Engineering multi-shell Mn-Co oxide for ultrasensitive electroanalysis of Pb(II) in mining subsidence area water with promotion of adsorption and electron mediation: Behaviors and mechanisms of Mn(II)/Mn(III) and Co(II)/Co(III) cycles

Abstract

It still remains unclear that the intrinsic structure-sensing property interplay of diverse transition metal oxides based sensing materials, although they have been applied in the field of environmental analysis and have achieved great progress. In this work, we performed X-ray photoelectron spectroscopy (XPS), Brunauer-Emmett-Teller (BET) and in situ electrochemical experiment to investigate the structure-sensing interplay of Mn-Co oxide (MnCo2O4) multi-shell hiberarchy microsphere. The comprehensive studies conclusively show that the active sites on MnCo2O4 surface work as key role in determining the electrochemical behavior through the aspect of adsorption and electrocatalytic activity. In detail, the exposed oxygen on the surface of MnCo2O4 forming amounts of –OH can act as grippers to adsorb the Pb(II) in water, and then the adsorbed Pb(II) can directly occur redox in situ by the mediation of Mn(II)/(III) and Co(II)/(III) cycle on the exposed Mn and Co active sites. As a result, an excellent electroanalytical behavior (sensitivity of 120.72 µA µM−1) toward Pb(II) could be effectively improved on MnCo2O4. The fabricated electrode also showed impressive electroanalytical performance for Pb(II) in mining subsidence area. Our findings will provide new insights and effective directions for designing ultr-sensitive nanomaterials based on variable valence mediation engineering in tuning the activity of transition metal oxides.