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The preparation of graphene oxide (GO) sheets with specified size was developed by simply controlling the time of ultrasonication to the large-size GO (LGO) sheets. The LGO sheets were synthesized by choosing large parent graphite, mild oxidation condition and a two-step centrifugation. The different-sized GO samples prepared under different ultrasonication times, are characterized by Scanning electron microscopy, X-ray photoelectron spectroscopy, Ultraviolet–visible spectroscopy, and X-ray diffraction. It is found that the size of the GO sheets, which has a Gaussian distribution, decreases from 231 to 17 μm 2 as the ultrasonication time increases. Moreover, the ultrasonication not only can exfoliate and break GO sheets, but also increase the oxidation degree of GO sheets, especially when the GO sheets have a weak oxidation degree. It is reasonable to believe that the size of GO sheets is closely correlated to the C–O content, which enables the size of GO sheets to be controlled. Our work demonstrates that ultrasonication is an important method to control the size and the oxidation degree of GO sheets, to a certain extent. [ABSTRACT FROM AUTHOR]

Abstract: Ultrasonication is often used to disperse nano-particles in aqueous solution. However, a good dispersion of nano-particles in aqueous solution is not always achieved, due to the fact that incoming ultrasonicwaves in liquid are usually reflected and damped at the gas/liquid interface. In this work, we report a so-called wet-grinding assisted ultrasonication (GU) method, in which wet-grinding of multi-walled carbon nanotubes (MWCNTs) in chitosan solution is carried out before ultrasonication. The dispersions of MWCNTs were characterized by visual comparison, UV/vis spectroscopy, and scanning electron microscopy (SEM). The results demonstrate that the dispersion quality of chitosan/MWCNT suspension prepared by wet-grinding assisted ultrasonication is much better than that by ultrasonication or wet-grinding alone. It was found that wet-grinding could improve the water wettability of MWCNTs and eliminate the barrier of air layer around MWCNTs to ultrasonicwaves. Meanwhile, the composite from the chitosan/MWCNTs suspension prepared by GU method has an obvious improvement in mechanical property compared to pure chitosan. This simple method for integrating MWCNTs and biocompatible chitosan into a homogeneous dispersion may have great potential application in biotechnology, such as preparing composite materials for medicine, bio-fiber, biosensor, antibacterial coating, and cell cultivation. [Copyright &y& Elsevier]