Electrochemical Water Treatment Using Graphene, Graphene Foam and Graphene / Metal Oxide Composites

Combining adsorption with electrochemical oxidation has been shown to be effective for the removal and oxidation of dissolved and dispersed organic contaminants from water, using a graphite flake adsorbent. In order to increase the adsorption capacity, we have investigated the use of graphene based adsorbents, which have high specific surface area combined with electrochemical activity. We have prepared and tested reduced graphene oxide (RGO), graphene foam and graphene metal oxide composite materials. RGO offer significantly higher adsorptive capacity than graphite flake. Similarly graphene foam was found to have a high adsorption capacity, although the adsorption kinetics were poor due to the slow diffusion of conatminants into the foam pores. A graphene foam would be more readily separated from the treated water and further work is planned to determine whether a flow through treatment process can be used to overcome the slow adsorption kinetics. However, during electrochemical oxidation, the structural integrity of the foam was compromised after only 1 or 2 cycles, presumably due to oxidation of the graphene. A graphene / iron oxide composite was preapred with ferromagnetic characteristics to enable separation from the treated water. The adsorption capcity was slightly reduced, but the electrochemcial regeneration performance was good. Oxidation of graphene remains a challenge, and work is ongoing to explore the use of graphene / titanium dioxide composites. The TiO2 will catalyse the organic oxidation and may also protect the graphene from oxidation.