Papers by Keyword: Photoreduction

Abstract: Photocatalytic reduction of 4-nitrophenol is one of the most promising methods to remove this hazardous pollutant from wastewaters and generated a raw compound widely use in industrial processes. In the present work, three Bi₂S₃/TiO₂ catalysts with different Bi₂S₃ content, were synthesized by a hydrothermal method. The materials were characterized by XRD, X-ray fluorescence, physisorption of N₂, HRTEM, UV-Vis reflectance spectroscopy and zeta potential measurements. The catalytic activity of the synthesized materials was tested in the photoreduction of 4-nitrophenol in aqueous medium. Although the results indicate the formation of heterojunction for all the samples, the physicochemical properties of each material depend on the Bi₂S₃ content. The material with 6%wt of Bi₂S₃ exhibit the major catalytic activity, reducing 80% of the target molecule within 60 minutes of reaction.

Abstract: The reactivity of 3,5-di-tert-butyl-o-benzoquinone and its bis-o-benzoquinone derivative in photoreduction reaction and polymerization of dimethacrylate (OCDMA) (in bulk and in the presence of 1-butanol) with using of them as photoinitiators under visible light irradiation under argon atmosphere or air were investigated. It was found that the kinetic parameters of the bis-o-quinone photoreactions have low sensitive to the presence of molecular oxygen. The high stability of the spectral characteristics of resulting polymers based on bis-o-quinones compositions for the long time was established.

Abstract: In this paper, visible-light-active monoclinic WO₃ powders were synthesized by thermal oxidation of W powders at 200 – 1000 °C in air atmosphere. Morphology and crystal structure of annealed W powders were characterized by Scanning Electron Microscopy (SEM) and X-ray Diffraction (XRD), respectively. Based on SEM and XRD results, a spherical orthorhombic-W₃O₈ obtained at 200 °C was transformed into a dendritic monoclinic WO₂ + tetragonal WO₃ + monoclinic WO₃ structures at 400 °C accompanied by a color transition from grey into green. At 600 °C, yellow monoclinic WO₃ + monoclinic WO_2.96 powder was produced that ascribed to oxygen vacancies. Photocatalytic activity of annealed W powders demonstrated 70.7% Cr (VI) removal after 150 min on sample annealed at 1000 °C. This ascribed to high photoactivity of monoclinic WO₃. Nevertheless, the dendritic monoclinic WO₂ + tetragonal WO₃ + monoclinic WO₃ obtained at 400 °C exhibited the lowest Cr (VI) photoreduction i.e. 45.2% implies less photoactive monoclinic WO₂ and sluggish electron transport at oxide-oxide interfaces.

Abstract: The TiO₂/Fe₃O₄ nanoparticle has been successfully synthesized and the material is then applied as a photocatalyst to reduce Pb(II). The Fe₃O₄ was synthesized through sono-coprecipitation method using NH₄OH as a precipitating agent. The coating TiO₂ onto Fe₃O₄ was performed respectively via hydrolysis reaction and sol-gel process using ammonium sulfate and TTIP as a reagent of TiO₂. This study investigated several parameters such as the effect of time, equilibrium state and material responsiveness toward ultraviolet light. The XRD measurement indicated the presence of Fe₃O₄ and TiO₂ while TEM image displayed the photocatalyst had a nanosized particle with approximately 60 nm in size. An activity test at pH 4, the equilibrium of photoreduction process showed at 60 minutes. The kinetic parameter of Pb(II) reduction at various catalyst presented that TiO₂/Fe₃O₄ nanoparticle had better reduction rate constant than that of TiO₂. Reusing of TiO₂/Fe₃O₄ photocatalysts showed the results of Pb (II) photoreduction were not significantly decrease and the results of photocatalysis were still better than TiO₂.

Abstract: Anodisation of zirconium, Zr at 40 V for 60 min in 0.1 wt.% NH₄F/ethylene glycol (EG) added to it 1 ml, 2 ml or 3 ml of water resulted in the formation of self-aligned ZrO₂ nanotube (ZNT) arrays. Water content did not affect the length and diameter of the ZNTs but was influencing surface etching whereby better surface etching was observed for sample anodised in 3 ml-water/NH₄F/EG. From transmission electron microcopy (TEM) image, the ZNTs were found to have an outer diameter of ~ 40 nm and wall thickness of 10 nm. Annealing at 400 °C was resulted in monoclinic (M-ZrO₂) and tetragonal (T-ZrO₂) formation, but at 600 °C M-ZrO₂ dominates. Cr(VI) reduction is higher for ZNTs annealed at 400 °C compared to 600 °C sample.

Abstract: A rotating horizontal electrode is used to substitute the classic vertical electrode in fabrication of anodic TiO₂ nanotube membrane, which alleviates the uneven length distribution. TiO₂ nanotube arrays membrane with more uniform length is thereby obtained and the mechanical property is improved. The CO₂ photoreduction ability of TiO₂ nanotube membrane was then tested.

Abstract: In order to decrease CO₂ level, converting the gas into hydrocarbon fuel gasses has been performed by using photoreduction method under TiO₂/SiO₂ photocatalysis. The silica (SiO₂) for TiO₂/SiO₂ preparation was purified from volcanic ash, that mixed with TiO₂ suspended in water. The photoreduction process of CO₂ was carried out in a batch technique, by exposing CO₂ and water vapor in the presence of TiO₂/SiO₂ photocatalyst with UV lamp for 24 h. The gasses produced from the photoreduction were determined by gas chromatography method. In the research, the effects of HCl and HNO₃ as hydrogen ion supplier were also evaluated. The research results indicate that the photoreduction of CO₂ with the water vapor over the photocatalyst of TiO₂/SiO_{2-volcanic ash} has successfully produced methane and ethylene as fuel gasses, while in the presence of TiO₂ no ethylene was resulted. The methane produced by TiO₂/SiO₂ was observed to be larger than by TiO₂ powder. The content of TiO₂ in TiO₂/SiO₂ with low level strongly influenced the yield of the products. In contrast, the yield was independent on the TiO₂ content in high level. The presence of the acids was found to increase the methane produced , and no ethylene was formed, but instead, methanol was resulted. The effect of HCl was higher than HNO₃.

Abstract: A novel synthetic approach to ultrathin (< 5 nm) multilayered single crystalline gold nanosheets using amphiphilic comb-like polymer as template was presented. The poly (oxyethylene) containing decyl-tri (oxyethylene) amphiphile as well as the thioether linking group in the side chain was synthesized via polymer analogous reaction. The polymer and the gold precursor, LiAuCl₄, were mixed and dried to afford a homogeneous complex. The gold precursors were reduced to gold crystals by photoreduction using long wave UV light (> 350 nm). The gold nanosheets with multilayered structure, where the layer spacing is about 3.6 nm, were obtained after 24 h. The formation of the multilayered nanosheets is due to the layered structure of the gold complex of the polymer and precursor.

Abstract: The photocatalytic reduction of Cu(II) under UV irradiation in presence of citric acid (CA) as acrificial agent has been investigated using TiO₂-modified bamboo charcoal as photocatalysts prepared with Sol-Gel method. The influence of the catalyst dosage, Cu(II) of the initial quality concentration, photocatalytic time, catalyst roasting temperature and the solution acidity to Cu(II) removal rate has been explored. The best conditions of Cu(II)-containing waste water treatment were determined.The results show that the effect is the optimum when the pH is 7.0, the photocatalytic reaction time is more than 60min, the usage amount of catalyst is 8 g/L and the photocatalyst is calcinated for 2h at 500°C.The degradation rate of Cu(II) ion can be improved using appropriate extension reaction time method.

Abstract: Photocatalytic removal of mercury was studied using TiO₂-modified bamboo charcoal prepared with Sol-Gel method as photocatalyst, and formate as hole scavengers under UV irradiation. In the absence of formate additives, approximately 95% of 30 mg/L Hg(II) ions was found to be removed from the solution by adsorption. Addition of formate resulted in the photoreduction of Hg(II) to its metallic form. The best conditions of Hg(II)-containing wastewater treatment were determined. The results show that the optimum amount of photocatalyst was 4 g/L,the optimum illumination time was 30 min,reached a plateau value at pH 6, the photocatalyst calcinated for 2h at 500°C. and the optimum formate addition amount was found to be 120mg/L, which doubled the adsorption capacity. Accordingly, it is believed that the method developed in this study is effective and practical in industrial wastewater treatment for Hg(II) disposal.