Insights into the Effect of Cation Distribution at Tetrahedral Sites in ZnCo2O4 Spinel Nanostructures on the Charge Transfer Ability and Electrocatalytic Activity toward Ultrasensitive Detection of Carbaryl Pesticide in Fruit and Vegetable Samples

Abstract

The recent advancement in designing novel spinel nanostructures has opened virtually infinite possibilities for the development of high-performance electrochemical sensors to detect target species. The electrocatalytic activity of spinel structures can be enhanced by tuning the cation distribution; however, the role of cation distribution at tetrahedral ions on the electrochemical sensing responses has rarely been considered. Herein, the effect of cation distribution at tetrahedral sites (Td) in the spinel nanostructure ZnCo2O4 on the electrochemical sensing performance toward carbaryl (CBR) was first investigated. The ZnCo2O4 nanoflake samples with different cation ratios of Zn/Co at tetrahedral sites were designed by using a facile solvothermal method. We found that a higher Zn ion content at tetrahedral sites significantly enhanced the electron transfer ability through the electrolyte/electrode interface. More interestingly, a higher Co ion ratio between octahedral sites and tetrahedral (CoOh/CoTd) promoted the electrochemical oxidation process of CBR with a higher catalytic rate constant (kcat). Under optimized conditions, the ZnCo2O4-NF-based electrochemical nanosensor showed a linear response from 0.15 to 100 μM with a limit of detection of 0.05 μM and a high electrochemical sensitivity of 2.04 μA μM–1cm–2. The designed nanosensor also exhibited good repeatability, long-time stability, high anti-interference ability, and excellent recovery with fruit and vegetable samples. Furthermore, this study offers insights into the cation distribution-dependent electrocatalytic activities of spinel nanostructures, which is helpful to the design of advanced spinel nanostructure-based electrocatalysts for improving the electrochemical sensing performance.