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"Double-yolk egg-like" Fe 3 O 4 /PBA@PPy nanoreactor is synthesized, where the confinement effect from the cavity, the protective effect from the PPy shell, and the magnetic property were successful integrated together. Therefore, it displayed the high degradation efficiency, low leaching, and rapid separation in Fenton-like reaction. [Display omitted] • k of Fe 3 O 4 /PBA@PPy-10 was 0.38 L·min·mol−1, 5.1 times than that of reference Fe 3 O 4 /PBA-10 in Fenton-like reaction. • The concentration of leached cobalt ions was reduced from 1.47 mg/L to 0.174 mg/L by the protective function from the PPy shell. • 84.5% of the degradation efficiency of the 1st cycle was still maintained after 4 cycles. • The core of Fe 3 O 4 make sure the catalyst can be rapidly separated by a magnet. • Mechanism of Fenton-like reaction is revealed in detail. Peroxymonosulfate (PMS)-based Fenton-like reaction is an effective technique for the pollutant degradation, and the Co-based metal organic frameworks displayed the excellent activity for the PMS activation. Nevertheless, how to further improve the catalytic activity, suppress the leaching of toxic cobalt ions, and realize the rapid separation were still challenges for practical application. In this work, a novel solution was proposed: encapsulating Fe 3 O 4 and Prussian blue analogue (PBA) into the polypyrrole (PPy) shell and constructing a "double-yolk egg-like" Fe 3 O 4 /PBA@PPy as a nanoreactor. In Fe 3 O 4 /PBA@PPy-10, the catalytic performance was remarkably enhanced with the help of confinement effect, and the degradation rate (0.38 L·min·mol−1) was 5.1 times than that of reference Fe 3 O 4 /PBA-10 (0.074 L·min·mol−1). In addition, the concentration of leached cobalt ions was reduced to only 0.174 mg/L by the protective function from the PPy shell. Moreover, the nanoreactor could be magnetically separated from the reaction solution due to the encapsulation of Fe 3 O 4 nanospheres, and 84.5% of activity still preserved after the 4th cycle. The main active species involved in Fe 3 O 4 /PBA@PPy-10 system was 1O 2 , while that in reference Fe 3 O 4 /PBA-10 system was OH. Electron spin resonance analysis and radical trapping experiment revealed that the different catalytic mechanisms were attributed to the confinement effect inside the hollow cavity. This work not only presents a feasible way to prepare rarely-reported double-yolk egg-like nanoreactor, but also provides a new insight to solve the bottlenecks in Fenton-like reaction. [ABSTRACT FROM AUTHOR]

In peroxymonosulfate (PMS)-based Fenton-like reaction, there were two pathways for PMS activation: radical path on transition metal surface and non-radical path on heteroatom-doped carbon surface. In this work, CoS 2 /nitrogen-atom doped carbon (NC)@SiO 2 yolk@shell nanoreactor was designed, on CoS 2 /NC surface, these two paths performed parallelly inside the nanoreactor, leading to an accelerated tetracycline degradation rate. 90.9% of removal efficiency was realized within 15 min, much higher than the reference samples, and the advantages of yolk@shell nanoreactor were illustrated in detail. Moreover, benefiting from the SiO 2 shell protection, the leached cobalt ion was only 0.27 mg/L, which was 1/20 of the reference CoS 2 /NC without SiO 2 shell. During the mechanism study, the two activation paths were identified by electron paramagnetic resonance tests, radical trapping experiments and electrochemical tests, where the SO 4 •- and 1O 2 were responsible for tetracycline (TC) degradation. This study provided a new strategy to simultaneously accelerate radical activation path and non-radical activation path by using the yolk@shell nanoreactor, and it might inspire other high efficient catalyst design for PMS-based Fenton-like reaction. [Display omitted] CoS 2 /NC@SiO 2 yolk@shell nanoreactor with CoS 2 /NC nanoparticles encapsulated inside the SiO 2 shell was prepared as a catalyst in Fenton reaction. • Radical and non-radical PMS activation paths are confined in CoS 2 /NC@SiO 2 nanoreactor. • Removal rate of CoS 2 /NC@SiO 2 is 3.6×10−2 L·min·mg−1, better than reference samples. • Co3+/2+ leaching is lowered to 0.27 mg/L due to the SiO 2 shell protection. • SO 4 •- and 1O 2 are responsible for TC degradation, and catalytic mechanism are studied. • Nanoreactor shows good versatility, recyclability, and anti-interference ability. [ABSTRACT FROM AUTHOR]

Yolk@shell nanoreactor with coordinately unsaturated metal sites on Prussian blue analogue nanocubes surface inside the polypyrrole capsule was prepared, in which improving catalytic activity and lowering metal leaching were simultaneously realized. [Display omitted] • Improving activity and lowering leaching are simultaneously realized in nanoreactor. • Nanoreactor show high PMS utilization efficiency and TC mineralization efficiency. • PMS activation is encouraged via Lewis acid-base reaction on CUMSs. • SO 4 − converts to OH and then to 1O 2 inside nanoreactor under confinement effect. • Metal leaching is suppressed under the protection of compacted PPy shell. In peroxymonosulfate (PMS)-based Fenton-like reaction, there was an irreconcilable contradiction between improving the catalytic activity and lowering the metal leaching, since the more catalytic sites exposed, the better activity and the easier leaching. In this work, we have provided a feasible method to address this problem by preparing yolk@shell structure with coordinately unsaturated metal sites on Prussian blue analogue (CUMSs-PBA) nanocubes surface inside the polypyrrole (PPy) capsule. On CUMSs-PBA surface, a large amount of metal sites were exposed and functioned as Lewis acid. As Lewis base, PMS adsorption and activation were encouraged via Lewis acid-base reaction, leading to an enhanced activation efficiency. PMS and pollutants were confined inside the yolk@shell nanoreactor with a limited cavity space, leading to an ultra-high concentration and accelerated degradation rate. In this case, the PMS activation path was altered, and the contributions of OH and 1O 2 were largely improved in comparison with SO 4 −. Generally, the metal leaching was worsened due to the lack of ligand protection on coordinately unsaturated metal sites. Fortunately, the PPy shell was compacted and the pore size on shell was narrowed during the heat-treatment, resulting in the suppression effect on outward diffusion of leached metal ions. Therefore, improving catalytic activity and lowering metal leaching were simultaneously realized in the CUMSs-PBA@PPy nanoreactor. [ABSTRACT FROM AUTHOR]