Effect of an improved gas diffusion cathode on carbamazepine removal using the electro-Fenton process

Abstract

The aim of this study was to investigate the effect of the diffusion layer of a gas diffusion cathode (GDC) on H₂O₂ production to enhance carbamazepine removal using the electro-Fenton process. The diffusion layer was made by carbon black and polytetrafluoroethylene with sodium sulfate (Na₂SO₄) as a pore former. Different ratios of Na₂SO₄ to carbon black (w/w) (i.e., 0%, 50%, 100%, 150%, and 200%) in the diffusion layer were tested. With an increase of the ratio, the average pore size in the diffusion layer and the electro-activity in the GDC increased simultaneously, which resulted in a higher mass transfer coefficient of oxygen and H₂O₂ production. In an undivided cell with platinum as the anode and 5.0 g L⁻¹ Na₂SO₄ as the electrolyte, a maximum H₂O₂ concentration of 630 mg L⁻¹ was achieved within 120 min in the GDC with the ratio of 150%. With an initial carbamazepine concentration of 50 mg L⁻¹ and a current density of 5.0 mA cm⁻², the maximum carbamazepine removal efficiency and rate reached 71% and 35.5 mg L⁻¹ h⁻¹, respectively. The removal rates in this study were much higher than those in the literature (35.5 vs. 0.03–10.0 mg L⁻¹ h⁻¹), mainly attributable to the diffusion layer modified by the pore former, which accelerated oxygen transfer and boosted H₂O₂ production. The results from this study should be useful to remove carbamazepine from wastewater treatment using the electro-Fenton (EF) process with improvement of pore structure in the diffusion layer of GDC.