XRD measurements were done to investigate the changes in
crystalline structure and intercalation of polymer (PPC) between GO
interlayers. Graphite (Fig.1A) presents a sharp diffraction peak at 2?=26o
corresponding to 0.3435 nm d-spacing. The XRD of GO displays a new peak at
2?=11.45o corresponding to 001 reflection with d-spacing = 0.7718
nm. The increase in the d-spacing is attributed to the presence of epoxide,
carboxylic and hydroxyl groups intercalated between the layers after oxidation.
Also the characteristic (002) peak of graphite at 45o was
disappeared indicating successful oxidation of graphite and the creation of
oxygen containing groups that are distributed between the basal planes leading
to their expansion 26, Regarding CS/GO (Fig.1B), the broad peak at 2? = 11.01o
can be explained by the intercalation of CS chains in the interlayer spacing of
GO. In addition, the disappearance of the 11.01o peak after
polymerization of PY was attributed to the destruction and exfoliation of the
regular layered structured GO sheets. In addition no crystalline feature was
observed for PPY in PPC/GO .

The FT-IR spectrum (Fig.2A) were carried out to investigate the
surface chemical nature of pristine graphite and exfoliated graphene. In the spectrum of graphite, the absorption bands
at               3448 cm-1 was known to be the O-H stretching
vibrations, the peak located at 1638 cm-1 could be attributed to the skeletal
vibration of C=C from unoxidized sp2 bonds. After the oxidation reaction,
the FT-IR spectra of GO apparently changed compared to that of graphite. Apart
from the O-H stretching vibrations and skeletal vibration, three new
representative peaks arising from GO could be indexed at 1736 cm-1, 1404 cm-1 , 1231cm-1, which
corresponded to the stretching band of C=O in carboxylic acid moieties, C-OH,
C-O-C, respectively. The FT-IR results indicated that oxygen-containing
functional groups were introduced onto the surface of graphite
confirming the successful oxidation of graphite into GO. 27-29. Also FT-IR
spectrum showed that the sharp characteristic band of hydroxyl group at 3448 cm-1
of graphite was shifted to 3428 cm-1 in the case of GO. Chitosan is a well-known
cationic polymer with multi-hydroxyl and amino groups, while GO is negatively
charged with plenty of hydroxyls and epoxides. For chitosan, the peaks at
3437cm?1 are corresponding to the N?H stretching vibration, and
the adsorption peaks at          1087cm-1 and 1157cm?1
are attributed to the primary alcoholic group of C6?OH and the
secondary alcoholic group of C3?OH. The peak at 1637cm?1
is assigned to the carbonyl stretching vibration of the acetylated amino group.
After mixing with GO, the band at 1736 cm-1 , 1404 cm-1 ,   1231cm-1 , 3428cm-1 which
corresponded to the stretching band of C=O in carboxylic acid moieties, C-OH,
C-O-C, -OH were shifted to 1711 cm-1, 1379 cm-1, 1155cm-1, 3424cm-1 respectively in
the case of CS/GO (Fig.2A), which indicating the formation of hydrogen bonding
and an electrostatic interaction between chitosan and GO. 30. For the Polypyrrole powders 
 (Fig. S1), FT-IR spectrum showed
the main characteristic peaks at 788 cm?1 corresponding to C-N bond,
1311 cm?1 corresponding to C-H deformation, 1546 cm?1 and
1458 cm?1 corresponding to the fundamental vibrations of polypyrrole
ring, the peak at 1633 cm?1 corresponding to C=C stretching, the
peak at 3423 cm?1 corresponds to the N-H stretching 31, 32. After insitu polymerization
of PY with CS/GO, the FT-IR spectrum (Fig.2B), of PPC/GO nanocomposite shows
the appearance of peaks at 1462 cm-1, 1550 cm-1 and 3415
cm-1 are related to the C=C, C=N and N=H stretching vibration in the
PPY ring, respectively. The absorption peaks found at 2919 cm-1 and
2844 cm-1 are ascribed to asymmetric stretching and symmetric
vibrations of CH2, respectively. The peak at 1711 cm-1characteristic
to C=O in CS/GO was shifted to 1721 cm-1 in the case of PPC/GO suggesting the ?-?
interaction between the graphene layers and aromatic PPY rings. The appearance
of peak at 787 cm-1 this may be due to additional bond formed
between pyrrole radical cation and residual carboxyl group of GO during polymerization. Sharp band at 1044
Cm-1 due to more skeletal stretching and presence of –NH group for
polypyrrole.

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After loading of P4R dye (Fig .2B), the adsorption peaks of PPC/GO
at 1462 cm-1, 1550 cm-1, and 3415 cm-1 that
are related to the C=C, C=N, and N=H stretching vibration in the PPY ring were
shifted to 1401cm-1, 1520cm-1 and 3449 cm-1 while
the absorption peaks found at  2919 cm-1
and         2856 cm-1
are ascribed to asymmetric stretching and symmetric vibrations of CH2
shifted to 2923cm-1 and 2865 cm-1, the C=O stretching
band shift from 1721cm-1 to 1780 cm-1 the bond formed
between pyrrole radical cation and residual carboxyl group of GO shifted from 787 cm-1 to 790 cm-1,
skeletal stretching of –NH of PPY shifted from 1044 cm-1 to 1029 cm-1,
this shifts confirms the electrostatic attraction between the anionic P4R dye
and the PPC/GO surface as shown in (table 1) .

 

To explore the successful intercalation of the polymer into GO
interlayers and gain insight into the state of dispersion GO layers within the
polymer matrix and calculate the average flake thickness, SEM analysis (Fig.3)
was performed at different magnifications for GO, CS/GO and PPC/GO. GO  powder is composed of aggregated stacked
nanosheets, this is due to its high surface area, the GO flakes (Fig.3 A,B,C)
connected to form these aggregations via ?-? interactions, vanderwaals forces
and H-bonding. Upon intercalation GO with CS 33, 34, disaggregation into thinner layers is observed in (Fig.3 D,E,F).
This suggests the intercalation of CS polymer chains between the GO sheets
to form CS/GO nanocomposites. The hydrogen bonding  intra chain between oxygen in -OH and -COOH
groups of GO sheets and hydroxyl group in CS and the ionic interaction between
-COO- and NH3+ would exceed the vanderwaals
forces and ?-? slacking interactions that maintain the aggregation of GO
sheets. This leads to the expanding of GO sheets during ultra-sonication
process. There is appearance of spherical structure in the case of PPC/GO (Fig.3
G,H,I)  that shows polypyrrole on the
surface of CS/GO. These results confirm that the intercalation of polymers into
GO interlayer induces dissagregation of the GO sheets resulting into thinner
sheets. Regarding PPC/GO nanocomposite a homogenous dispersion of GO flakes
within polymer matrix is observed, the flakes appear to be bended without
occurrence of clusters or agglomerate.

The morphology of GO, CS/GO ,PPC/GO was examined thoroughly by TEM
images,  (Fig.4) GO shows
the formation of several transparent thin sheets or films, as was observed in
SEM images (Fig.4 A,B) as similar micrographs done by several researchers 35, 36, the GO sheets have a
thickness between 20 nm and 23 nm. This thickness of a single GO layer is about
0.61 nm 37, it indicates that the sample consists mostly of few layers
graphene nanosheets. The presence of black curly lines in CS/GO indicated that
the GO sheets had been dispersed homogeneously in the CS matrix (Fig.4 C,D),
and no aggregation of GO was observed. Moreover, the presence of PPy within the
nanocomposite can be confirmed by the dark portion that appears on the
spherical shape (Fig.4 E,F). Both PY and carbon have similar characters,
pyrrole has an SP2 bond character which is identical to the bands of
carbons, It can be noticed that majority of CS/GO sheets are covered with polypyrrole
(spherical cluster structure). The large contact area of CS/GO sheets and
polypyrrole in the polymer composite resulted in a more uniform composite
structure. The SEM and TEM analyses are in good agreement with FT-IR and XRD
results of polymer composite, confirming a strong interaction between
polypyrrole and CS/GO to form PPC/GO nanocomposites.