Simultaneous adsorption of methylene blue and arsenic on graphene, boron nitride and boron carbon nitride nanosheets: Insights from molecular simulations

The occurrence of various pollutants in water bodies has become a serious concern. In this study, an attempt was made to find out the affinity of two-dimensional graphene (GRA), hexagonal boron nitride (h-BN) and hexagonal boron carbon nitride (h-BCN) towards the simultaneous adsorption of heavy metal (arsenic(III)) and organic dye (methylene blue) using molecular dynamics. The radial distribution functions obtained for the different systems showed that the O-W-O-W and O-W-As pairs peaked around 3 angstrom whereas, for the As-As pair, the distribution showed a maximum at similar to 9 angstrom. The observations were consistent for all three nanosheets, irrespective of whether the adsorption occurred individually or simultaneously. The simultaneous adsorption was synergistic on all three nanosheets, of which the effect was maximum for graphene, indicating better efficiency for real wastewater treatment. Further, by integrating the radial distribution function, a coordination number of 12 was obtained for the arsenic(III) ions. The diffusion properties of water molecules during various adsorption interactions were studied by calculating the diffusion coefficients from the mean squared displacement curves. The density distributions were also examined to highlight how the water molecules surround the adsorbate ions. The orientation of the adsorbate molecules and their distance from the nanosheets were evaluated to propose a possible pathway by which the adsorption occurred. This study revealed that the potency of GRA for simultaneous adsorption of methylene blue and arsenic(III) was better than h-BN and h-BCN.