Controllable Preparation Of Two-dimensional Material Mos₂ And Their Application In Catalysis

Recently,two-dimensional?2D?materials,like graphene,have attracted considerable attention due to their remarkable properties in electricity,mechanics and optics.Graphene has a high mobility(?10⁴ cm²·V^-1·s^-1),but it's a semi-metallic material with zero bandgap,which limit its applications in electronic devices.As a result,the scientists have turned their attentions to the layered transition metal chalcogenide such as MoS₂.MoS₂ is a typical semiconductor material,the band gap gradually increasing with the decrease of its thickness.When the thickness is reduced to monolayer,MoS₂ will transit from indirect band gap into direct band gap due to the quantum confinement effect.Because of its excellent physical and chemical properties,MoS₂ gained a promising expectation in catalysis,device,battery,gas sensor,photodetector and heterojunction.At the same time,the non-renewable of the fossil fuels and it's caused environmental pollution make the development of new energy become a hot topic in academic society.Electrocatalytic hydrogen production has been considered as one of the most effective ways to produce clean hydrogen energy.So far,Pt and other noble metals were the best electrocatalysts for the hydrogen evolution reaction.However,the limited resources and the high price of noble metals make their large-scale applications been hampered.So that looking for the new catalysts alternative to Pt become imminent.MoS₂ has become very hot in the field of catalysis due to its unique electronic band structure and high catalytic active sites density.Hydrothermal and chemical vapor deposition method are the traditional methods to synthesize nanostructured MoS₂.But the controllable growth by using these methods was still an urgent problem to be solved.At the same time,how to develop effective methods to optimize the catalytic performance of MoS₂,and analysis the optimization intrinsic mechanism are worth exploring in depth.In this paper,we realized the controlled growth of nanostructures MoS₂ with different morphologies by controlling the experimental parameters.Based on the stable growth of MoS₂,we have successfully realized the regulation of the electronic structure by surface modification or element doping.At the same time,we established the relationship between the MoS₂ morphology,electronic structure and the function of materials,and we also explored the hydrogen evolution reaction of the as-synthesized MoS₂ with different morphology and electronic structure.Experimental investgations showed that the optimization catalytic performance was achieved by regulating the morphology and electronic structure of MoS₂.Our work also provide new ideas for the synthesis and intrinsic regulation of other two-dimensional materials.The details are summarized as follows:?1?An effective strategy for the stable synthesis of nanostructures MoS₂ was developed by a hydrothermal method.By adjusting and controlling the experimental conditions during the experiments,the controllable regulation of the final product morphologies were realized.The relationships between the morphologies,the lattice strains and the optical properties?Raman spectra,energy bandgap?of MoS₂ were established by SEM,HRTEM,Raman spectroscopy and photoluminescence spectroscopy characterization.To further verify this relationship,we also systematically studied the optical properties of MoS₂ nanosheets prepared by micromechanical cleavage method.?2?The surface of MoS₂ hanosheets was modified by metal nanoparticles?Cr,Ag?using the solution based method.The photoluminescence intensity of the metal-MoS₂ was zero,indicating the hybrid structure could inhibit the recombination of photogenerated carriers.Based on this phenomenon,we combined this hybrid structure with CdS photocatalyst to study their photocatalytic hydrogen production efficiency.?3?We successfully synthesized large area monolayer MoS_2?1-x?Se_2x alloys by using the chemical vapor deposition method.By controlling the experimental conditions during the synthesis,we realized the adjusting of S/Se ratios in the alloys.The different S/Se ratios gave a rise to different electronic structures in the alloys.Based on this analysis,we studied the hydrogen evolution reaction performance of the MoS_2?1-x?Se_2x alloys with different electronic structures,and we also explored the intrinsic mechanism.?4?High quality single crystal MoS₂ nanobelts were firstly synthesized by a chemical vapor deposition method.It is found that the nanobelt structure comprised parallel stacked atomic layers with the basal plane vertical to the substrate,and the top surface of the MoS₂ nanobelts are fully covered by active edge sites.This novel structure made the top surface highly active,both optically and chemically.?5?The MoS_2?1-x?Se_2x nanobelt alloys were firstly synthesized by a chemical vapor deposition method.The alloys with different Se contents have different electronic band structures.The as-synthesized MoS_2?1-x?Se_2x nanobelt alloys with high active site density and tunable electronic structures exhibited excellent electrocatalytic performance.