Altering peroxymonosulfate activation path for ¹O₂ production on ZIF-67 with coordinatively unsaturated metal sites

Abstract

In Fenton-like reaction activated by peroxymonosulfate (PMS), compared to SO₄^•– produced via the electron acceptance path, ¹O₂ generated from electron donation path were more attractive. Herein, PMS activation path was altered from SO₄^•– to ¹O₂ through improving Lewis acidity on catalytic sites. During ZIF-67 preparation, vanillin (VAN) was introduced to regulate the chemical environment around the Co^3+/2+ nodes. The coordinated N atoms in 2-methylimidazole were partially substituted by O atoms in VAN, leading to the enhanced Lewis acidity on Co^3+/2+ sites. In this case, Lewis base PMS were likely to donate electrons to electron-deficient Co^3+/2+ sites, and ¹O₂ were generated as the primary radicals. Besides, coordinatively unsaturated metal sites (CUMSs) were produced during the substitution process, since Co^3+/2+ nodes were not fully bridged by VAN ligands. This improved the PMS utilization efficiency and ¹O₂ yield. Previous studies have indicated the metal leaching would be worsened by CUMSs, owing to the lack of ligand protection. To solve this problem, a Co₂SiO₄ shell was coated on VAN-ZIF-x surface. VAN-ZIF-x@Co₂SiO₄ yolk@shell nanoreactor not only suppressed the metal leaching, but also improved the environmental adaption. This paper gave a novel insight on altering the PMS activation path, together with the CUMSs creation on catalyst surface.

Graphical abstract

Keywords

Fenton-like reaction / Vanillin / Yolk@shell nanoreactor / Coordinatively unstaurated metal sites / PMS utilization efficiency

Highlight

	● Lewis acidity on Co3+/2+ sites are enhanced via simply introducing VAN molecule.
	● PMS activation path are changed from SO4•– to 1O2 by improving Co3+/2+ Lewis acidity.
	● CUMSs are generated on Co3+/2+ surface, leading to high PMS utilization and 1O2 yield.
	● k value in MB degradation over VAN-ZIF-1@Co2SiO4 is 6.8 times higher than ZIF@Co2SiO4.
	● Under Co2SiO4 shell protection, nanoreactor shows low leaching and high stability.

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