After the fabrication of GOM, 300 mL of VC aqueous solution with a VC content of 0 mg, 2 mg, 20 mg, 200 mg, 300 mg and 400 mg was very carefully added into the feed compartment of vacuum filtration setup, respectively. After the solution was completely filtrated out, the obtained VC reduced GOMs (VGMs) were dried in the air for 24 h. The samples were denoted according to their VC/GO mass ratio (e.g., VGM 200 stands for 400 mg of VC / 2 mg of GO).