Role of cobalt incorporation in the photo-Fenton activity of magnetite under natural solar irradiation

Magnetite based catalysts have been extensively studied for the decomposition of hydrogen peroxide for generation of hydroxyl radicals (HO • ) through Fenton reaction aiming environmental applications. A series of cobalt containing magnetite (Co x Fe 1-x )Fe 2 O 4 , with x = 0, 0.25, 0.50, 0.75, and 1) was synthesized and correlated to photo-Fenton process efficiency under natural solar irradiation under near neutral conditions. The magnetites were characterized by X-ray diffraction (XRD), specific surface area, scanning electron microscopy (SEM), zeta potential (ZP) and X-ray photoelectron spectroscopy (XPS). The cobalt incorporation on magnetite structure enhanced by two times the catalytic activity regarding H 2 O 2 decomposition (k = 3.98 × 10 −03 min −1 for (Co 0.25 Fe 0.75 ) Fe 2 O 4 against 2.06 × 10 −03 min −1 for Fe 3 O 4 ). (Co 0.25 Fe 0.75 )Fe 2 O 4 completely degraded trimethoprim (TMP) and sulfamethoxazole (SMX) after 170 kJ m −2 (∼90 min), achieving concentration below the limit of detection at pH 5.5, without metal leaching, ensuring a heterogeneous process. The catalyst demonstrated stability over four reuse cycles and high performance in an effluent from a local Wastewater Treatment Plant (WWTP), with 85% and 76% degradation of TMP and SMX, respectively. These findings highlight the viability of its use under natural solar irradiation for the treatment of WWTP effluents at circumneutral conditions and recyclability, overcoming the main limitations of conventional Fenton systems. • Cobalt doping increased H 2 O 2 decomposition rate by ∼13% for SMX degradation. • (Co 0.25 Fe 0.75 )Fe 2 O 4 removed 100% TMP and SMX 90 min under solar irradiation • No detectable metal leaching (< 0.125 mg L −1 for Fe and 0.05 for Co) was observed. • No activity loss was observed after four reuse cycles • 85% TMP and 76% SMX removal were achieved in real wastewater.