In-situ preparation and properties of gold nanoparticles embedded polypyrrole composite

Accepted Manuscript Title: In-situ preparation and properties of gold nanoparticles embedded polypyrrole composite Authors: Shruti Peshoria, Anudeep Kumar Narula PII: DOI: Reference:

S0927-7757(18)30584-3 https://doi.org/10.1016/j.colsurfa.2018.06.069 COLSUA 22638

To appear in:

Colloids and Surfaces A: Physicochem. Eng. Aspects

Received date: Revised date: Accepted date:

29-1-2018 24-6-2018 25-6-2018

Please cite this article as: Shruti P, Narula AK, In-situ preparation and properties of gold nanoparticles embedded polypyrrole composite, Colloids and Surfaces A: Physicochemical and Engineering Aspects (2018), https://doi.org/10.1016/j.colsurfa.2018.06.069 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

In-situ preparation and properties of gold nanoparticles embedded polypyrrole composite Shruti Peshoria and Anudeep Kumar Narula* Molecular Chemistry Laboratory, University School of Basic and Applied Sciences, Guru

SC RI PT

Gobind Singh Indraprastha University, Sector-16 C, Dwarka, New Delhi-110078, India. *Corresponding author. Tel: +91-11-25302423. Fax: +91-11-2530111.

E-mail addresses: [email protected] (Anudeep Kumar Narula), [email protected] (Shruti Peshoria)

CC

EP

TE

D

M

A

N

U

Graphical abstract

Abstract

A

A composite was formed by polypyrrole (Ppy), gold nanoparticles (AuNPs) and multi-

walled carbon nanotubes (MWCNT) using chloroauric acid (HAuCl4). MWCNT were carboxy functionalized by oxidation resulting into oxidized MWCNT (OMWCNT). The composite was characterized spectroscopically, structurally and morphologically by Fourier transform infrared (FT-IR) spectroscopy, Ultraviolet-visible (UV-Vis) spectroscopy, X-ray photoelectron 1

spectrocopy (XPS), X-ray diffraction (XRD), Scanning electron microscopy (SEM) and Highresolution transmission electron microscopy (HRTEM) studies which revealed about its successful formation. UV-Vis spectroscopy suggested the in-situ formation of AuNPs, their

SC RI PT

dispersion into the composite and presence of OMWCNT. XPS analysis revealed the existence of Au, C, N and O elements, signifying the desired formation of the composite. Morphological studies depicted the wrapping of OMWCNT by Ppy along with the presence of dispersed

AuNPs. Its electrochemical examination suggested good electron transfer ability of AuNPs and OMWCNT. The interaction of composite with Cd2+ ions was investigated both optically and

U

electrochemically, making it a potential candidate for Cd2+ sensing. Furthermore, its catalytic

N

activity was also shown, by reduction of methylene blue dye.

A

Keywords

A

CC

EP

TE

D

M

Polypyrrole, gold nanoparticles, multi-walled carbon nanotubes, dye mineralization, Cd2+

2

SC RI PT U N A

1. Introduction

M

A lot of efforts are being carried out by the scientific community to develop different nanomaterials because of their unique optical, electrical and structural properties at the nanoscale

D

level [1]. These are being used in sensing of different analytes for environmental, medical,

TE

pharmaceutical and biological purposes [1]; energy related applications such as in batteries,

EP

supercapacitors, fuel cells etc. [2] and for development of various kinds of solar cells [3]. Organic and inorganic pollutants including contamination of water by dyes and toxic metal ions

CC

is a serious issue. Widely used dye like methylene blue (MB), a cationic dye is a major waste effluent of textile industries. It is carcinogenic and harmful for the aquatic environment [4]. On

A

the other hand toxic metal pollution has increased over the years chiefly due to rise in battery, electronics, electroplating, paints and pigments industries; mining and excessive use of pesticides. It is hazardous and life threatening for living beings with their non-biodegradablity and bioaccumulative behavior and toxicity even at trace concentrations [5] with low permissible

3

limits of 3 ppb and 10 ppb for Cd2+ and Pb2+ respectively as given in the guidelines of the World Health Organization (WHO) [6]. Hence, research on the removal and degradation of MB dye [4, 7] and sensing of toxic metal ions [8-11] is being actively carried out. Materials like conducting

SC RI PT

polymers, carbonaceous nanomaterials including but not limited to carbon nanotubes, graphene and graphene quantum dots; metal oxides, noble metal nanoparticles are in huge demand for

fabrication of nanocomposites or composites for the above purposes. Polypyrrole, is one such

conducting polymer which has gained much importance due to its advantages like easy synthesis, good redox activity and conductivity, stability, environment friendly nature and biocompatibility

U

[12, 13]. It has been used in conjunction with other nanomaterials in order to further enhance its

N

properties for applications in catalysis [14-18], sensing [19-22], supercapacitors [23, 24],

A

batteries [25], solar cells [26] and as adsorbent for removal of water pollutants [27-29].

M

Consequently, multi-walled carbon nanotubes (MWCNTs), with good electrical and optical properties combined with their porous, layered and hollow nanostructures have garnered

D

immense interest in various fields [30]. Polypyrrole composites with MWCNT have been used in

TE

the recent past for many applications like in the research works of Bhaumik et al. [27], Zhang et

EP

al. [31], Gemeiner et al. [32] and Sharma et al. [33]. The π-π interaction between Ppy and MWCNT leads to the formation of a stable system with useful synergistic combination. Among

CC

the metal nanoparticles, gold nanoparticles (AuNPs) have attracted tremendous attention with their superior catalytic activity (electrochemical and chemical reactions), biocompatibility and

A

stability [34, 35]. The matrix used for the support of metal nanoparticles also plays a vital role in their effective usage [18]. AuNPs in combination with polymers which provide the required mechanical strength have been extensively used as high quality catalysts, chemical and biosensors [19, 35, 36].

4

Therefore, it was found noteworthy to synthesize a composite consisting of Ppy along with oxidized MWCNT and AuNPs (OMWCNT/Ppy/Au), prepared by chloroauric acid (HAuCl4) as the oxidant and investigation of its properties. Since pyrrole has a low oxidation

SC RI PT

potential, AuCl4- could easily oxidize it. AuNPs were generated in situ and OMWCNT helped in giving a tubular morphology to the resulting composite in which AuNPs were embedded thus

gaining stablity. It had excellent catalytic activity towards reduction of methylene blue dye and it

N

U

was also shown to interact with Cd2+ ions both optically and electrochemically.

A

2. Experimental

M

2.1 Materials and methods

Pyrrole monomer (99%, Spectrochem) was purified by distillation before use, chloroauric

D

acid (HAuCl4) and Methylene blue (MB, C.I. No. 52015) were purchased from Thomas Baker,

TE

Multi-walled carbon nanotubes (MWCNT, 95%) with outer diameter of 20-30 nm and length 10

EP

- 30 μm were purchased from SRL and rest of the chemicals were of AR grade and used without any purification - cadmium chloride, CdCl2.H2O (CDH), lead acetate, Pb(CH3COO)2.3H2O

CC

(CDH), zinc acetate, Zn(CH3COO)2.2H2O (CDH), nickel chloride, NiCl2.6H2O (S.D. Fine Chem. Limited), mercuric chloride, HgCl2 (CDH), cobalt(II) acetate tetrahydrate,

A

Co(CH3COO)2.4H2O (Fisher Scientific), potassium ferrocyanide, K4Fe(CN)6.3H2O (CDH), potassium ferricyanide, K3Fe(CN)6 (SRL), ammonium persulfate, (NH4)2S2O8 (APS) (CDH), sodium acetate, CH3COONa.3H2O (Fisher Scientific), glacial acetic acid, CH3COOH (SRL) and sodium borohydride, NaBH4 (Merck). Nafion D-520 dispersion (Alfa Aesar), Nitric acid (HNO3), Sulphuric acid (H2SO4) and absolute ethanol were also used as such. The use of 5

deionized water (D. I., resistivity: 18.2 MΩ cm at 25 oC) was carried out in the experiments and 100 ppm stock solutions of all metal salts (Cd2+, Pb2+, Co2+, Ni2+, Zn2+ and Hg2+) were used for making further dilutions.

SC RI PT

2.2 Characterization Shimadzu IRAffinity-1S instrument was used to obtain the FT-IR spectra in ATR mode with resolution of 4 cm-1 in the range 4000-400 cm-1. UV-Vis absorption spectra were recorded on Hitachi U-2900 spectrophotometer. The morphological analysis was performed on SEM

ZEISS EVO18 for Scanning Electron Microscopy (SEM) and Tecnai T20 (FEI) Netherland for

U

High-Resolution Transmission Electron Microscopy (HRTEM). Photoluminescence (PL) studies

N

were done on Cary Eclipse Fluorescence Spectrophotometer (Agilent Technologies) while

A

PANalytical’s X-ray diffractometer was used to take X-ray diffraction (XRD) pattern with Cu

M

Kα radiation (λ = 1.541 Å) and X-ray photoelectron spectroscopy (XPS) using Al Kα (1486.71 eV) as X-ray source was carried out on ESCA+ Omicron Nanotechnology Oxford instrument.

D

The fabrication of Ppy, OMWCNT/Ppy and OMWCNT/Ppy/Au electrodes was

TE

performed by drop casting technique. Uniform and homogeneous slurry of the material (~5 mg),

EP

nafion (5 μL) in isopropanol was prepared by ultrasonication and 20 μL of it was drop-casted onto pre-cleaned 1 cm × 3 cm indium tin oxide (ITO) electrode, limited to an area of 1 cm2. All

CC

electrochemical experiments including differential pulse voltammetry (DPV), cyclic voltammetry and electrochemical impedance spectroscopy (EIS) were executed in a three-

A

electrode electrochemical cell attached to a bipotentiostat (CS2350, CorrTest Instruments). Bare/unmodified ITO, Ppy, OMWCNT/Ppy and OMWCNT/Ppy/Au modified ITO were employed as the working electrodes, platinum wire was used as the auxiliary electrode with Ag/AgCl (3 M KCl) being the reference electrode. The electrolyte for cyclic voltammetry and

6

EIS was 1 mM Fe(CN)63-/4- (aq) combined with a supporting electrolyte of 0.1 M KCl and for DPV, 0.1 M sodium acetate-acetic acid buffer (HAc-NaAc), pH 5.3 was used. The electrochemical detection of Cd2+ (3 ppm) was found out by DPV with the following parameters-

SC RI PT

potential window: -1.0 V to 0 V, increment potential: 0.004 V, pulse amplitude: 0.050 V, pulse period: 0.2 s and pulse width: 0.03 s. EIS was carried out in a frequency range between 1 MHz and 0.1 Hz at a bias potential of 0.2 V and amplitude of 5 mV. 2.3 Preparation of oxidized MWCNT from pristine MWCNT

Oxidized MWCNT were synthesized according to a reported method in literature [37].

U

0.5 g of MWCNT were mixed in a solution of concentrated HNO3 and H2SO4 (50 mL, 1:3 v/v).

N

The dispersion was ultrasonicated for 1 h. After that, it was refluxed at 90 °C for 12 h, followed

A

by filtration and washing with copious amounts of D. I. water until pH 7 was attained. Later, the

M

product obtained was further dried at 60 °C for 24 h. 2.4 Preparation of OMWCNT/Ppy/Au composite

D

The composite was prepared by oxidative polymerization using chloroauric acid

TE

(HAuCl4) as the oxidant [16, 38]. Initially, the OMWCNT (0.2 g) were dispersed in 100 mL H2O

EP

by ultrasonication for 15 minutes. It was followed by addition of 0.8 mL pyrrole (0.1 M) and again ultrasonicated for 15 minutes. Thereafter, 30 mM aqueous solution of HAuCl4 was added

CC

dropwise to it with continuous stirring. The reaction mixture was allowed to stir for 24 h, followed by filtration and washing with D. I. water. The product obtained was further dried at 60

A

°C overnight.

OMWCNT/Ppy was also prepared for comparison purposes without AuNPs using

ammonium persulfate as the oxidant. It was prepared by the same method used for

7

OMWCNT/Ppy/Au composite, with the only difference being drop wise addition of APS (0.2 M) instead of HAuCl4. 2.5 Catalysis procedure

SC RI PT

Catalysis experiment was performed according to a reported method [39]. An aqueous MB dye solution was prepared by adding 6.7 mg MB dye to 100 mL H2O. It was diluted by H2O in the ratio (1:2 v/v). 20 mg of OMWCNT/Ppy/Au composite was added to 3 mL of diluted MB dye solution which was stirred and it was followed by immediate addition of 0.5 mL solution of NaBH4 ( 1.12 g in 10 mL H2O). The resulting color change was observed. The same catalysis

U

experiment was also carried out separately with only OMWCNT/Ppy/Au composite and NaBH4

A

N

to check their individual effects.

M

3. Results and discussion

3.1 Formation mechanism of OMWCNT/Ppy/Au composite

D

The composite was formed by a redox reaction between pyrrole and HAuCl4 in aqueous

TE

medium as reported by Selvan et al. [38], where HAuCl4 acted as the oxidant and pyrrole as the

EP

reductant. It was possible due to low oxidation potential of pyrrole monomer and its solubility in water. The tubular morphology was provided by OMWCNT. The functionalization of pristine

CC

MWCNT by oxygen containing functional groups like –COOH helped it to easily disperse in water and for further interactions such as hydrogen bonding. Initially pyrrole monomers

A

adsorbed on OMWCNT through non-covalent interactions and on addition of HAuCl4, polymerization occurred producing polypyrrole wrapped on to OMWCNT and simultaneously generated AuNPs embedded into the matrix of composite, (Fig. 1). 3.2 FT-IR analysis

8

Fig. 2A with insets represents the FT-IR spectra of MWCNT and OMWCNT. It was in accordance with literature [40, 41]. It was observed that the main peaks representing OMWCNT had developed and found at 1629 cm-1, 1720 cm-1 and 3446 cm-1 ascribed to carbonyl, carboxyl

SC RI PT

and hydroxyl group stretching vibration modes. Besides, other peaks observed at 1581 cm-1, 1381 cm-1, 1259 cm-1, 1104 cm-1 and 804 cm-1 were assigned to aromatic C=C stretching, O-H

deformation, C-C (phenyl carbonyl C-C stretch), C-O stretching vibration and aromatic C-C out of plane bending vibrations. In FT-IR spectrum of OMWCNT/Ppy/Au (Fig. 2B), it was noticed that tetrachloroaurate successfully polymerized/oxidized pyrrole monomer to polypyrrole. The

U

characteristic Ppy peaks attributed to ring and C-N stretching vibrations appeared at 1500 cm-1

N

and 1283 cm-1, while C-H in-plane deformation mode of vibration was observed at 1025 cm-1.

A

The doping state of Ppy was depicted by strong peaks at 1160 cm-1 and 900 cm-1 [42, 43].

M

Furthermore, carboxyl functional group of OMWCNT was observed around 1700 cm-1. The predominance of Ppy peaks in the FT-IR spectrum showed that OMWCNT were wrapped by

D

Ppy layer [44], as observed in morphological analysis by HRTEM. Also, the broad and weak N-

TE

H band denoted it being involved in interactions with other moieties- OMWCNT (through

EP

oxygen containing functional groups) and AuNPs [45]. Similar FT-IR spectrum was obtained for OMWCNT/Ppy (Fig. S1 supplementary data) that also depicted the typical Ppy peaks at 1550

CC

cm-1, 1460 cm-1, 1280 cm-1, 1174 cm-1, 1036 cm-1 and 900 cm-1 while the OMWCNT were represented by its carboxyl functional group at ~ 1700 cm-1. Thus, it suggested that both HAuCl4

A

and APS were able to successfully polymerize Ppy over OMWCNT surface. 3.3 HRTEM and SEM analysis The surface morphology of OMWCNT, OMWCNT/Ppy and OMWCNT/Ppy/Au was analyzed using SEM (Fig. 3) and HRTEM (Fig. 4). The SEM images of OMWCNT (Fig. 3a) and

9

OMWCNT/Ppy (Fig. 3b) established that the former were seen as thin long fibers whereas the latter comparatively had thicker fibers with an enlarged diameter due to polymerization of pyrrole around the OMWCNT. In the case of OMWCNT/Ppy/Au (Fig 3c), fibrous structures of

SC RI PT

OMWCNT/Ppy with AuNPs that were embedded into it were clearly visible. They were distributed over the surface of the composite thus justifying its formation by in-situ oxidation of pyrrole monomer using tetrachloroaurate.

Further insight into the surface morphology was provided by HRTEM analysis, whereby it can be seen from Fig. 4a that the long tubular structure of OMWCNT was maintained with an

U

average diameter of ~ 15 nm. The lattice fringes of OMWCNT were clearly visible in the

N

HRTEM micrograph (Fig. S2 supplementary data) with lattice spacing of ~0.34 nm

A

corresponding to (002) plane of OMWCNT [46] and SAED pattern also gave the same result,

M

with d= 0.34 nm. In OMWCNT/Ppy/Au composite (Fig.4b), Ppy was distinctly noticeable as a shell around the core of OMWCNT. It had liberally deposited and nicely coated the carbon

D

nanotubes. The thickness of the composite tubes was larger than OMWCNT with spherical

TE

AuNPs embedded into the composite. High magnification images (Fig. 4c) depicted the AuNP to

EP

be positioned in between OMWCNT. The SAED patterns of OMWCNT (Fig. S2 supplementary data), OMWCNT/Ppy and OMWCNT/Ppy/Au (Fig. S3 supplementary data) were also compared

CC

for further information which denoted that in the case of OMWCNT and OMWCNT/Ppy/Au better crystallinity was observed than in OMWCNT/Ppy. Thus, OMWCNT/Ppy represented

A

amorphous structure signifying the wrapping of crystalline OMWCNT by amorphous Ppy. Calculation of interplanar distance (d) from the SAED pattern of OMWCNT/Ppy/Au gave d=0.34 nm for (002) plane of OMWCNT (using first ring) and the second ring gave d=0.22 nm for (111) plane of AuNPs.

10

3.4 XPS analysis XPS analysis was carried out to know about the chemical composition of OMWCNT/Ppy/Au composite and interactions among the constituents (Fig. 5). The survey scan

SC RI PT

(Fig. 5a) revealed the existence of Au, C, N and O elements at their characteristic binding energies of 83.0 eV (Au 4f7/2) and 86.4 eV (Au 4f5/2) for Au (0) [47], 284.0 eV for C 1s, 399.4 eV for N 1s and 531.9 eV for O 1s [48] signifying the successful formation of composite. The high resolution XPS spectrum of C 1s (Fig. 5b) depicted the presence of six peaks with main peak at 284.0 eV and other peaks at 285.1 eV, 286.1 eV, 287.3 eV, 289.0 eV and 291.0 eV

U

attributed to C-C, C-C (carbon nanotubes defects), C-O/C-N, C=O/C=N, COOH and π species

N

respectively [49]. In addition, the high resolution N 1s spectrum (Fig. 5c) was deconvoluted into

A

four peaks revealing the existence of neutral nitrogen (-NH-) of pyrrole at 399.4 eV, imine

M

nitrogen (=N-) at 397.0 eV suggesting deprotonation of nitrogen and its interaction with AuNPs and carboxyl groups of OMWCNT, polaron (-N+) and bipolaron (=N+) species at 401.2 eV and

D

402.9 eV [48, 50] respectively. The interaction of pyrrolic nitrogen (-NH-) was also verified by

TE

FT-IR investigation of the composite wherein the band for N-H was very weak.

EP

3.5 X-ray diffraction study

XRD pattern of OMWCNT (Fig. 6a) depicted its typical reflections by (002) plane at 2θ

CC

= 25.8o, with interlayer spacing of d = 0.35 nm between graphitic layers similar to that obtained by HRTEM and its SAED pattern; (001) and (004) planes at 2θ = 42.7o and 53.2o respectively

A

[51]. The diffraction pattern due to the composite OMWCNT/Ppy/Au (Fig. 6b) showed a peak at 2θ = 25.8o with decreased intensity which was assigned to the combination of Ppy and OMWCNT, since Ppy also displays its diffraction peak at 2θ = 20-30o [52], therefore the decrease in the intensity of this peak denoted the covering of carbon nanotubes by Ppy [27].

11

Other peaks observed were due to the fcc lattice structure of Au (0) at 2θ = 37.9o, 44.1o and 64.6o attributed to (111), (200), (220) planes [45, 53] and a weak diffraction peak at 2θ = 53.0o due to OMWCNT. The size of AuNPs in the composite was calculated to be 4.3 nm using the peak at

SC RI PT

2θ = 37.9o by Debye-Scherrer equation and the interplanar distance (d) of (111) plane of AuNPs calculated from XRD data was 0.23 nm analogous to that obtained by SAED pattern. The XRD results were in line with other techniques, thus signaling the uniform hybridization of all the moieties. 3.6 UV-Vis spectroscopic analysis

U

The UV-Vis absorption spectrum of OMWCNT/Ppy/Au aqueous dispersion (Fig. 7)

N

showed the presence of mainly two peaks at 235 nm and 442 nm attributed to the transition of π-

A

electrons of OMWCNT and π→π* transition of Ppy combined with absorbance peak due to

M

AuNPs respectively [54, 55]. The Surface Plasmon Resonance (SPR) peak of AuNPs generally obtained at 520 nm was not visible here due to the overlapping of Ppy peak with this peak in the

D

same region. Moreover, this suggested that very small AuNPs were formed in-situ and dispersed

TE

into the composite as reported in literature [55]. Also, electron-hole type interaction between Au

EP

nanoparticles and doped polypyrrole caused its absence [56]. 3.7 Catalytic activity

CC

The catalytic activity of OMWCNT/Ppy/Au composite was evaluated by studying reduction of MB dye. It was carried out by observing the progress of the absorbance value at

A

λmax. The catalytic property was tested by the reduction of MB dye using NaBH4 as the reductant in water. Fig. 8 represents the corresponding UV-Vis absorption spectra of the dye under various circumstances such as pristine dye solution (Fig. 8a), with only the reducing agent (Fig. 8b) and with the composite along with the reducing agent (Fig. 8c). Absorption spectrum of the pristine

12

aqueous MB dye had the λmax at 663 nm with a shoulder at 612 nm attributed to its dimer. Fig. 8b representing the absorption spectrum that was taken immediately after addition and stirring NaBH4 into it indicated a decrease in the absorbance intensity at the λmax of MB dye, however

SC RI PT

complete vanishing of blue color was not observed and the color of the solution only slightly lightened. This solution was kept for 3-4 h that resulted in very light blue color but still it did not completely disappear. Fig. 8c, depicting the absorption spectrum of MB dye solution with NaBH4 in the presence of 20 mg of OMWCNT/Ppy/Au composite as a catalyst displayed

complete absence of absorbance at λmax with reduction of MB dye forming leucomethylene blue

U

(LMB) and its blue color vanished completely within a matter of few seconds (~ 5 s). The

N

absorption spectrum of the same solution was also studied in the range from 200 nm to 1100 nm,

A

that depicted the absence of peaks at ~ 300 nm and a decreased intensity of absorbance at 245

M

nm along with the disappearence of the peak at λmax thus inferring that reduction with mineralization of MB dye had occurred [57]. In another experiment, in which only the

D

composite was added to the MB dye solution without NaBH4, it was noticed that the complete

TE

disappearence of blue color of the dye did not take place and it only occurred in the presence of

EP

both the composite and NaBH4, revealing that the composite was indeed acting as a catalyst in the degradation process. Moreover, the activity of the composite was checked after recovery

CC

from a previous reaction in which it was kept for 24 h and it was still found to be working with similar rate. The above experiment proved that the OMWCNT/Ppy/Au composite had excellent

A

catalytic property making the process very fast. The efficiency of the heterogeneous catalyst depends on its easy separation from the solution and repeatability/reuse. This issue had also been solved by the composite as it could be effortlessly separated by common centrifugation. It was possible as polypyrrole increased the size of the composite. Furthermore, the catalyst was used

13

for nine consecutive cycles to check its repeatability. Each time after centrifugation it was rinsed with deionized water. The results indicated that same efficiency was there for three cycles and after that till ninth cycle the time period taken by the catalyst was just 1-1.5 minutes. The nano

SC RI PT

architecture and catalytic activity of AuNPs and OMWCNT combined with the good adsorbent property of the composite made this achievable.

The site of the reduction and degradation of MB dye by NaBH4 was AuNPs supported on OMWCNT and Ppy (Fig. 9). The advantages of the prepared composite were that AuNPs were not located deep inside into the matrix and hence were easily available for the reaction and

U

secondly high surface-to-volume ratio was made available by the AuNPs and OMWCNT [7d,

N

18]. The vital role of OMWCNT with sp2 hybridized carbon atoms and Ppy was to provide a

A

highly conductive support matrix with excellent electron tunneling channel and to adsorb the

M

aromatic dye molecules through π-π interactions and hydrogen bonding [4, 7d]. On the other side, Ppy which has positively charged backbone helped to bring BH4- in close vicinity of the

D

adsorbed dye molecules. After adsorption step, BH4- transferred the electron to the composite

TE

which in turn was donated to the electrophilic dye molecule. Thus, the composite acted as an

EP

electron relay system [57] which encouraged fast electron transfer as also evidenced by cyclic voltammetry and EIS studies, promoting the reduction and mineralization of MB dye. Moreover

CC

the mineralization of the MB dye was caused by the formation of reactive oxygen species (ROS) due to the reaction between the electrons that were captured by the composite acting as the

A

catalyst and the dissolved oxygen [57]. 3.8 Electrochemical analysis Electroactivity of bare ITO, Ppy, OMWCNT/Ppy and OMWCNT/Ppy/Au electrodes was checked by cyclic voltammetry within a potential window of -0.5 V to +1.0 V and at a scan rate

14

of 0.025 V s-1 (Fig. 10). It was observed that the voltammograms represented clear reductionoxidation peaks of Fe(CN)63-/4- species with quasi-reversible nature. The Ppy, OMWCNT/Ppy and OMWCNT/Ppy/Au electrodes exhibited increased redox current as compared to bare ITO

SC RI PT

proving the successful deposition on ITO by more conductive materials. Maximum peak current was recorded for OMWCNT/Ppy/Au electrode due to its better charge transfer capability owing to the superior electron channel provided by OMWCNT and AuNPs along with the high

conductivity of AuNPs [22]. Moreover the incorporation of OMWCNT and AuNPs made the

surface-to-volume ratio higher thus improving its charge transport property [58]. Furthermore,

U

OMWCNT electrode was also subjected to cyclic voltammetry studies at various scan rates (Fig.

N

S4 supplementary data) and it represented a pair of redox peaks of Fe(CN)63-/4- overlying on

A

background currents generated by electrical double layer capacitance as MWCNT exhibit this

M

property [59].

Electrochemical impedance spectroscopy was also carried out to demonstrate the changes

D

produced in electron transfer property of the modified electrodes. It was studied by the

TE

corresponding Nyquist plots (Fig. 10). They displayed a semi-circle at high frequency region

EP

which was attributed to the charge transfer resistance (Rct) and the lower frequency region indicated about diffusion process. Since, the diameter of the semi-circle is a measure of Rct, it

CC

suggested that OMWCNT/Ppy/Au electrode had the lowest Rct thus favoring the charge transfer vis-à-vis Ppy and OMWCNT/Ppy electrodes, corroborating the results of cyclic voltammetry.

A

Literature study has also shown that AuNPs are associated with lowering the Rct values by increasing conductivity and thus facilitating electron transfer [20,21]. 3.9 Study of detection of Cd2+by the composite- optically and electrochemically

15

Cd2+ (20 ppb) was added to the aqueous dispersion of the composite in order to study its interaction with it. The absorption spectrum of Cd2+ incorporated dispersion (Fig. 11) revealed the presence of new and additional peaks at 1031 nm, 746 nm, 591 nm and 540 nm, assigned to

SC RI PT

polaronic and bipolaronic transitions from valence band of Ppy [60, 61] and the peak at 540 nm signaled the SPR of AuNPs which was now noticeable as Cd2+ caused changes in the structure of composite attributed to coordination with nitrogen in Ppy and also with electron rich OMWCNT. The peak at 235 nm ascribed to the π-electrons of OMWCNT suffered a hypochromic shift

because of their interaction with Cd2+ ions. This was also shown by PL curves (inset of Fig. 11)

U

of OMWCNT/Ppy/Au aqueous dispersion. The emission spectra were obtained at 235 nm

N

excitation wavelength, before and after addition of Cd2+ ions (20 ppb). A peak at 473 nm was

A

observed in both the spectra with decreased intensity in the latter due to quenching of PL

M

depicting interaction of Cd2+ ions.

The composite OMWCNT/Ppy/Au was also electrochemically tested for its ability to

D

interact with Cd2+ ions and hence help in its detection using OMWCNT/Ppy/Au modified ITO

TE

electrode. DPV technique was used and the electrolyte was 0.1 M HAc-NaAc, pH 5.3 which was

EP

optimized in a range of pH 4 to 6. It was revealed from Fig. 12, that Cd2+ was clearly detected at a potential of -0.75 V and on addition of Cd2+ ions (0.1- 1.1 ppm), its peak current increased

CC

linearly with increasing concentration (R2= 0.99) as observed from the calibration graph, thus depicting its ability to detect Cd2+ ions. The electrode displayed good repeatability as the relative

A

standard deviation (RSD) for Cd2+ detection was found to be 2.74% (n=8). The interference to Cd2+ ions detection was checked by common interferents viz. Pb2+, Co2+, Ni2+, Zn2+ and Hg2+ at tenfold concentration with respect to it. It was noticed that no interference was there making it selective towards Cd2+ ions. The other electrodes viz. OMWCNT/Ppy and Ppy were also checked

16

for Cd2+ detection however poor linearity (R2= 0.80 and R2= 0.36 respectively) and a poor response was recorded for them. Furthermore, a comparison among different electrodes as a function of Cd2+ peak current obtained using a concentration of 1 ppm showed that

SC RI PT

OMWCNT/Ppy/Au electrode performed better than the other two electrodes (Fig. S5 supplementary data). 4. Conclusions

In summary, OMWCNT/Ppy/Au composite was synthesized in a facile way. Its

successful preparation was demonstrated by different analytical techniques. FT-IR and XPS

U

results indicated the involvement of pyrrolic –NH group in interactions with other components.

N

HRTEM results had good correlation with XRD analysis. UV-Vis studies also corroborated the

A

fact that the different moieties hybridized together with the dispersion of very small AuNPs. The

M

electron transfer properties enhanced, by incorporation of AuNPs and OMWCNT in Ppy owing to the high surface-to-volume ratio and electrical conductivity provided by them. It was also

D

shown that the composite was able to detect Cd2+ ions by DPV and PL technique making it a

TE

potential candidate to be explored further in this field of sensing. Furthermore, its ability to make

EP

the reduction and mineralization process of methylene blue in combination with NaBH4 extremely fast, made its catalytic and adsorption properties evident. Hence, it could be useful for

CC

toxic waste water analysis and treatment.

A

Acknowledgements Financial assistance was given by Guru Gobind Singh Indraprastha University (GGSIPU)

as Indraprastha Research Fellowship (IPRF)- GGSIPU/DRC/Ph.D/Adm./2014/1634 awarded to one of the authors (Shruti Peshoria). She wishes to thank GGSIPU for it. Also the authors would

17

like to thank Ms. Neeru Sharma for providing administrative services, Jamia Millia Islamia (New Delhi) for PL and MNIT, Jaipur for HRTEM and XPS facility.

A

N

U

SC RI PT

Conflicts of interest: none

M

References

[1] G. Aragay, F. Pino, A. Merkoçi, Nanomaterials for sensing and destroying pesticides, Chem.

D

Rev. 112 (2012) 5317-5338.

TE

[2] H. K. Liu, An overview—Functional nanomaterials for lithium rechargeable batteries,

EP

supercapacitors, hydrogen storage, and fuel cells, Mater. Res. Bull. 48 (2013) 4968-4973. [3] S. Kumar, M. Nehra, A. Deep, D. Kedia, N. Dilbaghi, K.-H. Kim, Quantum-sized

CC

nanomaterials for solar cell applications, Renew Sustain. Energy Rev. 73 (2017) 821-839. [4] J. Chen, J. Feng, W. Yan, Influence of metal oxides on the adsorption characteristics of

A

PPy/metal oxides for Methylene Blue, J. Colloid Interface Sci. 475 (2016) 26-35.

[5] H. Huang, T. Chen, X. Liu, H. Ma, Ultrasensitive and simultaneous detection of heavy metal ions based on three-dimensional graphene-carbon nanotubes hybrid electrode materials, Anal. Chim. Acta 852 (2014) 45-54.

18

[6] W.H. Organization, Guidelines for Drinking-Water Quality, World Health Organization, 2011. [7] a) R. Atchudan, T.N.J.I. Edison, S. Perumal, D. Karthikeyan, Y.R. Lee, Facile synthesis of

SC RI PT

zinc oxide nanoparticles decorated graphene oxide composite via simple solvothermal route and their photocatalytic activity on methylene blue degradation, J. Photochem. Photobiol. B 162 (2016) 500-510; b) K. Tahir, A. Ahmad, B. Li, S. Nazir, A.U. Khan, T. Nasir, Z.U.H. Khan, R. Naz, M. Raza, Visible light photo catalytic inactivation of bacteria and photo

degradation of methylene blue with Ag/TiO2 nanocomposite prepared by a novel method, J.

U

Photochem. Photobiol. B 162 (2016) 189-198; c) S. Mondal, M.E. De Anda Reyes, U. Pal,

N

Plasmon induced enhanced photocatalytic activity of gold loaded hydroxyapatite

A

nanoparticles for methylene blue degradation under visible light, RSC Adv. 7 (2017) 8633-

M

8645; d) D. Robati, S. Bagheriyan, M. Rajabi, O. Moradi, A.A. Peyghan, Effect of electrostatic interaction on the methylene blue and methyl orange adsorption by the pristine

D

and functionalized carbon nanotubes, Physica E 83 (2016) 1-6; e) H. Lachheb, E. Puzenat, A.

TE

Houas, M. Ksibi, E. Elaloui, C. Guillard, J.-M. Herrmann, Photocatalytic degradation of

EP

various types of dyes (Alizarin S, Crocein Orange G, Methyl Red, Congo Red, Methylene Blue) in water by UV-irradiated titania, Appl. Catal. B. 39 (2002) 75-90; f) V. Selen, Ö.

CC

Güler, D. Özer, E. Evin, Synthesized multi-walled carbon nanotubes as a potential adsorbent for the removal of methylene blue dye: kinetics, isotherms, and thermodynamics, Desalin.

A

Water Treat. 57 (2016) 8826-8838; g) D. Robati, B. Mirza, R. Ghazisaeidi, M. Rajabi, O. Moradi, I. Tyagi, S. Agarwal, V.K. Gupta, Adsorption behavior of methylene blue dye on nanocomposite multi-walled carbon nanotube functionalized thiol (MWCNT-SH) as new adsorbent, J. Mol. Liq. 216 (2016) 830-835; h) X. Bao, Z. Qin, T. Zhou, J. Deng, In-situ

19

generation of gold nanoparticles on MnO2 nanosheets for the enhanced oxidative degradation of basic dye (methylene blue), J. Environ. Sci. 65 (2018) 236-245; i) L. Fan, C. Wei, Q. Xu, J. Xu, Polypyrrole-coated cotton fabrics used for removal of methylene blue from aqueous

SC RI PT

solution, J. Text. Inst. 108 (2017) 1847-1852. [8] M.A. Deshmukh, M. Gicevičius, A. Ramanaviciene, M. Shirsat, R. Viter, A. Ramanavicius, Hybrid electrochemical/electrochromic Cu(II) ion sensor prototype based on PANI/ITOelectrode, Sens. Actuators B 248 (2017) 527-535.

[9] L. Dedelaite, S. Kizilkaya, H. Incebay, H. çiftçi, M. Ersoz, Z. Yazicigil, Y. Oztekin, A.

U

Ramanaviciene, A. Ramanavicius, Electrochemical determination of Cu(II) ions using glassy

N

carbon electrode modified by some nanomaterials and 3-nitroaniline, Colloids Surf. A 483

A

(2015) 279-284.

M

[10] A.D. Arulraj, R. Devasenathipathy, S.-M. Chen, V.S. Vasantha, S.-F. Wang, Femtomolar detection of mercuric ions using polypyrrole, pectin and graphene nanocomposites modified

D

electrode, J. Colloid Interface Sci. 483 (2016) 268-274.

TE

[11] M.R. Mahmoudian, W.J. Basirun, Y. Alias, A sensitive electrochemical Hg2+ ions sensor

EP

based on polypyrrole coated nanospherical platinum, RSC Adv. 6 (2016) 36459-36466. [12] A. Kausaite-Minkstimiene, V. Mazeiko, A. Ramanaviciene, A. Ramanavicius, Evaluation of

CC

chemical synthesis of polypyrrole particles, Colloids Surf. A 483 (2015) 224-231. [13] N. Aravindan, M. Kanagaraj, M.V. Sangaranarayanan, Tuning the magnetic and structural

A

properties of electrodeposited nickel-polypyrrole (Ni-PPy) composites through moderate stirring, Mater. Chem. Phys. 174 (2016) 6-10.

[14] L. Zhang, X. Liu, Y. Wang, S. Xing, Controllable silver embedding into polypyrrole, J. Alloys Compd. 709 (2017) 431-437.

20

[15] U. Mandi, S.K. Kundu, N. Salam, A. Bhaumik, S.M. Islam, Ag@polypyrrole: A highly efficient nanocatalyst for the N-alkylation of amines using alcohols, J. Colloid Interface Sci., 467 (2016) 291-299.

SC RI PT

[16] W. Wang, Y. Gao, X. Jia, K. Xi, A novel Au-Pt@PPy(polypyrrole) coral-like structure: facile synthesis, high SERS effect, and good electro catalytic activity, J. Colloid Interface Sci. 396 (2013) 23-28.

[17] X. Li, M. Zhu, B. Dai, AuCl3 on polypyrrole-modified carbon nanotubes as acetylene hydrochlorination catalysts, Appl. Catal. B 142 (2013) 234-240.

U

[18] T. Yao, T. Cui, H. Wang, L. Xu, F. Cui, J. Wu, A simple way to prepare

N

Au@polypyrrole/Fe3O4 hollow capsules with high stability and their application in catalytic

A

reduction of methylene blue dye, Nanoscale 6 (2014) 7666-7674.

M

[19] N. German, A. Ramanavicius, A. Ramanaviciene, Amperometric Glucose Biosensor Based

29 (2017) 1267-1277.

D

on Electrochemically Deposited Gold Nanoparticles Covered by Polypyrrole, Electroanalysis

TE

[20] M. Dervisevic, E. Dervisevic, E. Çevik, M. Şenel, Novel electrochemical xanthine biosensor

EP

based on chitosan–polypyrrole–gold nanoparticles hybrid bio-nanocomposite platform, J. Food Drug Anal. 25 (2017) 510-519.

CC

[21] M. Tertiș, A. Cernat, D. Lacatiș, A. Florea, D. Bogdan, M. Suciu, R. Săndulescu, C. Cristea, Highly selective electrochemical detection of serotonin on polypyrrole and gold

A

nanoparticles-based 3D architecture, Electrochem. Commun. 75 (2017) 43-47.

[22] A. Güner, E. Çevik, M. Şenel, L. Alpsoy, An electrochemical immunosensor for sensitive detection of Escherichia coli O157:H7 by using chitosan, MWCNT, polypyrrole with gold nanoparticles hybrid sensing platform, Food Chem. 229 (2017) 358-365.

21

[23] X. Wu, M. Lian, Highly flexible solid-state supercapacitor based on graphene/polypyrrole hydrogel, J. Power Sources 362 (2017) 184-191. [24] P. Atri, D.C. Tiwari, R. Sharma, Synthesis of reduced graphene oxide nanoscrolls embedded

SC RI PT

in polypyrrole matrix for supercapacitor applications, Synth. Met. 227 (2017) 21-28. [25] X. Zhou, X. Chen, T. He, Q. Bi, L. Sun, Z. Liu, Fabrication of polypyrrole/vanadium oxide

nanotube composite with enhanced electrochemical performance as cathode in rechargeable batteries, Appl. Surf. Sci. 405 (2017) 146-151.

[26] J. Wu, Z. Lan, J. Lin, M. Huang, Y. Huang, L. Fan, G. Luo, Y. Lin, Y. Xie, Y. Wei, Counter

U

electrodes in dye-sensitized solar cells, Chem. Soc. Rev. 46 (2017) 5975-6023.

N

[27] M. Bhaumik, S. Agarwal, V.K. Gupta, A. Maity, Enhanced removal of Cr(VI) from aqueous

A

solutions using polypyrrole wrapped oxidized MWCNTs nanocomposites adsorbent, J.

M

Colloid Interface Sci. 470 (2016) 257-267.

[28] H.N. Muhammad Ekramul Mahmud, A.K.O. Huq, R.b. Yahya, The removal of heavy metal

D

ions from wastewater/aqueous solution using polypyrrole-based adsorbents: a review, RSC

TE

Adv. 6 (2016) 14778-14791.

EP

[29] Y. Huang, J. Li, X. Chen, X. Wang, Applications of conjugated polymer based composites in wastewater purification, RSC Adv. 4 (2014) 62160-62178.

CC

[30] Y.-K. Lee, K.-J. Lee, D.-S. Kim, D.-J. Lee, J.-Y. Kim, Polypyrrole-carbon nanotube composite films synthesized through gas-phase polymerization, Synth. Met. 160 (2010) 814-

A

818.

[31] Y. Zhang, Y. Zhao, Z. Bakenov, M. Tuiyebayeva, A. Konarov, P. Chen, Synthesis of Hierarchical Porous Sulfur/Polypyrrole/Multiwalled Carbon Nanotube Composite Cathode for Lithium Batteries, Electrochim. Acta 143 (2014) 49-55.

22

[32] P. Gemeiner, J. Kuliček, M. Mikula, M. Hatala, Ľ. Švorc, L. Hlavatá, M. Mičušík, M. Omastová, Polypyrrole-coated multi-walled carbon nanotubes for the simple preparation of counter electrodes in dye-sensitized solar cells, Synth. Met. 210 (2015) 323-331.

SC RI PT

[33] S. Sharma, S. Hussain, S. Singh, S.S. Islam, MWCNT-conducting polymer composite based ammonia gas sensors: A new approach for complete recovery process, Sens. Actuators B 194 (2014) 213-219.

[34] A. Bilici, B. Ayten, İ. Kaya, Facile preparation of gold nanoparticles on the polyquinoline

matrix: Catalytic performance toward 4-nitrophenol reduction, Synth. Met. 201 (2015) 11-17.

U

[35] a) A. de Barros, C.J.L. Constantino, N.C. da Cruz, J.R.R. Bortoleto, M. Ferreira, High

N

performance of electrochemical sensors based on LbL films of gold nanoparticles,

A

polyaniline and sodium montmorillonite clay mineral for simultaneous detection of metal

M

ions, Electrochim. Acta 235 (2017) 700-708; b) E.G. Pineda, F. Alcaide, M.J.R. Presa, A.E. Bolzán, C.A. Gervasi, Electrochemical preparation and characterization of

D

polypyrrole/stainless steel electrodes decorated with gold nanoparticles, ACS Appl. Mater.

TE

Interfaces 7 (2015) 2677−2687.

EP

[36] A. Noschese, A. Buonerba, P. Canton, S. Milione, C. Capacchione, A. Grassi, Highly efficient and selective reduction of nitroarenes into anilines catalyzed by gold nanoparticles

CC

incarcerated in a nanoporous polymer matrix: Role of the polymeric support and insight into the reaction mechanism, J. Catal. 340 (2016) 30-40.

A

[37] S. Ramesh, Y. Haldorai, H.S. Kim, J.-H. Kim, A nanocrystalline Co3O4@polypyrrole/MWCNT hybrid nanocomposite for high performance electrochemical supercapacitors, RSC Adv. 7 (2017) 36833-36843. [38] S.T. Selvan, J.P. Spatz, H.A. Klok, M. Moller, Gold-Polypyrrole core-shell particles in

23

diblock copolymer micelles, Adv. Mater. 10 (1998) 132-134. [39] J. Wu, X. Zhang, T. Yao, J. Li, H. Zhang, B. Yang, Improvement of the stability of colloidal gold superparticles by polypyrrole modification, Langmuir 26 (2010) 8751-8755.

SC RI PT

[40] L. Stobinski, B. Lesiak, L. Kövér, J. Tóth, S. Biniak, G. Trykowski, J. Judek, Multiwall carbon nanotubes purification and oxidation by nitric acid studied by the FTIR and electron spectroscopy methods, J. Alloys Compd. 501 (2010) 77-84.

[41] Y.J. Kim, T.S. Shin, H.D. Choi, J.H. Kwon, Y.-C. Chung, H.G. Yoon, Electrical

conductivity of chemically modified multiwalled carbon nanotube/epoxy composites, Carbon

U

43 (2005) 23-30.

N

[42] X. Zhang, J. Zhang, Z. Liu, C. Robinson, Inorganic/organic mesostructure directed synthesis

A

of wire/ribbon-like polypyrrole nanostructures, Chem. Commun. (2004) 1852-1853.

M

[43] a) C. Tian, Y. Du, P. Xu, R. Qiang, Y. Wang, D. Ding, J. Xue, J. Ma, H. Zhao, X. Han, Constructing Uniform Core–Shell PPy@PANI Composites with Tunable Shell Thickness

D

toward Enhancement in Microwave Absorption, ACS Appl. Mater. Interfaces 7 (2015)

TE

20090-20099; b) S. Peshoria, A. K. Narula, Structural, morphological and electrochemical

EP

properties of a polypyrrole nanohybrid produced by template-assisted fabrication, J. Mater. Sci. 53 (2018) 3876-3888.

CC

[44] Y. Yu, C. Ouyang, Y. Gao, Z. Si, W. Chen, Z. Wang, G. Xue, Synthesis and characterization of carbon nanotube/polypyrrole core–shell nanocomposites via in situ inverse

A

microemulsion, J. Polym. Sci. Part A 43 (2005) 6105-6115.

[45] M. Aslam, L. Fu, M. Su, K. Vijayamohanan, V.P. Dravid, Novel one-step synthesis of amine-stabilized aqueous colloidal gold nanoparticles, J. Mater. Chem. 14 (2004) 1795-1797.

24

[46] O.V. Kharissova, B.I. Kharisov, Variations of interlayer spacing in carbon nanotubes, RSC Adv. 4 (2014) 30807-30815. [47] H. Wei, Z. Wang, L. Yang, S. Tian, C. Hou, Y. Lu, Lysozyme-stabilized gold fluorescent

SC RI PT

cluster: Synthesis and application as Hg2+ sensor, Analyst 135 (2010) 1406-1410. [48] C. Li, Y. Su, X. Lv, H. Xia, H. Shi, X. Yang, J. Zhang, Y. Wang, Controllable anchoring of gold nanoparticles to polypyrrole nanofibers by hydrogen bonding and their application in nonenzymatic glucose sensors, Biosens. Bioelectron. 38 (2012) 402-406.

[49] A. Miodek, N. Mejri, M. Gomgnimbou, C. Sola, H. Korri-Youssoufi, E-DNA Sensor of

U

Mycobacterium tuberculosis Based on Electrochemical Assembly of Nanomaterials

N

(MWCNTs/PPy/PAMAM), Anal. Chem. 87 (2015) 9257-9264.

A

[50] a) S. Akerboom, S.P. Pujari, A. Turak, M. Kamperman, Controlled Fabrication of

M

Polypyrrole Surfaces with Overhang Structures by Colloidal Templating, ACS Appl. Mater. Interfaces 7 (2015) 16507-16517; b) J. Tabačiarová, M. Mičušík, P. Fedorko, M. Omastová,

TE

Stab. 120 (2015) 392-401.

D

Study of polypyrrole aging by XPS, FTIR and conductivity measurements, Polym. Degrad.

EP

[51] Y.-C. Chiang, W.-H. Lin, Y.-C. Chang, The influence of treatment duration on multi-walled carbon nanotubes functionalized by H2SO4/HNO3 oxidation, Appl. Surf. Sci. 257 (2011)

CC

2401-2410.

[52] A.M. Bruck, C.N. Gannett, D.C. Bock, P.F. Smith, A.C. Marschilok, K.J. Takeuchi, E.S.

A

Takeuchi, The Electrochemistry of Fe3O4/Polypyrrole Composite Electrodes in Lithium-Ion Cells: The Role of Polypyrrole in Capacity Retention, J. Electrochem. Soc. 164 (2017) A6260-A6267.

25

[53] F.R. Caetano, L.B. Felippe, A.J.G. Zarbin, M.F. Bergamini, L.H. Marcolino-Junior, Gold nanoparticles supported on multi-walled carbon nanotubes produced by biphasic modified method and dopamine sensing application, Sens. Actuators B 243 (2017) 43-50.

SC RI PT

[54] H.A. Zeinabad, A. Zarrabian, A.A. Saboury, A.M. Alizadeh, M. Falahati, Interaction of single and multi wall carbon nanotubes with the biological systems: tau protein and PC12 cells as targets, Sci. Rep. 6 (2016) 26508.

[55] K. Xue, Y. Xu, W. Song, One-step synthesis of 3D dendritic gold@polypyrrole

nanocomposites via a simple self-assembly method and their electrocatalysis for H2O2,

U

Electrochim. Acta 60 (2012) 71-77.

N

[56] R. Gangopadhyay, A.D. Chowdhury, A. De, Functionalized polyaniline nanowires for

A

biosensing, Sens. Actuators B 171 (2012) 777-785.

M

[57] M.M. Khan, J. Lee, M.H. Cho, Au@TiO2 nanocomposites for the catalytic degradation of methyl orange and methylene blue: An electron relay effect, J. Ind. Eng. Chem. 20 (2014)

D

1584-1590.

TE

[58] E. Shamaeli, N. Alizadeh, Functionalized gold nanoparticle-polypyrrole nanobiocomposite with

EP

high effective surface area for electrochemical/pH dual stimuli-responsive smart release of insulin, Colloids Surf. B, 126 (2015) 502-509.

CC

[59] a) J. Koehne, J. Li, A. M. Cassell, H. Chen, Q. Ye, H. T. Ng, J. Han, M. Meyyappan, The fabrication and electrochemical characterization of carbon nanotube nanoelectrode arrays, J.

A

Mater. Chem. 14 (2004) 676-684; b) A. Afzal, F. A. Abuilaiwi, A. Habib, M. Awais, S. B. Waje, M. A. Atieh, Polypyrrole/carbon nanotube supercapacitors: Technological advances and challenges, J. Power Sources 352 (2017) 174-186.

[60] A. Singh, Z. Salmi, P. Jha, N. Joshi, A. Kumar, P. Decorse, H. Lecoq, S. Lau-Truong, D.K. Aswal, S.K. Gupta, M.M. Chehimi, One step synthesis of highly ordered free standing 26

flexible polypyrrole-silver nanocomposite films at air-water interface by photopolymerization, RSC Adv. 3 (2013) 13329-13336. [61] X.-G. Li, A. Li, M.-R. Huang, Y. Liao, Y.-G. Lu, Efficient and Scalable Synthesis of Pure

Nanoparticles, J. Phys. Chem. C 114 (2010) 19244-19255.

Figure captions

SC RI PT

Polypyrrole Nanoparticles Applicable for Advanced Nanocomposites and Carbon

Fig. 1. Schematic illustration for the preparation of OMWCNT/Ppy/Au composite.

U

Fig. 2. FT-IR spectra of A) (a) MWCNT (dotted line), (b) OMWCNT (solid line) with insets and

N

B) OMWCNT/Ppy/Au.

A

Fig. 3. SEM micrographs of (a) OMWCNT, (b) OMWCNT/Ppy and (c) OMWCNT/Ppy/Au.

M

Fig. 4. HRTEM images of (a) OMWCNT, (b) OMWCNT/Ppy/Au and high-magnification image showing (c) AuNP embedded in OMWCNT.

TE

1s and (c) N 1s.

D

Fig. 5. (a) XPS survey spectrum of OMWCNT/Ppy/Au and high resolution XPS spectra of (b) C

EP

Fig. 6. XRD pattern of (a) OMWCNT and (b) OMWCNT/Ppy/Au. Fig. 7. UV-Vis spectrum of OMWCNT/Ppy/Au composite.

CC

Fig. 8. UV-Vis absorption spectra of (a) pristine MB dye solution (b) solution of MB dye with NaBH4 taken immediately after its addition and stirring and (c) solution of MB dye with sodium

A

borohydride (NaBH4) in presence of 20 mg of OMWCNT/Ppy/Au as catalyst. Fig. 9. Schematic illustration for the proposed mechanism of MB dye reduction and mineralization by NaBH4 using OMWCNT/Ppy/Au as catalyst.

27

Fig. 10. (a) Cyclic voltammograms of (short dash dot line) bare ITO, (dot line) Ppy, (short dot line) OMWCNT/Ppy and (solid line) OMWCNT/Ppy/Au electrodes recorded under the following conditions: electrolyte: 1 mM Fe(CN)63-/4- (aq), supporting electrolyte: 0.1 M KCl,

SC RI PT

potential window: -0.5 V to +1.0 V and scan rate: 0.025 V s-1 and (b) Nyquist plots of (i) Ppy, (ii) OMWCNT/Ppy and (iii) OMWCNT/Ppy/Au electrodes recorded in 1 mM Fe(CN)63-/4- (aq)

with 0.1 M KCl in a frequency range between 1 MHz and 0.1 Hz at a bias potential of 0.2 V and amplitude of 5 mV.

Fig. 11. UV-Vis spectrum of OMWCNT/Ppy/Au with 20 ppb Cd2+ with inset representing PL

U

emission spectra of (i) OMWCNT/Ppy/Au without Cd2+ and (ii) OMWCNT/Ppy/Au with 20 ppb

N

Cd2+.

A

Fig. 12. Calibration curve of peak current versus different concentrations of Cd2+ ions with inset

M

representing the DPV responses at various concentrations of Cd2+ ions (0.1-1.1 ppm) obtained with OMWCNT/Ppy/Au electrode. The DPV conditions used for the experiment were-

D

electrolyte: 0.1 M HAc-NaAc buffer (pH 5.3), potential window: -1.0 V to 0.0 V, increment

A

CC

EP

TE

potential: 0.004 V, pulse amplitude: 0.050 V, pulse width: 0.03 s and pulse period: 0.2 s.

28

29

D

TE

EP

CC

A

SC RI PT

U

N

A

M

30

D

TE

EP

CC

A

SC RI PT

U

N

A

M

31

D

TE

EP

CC

A

SC RI PT

U

N

A

M

32

D

TE

EP

CC

A

SC RI PT

U

N

A

M

33

D

TE

EP

CC

A

SC RI PT

U

N

A

M