Immobilizing cobalt-iron bimetal on Al2O3 by electroless plating-calcination for peroxymonosulfate activation: Performance, mechanistic and practicality

Peroxymonosulfate (PMS) based advanced oxidation processes are promising technologies for emerging contaminants removal and exploring catalysts with high catalytic activity and low metal leaching for PMS activation gets a lot of attention. Herein, Co-Fe/Al2O3 was synthesized by electroless plating-calcination method. Characterizations indicated that Co and Fe were uniformly dispersed on the surface of Al2O3. Results demonstrated that Co-Fe/Al2O3-PMS system could achieve 100 % sulfamethoxazole (SMX) removal with kobs of 0.0552 min−1 under optimal conditions of [PMS] = 0.20 mM, [Co-Fe/Al2O3] = 50.0 mg/L, pH = 6.4. Compared with Co/Al2O3-PMS, Fe/Al2O3-PMS, Co-Fe/Al2O3 alone, and PMS alone, the developed Co-Fe/Al2O3-PMS system achieved a combination of high decontamination efficiency, efficient PMS utilization and insignificant Co leaching. The electrochemistry tests proved the electron transfer speed of Co-Fe/Al2O3 is much higher than that of Co/Al2O3 and Fe/Al2O3, suggesting the synergistic effect of Co and Fe to enhance catalytic activity. The catalytic mechanisms were proposed that both CoII and FeII could react with PMS to initiate activation with SO•− 4 formation as the major active species and the coexistence of Fe and Co on Al2O3 promoted the heterogeneous redox cycle of CoII/CoIII with CoII involving in PMS activation again. Furthermore, Cl− and H2PO − 4 facilitated SMX removal, while HCO3− and HA inhibited SMX removal. Co-Fe/Al2O3-PMS system could retain more than 80 % SMX removal within five cycles, indicating good stability and reusability of Co-Fe/Al2O3 for PMS activation. Aniline ring oxidation and isoxazole ring oxidation were proposed as dominant degradation pathways according to the detected intermediates of SMX degradation. This research was instructive to the development of PMS activation induced by supported bimetallic catalysts for wastewater treatment.