pKa determination of graphene-like materials: Validating chemical functionalization

We report a novel plCa determination for different graphene-like samples: graphene oxide (GO), reduced GO (rG0), graphene nanoribbons (GNR), oxidized GNR (GONR), thiol- and imidazole-functionalized GO (GOSH and GOIMZ, respectively) and thiol-functionalized GONR (GONRSH). Using the specialized computational program BEST7 for treating titration curves, pK(a)s for different functional groups were discriminated (confirmed by infrared spectra) and their composition quantified. Overall, three equilibria were distinguished, two relative to carboxylic acids exhibiting different acidic degrees (pK(a1) similar to 4.0 and pK(a2)similar to 6.0) and one relative to alcohols (pK(a4)similar to 10.0). Upon functionalization on carboxylate sites, thiol (pK(a)(GOSH/GONRSH) = 6.7) and imidazole (pK(a)(GOIMA) = 6.6) moieties were discerned, followed by a decrease of their carboxylate percentage (compared to the precursors), thus allowing determining the degree of functionalization (48% and 36% of thiol content for GOSH and GONRSH respectively, and 29% of imidazole for GOIMZ). The proposed method is innovative and simpler when compared to the traditional tools usually employed to quantify chemical functionalization. (C) 2016 Elsevier Inc. All rights reserved.