Preparation Of Ultrathin Inorganic Two-dimensional(2D) Nanosheets For Photocatalytic Hydrogen Evolution

Energy is the basic substances for the existence and development of our human being society.The large-scale use of tranditional energies such as coal,petroleum and natgas has caused a serious environmental pollution problem,which directly affects our human being's sustainable development.Hence,it's urgent to develop and use clear and renewable energies.Hydrogen as a clear and renewable energy with high enthalpy has attracted enormous attentions of the researchers.Recently,photocatalysis has been considered as a green,efficient and cost-effective approach to produce hydrogen,showing a great potential application in solving the environmental and energy issues.Recently,the ultrathin inorganic 2D nanosheets have shown distinct advantages in the field of photocatalytic hydrogen production.Their thickness just with several nanometers makes the catalytic activity sites fully expose and the migration path of the photo-generated carriers short,which represses the recombination of the carriers in bulk and achieves the efficient separation of the carriers.Additionally,The unique 2D structural feature provides a platform for modifying or grafting cocatalysts on photocatalyst surface,even coupling with other semiconductors to fabricate nanocomposite,further realizing the enhancement of the photocatalytic reaction quantum efficiency.In this thesis,top-down and down-top strategies were used to synthesize the ultrathin inorganic 2D nanosheets according to the crystal engineering.Furthermore,based on the structure-function relationship,we designed series of photocatalysts with superior photocatalytic hydrogen evolution activities via surface modification and semiconductor coupling.The main research contents and results are as follows:(1)Ultrathin niobium-based metal oxidation nanosheets such as HNb3O8,HSr2Nb3O10 and HCa2Nb3O10 nanosheets were prepared successfully via a top-down method.Taking HNb3O8 nanosheets as an example,the morphology and structure of the nanosheets were characterized well by XRD,SEM,TEM,Raman and XAFS.It demonstrated that nanosheets had a single-crystal structure with defects.Furthermore,niobium-based nanosheets were modified by Cu2O/Cu via in-situ photo-reduction of Cu2+.It was found that the photocatalytic activity of the niobium-based nanosheets after modification with Cu2O/Cu increased dramatically,as compared with corresponding pure nanosheets.The role of Cu2O/Cu for promoting photocatalytic hydrogen evolution activity over HNb3O8 nanosheets was revealed by EPR and electrochemical tests.(2)We developed a method,in which Cd2+ was used to flocculate CaNb3O8-colloidal suspension firstly and then the obtained mixture was sulfurated via a hydrothermal process,to fabricate CdS/HCa2Nb3O10 hybrid.XPS and TEM demonstrated that the hybrids had an intimated heterogenerous contact interface.EPR and photocurrent response tests showed that electrons transferred from CdS to HCa2Nb3O10,when the CdS/HCa2Nb3O10 hybrid was excited under visible-light irradiation(?>400 nm).Moreover,the effects on the photocatalytic hydrogen evolution activity were discussed.(3)Ultrathin MoS2 nanosheets with rich defects were prepared successfully via a facile one-pot hydrothermal method.The defects were S22-and MoOx in the MoS2 nanosheets,which were revealed by XRD,SEM,TEM,XAFS,EPR and Raman.LSV and EIS experiments demonstrated the MoS2 nanosheets had an excellent activity to catalyze hydrogen evolution.Furthermore,we designed a CdS/MoS2 nanocomposition via an electrostatic self-assembly method.Without a noble metal cocatalyst,the phtocatalytic hydrogen evolution ratio over CdS/MoS2 nanocomposition with optimal loading of CdS was up to 381.6 ?mol/h.