Study On The Porous Materials For Photocatalysis

Solar energy is an inexhaustible,widely distributed and huge renewable energy resource.Photocatalysis aimed at solar energy conversion and utilization has become one of the promising ways to alleviate the energy crisis.Recently,porous materials have been studied as a kind of effective photocatalyst due to their excellent structural properties such as adjustable porosity,large specific surface area,and permanently open pores,which makes full interaction between the reactant and the surface of photocatalyst for improved surface catalytic reaction.However,porous materials still have the problems of low charge separation efficiency,low photocatalytic activity and apparent quantum efficiency in the field of photocatalysis.In this dissertation,we investigated the applications of two typical porous materials,namely porous graphene(PG)and novel covalent organic frameworks(COFs),in photocatalysts by means of theoretical modulation and experimental research.The main results are summarized as follows:(1)We constructed a novel porous graphene using first-principles calculation method.By stacking this PG with blue phosphorus(BP)or transition-metal dichalcogenide compounds(TMDs),a series of porous graphene-based van der Waals(vdW)heterostructures with photocatalytic potential for water splitting were designed.We found that the constructed heterostructures have a weakly polarized electric field in the interface region,which is conducive to the separation of electrons and holes.Moreover,the type-II heterostructures promote the migration of electrons and holes to different monolayers.The positions of the bottom of the conduction band and the top of the valence band meet the redox potential requirements of photocatalytic water splitting.Compared with monolayer materials,the range and intensity of light absorption of heterostructures are significantly enhanced,and the energy barrier for hydrogen evolution reaction is reduced.(2)A novel porphyrin-based covalent organic framework material(Por-BC-COF)with high crystallinity,high specific surface area and high chemical stability was synthesized and applied to the photocatalytic oxidative coupling of primary amines to synthesize imines.The results show that Por-BC-COF can efficiently convert benzylamine to imine without metal loading,the turnover frequency(TOF)reaches 22.5 h-1,and the conversion rate does not decrease after 3 cycles.For primary amines with electron-withdrawing groups,electron-donating groups,and large sterically hindered groups,the conversion rate is more than 90%,which indicates that this material can stably and efficiently oxidize primary amines to imines.(3)A donor-acceptor(D-A)covalent organic framework(BTT-TATP-COF)containing triazine ring was synthesized and applied to photocatalytic hydrogen evolution and photocatalytic carbon dioxide reduction.The photocatalytic hydrogen production rate of 3 wt%Pt-BTT-TTP-COF was 7068 μmol g-1 h-1 in an aqueous solution with ascorbic acid as sacrificial agent.Moreover,photocatalytic reduction of carbon dioxide to carbon monoxide was achieved on 0.55 wt%Co-BTT-TATP-COF,and the carbon monoxide production rate is 1412 μmol g-1 h-1.