Preparation of Reduced Graphene Oxide (rGO). The preparation of
rGO was based on the previous report.40 Briefly, 1 mL of GO
dispersion in water (0.2 mg mL1) was mixed with 9 mL of MIM
aqueous solution (200 mM) in a glass vial under magnetic
stirring for 2 h at room temperature. After that, the mixture in
the glass vial was heated on a hot plate at 80 C under magneticstirring, and 0.2 mL of fresh-prepared NaBH4 aqueous solution
(100 mM) was added to reduce GO. After 20 min, the resulting
dark solution was centrifuged at 7500 rpm for 10 min, and the
precipitate was redispersed in aqueous MIM solution (100 mM)
for further use.