Effective removal of water-soluble methylated arsenic contaminants with phosphorene oxide nanoflakes: A DFT study

Abstract

This work explores by density functional theory the ability of oxidized phosphorene nanoflakes (PhosO) to simultaneously remove toxic water-soluble methylarsenicals from contaminated waters. We focused on the microscopic understanding of the PhosO-Methylarsenic complexes in solution, i.e., structure, stability, and intermolecular driving forces. In this way, adsorption energies and conformations, binding and energy decomposition analyses (ALMO-EDA), implicitly/explicitly solvated structures, and competitive adsorption with coexisting molecules in solution afford deep insights into the selectivity adsorption and interaction mechanisms. The PhosO nanoflakes form inner-sphere surface complexes with methylarsenicals in solution, even with enhanced adsorption stability compared to intrinsic phosphorene and without the competition of water molecules for adsorption sites. The inner-sphere surface adsorption of trivalent methylarsenicals is driven by electrostatic and charge-transfer (orbital) intermolecular forces. Surface complexation of pentavalent methylarsenicals occurs by a balanced contribution of orbital and long-range intermolecular forces, while anionic contaminants also show a high stabilization via extra polarization effects. PhosO nanoflakes turn convenient to recycle via simple treatment with alkaline eluents because of the increased affinity with hydroxide anions in solution compared with intrinsic phosphorene. Conceptually understanding the adsorption properties of phosphorene oxide towards hazardous methylarsenicals provides a valuable framework for new developments in future water and wastewater treatment technologies with adsorbents of large surface area, high adsorption capacity/selectivity, and easy recovery.