Fabrication Of Co₃O₄ Based Electrochemical Sensor For Hydrazine Detection In Water Environment

With the development of industries such as pharmaceuticals and chemicals,a large amount of hydrazine has entered the water body,causing the increment of toxicity for water environment.Short-term or long-term exposure to hydrazine can cause serious harm to animals,plants and humans.Therefore,it is necessary to find an accurate,easy-to-operate,fast and efficient detection method.In general,the traditional detection methods of hydrazine mainly include spectroscopy and chromatography.These methods are limited in practical applications due to the complicated operation,difficult derivative pre-processing and expensive equipment cost.In recent years,with the rapid development of electrochemical methods,electrochemical sensors applied to the analysis and detection of pollutants in the environment has attracted much attention.Due to the advantages of simple and easy operation,low cost and quickness,electrochemical sensors have great potential application in the analysis and detection of pollutants in water environment.During the electrochemical detection of hydrazine,there is a problem of high overpotential.So it is necessary to select suitable electrode materials to overcome the dilemma.Among the transition metal oxides,cobalt oxide(Co3O4)is a type of rich and wide variety of source,inexpensive,and highly catalytic material.The use of a cobalt oxide as an electrode material is expected to reduce the high overpotential in the electrochemical detection of hydrazine.In this paper,the cobalt oxide based electrode materials have been prepared to be utilized for hydrazine electrochemical detection in wastewater.In the experiment,the effects of synthesis method,reactant ratio,hydrothermal synthesis temperature,reaction time and calcination temperature on the morphology and electrochemical performances of the prepared cobalt oxide materials were systematically studied.To achieve the electrochemical detection of hydrazine in low concentration,then,some starategies were came up with to improve the catalytic activity and conductivity of Co3O4,such as mixing with other metal oxides or carbon nanotubes.In addition,the detection mechanism of hydrazine by electrochemical method and the electron transfer and reaction kinetics involved were also investigated.Seven different morphologies of Co3O4,such as porous chrysanthemum-like Co3O4,Co3O4 nanowire,Co3O4 nanosheet,Co3O4 nanowire&nanosheet,urchin-like Co3O4,Co3O4 nanoneedle bundle and flower-like Co3O4 were prpared via hydrothermal method by adjusting the type of cobalt source,the molar ratio of cobalt source and urea,and the hydrothermal temperature.The seven different morphologies of Co3O4 were used as electrode materials to reduce the overpotential during the electrochemical detection of hydrazine.The obtained results showed that the porous chrysanthemum-like cobalt oxide modified electrode had the best electrochemical performance.Its sensitivity reached 107.9 μA·mM-1 and the electrode reaction rate was found to be 0.12 s-1.Moreover,the porous chrysanthemum-like cobalt oxide also exhibited good reproducibility and anti-interference in the electrochemical detection of hydrazine.After being stored at room temperature for 5 days,the current response of the modified electrode still reached 91.5%of its initial value.To further improve the electrochemical performances of cobalt oxide,conducting carbon materials,such as multi-walled carbon nanotubes,glucose derived carbon and nitrogen-doped carbon,were utilized to prepare Co3O4 based hybrid composites.The results show that with the introduction of carbon materials,the conductivity of the composites was significantly enhanced and the electrode transfer resistance was only 87.8 Ω.The prepared Co3O4/MWCNTs/GCE had good response to hydrazine at low concentration range.The detection limit was 0.449 μM and the electrode reaction rate was 0.28 s-1.After covered by carbon to prepare Co3O4@carbon,the fabricated modified electrode showed a low detection limit of 0.589μM and a larger electrode reaction rate of 0.46 s-1.With further introduction of nitrogen doped carbon,the electrode reaction rate of Co3O4/nitrogen-doped carbon modified electrode was improved to 0.52 s-1.The modified electrode had a detection limit as low as 0.11 μM in the electrochemical detection of hydrazine,which was better than the results measured by liquid chromatography.Using the recovery method,the real test was simulated by river water,and the recovery of the modified electrode was more than 94%.