Promotion of Formaldehyde Degradation by Electro-Fenton: Controlling the Distribution of ·Oh and Formaldehyde Near Cathode to Increase the Reaction Probability

Abstract

The mismatch of pollutant concentration and ·OH concentration is the key reason for inefficiency degradation of formaldehyde in the electro-Fenton system. Therefore, formaldehyde and ·OH are adsorbed near the cathode and constructed the high-concentration reaction region to increase the reaction probability, which is called reaction region control. Appropriate nitrogen-doped activated carbons were adopted as electro-Fenton cathode to achieve reaction region control. The adsorption capacity of nitrogen-doped activated carbon cathode for formaldehyde and active species, and the synergistic effect on the selectivity of the two-electron oxygen reduction reaction were deeply analyzed. The promotion of formaldehyde degradation by electro-Fenton with nitrogen-doped cathodes was proved by reaction region control. The results show that mesoporous structure and nitrogen doping form of cathodes could significantly promote the adsorption of formaldehyde and H2O2, which are beneficial to realize reaction region control. Graphite nitrogen and pyrrolic nitrogen improve the adsorption of formaldehyde (8.897 mg·g-1) by enhancing van der Waals force, pyridinic nitrogen improve the adsorption of H2O2 (1.841 mg·g-1) by enhancing electrostatic interaction. Simultaneously, nitrogen doping improves the yield of ·OH which contributed to the degradation of formaldehyde. The realization of reaction region control through electro-Fenton cathode modification to achieve 35.1 mg·L-1 of formaldehyde degradation (48.51% higher than that of unmodified cathode), which provided a promising process for the treatment of formaldehyde.

Keywords: formaldehyde, Reaction region, electro-Fenton, Activated carbon, Nitrogen-doped, Density functional theory