Research On The Photocatalytic Performance Of S-type Protonated G-C₃N₄/MnS Heterojunctions

Hydrogen peroxide is an important green oxidant used for environmental protection and chemical production.Recently,the production of hydrogen peroxide by semiconductor photocatalysis has been considered as an emerging and promising method due to the use of sustainable sunlight as an energy source,using water and oxygen as feedstock.Meanwhile,semiconductor photocatalysis can directly use solar energy to activate molecular oxygen and generate reactive oxygen species to degrade hard-to-degrade pollutants by consuming in situ generated hydrogen peroxide.The tetracycline family of hygromycin is widely used as an antibiotic due to its broad-spectrum activity and low price.However,hygromycin in water bodies will affect human health and the ecology.Since in situ production of hydrogen peroxide can replace expensive commercial hydrogen peroxide for the degradation of hygromycin can be a new and promising research topic.Manganese sulfide as a transition metal sulfide material is considered as a promising photocatalyst due to its natural abundance,environmental friendliness,strong light absorption and charge separation.Protonated carbon nitride is mobile and positively charged,so it can easily attach to the surface of another semiconductor with strong chemical bonds.Therefore,it is important to construct heterojunctions between manganese sulfide and protonated carbon nitride to improve photocatalytic performance and to investigate the charge transfer mechanism of hydrogen peroxide generation and hygromycin degradation.In this thesis investigation,we constructed PCN andα-Mn S heterojunctions for improving the absorption efficiency of Mn S to visible light.The ability of PCN/Mn S heterojunctions to produce hydrogen peroxide as well as to degrade oxytetracycline were investigated separately,and the effect of environmental factors on the activity of this catalyst was examined.（1）In the investigations of this thesis,we constructed PCN andα-Mn S heterojunctions for improving the absorption efficiency of Mn S for visible light.The ability of PCN/Mn S heterojunctions to produce hydrogen peroxide was investigated separately,and the effect of environmental factors on the activity of this catalyst was examined.The PCN/Mn S heterojunctions were prepared by in situ synthesis and direct doping methods,respectively,and applied to the production of hydrogen peroxide.The catalytic system can efficiently produce hydrogen peroxide under mild conditions The catalysts were characterized structurally as well as photoelectrically,and the composites prepared by the two synthetic routes were compared.The one-step synthesized materials exhibit a nanosphere structure ofα-Mn S with ultrathin PCN dispersed on the surface.photogenerated charge separation and electron transfer are improved due to the interfacial effect of PCN/Mn S.Efficient production of hydrogen peroxide was achieved without the use of electron donor and pure O₂.Mechanistic studies present the contribution of the S-scheme p-n heterojunction to charge transfer.electrons in the conduction band（CB）of Mn S are responsible for the primary single-electron reduction of·O₂^-and the auxiliary two-electron reduction of O₂ to produce H₂O₂.（2）In situ degradation of oxytetracycline by photogenerated hydrogen peroxide in water,the constructed PCN/Mn S heterojunction material achieved 82.2%degradation efficiency of OTC under neutral environment,and the in situ capture experiments verified that·O₂^-from H₂O₂mainly promoted the oxidation of oxytetracycline.This work provides a new idea for the degradation of organic matter.