Understanding Aqueous Dispersibility of Graphene Oxide and Reduced Graphene Oxide through pK_a Measurements

Abstract

The chemistry underlying the aqueous dispersibility of graphene oxide (GO) and reduced graphene oxide (r-GO) is a key consideration in the design of solution processing techniques for the preparation of processable graphene sheets. Here, we use zeta potential measurements, pH titrations, and infrared spectroscopy to establish the chemistry underlying the aqueous dispersibility of GO and r-GO sheets at different values of pH. We show that r-GO sheets have ionizable groups with a single pK value (8.0) while GO sheets have groups that are more acidic (pK = 4.3), in addition to groups with pK values of 6.6 and 9.0. Infrared spectroscopy has been used to follow the sequence of ionization events. In both GO and r-GO sheets, it is ionization of the carboxylic groups that is primarily responsible for the build up of charge, but on GO sheets, the presence of phenolic and hydroxyl groups in close proximity to the carboxylic groups lowers the pKa value by stabilizing the carboxylate anion, resulting in superior water dispersibility .

Chitosan biopolymer functionalized gold nanoparticles with controlled cytotoxicity and improved antifilarial efficacy

“…Generally, particles with ζ-potential value more than + 30 mV or less than − 30 mV are considered to form stable dispersion due to inter-particle electrostatic repulsion [33]. GNP c (ZP value: + 47.4 mV) (Fig.…”

Easy on-demand self-assembly of lateral nanodimensional hybrid graphene oxide flakes for near-infrared-induced chemothermal therapy

“…To enhance the dispersion stability, cPEG was incorporated 25 with nGO@DOX flakes to prepare the nGO@DOX-cPEG flakes for appropriate chemothermal anticancer assessments; DOX covered the oxygen-containing functional groups (OH, COOH and C = O) on nGO surfaces that are responsible for maintaining aqueous dispersibility. 33 Importantly, this incorporation can minimize macrophage opsonization and increase the blood circulation time for efficient delivery to the tumor area. 25 On the basis of the zeta potential measurements, 20 w/w% was chosen for effective capping of the nGO@DOX flakes because the charge reversal was maximized at this condition.…”

Cholic Acid/Graphene Oxide Chiral Hybrid Material: Preparation and Characterizations

“…此外 GO 上还含有大量的含氧活泼 基团(如 COOH, OH 等), 使其便于和其他物质反应, 进 一步实现 GO 表面功能化. 含氧官能团还利于 GO 在水 中或其它强极性溶剂中分散 [2,3] . 由于其独特的共轭结 构、 低成本及良好的生物相容性, GO 近年来在许多领域 受到重视, 如制备高性能复合材料、传感器、生物医用 材料等 [3,4] .…”