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

Abstract

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.

Amplified Activity of Artesunate Mediated by Iron Oxide Nanoparticles Loaded on a Graphene Oxide Carrier for Cancer Therapeutics

“…This can be further visualized from the TEM images shown in Figure 4c,d. The selected area electron diffraction (SAED) pattern of the modified GO-PEG showed distorted fringes, shown in Figure 4c′, corroborating well with the literature, 59 whereas deposited Fe ATA on GO-PEG revealed well-defined lattice fringes (as can be seen in Figure S2g) suggestive of retention of crystallinity confirming the crystalline nature of iron oxide NPs, shown in Figure 4d′, which is in good agreement with the XRD analysis. Figure S7 clearly shows that the GO-PEG surface assisted in decreasing the average particle size of loaded Fe ATA substantially.…”

A “turn-off” photoluminescent sensor for H2O2 detection based on a zinc oxide–graphene quantum dot (ZnO–GQD) nanocomposite and the role of amine in the development of GQD

“…1); this pattern, shows a peak around 2 θ = 10° which normally is observed when the Hummers' method is used for the synthesis of graphene oxide. 27,29 In Fig. 1 the diffraction pattern from ZnNP coincides with JCPSD card 01-007-2551.…”

Size-Dependent Liquid Crystal Behavior of Graphene Oxides for Preparation of Highly Ordered Graphene-Based Films

“…In addition, co-acid molecules form hydrogen bonds between them, which increases the intercalation distance between graphite layers. As a result, it was reported that the interlayer spacing of graphite (3.35 Å) increases significantly over~8 Å [19], thereby decreasing the interlayer interactions between graphenes, as schematically shown in Figure 1a. After preparation of GOs with (and without) the intercalation step using co-acids, and their subsequent exfoliation in waters, the lateral size of L-GO flakes was 150 ± 29 µm (measured by 51 flakes), whereas that of GO flakes was 28 ± 24 µm (measured by 65 flakes; Figure 1b), although both exfoliations were performed using the same procedure (see experimental section).…”

“…− with graphenes in HOPG. This acid-based intercalation−oxidation chemistry of graphite is well known: H 3 PO 4 can be intercalated effectively between graphenes, and H 2 SO 4 predominantly causes the oxidation of graphenes [19,20]. In addition, co-acid molecules form hydrogen bonds between them, which increases the intercalation distance between graphite layers.…”