The Preparation Of Donor-acceptor Modified Carbon Nitride For Enhanced Photocatalytic Hydrogen Evolution

Currently,environmental problems and energy crisis have become two major challenges of human beings.Therefore,the exploitation of sustainable clean energy has attracted ever-increasing attention.Hydrogen energy,with the merits of renewable and environmental friendliness,is considered as a promising alternative to fossil fuels.Particularly,photocatalytic technology provides an ideal way to convert inexhaustible solar energy to eco-friendly hydrogen energy,which makes it become an alternative candidate for solving energy and environmental problems.The typical photocatalytic hydrogen evolution reaction includes three basic steps: light absorption,separation and transfer of photogenerated carriers and surface redox reaction.Polymeric carbon nitride(CN)has inspired intense concerns of researchers for its appropriate band structure,facile preparation,low cost and superior chemical stability.However,the photocatalytic activity of pristine CN is severely restricted due to the poor optical absorption and rapid recombination of photogenerated electron-hole pairs.Therefore,the development of efficient and stable CN-based photocatalytic materials has become one of the key points of the current research.The construction of conjugated copolymer with donor-acceptor(D-A)system has emerged as a promising strategy to improve the photocatalytic activity.The existence of D-A structure can not only improve the optical utilization but also facilitate the intramolecular migration of electrons and holes,leading to the increased photocatalytic hydrogen evolution rate.Herein,carbon nitride-based donor-acceptor conjugated copolymers with enhanced photocatalytic hydrogen activity are fabricated via molecular modification.The main contents of this paper are as follows:Firstly,a CN-based donor-acceptor conjugated copolymer is fabricated via facile thermal copolymerization of 2-aminobenzimidazole(ab IM)and urea.The experimental results demonstrate that the ab IM units are successfully incorporated into the framework of CN and the main chemical structure of CN is still preserved.These ab IM units could serve as electron acceptor,extending the π-conjugated system and inducing the intramolecular charge transfer via an internal electric field.As a result,the construction of D-A structure not only improves the optical utilization but also facilitates the intramolecular migration of electrons and holes,leading to enhanced photocatalytic hydrogen evolution,which is about 2.7 times higher that of pristine CN.Secondly,a CN-based donor-acceptor conjugated copolymer is fabricated via nucleophilic chemical reaction and facile thermal copolymerization of 4-amino-1Himidazole-5-methylnitrile(AICN)and urea.AICN is selected as the electron donor,which is successfully grafted into CN framework.The construction of D-A structure can significantly improve the visible light response of the catalyst and suppress the recombination of photoelectron-hole pairs.As a result,the AICN-mofied samples exhibit enhanced photocatalytic hydrogen evolution activity.The optimal photocatalytic hydrogen evolution rate of AICN-modified sample is approximately2.2 times that of pristine CN.