| For the sharp issues about energy shortage and pollution refractory,study on application of hydrogen energy garnered widespread attention.With the advantages of clean,high-heating-value,and extensive-source,hydrogen energy is one the future substitution of fossil fuel.However,difficulties on hydrogen preparation and its storage prevent the practical application of hydrogen energy.The state-of-the-art methods to prepare hydrogen are electrolysis of water,water gas reaction,etc.,most of which are high energy-consumption and inconvenient.Hydrogen is flammable and in gas state at normal pressure and temperature,leading to great efforts made for save storage and transportation.Recently photocatalysis draws much concerned,by which solar light energy is transferred into chemical energy.Prepare and transport hydrogen by photocatalytic reaction is thought as one of the approaches.There are two problems existing:1)how to improve the efficiency of photocatalytic reaction to fulfill the demand of practical application,2)how to exploit the relationship between the structure of photocatalysts and their performance to provide inspiration for the future study.Aiming to solve the problems mentioned above,metal-organic frameworks（MOFs）were used as platform for the study of relationship between structure and performance.Moreover,we attempted to design proper structure of MOF for enhanced photocatalytic efficiency.MOFs are porous crystalline materials constructed by the nodes of metal ions/clusters and organic linkers via coordination.They have been widely used in photocatalysis since their high surface areas and porosities,variable topologies and facile decoration.With high crystallinity,the structure of MOF is feasible to characterize as well as simulate,which is promising as platform for the study of relationship between structure and performance.This might be important for the design of efficient photocatalyst.The innovation and work of this thesis includes these following aspects:1.The acceptorless dehydrogenation of 1,2,3,4-tetrahydroquinoline was used as model to study the feasibility that porphyrin or porphyrin MOFs are able to catalyze the visible light driven dehydrogenation reaction of N-heterocycles with hydrogen release at room temperature.We found that both porphyrin and porphyrin MOFs are active for this reaction.When porphyrin MOFs are used as photocatalyst,heterogeneous catalysis was achieved conducive to recycle.Moreover,we found porphyrin is the active site for this reaction after parallel experiments and spectrographic characterization.This work is valuable for the field of hydrogen storage and pharmaceutical industry,and is fundamental for the future study about structure-performance relationship.2.To study the relationship between MOF structure and their performance,we synthesized a series of porphyrin MOFs with different topologies and used them for photocatalytic acceptorless dehydrogenation of 1,2,3,4-tetrahydroquinoline.We found that the performance is higher when the distance between active sites are shorter.Quantitatively,we found the linear relationship between the TOF value of porphyrin MOFs and their weighed average reciprocal of distance.This conclusion might be helpful for the select and design of inorganic catalysts.3.After proposed the relationship between photocatalytic performance and distance between active sites,we removed a ratio of porphyrin linkers out of specific crystallographic sites in MOF-525,which shows high efficiency in photocatalytic dehydrogenation reaction.By this method,mesopores were made for the improvement of substrate diffusion,expecting for further enhancement of the photocatalytic performance.The sample MOF-525-J33,with 33%porphyrin linker removed,exhibited the highest catalytic performance among the porphyrin MOFs,with the TOF value of 29.5 h-1.This work might be meaningful for the expansion of MOF catalyst,and provide inspiration for synthesis and design of inorganic catalysts. |
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