Mechanistic inference on the reaction kinetics of phenols and anilines in carbon nanotubes-activated peroxydisulfate systems: pp-LFERs and QSARs analyses

There is increasing interest in persulfate (peroxydisulfate (PDS) and peroxymonosulfate (PMS)) activation by (non-toxic) metal-free catalysts for advanced oxidation of organic contaminants. Nevertheless, the non-radical reaction mechanisms of these catalytic reactions are not well understood. Herein, we provide mechanistic inference on the non-radical reaction pathway of the carbon nanotubes (CNTs)/persulfate system and the associated kinetics. We determined the initial degradation rates of 18 phenols and 4 anilines at various initial concentrations by commercial multiwalled carbon nanotubes (MWCNTs) and peroxydisulfate (PDS), which followed binary Langmuir–Hinshelwood kinetics. Polyparameter linear free energy relationships (pp-LFERs) and quantitative structure-activity relationships (QSARs) were developed for the equilibrium adsorption constant (K) and the surface reaction rate constant (kr). QSAR analyses for logK suggested that affinity interactions between organics and MWCNTs are mainly related to π-π interactions. The molecular volume term (V) in the pp-LEFRs contributes the most to the interaction, indicating hydrophobic interactions are also significant. QSAR analyses for log kr indicated one-electron oxidation potential (Eox, representing single-electron transfer ability) and polarizability (α) are predominant factors affecting the reactivity of aromatic organics towards MWCNTs/PDS. Additionally, non-radical reactions occur between adsorbed aromatic compounds and adsorbed PDS, indicating that surface interactions and reactions with MWCNTs dominate the overall reaction rates.