Synthesis Of G-C₃n₄ Composite Materials And Research On Their Photocatalytic Performance

Since organic pollutants have the characteristics of high structural stability,strong persistence,and high toxicity,they seriously affect the balance of the ecosystem and pose a threat to biodiversity.Therefore,a green,efficient,and pollution-free technology is needed for the treatment of organic wastewater.Photocatalytic technology makes use of the photoelectric conversion performance of semiconductors to convert light energy into potentials with strong oxidizing and strong reducing properties,stimulating active species with strong oxidizing properties,thus achieving deep degradation of organic pollutants.Due to the stable properties of graphite carbon nitride（g-C₃N₄）and its good response to visible light,it is widely used in photocatalytic degradation of organic pollutants.However,g-C₃N₄ has a high carrier recombination rate,a large resistance of charge transfer between layers,and a small visible light absorption range,which seriously inhibits its photocatalytic performance.Therefore,in this paper,the chemical and electronic structure of g-C₃N₄ can be adjusted by element doping to enhance the adsorption of visible light,promote the excitation of electrons,inhibit the recombination of carriers,and increase more active species to participate in the degradation of organic pollutants.The main research contents are as follows:（1）Using KCl and NH₄Cl as dopants,melamine as the precursor,the Cl and K co-doped g-C₃N₄ was prepared by in-situ mixing and calcination.Systematic characterization analysis shows that Cl and K enter the g-C₃N₄ layer and form a double element charge transport channel between these layers,thereby promoting the transport of electrons.The introduction of NH₄Cl increased the specific surface area of the composite material to 2.26 times that of the original g-C₃N₄,thereby providing abundant adsorption and reaction sites.The addition of KCl and NH₄Cl can reduce the band gap of carbon nitride,improve its light absorption performance,and promote the separation of charges,thereby exhibiting good photodegradation activity.Therefore,the degradation efficiency of the optimized photocatalyst CN-NH₄Cl-0.05KCl for rhodamine B（Rh B）is 4.24 times that of unmodified g-C₃N₄,and its first-order reaction rate constant is 0.03422 min^-1.Through free radical capture experiments,it was found that superoxide radicals（·O₂^–）and holes（h⁺）played a leading role in the degradation process.（2）The modified g-C₃N₄ was successfully prepared by calcination of ionic liquid1-butyl-3-methylimidazolium salts（[Bmim]Cl,[Bmim]Br,[Bmim]BF₄,and[Bmim]PF₆）and urea.The doped hetero atoms（such as N,Cl,Br,B,P,and F）extend the electron conjugation system and enter g-C₃N₄ to optimize the electronic structure.The modified g-C₃N₄ can effectively degrade organic pollutants.Among them,[Bmim]Cl modified g-C₃N₄ showed better photocatalytic activity and stability.The degradation efficiency of Rh B is 2.91 times that of unmodified g-C₃N₄,and its first-order reaction rate constant is 0.02888 min^-1.In terms of morphological structure,the addition of ionic liquid[Bmim]Cl changed the polymerization mode of urea,induced the self-assembly of urea molecules,and changed the morphological structure of the tightly packed g-C₃N₄.In the electronic structure and energy band structure,the modified g-C₃N₄ expands theπ-electron conjugate system,introduces interlayer charge transport channels,promotes charge transport,reduces the energy band gap,enhances the absorption of visible light,and suppresses electron-hole recombination.Finally,through free radical capture experiments,it was found that·O₂^–and h⁺played a leading role in the degradation process.