Electrochemical Response Mechanism Based On Cobalt-based Oxide Composites To Toxic Pollutants

The rapid development of social industrialization has brought serious harm from toxic pollutants.Among all pollutions,heavy metal ions and organic pollutants have particularly prominent impacts on the environment and human body.In order to realize harmful pollution assessment and safe water use,it is necessary to carry out efficient,accurate and stable analysis and detection of toxic pollutants in the environment.Unfortunately,the pollution of heavy metal ions and toxic organic matter in groundwater environment has been characterized by multi-component,complex background and trace amount,so the accurate qualitative and quantitative analysis of heavy metal ions and toxic organic matter has been a difficult problem in the field of analytical chemistry.It is very urgent to explore new electrode sensitive materials and detection methods for trace detection of toxic pollutants.Cobalt oxide nanomaterials have significant advantages in constructing electrochemical sensitive interfaces for toxic pollutants due to their advantages of environmental protection,low cost and high catalytic activity.Meanwhile,compared with the traditional methods for the detection of toxic pollutants,electrochemical detection method has been widely concerned because of its advantages such as fast,high sensitivity,easy operation and on-line monitoring.To solve the above problems,this paper aims to construct a simple and highly sensitive electrochemical sensor based on cobalt-based oxide nanomaterials to investigate the electrochemical detection of toxic pollutants in real water samples,and further discusses the electrochemical response mechanism of cobalt-based materials as sensitive interface detection.The specific research contents are as follows:1.Co₃O₄/Zn O nanocomposites with different Co-Zn ratios and pure Co₃O₄ with Zn O were prepared by one-step hydrothermal process and subsequent annealing in air（The mole ratios of Co-Zn were 2:1,1:1 and 1:2,respectively.The samples obtained were named 2Co/Zn,1Co/Zn,Co/2Zn）.The adsorption and electrochemical experiments confirmed that the introduction of Zn O improves the adsorption capacity of Hg（II）in nanocomposites,and the unique Co（II）/Co（III）cycle of Co₃O₄ promotes the redox activity of the detection process.The electrochemical detection results showed that 2Co/Zn with a Co-Zn molar ratio of 2:1 has the best electroanalytical performance for Hg（II）with a sensitivity of 504.74μAμM^-1 cm^-2.The satisfactory electrochemical performance of 2Co/Zn is mainly attributed to its excellent redox activity and oxygen vacancy on the surface,as well as its large specific surface area and loose structure,which provides more active sites for electrochemical detection.In addition,the study also confirmed that the Co₃O₄/Zn O nanocomposite modified electrode showed impressive stability and reproducibility for the detection and analysis of Hg（II）.2.Cobalt oxide nanomaterials with different oxidation states was prepared by annealing ZIF-67 under N₂ protection and subsequent oxidation in air.The products obtained by oxidation without oxidation,4 hours and 8 hours were Co,Co-Co O-Co₃O₄ and Co₃O₄,respectively.Compared with Co and Co₃O₄,incompletely oxidized Co-Co O-Co₃O₄ showed the best detection performance for 4-nitrochlorobenzene（4-NCB）,with a sensitivity of 2.29μAμM^-1 and limit of detection is 0.03μM in the concentration range of 0.5-4μM.The results showed that the adsorption capacity of Co-Co O-Co₃O₄ composite for 4-NCB decreased slightly after oxidation,but its catalytic reduction performance increased nearly 4 times,which makes it have better electrochemical detection performance.This work confirmed that adsorption and catalysis synergistic affect the electrochemical detection performance of organic pollutants,and the catalytic performance of materials is a more critical factor affecting electrochemical detection.