Effect of graphene oxide on morphological and structural properties of graphene reinforced novolac-derived carbon aerogels: A modified Quasi-Percolation Model

Abstract

Graphene reinforced polymer derived carbon (carbon/graphene) aerogels were synthesized by carbonization of novolac/graphene oxide aerogels. Novolac/graphene oxide aerogels were synthesized using solvent-saturated-vapor-atmosphere technique. To this aim, 20 wt% solution of novolac resin with 0, 2, and 5 wt% graphene oxide in 2-propanol were made and were cured in an autoclave. Wet aerogels were dried in air and were carbonized at 800 °C in nitrogen atmosphere. Eliminating the time-consuming methods of drying like supercritical and freeze drying is one of the advantages of this method of synthesis of organic aerogles. Fourier transform infrared spectroscopy, field emission scanning electron microscopy, X-ray diffraction, nitrogen adsorption/desorption, and small angle X-ray scattering measurements were used to characterize the samples. It was shown that the density, the average pore size, and the pore size distribution were affected by addition of graphene oxide nanosheets. Total pore volumes of carbon/graphene aerogels were increased and the apparent density of the samples were decreased by addition of graphene oxide nanosheets. The effect of addition of graphene oxide on pore structure was mainly on mesopore and macropore region and there was fewer changes in micropore volume. Carbon/graphene aerogels with 5 wt% graphene oxide revealed the lowest density (0.167 g cm−3) with the largest BET surface area of 580.6 m2 g−1. The surface area of the carbon aerogels in this research (>500 m2 g−1) is the largest surface area achieved by ambient drying of the wet gel. It was shown that the crystallite sizes were increased by addition of graphene oxide. Graphene oxide nanosheets acted as templates for crystallization of carbon atoms which resulted in formation of bigger crystallites during carbonization. A model has been proposed based on Quasi-Percolation Model to explain the formation of bigger crystallites in presence of graphene nanosheets.