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

TL;DR

This study uses nonempirical modeling to identify hydroxyl groups as a key source of acidity in aqueous graphene oxide solutions, highlighting the influence of molecular structure on pH behavior.

Contribution

It uncovers the molecular origins of GO acidity, emphasizing the role of hydroxyl dissociation and structural features in determining pH properties.

Findings

Hydroxyl dissociation significantly contributes to GO acidity.

Adjacent π-conjugated segments promote hydroxyl ionization.

pKa values range from approximately 2.0 to 5.3.

Abstract

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 $pK_a$ values of the groups fall in a range of ca. 2.0 to 5.3. Under certain conditions the ionization may become spontaneous.