Polypyrrole-Wrapped Carbon Nanotube Composite Films Coated on Diazonium-Modified Flexible ITO Sheets for the Electroanalysis of Heavy Metal Ions.

Momath Lo,Rémy Pires,Mahamadou Seydou,Mohamed M Chehimi,Joseph Delhalle,Diariatou Gningue-Sall,Asma Bensghaïer,Zineb Mekhalif,Jean-Jacques Aaron

doi:10.3390/s20030580

Abstract

Highly sensitive multicomponent materials designed for the recognition of hazardous compounds request control over interfacial chemistry. The latter is a key parameter in the construction of the sensing (macro) molecular architectures. In this work, multi-walled carbon nanotubes (CNTs) were deposited on diazonium-modified, flexible indium tin oxide (ITO) electrodes prior to the electropolymerization of pyrrole. This three-step process, including diazonium electroreduction, the deposition of CNTs and electropolymerization, provided adhesively-bonded, polypyrrole-wrapped CNT composite coatings on aminophenyl-modified flexible ITO sheets. The aminophenyl (AP) groups were attached to ITO by electroreduction of the in-situ generated aminobenzenediazonium compound in aqueous, acidic medium. For the first time, polypyrrole (PPy) was electrodeposited in the presence of both benzenesulfonic acid (dopant) and ethylene glycol-bis(2-aminoethylether)-tetraacetic acid (EGTA), which acts as a chelator. The flexible electrodes were characterized by XPS, Raman and scanning electron microscopy (SEM), which provided strong supporting evidence for the wrapping of CNTs by the electrodeposited PPy. Indeed, the CNT average diameter increased from 18 ± 2.6 nm to 27 ± 4.8, 35.6 ± 5.9 and 175 ± 20.1 after 1, 5 and 10 of electropolymerization of pyrrole, respectively. The PPy/CNT/NH2-ITO films generated by this strategy exhibit significantly improved stability and higher conductivity compared to a similar PPy coating without any embedded CNTs, as assessed by from electrochemical impedance spectroscopy measurements. The potentiometric response was linear in the 10−8–3 × 10−7 mol L−1 Pb(II) concentration range, and the detection limit was 2.9 × 10−9 mol L−1 at S/N = 3. The EGTA was found to drastically improve selectivity for Pb(II) over Cu(II). To account for this improvement, the density functional theory (DFT) was employed to calculate the EGTA–metal ion interaction energy, which was found to be −374.6 and −116.4 kJ/mol for Pb(II) and Cu(II), respectively, considering solvation effects. This work demonstrates the power of a subtle combination of diazonium coupling agent, CNTs, chelators and conductive polymers to design high-performance electrochemical sensors for environmental applications.

Highlights

Extensive research on carbon nanotubes (CNTs) in the fields of applied physics, chemistry, and materials science and engineering has progressed at a remarkable pace owing to CNTs’ outstanding mechanical properties, good electronic conductivity, 1D structure, nanometer size diameter and high-accessible surface area [1]
The pending question was: is it necessary to apply an adhesive layer on indium tin oxide (ITO) for the attachment of CNTs, or do they stick efficiently to bare ITO? The first trials demonstrated that CNTs had poor adhesion to bare ITO, a behavior similar to that of PPy
We noted a better adhesion and resistance of CNTs to intensive washing with water and even to ultrasonication. This has motivated us to explore this route in view of building PPy/CNT composite coatings on flexible ITO in three steps: (i) preparation of aminophenyl-modified flexible ITO (NH2 -ITO) [28], (ii) purification and ultrasonic dispersion of CNTs prior to deposition on NH2 -ITO, (iii) electropolymerization of pyrrole in the presence of ethylene glycol-bis(2-aminoethylether)-tetraacetic acid (EGTA) on CNT-coated NH2 -ITO

Summary

Introduction

Extensive research on carbon nanotubes (CNTs) in the fields of applied physics, chemistry, and materials science and engineering has progressed at a remarkable pace owing to CNTs’ outstanding mechanical properties, good electronic conductivity, 1D structure, nanometer size diameter and high-accessible surface area [1]. Conductive polymers (CPs), including polypyrrole (PPy), polyaniline (PANI) and polythiophene (PT), constitute a class of materials which is widely investigated for their attractive applications in electronic devices [6], super-capacitors [7,8], thermoelectric power generators [9], and gas and ion sensors [10,11,12]. PPy and its derivatives play a leading role due to the relative low oxidation potential of the corresponding monomers, high stability and excellent electrical properties in organic and aqueous solvents [13]. Owing to these features, polypyrroles are considered as ideal polymeric materials for building various sensors. Taking advantage of the salient and complementary features of CNTs and PPy, various electrochemical sensing systems based on PPy/CNT nanocomposites have been proposed for biomedical and environmental applications [22,23,24,25,26,27]

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