Preparation Of Nitrogen Vacancy G-C₃N₄ Tube And Mechanisms For Photocatalytic Hydrogen Production And Pollutants Degradation

In recent years,the problems of global environmental pollution and excessive energy depletion are increasingly serious.Many scholars are committed to researching an eco-friendly and sustainable strategy to solve these issues.Semiconductor photocatalysis technology is one of the important strategies for the treatment of organic pollution in water.It has the advantages of low cost,no pollution,fast reaction and so on.The visible light catalytic hydrogen evolution reaction using solar energy as energy source can alleviate energy shortage effectively.Thus,the development of catalysts with high-efficiency photocatalytic activity is the key for pollutants degradation and hydrogen production.Graphitic carbon nitride（g-C₃N₄）has been paid more attation because of its high stability,suitable band gap and other advantages.However,the bulk g-C₃N₄ obtained by traditional calcination method also has some disadvantages,such as low utilization efficiency of solar energy and small specific surface area.In this paper,in order to improve the photocatalytic performance of g-C₃N₄,it was modified by adjusting the morphology and constructing defect sites.The morphology,structure and composition of the prepared photocatalysts were analyzed by a series of characterizations.The reaction mechanism of degradation of chlortetracycline hydrochloride（CTC·HCl）and photocatalytic hydrogen production under visible light was explored.The main research results are as follows:A hollow tubular g-C₃N₄（TCN）and hollow tubular g-C₃N₄ with nitrogen vacancy（ND-TCN-x,x represents the mass of potassium hydroxide（KOH）,5,10,20,40 mg,respectively）photocatalysts were successfully prepared via simple hydrothermal method combined with calcination method.The hydrogen evolution reaction activity and photocatalytic degradation performance for CTC·HCl of different materials under visible light were investigated.The experimental results show that,compared with the bulk g-C₃N₄（CN）,the specific surface area of the optimized TCN and ND-TCN-10 increased significantly,from 11.1801 m²/g to35.1347 and 47.1878 m²/g,respectively;In addition,under visible light irradiation,ND-TCN-10 has the best photocatalytic degradation effect,reaching 84.29%;The experimental results of photocatalytic decomposition of water to produce hydrogen further verified the performance superiority of the ND-TCN-10 catalyst.Compared with other catalysts,ND-TCN-10 has the highest hydrogen generation rate of 235.68μmol g^-1 h^-1.The main reason for this is that the hollow tubular structure increases the specific surface area of the catalyst,promotes the multiple reflection effect of light,and endows the function of directional transfer of electrons.Meanwhile,the introduction of nitrogen deficiency can change the electronic structure of g-C₃N₄ with narrow band-gap and excellent charge carrier behavior.Therefore,the photocatalytic properties of the modified ND-TCN-10 is significantly better than that of original CN.Finally,the possible reaction mechanisms were proposed according to the energy band structure of photocatalyst,the tests of free radical and ESR.