Origins of selective differential oxidation of β-lactam antibiotics with different structure in an efficient visible-light driving mesoporous g-C3N4 activated persulfate synergistic mechanism

Abstract

In the study, an efficient ‘1 + 1 > 2′ synergistic coupling system driven by visible light consisting of mesoporous g-C3N4 (MCN) and persulfate (PS)was constructed. The free radical transformation, electron transfer and non-covalent interaction between the MCN layer and PS in the system were explored via experiments and DFT calculations. The similarity for the fate of the seven β-lactam antibiotics with typical structures in the oxidation system was studied systematically in depth. First, the consistencies and differences of the seven antibiotics were summarized from three aspects: three-dimensional structures, electron cloud distributions, and the vulnerable sites. Notably, the selective differential degradation of β-lactam antibiotics in the MCN/PS system was speculated to be related with the molecular ionization potential (MIP), as a key index to describe the difficulty of oxidation. The distribution relationship between MIP and the oxidation kinetic constant (K) was explored and showed the following trend: a higher MIP indicates a weaker ability to provide electrons, and this leads to a greater resistance to oxidative degradation. In total, four main oxidation pathways of β-lactam antibiotics were systematically summarized combining HPLC-QTOF-MS and the simplified Fukui function calculation. The toxicity assessment of intermediate products provided by the T.E.S.T software of USEPA also shows a decreasing trend in the oxidation process. In the end, the superior practicability and stability of the MCN/PS system was verified by complex environment simulation and cyclic test. This research clarified the selective differential degradation mechanism of β-lactam antibiotics and provided a possible idea for the effective removal of refractory organic pollutants in water.