Two-Dimensional Hydrous Silica: Nanosheets and Nanotubes Predicted from First-Principles Simulations

Two-dimensional (2D) hydrous silica sheets (HSSs) and hydrous silica nanotubes (HSNTs) have many unique properties and potential applications. Although preparation of 2D HSSs was patented already about half a century ago, very little is known about their structure and physical properties. Here we predict formations of various kinds of 2D structures. For this purpose, a first-principles study was performed using density-functional theory (DFT) with van der Waals dispersion interaction corrections (optB88-vdW). The uneven hydrous silica sheets and nanotubes have a high stability and are composed of hexagonal rings. The calculations also showed that a bilayer of anhydrous silica sheets is highly stable. Furthermore, the formation of defects which can induce a transition to glassy silica was investigated. The predicted high stability and versatility of these 2D materials offer many opportunities for more extensive developments, including doping with extrinsic elements to functionalize the nanosheets and nanotubes. The present simulation findings pose a challenge to experimentalists for finding useful synthesis routes to access these novel 2D materials.