| In today's society,energy and environmental issues are two significant topics.Huge productivity changes have hastened the demand for huge fossil fuels since industrial revolution of the 18th century.In the meantime,numerous environmental issues have arisen.Photocatalytic water splitting into hydrogen has been regarded as the ideal technology for it only driven by solar light.Cocatalysts are the essential part of photocatalytic hydrogen production system,for the reason that cocatalysts can facilitate the photocatalytic reactions as it can reduce the overpotential,provide active sites and suppress the charge recombination.Nickel-based materials have been reported frequently as the potential substitutes for noble metals in photocatalytic hydrogen evolving.The previous works have indicated that Nickel and its oxides served as efficient and cost-effective cocatalysts showed a good performance in promoting the photocatalytic activities.Therefore,it is essential to explore the cocatalytic performance and the mechanism of the nickel species.In this thesis,we choose the graphitic carbon nitride?g-C3N4?as the host photocatalyst.Simple impregnation-calcination method and chemical method are used to synthesize g-C3N4 modified with nickel species composite photocatalyst.The following is as follows:?1?Nickel based hydroxide and oxide modified g-C3N4 are prepared via one step calcination.The temperatures are set as 60,250,300,and 500?.Correspondingly,the photocatalytic hydrogen production rate is 185.13,77.22,82.88,67.78 and 14.59?mol·h-1·g-1.The analysis result of X-ray photoelectron spectrum proves that the nickel species are Ni?OH?2,Ni?OH?2+NiO,NiO and NiO+Ni2O3.Combing with the electrochemical impedance spectroscopy?EIS?and photocurrent response spectrum,the order of cocatalytic activity of nickel species is Ni?OH?2>Ni?OH?+NiO>NiO>NiO+Ni2O3.Ni?OH?2 modified g-C3N4 exhibited the highest photocatalytic H2-evolution,due to their well-matched energy band positions and effective separation of photocarriers.?2?Amorphous nickel boride?NiBx?modified graphitic carbon nitride?g-C3N4?was fabricated successfully for the first time.The loading amount of Ni Bx is 0.5,2.0,5.0,8.0 and 10 wt%respectively.Photocatalytic hydrogen evolving results reveals that the highest hydrogen production rate is 174.90?mol·h-1·g-1 with the loading amount of 5.0 wt%of NiBx,and the actual loading amount is 3.65 wt%.The recycle test of photocatalytic hydrogen generation demonstrates that the hybrid photocatalyst consisting with g-C3N4 and NiBx has a good stability during the photocatalytic process.Moreover,the electrochemical technology applied elucidates the cocatalytic mechanism of NiBx from the micro charge level.We do believe that NiBx will be a promising cocatalyst for application in the future. |
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