Fine Regulation On Two Dimensional Nanosheets Surface Realized Enhanced Photocatalytic/Electrocatalytic Properties

Photocatalysis and electrocatalysis techniques contribute a lot in solving energy crisis and environment protection,photocatalytic and electrocatalytic materials has always been the research subjects for the scientists.It is a necessity for people to modify the present catalysts to improve the pristine catalytic activity or develop new type of highly active materials to replace them to deal with the issues about low availability of incident light and relatively low quantum efficiency of photocatalysis and poor selectivity of product with severe side-effect of electrocatalysis.Two-dimensional nano-materials possess huge surface area when compared to the bulk materials and often demonstrate a serial of new qualities due to the dimensional confinement effect,not only for the dimensionality reduction,so the finding and development of two dimensional nano-materials truly fulfill many blanks of the practical application fields.Nowadays,the synthesis and preparation methods for two dimensional nano-materials have been developed systematically and maturely,people could obtain the expected two dimensional semi-conductor materials through many physical and chemical approaches and gain much deeper understanding of photocatalytic and electrocatalytic reaction process when using these emerging two dimensional nano-materials.In this thesis,we focused on the application of two dimensional nano-materials in photocatalytic water oxidation,photocatalytic nitrogen fixation and electrocatalytic carbon dioxide reduction,then we have carried out three research subjects on surface modification of present materials to improve the pristine catalytic activity and developing new type of highly activie nano-materials realizing enhanced energy conversion efficiency:(1)After the photo-assisted surface etching of BiOCl nanosheets,we realized the enhanced photocatalytic water oxidation and photo-degration of RhB,the maximum O2 evolution rate of etched nanosheets was 37 times over the unmodified nanosheets,86 times over the nanoplates of BiOCl and the degration rate of RhB was also significantly enhanced by 5 times over the nanosheets,15 times over the nanoplates of BiOCl.The reason for this enhancement was not only for the extra exposed surface area and increase of catalytic activity centers originate from the decrease of the layers of nanosheets/nanoplates,but the synergistic effects of the surface pit reconstructure resulted from the surface etching process,which brought a large degree of edge areas exposed,and the much exposed atomic[Bi2O2]2+ active layers from the exchange of the surface adsorbed anions,thus contributed to the superior photocatalytic oxidation activity of etched defect-rich BiOCl nanosheets.(2)We loaded and stabilized the single Cu atoms into the selective defect structures in polymer carbon nitride via simple impregnation and post-annealing process.The coordination situation of single Cu atoms in T-defect was obtained based on the XAFS characterization and simulation combined with the results of density functional theory.The photocatalytic dinitrogen fixation performance of ultrathin polymer carbon nitride nanohseets could be significantly improved by 8 times after the loading of single Cu atoms,and so did the quantum efficiency.Comparing the ESR signals we obtained before the light irradiation and after the irradiation and the PDOS theoretical calculations,we acquired that valence electrons distribution of the N atoms which coordinated with the loaded single Cu atoms got delocalized and the valence electrons would get easily activated under the light irradiation so as to increase the amount of available active electrons,which appeared to be the increase of the ESR response signals.While for the unloaded polymer carbon nitride ultrathin nanosheets,the amount of limited available active electrons restrained the photocatalytic dinitrogen fixation performance.(3)Through a simple sacrifice template method we realized precursors insertion in relatively low temperature section and calcination of the carbon-based materials in high temperature section and finally prepared the single Mo atoms loaded ultrathin N-doped graphene nanosheets.The HADDF-STEM images gave us the visual distribution of the single Mo atoms and we speculated the structure of single Mo atoms loaded ultrathin N-doped nanosheets and potential loading formation of Mo atoms via the XPS analysis of surface element content and split peak proportions.After the electrical experiments of the serial loaded concentrations electrocatalysts we found out the Mo@NG-2 sample possessed the lowest overpotential,higher current density and lower Tafel slope.Comparing the electrocatalytic carbon dioxide reduction performance of Mo@NG-2 and unloaded N-doped graphene we realized that the yield of Mo@NG-2 was always higher than the N-doped graphene and got further improved when higher potential applied.The selectivity of formate of Mo@NG-2 was also higher even twice of that in N-doped graphene.The Mo@NG-2 electrocatalysts demonstrated a consistent stability during the electrocatalytic carbon dioxide reduction process.