Acidity of graphene oxide aqueous solutions: the role of hydroxyls unveiled

Nonempirical modeling of hydrated single-layer graphene oxide (GO) fragments revealed that at least one, but substantial origin of the acidity of aqueous GO solutions is the dissociation in closely grouped and favorably H-bonded hydroxyls. The process can further be promoted by the adjacent $\pi$-conjugated carbon segments at the edges of GO flakes or their inner defects. The apparent $p{K}_a$ values of the groups fall in a range of ca. 2.0 to 5.3. Under certain conditions the ionization may become spontaneous.