Preparation And Photocatalytic Performances Of The Photocatalysts Based On Bismuth Phosphate

Photocatalytic technology has provided an effective way to solve the environmental pollution and energy shortage due to its excellent protocatalytic activity and environmental friendly property. BiPO₄ is a new photocatalyst, which has become the new focus for the researchers owing to its low cost and significant photocatalytic oxidative ability. However, its low quantum efficiency and narrow visible spectral response range limit its practical applications. In this paper, a series of highly activity and efficiency energy BiPO₄-based photocatalysts were fabricated by doping rare earth element and building heterogeneous structure to tune the energy band and modify the surface property of BiPO₄, and thus improve the photo-induced carrier separation efficiency, extended the scope of spectral absorption. Using simulated dye wastewater as the degradation object, the influence factors were discussed in the photocatalytic system and the mechanism of photocatalysis was revealed. It has important theoretical significance and application value in the development of photocatalytic oxidation technology and utilization of solar energy. The main results were as follows: 1. The Preparation and photocatalytic performances of La³⁺- doped BiPO₄ photocatalystsLa³⁺- doped BiPO₄ photocatalysts were fabricated via a one-step hydrothermal process using bismuth nitrate, lanthanum nitrate, and tri-butyl-phosphate as precursors. The morphologies, structures, and light absorption properties, and valence bond structure of BiPO₄ before and after doping La were characterized by a series of techniques. The influence mechanism of preparation conditions was revealed. It was found that with the increase of hydrothermal temperature and time, the crystal phase of BiPO₄ was transformed from the hexagon structure to the monoclinic structure, which showed higher photocatalytic activity. When glycerin content increased, the particle size of the samples became bigger and their photocatalytic activity reduced. And the photocatalytic activity of BiPO₄ was significantly improved by appropriately doping La. In the scope of this experimental study, the photocatalytic activities of the La³⁺-BiPO₄ spherical particles prepared at 200℃ and 3h was optimal while the optimal doping amount of La was 2 mol%, using water as solvent. Its stability was good and its apparent reaction rate was 3.24 times higher than that of BiPO₄.The photocatalytic performance and its influencing factors of the La³⁺-BiPO₄ photocatalysts were investigated in the decomposition of methylene blue（MB） under UV light. The degradation effect of MB was good in strong acidic or neutral condition while the dosage of photocatalyst was 0.5².0 g/L. In the concentration range of 4 30 mg/L, the photocatalytic degradation process complied with pseudo-first-order kinetics. Moreover, radical scavenger experiments confirmed that holes were the dominant active species. The high photocatalytic activity of La³⁺-BiPO₄ under UV light was owing to larger specific surface area, lower valence band position that could enhance the oxidation ability of holes and thus more hydroxyl radicals were produced, and higher conduction band position for effective electron-hole pair separation. 2. The Preparation and visible-light photocatalytic activity of H₃PW₁₂O₄₀/BiPO₄ photocatalystsHPW/BiPO₄ composite photocatalysts were obtained by impregnation method. Their photocatalytic activity was greatly influenced by phosphorus source, synthesis methods, calcination temperature, calcination time, and impregnation amount of HPW. In the scope of this experimental study, the photocatalytic activities of the HPW/BiPO₄ prepared room temperature synthesis-impregnation method using ammonium dihydrogen phosphate as phosphorus source and calcinated at 500℃ and 3h was the best while the phosphotungstic acid content was 30%, the degradation efficiency of rhodamine B（Rh B） in 180 min reached 90.8% under the xenon lamp irradiation. Its apparent reaction rate was 14.75 times higher than that of BiPO₄.The visible photocatalytic performance and its influencing factors of HPW/BiPO₄ photocatalysts were discussed while Rh B was selected as probe molecule. The results showed that the degradation effect of Rh B was good in leaning neutral condition while the dosage of photocatalyst was 0.5⁰.8 g/L. The sequence of inhibition for the adsorption and the photoreaction of inorganic anions werePO43- >SO42-> Cl- ≈NO3-. According to circulation use experiment, the stability of HPW/BiPO₄ photocatalysts should be further strengthened. In the concentration range of 0.35².20×10-5mol/L, the photocatalytic degradation process complied with pseudo-first-order kinetics. Moreover, radical scavenger experiments confirmed that holes constituted the active species. After forming the composite with HPW, the absorption band edge of BiPO₄ shifted to 415 nm, and the composite was easily excited by the visible light. The recombination between photoinduced electrons and holes were effectively inhibited because of HPW was a good electron capture agent, and HPW/BiPO₄ composite photocatalysts exhibited much higher visible light catalytic activity. 3 The Preparation and visible-light photocatalytic activity of PANI/BiPO₄ photocatalystsPANI/BiPO₄ hybrid photocatalysts were prepared by a facile chemisorption method. It is found that the photocatalytic performance of PANI/BiPO₄ hybrid photocatalysts increased at first and then decreased with the increase of PANI content. 10%PANI/BiPO₄ exhibited superior catalytic activity, the degradation efficiency of Rh B and the removal rate of TOC in 4h respectively reached 90.9% and 56% under the xenon lamp irradiation（λ>400nm）, but not for BiPO₄ in the same condition.With Rhodamine B as a target pollutant, the visible photocatalytic performance and its influencing factors of PANI/BiPO₄ photocatalysts were studied. The research indicated that the degradation rate of Rh B increased with the photocatalyst dosage in the range of 1.0¹0.0 g/L. With the increase of solution p H, the degradation rate of Rh B first increased then decreased, degradation effect is better in weak acid condition.PO43- showed stronger inhibitory effect for the adsorption and the photoreaction than Cl-, NO3-, and SO42-. In the concentration range of 3.23¹1.39×10-5mol/L, the photocatalytic degradation process complied with pseudo-first-order kinetics. Radical scavenger experiments confirmed that HO2·/O2- were the dominant active species. After modified by PANI, the absorption band edge of BiPO₄ shifted to 474 nm, and the visible light was absorbed by the hybrid photocatalysts more easily. At the same time, heterostructure was formed at their interface and a built-in electric field was built due to the effective migration of carrier between PANI and BiPO₄. Therefore, the rapid separation of photogenerated holes and electrons would bring about significant visible-light activity.