Properties And Mechanism Of G-C₃N₄-based Heterojunction Photocatalysts Modified By Nanoclusters

Graphitic phase carbon nitride（g-C₃N₄）has attracted wide attention due to its simple and mild preparation conditions,good chemical and thermal stability,suitable band gap（2.78 e V）and environmental friendliness.However,as a non-metallic semiconductor material,massive g-C3N4 has serious shortcomings such as fast electron hole recombination speed and chaotic electron migration direction,which will inevitably lead to the decrease of photocatalytic activity.Researchers have proposed a number of possible methods,such as element doping,micro-and nano-structure adjustment,and semiconductor coupling.Compared with other methods,the essence of these regulatory strategies is to effectively prolong exciton annihilation time,but these strategies have been unable to meet people’s demand for photocatalytic performance.Due to the single driving force and lack of electron trap,the performance of g-C₃N₄-based ternary heterojunction photocatalyst is greatly restricted.This not only increases the cost for researchers to explore the material field,but also greatly reduces the stability of the material.In this paper,the micro-morphology,photogenerated charge separation and visible light absorption range of g-C₃N₄ heterojunction were regulated by means of morphology regulation and the introduction of zero-nanometer clusters,and the mechanism of the catalyst’s influence on the photocatalytic performance was investigated,which provided a new strategy and method for the construction of g-C₃N₄-based heterojunction photocatalyst.The main research contents are as follows（1）A quasi-ternary Z-type heterojunction photocatalyst CQD/Cd S/g-C₃N₄（CSCN）composed of CQD,Cd S and g-C₃N₄ has been successfully constructed,and its electron transfer pathway has been studied by comparison.The intrinsic electric field at the interface between Cd S and g-C₃N₄ causes exciton separation.The barrier between CQD and Cd S accelerates charge transfer,further preventing exciton annihilation.The photocatalytic degradation performance of CQD/Cd S/g-C₃N₄ was improved,and the role of CQD as an active center in the photocatalytic reaction was further proved.The prepared CSCN photocatalyst showed a good effect on the degradation of Rhodamine B and sulfadiazine,with the degradation rates reaching 94.7%and 76.0%within 3h.（2）Ni Cu Co Fe medium-entropy alloy nanoclusters（MEAs）were designed and used to modify the Z-type heterojunctions of Bi₃O₄Br/CNNs（MBC）.The cocktail effect of MEAs leads to hybridization of 3d orbital electrons in various metallic elements,promoting the release of charge carriers.The higher the carrier concentration,the stronger the LSPR effect produced by MEAs.Three working mechanisms of MEAs on heterojunctions were further studied.The D-orbital coupling realized the precise regulation of the photogenerated carrier transfer path,and revealed the intrinsic relationship between the carrier transfer path and catalytic activity.At the same time,the norfloxacin removal rate of the new MBC system was 2.35 times higher than that of Bi₃O₄Br/CNNs.