Then, we employed ultra-sonication followed by a high-speed centrifugation step to yield purified s-GO and us-GO materials (Figure ). The process to obtain either s-GO or us-GO differed only in the duration of the sonication step (5 minutes and 4 hours, respectively). During sonication, GO flakes were shown to undergo physical breakdown due to the formation and propagation of cracks that are catalysed by the presence of sp 3 defects in the basal plane of the graphene lattice . Gonçalves et al. also postulated that ultrasound waves induce cavitations that could result in local increase of temperature, promoting the release of both adsorbed water molecules and oxygen functionalities. Thus, we attempted to minimise a potential thermal reduction of GO by performing ultra-sonication in a sonication bath kept under a set temperature (T < 40ºC), instead of directly sonicating the dispersion using a probe that could contaminate our final s-GO and us-GO materials with by-products coming from the probe .