. Synthesis procedure of GO
Synthesis of GO was achieved in accordance with previously
published literatures [37,48]. Briefly, graphite was oxidized by
KMnO4 and NaNO3 in concentrated H2SO4 to graphite oxide, and
2 g of the obtained graphite oxide was exfoliated into GO by
400 mL of water under sonication for 60 min. This concentration
was used for the synthesis of Fe3O4@GO. Also, it was diluted 10
times and the conductivity was measured by conductometer to
evaluate the extent of exfoliation. Accordingly, the conductivity
was obtained 5900 S/m which is comparable with that of previously
reported data for GO which is chemically oxidized by chemical
reagents [49].
4.2. Synthesis of Fe3O4@GO
Synthesis of Fe3O4@GO was performed by according to literature
[50] with slight modifications.
Accordingly, FeCl36H2O (3.51 g, 0.013 mol) and FeCl24H2O
(1.29 g, 0.0065 mol) are added to 100 mL solution of distilled water
containing 3 mL glacial AcOH under vigorous stirring. Then, 10 mL
of as-prepared GO solution (previously sonicated for 10 min) was
added to the mixture and the temperature raised to 80 C. In that
temperature, 20 mL ammonia (25 wt%) was added to the reaction
mixture under the vigorous stirring and allowed to proceed for
15 min. Finally, the reaction was stopped and the black precipitate
was collected by an external magnet and washed several times
with distilled water and methanol. Then, it was dried in oven at
70 C for 3 h.
4.3. Synthesis of Fe3O4@GO-Pr-SO3H
For the synthesis of Fe3O4@GO-Pr-SO3H, 0.5 g of Fe3O4@GO was
dispersed in 20 mL of MeOH and 1.5 mL of MPTMS was added to
the reaction media and it was allowed to stir vigorously for 24 h.
Then the product was collected by magnet, washed and dried.
Afterwards, it was redispersed in 10 mL distilled water and stirred
vigorously. 10 mL of H2O2 (30 wt%) was added to the dropwise
during 30 min at room temperature. The reaction was allowed to