Study On Electrochemical Detection And Degradation Of Typical Pollutants By Graphene-Based Nanocomposites

With the rapid development of urbanization,industrialization and modern agriculture,a large number of emerging pollutants with biological accumulation,toxicity and persistence enter the aqueous environment,posing a serious threat to human health and ecological environment.Therefore,it is getting increasingly important to develop a series of simple,low-cost and highly sensitive pollutant detection technologies as well as environmentally friendly and efficient treatment technologies.In recent years,electrochemical（EC）methods have gradually attracted widespread attention from domestic and foreign researchers due to their advantages of simple operation,fast analysis,low cost and easy miniaturization,as well as the advantages of peroxymonosulfate（PMS）advanced oxidation technology with fast reaction speed,wide application range and high removal capacity.However,in the process of electrochemical detection,the sensitivity and accuracy of the electrode will be affected due to the complex matrix of ambient water and various interfering substances.In addition,the high applied potential and low sensitivity of bare electrodes further limit their application in contaminant detection.Choosing suitable nanocomposite to modify the electrode is considered an effective solution,which can not only improve the catalytic performance towards pollutants but also expand the detection range and reduce the detection limit.In terms of contaminant degradation,catalytic methods based on transition metals or metal oxides can effectively activate PMS,but there are always potential risks of secondary pollution such as metal leaching.In view of the above,a non-toxic graphene material with diverse structures,large specific surface area,good electrical conductivity and easy surface modification is selected as the substrate material of this paper.Graphene is systematically combined with metal nanoparticles,metal oxides,graphitic-like nitrogen-doped carbon materials,etc.,and a series of nano-electrochemical methods were constructed based on the prepared composite materials for detecting pollutants in water environment.Furthermore,nitrogen-doped three-dimensional graphene was used for the efficient degradation of tetracycline（TC）by activating PMS,providing new methods and technologies for controlling pollutants such as drugs in environmental water.The following work was specifically carried out:（1）Study on Determination of chloramphenicol by reduced graphene oxide/Pd nano-electrochemical methodIn this work,nitrogen-doped reduced graphene oxide（RGO）was synthesized by one-step reduction method using GO as precursor and ethylenediamine as reducing agent.Then,the reduced graphene oxide/palladium nanoparticle composite（RGO/Pd NPs）was prepared by loading palladium nanoparticles（Pd NPs）onto the RGO surface using Pd Cl₂ as the precursor.The RGO/Pd NPs composites exhibited excellent electrochemical properties due to the excellent synergistic effect between Pd NPs and RGO.A nano-electrochemical method for the determination of chloramphenicol（CAP）was constructed by modifying it on a GCE.Under optimal experimental conditions,the linear range of the proposed method is 50-1000 nmol L^-1 with a limit of detection（LOD）of 50 nmol L^-1（S/N=3）.At the same time,the method has high sensitivity,good stability,excellent reproducibility and great practical application potential.（2）Study on the determination of nitrite by PDDA-reduced graphene oxide/flower Ni O nano-electrochemical methodIn this work,poly-dimethyl diallyl ammonium chloride（PDDA）was used to functionalize reduced graphene oxide（RGO）,improving the dispersibility of RGO.In addition,PDDA functionalized RGO also showed excellent conductivity,solubility and biocompatibility.On this basis,Ni O/PDDA-RGO composite was prepared by ultrasonically compounding flower-like Ni O of excellent adsorption and catalytic properties with PDDA-functionalized graphene.The material used RGO as the carrier of Ni O,which overcame the poor electrical conductivity of Ni O,improved the adsorption properties to the analyte and enhanced its electrochemical properties.The NO₂^-electrochemical sensor was constructed based on this composite material,and its electrochemical performance for NO₂^-detection was investigated.The results showed that Ni O/PDDA-RGO/GCE showed high electrochemical activity for NO₂^-detection,with a linear range of 5.0μmol L^-1-8.0 mmol L^-1 and a LOD of 0.98μmol L^-1（S/N=3）.In addition,the above sensing method has good selectivity,and the analysis results for NO₂^-in actual sample was consistent with those obtained by HPLC.（3）Study on the determination of metformin by reduced graphene oxide/copper ferrite/γ-CD nano-electrochemical methodIn this work,γ-CD was selected as a protective agent to improve the dispersion and solubility of RGO.Cu Fe₂O₄ bimetallic oxides,which benefit from the synergistic effect of different metal cations,have better conductivity and catalytic activity than mono-metal oxides,which is a promising electrode modifier.Cu Fe₂O₄/RGO/γ-CD was synthesized by sonochemistry-coprecipitation method and used as an active electrocatalyst to achieve sensitive electrochemical detection of MET.Cu Fe₂O₄/RGO/γ-CD nanocomposite has excellent catalytic activity,high conductivity and more ion diffusion channels,which is beneficial to the electrochemical response of MET.In addition,the combination of Cu Fe₂O₄/RGO withγ-CD is advantageous for the enrichment of the analyte MET,amplifying the detection signal.The constructed sensing platform based on Cu Fe₂O₄/RGO/γ-CD has good reproducibility,selectivity and stability,and has been successfully applied to the detection of MET residues in environmental soil and water samples.The detection results were consistent with those measured by standard UV-vis spectroscopy.The development of this sensor provides a feasible scheme for the detection of MET in the environment.（4）Study on the simultaneous determination of acetaminophen and levofloxacin by graphene oxide/graphite phase carbon nitride nano-electrochemical methodEnvironmental water matrices are complex with a wide variety of contaminants,and achieving simultaneous detection techniques for multiple contaminants can improve detection efficiency,increase material utilization.In this work,graphene oxide/graphite phase carbon nitride nanosheet composite（GO/CNNS）was successfully synthesized by a simple ultrasonic method,which is low-cost,environmentally friendly and non-toxic.The material was modified onto a GCE to construct an electrochemical sensor platform for simultaneous detection of acetaminophen（AC）and levofloxacin（LEV）.By immobilizing CNNS on the GO surface throughπ-πinteractions,the resulting GO/CNNS can provide a larger specific surface area for the oxidation of AC and LEV and improve the electron transfer rate.At the same time,the material has low cost,environmental protection and non-toxic.In addition,the composites were characterized by TEM and SEM.Separate and simultaneous detection of AC and LEV using the DPV technique under optimal experimental conditions.The linear ranges of the constructed sensors for simultaneous detection of the two substances were 5×10^-7-3.0×10^-5 mol L^-1（AC）and 5×10^-7-1.5×10^-5 mol L^-1（LEV）with detection limits of 1.7×10^-8 and 7.9×10^-8 mol L^-1,respectively.In addition,the sensor has a low cost,high sensitivity and satisfactory recovery.The present work provides a novel,low-cost,environmentally friendly and convenient nano-electrochemical sensing platform for the quantitative determination of AC and LEV drugs.（5）Study on nitrogen-doped 3D graphene activated persulfate degradation of tetracycline in waterThe previous four sections constructed a series of graphene-based nano-electrochemical methods to achieve sensitive detection of NO₂^-and various pharmaceutical contaminants.In this study,we prepared 3D N-RGO-x by hydrothermal reaction and calcination of graphene oxide mixed with two nitrogen-rich organic compounds at different ratios.Compared with two-dimensional graphene,three-dimensional graphene has better flexibility,multi-space penetration network structure,large specific surface area and excellent mass transfer and adsorption properties.At the same time,the carbon material is stable,low cost,non-toxic and pollution-free.The structure,morphology and elemental composition of the samples were analyzed in detail using SEM,XRD,FT-IR,BET,XPS and Raman characterization techniques.The effect of nitrogen source type,precursor mass ratio and calcination temperature on the nitrogen content of the material and then on the tetracycline（TC）degradation performance were studied.3D N-RGO-x was used to activate PMS for efficient degradation of TC.The effects of different parameters on the TC degradation performance were investigated.The active oxygen species and activation mechanism in the reaction system were studied through quenching experiments,EPR testing and XPS characterization of the catalyst before and after the reaction.The intermediate products and potential degradation pathways of TC were studied using HPLC-MS analysis technology.The toxicity of the intermediate products was estimated using the toxicity estimation software tool（TEST）.The results showed that the catalytic material had good activation performance for PMS,mainly degrading TC through free radical(O₂^?-)and non-radical（¹O₂ and electron transfer）pathways.The electron rich C=O functional group and graphite N may be active centers that promote TC degradation.Meanwhile,the system has a good p H tolerance and good cycling stability,and has good resistance to environmental background substances,making it has great potential for environmental remediation.In addition,this work expands the application of graphene carbon materials in degradation and provides ideas for the preparation of new efficient non-metallic catalysts with multiple active centers.