Journal
JOURNAL OF PHYSICAL CHEMISTRY C
Volume 117, Issue 44, Pages 23272-23278Publisher
AMER CHEMICAL SOC
DOI: 10.1021/jp4057048
Keywords
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Funding
- Greek General Secretariat for Research and Technology and the European Commission
- NSRF action Development of Research Centers KPHPiISigma
- Belgian Fund for Scientific Research (FRS-FNRS) under FRFC [2.4577.11]
- COST action [MP0901]
- European Research Council under the 7th Framework Program (FP7) ERC [246791]
- project New Multifunctional Nanostructured Materials and Devices POLYNANO
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The effect of ultrasonication parameters, such as time and power applied, to exfoliate graphite in o-dichlorobenzene (o-DCB) and N-methyl-1,2-pyrrolidone (NMP) was examined. It was found that the concentration of graphene was higher in o-DCB, while its dispersibility was increased when sonication was applied for a longer period and/or at higher power. However, spectroscopic examination by X-ray photoelectron spectroscopy (XPS) revealed that ultrasonication causes defects and induces oxygen functional groups in the form of carboxylic acids and ethers/epoxides onto the graphene lattice. Additional proof for the latter arose from Raman, IR, and thermogravimetry studies. The carboxylic acids and ethers/epoxides onto exfoliated graphene were derived from air during ultrasonication and found independent of the solvent used for the exfoliation and the power and/or time ultrasonication applied. Quantitative evaluation of the amount of oxygenated species present on exfoliated graphene as performed by high-resolution XPS revealed that the relative oxygen percentage was higher when exfoliation was performed in NMP. Finally, the sonication time and/or power affected the oxygen content on exfoliated graphene, since extended ultrasonication resulted in a decrease in the oxygen content on exfoliated graphene, with a simultaneous increase of defected sp(3) carbon atoms.
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