Synthesis and Characterization of Expandable Graphite using different Oxidizing Agents

Graphite intercalation compounds (GIC), i.e., graphite flakes embedding small molecules or ions, have been described in the literature since 1851 by Schafheutl. These extraordinary materials can be exploited for a number of technological applications, in different industrial ?elds (for example, they have been used for the industrial preparation of expanded graphite, novel superconductors, catalysts, anode materials, etc.). Some GICs (e.g., graphite nitrate and graphite bisulfate) are able to expand remarkably by thermal heating, and the achieved expanded graphite can be used to prepare graphite nanoplatelets (GNP), Few Layer Graphene (FLG), and graphene monolayer. Here an expandable graphite (graphite bisulfate) is prepared by intercalation of graphite with sulfuric acid, in presence of an oxidizing agent. In this study, different chemical formulations for the synthesis of highly intercalated graphite bisulfate have been tested. In particular, nitric acid, potassium nitrate, potassium dichromate, potassium permanganate, sodium periodate, sodium chlorate, and hydrogen peroxide have been used in this synthesis scheme as the auxiliary reagent (oxidizing agent). The intercalation reaction was performed in a glass-flask reactor (placed in a thermostatic bath), using air bubbling as homogenizing approach. The reaction time always was 1h and the H2SO4: oxidizing agent ratio was 9 : 1 by volume for all reactive mixtures. Graphite flakes were placed in the glass reactor and then the oxidizing compound, dissolved in absolute H2SO4, was added. The reactions were stopped by adding deionized water to the systems. In order to evaluate the presence of delamination, and pre-expansion phenomena, and the achieved intercalation degree in the prepared samples, the obtained graphite intercalation compounds have been characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray powder diffraction (XRD), infrared spectroscopy (FT-IR), micro-Raman spectroscopy (à,µ=RS) and thermal analysis (TGA). Delamination and pre-expansion phenomena were observed only for nitric acid, potassium dichromate and hydrogen peroxide, while the presence of strong oxidizers (KMnO4; NaIO4) led to stable graphite intercalation compounds. The largest content of intercalated bisulfate is achieved in the GICs obtained from NaIO4 and NaClO3.