Permeation selectivity of defected hexagonal boron nitrides sheets towards H2

Abstract

Membranes are selective filters, can offer separation efficiencies which are difficult or impossible to achieve otherwise. Herein, the permeability potential of defected hexagonal boron nitride sheet for several environmentally important gaseous molecules is explored. The considered defects are mono-vacancy, divacancy and tri-vacancy. The results illustrate that the nature of the defect besides pore morphology has significant effect on the permeation ability for gas molecules. The barriers are drastically higher for boron vacancy hexagonal boron nitride sheet V_B-h-BN and range from 73 kcal mol⁻¹ for H₂ to 442 kcal mol⁻¹ for CO. The barriers are drastically higher for species where incoming atom is electronegative and has highly unfavorable interactions with the nitrogen atoms in the defect. An inverse effect is observed for permeation through V_B-h-BN defect mainly due to the presence of electropositive boron atoms in the defect. Quite significant selectivity for H₂ permeation is observed for V_B(2N)-h-BN sheet where the barriers for H₂ permeation is at least 20 kcal mol⁻¹ lower than any other species (BeH₂ and BeF₂). The lowest barrier for H₂ permeation (8.38 kcal mol⁻¹) with even higher selectivity is observed for V_N(2B)-h-BN sheet. The lower permeation barrier is seen for H₂ gas which is 1.01 kcal mol⁻¹ large size V_B(2N)-h-BN nanosheet which is further decreases in aqueous medium. These results clearly demonstrate that fine tuning the nature and size of defect can offer purification of H₂ from a mixture of gases which is quite for hydrogen economy. These results will promote exploration of other functional materials for the purification of H₂.