Electron-rich ketone-based covalent organic frameworks supported nickel oxyhydroxide for highly efficient peroxymonosulfate activation and sulfadiazine removal: Performance and multi-path reaction mechanisms

Abstract

NiOOH/PMS system suffers from relative lower catalytic performance of PMS activation on the degradation of extremely recalcitrant organic pollutants and potential high risk of leaching Ni(II) ions. To address these, ketone-based covalent organic frameworks (COFs) with electron-deficient and electron-rich areas and large surface area was employed as a novel 2D carbon supporter to synthesize NiOOH@COFs composite. It turned out that the reaction rate constant of sulfadiazine in the NiOOH@COFs/PMS (0.1221 min−1) was 2.06 and 2.39 times than that in the NiOOH/PMS (0.0594 min−1) and COFs/PMS system (0.0509 min−1), respectively. This was attributed from the efficient synergic effect of NiOOH and COFs on the PMS activation, resulting in faster and more production of multiple reactive oxygen species (ROS) (SO4−, OH, O2− and 1O2). Specifically, the PMS could be reduced around the electron-rich oxygen atom of the ketone for radical (SO4−, OH) generation, and could be oxidized over the electron-deficient carbon atom of the ketone for the non-radical (1O2) generation. Moreover, NiOOH can active PMS to simultaneously generate non-radical (1O2) and radicals (SO4−, OH, and O2−). 1O2 is distinguished as the dominant ROS contributing to the degradation of sulfadiazine. Furthermore, the leaching of total Ni ions is reduced by 72% than counterparts from NiOOH, demonstrating improved stability and reusability. Hence, this study provides new insights into the multi-path mechanism of the synergistic PMS activation by NiOOH and ketone-COFs, and sheds new light on the development of efficient metal-free catalysts with rich-electronic structure for peroxymonosulfate-mediated environmental remediation.