The penetration barrier of water through graphynes' pores: first-principles predictions and force field optimization

Abstract: Graphynes are novel two-dimensional carbon-based materials that -due to their nanoweb-like structure- have been proposed as molecular filters, especially for water purification technologies. In this work we carry out first principles electronic structure calculations at the MP2C level of theory to assess the interaction between water and graphyne, graphdiyne and graphtriyne pores. The computed penetration barriers suggest that water transport is unfeasible through graphyne while being unimpeded for graphtriyne. Nevertheless, for graphdiyne, which presents a pore size almost matching that of water, a low barrier is found which in turn disappears if an active hydrogen bond with an additional water molecule on the opposite side of the opening is taken into account. These results support the possibility of using graphtriyne as an efficient membrane for water filtration but, in contrast with previous determinations, they do not exclude graphdiyne. In fact, the related first principles penetration barrier leads to water permeation probabilities which are at least two order of magnitude larger than those estimated by employing commonly used force fields. A new pair potential for the water--carbon non-covalent component of the interaction has been built and it is recommended for molecular dynamics simulation involving graphdiyne and water.