Manganese oxide-functionalized graphene sponge electrodes for electrochemical chlorine-free disinfection of tap water

Abstract

Low-cost reduced graphene oxide sponges functionalized with manganese oxide were used as electrodes for the disinfection of Escherichia coli in water. Manganese oxide was doped with amino groups (MnxOyNH2) to strengthen the bond with the graphene coating and improve the electrochemical stability of the sponge. The Mn II and Mn III incorporated into the graphene coating favored the formation of oxygen vacancies and enhanced the electric and catalytic properties of the anode. Electrooxidation of real tap water at 29 A/m−2 resulted in 2.2 log removal of E. coli. After storing the treated samples for 18 h at 25 and 37 °C, the removal of E. coli increased to 3.3 and 4.6 log, respectively, demonstrating the irreparable damage to the bacterial cells via low-voltage electroporation, and the key role of storage temperature in their further inactivation. The energy consumption of the system treating real low conductivity tap water was 1.2–1.6 kWh m−3. Finally, experiments with intermittent current suggest the contribution of the pseudo-capacitance of the graphene sponge to electrochemical disinfection during the OFF periods. This study demonstrates the feasibility of manganese oxide-functionalized graphene sponges for the chlorine-free disinfection of water.