Solvent-free Synthesis And Photoactivity Of Bismuth Oxychloride Microflowers,Large Nanosheet,and Homojunctions

Environmental contamination and energy crisis accompanied with quick advancement of economy restrict sustainable development of our society.Semiconductor photocatalysis technology is considered as the most promising way to solve these problems.BiOCl,as a bismuth-based photocatalyst,attracts much attention researchers,because of its layered crystal structure,self-generated internal electric field,low cost,high chemical stability,and non-toxicity.To improve photoactivity of BiOCl,morphology control and constructing heterojunctions(or homojunctions)are common methods.BiOCl with different structures are mainly synthesized via solvothermal routes with necessary addition of structure-directing agents(e.g.organic solvents and surfactants),but massive solvents and organics will cause serious environmental pollution,which is not favorable for industrial production.Besides,the preparation of heterojunctions is complicated with stepwise synthesis.constructing BiOCl homojunctions does not need introduction of any other elements,compared with fabricating heterojunctions,but can also significantly enhance photogenerated charge carrier separation and photoactivity.However,research on BiOCl homojunctions with one-step synthesis is still rare,and new preparation techniques need be developed.In this thesis,a solvent-free low-temperature way was used to successfully prepare BiOCl microflowers(MFs),large nanosheet(LN)and MF/LN homojunctions.The photoactivity of samples are comparable to some reported BiOCl photocatalysts,but this preparation method is more energy-saving and environment-friendly,revealing great potential for application.The concrete research contents are listed as follows:1.BiOCl MFs,LN and MF/LN homojunctions were synthesized by a "one-pot"solid-state reaction method at 120-160 0C,using chlorobutanol and Bi(NO3)3·5H2O as Cl and Bi sources,respectively.The MFs are composed of small nanosheets with highly exposed(001)crystal facets and thickness of～15 nm,while the LNs with thickness of several hundred of nanometers dominantly expose(010)facets.With increasing reaction temperature,MF contents in the samples decrease while LN contents increase gradually.With increase of Cl/Bi molar ratios from 1 to 3,LN contents in the samples sharply reduce,with some MFs disassembling to form stacking structure.The LNs come from melting of MFs at high temperature and high temperature can accelerate the melting process.The LNs possess higher ultraviolet photoabsorption,a wider bandgap,and smaller specific surface area than the MFs.The MFs are easy to form because massive MFs can be observed to form even though the reaction lasts for only 0.5 h at 120 ℃.2.Close contact between BiOCl hierarchical MFs and LNs leads to the formation of homojunctions.High-resolution transmission electron microscopy images clearly show the homojunction interface and close contacting MF and LN with different dominant exposure of facets.Ultraviolet-visible spectroscopy,X-ray photoelectron spectroscopy,and Mott-Schottky tests were performed and confirm that the MFs and the LNs possess different energy band structures and their energy band levels match each other to form homojunctions.Fluorescence spectroscopy and photoelectrochemical tests indicate the prominent enhancement in photogenerated charge carrier separation caused by the homojunction construction,which makes the samples contain more MF/LN homojunctions exhibit higher photoactivity.