Synthesis Of BiOX Micro-flowers Induced By Polysaccharide And Their Photocatalytic Performance

Photocatalytic technology is a method with great potential for removing pollutants in the field of water treatment due to its advantages of high degradation efficiency,strong removal capacity,long service life,and low secondary pollution.In recent years,a variety of modification techniques have been used to synthesize new photocatalysts to solve these problems of photocatalyst that high photo-generated electron-hole recombination efficiency,small visible light absorption range and easy agglomeration in actual water pollution treatment.Among them,natural polymer materials have gradually attracted widespread attention that could be used as a template,inducer,dopant,surface modifier to synthesize semiconductor nanomaterials with special structures due to their weaker stability.In this paper,chitosan（CS）and sodium alginate（SA）,two different types of polysaccharide natural polymers with different functional groups,are used as templates,inducers and dopants to prepared a series of highly active BiOX photocatalysts by hydrothermal method and applied to the treatment of water pollutants.Based on the review of polymer-modified semiconductor photocatalyst,the thesis mainly carried out the following contents:Firstly,SA was used as a natural polymer inducer and dopant,and its side chain-COO^-was complexed with Bi³⁺to form microgel,and then BiOBr micron-flower photocatalyst（BiOBr-SA）was synthesized through hydrothermal reaction.BiOBr-SA was characterized by XRD,XPS,SEM,TEM,PL,DRS,FT-IR and electrochemical methods.It was found that the complexation of SA side chain-COO^-with Bi³⁺makes C atoms doped into the BiOBr lattice to form C-doped BiOBr.Using the prepared BiOBr-SA as a photocatalyst for the treatment of tetracycline（TC）wastewater,the results indicated that the degradation rate of BiOBr-SA_0.5 to TC can reach 88.9%within18 min under simulated sunlight（>420 nm）.This also further confirmed that it is a fast and excellent photocatalytic material for TC wastewater treatment.Through the capture experiment,the photodegradation mechanism of the photocatalyst was discussed,and it was determined that h⁺and·O₂-were the main active species in the photocatalysis process.Secondly,CS was used as a natural polymer morphology inducing agent,lattice structure guiding agent,and its side chain-NH₂ was complexed with Bi³⁺to form microgel,and then BiOBr micron-flower photocatalyst（BiOBr-CS）was synthesized through hydrothermal reaction.BiOBr-CS was characterized by XRD,XPS,SEM,TEM,PL,DRS,FT-IR and electrochemical methods.It was found that during the reaction,CS was completely decomposed and removed and the presence of-NH₂ could also induce lattice growth and construct specific crystal faces,which made the BiOBr-CS photocatalyst have a highly exposed（110）crystal plane.Using the prepared BiOBr-CS as a photocatalyst for the treatment of Rhodamine B（RhB）wastewater,the results indicated that the degradation rate of BiOBr-CS_0.45 to RhB can reach 99.7%within 30 min.This also further confirmed that it is a predictable photocatalytic material for RhB wastewater treatment.The investigation of the photodegradation mechanism revealed that the BiOBr-CS_0.45 photocatalyst mainly relies on h⁺and·O₂-to degrade pollutants.Thirdly,CS was used as a natural polymer morphology inducing agent,lattice structure guiding agent,and its side chain-NH₂ was complexed with Bi³⁺to form microgel,and then hollow micron-flower photocatalyst（BiOCl-CS）was synthesized through hydrothermal reaction.BiOBr-CS was characterized by XRD,SEM,PL,DRS and FT-IR.It was found that during the reaction,CS was completely decomposed and removed and the presence of-NH₂ could also induce lattice growth and construct specific crystal faces,which made the BiOCl-CS photocatalyst have a highly exposed（001）and（110）crystal plane.Using the prepared BiOCl-CS as a photocatalyst for the treatment of TC wastewater,the results demonstrated that the degradation rate of BiOCl-CS_0.5 to TC can reach 93.7%within 35 min under visible light.This also further confirmed that it is a promising photocatalytic material for TC wastewater treatment.In summary,a series of BiOX photocatalysts were prepared using natural polymers as structural inducers,templates and carbon sources.In the above three systems,natural polymers can not only construct BiOX photocatalysts with micro-flower morphology,but also can be easily removed by hydrolysis,carbonization and other methods,which eliminated the process of removing the template by secondary calcination of the material.Furthermore,it also can enhance the light absorption in the visible region of the photocatalyst by inducing the formation of specific crystal plane of the photocatalyst and carbon doping.It is considered that the prepared BiOX photocatalysts have very high photocatalytic activity and are expected to be used for the degradation of organic pollutants in wastewater.