Quantitative structure-activity relationship study on the degradation of polyhalogenated carbazoles by sulfidated zero-valent iron/peroxymonosulfate system

Abstract

Polyhalogenated carbazoles (PHCs) are an emerging class of halogenated organic contaminants, which have widespread occurrence and dioxin-like toxicities. However, effective approaches for PHCs degradation are lacking. Recently, persulfate based advanced oxidation processes (AOPs) are considered as promising technologies for aqueous organic contaminants destruction due to the high reactivity and selectivity of sulfate radical. In this study, the degradation kinetics and mechanism of PHCs by sulfidated zero-valent iron/peroxymonosulfate (S-ZVI/PMS) system were investigated. The pseudo-first-order rate constants (k) of 11 PHCs ranged from 0.051 to 1.623 min−1. Seventeen quantum chemical descriptors were calculated based on density functional theory (DFT). By using correlation analysis, principal component analysis (PCA) and multiple linear regression (MLR), a quantitative structure activity relationship (QSAR) model was developed: log k = 8.681 ×f(0)n + 0.231 × #X – 0.593, where f(0)n and #X represent the minimum value of Fukui index for radical attack and the halogen number, respectively. The correlation analysis and model interpretation indicate that radical addition is the dominant reaction pathway for PHCs instead of single electron transfer (SET). Results of validation and applicability domain indicate that the developed QSAR model has good robustness and satisfactory predictive performance. Finally, the degradation kinetics of five frequently detected but commercially unavailable PHCs were predicted. The overall purpose of this study is to develop a predictive model and interpret the degradation mechanism of PHCs in PMS-AOP, which is difficult to be distinguished by experimental results alone.