Preparation Of Modified AgInS₂ And Their Applications In Photocatalysis,Fluorescence And Photochemical Detection

AgInS₂（AIS）is a typical representative of new materials.Compared with materials containing toxic elements such as Cd and Hg,AIS has attracted much attention due to its advantages such as low toxicity,strong absorption of visible light,high optical conductivity,high stability,controllable morphology and easy modification.It shows potential applications in light emitting diode,nonlinear optical device,solar cell,photocatalysis,biomedicine detection and other fields.In this paper,modified AIS was prepared and their application in photocatalysis,photochemistry and fluorescence detection of drugs were investigated.The aim of this project is to prepare AIS photocatalyst doped with cobalt metal（Co）（Co-AIS）and AIS QDs composited with ZnS（AIS/ZnS QDs）under different modification conditions.Part I:The photocatalytic performance of AIS and Co-AIS was studied by using photocatalytic technology,and the optimal proportion of Co doping AIS was explored to degrade organic pollutants.X-ray diffractometer（XRD）,X-ray photoelectron spectrometer（XPS）,Scanning electron microscope（SEM）,Transmission electron microscope（TEM）,Ultraviolet-visible spectrophotometer（UV-vis）,and Fluorescence spectrophotometer（PL）were used for the characterization of the crystal structure,surface elements,binding energy,particle morphology and optical properties of AIS and Co-AIS nanomaterials prepared by low temperature liquid phase method.Rhodamine B（Rh B）and 4-nitrophenol（4-NP）were used as the model pollutants,and the photocatalytic activities of AIS and Co-AIS were evaluated.Based on the capture experiment of active species,EPR technique,optical characterization and flat band potential measurement,the photocatalytic mechanism was proposed.In addition,the photocatalytic water splitting performance of Co-AIS before and after modification with multi-walled carbon nanotubes（MWCNTs）was studied,and remarkable hydrogen production effect was obtained.The results of photocatalytic test indicate that doping metal Co improves the photocatalytic activity of AIS.Co-AIS showed high visible photocatalytic activity for the degradation of Rh B and 4-NP.The optimal doping ratio of Co:In was 10.7:6.3.With the optimal ratio,Co-AIS degraded 95%Rh B and 76%4-NP within 1.5 h and 2.5 h,respectively.The results of active species capture experiment and EPR technology showed that·O₂^-,h⁺,e^-,·OH and ¹O₂ were all involved in the photocatalytic degradation process of AIS and Co-AIS,while·O₂^-was the dominant active species in the degradation of Rh B and 4-NP.In addition,the experiment of photocatalytic hydrogen production shows that:photocatalytic hydrogen production rate of AIS is 48μmol·h^-1·g^-1,after Co doping,Co-AIS（10.7:6.3）photocatalytic hydrogen production rate increased to 66μmol·h^-1·g^-1,loading 1.0 wt.%of MWCNTs significantly improved the Co-AIS（10.7:6.3）photocatalytic hydrogen production rate,reached 164μmol·h^-1·g^-1,about 3.4 times that of AIS and 2.5 times that of Co-AIS（10.7:6.3）.These results indicate that the modification of AIS with Co and MWCNTs can effectively improve the photocatalytic performance of AIS.This study will open up a new way to synthesize AgInS₂-based materials and explore their application in photocatalysis.Part II:Co-AIS-ITO electrochemical sensor was constructed using Co-AIS,and a photoelectric chemical method was established for the determination of OTC in tap water based on the reduction effect of oxytetracycline（OTC）on the Co-AIS photocurrent.The influence of OTC with different concentrations on the photocurrent of Co-AIS-ITO sensor was studied through the electrochemical workstation,and the standard curve was plotted.The recoveries of the added standard was determined by using tap water as the measured sample.Through current-time method（I-t curve）,the optimal experimental conditions for OTC detection by Co-AIS were explored,and the stability,sensitivity and anti-interference performance of Co-AIS-ITO sensor were analyzed.The optimal experimental conditions for OTC detection by Co-AIS-ITO photoelectric sensor are as follows:the concentration of Co-AIS in the Co-AIS-aqueous ethanol-glycol mixture is0.35 mg/m L,the coating amount is 25.00μL,and the additional voltage in the detection process is 0.25 V.The standard curve was established based on the relative reduction value of photocurrentΔI/I₀ versus the logarithm of concentration of OTC（log C）.The linear range of the detection of OTC was 4×10^-9～4×10^-3 mol/L,R²=0.9936,and the detection limit LOD was 2.5×10^-9 mol/L.The average recoveries of OTC at different concentrations in tap water ranged from 100.0%～107.5%.Part III:The water-soluble AIS/ZnS QDs were synthesized by"one-pot water phase method".Based on the fluorescence quenching effect of OTC on AIS/ZnS QDs,AIS/ZnS QDs was used as a fluorescence probe to establish a method for detecting OTC residual in milk.The optimal experimental conditions were explored and the possible quenching mechanism was proposed.By optimizing the experimental conditions,AIS/ZnS QDs prepared at p H 5.5 and adjusted with a sodium hydroxide solution exhibit the best fluorescence intensity.When 0.16 mg/m L AIS/ZnS QDs solution was used at 20℃,AIS/ZnS QDs could be used for quantitative detection of OTC in milk after 25 min interaction with OTC.It is concluded that the relative fluorescence quenching quantityΔF/F₀ of AIS/ZnS QDs by OTC has a good linear response to the logarithm of OTC concentration（log C）.The linear equation wasΔF/F₀=0.2933 log C+2.3388,R²=0.9984,the linear range of detection of OTC was 1.22×10^-8～2.5×10^-5 mol/L,and the detection limit LOD was calculated to be 1.81×10^-9 mol/L（n=10）.The recoveries ranged from 96.0%～101.8%.In this experiment,AIS and Co-AIS photocatalysts were successfully synthesized by low temperature liquid phase method.The effect of Co doping on AIS photocatalytic activity was studied,and a method was established to detect OTC residue in natural water based on the photoelectric effect of Co-AIS.AIS/ZnS QDs were synthesized by one pot water phase method（the dispersion in water is better）and used for establishing a method to detect OTC residue in milk based on the fluorescence quenching effect of AIS/ZnS QDs by OTC.The results were satisfactory.The two methods established in this work are simple,economical,fast and accurate,which will open up a new way for synthesizing AIS-based materials and exploring their applications in photocatalytic activity,photochemistry and fluorescence analysis.