Separation of Ethanol and Water Using Graphene and Hexagonal Boron Nitride Slit Pores: A Molecular Dynamics Study

A Kommu and JK Singh, JOURNAL OF PHYSICAL CHEMISTRY C, 121, 7867-7880 (2017).

DOI: 10.1021/acs.jpcc.7b00172

The industries discharge a variety of pollutants, such as heavy metals, organic toxins, and oils, in water resources. Exposure of these contaminants in water causes adverse health effects on various forms of life. Novel materials are needed for the effective removal of pollutants from industrial wastewater. Graphene and hexagonal boron nitride (hBN) sheets are promising materials for removal of organic pollutants. In this work, the suitability of the sheets for the separation of the ethanol-water mixture is investigated by studying the adsorption and structural behavior of ethanol-water mixtures in slit pores with variable width (7-13 angstrom) using molecular dynamics simulations. The selectivity of ethanol is found to depend on the pore-width.and nature of the pore walls. The selectivity of ethanol is highest for 9 angstrom pores and lowest for 7 angstrom pores, irrespective of the nature of the pore walls. However, selectivity of ethanol is relatively higher for hBN pores compared to the graphene pores, for all the considered pore widths. At a lower pore width, molecular sieving plays an important role for selective adsorption of ethanol molecules. On the other hand, at a higher pore width, selective adsorption of ethanol molecules is affected by the nature of the pore walls. The diffusion coefficients of water and ethanol molecules substantially decrease with a decrease in pore width for both graphene and hBN surfaces. The resident time of water and ethanol molecules decreases with increase in the slit-width. Furthermore, water and ethanol molecules confined in hBN pores show higher residence time and lower diffusion coefficient values compared to graphene pores. The adsorption behavior of water and ethanol molecules in the slit pores are analyzed using the potential mean forces, for water and ethanol molecules on the graphene and hBN surfaces, which are determined by umbrella sampling technique.

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