Insight into structural and chemical transformations of graphite during the synthesis of graphene oxide (GO) and reduced graphene oxide (RGO) via modified hummers method: A comprehensive XRD and Raman spectroscopy analysis

Abstract

The conversion of graphite(G) to GO and RGO, synthesized using a modified Hummer's method, involves complex chemical processes that introduce functional groups and defects, significantly altering their properties. This study conducts a comparative analysis of structural parameters, including average crystallite width (D), in-plane crystallite size (L) and the average number of graphene layers per region (n), across G, GO and RGO samples using XRD technique. G exhibited a large D of 30.14 nm, indicative of its high degree of crystallinity. GO displayed a reduced D value of 12.87 nm, reflecting a decrease in crystallinity due to the introduction of oxygen-containing functional groups and structural disruptions during oxidation. Reduction to RGO further decreased the average crystallite width to 1.02 nm, suggesting a partial restoration of crystallinity but with residual defects and disorder. G exhibiting a L value of 66.31 nm, indicative of large graphene domains. Oxidation to GO resulted in a decrease in L to 16.44 nm, indicating a disruption of the graphene layers into smaller, more disordered domains. Reduction to RGO partially restored the L value to 3.28 nm, suggesting a partial recovery of structural coherence. G displayed a high n value of 124, reflecting its well-defined layered structure. Oxidation to GO led to a reduction in n to 17, indicating a disruption of the layered structure due to the introduction of oxygen-containing functional groups. Reduction to RGO further reduced n to 8, indicating a partial restoration of layer stacking. Raman analysis was performed focusing on key structural parameters derived from the intensity ratio of the D band to the G band (ID/IG), including the in-plane size of sp² domains (Lsp²), average defect distance (LD) and defect density (nD). G exhibited a low ID/IG ratio of 0.26, indicating a high degree of graphitic order with minimal defects. Oxidation to GO increased the ID/IG ratio to 0.91 due to structural disruptions from oxygen functional groups, and reduction to RGO further raised the ratio to 1.10, suggesting partial restoration of the graphitic structure. G exhibited Lsp² of 63.11 nm compared to GO (18.03 nm) and RGO (14.90 nm), indicating the extent of structural ordering. The LD was observed to decrease from G (25.38 nm) to GO (13.56 nm) to RGO (12.34 nm), reflecting the increased density of structural defects and disorder introduced during oxidation. nD was found to be higher in GO (3.12 × 1011 cm⁻²) and RGO (3.78 × 1011 cm⁻²) compared to G (0.89 × 1011 cm⁻²), corroborating the presence of more structural disruptions and defects in the oxidized samples. This study presents a novel investigation into the structural transformations and chemical modifications of G during the synthesis of GO and RGO, employing XRD and Raman spectroscopy analyses.