Preparation And Photocatalytic Performance Of Modified G-C₃N₄ Nanosheets Composites

Graphite carbon nitride（g-C₃N₄）is widely used in the field of photocatalysis due to its advantages of adjustable electronic structure,moderate band gap,and high chemical stability.However,g-C₃N₄ has a smaller specific surface area,a higher recombination rate of photogenerated electron-hole pairs,and a narrower absorption edge for visible light.Here,we combined the modification methods of morphology control,expanding conjugated structure by Schiff-base reaction and composite sulfur-containing quantum dots to modify g-C₃N₄ to improve its ability to degrade methyl orange under visible light.First,using melamine as the precursor,g-C₃N₄（CN）is stripped off by thermal etching through two-step calcination to obtain porous nanosheets（CNS）.The Schiff base reaction between CNS and terephthalaldehyde is used to obtain a conjugated polymer CNS-TPAL.The conjugated polymer CNS-TPAL has enhanced photocatalytic degradation performance for methyl orange.Under visible light irradiation,CNS-TPAL-5 can degrade methyl orange by 4.69 mg/0.1g within 180minutes,which is 2.8 times of CNS（1.67 mg/0.1g）.The excellent photocatalytic degradation performance of the composite CNS-TPAL for methyl orange is attributed to the increased specific surface area,enhanced visible light absorption and efficient electron-hole pair separation efficiency.Secondly,using melamine as the precursor and thiourea as the sulfur source,sulfur doped carbon nitride quantum dots（S-CNQDs）were synthesized by bottom-up one-pot copolymerization,and CNS-TP/S-CNQDs composites were prepared by quantum dots synthesis and doping simultaneously.After loading S-CNQDs,the adsorption and degradation performance of the material is significantly improved.7:1-CNS-TP/S-CNQDs has the highest degradation performance,and the degradation rate of methyl orange reaches 4.19 mg/0.1g·h,which is 1.70 times of CNS-TPAL-5（2.47 mg/0.1g·h）.The enhanced photocatalytic degradation performance of the composite materials is attributed to the increase of reactive active sites and the improved separation efficiency of photogenerated electron hole pairs after S-CNQDs composite.