Rapid electron transfer reinforced by interfacial Co-O bonding in MOF/COF hybrids for highly efficient degrade tetracycline by activating peroxymonosulfate

Abstract

Due to the low electron transfer rate of zeolitic imidazolate framework-67 (ZIF-67)/ peroxymonosulfate (PMS) system, it suffers from a weak degradation ability for refractory pollutants and a risk of leaching of Co2+. In order to overcome these, covalent organic framework (COF) materials with excellent electron excitation and transfer ability are formed into a core-shell structure with ZIF-67. Thanks to the tight contact between the two materials, electrons could migrate rapidly between materials after being excited, helping to stimulate PMS to produce more reactive oxygen species (ROS) to participate in the degradation process. The abundant N and O elements in COF are also attracted to Co2+ in ZIF-67, forming more stable Co-O and Co-N sites. The formation of the Co-N site contributes to the release of CO, which is previously inhibited by N in COF. In this way, the catalytic activity of PMS is further enhanced. According to the experimental results, COF@ZIF-2/PMS system shows excellent TC degradation performance, with a degradation rate of up to 90.20% at 30 min, which is 15.03 times that of COF (6.00%) and 2.24 times that of ZIF-67 (40.12%). In order to be closer to the experimental environment of natural water, the influence of anions is explored. Through liquid chromatography-mass spectrometry (LC-MS) experiment, the intermediate products existing in TC degradation are analyzed and their toxicity is explored. To further explore the free radical pollution that plays a role in the degradation process, a free radical trapping test is carried out. Single oxygen (1O2) and sulfate radicals (SO4•-) act as the major ones in the system. Generally, this work provides a new idea for improving the catalytic activity of PMS by accelerating the electron transfer of the material through the construction of core-shell structure and the formation of Co-O/Co-N sites.