Convergence tolerance values of 1×10 -8 and 3×10 -5 Ha were used for energies and geometry optimizations; the geometries were converged with tolerance values in gradients and coordinate displacements of 2×10 -3 Ha/Bohr and 1×10 -2 Bohr, respectively. Phosphorene (Phos, P126H30) and phosphorene oxide (PhosO, P126O12H30) nanoadsorbents were modeled as finite clusters with a surface area of 1583-1611 Å 2 (considering its electron density), which is larger compared to methylarsenicals (115-135 Å 2 ). Then, the 126-phosphorous atoms finite model has already been validated to obtain well-converged adsorption energies for arsenical removal . Dangling bonds at the edges are saturated with hydrogen atoms to avoid vacant orbitals . According to previous results, the phosphorene oxide was modeled using the 25% oxygen atoms in the structure . PhosO with 25% of oxygen content displays the following advantages: (i) the higher stability based on indirect and direct band gaps ; (ii) it conserves the phosphorene skeletal structure after active surface oxidation; (iii) the active surface contains equal oxygen and phosphorous atoms as electron donor and acceptor sites, respectively; (iv) a medium content of oxygen atoms reduces the repulsion between negatively charged oxygen atoms and anionic methylarsenicals. The computed cohesive energies are 3.36 and 3.42 eV/atom for Phos and PhosO, denoting the geometrical and energetic stability of the proposed systems.