Removal of 1,4-dioxane by titanium silicalite-1: Separation mechanisms and bioregeneration of sorption sites

Abstract

1,4-Dioxane is a probable carcinogen and trace contaminant that is difficult to remove from water because of its high solubility and low volatility. Removal of 1,4-dioxane from aqueous solutions by a set of potential adsorbents was investigated using batch experiments that revealed Titanium Silicate-1 (TS-1) as a high-capacity adsorbent (85.17 mg/g) with rapid kinetics (2 min equilibration time). The specific adsorption mechanisms at the molecular level were investigated using multiple approaches including FTIR spectra and molecular dynamics simulation of 1,4-dioxane adsorption on TS-1, which imply that the shape and size of 1,4-dioxane fits tightly into the hydrophobic straight channels of TS-1 with a diameter of 0.56 nm, and thus TS-1 provides strong van der Waals attraction within the channels. Additionally, 1,4-dioxane-water complexation was observed to connect to the frame oxygens of TS-1 via hydrogen bonds inside the channels. The calculated adsorption free energy of 1,4-dioxane was between −24.59 and −27.17 kJ/mol, which was consistent with the value of −24.89 kJ/mol derived from the adsorption isotherms at 298 K. The strong adsorption competition from nonpolar compounds 1,1,1-trichloroethane (TCA) and benzene onto TS-1 further confirmed that the adsorption was attributed to a combined mechanism of host-guest interactions including van der Waals interactions, hydrophobic interactions, and hydrogen bonding. Furthermore, 1,4-dioxane-loaded TS-1 was found to be efficiently regenerated by an enriched bacterial consortium (BD1) with recovery efficiencies for three cycles of 88.2%, 96.47% and nearly 100%, suggesting that TS-1 holds promise as a cost-effective renewable absorbent for eliminating hydrophilic organics from contaminated water supplies.