Flame modified graphene oxide: Structure and sorption properties

The applications of graphene oxide (GO), advancing on its layered structure, such as selectively permeating membranes and sorption, heavily depend on changing/controlling the distance between the constituting layers. For the sorption, it is also critical to impede exfoliation of GO in solution to simplify the post-sorption separation. In this study, we demonstrate a new method for modifying the structure of solid graphite oxide. The method involves ultrafast passing of graphite oxide particles through a flame of a propane-oxygen gas burner. The resulted material (GOgts) retains the particulate morphology of the original graphite oxide, but has interlayer openings of varying width. The surface area of GOgts is increased 27 times, due to massive formation of narrow 3.5-6.0 nm sized pores. Chemically, GOgts retains the fine chemical structure of original GO with partial deoxygenation. State of the art HRTEM analysis reveals different structure of different GO layers, depending on their closeness to the formed openings. Some layers have large intact graphenic domains with the size of >30 nm. Finally, GOgts exhibits good sorption properties with respect to methylene blue, demonstrating higher sorption capacity, and faster kinetics than the original graphite oxide. Most importantly, in solution, GOgts particles do not disintegrate to single-atomic-layer sheets, affording simple separation of used GOgts from the purified water. The method of GOgts production is simple, scalable and can be used to create new filters for wastewater treatment. Methodologically, we perform HRTEM analysis of GO flake, comprising structurally different layers, with atomic resolution by applying selective Fourier filtering.