The Preparation and Properties of BiOX(X=Cl,Br) Composite Photocatalysts

Author:Song Ling Jun

Supervisor:zheng yan jun


Degree Year:2017





With the development of the social economy,a series of energy crisis occurs,such as energy shortage,greenhouse effect and environmental deterioration.So it is urgent to solve these problems as soon as possible.In this respect,the exploitation of new energy project,the emissionreduction of the greenhouse gases,the reduction of CO2 into hydrocarbon fuel,and the degradation of pollutants in the water or the solid waste on the surface of the earth,etc.become the imperative problems to be solved.Renewable resources in the nature,such as biological resources and climatic resources,are expected to be used instead of the non-renewable fossil fuels to prevent the resource depletion.Solar power,one kind of non-fossil energy,is affluent in the nature.It needn’t specific of expensive equipment to collect and even need’t to be transformed.As for semiconductors,they gradually become the hot issues because they can transfer the solar energy to chemical energy.Followed by the progress of the semiconductors in the energy transformation field,the researchers have paid more and more attention in expanding the application fields.Based on the summary of a plenty of relevant literatures both at home and abroad,this study has been concentrated on the exploration of bismuth oxyhalides and the constructions of composites.Several synthesis methods have been selected to prepare the composites.All of the research results demonstrated that the heterostructure contributes to the separation of the photoinduced charge carriers and the suppression the recombination of them.The light absorption of the semiconductors with heterojuntions was extended and the photocatalytic activities of them also were enhanced.The composite photocatalysts possess practical application in photocatalysis due to their stable performance and can be recycled and went into service in degradation for several times.The main research focuses and conclusions are listed as follow:(1)G-C3N4/BiOCl nanodiscs were successfully synthesized by hydrothermal method.The analysis results of XRD spectra and SEM images demonstrated that the additional amount of g-C3N4 powder would inhabit the growth of BiOCl particles.The surface of the composite catalyst was rough,the ultrathin g-C3N4 nanosheets dispersed randomly on the surface of BiOCl nanodiscs.The UV-vis diffuse reflectance spectra of the samples displayed the extension of the light absoption of the composites with the hybridation of g-C3N4.Within 30 min’s degradation of RhB,the g-C3N4/BiOCl hybrids showed higher photodegradaton rate which was more than 2 times than that of pure BiOCl.The g-C3N4/BiOCl kept stable and the crystal structure was not destroyed even after four irradiation cycles.(2)A series of g-C3N4/BiOCl nanosheets were prepared by sonication-assisted deposition-precipitation route.XRD spectra of the composites showed the influence of g-C3N4 on the crystal size and the exposed plane of BiOCl.The degradation experiments indicated the exposed facets had minor effect on the photocatalytic performance.The dominant factor was the heterostructure between the two kinds of semiconductor materials and the indirect photosensitization of RhB.(3)BiOCl/BiVO4 microspheres were synthesized by a coprecipitation method combined with hydrothermal treatment.The construction units were porous micro-nanosheets.The morphology of BiVO4 was dendritic crystal while that of BiOCl/BiVO4 was microsphere consisted of porous micro-nanosheets.It canbe inferred that BiOCl with lamellar structure acted as a structure-directing agent in the synthesis approach.The composites displayed expand absorption in visible light range.Evaluated by the photodegradation,it verified the porous and hierarchical structure improved the separation effect of the photogenerated carriers.(4)The pre-synthesized BiOCl powders were dispersed into a certain amount of deionized water.And then different mass of KBr was added in the system.The mixture was under hydrothermal treatment after adjusting the pH value of the suspension and finally the BiOCl/BiOBr nanoflakes were obtained.The SEM images revealed the composite nanoflakes owned irregular nanoflake morphology with relative smooth surface except some tiny terrace-shaped steps while BiOCl exhibited flower-shaped microspheres with agglomeration.In the catalytic process,the active oxidizing species,such as·O2ˉand·OH,were actually generated.Both of them and the photoinduced holes took part in the oxidative degradation of RhB and 2,4-dichlorophenol.The degradation results confirmed the enhanced affect of the hybridation of BiOBr.