Degradation Of Organic Pollutants By Carbon Nitride Activated Persulfate Prepared By Supramolecular Self-Assembly Method

The rapid growth of modern dyeing and textile industries has made dye wastewater one of the major sources of water pollution today,and it is urgent to find a green and efficient solution to this problem.Semiconductor photocatalysis technology uses solar energy to generate highly reactive radicals,which can completely oxidize and decompose organic pollutants in water bodies.This technology shows great potential and good application prospects for solving environmental pollution and energy shortage issues.Carbon nitride（g-C₃N₄）,a promising visible light responsive photocatalyst,has a narrow energy band gap,simple preparation process,low cost,and environmental friendliness.However,its application is limited by its small specific surface area and low charge separation efficiency.Moreover,the efficiency of photocatalytic degradation of organic pollutants can be further enhanced by combining technologies.For example,sulfate radical-based advanced oxidation processes（SR-AOPs）have become a novel method for treating pollutants due to their strong oxidative properties and high selectivity.Photo-activated sulfate radical-based advanced oxidation processes not only improve photocatalytic efficiency,but also generate highly reactive radicals such as SO₄^·-and¹O₂ in the system.These ultimately result in rapid and complete degradation of organic pollutants.In this study,we successfully prepared three highly active g-C₃N₄ photocatalysts using the supramolecular self-assembly method to improve their structure and properties through different reactant precursors and preparation conditions.We then applied these photocatalysts in combination with SR-AOPs for the degradation of organic pollutants.The specific studies are as follows:（1）The supramolecular self-assembly method was utilized to prepare g-C₃N₄/NaCl-x catalysts via thermal polymerization of melamine and urea with sodium chloride as a molten salt additive,with different raw material mass ratios.XRD,SEM,UV-Vis,and PL analyses showed that tubular g-C₃N₄ could be synthesized via this method,and the presence of NaCl effectively reduced the agglomeration of the tubular g-C₃N₄.The catalytic activity of the resulting tubular g-C₃N₄ in degrading the target contaminant RhB was investigated by activating peroxymonosulfate（PMS）,and the g-C₃N₄/NaCl-10 catalyst,produced at a mass ratio of 1:10:10 for melamine,urea,and sodium chloride,demonstrated the best performance in activating PMS to degrade RhB.The degradation rate of RhB at a concentration of 10 mg/L was up to 99.05%within 30 min.The effects of catalyst dosage,PMS dosage,pH value,and initial concentration of RhB on pollutant degradation by the g-C₃N₄/NaCl-10/PMS/Vis system were also investigated.Radical capture experiments indicated that superoxide radicals(O₂^·-)and singlet oxygen（¹O₂）were the main reactive groups present in the system.After five cycles of the experiments,the degradation rate of RhB remained at 90%,and XRD of the catalysts before and after the cycles showed that g-C₃N₄/NaCl-10 had good structural stability.（2）The photocatalyst MCA-CN-y was synthesized using melamine and cyanuric acid as raw materials,and dimethyl sulfoxide as solvent.The precursor（MCA）was synthesized by the supramolecular self-assembly method and then heat-treated at different temperatures.The photocatalyst with the largest surface area showed the lowest photogenerated electron-hole complexation rate.MCA-CN-y was applied to activate PMS to degrade RhB,and achieved a degradation rate of 98%within 12 min.The effects of different process conditions on the degradation of RhB by the MCA-CN-550/PMS/Vis system were investigated,and the optimal conditions were found to be 50 mg/L for MCA-CN-550,50 mg/L for PMS,10 mg/L for RhB,and a pH range of 5～7.Radical capture experiments indicated that the main active substances of the MCA-CN-550/PMS/Vis system were non-radicals,including singlet oxygen（¹O₂）,superoxide radicals(O₂^·-)and holes（h⁺）.Cycling experiments and XRD results demonstrated that the catalysts exhibited good stability over multiple cycles.（3）The photocatalyst g-C₃N₄-z was obtained by thermal polycondensation at high temperature after ultrasonic treatment with melamine and cyanuric acid as raw materials and water as solvent.The structure,morphology,and optical properties of the catalyst were characterized.The results showed that g-C₃N₄-4 obtained by thermal polymerization for 4 h after ultrasonic treatment had a nanosheet morphology,a larger surface area,and a higher photogenerated charge carrier separation rate,thereby exhibiting the best performance in activating PMS for RhB degradation.The factors influencing the activation of PMS for RhB degradation by the catalyst were investigated,and the optimal conditions were determined to be a catalyst dosage of 50 mg/L,PMS dosage of 50 mg/L,RhB concentration of 10 mg/L,and pH of 5～7,resulting in a degradation rate of 97.08%within 10 min in the g-C₃N₄-4/PMS/Vis system.The influence of inorganic anions on RhB degradation was further explored,revealing that Cl^-and NO₃^-had a promoting effect,SO₄^2-had an inhibiting effect,and CO₃^2-had a significantly inhibiting effect.The mechanism of RhB degradation in the g-C₃N₄-4/PMS/Vis system was attributed to the generation of ¹O₂,O₂^·-,and h⁺as the main active species.The g-C₃N₄-4 photocatalyst exhibited good cycling stability.