourth of that of pure TiO2 suspension.
Abstract: By monolayer coverage of highly acidic semiconductors, such as MoO3 and WO3 on the surface of TiO2 nanoparticles (Degussa P25), the stability of colloidal suspensions in aqueous solution can be greatly improved. The average diameter of agglomerated MoO3/TiO2 and WO3/TiO2 particles in aqueous suspension is only 85−110 nm, respectively, which is about one-fifth to one-fourth of that of pure TiO2 suspension. The optically transparent photocatalytic films have been prepared with deposition of these colloidal suspensions. The colloidal particles in aqueous solution and the prepared transparent photocatalytic films were characterized with TEM, SEM, AFM, and other spectroscopic techniques. It has also been found that the photocatalytic activity of WO3/TiO2 film is 2.8−3 times that of pure TiO2 film in decomposing gas-phase 2-propanol, while MoO3/TiO2 film is less effective.
TL;DR: In this paper, a modified sol-gel process was used to prepare nanostructured TiO 2 catalysts of controlled particle size (i.e. 6, 11, 16 and 20 ).
Abstract: A modified sol–gel process was used to prepare nanostructured TiO 2 catalysts of controlled particle size (i.e. 6, 11, 16 and 20 nm). The influence of the TiO 2 particle size in the gas phase photocatalytic oxidation of toluene was investigated under both dry and humid conditions. The main products of reaction were carbon dioxide and water, although small amounts of benzaldehyde were also detected. The smaller particle size (i.e. 6 nm) lead to higher conversion and complete mineralization of toluene into CO 2 and H 2 O. Both electronic and structural effects (i.e. size and ensemble effects) are responsible for the excellent performance of 6 nm TiO 2 catalyst for toluene photo-degradation. The structural differences between 6 nm TiO 2 and larger catalysts were analyzed using EPR spectroscopy.