Surface Modification And Enhanced Performance Of Graphitic Carbon Nitride Photocatalytic Materials

Compared with the traditional semiconductor of photocatalytic materials,noble-free metal semiconductor g-C₃N₄ photocatalytic material has caused many photocatalytic researchers of great interest.Semiconductor g-C₃N₄ has many merits,such as,an appropriate band structure,two-dimensional plane structure similar to that of graphene,stable physical and chemical properties,and abundant material source so on.All of these provide a possible for the great application potential in photocatalytic hydrogen production.But in the practical application,researchers have found that the g-C₃N₄ material has a problem of low electrons and holes separation efficiency.This is mainly attributed to the g-C₃N₄ material has very few catalytic reaction activity sites on the surface and thus causes a weaker driving force of the separation of electrons and holes.Eventually,it leads to the photocatalytic hydrogen production performance of the g-C₃N₄ body material is far less than the theoretical value.However,the photocatalytic performance of g-C₃N₄ can be enhanced effectively through some modification methods,such as semiconductor coupling,co-catalyst modification,element doping,dye sensitization,and microstructure design so on.In these modified methods,co-catalyst modification is considered to be the most effective means of modification owe to the characteristics that a small amount of dosage can significantly improve the catalytic performance of catalyst.Eletron co-catalyst as a commonly used co-catalyst modification method can efficiently improve catalytic H₂-evolution by increasing the hydrogen reduction reaction active sites.Commonly-used efficient electron co-catalysts mainly focused on the rare and precious metals,such as Pt,Au,Pd,etc.So it is necessary to find a simple method to synthesize a kind of low price and efficient co-catalysts to improve the photocatalytic performance of new-type g-C₃N₄ material.Based on the above definite research purpose,we carried out experimental research work smoothly.The main experimental research methods and the final results were summarized as follows:Firstly,we synthesized a kind of cheap co-catalyst NiS₂ modified g-C₃N₄composite material and the NiS₂ were tightly modified on the surface of g-C₃N₄ by a low temperature water bath method.Compared with common hydrothermal synthesis of NiS₂,our method is simpler and has less influence to the microstructure of the substrate material g-C₃N₄.When the Ni content is 3 wt%,the resultant NiS₂/g-C₃N₄?3wt%?sample achieves the optimal value(5.82mmol h^?1)of the photocatalytic H₂-evolution performance that is higher than the pure g-C₃N₄ by a factor of 38 times and also has a good cycle performance.Secondly,we successfully synthesized g-C₃N₄/Ag–SCN photocatalytic composite material by a simply impregnation method.Existing researches show that the Ag as a kind noble mental which of price is much lower than Pt,Au and Pd metals has a stronger electronic storage ability than them but the release ability of electronic is a bit poor.The significance of this study is that we can use the affinity between Ag and S to enhance the capacity of the release of electronic on the Ag.The results show that when the concentration of SCN^–reaches 0.3 mM in the reaction solution,the hydrogen production rate of the resultant g-C₃N₄/Ag–SCN?0.3mM?sample reaches the maximum value(3.89mmol h^–1)which is higher than g-C₃N₄ and g-C₃N₄/Ag by factors of 26 and 4.5 times,respectively.And the g-C₃N₄/Ag–SCN?0.3mM?material has a good photocatalytic stability.Therefore,the optimized g-C₃N₄/Ag–SCN complex system can be seen as a new kind of promising co-catalyst modified photocatalytic materials with useful and research value.