Efficient anisotropic desalination by layer-stacked black phosphorus carbide (α-PC) membrane

Abstract

The crisis of global water scarcity is one of the most serious challenges that scientists and policymakers currently face. Breakthroughs in two-dimensional structures have provided a viable solution for the design and fabrication of filters in reverse osmosis (RO) desalination technologies. In this study, through molecular dynamics simulations, we show that the newly synthesized layer-stacked phosphorus carbide (α-PC) membrane can act as an auspicious performance filter for water desalination. The water permeability can reach ~30 L/cm2/day/MPa with wide interlayer distance (8 Å–12 Å) while blocking the salts, higher by two orders of magnitudes than the industrial RO membranes. Free energy analysis implies that the high ionic rejection (>98%) results from the large energy barriers (>8 kJ/mol) experienced by the ions entering α-PC nano-channels, while a considerably smaller barrier (<3 kJ/mol) is found for water transport. More interestingly, in striking contrast to previous desalination filters, the water translocation inside adjacent α-PC layers is determinant to the crystallographic directions of the buckled α-PC, resulting in highly anisotropic water permeability. Overall, our results provide a prospective candidate membrane for seawater desalination with inherently anisotropic filtering, which sheds light on the future design of the efficient filter.