Synthesis, Characterization and Application of Graphene Based Materials

Abstract

Graphene is being exponentially utilized across diverse research fields due to its extraordinary ability to enhance material properties with its miraculous attributes. Still, the material is expensive due to difficulties in the production of high-quality graphene. In this study, a few initiatives were approached to reduce the production costs of graphene with improved properties. At first, Tour's modified Hummer’s method was adopted to synthesize improved graphene with the feed acid liquor (FAL) recycling technique. About 90% of the FAL were recycled and reused five times as feed for successive production batches. Another focus was on the oxidation reaction to achieve graphene oxides (GOs) with higher oxygen to carbon ratios. The changes in recycled FAL and synthesized GOs properties due to repeated recycling were evaluated. The synthesized GOs were utilized for the removal of arsenic (As3+) ions from water, showing a qmax of 343.14 mg/g with 98.4% removal efficiency from 300 ppm to 22 ppm. The GOs were then reduced thermally at various temperatures in water, kerosene, and kerosene followed by ascorbic acid methods and times. The major objective of the reduction was to achieve maximum reduction of GO. The synthesized reduced graphene oxides (rGO) were evaluated for the antimicrobial properties. Although the Hummer’s method produces GO and rGO with improved properties, the method is difficult to carry out, very slow, and expensive. To obtain an easy and faster method for the production of graphene in bulk, a microwave assisted rapid exfoliation process of graphene exfoliation was examined along with the effect of variation of the intercalating agent ratio. All the products of FAL, GOs, rGOs, and microwave graphene (MG) were characterized using a Karl-Fischer moisture analyzer, IC, AAS, FT-IR (ATR), FT-Raman, UV-Visible Spectroscopy, PS-Zeta potential, XPS, XRD, STA, TGA, FE-SEM, and TEM analyzer. The FAL had increased moisture content with the successive recycling, but had no significant changes in properties and composition of GO. However, GO properties greatly changed with temperature and time of reaction, and the amount of oxidizing agent. The degree of reduction of GOs in N2 atmosphere at 193.4 oC was 95% of its initial mass, even at a slow rate of heating, but at this temperature, GO explosively degraded. In water medium as well as in kerosene, the explosive degradation can be omitted, and even at 220 oC, affording 40% reduction, which was mainly due to the removal of oxygen atoms as evident from the XPS analysis. The extremely reduced rGO contained an oxygen-to-carbon ratio of only 2.49% based on its initial oxygen content. In this study, XRD data also supported the composition of rGO and showed that it contained a homogeneous amorphous or viii nanocrystalline structure, as demonstrated by the 2θ = 24.91° peak in the (002) plane, which was shifted from the GO peak at 2θ = 12.86° in the (001) plane. The SEM image measured by ImageJ software showed that the obtained grain sizes were between 100 and 200 nm for both the GO and rGO. These rGO also showed strong activities against gram-positive and gram-negative bacteria, such as B. subtilis, S. aureus, E. coli, and S. typhi. In the case of MG, the degree of exfoliation was directly proportional to the intercalating agent ratios, and this method directly produces pristine graphene. This MG was highly thermo-stable up to 700-800 oC with high crystallinity, having 2θ = 26.56° at the (002) plane. The crystalline graphene showed excellent adsorption of acid blue-25 dyes with qmax 472.8 mg/g and 94.56% removal efficiency in the case of a 300-ppm dye solution.