Control of Functionalities in GO: Effect of Bronsted Acids as Supported by Ab Initio Simulations and Experiments

[Image: see text] Graphene oxide (GO) is an attractive precursor for graphene, provided by the well-known wet-chemical oxidative process. The intercalation of acid in graphite is considered as a crucial step, and its subsequent oxidation holds special relevance in synthesis. So far, the above chemistry is dominated by usage of H(2)SO(4). Recently, H(3)PO(4) appeared as a suitable intercalant for graphite. However, its role is not well understood in the formation of GO, especially when present as a co-acid with H(2)SO(4). Additionally, a relatively lower toxicity of H(3)PO(4) as compared to H(2)SO(4), elimination of toxic NaNO(3) usage, and a facile purification protocol are encouraging in terms of low-cost production of GO with a reduced environmental impact. Here, we report the systematic synthesis and characterization of GOs prepared with the variation in the ratio of H(2)SO(4) and H(3)PO(4). Ab initio simulations revealed that intercalation is primarily affected because of the usage of a mixture of co-acids. Interestingly, the ratio of the acids dictated the nature of the functionalities, extent of the defects, and morphology of the GOs, accounting for a pronounced effect on thermal stability, contact angle, zeta potential, and hydrodynamic size. The oxidation mechanism showed a predominance of H(2)SO(4) content, whereas H(3)PO(4) is found to mainly govern the intercalation of graphite, thereby affecting the acid-based intercalation–oxidation chemistry of graphite. The as-prepared GO suspension exhibited a high adsorption capacity for methylene blue dye removal in water, suggesting its potential as an adsorbent material in water treatment. The utility of the two acids affects the acid-based intercalation–oxidation chemistry of graphite and simultaneously may open up new opportunities for synthesized GOs, on tenets of green chemistry, in a wide arena of applications.