Study Of Heavy Metal Electrochemical Sensors Based On Graphene Oxide-Co₃O₄ Composites

People's daily life is inseparable from water,the quality of water directly affects human health.With the development of the global economy,the content of heavy metals in water has gradually increased,which has become a global problem.Heavy metal ion pollution mainly includes natural pollution and man-made pollution,natural pollution is mainly rain,rock weathering products,and soil,generally has less impact on water body;man-made pollution includes some industrial and chemical activities,waste electronic battery treatment and domestic sewage,which directly affects human health.At present,the detection methods of heavy metal ions in water mainly include atomic fluorescence spectrometry(AFS),atomic absorption spectrometry(AAS),inductively coupled plasma atomic emission spectrometry(IMP-AWS),inductively coupled plasma mass spectrometry(IMP-MS),UV-vis spectrophotometry(UV-Vis),High-performance liquid chromatography spectrophotometry(HPLC-SP)and other biological methods(such as DNA,biological enzymes and immunity)analysis method).However,these detection methods are expensive equipment,cumbersome operation,mainly used for laboratory testing,it is difficult to achieve the detection of heavy metal ions in water.Electrochemical detection and analysis have the characteristics of low cost,simple operation,convenient hand-held operation,and suitable for rapid detection on-site,which has attracted many people's attention.Graphene has a high specific surface area,excellent conductivity,and good flexibility,which can accelerate the electron transfer rate.Co₃O₄ is a typical spinel structure with good conductivity and high electrochemical activity.In this paper,graphene,Co₃O₄,and graphene composite active materials with different Co₃O₄content were prepared by hydrothermal decomposition.The morphology,composition and electrochemical properties of the materials were analyzed by X-ray diffraction,Fourier transform infrared spectroscopy,Raman spectroscopy and scanning electron microscopy The graphene-Co₃O₄ active materials were further optimized to achieve rapid,sensitive and accurate detection of heavy metal ions.Firstly,graphene was characterized,and graphene was used as the modified material of glassy carbon electrode.The concentration of graphene-modified material,Nafion mass concentration,and dropping amount were studied by orthogonal experiment.To obtain a better current response of heavy metal ions,the effects of electrolyte type,p H,deposition potential,and deposition time were studied It has been optimized and tested.The results show that graphene is a single-layer folded structure,which is conducive to the attachment of heavy metal ions.The optimal experimental parameters for the detection of heavy metal ions by differential pulse anodic stripping voltammetry(DPASV)are as follows:graphene concentration is 0.25mg/m L,Nafion concentration is 0.5%,dropping amount is 5?L,the buffer solution is 0.1 M,HAc-Na Hc solution p H=4.5,deposition potential is-1.2 V,The deposition time was 120 s.The detection range for Cd²⁺is 1.0-7.78?M,the sensitivity is 0.56?A??^-1,the RSD is 0.055,and the detection limit is 0.29??.The detection range for Pb²⁺is 1.0-6.69??,the sensitivity is1.86?A??^-1,the RSD is 0.026,and the detection limit is 0.04??.Then,Co₃O₄ nanomaterials were prepared by hydrothermal decomposition method using CO(NO₃)₂·6H₂O as a cobalt source.The electrode materials were characterized,and the heavy metal ions were detected by differential pulse anodic stripping voltammetry(DPASV).The experimental results show that the synthesized Co₃O₄ material is a hexagonal lamellar structure.The detection range of Cd²⁺was 1.0-5.93??,the sensitivity was 0.29?A??^-1,the RSD was0.019,and the detection limit was 0.20??.The detection range for Pb²⁺is 1.0-5.93??,the sensitivity is 1.18?A??^-1,the RSD is 0.046,and the detection limit is 0.11??.Finally,graphene-Co₃O₄ nanocomposites with different Co₃O₄ content were prepared by hydrothermal decomposition method using CoCl₂·6H₂O as a cobalt source.The samples were characterized,and the heavy metal ions were detected by electrochemical detection.The experimental results show that the growth of graphene is uniform with the growth of graphene in the case of less Co₃O₄ content With the increase of Co₃O₄ content,the particles grow in three dimensions on graphene and become small and round.The increase of active sites is helpful for electron transport.The detection range of Cd²⁺was 0.3-6.41??,the sensitivity was 1.15?A??^-1,the RSD was 0.022,and the detection limit was 0.05??.By differential pulse anodic stripping voltammetry(DPASV),the detection range of Pb²⁺is 0.33-6.41??,the sensitivity is4.00?A??^-1,the RSD is 0.039,and the detection limit is 0.029??.Besides,graphene-Co₃O₄ nanocomposites with the optimal proportion were used as electrode materials to test a variety of heavy metal ions at the same time.