Highly efficient recovery of graphene oxide by froth flotation using a common surfactant

In this work, it is shown that graphene oxide (GO) sheets can be effectively recovered from aqueous solution by a simple froth flotation method. Small amounts of cetyltrimethylammonium bromide (CTAB) are added to assist with flocculating and driving the GO to the airewater interface, then ultrasonication is employed to form a foam that entrains the GO. The surfactant is essential in this process by firstly destabilising the GO dispersion through surface charge neutralisation, allowing the particles to aggregate. Furthermore, the hydrophobic component of the adsorbed surfactant molecules enhances adsorption of the GO at the air-water interface. Positioning the sonicator tip precisely at the air-water interface is crucial for foam formation by ensuring air bubbles are entrained into the sample. The nature of the foam can also be manipulated by altering the sonication intensity or by incorporating additional surfactant additives. At ideal GO: CTAB ratios, almost full removal (> 99%) of the GO from an aqueous dispersion is achieved, with minimal overall change in the particle size distribution of the GO. It is shown that this process can also be used when GO is employed as an adsorbent for removing toxic metals and organic species from aqueous solution. (C) 2018 Elsevier Ltd. All rights reserved.