Preparation Of MoO₃ And Carbonitride Carbon Composite And Study On Synergistic Improvement Of Photocatalytic Activity

The widespread of pharmaceuticals and personal care products（PPCPs）in the environment has raised attention all around the world,and the effects,fate and threats related to the existence of drugs residues are increasingly researched.Photocatalysis is an efficient and clean treatment technology,which is used for the degradation of PPCPs in aquatic environment.Graphitic carbon nitride（g-C₃N₄）as a new visible light-driven photocatalyst has attracted enormous attention due to its low toxicity,high stability,and low cost.However,the high recombination rate of the photogenerated electron-hole pairs and the low specific area of pure g-C₃N₄ greatly limited its photocatalytic activity.Thus,in this paper,the photocatalytic activity of g-C₃N₄ was improved by composite MoO₃ semiconductor.At the same time,the methods that can form synergistic effect to improve photocatalysis are explored.The main research contents and results are as follows:（1）MoO₃/g-C₃N₄ composites were successfully prepared by a simple hydrothermal-calcination synthesis method.The morphology and optical properties of the composites were characterized by SEM,TEM,XRD,FTIR,UV-vis and PL.The results show that MoO₃ and g-C₃N₄ are successfully combined.The red shift of absorption band,the stronger absorption spectrum and the low recombination of photogenerated carriers of g-C₃N₄ should be owed to the function of MoO₃.The photocatalytic activity of MoO₃/g-C₃N₄ composite was systematically studied with the Non-Steroidal Anti-Inflammatory Drug（NSAID）naproxen as the target pollutant.The experimental results showed that the removal rate of Naproxen by photocatalyst MoO₃/g-C₃N₄ was 1.75 times that of pure g-C₃N₄ under the same conditions.The study of different influencing factors showed that the degradation of NPX was better under the condition of 3%MoO₃ and acidity.Increasing MC 3 usage and reducing initial concentration of NPX can also accelerate the degradation rate of NPX.The singlet oxygen and superoxide radicals were key active species through quenching experiments.The existence of singlet oxygen determined by ESR confirmed the mechanism of degradation of NPX by Z-scheme MoO₃/g-C₃N₄.This study provides a new efficient and environmentally friendly method for the application of MoO₃/g-C₃N₄ composite photocatalyst in the degradation of non-steroidal anti-inflammatory drugs.（2）Carbon quantum dots（CDs）have been frequently used for broadening spectrum light response due to their superior up-conversion photoluminescence（UPPL）property and effective charge separation capacity.In this study,a novel CDs modified Z-scheme photocatalyst（CDs/g-C₃N₄/MoO₃）was successfully constructed.The morphologies,chemical compositions,and optical properties of the prepared catalysts were investigated via a series of characterization techniques.Systematic studies indicated that the CDs/g-C₃N₄/MoO₃photocatalyst exhibited remarkably enhanced visible-light photocatalytic activity for the degradation of tetracycline（TC）compared to pristine g-C₃N₄ and MoO₃/g-C₃N₄ composite.Doping 0.5%CDs resulted in the highest TC degradation rate,which was 3.5 and 46.2 times higher than that of MoO₃/g-C₃N₄ and g-C₃N₄,respectively.The enhanced photocatalytic performance of CDs/g-C₃N₄/MoO₃ can be attributed to the synergistic effects of CD properties（i.e.,excellent UPPL activity and high charge separation capacity and the Z-scheme heterojunction structure）.Reactive species scavenging experiments revealed that photogenerated holes are the main active species during the photocatalytic process.Possible photocatalytic degradation pathways of TC were proposed through the identification of intermediates using HPLC-MS and the frontier electron density calculation.Experimental results showed that the newly fabricated Z-scheme CDs/g-C₃N₄/MoO₃ is a promising photocatalyst for the removal of TC from the environment.（3）The advanced oxidation processes（AOPs）was regarded as one of the effective strategies for the degradation of organic pollutant.Herein,a novel Z-scheme type MoO₃/g-C₃N₄ composite photocatalyst synergize with peroxydisulfate（PDS）to enhanced photocatalytic activity.Systematic studies indicated that the synergistic MoO₃/g-C₃N₄/PDS photocatalytic system exhibited significantly enhanced photocatalytic activity for the degradation of ofloxacin（OFLX）in contrast to MoO₃/g-C₃N₄ and pure g-C₃N_4.A 94.4%removal efficiency could be accomplished with 0.6 g/L catalyst and 5 mM peroxydisulfate（PDS）under visible light within 120min.The enhanced photocatalytic performance of MoO₃/g-C₃N₄/PDS could be attributed to the capture of the photoinduced electrons of PDS as well as the generation of SO₄^·-which can oxidize water to generate·OH.Quenching experiments revealed that O₂^·-and h⁺were the dominant active species involved in the MoO₃/g-C₃N₄/PDS system under visible light irradiation.Degradation pathways of OFLX were then proposed based on the identification of intermediates.A little effect on photodegradation of OFLX with inorganic anions showed that MoO₃/g-C₃N₄/PDS system provided a superior approach for the remediation of OFLX from aqueous solutions.