Selective Arsenic Removal from Groundwaters Using Redox-Active Polyvinylferrocene-Functionalized Electrodes: Role of Oxygen.

In this work, we investigate selective sorption of arsenic from simulated groundwaters at pH 8 by a redox-active polyvinylferrocene (PVF)-functionalized electrode using a modified double potential step chronoamperometry (DPSC) method. Our results show that effective and sustainable As(III) removal can be achieved at 0 V once the electrode is activated via anodic polarization. During activation, ferrocene (Fc) in PVF is oxidized to the ferrocenium ion (Fc+) with the latter facilitating As(III) sorption and subsequent oxidation as well as As(V) sorption. The high affinity of Fc+ to As and weak attraction to competing anions at 0 V ensure high selectivity of As over Cl-, SO42-, and NO3- at concentrations typical of groundwaters. Following the removal process, efficient regeneration of the electrode is achieved at -1.2 V wherein Fc+ is reduced to Fc thereby facilitating As desorption from the electrode surface. Our results further show that O2 and associated generation of hydrogen peroxide during the regeneration step drive the oxidation of Fc to Fc+, thereby maintaining the constant generation of Fc+ required to achieve As(III) removal in subsequent cycles. Our results show that 91.8 ± 0.6% of As(III) could be selectively removed from simulated groundwater over 10 cycles at an ultralow energy consumption of 0.12 kWh m-3.