Construction Of Z-scheme Photocatalytic System With Reduced Graphene Oxide (RGO) As An Electron Mediator And Its Properties Investigation

The use of fossil energy such as petrol and coal which resulting in a series of environmental and energy problems,greatly threatening the human survival.Since solar energy is a kind of widespread green energy on Earth,one of the best solutions to the current environmental and energy problem is to convert solar energy to other energy such as chemical energy and electronic energy.Photocatalysis,which is able to produce hydrogen from water splitting and reduce CO2 into chemical fuels under solarirradiations,is a promising pathway in the direct transformation of solar energy to chemical energy.Developing highly efficient photocatalyst is much significant for the solar energy utilization.Z-scheme photocatalytic system is composed of two suitable energy band semiconductor photocatalyst connected by electron mediator,which simulating the process of photosynthesis in plants.By simultaneous excitation of the two photocatalysts,redox reaction can be achieved over the Z-scheme system without energy wastes,which is benefit for the efficient conversion of solar energy to chemical energy.In this thesis,a Z-scheme photocatalytic system RGO as electron mediator was achieved.By mixture of RGO/ZnIn2S4 nanocomposite and BiVO4 and tring to prepare the ZnIn2S4/RGO/BiVO4 three componant compounds.And then we investigated the photocatalytic performance of the prepared photocatalytsts for water splitting,degradation of RhB and reduction of Cr6+ in water and CO2 reduction with the oxidation of benzyl alcohol under visible light irradiation.The main contents obtained from the present research are as follows:(1)We have obtained the RGO/ZnIn2S4 nanocomposite with highly reductive RGO by a facile one-pot solvothermal method.The prepared RGO/ZnIn2S4 showed higher photocatalytic performance for photocatalytic hydrogen evolution than pure ZnIn2S4 under similar condition,which is because that RGO can act as a good electron acceptor and mediator facilitating the separation of the photo-generated carriers.(2)RGO/ZnIn2S4 microspheres was obtained by microwave-assisted method.The obtained RGO/Znln2S4 showed photocatalytic performance for hydrogen evolution even higher than that prepared via solvothermal method.EIS analyses revealed that the microspheres RGO/ZnIn2S4 is much more benefit for the electron transfer and thus showed high photocatalytic activity.(3)We have prepared RGO/BiVO4 nanocomposites and investigated the photocatalytic performance for photocatalytic oxygen evolution.Due to the high electrical conductivity of RGO,the prepared RGO/BiVO4 showed higher photocatlaytic activity than pure BiVO4 under similar condition.(4)We studied the photocatalytic performance of the Z scheme photocatalytic system including the mixture of RGO/ZnIn2S4 and BiVO4(denoted as RGO/ZnIn2S4-BiVO4)and different co-catalyst doped RGO/ZnIn2S4-BiVO4 for various reactions including photocatalytic water splitting,degradation of RhB and Cr6+,CO2 reduction and benzyl alcohol oxidation.However,the above reaction can not proceed probably because that the electron transfer inside of the semiconductor is faster than that on the interface.Therefore,we tried to prepare the ZnIn2S4/RGO/BiVI4 three componant compounds,but failed,probably due to the large particle size of both ZnIn2S4 and BiVO4.(5)Since Cu2O has small size and is photoactive for various reactions such as hydrogen evolution,CO2 reduction and so on,we choose it to replace ZnIn2S4 to build the Cu2O-RGO/BiVO4 Z scheme system.The prepared Cu2O-RGO/BiVO4 showed activity for CO2 reduction to form HCOO-accompanied with the oxidation of benzyl alcohol to benzaldehyde under visible light irradiation.