Abstract
Generally, large-scale production of graphene is currently not commercially viable due to expensive raw materials, complexity and the high-energy consumption of the processes currently used in the production. The use of biomass precursors and energy efficient procedures for carbonization have been proposed to reduce the cost of the graphene materials. However, low-cost graphene production has not been accomplished yet. Herein, we present a sustainable procedure and renewable starting materials to synthesize carbon nanostructures with graphene-like features. First, a SiC/C composite was synthesized from phytoliths and sucrose through magnesiothermic reduction. The phytoliths were obtained from barley husk that is an abundant side stream of agricultural industry. Second, graphene-like structures were achieved by the graphitization of SiC/C composite with high temperature induction annealing at 2400 °C under atmospheric pressure. The formation of graphene-like carbon was initiated by vaporization of silicon from the pre-ceramic SiC/C. Complete transformation of SiC/C to hollow, spherical graphene-like carbon structures and sheets were verified with thermogravimetry, x-ray diffraction, energy dispersive spectroscopy, electron microscopy and Raman spectroscopy. Also, the theoretical thermodynamic consideration of the phase separation of silicon carbide and the role of free carbon in the process has been discussed.
Highlights
Graphene is a single atom layer thick sheet of carbon that was first found in 2004 [1, 2]
The extracted nanostructured SiO2 (nSiO2) was mixed with sucrose and treated under magnesiothermic reduction resulting in the formation of a Nanostructured silicon carbide (nSiC)/C composite
The mixture contained sucrose above the stochiometric amount needed for the formation of SiC in order to increase the amount of free carbon in the composite
Summary
Graphene is a single atom layer thick sheet of carbon that was first found in 2004 [1, 2]. From the industrial production point of view these techniques suffer from high cost, low purity, heterogeneous features and limited upscaling [5, 6] For this reason more sustainable and cost-efficient methods and starting materials are needed for the production of high purity graphene [7]. Biomasses contain inherently heteroatoms (H/N/O/S) bound to carbon and other elements (K, Na, Mg, Fe etc), which can be problematic in the synthesis [8,9,10] Approaches such as the use of catalysts or the pre-treatment of the biomass are required to obtain ordered graphitic or graphene-like structures [11, 12]. Silicon in the form of silicon carbide has been reported to favor the formation of graphene type carbon structures [2] This reaction is usually conducted at high temperatures in vacuum. Pre-ceramic, nanocrystalline SiC is a promising starting material in the production of graphitic carbon structures as it favors the formation of high carbon content materials [16]
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