The Shape-controlled Synthesis And Performance Study Of Non-noble Metal Carbide Modified G-C₃N₄

As the rapid development of industry,energy shortage and environment pollution have gradually become more and more serious.Among various energy carriers,hydrogen could be potential substitutes for the traditional fossil fuels because it is one of the most ultra-clean,environmentally friendly,powerful and promising alternative energy carriers.Many semiconducting systems,such as TiO₂ and CdS,have been successfully utilized in photocatalytic splitting of water into hydrogen over the past decades.Unfortunately,poor visible light harvesting and low quantum yield of these semiconductors seriously limit their numerous renewable energy applications.Recently,graphitic carbon nitride（g-C₃N₄）,as a noble metal-free polymeric graphite-like semiconductor,has proven to be promising candidate for extremely widespread application in photocatalytic H₂ evolution,pollutant degradation and CO₂ reduction,owing to its excellent performance,such as easy fabrication,high chemical stability,excellent absorption properties,low cost and suitable band gap and positions.The structure and optical property of catalysts were measured by XRD,TEM,BET and DRS.Their photocatalytic activities were also investigated.The possible mechanism was characterized by electrochemical measurements and PL.The results are as follows:（1）Ni₃C nanoparticles were facilely fabricated through the low-temperature thermolysis of nickel acetylacetonate in oleylamine under a nitrogen atmosphere,which were then coupled with g-C₃N₄ by the simple grinding method.The photocatalytic performances of g-C₃N₄/Ni₃C nanoheterojunctions were tested under visible light irradiation using triethanolamine（TEOA）as a hole scavenger.The optimal H₂-production rate of 303.6μmolh^-1g^-1 over 15 wt%Ni₃C nanoparticles decorated g-C₃N₄ is approximately 116.7 times higher than that of pure g-C₃N₄,which is even larger than that of the 0.5 wt%Pt/g-C₃N₄ sample.（2）An intimate Schottky junctions g-C₃N₄ nanosheet/Ni₃C@Ni core–shell catalyst is fabricated by in-situ decomposition reaction.In this work,the outer layer of Ni₃C can break down into the Ni layer and then the Ni layer on g-C₃N₄ can develop the Ni/g-C₃N₄heterojunction during the high-temperature processing and the Ni interfaces layer play an important role in improving the charge trapping and transfer in nanocomposite materials.The maximum H₂-production rate of 1128.6μmolh^-1g^-1 over 8 wt%Ni₃C@Ni/g-C₃N₄ is nearly 5.44 times higher than that of pure 8 wt%Ni₃C/g-C₃N₄,which is even larger than that of the 1 wt%Pt/g-C₃N₄ sample.（3）The composite photocatalysts of g-C₃N₄ nanosheets and WC co-catalysts have been firstly synthesized via a one-step high-temperature calcination strategy.The results showed that the loading of WC co-catalysts could significantly boost the photocatalytic performance of g-C₃N₄ nanosheets under visible-light irradiation.Impressively,it is demonstrated that g-C₃N₄ nanosheets loaded by 15 wt%WC cocatalyst could achieve the highest hydrogen production rate of 146.1μmolg^-1h^-1.（4）An intimate g-C₃N₄ nanosheet/NiS cocatalyst heterojunction is fabricated by in situ one-step calcination of urea,thiourea and nickel acetate.Interestingly,thiourea could act as both the precursor of g-C₃N₄ and the sulfur source of NiS.The maximum H₂-production rate of 593.6μmolg^-1h^-1 could be achieved,which is nearly comparable to that of 0.5 wt%Pt loaded sample.（5）The novel WO₃/g-C₃N₄/Ni（OH）_x hybrids have been successfully synthesized by a two-step strategy of high temperature calcination and in situ photodeposition.Their photocatalytic performance was investigated using TEOA as a hole scavenger under visible light irradiation.The loading of WO₃ and Ni（OH）_x cocatalysts boosted the photocatalytic H₂ evolution efficiency of g-C₃N₄.WO₃/g-C₃N₄/Ni（OH）_x with 20 wt%defective WO₃ and 4.8 wt%Ni（OH）_x showed the highest hydrogen production rate of 576μmolg^-1h^-1,which was 5.7,10.8 and 230 times higher than those of g-C₃N₄/4.8wt%Ni（OH）_x,20 wt%WO₃/g-C₃N₄ and g-C₃N₄ photocatalysts,respectively.In this study,Ni₃C,Ni₃C@Ni,WC,NiS and Ni（OH）x as cocatalysts can increase the active sites of g-C₃N₄,which facilitate charge separation to hinder recombination,thus enhance the photocatalytic efficiency.Therefore,our work generate a new idea for constructing intimate g-C₃N₄-based material for photocatalytic applications by in-situ decomposition reaction.