Markedly Enhanced Visible-light Photocatalytic H₂ Generation Over G-C₃N₄ Nanosheets Modified By Robust Ni-based Cocatalyts

The consumption of fossil fuels and a series of environmental pollution problems are identified as the two major challenges influencing human existence.Among all technologies developed on sustainable energy,photocatalysis is considered to be one of the most promising technologies for direct harvesting,conversion and storage of renewable solar energy.The g-C₃N₄ has many virtues,such as moderate band gap and CB position,rich source of raw materials,visible light absorption,non-toxic and pollution-free.Unfortunately,the quantum efficiency of g-C₃N₄ is extreme low.Therefore,it is urgen need to develop effective modification strategies to enhance the performance of g-C₃N₄.However,loading cocatalysts are considered to be one of the easiest and effective strategies.This paper constructed cheap non-metallic carbon materials and non-noble nickel based cocatalysts in the g-C₃N₄ nanosheets semiconductor for efficient photocatalytic performance,which can reduce band gap and CB position,increase the effective activation sites and surface area.The material structure and optical property were characterized by XRD,TEM,HRTEM,EDX,BET,and DRS.Their photocatalytic activity of hydrogen evolution were also performed.The possible mechanism was investigated by PL and electrochemical measurements.The results are as follows:?1?The g-C₃N₄/Ni₁₂P₅ photocatalysts were successfully fabricated by mechanical mixing method,which exhibited the highest hydrogen evolution of of 126.61?molg^-1h^-1.It is believed that the N i₁₂P₅ on the g-C₃N₄ can act as the active sites,which can promote the charge transfer and photocatalytic efficiency.?2?The g-C₃N₄/CB/NiS hybrid was obtained by a facile two-step process:ultrasonic teatment and wet-chemistry reaction.It found the the g-C₃N₄-0.5%CB-1.5%NiS sample exhibited the hightest hydrogen evolution of 992?molg^-1h^-1,which is the 2.51 times of g-C₃N₄-1.5%NiS(395?molg^-1h^-1).?3?The g-C₃N₄/Ni/N iS nanocomposites have been successfully synthesized by high temperature reduction and precipitation method.The g-C₃N₄-0.5%Ni-1.0%NiS photocatalytic samples showed the best hydrogen yield of 515?molg^-1h^-1,which were 2.8and 4.6 times higher than that of g-C₃N₄-1.0%NiS and g-C₃N₄-0.5%Ni,respectively.?4?The carbon black,acetylene black,reduced graphene oxide,carbon nanotubes and graphite nano materials have been successfully coupled in to the interace between g-C₃N₄semiconductor and N iS cocatalyst.The g-C₃N₄-0.5%CB-1.0%NiS and g-C₃N₄-0.5%AB-1.0%NiS samples reached the highest hydrogen yield 366.4 and 297.7?molg^-1h^-1,which were 3.17 and 2.51 times higher than that of g-C₃N₄-1.0%NiS,respectively.?5?g-C₃N₄/AB/N i?OH?₂ nanocomposites were synthesized by ultrasonic dispersion treatment and subsequent precipitation of N i?OH?₂ cocatalyst.The g-C₃N₄/AB/N i?OH?₂photocatalytic samples showed the best hydrogen yield of 515?molg^-1h^-1,which were 300,100 and 3.31 times higher than that of g-C₃N₄,g-C₃N₄-0.5%AB and g-C₃N₄-1.0%Ni?OH?₂,respectively.In this study,for the first time,we presented the enhanced photocatalytic H₂ evolution over g-C₃N₄ modified by N i₁₂P₅ and amorphous N iS as an efficient earth-abundant cocatalyst,which can achieve the greatly enhanced hydroge n generation.Meanwhile,this study demonstrated that semimetallic nanocarbons and N i layers have been successfully coupled into the interface between g-C₃N₄ and cocatalyst,which could accelerate the rapid separation of photogenerated electrons and holes,enhance the reaction kinetics of hydrogen production and increases the ability of holes oxidation that improved the photocatalytic activity.