Realizing higher activity in Fenton-like reaction on less catalytic sites by using Zn²⁺ to regulate electronic structure of ZIF-67

In peroxymonosulfate (PMS)-based Fenton-like reaction, more catalytic sites could improve PMS activation but also increase metal leaching. Could the activity be well-preserved, or even improved under the low catalytic site numbers? Herein, Zn²⁺ were introduced into ZIF-67 to regulate Co^3+/2+ electronic structure. By manipulating the reaction kinetics between 2-methylimidazole and two metallic ions, ZnCo-ZIF-x (60% ≤ x ≤ 90%, x was molar ratio of Zn²⁺/(Zn²⁺+Co²⁺)) with homogeneous distribution of bimetallic nodes were prepared. Compared to other ZnCo-ZIF-x (10% ≤ x ≤ 50%) with Co-rich core@Zn-rich shell structure, ZnCo-ZIF-90% exhibits: (i) more exposed Co^3+/2+ sites; (ii) more pronounced regulated effect of Zn²⁺ on Co^3+/2+ electronic structure; (iii) higher Lewis acidity on electron-deficient Co^3+/2+ sites; (iv) faster electron transfer between bimetallic sites. Although Co^3+/2+ sites in ZnCo-ZIF-90% was only one tenth of ZIF-67, PMS activation and degradation performance were better. Meanwhile, Co^3+/2+ leaching was only 0.14 mg·L⁻¹, due to less Co^3+/2+ sites. Mechanism study disclosed the important role of Co^3+/2+ electronic structure reconstructed by Zn²⁺, and the regulated effect was amplified by uniform dispersion of bimetallic sites. Zn²⁺ altered PMS activation path from radical path to non-radical one on ZnCo-ZIF-90%. This work provides an insight for designing effective catalysts with low environmental risks, and offers significant potential for environmental remediation.