Processing of ethanol soluble few-layer graphene nanosheets

Dispersions of few-layer graphene nanosheets (FLGs) in ethanol were prepared for the first time utilizing ultrasonic-treatment of HNO₃ modified-expanded graphite in ammonia-ethanol solution. This treatment results in the esterification of carboxylic groups chemically attached on graphite edges, therefore significantly enhancing the dispersion of graphene nanosheets in ethanol. The solubility of FLGs in ethanol was determined to be 42 mg/L. The thickness and microstructure of FLGs were characterized using atomic force microscopy (AFM) and high-resolution transmission microscope (HRTEM), respectively. FLGs with lateral size up to several tens of micron and thickness in the ranges of 2.5 - 2.9 nm, were successfully obtained. Moreover, the thickness can be further thinned down to ~1.0 nm through a simple plasma process. This method of exfoliating expanded graphite into graphene nanosheets could provide a facile route to fabricate grapheme-based electronic devices or composites with highly electrical-mechanical/thermal performances.