Graphene Oxide Fibers: Synthesis Method and Correlation among Compositional, Vibrational, and Electrical Properties

Abstract

The synthesis method and correlation among compositional, vibrational, and electrical properties in graphene oxide fibers (GOF) are presented and discussed here. The GOF samples were synthesized from rice husk (RH) as source material, via a thermal decomposition method employing an automated pyrolysis system with a controlled nitrogen atmosphere, varying carbonization temperature (TCA) from 773 to 1273 K. The samples were characterized through scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and current-voltage curves at four points of collinear electrical contacts. Oxide concentration (OC) of samples varied from 0.21 (at TCA = 1273 K) to 0.28 (TCA = 773 K), influenced by TCA. The GOF samples exhibited fiber morphology composed of porous structures with sizes between 5 and 30 μm; peaks in the XPS spectrum at ≈ 538 and 284 eV were associated with O1s and C1s, respectively. Analysis of the results corroborates the graphite oxide vibrational behavior with crystal sizes varying from 3.52 to 4.88 nm, and boundary defects density of 3.12-3.6 x 10-4 cm-2, as expected. The electrical response shows that OC decreases and increases electrical conductivity from 4.66 x 10-2 to 4.45 S/m at the polycrystalline phase, possibly attributed to the desorption of some oxides and organic compounds. Likewise, the physical correlations between OC and vibrational response revealed that decreased OC generates an increase in boundary defects density and decreased crystal size, as a consequence of thermal decomposition processes. The correlations between electrical and vibrational properties revealed that increased electrical conductivity increases defects density and decreases crystal size in GOF samples, possibly attributed to hydroxyl and epoxy bridges getting carbons atoms out of plane and modifying the band-gap energy (Eg) and graphitic structure. These results suggest that by controlling the TCA and OC in the synthesis of GOF samples, modification of vibrational and electrical properties, of great interest in the electronic development of sensors and devices, has been made possible.