Heterojunctions engineered electron-deficient Co/oxygen vacancy-rich MnO2 triggers local built-in electric field within porous carbon fiber for PMS activation and rapid pollutant degradation

Abstract

The advanced oxidation process presents a perfect solution for eliminating organic pollutants in water resources, and the local microenvironment and surface state of metal reactive sites are crucial for the selective activation of peroxomonosulfate (PMS), which possibly determines the degradation pathways of organic contaminants. In this study, by virtue of the precursor alternation, we constructed the state-switched dual metal species with the porous carbon fibers through the electrospinning strategy. Impressively, the optimal catalyst, featuring the electron-deficient cobalt surface oxidative state and most abundant oxygen vacancies (Ov) with MnO₂ within porous carbon fibers, provides abundant mesoporosity, facilitating the diffusion and accommodation of big carbamazepine molecules during the reaction process. Benefiting from the tandem configuration of carbon fiber-encapsulated nanocrystalline species, a p–n heterojunction configuration evidenced by Mott–Schottky analysis induced local built-in electric field (BIEF) between electron-deficient cobalt and Ov-rich MnO₂ within carbon matrix-mediated interfacial interactions, which optimizes the adsorption and activation of PMS and intermediates, increases the concentration of reactive radicals around the active site, and significantly enhances the degradation performance. As a result, the optimal catalyst could achieve 100% degradation of 20 ppm carbamazepine (CBZ) within only 4 min with a rate constant of 1.099 min⁻¹, showcasing a low activation energy (50 kJ mol⁻¹), obviously outperforming the other counterparts. We further demonstrated the generation pathways of active species by activation of PMS mainly including sulfate radical (·SO₄⁻), hydroxyl radical (·OH), superoxide radicals (·O₂⁻), and singlet oxygen (¹O₂), unveiling their contribution to CBZ degradation. The degradation route of CBZ and toxicity analysis of various intermediates were further evaluated. By anchoring the optimal catalyst onto polyester fiber sponge, the photothermal conversion synergistic monolith floatable catalyst and its easy recovery can be achieved, showing good reproducibility and generalizability in the practical application.

Graphical abstract