Synthesis,Characterizations And Photocatalytic Performances Of Novel Bismuth Selenate And Its Composites

Aurivillius oxides have attracted considerable attention for their unique chemical functionalities and structural properties.Bismuth selenate(Bi2SeO5)is one of the Aurivillius oxides with alternate layers of(Bi2O2)2+ cations and(SeO3)2-anionic block.It was reported as a material with high dielectric and piezoelectric properties.However,the application of Bi2SeO5 in photocatalysis and how to effectively improve its activity has never been investigated.It may be due to the fact that the preparation of the pure Bi2SeO5 is very difficult.In the present thesis,orthorhombic Bi2SeO5 with pure phase have been synthesized by thermal oxidation process using Bi2Se3 as precursor.To enhance the photocatalytic activity of Bi2SeO5 and the utilization of visible light,the as-prepared Bi2SeO5 was modified by the narrow band gap semiconductors AgI and g-C3N4.The main results and conclusions obtained from the present studies are as follows:(1)Bi2SeO5 has been successfully prepared by a thermal oxidation process and applied as a photocatalyst for both the degradation of organic contaminants and selective organic synthesis under simulated sunlight irradiation for the first time.The as-prepared Bi2SeO5 exhibits a hierarchical flower-like morphology.The band gap of Bi2SeO5 is about 3.54 eV.The photocatalytic activities of Bi2SeO5 have been evaluated by the degradation of rhodamine B,methyl orange,bisphcnol A.It is found that the samples exhibit the high photocatalytic activities under simulated sunlight irradiation.Furthermore,there is no obvious decline in the activity after five recycles.The controlled experiments show that ·O2-and the photogenerated holes play important roles in the RhB degradation process.Additionally,In the selective oxidation of benzyl alcohol,Bi2SeO5 could catalyze the transformation of benzyl alcohol of 8.4%into benzaldehyde under simulated sunlight irradiation for 4 h(2)Novel AgI/Bi2SeO5 photocatalysts are synthesized via an in-situ precipitation method for the first time,which realize the wide band-gap Bi2SeO5 with visible light response.Furthermore,the photoelectric response of the samples and the separation efficiency of the photogenerated carrier of the samples have been enhanced.Under visible light irradiation(>400 nm),the Bi2SeO5/AgI composites exhibit the higher photocatalytic activities than single Bi2SeO5 and AgI.When the mole ratio of AgI and Bi2SeO5 is 1:1,the composite shows an optimal photocatalytic activity.This sample could completely degrad RhB under visible light irradiation for 40 min.The result of ESR experiment shows that ·O2-is the main active species in the reaction process.Meanwhile,the photocatalytic activity of the composite is enhanced by about 11 times compared with single Bi2SeO5 in the selective oxidation of benzyl alcohol.(3)In order to develop the Bi2SeOs composite photocatalyst with high stability and visible light response,the g-C3N4/Bi2SeO5 composite photocatalysts have been prepared by a thermal annealing method for the first time.Although the conversion rates of benzyl alcohol over g-C3N4 and Bi2SeO5 are only 9.8%and 1.5%,respectively,the g-C3N4/Bi2SeO5 composite shows a much higher photocatalytic activity and the yiled of benzaldehyde reaches to 28.6%.Meanwhile,the g-C3N4/Bi2SeO5 composites also exhibit high photocatalytic activities for the degradation of RhB under visible light irradiation.The superior photocatalytic activities may origin from the wide range of the photoabsorption,the strong photoelectric response and the high migration and separation of the photogenerated charge carriers.The original results of this study are as follows:(1)Pure Bi2SeO5 has been synthesized by a mild method for the first time and it is appilied in photocatalytic selective organic synthesis and environmental photocatalysis.The main active species have been studied and the photocatalysis mechanism is also proposed.(2)The as-prepared Bi2SeO5 has been modified by the narrow band gap semiconductor for the first time.The photoabsorption range of Bi2SeO5 is widened.The photoelectric response of the sample and the separation efficiency of photoinduced electron-hole pairs have also been improved.Finally,the visible light-driven Bi2SeO5-based composites with high photocatalytic activities have been obtained.