Preparation And Photocatalytic Properties Of Porous G-C₃N₄

Graphite carbon nitride（g-C₃N₄）has been focused on the field of photocatalysis because of its cheapness,chemical stability and tunable electronic structure.Nevertheless,the conventional bulk g-C₃N₄ has unsatisfactory photocatalytic efficiency,which restricts its use in photocatalytic degradation of organic pollutants due to small specific surface area,limited visible light absorption range,rapid recombination of photogenerated carriers.Therefore,improving the photocatalytic activity of g-C₃N₄ through morphology control and element doping is the current research hotspot and difficulty in this field.Melamine and cyanuric acid were used as raw materials to prepare porous g-C₃N₄（pCN）material through combining with supramolecular self-assembly and thermal polymerization strategies in this paper.On this basis,the copper-doped porous g-C₃N₄（Cu-pCN）was obtained by a ternary metal supramolecular network framework including copper acetate.Tetracycline hydrochloride（TC）was used as pollutant to explore the structure,physical and chemical properties,photocatalytic properties of catalyst under different preparation process parameters such as the addition of copper acetate,heating rate and holding time.Furthermore,the photocatalytic degradation performance of Cu-pCN was studied under different dosage,p H and TC concentration,and its photocatalytic stability and degradation mechanism were discussed.The obtained research results are as follows:（1）Preparation and photocatalytic performance of porous g-C₃N₄:Porous g-C₃N₄ was prepared by thermal polymerization of melamine-cyanuric acid supramolecular precursor.In the process,heating rate and holding time affect the microstructure and photocatalytic efficiency of pCN.When heated to 550°C at a heating rate of 1.5°C/min and calcined for 6 hours,the pCN showed the best overall performance.Its specific surface area（109.1 m²/g）is 11 times as large as the bulk g-C₃N₄.The photoelectric test found that pCN has higher carrier separation efficiency,faster carrier migration and stronger photoelectric conversion ability than bulk g-C₃N₄,indicating that pCN has good photocatalytic activity.When the initial concentration of pCN was 1 mg/m L and TC was 15 mg/L at p H=9,the degradation ratio of TC reached 80%at 120 min.（2）Preparation and photocatalytic performance of copper-doped porous g-C₃N₄:Further,copper acetate was introduced into the melamine-cyanuric acid system,and copper-doped porous g-C₃N₄ was successfully prepared by thermal condensation polymerization of ternary supramolecular precursors.XPS test showed that Cu element was successfully doped in porous g-C₃N₄ material in the form of Cu²⁺.Compared with pCN,Cu-pCN possesses more pore morphology,its specific surface area and pore volume are increased to 142.8 m²/g and 1.1547 cm³/g respectively.PL and UV-vis test found that Cu²⁺doping improved the carrier separation efficiency and made the light absorption boundary blue shift.Electrochemical impedance and photocurrent test results showed that Cu-pCN had faster electron transport efficiency and stronger photoelectric conversion ability than pCN.The high specific surface area and stronger photoelectric properties endow Cu-pCN with more excellent photocatalytic activity.When the initial concentration of Cu-pCN was0.3 mg/m L and TC was 30 mg/L at p H=9,the degradation ratio of the sample reached 98%to tetracycline hydrochloride at 120 min.In addition,due to the strong interaction between Cu²⁺and g-C₃N₄,Cu-pCN exhibits good cycle stability.The catalytic efficiency is still as high as 80.6%after 7 cycles.Superoxide radicals(·O^2-),hydroxyl radicals（·OH）and holes（h⁺）are the active species in the reaction,which can degrade TC into small organic molecules.In this article,pCN and Cu-pCN with porous structure were successfully prepared by thermal polymerization of supramolecular precursors.Compared with the pCN,Cu-pCN has rich porous structure,wider light absorption range,stronger photocurrent response intensity,and higher carrier separation and transmission efficiency,thus showing a stronger visible light catalytic degradation performance and catalytic stability.The above work provides theoretical support and data reference for the development of cheap,visible light response,good durability and high reactivity photocatalyst.