The effect of the parent graphite on the structure of graphene oxide

Abstract

The effect of the parent graphite on the structure of graphene oxide (GO) is investigated using high purity graphites with a uniform crystallite size. Our results provide direct evidence of how the size of the graphite crystal affects the oxidation process and the functionality and sheet size of the resulting GO. The important role of the crystal boundaries in the graphite with smaller crystallites is confirmed by the smaller size of the GO sheets obtained and also by the presence of carboxylic groups, located at the edges of the sheets. However, functionalization in the graphite with larger crystals mainly occurs in the vicinity of basal plane defects, as evidenced by the larger number of epoxy groups. Thus, this study leads to a better understanding of the oxidation process of graphite and provides a way to produce GOs suitable for different applications.

Critical temperatures in the synthesis of graphene-like materials by thermal exfoliation–reduction of graphite oxide

“…GO was prepared from the commercial graphite powder using a modified Hummers' method [4,12]. This method makes use of the Hummers' reagents with additional amounts of NaNO 3 and KMnO 4 .…”

“…This method makes use of the Hummers' reagents with additional amounts of NaNO 3 and KMnO 4 . Concentrated H 2 SO 4 (360 mL) was added to a mixture of graphite (7.5 g) and NaNO 3 (7.5 g), and the mixture was cooled down to 0 °C by means of an ice bath.…”

“…The reaction mixture was stirred for 30 min and, finally, the mixture was centrifuged (3700 rpm for 30 min), the supernatant being decanted away. The remaining solid material was then washed with 600 mL of water and centrifuged again, this process being repeated until the pH was neutral [4]. When required, GO was dried under vacuum at 40 ºC overnight and stored in the presence of P 2 O 5 as desiccant.…”

“…The exfoliation of GO to yield graphene oxide [2] followed by a reduction process offers a simple method to obtain graphene [3]. This method has the advantage of being readily scalable and also has the ability to produce graphene materials with a tuneable amount of oxygen, depending on the characteristics of the parent graphite [4] and the experimental conditions of both oxidation and reduction [2,5]. Several processes have been considered for the reduction of graphene oxide.…”

“…A commercial synthetic graphite powder was oxidized by a modified Hummers' method [4,12] and thermally treated at temperatures ranging from 127 ºC to 2400 ºC in order to: i) determine the optimum temperature for the preparation of graphene-like materials (TRGs) with a minimum oxygen content and a minimum amount of structural defects; ii) obtain graphene-like materials with different degree of functionalization; and iii) study the effect of the temperature on the degree of association of the sheets. Elemental analysis, TPD (temperature programmed desorption), XRD, Raman spectroscopy, XPS, FTIR, SEM, TEM, high resolution TEM and AFM were used to monitor the chemical and structural changes occurring in the TRG produced at each temperature.…”