We also analyzed the adsorption stability of water molecules (H2O) and hydroxide anions (OH -) onto phosphorene oxide (Fig. ). First, the adsorption energy of the H2O-Phos(PhosO) complexes is always lower (at least 65 %) compared to those reached by complexation of arsenicals, indicating arsenicals are selectivity adsorbed in an aqueous solution. In other words, water molecules are non-competitive factors for arsenic removal with phosphorene oxide-based materials.