  Using first-principles calculations, we show that the formation of
carbohydrate directly from carbon and water is energetically favored when
graphene membrane is subjected to aqueous environment with difference in
chemical potential across the two sides. The resultant carbohydrate is
two-dimensional, where the hydrogen atoms are exclusively attached on one side
of graphene while the hydroxyl groups on the other side form a herringbone
reconstruction that optimizes hydrogen bonding. We show that graphene undergos
semi-metal-insulator transition upon hydration which is readily detectable from
the significant shift in the vibration spectrum. The hydrate form of graphene
suggests new applications for graphene in electronics, either deposited on a
substrate or in solution.
