| With the rapid development of social economic,traditional energy sources such as coal,oil,natural gas dried up increasingly.The energy shortage has gradually become the main obstacle of restricting economic development.Moreover,the application of fossil fuels destroys the environment to the survival of people.Being capable of splitting water to generate hydrogen,reducing CO2 to generate hydrocarbon fuels,and degrading toxic pollutants,semiconductor photocatalysis is regarded as a promising technology to solve the problems of energy crisis and environmental pollution.The traditional photocatalysts,such as TiO2 and ZnO,their large band gap limits their application under visible light irradiation.Thus,it is urgent to develop novel visible-light responsive photocatalysts photocatalysts.As a kind of potential photocatalysts,bismuth oxyhalides(BiOX,X = Cl,Br or I)have attracted extensive attention.It is generally believed that the activity of photocatalysts could be largely influenced by their specific surface areas,photoabsorption ability,surficial morphologies,exposed facets,particle sizes,and so on.Therefore,the catalytic performance of BiOX can be effectively improved by regulation and control its morphology,structure,composition,crystal,forming complexes and elements doping.In this thesis,the controllable preparation of BiOX crystal structure and visible light catalytic properties of ascension are studied,to provide the basis for the development of Bi-based visible light photocatalysts.Based on the above research progress,the main contents and conclusions of this report are listed as follows:1.Synthesis and photocatalytic activity of BiOBr nanosheets with tunable crystal facets and sizesCrystal facet engineering is one of the most important ways to enhance the photoactivity of photocatalysts,but it remains challenging so far.In addition,the effects of exposed facets and crystallite sizes on the photoactivity for BiOX(X = Cl,Br,or I)nanosheets have been widely investigated.However,it is still unclear that which one of exposed facets and crystallite sizes are more important for photoactivity of BiOX nanosheets.In this work,a series of BiOBr nanosheets with tunable exposed facets and crystallite sizes were solvothermally synthesized in a mixed solvent of n-propanol,water and acetic acid.The regulation of the exposed facets and crystallite sizes was achieved simply by changing the n-propanol/water volume ratios(Rp/w,0/30-30/0)of the mixed solvent.At low n-propanol contents(Rp/w<15/15),the obtained BiOBr nanosheets expose dominantly(001)facets,while at high n-propanol contents(Rp/w>20/10).they expose dominantly(010)facets.With increasing Rp/w.the lateral size and thickness of the BiOBr nanosheets all decrease,from 1700 to 174 nm and from 156 to 17 nm,respectively.The effects of exposed facets and thicknesses of BiOBr nanosheets on the photocatalytic activity,evaluated by degradation of salicylic acid(SA)and Rhodamine B(RhB)under visible-light irradiation,were investigated.The exposed facet and thickness of BiOBr nanosheets are both important for their photocatalytic performance.The(001)facts exhibit a higher photocatalytic activity than the(010)facets.For the BiOBr nanosheets with the same(001 or 010)exposed facets,the photocatalytic activity increases with a decrease in their thickness.This study provides a new facile way to adjust the exposed facets and crystallite sizes of BiOX,and the finding may give guidance for crystal facet engineering of other photocatalysts.2.One-pot synthesis of belt-like Bi2S3/BiOCl hierarchical composites with enhanced visible light photocatalytic activityOne-dimensional(1D)belt-like Bi2S3/BiOCl composites were synthesized by a facile one-pot solvothermal method,using bismuth subsalicylate(BiSSA)as the Bi source and,in particular,as the morphological template.The synthesized composites were characterized by many techniques,such as XRD,SEM,XPS,TEM and UV-Vis diffuse reflectance and photoluminescence spectra.Photocatalytic activity of the composites was evaluated via catalytic degradation of SA and RhB under visible light irradiation.The belt-like composites show a heterojunction structure in which the Bi2S3 nanoparticles are uniformly dispersed in the BiOCl matrix with dominant exposed(010)facets.They exhibit enhanced photodegradation efficiency in comparison with pure belt-like Bi2S3 and BiOCl.With increasing Bi2S3 content,the photodegradation efficiency of the composites increases then decreases.The Bi2S3/BiOCl composite with a Bi2S3 content of～2%exhibits the highest photocatalytic activity.The apparent first-order photodegradation rate constants of the composite for SA(～0.048 h-1)and RhB(～0.299 min-1)are significantly higher than those of the pure BiOCl and Bi2S3 for SA(～0 and-0.0007 h-1)and RhB(～0.102 and～0.002min-1),respectively.The enhancement in photocatalytic activity is attributed to the efficient separation of photoinduced electrons and holes along with the increased specific surface area and visible-light absorption.The holes(h+)and superoxide radicals(·O2-)are the major active species.In addition,the belt-like Bi2S3/BiOCl photocatalysts exhibit excellent stability and reusability.This work provides a facile strategy for synthesis of 1D hierarchical Bi-based composite photocatalysts and demonstrates the potential of belt-like Bi2S3/BiOCl composites for application in environmental remediation.3.Synthesis of belt-like Bi4O5Br2 hierarchical nanostructure with high photocatalytic performanceBelt-like Bi405Br2 hierarchical nanostructures were synthesized through a facile one-step hydrolysis method performed at different temperatures(0-160 ℃),using belt-like bismuth subsalicylate as the morphological template and bismuth source.The belt-like Bi4O5Br2 samples are found to be composed of irregular single-crystal nanosheets with highly exposed(010)facets.The photocatalytic activity of the belt-like Bi4O5Br2 was evaluated by referring to the degradation of salicylic acid and resorcinol under visible-light irradiation,and compared with those of belt-like BiOBr dominantly exposing(010)facets and plate-like Bi4O5Br2 dominantly exposing(10-1)facets.The belt-like Bi4O5Br2 shows higher photocatalytic activity than belt-like BiOBr owing to the more negative conduction band potential,narrower band gap,and larger specific surface area(SBET)of the former.In addition,the belt-like Bi4O5Br2 also exhibits higher photocatalytic activity than plate-like Bi4O5Br2,mainly due to the larger SBET of the former.Interestingly,the belt-like Bi4O5Br2 obtained at room temperature(25 ℃)shows the highest photocatalytic activity,because it has the largest SBET.Moreover,the as-synthesized belt-like Bi4O5Br2 exhibits excellent stability and reusability.This study provides a simple,energy-saving route for the synthesis of belt-like bismuth-rich bismuth oxyhalide hierarchical nanostructures.4.Synthesis and characterization of Bi2S3/Bi4O5Br2 composites with enhanced visible light photocatalytic activityHeterojunction composites of Bi2S3 and Bi4O5Br2 were solvothermally synthesized and characterized by XRD,XPS,SEM and TEM methods.The heterojunction composites exhibited higher photocatalytic activity for RhB and SA than pure Bi2S3 or Bi4O5Br2 under visible light irradiation.The photocatalytic activity of the composites increased then decreased with increasing Bi2S3 content.The Bi2S3/Bi4O5Br2 heterojunction with a Bi2S3 content of 8%exhibited the highest photocatalytic activity.The enhanced photocatalytic activity of the Bi2S3/Bi4O5Br2 heterostructure photocatalyst was attributed predominantly to the efficient separation of photoinduced electrons and holes.The Bi2S3/Bi4O5Br2 composites photocatalyst exhibited potential value for application. |
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