SURFACE FUNCTIONALIZATION OF REDUCED THREE-DIMENSIONAL GRAPHENE OXIDE
Rótulo Adsorption, Point, of, Zero, Charge, Indirect, Potentiometric, Titration
ResumoIn recent years, applications of graphene as an adsorbent material have grown exponentially, and structures based on three-dimensional graphene have been highly widespread in the environmental field as a promising new material in water treatment. Among numerous factors that can influence the adsorption of contaminants in a material is the presence of oxygenated functional groups on the surface of the material. As it is possible to determine whether the surface of an adsorbent will be negatively or positively charged using the pH of the zero charge point (pHPZC), this can be an excellent way to characterize the surface of a material and estimate whether the best adsorption results will be obtained when the adsorbates are cations or anions. Thus, the present work aimed to determine the concentration of oxygenated functional groups on the surface of graphene-based three-dimensional nanomaterials and to relate the results obtained to the pHPZC values of the same materials. For this, four different samples of reduced three-dimensional graphene oxide were used. Three of these were synthesized with three different amounts of reducing agent, employing a thermochemical route, in addition to material without adding a reducing agent (thermal route). The materials were characterized by FTIR. The concentration of acid groups was determined through indirect potentiometric titration, according to the methodology proposed by Hanelt et al. (2011). The pHPZC was determined using a NaCl solution with pH values ranging from 2 to 10. The materials were kept in solution for 48 hours, and at the end of that period, the pH variation was calculated. The results showed that the lower the amount of reducing agent, the greater the pH variation observed in the pHpzc experiment. Corroborating results, the indirect potentiometric titration showed that the materials with the addition of reducing agent were quite similar to each other, but with a decrease in the presence of oxygenated functional groups with the increase in the amount of reducing agent (3,08 ± 0,12 mmol.g-1, 2,89 ± 0,11 mmol.g-1 e 2,52 ± 1,34 mmol.g-1, respectively). On the other hand, the material synthesized without adding a reducing agent showed the largest amount of oxygenated functional groups (10,62 ± 1,84 mmol.g-1), as expected and confirmed by the FTIR results, which also indicated which functional groups were present in the materials. Thus, it can be concluded that the simple methods of surface characterization used were efficient in determining the concentration of oxygenated functional groups present in the sample and the pH of the zero charge point. The realization of this type of experiment helps to estimate the type of adsorbate that can be better adsorbed on the surface of the material, helping in the experimental optimization.
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LEÃO, M.; FERREIRA DE MATOS JAURIS, C. SURFACE FUNCTIONALIZATION OF REDUCED THREE-DIMENSIONAL GRAPHENE OXIDE. Anais do Salão Internacional de Ensino, Pesquisa e Extensão, v. 12, n. 2, 20 nov. 2020.