Study On Preparation And Photocatalytic Properties Of Magnetically Modified G-C₃N₄-based Nanocomposites

In recent years,photocatalysis has attracted increasing attention due to its potential for environmental safety.Metal-free graphitic carbon nitride（g-C₃N₄）has attracted much attention in the field of photocatalysis due to its suitable band edge position,visible light response,and easy preparation.However,g-C₃N₄still has defects such as low utilization rate of sunlight,high recombination rate of photogenerated carriers,and difficulty in recycling.In view of the above defects,g-C₃N₄was modified from two aspects:imparting magnetic properties and enhancing photocatalytic activity.This provides a theoretical basis for the preparation of photocatalysts with high photocatalytic performance and magnetic recovery.（1）In this work,g-C₃N₄/ZnFe₂O₄（CN/ZFO）magnetic heterojunction photocatalyst was first prepared and then modified with ultrathin MoS₂by simple ball-milling method to obtain CN/ZFO/MoS₂magnetic ternary heterojunction.Then the photocatalytic removal of Cr（Ⅵ）performance of the prepared series photocatalysts was evaluated in detail.The optimum CN/ZFO/MoS₂can achieve 99.3%Cr（Ⅵ）removal under 200-min simulated sunlight illumination,which is much higher than CN/ZFO（54.0%）.The enhanced photocatalytic performance benefits from the modification of MoS₂,which improves the light absorption performance,facilitates the transfer of photogenerated carriers,increases the concentration of photogenerated carriers and promotes the effective separation of photogenerated carriers.（2）Firstly,MoS₂with the same lamellar structure was used to modify g-C₃N₄by ball milling technology,and then a magnetic recyclable ternary composite photocatalyst g-C₃N₄/MoS₂/Fe₂O₃was prepared by further compounding withα-Fe₂O₃.The experimental results of photocatalytic removal of Cr（Ⅵ）show that the photocatalytic removal rate of Cr（Ⅵ）by g-C₃N₄/MoS₂/Fe₂O₃-20%is 94.6%under 140-min simulated sunlight illumination,while that of pure g-C₃N₄is only 51.7%.The co-modification of MoS₂andα-Fe₂O₃contributes to the improvement of photoabsorption and photogenerated carriers migration efficiency,and thus enhances the removal activity of Cr（Ⅵ）.（3）Porous 1D rod-like ZnFe₂O₄was synthesized by solvothermal method,and Au nanoparticles were further deposited on ZnFe₂O₄nanorods by in-situ chemical reduction.Finally,the ultrathin g-C₃N₄was coated on the rod-like structure by mechanical stirring to obtain magnetic recyclable ZnFe₂O₄/Au/g-C₃N₄（ZFO/Au/CN）composite photocatalyst.Physical characterization results show that 1D rod-shaped ZnFe₂O₄consists of a large number of ZnFe₂O₄nanoparticles,Au nanoparticles are uniformly loaded on the surface of rod-shaped ZnFe₂O₄,and g-C₃N₄is coated in the outermost layer.The experimental results of photocatalytic removal of Cr（VI）showed that the photocatalytic removal rate of Cr（VI）by ZFO/Au/CN-5%is 95.6%under the condition of simulated sunlight irradiation for 50 min with methanol as the hole scavenger,while pure rod-shaped ZnFe₂O₄is only76.6%.The enhanced photocatalytic performance of ZFO/Au/CN can be attributed to the construction of Z-type heterojunction with Au as the intermediate electron transporter.