Model study on potential removal of toxic Se(VI) by organically modified montmorillonite

Abstract

The theoretical DFT-D3 approach was used in the model study of the immobilisation of the toxic selenate oxyanion, with montmorillonite clay modified by poly(2-methyl-2-oxazoline) polymer represented by a pentamer unit, and tetrabutylphosphonium cation. The calculated basal spacing for Se-POx-Mt and Se-TBP-Mt models provided similar results differing by 0.2 Å (18.3 Å for Se-POx-Mt and/or 18.5 Å for Se-TBP-Mt, respectively). The calculated intercalation energy, ΔE_int, showed a suitability of both modified Mts for trapping of (SeO₄)^2– oxyanions favouring the Se-TBP-Mt (–210.7 kJ/mol) system compared to Se-POx-Mt (–124.5 kJ/mol). The main interactions in both models were classified as hydrogen bonds of weak (CH···O) and moderate-to-strong (OH···O) strength. The calculated total and projected vibrational density of states of the Se-POx-Mt and Se‑TBP‑Mt models, obtained from the ab initio molecular dynamics simulations, were used for distinct identification of vibrational modes of the intercalated (SeO₄)^2– ion in the interlayer space of both models.