Synthesis And Assembly Of Ultrathin Two-Dimensional Materials And Their Applications In Catalytic Hydrogen Production And Membrane Separation

Ultrathin two-dimensional(2D)materials show great potential application prospects in the fields of catalysis and separation due to their unique properties and structural advantages.Compared with traditional nanoparticles,ultrathin 2D materials have intrinsic structural advantages in catalysis:1)the ultrathin feature of nanosheets offers a high fraction of active sites on their surface to increase activity;2)the specific facet of nanosheets provides a simple type of active sites to identify small changes during catalytic process by in-situ techniques and reveal the real active sites.Recently,2D materials assembled membranes show efficient mass transport and molecular sieving properties through their subnanometer interlayer galleries.The membrane assembly process plays an important role in the alignments and defects of the laminar membrane structure,which significantly influence the membrane performance.Therefore,the thesis will focus on the following two directions:1)synthesis of ultrathin 2D materials and use as model catalyst to study the structure-catalysis relationship.2)study how the assembly process of 2D materials influence the membrane separation performance,and prepare pH responsive smart membrane.The main results are showed as follows:Chapter 1.Introduction of the synthesis and assembly method of ultrathin two-dimensional(2D)materials and their applications in catalytic hydrogen production and membrane separation.Then the meanings and content of this thesis were listed.Chapter 2.Synthesis of ultrathin 2D PdAg nanosheets and use as model catalysts to study the interfacial effect in catalytic formic acid decomposition.The catalytic activity shows a volcano type relation with Pd/Ag ratio.PdAg bimetallic nanosheets with Pd/Ag ratio of 1 shows the highest catalytic activity.The electronic effect and geometric effect between Pd and Ag jointly promote the catalysis.Chapter 3.2D nanosheets of a Ni-S coordination polymer have been successfully synthesized and used for hydrogen evolution reaction(HER).In-situ X-ray absorption spectroscopy reveal that the as-prepared catalyst entirely transformed into ultrathin Ni nanosheets under alkaline reductive conditions.The in-situ generated catalysts exhibit superior activity towards HER.Studies reveal that the large area ultrathin Ni nanosheets serve as active sites for H2 generation,while the trace sulfur adsorbed on Ni surface promote the water dissociation.Chapter 4.We study the assembly process of graphene oxide(GO)membrane,reveal the evolution of defects in the assembly process and identify key dominating parameters by experimental observation and the Mote Carlo simulation.We further demonstrate the modulation of assembly process,which lead to defect-free GO membrane thinner than 8 nm,and could advance the development of high-efficient nanofiltration technology.Chapter 5.Preparation of pH-responsive smart MoS2 membrane and study the influence of phase and pH on the water transport and molecular sieving properties.The presence of hydrated cations between the interlayer of MoS2 membranes results in the high permeation of water governed by adsorption-diffusion mechanism.The concentration(separation)of intercalated cations can be precisely controlled by pH,resulting in the reversible change of water permeation and molecular sieving properties.