Abstract
The liquid-phase exfoliation (LPE) method has been gaining increasing interest by academic and industrial researchers due to its simplicity, low cost, and scalability. High-intensity ultrasound energy was exploited to transform graphite to graphene in the solvents of dimethyl sulfoxide (DMSO), N,N-dimethyl formamide (DMF), and perchloric acid (PA) without adding any surfactants or ionic liquids. The crystal structure, number of layers, particle size, and morphology of the synthesized graphene samples were characterized by X-ray diffraction (XRD), atomic force microscopy (AFM), ultraviolet visible (UV–vis) spectroscopy, dynamic light scattering (DLS), and transmission electron microscopy (TEM). XRD and AFM analyses indicated that G-DMSO and G-DMF have few layers while G-PA has multilayers. The layer numbers of G-DMSO, G-DMF, and G-PA were determined as 9, 10, and 21, respectively. By DLS analysis, the particle sizes, polydispersity index (PDI), and zeta potential of graphene samples were estimated in a few micrometers. TEM analyses showed that G-DMSO and G-DMF possess sheet-like fewer layers and also, G-PA has wrinkled and unordered multilayers.
Highlights
Graphene is a versatile nanomaterial with a wide range of chemical, environmental, medical, industrial, and electronical applications by means of its remarkable thermal conductivity, superior mechanical properties with a Young’s modulus of 1 TPa, an extraordinary large specific surface area (2620 m2 g−1 ), intrinsic strength of 130 GPa, and an extremely high electronic conductivity [1,2,3]
Few-layered graphene has been synthesized by numerous methods including mechanical cleavage, liquid-phase exfoliation, gas-phase synthesis, Hummers’ method, unrolling of multi-walled carbon nanotubes (MWCNTs), chemical vapor deposition (CVD), epitaxial growth, and electrochemical reaction [2,5,6,7,8,9,10,11,12,13,14,15]
transmission electron microscopy (TEM) analysis revealed that G-dimethyl sulfoxide (DMSO) and G-dimethyl formamide (DMF) have fewer layers while G-perchloric acid (PA) has multilayers
Summary
Graphene is a versatile nanomaterial with a wide range of chemical, environmental, medical, industrial, and electronical applications by means of its remarkable thermal conductivity (above3000 W m K−1 ), superior mechanical properties with a Young’s modulus of 1 TPa, an extraordinary large specific surface area (2620 m2 g−1 ), intrinsic strength of 130 GPa, and an extremely high electronic conductivity (room-temperature electron mobility of 2.5 × 105 cm V−1 s−1 ) [1,2,3]. Few-layered graphene has been synthesized by numerous methods including mechanical cleavage, liquid-phase exfoliation, gas-phase synthesis, Hummers’ method, unrolling of multi-walled carbon nanotubes (MWCNTs), chemical vapor deposition (CVD), epitaxial growth, and electrochemical reaction [2,5,6,7,8,9,10,11,12,13,14,15]. These methods have some drawbacks, such as low yield ratio, high-energy consumption, the use of expensive substrates, as well as the difficulty of obtaining a high-quality product. The final products attained by Hummers’ method have many functional groups, such as hydroxyls, carbonyls, and carboxyls, which cannot be completely removed by additional reduction and Crystals 2020, 10, 1037; doi:10.3390/cryst10111037 www.mdpi.com/journal/crystals
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