In-situ growth of zero-valent iron in FeOx/Mn3O4 to improve the surficial redox for high-efficient electrocatalysis of Pb(II)

Fruitful achievements on electrochemically detecting Pb(II) have been achieved in virtue of the excellent adsorption property of nanomaterials, while ignoring the surficial redox and electrons transfer process. Due to the severe toxicity, trace concentration of Pb(II) in complex samples, the efforts to improve the sensitivity and selectivity of the sensing interface are still ongoing. Herein, FeOx/Mn3O4 nanocomposites have been successfully prepared with the generation of high-energy structures of Mn-O-Fe bonds. Surprising, electrons outflowed from Mn3O4 through Mn-O-Fe, thus in-situ growing zero-valance Fe metal. Although FeOx/Mn3O4 showed worse adsorption of Pb(II) than Mn3O4, the electrochemical sensing interface based on which obtained an ultrahigh sensitivity of 111.89 mu A mu M-1 with a limit of detection (LOD) of 0.01 mu M toward Pb(II), far more significant than the reported results. Moreover, the high-energy interfacial Mn-O-Fe in FeOx/Mn3O4 promoted the process of electrons transfer, which also have a strong interaction with Pb(II). Besides, Mn(II)/Mn(III) and Fe(II)/Fe(III) cycles on the surface of FeOx/Mn3O4 were confirmed to actively participate in the electrocatalysis of Pb(II), and Fe(0) with plentiful electrons further accelerated the surficial redox, thus ensuring the high sensitivity. Significantly, FeOx/Mn3O4 modified electrodes showed high selectivity due to the selective adsorption, which also has excellent stability, reproductivity and practicability in actual water samples. This work provides guidelines for constructing sensitive interfaces toward ultra-low concentrations of pollutants, which is of great significance for practical engineering application of electrochemical sensors.