Preparation,Modification And Catalytic Performance Of BiOCl Nanosheets

Bismuth oxychloride（BiOCl）is a representative Bi-based material,which has drawn much attention for the excellent photocatalytic performance.In order to study the effect of the size of BiOCl nanosheets on various physical and chemical properties including specific surface area,light absorption and the separation efficiency of photogenerated charge carriers,a series of BiOCl nanosheets of different sizes were prepared in this thesis.The photoresponsivity and catalytic performance were studied.The preparation of metal-BiOCl photocatalysts by loading Pd and Au nanoparticles on ultrathin BiOCl nanosheets can further increase the generation,separation and migration of charge carriers,and thus provides a high-efficiency photocatalyst.The main content are as follows:1.A series of BiOCl nanosheets with different sizes were synthesized via a hydrothermal method by changing the reaction conditions.The effect of the thickness on various physicochemical properties including specific surface area,light absorption,and the separation efficiency of photo-generated charge carriers were studied.As a photocatalyst,the ultrathin BiOCl sample displayed the highest photocatalytic activity and photocurrent density under visible light owing to its enhanced adsorption in visible light and the prolonged lifetime of carriers.Besides,the BiOCl nanosheets were found to be a cost-effective catalyst for the reduction of nitrophenols by sodium borohydride,without any light irradiation.The high catalytic activity of BiOCl nanosheets was proved to be due to the metallic Bi⁰ clusters that were produced by surface Bi（III）reduction.The catalytic activity increased greatly with a decrease in the average thickness from 106.42 nm of BiOCl（H₂O）to 3.47 nm of ultrathin BiOCl,because the increased specific surface area provided more active sites for catalytic reactions.In this respect,the replacement of precious metals such as gold,palladium and platinum for the reduction of nitrophenols with the non-precious metals such as bismuth is of greatly economic importance as it would provide less expensive and green methods for organic synthesis.2.Inspired by the distinct advantages of BiOCl（001）ultrathin nanosheets being rich in oxygen vacancies（V_O）and metal nanoparticles（NPs）with unique surface activity for the adsorption-activation of alcohols,the enhanced photocatalysis of metal-decorated BiOCl（001）ultrathin nanosheets was expected for the selective oxidation of aromatic alcohols.A small quantity of metal NPs（Au or Pd）were anchored on the ultrathin BiOCl nanosheets to obtain Au-BiOCl and Pd-BiOCl photocatalysts,respectively.The EPR test found that the signal of oxygen vacancies was significantly increased after the noble metal nanoparticles were loaded on the BiOCl nanosheets.The steady-state and time-resolved PL spectra,transient photocurrent response and EIS study further confirmed the higher charge carrier generation,separation and migration in the metal decorated BiOCl ultrathin nanosheets,especially in Pd-BiOCl photocatalyst.The calculations verified a stronger electronic coupling between Pd and BiOCl（001）surface than that between Au and BiOCl（001）surface.The metal decorated BiOCl ultrathin nanosheets exhibited improved photocatalysis,in comparison to the pristine BiOCl ultrathin nanosheets and the light-irradiated BiOCl ultrathin nanosheets,in the photocatalytic selective oxidation of aromatic alcohols to the corresponding aldehydes in ambient conditions.Moreover,Pd-BiOCl photocatalyst exhibited superior photocatalytic activity than Au-BiOCl one.The improved photocatalysis of Pd-BiOCl for selective oxidation of aromatic alcohols in air atmosphere can be attributed to the following distinct advantages:preferential adsorptions of aromatic alcohol on Pd NPs and molecular O₂ on V_O sites of BiOCl,effective spatial separation of photogenerated carriers,the cooperative actions of holes accumulated in Pd NPs and·O₂^-produced in OVs of BiOCl.In consequence,this work affords a potential photocatalyst of high efficiency for highly selective conversion processes with environmentally benign oxidants such as O₂ and sheds some light on the rational design of highly efficient photocatalysts via surface engineering.