Preparation And Photocatalytic Hydrogen Production Performance Of G-c₃n₄ Based Composites

With the continuous progress and development of human society,fossil fuels on the earth are continuously consumed,and the energy problem is becoming increasingly prominent.Using safe and pollution-free hydrogen energy to replace fossil energy is a feasible method.By using photocatalytic technology to decompose water,hydrogen gas can be obtained,which completes the conversion of solar energy to hydrogen energy.In order to increase the amount of photocatalytic hydrogen production,adding a certain amount of photocatalyst can effectively improve the conversion efficiency.Therefore,it is worthwhile to study photocatalysts with low cost and high hydrogen production efficiency.Graphite phase carbon nitride（g-C₃N₄）,as a non-metallic semiconductor,has excellent energy band positions and structures,but its visible light response and utilization efficiency for photogenerated electrons are poor,so it cannot be widely used in photocatalytic hydrogen production.In this paper,the morphology of g-C₃N₄ and the utilization rate of photogenerated electrons were studied,and the morphology of g-C₃N₄ was changed by sulfuric acid treatment.And then,g-C₃N₄based photocatalysts were prepared by compounding with carboxyl functionalized graphite oxide（GO-COOH）and TiO₂,and the hydrogen production performance was tested and analyzed.g-C₃N₄ was obtained by calcining melamine and subjected to hydrothermal treatment with sulfuric acid at different concentrations(0.2,0.4,0.6,and 0.8 mol·L^-1)to obtain H⁺/g-C₃N₄.Using SEM,N₂ adsorption and desorption methods to analyze H⁺/g-C₃N₄,it was found that after sulfuric acid treatment,H⁺/g-C₃N₄ disintegrated from large blocks into small pieces,and the specific surface area was improved.Comparing the photocatalytic hydrogen production performance of H⁺/g-C₃N₄ treated with different concentrations of sulfuric acid,it was found that the hydrogen production performance of 0.4 H⁺/g-C₃N₄ was the best,reaching 865.54μmol·h^-1·g^-1。In order to further improve the hydrogen production performance of g-C₃N₄,GO-COOH was then compounded on the basis of 0.4 H⁺/g-C₃N₄.Firstly,graphene oxide（GO）was functionalized using hydrochloric acid and oxalic acid to convert some hydroxyl groups（-OH）in GO into carboxylic groups（-COOH）.Then,H⁺/g-C₃N₄ and GO-COOH were synthesized by self-assembly method to obtain H⁺/g-C₃N₄/GO-COOH.The introduction of GO-COOH significantly improves the response of H⁺/g-C₃N₄ in the visible light region and the electron absorption effect of GO-COOH will increase the utilization of photogenerated electrons.Finally,the photocatalytic hydrogen production performance of H⁺/g-C₃N₄/GO-COOH reached 1315.43μmol·h^-1·g^-1。In addition to using the electron absorption effect of-COOH to improve the transfer and transmission efficiency of photogenerated electrons,this paper also uses TiO₂ and H⁺/g-C₃N₄to form a heterojunction to improve the utilization efficiency of photogenerated electrons.The method of calcining TiO₂ and H⁺/g-C₃N₄ was used to prepare TiO₂@H⁺/g-C₃N₄。Through TEM and XPS characterization,it was found that a heterojunction was formed between TiO₂ and H⁺/g-C₃N₄,and when the loading amount of TiO₂ was 25%of H⁺/g-C₃N₄,25-TiO₂@H⁺/g-C₃N₄has the best photocatalytic hydrogen production performance,reaching 3469.2μmol·h^-1·g^-1。...