Study On Enhanced Modification Of Visible Light Photocatalytic Property Of Bismuth Oxide

Along with the development of modern industry, the emission of a large number of organic pollutants is a serious threat to human health and environmental safety. The solving of these environmental problems in efficient and economical ways has become an important project in academia. Among all kinds of pollutant treatment technologies,photocatalysis as new advanced oxidation processes ?AOPs?, which have the advantages of easy-operated, effective, green and safe, can be used to solve this problem. Bismuth oxide semiconductor catalytic materials, because of its high conductivity, good dielectric,optical, and ion-conductive, are considered to be a promising visible light photocatalyst.Herein, based on the environmental water pollution improvement, the researches mainly focus on the modification of bismuth oxide to improve its photocatalytic activity. The main contents and results are enclosed as follows.?1? The relationship between crystal structure, electronic structure and photocatalytic performance is studied, and the effect of the synergistic effect of crystal structure and electronic structure on the photocatalytic properties of bismuth oxide was discussed by using the first principle method. A theoretical investigation on the geometric structures,band structures, electronic density of states and optical properties of ?-Bi₂O₃??-Bi₂O₃?were calculated using CASTEP module of MS software. The theoretical calculated results show that ?-Bi₂O₃ and ?-Bi₂O₃ belong to the layered structure, while ?-Bi₂O₃ and ?-Bi₂O₃ are network cross-linked structure, in which ?-Bi₂O₃ has a high degree of cross-linking and its band structure exhibits the characteristics of conductor. The conduction bands of all the four crystalline phases are mainly generated by Bi 6p orbitals, while the valence bands are contributed by O 2p orbitals. The absorption edge of ?-Bi₂O₃ and ?-Bi₂O₃ are extended to the visible region, so they have visible light catalytic activity. The absorption edge of ?-Bi₂O₃3 and ?-Bi₂O₃ are extended to the infrared region, so they have certain characteristics of infrared excitation. These theoretical results provide important theoretical guidance for the design and application of novel Bi₂O₃ photocatalytic materials.?2? Using theoretical design and experimental verification method, a novel visible-light photocatalytic ?-Bi₂O₃ doped with Pr was prepared using polyacrylamide sol-gel method. The theoretical calculation of Pr doped -Bi₂O₃ system was carried out by first principles method. The calculated results show that Pr 4f orbital split in two,High-energy orbit appeared in the conduction band of ?-Bi₂O₃ and hybridized with O 2p?Bi 6p orbitals, Low-energy orbit appeared in the forbidden band and formed a new impurity levels. The narrowed band gap and red-shift of light absorption edge, Pr doping can effectively improve the visible light catalytic activity of ?-Bi₂O₃. The ?-Bi₂O₃ and Pr doped ?-Bi₂O₃ nano catalyst particles were prepared, based on the theoretical calculation results. The photocatalytic activity of prepared samples was evaluated by degrading methyl orange under the irradiation of visible light. Compared to bare ?-Bi₂O₃ nanoparticles, Pr-doped ?-Bi₂O₃ exhibit significantly enhanced photocatalytic activity.This provides a new research idea for the development and performance improvement of new and efficiency visible light catalytic materials.?3? ?-Bi₂O₃/GR composites were fabricated by a simple ethanol evaporation method.The photocatalytic activity of prepared samples was evaluated by degrading Methylene Blue ?MB? under the irradiation of visible light. Compared with pure ?-Bi₂O₃, the?-Bi₂O₃/GR composites exhibit an enhanced photocatalytic performance in the degradation of MB under visible light irradiation. Being an excellent electron acceptor and conductor, the GR can promote the effective separation of e--h+ pairs. Thus, the photo-generated electrons are then quickly transferred to the surface of GR sheets. More of the photo generated charge is involved in the photocatalytic reaction, which is beneficial to the improvement of the photocatalytic activity.?4? A new polyaniline ?PANI?/?-Bi₂O₃ composite was prepared in aqueous ethylene glycol solution medium via the chemical oxidative polymerization. The photocatalytic activity of prepared samples was evaluated by degrading Acid orange 7?AO 7? under visible light irradiation, and 5% PANI/?-Bi₂O₃ composite showed the hightest photocatalytic activity. Compared to bare ?-Bi₂O₃ nanoparticles, PANI/?-Bi₂O₃ composite exhibit significantly enhanced photocatalytic activity. The possible photocatalytic mechanism of the PANI/?-Bi₂O₃ composite was proposed. Being an excellent hole acceptor, the PANI can promote the effective separation of photogenerated charge, and relatively reduce the recombination of e-h+ pairs, which significantly enhances the photocatalytic activity of the ?-Bi₂O₃.?5? The sonocatalytic activity and the photocatalytic synergistic effect of?-Bi₂O₃ nanoparticles to degrade Rhodamine B ?RhB? were studied by ultrasonic coupling. The results show that ?-Bi₂O₃ nanoparticles exhibit a good sonocatalytic activity. The effects of various experimental factors including ultrasonic frequency ?f?,solution temperature ?T?, catalyst dosage ?Ccatalyst? and initial RhB concentration ?CRhB? on the sonocatalysis efficiency were investigated. The optimum conditions for sonocatalytic degradation of RhB are obtained to be f=60 kHz, T=40 ?, Ccatalyst = 3 g·L-1, and CRhB=5 mg·L-1. The percentage degradation of RhB after sonocatalysis for 90 min is 98.7%.Based on the experimental results, ·OH radicals are suggested to be the major active species which are responsible for the degradation reaction. In addition, the Sono-photocatalytic activity of ?-Bi₂O₃ nanoparticles was studied. The results showed that the photocatalytic synergistic effect by ultrasonic coupling could effectively improve the catalytic activity of ?-Bi₂O₃ nanoparticles for the catalytic degradation of organic dyes.