Application Of Zn/AgIn_xS_y In Visible Light Photocatalytic Degradation And Cephalosporin Detection

As a kind of ternary semiconductor,AgIn_xS_y has been widely concerned and applied in the fields of light-emitting diodes,lasers,solar cells and biomarkers due to its excellent biocompatibility,optical performance and unique size.In the field of photocatalytic applications,TiO₂ is the most studied photocatalyst.Compared with TiO₂,AgIn_xS_y has narrower band gaps,and its absorption of visible light is obviously better than that of TiO₂.Meanwhile,the research of AgIn_xS_y in quantum dots（QDs）is increasing gradually due to the absence of toxic elements.In this paper,the applications of AgIn_xS_y in the fields of photocatalysis and quantum QDs detection was explored.AgIn_xS_y was synthesized by"one-pot"method and different amounts of Zn²⁺were introduced into it to further improve the visible light photocatalytic activities.The obtained Zn/AgIn_xS_ysamples were analyzed by XRD,XPS,SEM,etc.The photocatalytic activity of AgIn_xS_y was evaluated by photocatalytic decomposition of rhodamine B（Rh B）,p-nitrophenol and cefalexin under visible light irradiation.A 1000 W tungsten halide lamp equipped with a condenser water jacket（the wavelengths<420 nm was filtrated）was used as the visible light source.The experimental result shows that the structure of as-synthesized AgIn_xS_y changed from facecentered cubic phase AgIn₅S₈ to orthorhombic phase AgInS₂ when the ratio of Zn to In is>5:12.Doping of Zn²⁺increased the regularity,dispersibility,visible light absorption and separation of photogenerated charge of AgIn_xS_y.The optimum ratio of Zn to In is 4:13,Zn/Agln_xS_y with the optimal ratio showed the highest visible light photocatalytic activity,and Rh B could be completely degraded within60 minutes.The degradation efficiency of Zn/Agln_xS_y for cefalexin was 62%after visible light irradiation for 120 min under the same conditions.The capture experiments were carried out by introducing different trapping agents to study the reactive radicals involved in the reaction processes.The band gap was determined by Ultraviolet–visible Diffuse Reflection Spectroscopy;and the semiconductor type and position of flat band potential of AgIn_xS_y and Zn/AgIn_xS_y were measured by electrochemical experiments.The experimental results show that the the band gap and flat band potential of AgIn_xS_y are 1.61 e V and-0.60 V,while that of Zn/AgIn_xS_y（Zn:In=4:13）are 1.45 e V and-0.55 V,respectively;and the degradation of Rh B by Agln_xS_y is mainly due to hydroxyl radical（·OH）,while the degradation of Rh B and cefalexin by Zn/Agln_xS_y is mainly due to superoxide radical(·O^2-).This result indicated that the doping of Zn²⁺changed the mechanism of degradation of pollutants by AgIn_xS_y.Water-soluble AgInS₂ QDs were synthesized by aqueous-phase method.Zn²⁺was introduced into the reaction mixtures to prepare the Zn/AgInS₂ QDs during the preparation process,and the effect of Zn²⁺on the fluorescence intensity of AgInS₂ QDs was investigated.The composition and morphology were determined by XRD,XPS and HRTEM.Zn/AgInS₂ QDs were used as the fluorescent probes,cefalexin and cefixime with different concentrations were added into the test solution to investigate the degree of fluorescence quenching of QDs.The results showed that the fluorescence intensity of the QDs was the highest at the ratio of Zn to In is 0.02:1.The linear range of cefalexin detection was 1-20μg/m L,limit of detection（LOD）was 0.45μg/m L,and the adding standard recovery was between 97.38%and 102.00%.The linear range of cefixime detection was 1-10μg/m L,LOD was 0.15μg/m L,and the adding standard recovery was between 96.67%and 104.17%.The mechanism of cefalexin and cefixime quenching the fluorescence intensity of AgIn S₂ QDs was basically the same,both are the dynamic quenching caused by the collision of drug molecules and QDs.