Morphology effects on electrical and thermal properties of binderless graphene aerogels
Graphical abstract
Highlights
► Graphene aerogels are successfully developed at low temperature. ► Relationship among morphology, electrical and thermal properties is studied comprehensively. ► Electrical conductivity is improved by four times after a simple annealing.
Introduction
Graphene, a two-dimensional honeycomb lattice structure of carbon atoms has attracted much attention due to its excellent electrical, thermal and mechanical properties [1], [2], [3], [4]. Recently, a great deal of research has been done to develop graphene or graphene-based materials into various applications such as energy storage devices [5], [6], [7], sensors [8], [9] and composites [9], [10], [11]. To date, the realization of a three-dimensional graphene nanostructure is believed to be one step closer to more extensive applications. However, reported methods for the fabrication of 3D graphene nanostructures are still very limited, and a binder was usually required to achieve the assembly [12], [13], [14], [15], [16], [17], [18]. Worsley et al. [12], [13] reported the synthesis of ultra-low-density GAs with rather high electrical conductivity (87 S/m) and large surface area (584 m2/g) by using resorcinol (R) and formaldehyde (F) as an organic binder to produce carbon cross-links in the graphene network. Tang et al. [14] and Jiang et al. [15] developed an ion linkages method for the preparation of 3D architectures of graphene. However, it is still a great challenge to fabricate GAs with no binder in a simple and efficient way. Xu et al. [16] presented a one-stop hydrothermal technique to prepare electrical conductive and binderless GAs, but the requirements for high temperature and pressure during the process strongly limit its fabrication on a large scale. Zhang et al. [17], [18] reported an easy and environmentally friendly method to synthesize GAs by a simple reduction of GO with l-ascorbic acid (LAA). The self-assembled aerogel had a large surface area approximately 512 m2/g and a high electrical conductivity measured by a four-probe method approximately 102 S/m. Nevertheless, the morphologies, electrical and thermal properties of the GAs prepared by the simple reduction method depend strongly on the reaction conditions, such as initial GO concentration, reduction temperature and reduction time. Up to now, there were few studies on the synthetic parameters’ effects on the morphologies and properties of GAs [19].
Here, we report a systematic research to effectively control the GA morphologies and their effects on electrical conductivities and thermal stability of GAs through a simple LAA reduction self-assembly method under ambient pressure. Reduction of GO was confirmed by X-ray diffraction and the thermal stability of the GAs was investigated by thermal gravimetric analysis (TGA). Excess l-ascorbic acid can easily be removed during the solvent exchange process. The developed fabrication method reported here is environmentally friendly and effective for the fabrication of GAs, while the nanostructure, electrical and thermal properties of GAs can be easily controlled by adjusting the synthesis conditions.
Section snippets
Materials
Graphite powder, sodium nitrate (NaNO3), potassium permanganate (KMnO4), concentrated sulfuric acid (H2SO4), hydrogen peroxide (30% H2O2), hydrochloric acid (HCl) and l-ascorbic acid were purchased from Sigma–Aldrich Company Ltd. Ethanol was purchased from Fluka. All the chemicals were used without further purification.
Synthesis of graphene oxide
Graphene oxide (GO) was prepared by a modified Hummers’ method [20], [21], [22]. Briefly, 2 g NaNO3 and 4 g graphite powder were added into 100 ml concentrated H2SO4 in an ice bath.
Results and discussion
After sonication for several minutes, GO can be dissolved into water to form a uniform aqueous mixture. The reduction of GO by reducing agents, such as L-ascorbic acid, NaHSO3, Na2S and sodium ascorbate, in aqueous suspensions under mild conditions could result in the formation of hydrophobic graphene structures [17], [23], [24]. In this Letter, LAA was selected as the reducing agent, since it was found to be efficient and environmentally friendly for the reduction of the GO into graphene and
Conclusions
In conclusion, the GAs were synthesized in a simple way with different conditions, various initial GO concentrations, reduction temperatures and reduction times. A morphology control of the as-prepared GAs can be achieved by changing synthesis parameters appropriately. The experimental results showed that the GA synthesized from higher GO concentration possessed higher surface area and electrical conductivity, while higher reduction temperature and reduction time made GA a packed structure with
Acknowledgements
The authors deeply acknowledge the Start up grant R-265-000-361-133 and SERC 2011 Public Sector Research Funding (PSF) Grant R-265-000-424-305 for the funding support. We also thank Ms. Wong Pei Wen Janet for the English correction of the manuscript.
References (27)
- et al.
Nat. Nanotechnol.
(2008) - et al.
ACS Nano
(2010) - et al.
Carbon
(2009) - et al.
Carbon
(2011) - et al.
Colloids Surf. A
(2012) - et al.
Carbon
(2006) - et al.
New Carbon Mater.
(2011) - et al.
Electrochim. Acta
(2010) - et al.
Science
(2004) - et al.
Nat. Mater.
(2007)
Science
Nano Lett.
ChemSusChem
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