Interactions between liquid ammonia and graphitic materials

Abstract

Interactions between ammonia gas and graphitic materials, including adsorptions and N-doping at elevated temperatures, are known. However, liquid ammonia has rarely been studied other than for the Birch reduction reaction. Here, we report influences of liquid ammonia on graphite oxide (GO) and reduced graphite oxide (rGO), at both the atomic and macroscopic scales. It is demonstrated that GO and rGO do not disperse in liquid ammonia regardless of charge transfer due to the incompatible surface energy and polarity. X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and Raman spectroscopy studies of GO sheets treated with liquid ammonia, and liquid nitrogen as a control, for different time periods demonstrate ∼0.6 at% pyridinic N-doping and non-restoration of conjugation in the absence of thermal energy. Macroscopically, liquid ammonia is incapable of altering the shape or size of assembled GO and single walled carbon nanotube (SWCNT) freestanding membranes. However, loud popping sounds along with the generation of pockets, which leads to lower stiffness within the GO membranes, were observed after treating with liquid ammonia. In addition, shrinkage of porous rGO aerogels and counter-intuitively an increase in electrical resistance of SWCNT/cellulose composite membranes after treatment with liquid ammonia, are reported.