For the fabrication of GO and PEI-GO films, GO and PEI-GO suspensions were prepared in 10 mL of water at 5 mg mL−1, and the resulting suspensions were vacuum-assisted filtered with a cellulose ester (CE) membrane of 0.45 μm pore size, respectively. After the completion of the filtration, the GO and PEI-GO films were taken off from a CE membrane and dried in an oven at 60 °C for 12 h.