Designing Mg-enhanced cobalt silicate @13X core-shell nanostructures via in-situ growth: synergistic PMS activation and anti-leaching for efficient metronidazole mineralization

Abstract In this study, the core-shell nanostructure of magnesium reinforced cobalt silicate@13X was synthesized by a two-step reaction using zeolite 13X as the initial silicate material and carrier, and the organic pollutant metronidazole was degraded by activating PMS. It was found that 6CoMg-13X had excellent and stable catalytic performance on PMS activation, with a degradation rate of 99.7% in 5 min and a removal rate of more than 99.4% after 5 cycles. Under hydrothermal conditions, 13X gradually dissolved into silicate anion under the action of urea, while Co²⁺ and Mg²⁺ reacted on 13X surface to form ultra-thin core-shell nanostructures. The calcination process further improves the stability of the catalyst while reducing cobalt leaching, after calcination, cobalt leaching is only 0.16 mg l⁻¹. In addition, the catalyst had high degradation rates for norfloxacin (NFA), 5-fluorouracil (FLU), tetracycline (TC) and Rhodamine B (RhB), which were 90.29%, 97.36%, 96.24% and 99.69%, respectively. EPR and quenching experiments indicated that SO₄‧⁻ and ¹O₂ are the main active substances in the 6CoMg-13X-PMS system, and ‧OH and ‧O₂ ⁻ also play a certain role in the degradation system. This research provides a feasible solution for developing high performance cobalt-based environmental purification catalysts.