NaOH-modified biochar supported Fe/Mn bimetallic composites as efficient peroxymonosulfate activator for enhance tetracycline removal

The activation mechanism of PMS on Fe-Mn/AW-BC for TC degradation. • Nanosheets-like Fe-Mn co-doped NaOH-modified porous BC (Fe-Mn/AW-BC) are prepared. • The biochar inhibits metal ion release and improves the stability of the composite. • Fe-Mn/AW-BC activating PMS for treatment of various pollutants and water environments. • The mechanism of Fe-Mn/AW-BC activating PMS was revealed. In this study, NaOH-modified biochar supported Fe/Mn bimetallic composite (Fe-Mn/AW-BC) was prepared to remove tetracycline (TC) through activating peroxymonosulfate (PMS). Results showed that about 97.9% of TC was degraded and the rate constant of Fe-Mn/AW-BC+PMS system was 37 folds higher than BC+PMS system. Experimental results confirmed that both radical and non-radical pathway were contribute to the catalytic system. Density functional theory (DFT) results also suggested that Fe-Mn/AW-BC sample was favorable for adsorbing PMS based on the length O-O bond from PMS and the E ads of catalysts. The superior activation ability was ascribed to the accelerating formation of reaction active species and other oxidation species by bimetallic structures of Fe-Mn and oxygenated functional groups of BC. Additionally, the redox cycles of Fe 3+ /Fe 2+ and Mn 3+ /Mn 2+ under Fe-Mn-BC synergism promoted the generation of the radicals, whereas the carbon shell effectively inhibited metals leaching of Fe-Mn/AW-BC, and 77.8% of TC can be still removed within 60 min after five consecutive cycles. Notably, Fe-Mn/AW-BC system has special characteristic of wide pH usable range and broad-spectrum adaptability towards various organic pollutants and various water environments. Based on intermediate identification and Fukui function calculation, the degradation pathways of TC were also proposed. This study highlights the applications of biochar for the environmental catalysis.