Study On The Surface Structure Modification And Photocatalytic Performance Of Bismuth Oxychloride

Photocatalytic technology seems promising in solving environmental problems and energy crisis.As a new semiconductor photocatalytic material,bismuth oxychloride?BiOCl?has attracted great attention due to its unique optical and electronic structure.However,due to its wide band gap,the single BiOCl can only be excited under the ultraviolet light which only accounts for 5%of the sunlight.At the same time,its fast recombination rate of photogenerated carriers and slow reaction dynamics seriously affect the photocatalytic performance of BiOCl.In order to solve these constraints,this paper devoted to the modification of BiOCl from three aspects:improving the optical absorption capacity,improving the catalytic reaction kinetics and enhancing the charge separation efficiency to improve its photocatalytic performance.The photocatalytic performance of the as-obtained samples was evaluated by organic pollutant molecules,and the corresponding characterization and analysis were carried out.The details are as follows:1.Preparation and photocatalytic properties of a novel ternary Ag@Ag₂O/BiOCl photocatalyst.Ternary Ag@Ag₂O/BiOCl photocatalyst driven by visible light was obtained by successfully modifying Ag@Ag₂O cocatalyst onto{001}facets of BiOCl nanosheet through a simple two-step route.As controls,BiOCl nanosheets,Ag₂O nanoparticles and Ag/BiOCl composites were synthesized by appropriate methods.The synthesized samples were investigated by various characterization methods.UV-vis DRS showed that the absorption range of Ag@Ag₂O/BiOCl was broadened from UV region to visible region.The photodegradation experiment showed that Ag@Ag₂O/BiOCl composite had a good degradation efficiency on Rhodamine B?RhB?under visible light irradiation.The degradation rate reached 91.2%in 120 min,and the reaction rate was about 32,3 and 5 times of BiOCl,Ag₂O and Ag/BiOCl samples.The results of photoluminescence?PL?and electrochemical impedance?EIS?showed that heterojunction may be formed in Ag@Ag₂O/BiOCl system to enhance the interface charge transfer and inhibit the photogenerated carrier recombination.Finally,the possible mechanism of RhB degradation of Ag@Ag₂O/BiOCl composite was explored by energy band structure and free radical analysis.2.Oxygen vacancy and energy band engineering to improve the kinetics of BiOCl photocatalytic oxidation of organic pollutants.OV-BOC with oxygen vacancy and BOC without oxygen vacancy were synthesized by solvothermal modification strategy.The results of photocatalytic degradation of RhB,methyl orange?MO?and phenol showed that OV-BOC had a certain degradation ability under visible light irradiation.At the same time,the kinetic constants of OV-BOC degradation increased by 2.6,3.1 and 2.4 times respectively after adding 1mM H₂O₂.The results of Valence band spectra of X-ray Photoelectron Spectroscopy?VB-XPS?and Electron Spin Resonance?ESR?showed that different solvothermal methods could not only introduce oxygen vacancy into the material,but also regulated the band structure.UV-vis DRS showed that oxygen vacancy bring new impurity energy levels under the conduction band,thus improving the light response range.At the same time,oxygen vacancy was conducive to the production of ¹O₂ in the system,which was conducive to photocatalytic degradation.On the other hand,compared with BOC,the valence band of OV-BOC shifted down 0.17 e V,which wass conducive to the direct oxidation of organic pollutants by holes?h⁺?.Through the free radical analysis experiment,after adding H₂O₂,the content of·O₂^-in the system increased by 2-3 times,which was caused by the activation of H₂O₂ from h⁺.The surface kinetics of photocatalytic oxidation was improved by introducing oxygen vacancy and adjusting the position of valence band,so as to further improve the photocatalytic performance.3.The construction of Z-scheme{001}/{110}surface heterojunction to promote spatial charge separation in Bi OCl.Herein,the co-exposed{110}/{001}facets BiOCl nanoplates were obtained by hydrolysis in strong acid.The results of photocatalytic degradation showed that the photocatalytic removal of pollutants by BiOCl was related to the ratio of these two facets.PL,Time-Resolved Photoluminescence?TRPL?,Surface Photovoltage?SPV?and EIS were used to analyze the separation of photogenerated carriers.In addition,the theoretical calculation showed that the band structure of{001}and{110}facets presented staggered band arrangement,which made it possible for BiOCl to form surface heterojunction.Furthermore,the electronic flow direction between crystal surfaces was determined by the calculated work function.Based on these experimental and theoretical results,the charge transfer mechanism of Z-scheme facets heterojunction was proposed.