Quantitative structure-activity relationship for the apparent rate constants of aromatic contaminants oxidized by ferrate (VI)

Hexavalent ferrate, Fe(VI), is a promising oxidation-coagulation dual-functional reagent for removing aromatic contaminants (ACs) in water engineering systems. Recognizing that an increasing number of ACs are being used and introduced to the engineered waters, experimental measurements of the Fe(VI) oxidation kinetics, especially apparent second-order rate constants (k(app)) are relatively expensive for these numerous organic compounds. Therefore, reliable models are highly demanded for predicting k(app) of Fe(VI) oxidation of ACs with wide structural diversity and reactivity. In the present study, a quantitative structure-activity relationship (QSAR) model was developed for the k(app) predication at pH = 7 using stepwise multiple linear regression analysis (MLR) with the training set (n = 26). The standardized QSAR model was obtained: lnk(app) = 34.7 4.80 x IP, where IP is the ionization potential. The internal (Q(Loo)(2) = 0.81, n = 26) and external validation (Q(ext)(2) = 0.82, n = 8) indicates a robust prediction for k(app). Further, we compared the predicted k(app) with experimental k values for Fe(VI) oxidation of phenolic compounds, and demonstrated that possible first step reaction pathways depends on different electron donating/withdrawing abilities of the functional groups, corroborating the mechanistic meaning of IP in the QSAR model. The QSAR model developed is helpful in understanding the degradation mechanisms of ACs by Fe(VI), and the predicted kapp values provide a basis to optimize the Fe(VI) oxidation of ACs during wastewater treatment processes. (C) 2017 Elsevier B.V. All rights reserved.