Electromagnetic-wave assisted rapid synthesis of MOF with coordination unsaturated metal sites for enhanced activity in Fenton-like reaction

As Lewis acidic sites, coordination unsaturated metal sites (CUMSs) on ZIF-67 surface were widely employed to accelerate PMS (Lewis base) activation in Fenton-like reaction. Nevertheless, it usually took at least several hours to produce CUMSs, resulting in a low-efficient process and limited yield. To overcome the shortcoming, herein, an alternating electromagnetic field was used to shorten preparation time by precisely generating heat-energy on magnetic Co 3+/2+ sites. Merely 2.0 min later, the CUMSs number had peaked in yolk@shell ZIF-67@Co 2 SiO 4 -2 nanostructure. They displayed better PMS utilization efficiency (49.7 %) and MTZ degradation efficiency (99.8 %) than reference catalysts in Fenton-like reaction. The activation energy of MTZ degradation over ZIF-67@Co 2 SiO 4 -2 was 31.51 kJ/mol, which was much lower than the activation energy in absence of catalysts (103.14 kJ/mol). In mechanism study, the important role of Co 2 SiO 4 shell in controllable CUMSs production, the degradation contribution of various reactive species, the source the primary 1 O 2 , the confinement effect inside the yolk@shell nanostructure and the enhanced Lewis acidity on CUMSs were revealed by Electron Paramagnetic Resonance analysis, radical trapping experiment and NH 3 -Temperature Programmed Desorption analysis. This study provides a feasible method for the rapid removal of organic groups on the outer surface of ZIF-67 to prepare more CUMSs. ZIF-67@Co 2 SiO 4 -2 with CUMSs were rapidly prepared within several seconds under the electromagnetic-wave field, and they showed outstanding catalytic activity in Fenton-like reaction. • CUMSs are created on ZIF-67 surface within only 2.0 min by electromagnetic-wave. • PMS activation efficiency is 49.7 % on ZIF-67@Co 2 SiO 4 -2, higher than ZIF-67@Co 2 SiO 4 . • MTZ degradation rate on ZIF-67@Co 2 SiO 4 -2 is quicker than those on reference samples. • Co 2 SiO 4 shell played key role in controllable creation of CUMSs. • Contribution of radicals and 1 O 2 followed order: 1 O 2 (41.9 %)> • OH+SO 4 •- (37.8 %)> • O 2 - (20.3 %).