Graphene Oxide was purchased from Donostia, Spain, (1 mg/mL, water dispersion) and sonicated for 30 min at 125 W by a vibra cell sonicator VC505 (Sonics and Materials, Newtown, UK) equipped with a 2 mm stepped microtip (Sonics and Materials, Part No. 630-0423). The GO solution was then centrifuged at 15,000× g for 100 min (Hermle Z 216 MK, Hermle Labortechnik). Lastly, the supernatant was recovered for subsequent use and its concentration (30 μg mL−1) was determined by UV-VIS experiments [49 (link)].
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