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, ΔEint, 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.