Efficient degradation of bisphenol A based on electron transfer pathway: ZIF-67@ZIF-8 and ZIF-8-derived nitrogen-carbon materials

Persulfate-based electron-transfer process (ETP) is appealing due to its high efficiency and tolerance of anions, natural organic matters and pH value in wastewater purification. Therefore, it is of great interest to design heterogeneous catalysts for achieving ETP. The pyrolyzation of zeolite imidazolate framework structure material (ZIF) is an ideal strategy to produce carbonaceous materials with evenly distributed metal atoms and repetitive properties. However, there are few studies on the active sites and mechanisms of BPA degradation catalyzed by PMS with different proportions of ZIF mixed material derivatives. In this study, three carbon-based composites obtained by control the ratio of Zn/Co at 1∶0, 40∶1 and 10∶1 in ZIF precursors were named as nitrogen carbon (NC), CoNx-rich amorphous cobalt nitrogen carbon (AP-CoNC) and nano cobalt nitrogen carbon (NP-CoNC), and their properties in the degradation of BPA via PMS activation were studied systematically. The experimental results showed that ETP was the dominant mechanism in the three PMS/BPA catalytic degradation systems, and more than 92% of BPA could be degraded in 10 min, and adsorption had a great impact on BPA degradation. In-situ Raman spectroscopy, open-circuit potential and ionic strength experiments indicated that nano-cobalt, CoNx and graphite nitrogen were the main active sites, and the adsorption mode was endospheric interaction, and coordinated compounds formed between terminal oxygen atom of the absorbed PMS and these active sites, and BPA provided electrons for ETP. At the same time, the degradation pathways of BPA in the three catalytic systems were mainly the classical coupling and oxidative ring-opening reactions by the electron transfer pathway, and all of them had the ability to resist anion, humic acid and pH change, but the reproducibility was poor. This study expands the application of ZIF-derived catalytic materials and provides the mechanism insights into the interaction between PMS and active sites.