pKa determination of graphene-like materials: Validating chemical functionalization

Abstract

We report a novel pKa determination for different graphene-like samples: graphene oxide (GO), reduced GO (rGO), 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, pKas 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 (pKa1∼4.0 and pKa2∼6.0) and one relative to alcohols (pKa4∼10.0). Upon functionalization on carboxylate sites, thiol (pKa(GOSH/GONRSH)=6.7) and imidazole (pKa(GOIMZ)=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.

Cationic Porphyrin‐Graphene Oxide Hybrid: Donor‐Acceptor Composite for Efficient Photoinduced Electron Transfer

“…At first a stronger interaction of TMAP 6+ with the GO compared to the TMAP 4+ might be expected due to the increase of the positive charge on the porphyrin molecules. On the other hand the p K a of the COOH groups in GO was reported to be ∼4.0, which indicates that GO sheets exist at an acidic pH mostly in the protonated form . The plausible explanation for the weakening of the interaction between protonated porphyrin TMAP 6+ and GO can be related to the weakening of the Columbic interaction due to protonation of the oxygen containing groups in GO at low pH.…”

“…On the other hand the pK a of the COOH groups in GO was reported to be~4.0, which indicates that GO sheets exist at an acidic pH mostly in the protonated form. [10] The plausible explanation for the weakening of the interaction between protonated porphyrin TMAP 6 + and GO can be related to the weakening of the Columbic interaction due to protonation of the oxygen containing groups in GO at low pH. In addition the change of geometry and electron density of the porphyrin after double protonation might also play a role.…”

Degrading Pesticides with Waste Product: Imidazole-Functionalized Rice Husk Catalyst for Organophosphate Detoxification

“…Titrations were carried out following well-established methods 23 in a thermostated cell at 25.0 °C. The pH was monitored by a pHmeter upon addition of small increments of CO 2 -free KOH (9.95 × 10 -3 mol L -1 ) using a manual burette.…”

“…The data were fitted using the program BEST7, 24 which we have shown to be a powerful tool to characterize complex samples such as biopolymers and nanostructured materials. 20,23 Even for low degrees of functionalization, we were able to characterize the functional groups, that other commonly used techniques cannot properly distinguish. Indeed, due to the complex nature of RH, we expect low degrees of functionalization, as will be confirmed in the following.…”

“…These values agree with other reported complex structures, i.e., typical values for hydroxyl groups, although less acidic carboxylic acid that can be accounted to the neighboring groups that increase the carboxylic acid pK a . 20,23 For RHIMZ, three pK a 's were determined (pK a1 = 6.14 ± 0.02; pK a2 = 7.44 ± 0.02; pK a3 = 9.52 ± 0.02), since fitting required an additional pK a , consistent with the IMZ group anchored. Commonly, IMZ has a pK a ca.…”