Preparation And Characterization Of Bi₂MoO₆ And Bi₂Ti₂O₇ Photocatalysts

Degradation of organic pollutants by photocatalytic has profound significance for solving environmental problems and energy crisis. Developing highly effective visible-light-active photocatalysts is the key to utilize solar energy more efficiently. A new type of Bi-based photocatalysts such as:Bi2O3, Bi₂MoO₆, Bi OX（X=Cl,Br,I） has drawn increasing attention in current photocatalysis research. In this thesis, the synthesis and photocatalytic activity for the visible-light photocatalyst bismuth molybdatc and bismuth titanate were investigated. Construction of a heterostructure and element doping were used to enhance the visible light photocatalytic activity.A visible-light-sensitive Bi₂MoO₆-Bi OCl heterojunction photocatalyst was synthesized via a hydrothermal process. The structural features of the heterojunction and the photocatalytic activity were confirmed using XRD, HRTEM, SEM, ESR etc. characterization techniques. The optimal Bi₂MoO₆ content for the photocatalytic activity of the Bi₂MoO₆-Bi OCl composites is 30%. Compared to pure Bi₂MoO₆, the photocatalytic activity of the Bi₂MoO₆-Bi OCl composites is almost 2.0 times for the Rh B photodegradation, and 1.5 times for the phenol photodegradation under visible light irradiation. The formation of heterojunctions between Bi OCl and Bi₂MoO₆ promoted the separation of the photogenerated electron–hole pairs and resulting in enhancement of photocatalytic activity.The formation of fluorine doping on Bi₂MoO₆ can be easily attained by a hydrothermal process. It could be speculated that oxygen ion was substituted by fluorine ion in the crystal lattice of Bi₂MoO₆ on the basis of XRD results. The bandgap structure and photocatalytic activity of the materails were confirmed using HRTEM, SEM, DFT calculation method. etc. characterization techniques. The photocatalytic activity of Bi₂MoO₆ by fluorine doping samples were comparing with the pure Bi₂MoO₆. Additionally, the trapping experiment and ESR were conducted for detecting active species. Finally, a possible charge transfer mechanism of the enhanced photocatalytic activity was proposed.Heterostructured Bi₂Ti₂O₇/Bi₄Ti₃O₁₂ nanocomposites were successfully synthesized through a simple hydrothermal and calcination process. The structure, morphology and the photocatalytic activity of the materials were confirmed using XRD, HRTEM, SEM, ESR, SPV etc. characterization techniques. The Bi₂Ti₂O₇/Bi₄Ti₃O₁₂ nanocomposite calcined at 600°C has the highest visible light photocatalytic activity, which is almost 1.15 times as high as that of the pure Bi₂Ti₂O₇ for Rh B photodegradation, and 1.35 times the rate of 2,4-dichlorophenol removal under simulated solar irradiation. The h+ played a key role in the degradation reaction via the Bi₂Ti₂O₇/Bi₄Ti₃O₁₂ composite. This enhancement of the photocatalytic activity is due to the heterojunction interfaces between Bi₂Ti₂O₇ and Bi₄Ti₃O₁₂, which is helpful for the separation and transfer of electron-hole pairs.