Photocatalyst Mass Research Articles

Enhancement of photocatalytic properties of TiO2 for NO photo-oxidation by optimized sol–gel synthesis

TiO2 samples were prepared by the sol–gel method applying a factorial design in order to improve the photocatalytic properties of the semiconductor oxide for the nitric oxide (NO) photo-oxidation reaction. The temperature of calcination and the amount of alcohol and acid used in the course of the sol–gel reaction were selected as critical experimental variables. As the products of the factorial design, 27 TiO2 samples were obtained and characterized by X-ray powder diffraction, scanning electron microscopy, transmission electron microscopy, diffuse reflectance spectroscopy, and adsorption–desorption N2 isotherms. The photocatalytic activity of the TiO2 samples was evaluated in the NO photo-oxidation reaction under UV irradiation. The conversion degree of NO reached by each sample was associated with its physicochemical properties, finding a stronger dependence with the temperature of calcination and morphology of the samples. Different photocatalytic reaction parameters were modified such as mass of photocatalyst, irradiance, flow rate of gas, and relative humidity in order to evaluate their effect in the constants of velocity and adsorption. The TiO2 sample with the highest photocatalytic activity was exposed under different experimental conditions to evaluate its selectivity for the formation of innocuous nitrate ions as final product of the NO photo-oxidation reaction.

Synthesis and characterization of [Zn–Al] LDH: Study of the effect of calcination on the photocatalytic activity

The photocatalytic decolorization of methylene blue (MB) was performed using [Zn–Al] layered double hydroxides (LDH) either as such or calcined. The prepared photocatalysts were characterized by XRD, ICP, TEM, nitrogen physisorption at −196°C and DRS. Photocatalytic study showed that [Zn–Al] LDH without any treatment presented the best photocatalytic activity which was even better than that of commercial ZnO nanoparticles. It provided a decolorization percentage of 90% after 1h irradiation time.The influence of dye concentration, solution pH, photocatalyst dose and some inorganic anions on the photodecolorization of MB was investigated. Results showed that an acidic pH reduced the effectiveness of the photocatalytic process however an alkaline pH slightly improved the reaction. The presence of Cl−, NO3− and CO32− leads to a decrease in the decolorization rate of the dye contrary to SO42− which improved the reaction. The optimum mass of photocatalyst corresponded to 0.49mmol of Zn.The decolorization reaction followed a Langmuir–Hinshelwood model only at low concentrations of MB.

Experimental design as a tool to study the reaction parameters in hydrogen production from photoinduced reforming of glycerol over CdS photocatalyst

The aim of this study was to set the reaction conditions of the photoinduced reforming of glycerol aqueous solution over Pt/hex-CdS under visible light irradiation for enhancement of hydrogen production by using a fractional factorial experimental design followed by a Box–Behnken design. The parameters assessed were irradiation time, mass of photocatalyst, concentration of glycerol, pH and electrolyte concentration (NaCl). The preliminary two-level fractional factorial design (25−1) showed that all of the investigated factors have significant effect in hydrogen production, being pH the most important parameter. The three factors Box–Behnken design showed maximum response for hydrogen production in pH 4.0, 55% glycerol and 1.5 mol L−1 NaCl. The amount of hydrogen obtained under these conditions was 270% higher than our previous result, using the same photocatalyst and electron donor. In the ideal pH, >CdSH2+and >CdOH species are predominant before irradiation, indicating that such species play an important role in the primary steps of the photoelectrochemical mechanism, which served as the basis for proposing a mechanism for hydrogen generation as well as glycerol photooxidation. Based on the surface response [NaCl] × [glycerol], a solution with salinity equivalent to approximately the natural seawater was tested and the result for hydrogen production was comparable to the best condition; besides, under this condition, the solubility of CdS in aqueous solution is reduced.

Hydrothermal Growth of Layered Titanate Nanosheet Arrays on Titanium Foil and Their Topotactic Transformation to Heterostructured TiO2 Photocatalysts

Layered titanate nanostructures have been recognized as an important intermediate in preparing TiO2 nanostructures due to their availability in various morphologies, among which ultrathin nanosheets have attracted particular attention due to their unique properties arising from their high surface area and confined thickness in nanoscale. Herein, we report a simple approach to fabricate heterostructured TiO2 nanosheet array film by (1) hydrothermal growth of sodium trititanate nanosheet array on Ti foil in alkaline solution, (2) ion exchange of Na+ in titanate naosheet with H+, and (3) topotactical transformation into TiO2 nanosheet via thermal annealing. XRD and Raman as well as HRTEM analyses proved the formation of a novel anatase/TiO2(B) heterostructured nanosheet array with coherent interface between the two phases, which exhibited superior photocatalytic efficiency under UV illumination as compared with the relevant commercial products P25 and anode oxidized TiO2 nanotube film of the same thickness but with greater mass of photocatalyst. The high photocatalytic activity of the TiO2 nanosheet array film can be ascribed to the synergistic effect of large surface area and high crystallinity as well as heterojunction between TiO2(B) and anatase phase.

Inactivation and Mineralization of Aerosol Deposited Model Pathogenic Microorganisms over TiO2and Pt/TiO2

Air disinfection from bacteria and viruses by means of photocatalytic oxidation is investigated with microorganisms loaded over photocatalysts' films from aerosols. Deposition method and equipment have been developed to load Mycobacterium smegmatis , Bacillus thuringiensis , vaccinia virus, and influenza A (H3N2) virus on slides with undoped TiO(2) and platinized sulfated TiO(2) (Pt/TiO(2)). Inactivation dynamics was measured under UVA irradiation and in the dark. About 90% inactivation is reached in 30 min irradiation on TiO(2) and from 90 to 99.8% on Pt/TiO(2). The first-order inactivation rate coefficient ranged from 0.18 to 0.03 min(-1), over Pt/TiO(2) being higher than on TiO(2) for all microorganisms except Bacillus thuringiensis. The photocatalytic mineralization of Bacillus thuringiensis was performed on TiO(2) and Pt/TiO(2) with different photocatalyst and microorganism loadings. Completeness of mineralization depended on the TiO(2) to bacteria mass ratio. The rate of the photocatalytic carbon dioxide production grows with both the cell mass increase and the photocatalyst mass increase. Pt/TiO(2) showed increased rate of mineralization as well as of the inactivation likely due to a better charge carrier separation in the doped semiconductor photocatalyst. The results demonstrate that photocatalytic filters with deposited TiO(2) or Pt/TiO(2) are able to inactivate aerosol microorganisms and completely decompose them into inorganic products and Pt/TiO(2) provides higher disinfection and mineralization rates.

Microfibrous TiO2 supported photocatalysts prepared by metal-organic chemical vapor infiltration for indoor air and waste water purification

The photocatalytic degradation of gaseous (toluene) and aqueous (imazapyr, malic acid, orange G) pollutants over TiO2 supported photocatalysts is investigated using a batch reactor. A strong influence of the microstructural characteristics of TiO2 on the decomposition kinetics of the pollutants is found. Well crystallized, porous TiO2-anatase films grown under low pressure at 400–500°C by MOCVD on glass plates and by MOCVI on glass micro-fibers are the best heterogeneous photocatalysts, showing the highest activity. We demonstrate a good control of these characteristics by choosing the deposition parameters. Achieving conformal coverage (i.e. good infiltration) of glass micro-fibers by the TiO2 thin films has also a strong influence on the photocatalytic activity. A correlation between optimal infiltration, film microstructure and photocatalytic activity is established. Strong similarities between optimal photocatalytic decomposition rate in gas and liquid phase were found with respect to the film microstructure and the photocatalyst mass. The total mineralization of the toluene was prevented because of the deactivation of the photocatalyst surface. However the reactivation of the photocatalyst was achieved by UV irradiation under oxygen stream. This allows a long-term use of the photocatalyst.

CuCr 2O 4/TiO 2 heterojunction for photocatalytic H 2 evolution under simulated sunlight irradiation

CuCr 2O 4/TiO 2 heterojunction has been successfully synthesized via a facile citric acid (CA)-assisted sol–gel method. Techniques of X-ray diffraction (XRD), transmission electron microscopy (TEM), and UV–vis diffuse reflectance spectrum (UV–vis DRS) have been employed to characterize the as-synthesized nanocomposites. Furthermore, photocatalytic activities of the as-obtained nanocomposites have been evaluated based on the H 2 evolution from oxalic acid solution under simulated sunlight irradiation. Factors such as CuCr 2O 4 to TiO 2 molar ratio in the composites, calcination temperature, photocatalyst mass concentration, and initial oxalic acid concentration affecting the photocatalytic hydrogen producing have been studied in detail. The results showed that the nanocomposite of CuCr 2O 4/TiO 2 is more efficient than their single part of CuCr 2O 4 or TiO 2 in producing hydrogen. The optimized composition of the nanocomposites has been found to be CuCr 2O 4·0.7TiO 2. And the optimized calcination temperature and photocatalyst mass concentration are 500 °C and 0.8 g l −1, respectively. The influence of initial oxalic acid concentration is consistent with the Langmuir model.

Photoreduction of Cr(vi) using hydroxoaluminiumtricarboxymonoamide phthalocyanine adsorbed on TiO2

Hydroxoaluminiumtricarboxymonoamide phthalocyanine (AlTCPc) adsorbed at different loadings on TiO(2) Degussa P-25 was tested for Cr(vi) photocatalytic reduction under visible irradiation in the presence of 4-chlorophenol (4-CP) as sacrificial donor. A rapid reaction takes place in spite of the presumable aggregation of the dye on the TiO(2) surface. The removal of Cr(vi) is fairly negligible under visible-light irradiation, either without photocatalyst or in the presence of bare TiO(2). The fast capture of conduction band electrons by Cr(vi), which forms a surface complex with TiO(2), inhibits the formation of reactive oxygen species in the reductive pathway. This fact and the easier oxidation of 4-CP as compared to AlTCPc hinder the photobleaching of the dye and make feasible Cr(vi) reduction under visible irradiation. The consumption of Cr(vi) follows a pseudo-first order kinetics; the decay constant depends, in the studied range, on the photocatalyst mass, but it is barely affected by dye loading. The presence of 4-CP is essential, but its concentration has no effect on the Cr(vi) decay rate. Oxidation products of 4-CP, such as hydroquinone, catechol or benzoquinone, are not observed. Direct evidence of the one-electron reduction of Cr(vi) to Cr(v) was obtained by EPR spectroscopy using citric acid as Cr(v) trapping agent. In this case, disappearance of Cr(v) also follows a first order decay, but conduction band electrons do not seem to be involved. The fact that oxidation products of 4-CP are not observed is consistent with the fast dark removal of reaction intermediates by Cr(v), proved by EPR.

Photocatalytic activity evaluation of tetragonal CuFe 2O 4 nanoparticles for the H 2 evolution under visible light irradiation

Copper ferrite (CuFe 2O 4) nanoparticles have been successfully synthesized via a citric acid-assisted sol–gel method. For comparison, CuFe 2O 4 materials were also fabricated by solid-state reaction and co-precipitation method. Techniques of X-ray diffraction (XRD), transmission electron microscopy (TEM) and UV–vis diffuse reflectance spectrum (UV–vis DRS) have been employed to characterize the as-synthesized CuFe 2O 4 products. The CuFe 2O 4 sample prepared by sol–gel approach is composed of almost uniform nanoparticles with a grain size of about 80 nm and crystallized in a tetragonal crystal phase structure. Moreover, the photocatalytic activity of the as-obtained CuFe 2O 4 has been evaluated based on the H 2 evolution from aqueous oxalic acid solution under visible light irradiation. The effects of preparation routes, photocatalyst mass concentration, initial sacrificial reagent concentration and the durability of the as-obtained CuFe 2O 4 have been investigated in detail. The best result of the photocatalytic H 2 evolution activity (1.72 mmol h −1 g cat −1) was obtained over the sol–gel synthesized CuFe 2O 4 nanoparticles when the photocatalyst concentration is 1.0 g l −1 and the oxalic acid concentration is 0.05 M.

Enhancement of TiO2 photocatalytic activity by structuring the photocatalyst film as photonic sponge

A TiO2 film having "photonic sponge" architecture (ps-TiO2) has been prepared using titania Degussa P25 nanoparticles that have been infiltrated into a template obtained through the arrangement of a mixture of different size latex spheres. The resulting photonic sponge exhibits 3.3 fold higher initial photocatalytic degradation rate for succinonitrile disappearance than analogous films of the same thickness made of unstructured P25 TiO2 nanoparticles. When corrected for the three fold lower mass of the ps-TiO2 films with respect to more dense P25, the enhancement of the photocatalytic activity by the photonic sponge morphology for the same mass of photocatalyst is about one order of magnitude. It was also observed that films of photonic sponge of 3 microm depth are more efficient than thicker films (5 and 7 microm).

Etude des Conditions Experimentales Optimales Pour La Degradation Photocatalytique D'un Herbicide Study of Optimal Experimental Conditions in the Photocatalytic Degradation of an Herbicide

Photocatalytic degradation of an herbicide - Carb 343ial design method. Among experimental parameters, the photonic flux and the herbicide concentration increase the initial rate. Mass of photocatalyst and oxygen pressure are not the main factors. Low photonic fluxes give large quantum yields.