Preparation of a stable graphene dispersion with high concentration by ultrasound.

With unique structure and extraordinary electronic, thermal, and mechanical properties, graphene fascinates the scientific community. Due to its hydrophobic feature, preparation of a stable and highly concentrated graphene dispersion without the assistance of dispersing agents has generally been considered a challenge. Chemical reduction of graphene oxide (GO) is one of the most important methods for preparing a graphene dispersion. The aggregation of graphene sheets is a key reason to destabilize the resulting dispersion during conversion of aqueous GO dispersion to graphene. In this study, by replacing mechanical stirring with ultrasonic irradiation, the aggregation of various intermediates is effectively suppressed during the process of reduction of GO. Hence, a stable graphene dispersion with a high concentration of 1 mg.mL(-1) and relatively pure graphene sheets are achieved, and the as-prepared graphene paper exhibits a high electric conductivity of 712 S.m(-1). Ultraviolet-visible absorption spectroscopy and X-ray photoelectron spectroscopy show that ultrasound is the essence of enhancing chemical reaction rate. Fourier transformed infrared spectra and Raman spectra indicate that ultrasound has less damage to the chemical and crystal structures of graphene.