An Environmentally Benign Green Approach for the Reduction of Graphene …
377
the removal of oxygen functionalities resulting in exfoliation of the layers in MRGO.
The d-spacing of MRGO is considerably lower than that of GO but slightly higher
than that of well-ordered graphite (0.3397 nm), implying reduction of GO. The
appearance of the broad band is suggestive of the fact that the graphene flakes are
randomly oriented in the stacking direction.
3.2 Raman Spectra Analysis
Raman spectroscopy is sensitive to the electronic configuration of “C=C” which
exhibits high Raman intensities and therefore it is an important characterization tool
of graphitic materials. The results of the Raman spectroscopy of GO and MRGO are
shown in Fig. 2a, b. The spectra of pure GO (Fig. 2a) exhibited a relatively broad
G-band centered at 1582 cm
−1 that originated from the first-ordering scattering of
the E 2g vibration mode of sp
2 carbon atoms and a prominent D-band at 1355 cm
−1
due to the breathing mode of k-point photons of A 1g symmetry (Bose et al. 2017a,
b). The results suggested that the C-sp
2 character of graphite flakes was significantly
reduced upon oxidation in addition to the introduction of defects in the GO sheets.
The ratio of the intensity of the D-band to G-band was found to be almost similar
both in case of GO (I D /I G = 0.99) and RGO (I D /I G = 0.98). The trend in the
I D /I G ratio suggested that the GO and MRGO had similar defect density within
their structure. In case of MRGO, the D-band shifted slightly to 1585 cm
−1 while
the G-band shifted to 1349 cm
−1 . The change in peak position inferred the change
in chemical atmosphere indicating that the apple extract could act as a reducing
agent. The most important observation is that the appearance of 2D band for RGO
at 2690 cm
−1 (Fig. 2b). The appearance of weak 2D band in the Raman spectrum
of MRGO ascribed to the second-order of the zone-boundary phonons generated
by the double resonance Raman scattering with two-phonon emission. Generally,
single Lorentzian peak fitting for the 2D band implies the formation of single-layer
graphene at 2679 cm
−1 . However, if the afore-mentioned 2D peak is broadened and
Fig. 2 Raman spectrum of a GO and b MRGO (Lorentzian fitting of the 2D band is shown in the
inset)
377
the removal of oxygen functionalities resulting in exfoliation of the layers in MRGO.
The d-spacing of MRGO is considerably lower than that of GO but slightly higher
than that of well-ordered graphite (0.3397 nm), implying reduction of GO. The
appearance of the broad band is suggestive of the fact that the graphene flakes are
randomly oriented in the stacking direction.
3.2 Raman Spectra Analysis
Raman spectroscopy is sensitive to the electronic configuration of “C=C” which
exhibits high Raman intensities and therefore it is an important characterization tool
of graphitic materials. The results of the Raman spectroscopy of GO and MRGO are
shown in Fig. 2a, b. The spectra of pure GO (Fig. 2a) exhibited a relatively broad
G-band centered at 1582 cm
−1 that originated from the first-ordering scattering of
the E 2g vibration mode of sp
2 carbon atoms and a prominent D-band at 1355 cm
−1
due to the breathing mode of k-point photons of A 1g symmetry (Bose et al. 2017a,
b). The results suggested that the C-sp
2 character of graphite flakes was significantly
reduced upon oxidation in addition to the introduction of defects in the GO sheets.
The ratio of the intensity of the D-band to G-band was found to be almost similar
both in case of GO (I D /I G = 0.99) and RGO (I D /I G = 0.98). The trend in the
I D /I G ratio suggested that the GO and MRGO had similar defect density within
their structure. In case of MRGO, the D-band shifted slightly to 1585 cm
−1 while
the G-band shifted to 1349 cm
−1 . The change in peak position inferred the change
in chemical atmosphere indicating that the apple extract could act as a reducing
agent. The most important observation is that the appearance of 2D band for RGO
at 2690 cm
−1 (Fig. 2b). The appearance of weak 2D band in the Raman spectrum
of MRGO ascribed to the second-order of the zone-boundary phonons generated
by the double resonance Raman scattering with two-phonon emission. Generally,
single Lorentzian peak fitting for the 2D band implies the formation of single-layer
graphene at 2679 cm
−1 . However, if the afore-mentioned 2D peak is broadened and
Fig. 2 Raman spectrum of a GO and b MRGO (Lorentzian fitting of the 2D band is shown in the
inset)