Yolk@Shell nanoreactors with spatial confinement cobalt species activate peroxymonosulfate for efficient degradation of bisphenol S

Abstract

Cobalt-based multiphase catalysts can effectively activate peroxymonosulfate (PMS) and degrade organic pollutants. However, their practical application faces critical challenges, including insufficient exposure of active sites, slow reaction kinetics, and cobalt ion leaching, which collectively reduce catalytic efficiency and sustainability. Although there have been attempts to improve the catalytic efficiency through structural modifications such as core-shell structure or porous design, these strategies are still difficult to optimize the active site exposure and cobalt ion stability simultaneously. To overcome these limitations, here we propose a novel triple-shell yolk@shell architecture (3YS-Co@NC) constructed via a stepwise strategy involving crystal extension growth, selective etching, and calcination. The optimized nanoreactor degraded 100 % of bisphenol S (BPS) within 12 min with a rate constant (0.342 min⁻¹) 9.5-, 2.34-, and 1.49-fold higher than solid nanoparticles (Co@NC), single-shell (1YS-Co@NC), and double-shell (2YS-Co@NC) counterparts, respectively. Notably, the TOC removal rate of 3YS-Co@NC reached 71 %, surpassing those of 1YS-Co@NC (53 %), 2YS-Co@NC (65 %), and Co@NC (21 %). The enhanced performance results from (i) the yolk@shell structure providing nanoreaction cavities and abundant active sites, and (ii) the robust Co⁰/Co²⁺/Co³⁺ redox cycling. Quenching experiments and EPR analysis revealed that SO₄^•- and •OH dominated PMS activation, while O₂^•- played an auxiliary role. In contrast, ¹O₂ exhibited negligible contribution. LC/MS analysis identified key degradation intermediates, and the ECOSAR model predicted reduced biotoxicity of these products. This study not only promotes the development of advanced oxidation processes, but also provides a new insight into the design of cobalt-based catalysts.