Solid-state Chemical Synthesis And Property Of Several Bi-based Visible Light Photocatalytic Materials

Semiconductor photocatalytic technology is regard as a green strategy to solve the energy problems and environmental pollution. Over the past decades, researchers focused on the TiO2 photocatalyst due to the inexpensive cost and high chemical stability. TiO2 was only sensitive to the ultraviolet light, which restricted its practical applications. In order to take full advantage of visible light in the sunlight, the exploration of non-TiO2 based visible light-response photocatalysts have became the research focus in the field of photocatalysis. The Bi-based photocatalysts have drawn much attention owing to the appropriate energy band gap, good absorbability and photocatalytic activity under visible light irradiation. These existing methods for the synthesis of bismuth-based photocatalytic materials mostly required the use of solvents, complex process or harsh conditions. In our thesis, several Bi-based photocatalysts with visible-light response were synthesized by simple, solvent-free solid-state chemical reaction. Methyl orange（MO）, methylene blue（MB） and Rhodamine B（Rh B） as simulated pollutants of these materials under visible light, the photocatalytic degradation performance was investigated. The influence of morphology and the band gap on the photocatalytic performance were discussed. The main active species for the photocatalytic degradation of simulated pollutants of these materials were explored. The main research contents of this thesis are as follows.（1） The lentils angular-like β-Bi₂O₃ was fabricated by the decomposition of precursor that was synthesized by room-temperature solid-state chemical reaction between bismuth nitrate and oxalate. The photocatalytic degradation of irregular morphology β-Bi₂O₃ under visible light for MO, MB and RhB, performance was studied and the degradation rates were 75.7%, 20.3% and 10.9% after 2 h irradiation, respectively. By adding the surfactant in the above reaction system, the reaction microenvironment of solid-state chemical reaction was changed and the rod-like β-Bi₂O₃ was synthesized. The photocataytic activity of rod-like β-Bi₂O₃ for the MO degradation is higher than the irregular morphology β-Bi₂O₃. The scavenger experiments displayed that negative oxygen free radicals was the major active species during the process of photodegradation.（2） In order to improve the photocataytic activity of the pure β-Bi₂O₃, we prepared the fluorine doped β-Bi₂O₃ by solid-state chemical reaction. The fluorine doped β-Bi₂O₃ has better photocataytic activity which is two times higher than that of pure β-Bi₂O₃ for the degradation of high concentration MO. The degradation rate reached 82.3% after 2 h irradiation under visible light. The enhanced properties of the fluorine-doped samples attribute to their higher separation efficiency of electron-hole pairs and strong oxidation potential of valance band holes. The photogenerated hole was the major active species during the process of photodegradation.（3） The monoclinic sheelite BiVO₄ and Bi₂WO₆ was fabricated by the decomposition of precursor that was synthesized by room-temperature solid-state chemical reaction between bismuth nitrate and sodium metavanadate or sodium tungstate. Two Bi-based materials have good photocatalytic degradation for MB under visible light. The degradation rate of BiVO₄ samples with different morphologies on MB were more than 86.7%, in which rice-like structure has the best photocatalytic activity, the degradation rate reached 96.1% after 2 h irradiation under visible light. The rice-like BiVO₄ has the smallest size, photogenerated electrons and holes can be effectively seperated, resulting in high photocatalytic activity. The degradation rate of Bi₂WO₆ was only 50.3% after 2 h irradiation under visible light. The hydroxyl radical was the major active species during the process of photodegradation.