Ultra-sensitive electroanalysis of toxic 2,4-DNT on o-CoFeSe solid solution: Fe-doping-induced c-CoSe phase transition to form electron-rich active sites.

How to achieve the sensitive electroanalysis of organics pollution in water environment is vital significance, but it is limited by their redox inert and the ambiguous detection mechanism. Herein, Fe-doping-induced structural phase transition engineering is designed to make the cubic (c-) CoSe to orthorhombic (o-) CoSe, accompanying with the formation of o-CoFeSe solid solution. By controlling the Fe doping amount, the fully orthogonalized C1F1 (the mole ratio of Co/Fe is 1:1) electrode acquires a high sensitivity of 0.293 μA μM toward 2,4-Dinitrotoluene (2,4-DNT) detection. Besides, C1F1 exhibits excellent stability, reproducibility and practicality for 2,4-DNT detection. Combined with experimental studies and theoretical calculations, it is shown that during the phase transition, electrons are transferred from Co to Fe, forming electron-rich Fe active sites. The Fe sites can match well with free 2,4-DNT molecules and then accelerate the reduction process of 2,4-DNT. A series of experiments including DFT and electrochemistry demonstrate that the doping-induced structural phase transition strategy can improve the adsorption performance of the material and also enhance the catalytic ability, thereby enhancing the electrochemical sensitivity. The co-engineering of morphology and phase transition of metal selenides by doping will provide inspiration for the design of sensitive sensing interfaces for organic pollutants.