Sulfate Radical Oxidation of Aromatic Contaminants: A Detailed Assessment of Density Functional Theory and High-Level Quantum Chemical Methods

TL;DR

This study compares density functional theory and high-level quantum methods to accurately predict the reaction kinetics of sulfate radical-driven oxidation of aromatic contaminants, highlighting the strengths and limitations of various computational approaches.

Contribution

It provides a comprehensive assessment of computational methods for modeling sulfate radical oxidation, emphasizing the need for high-level calculations for accurate environmental chemistry predictions.

Findings

M06-2X DFT is more accurate for HO-additions than for SO4•- reactions.

High-level coupled-cluster methods reveal limitations of common DFT functionals.

Recommendations for using high-level calculations to validate environmental reaction models.

Abstract

Advanced oxidation processes that utilize highly oxidative radicals are widely used in water reuse treatment. In recent years, the application of sulfate radical (SO$_4\cdot^-$) as a promising oxidant for water treatment has gained increasing attention. To understand the efficiency of SO$_4\cdot^-$ in the degradation of organic contaminants in wastewater effluent, it is important to be able to predict the reaction kinetics of various SO$_4\cdot^-$-driven oxidation reactions. In this study, we utilize density functional theory (DFT) and high-level wavefunction-based methods (including computationally-intensive coupled cluster methods), to explore the activation energies and kinetic rates of SO$_4\cdot^-$-driven oxidation reactions on a series of benzene-derived contaminants. These high-level calculations encompassed a wide set of reactions including 110 forward/reverse reactions and 5 different computational methods in total. Based on the high-level coupled-cluster quantum calculations, we find that the popular M06-2X DFT functional is significantly more accurate for HO-additions than for SO$_4\cdot^-$ reactions. Most importantly, we highlight some of the limitations and deficiencies of other computational methods, and we recommend the use of high-level quantum calculations to spot-check environmental chemistry reactions that may lie outside the training set of the M06-2X functional, particularly for water oxidation reactions that involve SO$_4\cdot^-$ and other inorganic species.