Preparation Of Non-precious Metal/gC₃N₄ Composite Photocatalyst And Study On Its Performance In Water Decomposition And Hydrogen Production

Exploring cheap and stable photocatalytic materials which can make full use of and effectively convert solar energy is the key of current and future photocatalytic research.Polymer carbon nitride(g-C3N4)is considered to be a very promising photocatalytic material.It is usually necessary to add noble metal co-catalysts such as Pt to enhance the hydrogen evolution activity of g-C3N4.However,reserve and price of noble metal limit its large-scale use.Non-noble metal co-catalyst loading becomes a valuable route to modifying g-C3N4.Surface active sites of co-catalyst and charge transfer at the interface are the key to enhance the photocatalytic activity.Therefore,it is of great significance for the modification of g-C3N4 to design and construct co-catalysts with specific microstructure,morphology,crystal structure and crystallinity,to control interface interactions,to synthesize an efficent non-noble metal/g-C3N4 composite photocatalyst,and to reveal the essential roles of co-catalyst in charge transfer and the nature of chemical reactionTo solve the above problems,we prepared non-noble metal Ni species/g-C3N4 composite photocatalyst by using non-noble metal Ni species as co-catalysts and regulating morphology and crystal structure of co-catalyst and studied the effect of microstructure and crystal structure of co-catalyst on increased photocatalytic performance of g-C3N4 by systemic characterization and detailed evaluation of photocatalytic performance.We carried out the following research work:(1)Ni(OH)2 nanowire non-noble metal co-catalyst was supported on g-C3N4 by using a facile impregnation method and controlling pH with ammonia to investigate the effect of the microstructure and morphology of the co-catalyst on the enhanced visible light photocatalytic hydrogen evolution from water splitting over g-C3N4.(2)NiO co-catalyst was supported on the surface of g-C3N4 to improve its photocatalytic activity of water-splitting for hydrogen evolution.The influence of crystallinity of NiO co-catalyst on formation ofNi-O-C interfacial junction and light absorption of g-C3N4 and its role in charge migration and surface hydrogen release were studied.The main innovative results and conclusions of the thesis are as follows:(1)1D Ni(OH)2 nanowire co-catalyst modified g-C3N4 photocatalyst was obtained by controlling pH>12 with ammonia.The interfacial contact area between 1D Ni(OH)2 nanowires and g-C3N4 is much larger than the interfacial contact area between Ni(OH)2 nanoparticles and g-C3N4,which is more beneficial for the migration and transfer of photogenerated electrons from g-C3N4 to Ni(OH)2 co-catalyst across heterojunction.The 1D nanowire structure allows the photocarriers on Ni(OH)2 migrated from g-C3N4 to more easily flow and to quickly transfer to the active sites for hydrogen evolution.(2)The crystallinity of the NiO co-catalyst on the g-C3N4 surface could be controlled by changing the post-treatment temperature.It was found that the amorphous NiO co-catalyst was more active to improve the photocatalytic hydrogen evolution performance of g-C3N4.The amorphous NiO co-catalysts provided more active sites for H2 evolution;amorphous NiO modification broadened visible-light absorption of g-C3N4;More C-O-Ni electron transport channels were formed at amorphous NiO/g-C3N4 heterojunctions,which significantly promote the migration and separation of photogenerated charge carriers.These findings provide new insights for understanding the role of co-catalysts in promoting photocatalytic performance of g-C3N4,and provide a reference strategy for the design and prepare of high-efficiency non-noble metal co-catalyst loaded g-C3N4 composite photocatalyst.