Modification Of G-C₃N₄ Photocatalyst And Its Photocatalytic Properties

Photocatalytic technology has unique advantages in solving environmental and energy problems.Graphite phase carbonitride（g-C₃N₄）is a novel semiconductor photocatalyst with a narrow band gap（2.7 eV）,good thermal and chemical stability.Besides,in addition to being able to degrade pollutants,it also has a good application prospect in photohydrolysis of water to produce hydrogen due to its suitable conduction band and valence band positions.In this paper,we took g-C₃N₄ as the research object and modified it to improve its catalytic activity.The main work is as follows: 1.Preparation of g-C₃N₄-W₁₈O₄₉ photocatalyst and its photocatalytic mechanismThe g-C₃N₄-W₁₈O₄₉ composite photocatalysts were successfully prepared by simple solvothermal method.The phase structure,morphology and optical properties of the obtained catalysts were characterized by XRD,SEM,TEM and UV-vis methods.The catalytic properties of the catalysts were studied by degradation of methyl orange.It was found that the degradation performance of g-C₃N₄-W₁₈O₄₉ photocatalyst was the best when the content of W₁₈O₄₉ was 50%,and the degradation rate was 48% higher than that of pure g-C₃N₄ nanosheets.In order to further study the electron-hole transfer mechanism,the photolysis of hydrogen production experiments and PL analysis were carried out.The results show that the increase of the activity of the composite catalyst is due to the formation of a typical type II heterojunction between g-C₃N₄ and W₁₈O₄₉,which results in the effective separation of carriers.2.Surface modification of g-C₃N₄ and its photocatalytic activity for hydrogen productionThe g-C₃N₄ modified by C quantum dots and hydroxyl groups were prepared through high temperature thermal decomposition.The catalytic properties of the catalysts were studied by photolysis of water to produce hydrogen using noble metal Pt as cocatalyst.It was found that the catalytic performance of modified g-C₃N₄ was significantly improved.Among them,when the C quantum dot content is 0.15%,the hydrogen evolution rate of the obtained catalyst is 4.15 times higher than that of unmodified g-C₃N₄,and the optimal rate of hydrogen evolution after hydroxyl modification was 15.2 times that of unmodified g-C₃N₄.3.Preparation of non-noble metal NiS₂ cocatalyst supported g-C₃N₄ and its photocatalytic activity for hydrogen productionThe non-precious metal NiS₂ co-catalyst was successfully supported on g-C₃N₄ by simple hydrothermal method.The catalysts were characterized by various analytical methods.According to the photocatalytic property test,NiS₂ exhibits good co-catalytic performance,and its co-catalytic effect is significantly higher than that of precious metal Pt.When the content of NiS₂ is 7%,g-C₃N₄ exhibits the highest hydrogen production activity,which is 2.75 times as high as that of 2 wt% precious metal Pt as a co-catalyst.In addition,the obtained catalyst still shows prominent photocatalytic performance for H₂ evolution after three continuous photocatalytic reaction cycles for 9 h.