Density functional theory study of hydrophobic zeolites for the removal of triclosan from aqueous solution

The chlorinated biphenyl ether triclosan (TCS), used as a disinfectant in health care settings and in various personal care products, is an emerging organic contaminant of significant concern. Adsorption-based methods have been proposed as one potential pathway for the removal of TCS from wastewaters. Hydrophobic high-silica zeolites could constitute suitable adsorbent materials for such applications. In order to gauge the impact of pore size, topology, and framework composition, the adsorption of TCS in six different all-silica zeolites (AFI, BEA, CFI, FAU, IFR, MOR frameworks) and two highly siliceous protonated zeolites (H-FAU, H-MOR) was investigated using dispersion-corrected density functional theory (DFT). While pore size was found to affect the interaction strength, the rather flexible TCS molecule can adjust to different pore shapes, resulting in very similar adsorption energies for most all-silica zeolites. Although the interaction with TCS is enhanced in protonated zeolites, the affinity towards water increases even more. In DFT-based molecular dynamics simulations of TCS and water co-adsorption, H2O molecules quickly replace TCS in the vicinity of the framework protons, deprotonating the framework and forming positively charged clusters. In addition to delivering atomic-level insights into TCS adsorption, the calculations indicate that a fine-tuning of pore size with a concurrent maximization of hydrophobicity should constitute a promising strategy to develop optimized zeolite adsorbents for TCS removal.