Oxygen Functional Groups in Graphene Oxide Using Titration Methods: Quantitative Analysis and New Quality Parameters

Graphene oxide (GO), an oxidized form of graphene containing various oxygen functional groups, is recognized for its exceptional properties and one of the most valuable graphene-related 2D materials (GR2Ms). Large-scale industrial production of GO materials from graphite involves various chemical oxidation methods, leading to significant variability in their properties, structures, types and composition of oxygen functional groups, which are critical for their practical applications. The quantification of oxygen functional groups in industrially manufactured GO remains largely unexplored and undisclosed in technical data sheets, creating challenges for end-users. Conventional characterization techniques for graphene materials, including SEM, EDAX and XPS, are limited by their spot-characterization nature and inability to reliably assess the bulk chemical properties of GO materials. To address these challenges, in this paper, we present a demonstration of a simple and industrially affordable analytical method using potentiometric titration to quantify the concentration of oxygen functional groups in GO powders and pastes on a bulk scale. Specifically, Boehm and acid-catalysed titrations were combined and successfully employed to determine the concentrations (mmol/g and mass %) of carboxylic, lactone, hydroxyl, carbonyl, epoxy groups and the total oxygen groups. This method has been validated by quantifying oxygen functional groups in industrially GO samples from three different manufacturers. The results revealed substantial differences in the concentrations of oxygen functional groups and total oxygen level of these GO samples, with carboxylic acid groups ranging from 0.89 ± 0.01 to 1.91 ± 0.08 mmol/g, lactone groups from 0.20 ± 0.01 to 1.76 ± 0.26 mmol/g, phenolic groups from 1.12 ± 0.15 to 2.73 ± 0.05 mmol/g, carbonyl groups from 0.65 ± 0.19 to 2.21 ± 0.26 mmol/g, and epoxy groups from 1.15 ± 0.05 to 1.37 ± 0.05 mmol/g. These variations, likely stemming from different GO manufacturing processes, highlight the importance of accurately determining these parameters. Furthermore, based on these measurements, we introduce, for the first time oxygen group indexes (OGI) as a novel quality parameter for distinguishing the quality of industrially produced GO materials. This study demonstrates how these simple, cost-effective methods, when implemented and adopted can significantly contribute to the chemical characterization and quality control of GR2Ms, addressing a critical gap in the graphene industry.