where EPhos, EAs, and EPhos-As are the total energies of the free phosphorene-based nanoadsorbent, free arsenic contaminant, and adsorbent-adsorbate system, respectively; then, the more positive the Eads values, the more stable the adsorption is. The standard counterpoise correction was used to avoid basis set superposition errors . Adsorption energies in water were further decomposed into physically meaningful terms for quantitative characterization of the adsorption mechanism via the energy decomposition analysis based on absolutely localized molecular orbitals (ALMO-EDA) in the Q-Chem5.2 program .