Preparation Of Porous Structure G-C₃N₄ And Its Application In The Degradation Of Sulfonamide Antibiotics

Carbon nitride（g-C₃N₄）has been considered as a promising metal-free photocatalyst for solving the energy crisis and environmental problems.Nevertheless,due to the low-charge carrier mobility,and low surface area,its photocatalytic efficiency is limited.Because of its unique band structure,coupling it with a large bandgap semiconductor to produce a heterojunction composite offers a promising way to improve the charge separation,expand the surface area,and boost light absorption.For that,g-C₃N₄as a robust photocatalyst together with numerous synthesis methods has been highlighted.Approach I prevents the stacking of the material during thermal condensation by ammonium chloride as an auxiliary for the template-free method,which continuously releases ammonia and hydrogen chloride gas during the thermal condensation process and generates a large number of mesopores.In method II,the sparse melamine was produced by etching of the precursor melamine with sulfuric acid,followed by calcination,and graphite-phase carbon nitride materials with high surface area and excellent photocatalytic properties were also produced.The main research works are as follows.（1）Graphitic phase（g-C₃N₄）samples were prepared by one-step calcination after co-milling with melamine using ammonium chloride as a bubbling agent.The microstructure of the material was analyzed by scanning electron microscopy（SEM）and nitrogen isothermal adsorption and desorption（BET）,and the chemical structure of the material was analyzed by X-ray diffraction（XRD）,infrared spectroscopy（FTIR）,laser Raman spectroscopy（Raman）and X-ray energy spectrometry（XPS）,and the photoelectric properties of the material were analyzed by UV-Vis diffuse reflectance（DRS）,fluorescence spectroscopy（PL）and electrochemical The photoelectric properties of the material were analyzed by workstation.The melamine was decomposed and impacted by NH₄Cl to form a foam-like porous structure with a2-fold increase in specific surface area and a thinning of the stacking layer to form a three-dimensional sponge-like structure.The enhancement of the optoelectronic properties of the material,the electron complex rate becomes lower,the photocurrent response improves and the impedance value becomes smaller.The materials PCNs prepared by the above method were used to degrade five common sulfonamide antibiotics sulfadiazine（SDZ）,sulfathiazole（STZ）,sulfamethazine（SMZ）,sulfadimethylpyrimidine（SM2）,and sulfamethoxazole（SMX）in water bodies.The effect of CN/NH4Cl mass ratio on the performance of PCNs was analyzed,and the discussion revealed that the degradation ability of PCNs for sulfonamides was as follows in order:PCN-1>PCN-1.5>PCN-0.5>PCN-2>PCN-0.The reaction rate of PCN-1（CN/NH₄Cl of 1:1）was enhanced by 2-3 times compared with that of pure g-C₃N₄.The effects of catalytic conditions such as the initial concentration of sulfonamide and p H on the catalytic performance were further investigated.The main radicals acting on pollutants during degradation were explored by radical quenching experiments as superoxide radicals and photogenerated holes.the results of HPLC-DAD,FIIR and other analysis of degradation products showed that pollutant degradates were more water-soluble substances.（2）Protonation of precursors using sulfuric acid yielded sparse melamine precursors,whose one-step calcination yielded graphitic phase carbon nitride（g-C₃N₄）with high surface area.The surface structure,chemical structure and optoelectronic properties of the catalytic materials were analyzed,and the synthesized materials were found to have high specific surface area by nitrogen isothermal adsorption（BET）,which is about twice that of pure g-C₃N₄.The chemical structure and crystalline shape of the synthesized materials were investigated by X-ray diffractometry（XRD）,and it was found that the chemical structures of the synthesized materials were consistent with those of pure g-C₃N₄,and both of them showed only two characteristic peaks of graphitic phase carbon nitride.The photoelectric properties of the materials were investigated by UV diffuse reflectance spectroscopy（DRS）and fluorescence spectroscopy（PL）,and it was found that the synthesized materials have stronger absorption of light and lower fluorescence values than pure g-C3N4,which is believed to have lower photogenerated carrier complex effect.The degradation experiments of five sulfonamide antibiotics under simulated solar illumination could completely degrade a mixed class of pollutants composed of five sulfonamide antibiotics within 100 min,and its photocatalytic capacity was enhanced by more than50%compared with the untreated pure g-C₃N₄.The quenching experiments revealed that the main active species produced were superoxide radicals,photogenerated vacancies and hydroxyl radicals.