BiPO₄/Bi₃O（PO₄）₂（OH） Composites By Biological Template Method For Photocatalytic Reduction Of Cr（Ⅵ） Under Visible Light

Photocatalytic technology can be used to simultaneously solve the problems of energy shortage and environmental pollution.The photocatalytic reduction of highly toxic Cr（Ⅵ）to less toxic Cr（Ⅲ）is considered as a promising approach.As a new type of photocatalyst,bismuth phosphate（BiPO4）has received wide attention due to its excellent photoelectric performance,high photochemical stability,high crystallinity,and non-toxicity.Compared with commercially available TiO2（P25）,BiPO4 exhibits far higher photocatalytic efficiency in the degradation of organic pollutants.Since BiPO4 can only be excited by ultraviolet light,its practical application is limited.Constructing a heterostructure with another semiconductor is one of the effective ways to improve the photocatalytic activity of BiPO4 under visible light.However,the BiPO4-based heterostructure materials in the existing research requires harsh photocatalytic reaction conditions,which limits its application in actual wastewater treatment.Compared with BiPO4,which has attracted much attention,Bi3O（PO4）2（OH）（BOHP）found in minerals,has only one report on its degradation of perfluorooctanoic acid under ultraviolet light.So far,the photocatalytic reduction performance of BOHP has not been reported,nor has the BiPO4/BOHP composites.Not to mention the application of biological templates to BiPO4/BOHP composites for photocatalytic reduction performance research.In this thesis,the BiPO4/BOHP heterostructure photocatalyst was synthesized for the first time by a one-pot precipitation method,with Cr（Ⅵ）as the target pollutant,and the performance and mechanism of visible light catalytic reduction of Cr（Ⅵ）were studied.The photocatalytic activity of BiPO4/BOHP heterostructure is further improved by the biological template method.The research results of this thesis are as follows:（1）The BOHP nanoparticle-wrapped BiPO4 rod-like structure was successfully synthesized for the first time through the one-pot precipitation method without the using autoclave.The formation process was studied by changing the synthesis conditions.The change of the P/Bi mass ratio in the synthesis conditions led to the transformation of the material type and BiPO4 crystal phase.Nitric acid and D-sorbitol were used to control the morphology of BiPO4,and the urea and reaction time affected the growth of BOHP.The BiPO4/BOHP heterostructure with the best photocatalytic activity was prepared by optimizing the synthesis conditions.The BiPO4/BOHP heterostructure as ultraviolet photocatalyst exhibited highly effective visible-light photocatalytic reduction of Cr（Ⅵ）by the self-photosensitization of adsorbed Cr（Ⅵ）combined with the Z-scheme heterojunction charge transfer mechanism.The BiPO4/BOHP heterostructure significantly enhanced the photocatalytic activity to 44.6 times the value afforded by pure BiPO4 without using hole scavenger.（2）Combining sensitization method and template method,using edible Gardenia Blue Pigment（GBP）as template,BiPO4/BOHP heterostructure（GBi series materials）were synthesized by the one-pot precipitation method.Compared with the pure BiPO4/BOHP heterostructure,the BET of GBi series materials has been increased from 19.3 m2/g to 396.0 m2/g,and the band gap gradually narrows.The photocatalytic reduction efficiency of GBi（30）is about 1.4 times and 63.0 times that of BiPO4/BOHP heterostructure and pure BiPO4,respectively.The existence of the gardenia blue pigment（GBP）and the carbon doping introduced with the GBP has enabled the efficient transfer of photogenerated electrons,and simultaneously solve the problem of the instability of the BiPO4/BOHP heterostructure under acidic conditions.（3）An independent two-step process of carbonization and activation was employed to increase the specific surface area of coffee-shells.The BiPO4/BOHP/BC series materials were successfully synthesized by using coffee-shells biochar template.Compared with the pure BiPO4/BOHP heterostructure,the BET of BiPO4/BOHP/BC series materials is increased from 19.3 m2/g to 326.1 m2/g,and the band gap gradually narrows.The photocatalytic reduction efficiency of the BiPO4/BOHP/BC（20）is about 1.9 times and 84.0 times that of BiPO4/BOHP heterostructure and pure BiPO4,respectively.Loading biochar not only allows the effective migration of photogenerated electrons,but also solves the problem of instability of the pure BiPO4/BOHP heterostructure under acidic conditions.The research results presented in this paper not only expand the method of using BiPO4-based materials to improve the photocatalytic activity under visible light,but also provide more possibilities for BOHP in efficient environmental remediation or solar energy conversion applications.