Influence of Surface Chemistry on Water Absorption in Functionalized Germanane

The graphane analogues of group 14 are a unique family of 2D materials due to the necessity of a terminal ligand for stability. Here we highlight how changing the surface ligand can lead to nonobvious interactions with other chemical species. We show using XRD, FTIR, and TGA that GeCH₃ reversibly absorbs water into the van der Waals space, whereas GeH does not intercalate water. Molecular dynamics and density functional theory simulations predict that water datively interacts with the Ge-C σ∗ pocket on the Ge framework, resulting in local structural distortions. Surprisingly, these distortions give rise to an intense above band gap luminescence state of 1.87 eV, with an average lifetime of hundreds of picoseconds. This work opens potential applications for exploiting surface functionalization chemistry of 2D materials to create membrane and separation technologies.