Engineering surface electron and active site at electrochemical sensing interface of CN vacancy-mediated Prussian blue analogue for analysis of heavy metal ions

Highlights: • An unconventional CN vacancy-mediated Mn-Fe Prussian blue analogue hollow structure is synthesized. • A highly sensitive electrochemical sensing interface is constructed via engineering surface electron and active site. • The surface electron transfer dynamic and active sites are optimized via plasma treatment. • The electron transfer from Fe to Mn atoms is caused by vacancy, rendering the Mn as reactive sites. • Pb(II) has a strong interaction with active site of Mn atom. The concept of creating crystal defect sites at interface of sensing materials is of ultimate importance for electrochemical sensing performance, yet the status of surface electron transfer and specific location of active sites for analyte remain unclear at the atomic level. Here, we construct a highly sensitive electrochemical sensing interface via engineering surface electron and active site on the unconventional CN vacancy (V_CN)-mediated Mn-Fe Prussian blue analogue (PBA) hollow structure. We modulate the surface electron transfer dynamic and identify specific reaction location of V_CN-mediated Mn-Fe PBA to obtain a limit of detection of 0.013 μM (3σ method) with a high sensitivity of 7193.64 μA cm⁻² μM⁻¹ toward Pb(II), which is fifteen that of pristine Mn-Fe PBA (without V_CN). By combining experiments with theoretical calculations, we demonstrate that the V_CN regulate the electron transfer from metal Fe to Mn atoms, rendering the Mn atoms as active sites for Pb(II) reaction. We also identify a relatively strong interaction between Mn atom and analyte Pb(II) by calculation result of great orbital overlapping of Mn–Pb bond. The adsorbed Pb(II) will undergo redox reaction in situ without considering adsorption-desorption rate on the surface of the sensing material.