Evidence of Two-Dimensional Porous Ice at Room Temperature

The phase behavior of water and ices is remarkably complex because of the high flexibility of their underlying hydrogen-bonding networks. Even for two-dimensional (2D) ice, rich forms of monolayer and bilayer ice phases have been observed in molecular dynamics (MD) simulations, including, among many others, flat-square monolayer ice, bilayer hexagonal ice, twisted bilayer ices with moiré patterns, and monolayer and bilayer superionic ices. In contrast to the large family of 3D ice structures, however, the 2D ice family still lacks porous ice structures, as it is generally believed that 2D porous ices are stable only under negative pressures. As a result, even in MD simulations, the spontaneous formation of a 2D porous ice is challenging. Here, for the first time, we report simulation evidence of three distinct types of 2D porous ice. Additionally, on the basis of first-principles computations, we show that these 2D porous ices are stable under negative pressures. More importantly, inspired by host-guest chemistry, we demonstrate the spontaneous formation of one of these 2D porous ices (on the time scale of microseconds in MD simulation) from liquid water at 300 K by employing suitable guest particles on a model surface. The nucleation and growth mechanisms of the 2D porous ice are also illustrated at the molecular level. Through extensive MD simulations with tunable molecular and surface parameters, we identify the key factors governing the formation of 2D porous ices.