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Investigation of opto-electrical properties of MWCNT/rGO -Poly[3-hexylthiophene] ternary composites

Prakash Chandra Mahakul1, Kadambinee Sa1, B.V.R.S. Subramanyam1, Khirod Chandra Patra2,

Pitamber Mahanandia1*

1Department of Physics and Astronomy, National Institute of Technology, Rourkela, 769008, India2 Institute Of Physics, Sachivalaya Marg, Bhubaneswar, 751005, India

2.1 Samples: Synthesis of MWCNT, GO and rGO

(i) Preparation of MWCNT

MWCNTs have been synthesized by pyrolyzing benzene in a cylindrical quartz tube at

900° as per our earlier reported article [1]. In short, around 3 ml of precursor benzene and 20 mg

of ferrocene as catalyst were taken in a quartz tube fused at one end. The other end of the tube

was closed with a rubber bladder to collect the residual toxic gases. Then the tube was placed in

a cylindrical reactor furnace at 9000C for 3 hours. The black materials on the inner wall of the

tube were collected and purified by oxidation and acid bath treatment [2].

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100 nm 20 nm

20 nm500 nm2 μm

e

5 μm 200 nm

d gf

cba

SI Fig.1 (a) SEM (b) TEM (c) HRTEM images of MWCNT (d) SEM of GO (e) SEM of rGO (f) TEM and (g) HRTEM image of rGO

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(ii) Preparation of graphene oxide (GO) and rGOModified Hummers’ method has been employed for synthesis of the GO from graphite

powder [3]. The synthesized

GO was exfoliated

mechanically using a bath

sonicator (Labman LMUC

series) for 4 hours. Exfoliated

graphene oxide has been

reduced at 1200C in an oil

bath using hydrazine hydrate

as the reducing agent [4] to

get rGO dispersion. RGO

flakes have been recovered

from the dispersion by

filtration with the help of a

membrane filter paper and washed copiously for several times with distilled water.

Characterizations of CNTs and rGO

SI Fig.1 represents SEM, TEM and HRTEM images of CNTs, graphite, GO and rGO as

labelled in the figure. From the SEM and TEM micrograph [SI fig: 1 (a and b)] the tube like

structure of the

synthesized CNTs

can be observed. The

HRTEM image (SI

Fig.1c) confirms the

multiwalled nature of

the synthesized

CNTs. The SEM

image of the

exfoliated GO

prepared from highly

stacked graphite flakes has been presented in fig.3d. The GO sheets could be observed to be

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b

ca

SI Fig.2 (a) XRD plot (b) FTIR spectra (c) Raman spectra of MWCNT, GO and rGO

5 µm 5 µm

1.5 µm

SI Fig.3 (a and b) AFM image of the composite 200 nm

1.8 µm

200 nm

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comparatively thicker can be ascribed to the accumulation of covalently bonded functional

groups on the basal planes as well as edges of the sheets [40]. SEM image of the thin crumpled

rGO sheets is presented in fig. 3(e). The HRTEM image (Fig.3g) signifies the few layer (mostly

4-6 layers) nature of the prepared rGO sheets.

The XRD pattern of the prepared CNTs (SI Fig.2a) revealed a broad diffraction peak at

26.5° corresponding to (002) planes which suggests the crystalline graphitic nature of the CNTs

[5]. For GO the graphitic peak is shifted

towards 10.25° with d-spacing 0.821nm.

Again this broad reflection peak was shifted to

26.5° with inter-planar spacing of 3.33 nm

after reduction using hydrazine hydrate in case

of rGO. From the FTIR spectra of MWCNT,

GO and rGO shown in SI fig.2b, the broad

absorption band observed around 3550 cm-1

represents the adsorbed –OH groups on the

surface. In addition the functional groups

C=C, C-O, C=O, C-OH, COOH observed from the spectra of GO as labelled in the fig.2b

confirms the adherence of oxygen functional groups on graphite surface during oxidation [6].

However, almost all the functional groups are diminished in the spectra of rGO that signify the

efficient elimination of the functional groups during the reduction process. Likewise, the

absorption peak observed around 1635 cm-1 in the FTIR spectra of MWCNT corresponds to the

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SI Fig.4 Solid state absorption spectra of CNT:rGO:p3HT composites

ba

SI Fig.5 (a) Change in oxidation potential of the composites with MWCNT loading (b) Oxidation potential at different scan rates for P3HT (black line) and composite P4 (red line)

SI Fig.4 Solid state absorption spectra of CNT:rGO:p3HT composites

SI Fig.4 Solid state absorption spectra of CNT:rGO:p3HT composites

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C=C stretching vibrations [7]. As observed from the Raman spectra (SI Fig.2c), the D-peak and

G-peak appears at 1347 cm-1 and 1580 cm-1 corresponding to the defect states and graphitic

structure of MWCNT respectively. Likewise for GO and rGO the D-peak were observed to be

concentrated around 1346 cm-1 and 1347 cm-1 respectively whereas G-peak at 1572 cm-1 and

1576 cm-1 respectively.

The AFM topographical images of the composites have been shown in SI fig.3. An

increase in the roughness was observed from the profilometer surface analysis with increasing

filler wt% in the composite.

The solid state absorption t with varying filler wt% is shown in SI fig.4. SI fig.5a and b

represents the variation in oxidation potential with respect to CNT wt% and scan rate

respectively. Oxidation potential was observed to decrease with filler wt% in the composites

compared to P3HT.

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