Design,Synthesis And Photocatalytic Performance Of Porous Framework Materials

Photocatalytic water splitting has been regarded as a feasible strategy for the effective use of solar energy to solve increasingly serious environmental and energy problems.Since the pioneering work of Fujishima and Honda in 1972 on photoelectrochemical water splitting using a Ti O₂ electrode,numerous semiconductor materials,such as metal oxides,nitrides,and sulfides,have been explored and great progress has been made in photocatalytic hydrogen production from water splitting.Up to now,the traditional inorganic semiconductor photocatalysts are still lack of surface active sites,and the recombination problem of photogenerated excitons（electron-hole pairs）is still serious.Therefore,the exploration of photogenerated charge separation,migration and surface reaction kinetics promotion methods have always been the difficulty and focus of Semiconductor Photocatalysts.On the one hand,the recombination of photogenerated excitons can be suppressed by introducing a variety of semiconductors or electronic media to form built-in electric fields or electron traps.However,this strategy is still challenging in practice,mainly because it is difficult to form close interface contact between components with different physical properties;On the other hand,the surface reaction kinetics can be controlled by the supported cocatalyst unit.In addition,to implement the above two strategies at the same time,one often needs a more complex multi-step synthesis process.For this reason,it is urgent to develop and utilize new multifunctional materials to construct efficient photocatalytic system,improve the photocatalytic reaction efficiency and gain deeply understanding of the structure-activity relationship.In the first chapter of the thesis,we have developed a 0D/2D Z-scheme heterojunction photocatalyst linked by chemical bond.We selected cadmium-based MOFs（Cd-TBAPy）with two-dimensional layered structure,which has good optical stability and visible light absorption.The Cd nodes can not only act as active sites for water redox reactions but also serve as the metal source for in situ fabrication of Cd S.With such a homologous bridge,intimate interfaces between Cd-TBAPy and Cd S can be achieved.Baring these considerations,we propose a research model of in-situ connected Cd S/Cd-TBAPy Z-scheme heterojunction photocatalyst integrating effective charge separation,active metal sites and facilitate interfacial charge migration all-in-one.Furthermore,considering the poor conductivity of MOFs,Cd-TBAPy was pre-exfoliated into few-layered 2D nanosheets to shorten the bulk-to-surface pathway of charge transfer,which also expose more metal sites for catalysis and in-situ Cd S loading.Thereby,in this thesis,the 0D/2D Cd S/Cd-MOL Z-scheme heterojunction system was in-situ constructed with multi-aspect optimizations.Eventually,such a composite system achieved visible-light photocatalytic H₂ evolution from pure water without using any cocatalysts and sacrificial reagents.In addition to the construction of 0D/2D Cd S/Cd-MOL Z-scheme heterojunction system,in this thesis,a two-dimensional layered stacking HOF（PFC-42（PFC=Porous materials from FJIRSM,CAS））integrated the well-known photoreactive C₃N₄ has been designed,synthesized,and structurally characterized by single-crystal X-ray diffraction analysis.Under visible-light irradiation,the Pt nanoparticles loaded PFC-42（PFC-42-Pt）continuously produces hydrogen from water in the presence of scavengers with the evolution rate of 26.67 mmol/g,which is outstanding in all the reported Pt/porous composite materials.The significantly high H₂ evolution of PFC-42-Pt compared with those of amorphous analogue bulk C₃N₄-Pt,and nanosheet C₃N₄-Pt demonstrates that the ordered arrangement of photosensitizers dramatically improves the photocatalytic activity of material,which is further proved by the recrystallization experiment.This thesis represents the first example of HOF capable of photocatalysis,not only demonstrating the great application potentials of HOF in heterogeneous photocatalysis but also rendering an excellent opportunity to reveal structure-activity relations.