Mediation Of Defect And Active Sites Of Carbon Nitride For Promoting Photocatalytic Hydrogen Evolution

The development of clean and renewable energy is the key way to satisfy the increasing global energy demands and to resolve the environmental issues caused by the overuse of fossil fuels.One of the most attractive options is the conversion of solar energy into hydrogen through a water splitting process,with the help of semiconductor-based photocatalysts.Graphitic carbon nitride（g-C₃N₄）has become a hot research topic in recent years because of its unique physical and chemical properties,However,many challenges still need to be overcome,such as the photogenerated electron hole recombination is serious,the photocurrent response and the quantum efficiency is low.In this work,we aim to adjusting the morphology,control aggregation state of g-C₃N₄ and doping metal to improve the photocatalysis activity.g-C₃N₄ with hollow morphology of coral stone was obtained by pyrolysis urea and in this process the active gas is introduced which can decomposition.The existence of hollow morphology makes the pore size of g-C₃N₄ only has a microporous structure,and the specific surface area decreases from 20.242m-2g-1 to4.073m-2g-1.Comparaed with pure g-C₃N₄,the cyclic stability of hollow g-C₃N₄ is good.With the increase of the number of cycles,the hydrogen evolution activity increased,after 5 cycles,the activity increased 1.45 times,which is about 1.37 times of the pure g-C₃N₄.The mixture of g-C₃N₄ were prepared by controlling the pyrolysis temperature.Compared with the graphite like g-C₃N₄,the mixture of g-C₃N₄ aggregation degree increased,the hardness increased,the specific surface area is 1.92 times of graphite like g-C₃N₄.Under simulated solar light irradiation,the hydrogen evolution activity of mixed phase g-C₃N₄ is 2.9 times that of graphite like g-C₃N₄.To elucidate the roles of aggregation degree is important for photocatalytic hydrogen evolution activity.Ni doped g-C₃N₄ were prepared by pyrolysis urea and introduction of metal Ni as the reactive site.By changing the content of doped metal Ni,the composite photocatalyst with different load was obtained.When the doping amount of Ni is10 mg,the hydrogen evolution activity can reach 273.21 umol,which is 1.91 times of Ni00,1.12 times of Ni5,1.2 times of Ni20,2.09 times of Ni40.Meanwhile,the cyclic stability of Ni10 is good,the hydrogen evolution activity of each cycle is increased,the fifth is 1.28 times of the first hydrogen production.