Graphite Oxide Reoxidation and Sonication

Graphite oxide was prepared by a modified Hummer’s method utilizing expandable graphite flake (XF NANO Co., Ltd. China). For reoxidation, 12 mg of graphite oxide was mixed with nitronium ion solution in a microwave reaction kettle (Xi’an Often Instrument Equipment Co. Ltd.) for 20 s, and then the entire mixture was placed into a microwave reactor chamber (Midea, MM823LA6-NS) to be heated for 3.75 min at the power of 160 W. After the reactant was cooled by ice bath, the reaction was quenched with 100 mL of deionized water, neutralized by NaOH and Na₂CO₃, and ultrafiltered repeatedly through a 30-kDa filter (Millipore) to remove the inorganic salt. At last, the graphite oxide of reoxidation was sonicated (Xin Zhi, JY92-2D) at 612 W for 1 h in an ice bath to obtain nGO. nGO-0, as a control, was fabricated by sonication (Xin Zhi, JY92-2D) of graphite oxide flake at 612 W for 1 h in an ice bath as described previously [9 (link)].