Synthesis Of Cu_2-xS-MnS Nanoheterostructures For Photocatalytic Hydrogen Evolution

The world is seeking sustainable and clean energy solutions for increasingly energy and environmental crisis.Solar-driven hydrogen production by photocatalytic water splitting is one of the most promising clean energy technologies.The key to photocatalytic hydrogen evolution lies in the design and preparation of efficient photocatalysts.The main reasons for the limited photocatalytic hydrogen evolution performance are usually the low spectral utilization efficiency of semiconductor catalyst and the low separation efficiency of photogenerated carriers.In addition,the photocatalytic hydrogen reaction is generally catalyzed by precious metals to achieve favorable reaction kinetics.Unfortunately,noble metals suffer from low abundance and high cost,hindering their commercial application.Based on the above critical scientific problems,this paper started with low-cost Cu_2-xS catalyst,and the parent nanocrystals were synthesized by optimizing the microstructures and morphology.Furthermore,based on structural design and energy level matching,the efficient,stable and noble-metal-free Cu_2-xS-Mn S nanoheterostructured photocatalysts were synthesized via a cation exchange reaction by employing the as-prepared Cu_2-xS nanocrystals as initial templates.The developed photocatalysts realized the efficient conversion of solar energy to hydrogen energy.The main research results are as follows:（1）Stable and controllable synthesis of high-quality Cu_2-xS nanoparticlesBased on thermal decomposition method,djuleite Cu_1.94S spherical nanoparticles and roxbyite Cu_1.81S platelike nanoparticles with uniform morphology and good crystallinity were obtained in two phosphorous-free reaction systems.Furthermore,the influence of each reactant on the morphology and particle size of the Cu_2-xS was determined through changing the contents of reactants,and the sensitivity to time and temperature of the reaction system in a certain range was minimal.This work provides a stable matrix material source for subsequent research and lays a theoretical foundation for the batch preparation of high-quality Cu_2-xS nanoparticles.（2）Core-shell Cu_1.94S-Mn S nanoheterostructures for enhanced photocatalytic hydrogen evolutionCore-shell Cu_1.94S-Mn S nanoheterostructured photocatalyst was synthesized via a cation exchange reaction by employing the spherical djuleite Cu_1.94S nanocrystals as initial templates.The exchange reaction process of Cu_1.94S to Mn S was determined by analyzing the microstructure and chemical structure of the material.The photochemical properties and photocatalytic hydrogen evolution experiment results showed that the prepared Cu_1.94S-Mn S nanostructures had good light absorption and photogenerated electron-hole migration ability.In addition to the advantages of a small core-shell structure and many active sites,it showed a hydrogen evolution efficiency as high as 878.1μmol·h^-1·g^-1,representing60-fold and 41-fold enhancement compared with pure Cu_1.94S and Mn S,respectively,and a great stability in a certain time range.（3）Janus and bilayer Cu_1.81S-Mn S nanoheterostructures for enhanced photocatalytic hydrogen evolutionJanus structure and the bilayer structure of Cu_1.81S-Mn S heterostructured photocatalysts were synthesized by the cation exchange reaction by employing the roxbyite Cu_1.81S nanocrystals as the initial templates.The exchange reaction process of Cu_1.81S to Mn S was determined by analyzing the microstructure and chemical structure of the material.The photochemical experiment results showed that the prepared Cu_1.81S-Mn S had excellent photochemical properties,which can promote the separation of photogenerated carriers and improve the utilization of photons.The single-particulate Cu_1.81S-Mn S photocatalyst prepared by cation exchange reaction had continuous anionic sublattice,which enables high quality heterogeneous interface with less lattice distortion and interface defects in nanoheterostucture,reducing the electron-hole recombination.This kind of single-particulate catalyst integrated the light-harvesting and hydrogen evolution performance,which showed a hydrogen evolution efficiency as high as 624.5μmol·h^-1·g^-1,representing47-fold and 25-fold enhancement compared with pure Cu_1.81S and Mn S,respectively.Although it is slightly lower than Cu_1.94S-Mn S nanoheterostructures,but has better long-term stability.This dissertation contains 45 figures,5 tables and 155 references...