Nanostructured poly(N-methyl pyrrole) with enhanced conductivity and capacitance
Graphical Abstract
Introduction
Conjugated polymers have gained vast attention in the past decade, especially in the field of material science due to their interesting optoelectronic properties, high conductivity, excellent environmental stability, easy and inexpensive synthesis. Besides these, conducting polymers allow easy designing or structure modification in the polymer chain and therefore variety of their derivatives with desirable distinct properties are on focus [1], [2], [3]. Polypyrrole (PPy) is one of the successful conducting polymers and exhibits stability towards chemical substitution or functionalization [4], [5]. Several studies have been performed for the synthesis or designing of derivatives of PPy [6]. Among them, N-substituted and 3-substituted PPy have captured considerable interest [7]. The substitution in the pyrrole ring results in higher oxidation potential and lower conductivity, thereby reduces the electroactivity of the polymerized product because of the loss in the ring planarity [8]. However, N-substituted pyrrole has better symmetry and planarity compared to its 3-substituted counterpart [6].
Poly(N-methyl pyrrole) (PNMPy) possesses greater mechanical strength than PPy which provides an avenue for futuristic applications [9], [10]. Also, the electrochromic behavior of PNMPy was studied using a variety of anions such as chloride and p-toluene sulfonate for investigating the effects on their morphology and conductivity [10]. Ahmad et al. fabricated an electrochromic device using PNMPy functionalized by carbon nanotubes and attained smooth and uniform morphology of the polymer which allow their electronic applications [9]. Additionally, PNMPy demonstrated better corrosion protection performance in comparison to PPy which was explained by the hydrophobic effect offered by the methyl group present in PNMPy [11]. The polymerization of N-methyl pyrrole (NMPy), mostly by electrochemical method on various substrates, such as steel, copper, gold, carbon fiber etc., are described in the literature and their electrochemical properties, film stability, surface morphology, spectroscopic behavior, etc. have been examined [12], [13], [14], [15]. Furthermore, PNMPy and its nanocomposites with indium (III) oxide, tungsten (VI) oxide or manganese (II) oxide, etc. were employed in antibacterial [16], [17], supercapacitors [18] and biosensors [19] applications. Such materials were synthesized either by oxidative chemical or by interfacial polymerization method [16], [17], [18], [19]. Very recently, Mohammed et al. reported the preparation of PNMPy nanocomposites with the incorporation of reduced graphene oxide which showed enhanced carbon monoxide sensing ability [20].
Recently, 1-D nanostructured conducting polymers have provoked a significant interest in the field of material science due to their diverse applications in capacitors [21], batteries [22], catalysis [23] and sensors [24]. Moreover, conducting polymers have found importance in biomedicine, for example, PPy nanotubes in composition with silver nanoparticles imparted promising antibacterial activity [25]. In another study, nanofibrillar PPy were perceived by the support of an organic dye, and provided improved capacitance and antibacterial properties [26]. Usually their preparation requires the use of various soft or hard templates during the synthesis [27]. Particularly, organic dye as a template, has gained much attention in defining the elongated nanostructured morphology such as nanofibers, nanotubes, nanowires, etc., together with the tuning of the conductivity for PPy [26], [28], [29]. However, regarding substituted PPy, such studies with organic dyes, are not known in the literature. Thus, in the present paper we have examined the effect of organic dyes on the morphology, conductivity and electrochemical properties of PNMPy.
We have used two organic anionic dyes i.e. methyl orange (MO) and Acid Blue 25 (AB) (Fig. 1a and 1b) as a structure-guiding agents, for the polymerization of NMPy using iron (III) chloride as an oxidant (Fig. 1c). 1-D PNMPy nanotubes and nanofibers with enhanced specific surface area were attained using MO and AB dyes respectively. Both the dyes resulted in better electrochemical activity with enhanced gravimetric capacitances of PNMPy in comparison to pristine PNMPy. The improvement in the conductivity, capacitance and specific surface area of the PNMPy allows potential applications in sustainable and energy storage devices.
Section snippets
Chemical and reagents
N-methyl pyrrole (NMPy), iron (III) chloride hexahydrate, methyl orange (MO; sodium 4-[(4-dimethylamino)phenylazo]benzenesulfonate, dye content 85%), Acid Blue 25 (AB; sodium 1-amino-4-anilino-9,10-dioxo-9,10-dihydroanthracene-2-sulfonate, dye content 45%) and Naphion 117 solution (lower aliphatic alcohol and water mixture) were provided from Sigma Aldrich and were used without further purification.
Synthesis of PNMPy in the presence of MO or AB
PNMPy was prepared by the oxidation of 0.15 M NMPy using 0.3 M iron (III) chloride as an oxidant (
Morphology
Pristine PNMPy shows globular morphology (Fig. 2a, 2b), similar to its parent polymer, PPy. The globular particles obtained using the polymerization of NMPy have approximately 100 nm larger diameter relative to PPy, under similar reaction conditions [26]. It is well reported in literature, that the morphology of PPy can be tuned to various nanostructures such as nanofibers [26], nanowires [29], irregular shape [30], nanotubes [28], etc. using different organic dyes. Herein, we have investigated
Conclusions
We have presented the role of organic anionic dyes (MO and AB) in the preparation of PNMPy. The addition of MO dye resulted in a nanotubular morphology, whereas PNMPy nanofibers were obtained with the help of AB. An improvement in the conductivity up to one order of magnitude was attained with the introduction of either of the anionic dye to the polymerization process of PNMPy. The molecular structure of PNMPy and its interaction with the two dyes, were confirmed using FTIR and Raman
CRediT authorship contribution statement
Sonal Gupta: Conceptualization, Methodology, Investigation, Writing – original draft, Writing – review & editing. Oumayma Taboubi: Investigation, Writing – review & editing, Udit Acharya: Investigation, Writing – review & editing. Miloslav Lhotka: Investigation, Writing – review & editing. Václav Pokorný: Investigation, Writing – review & editing. Zuzana Morávková: Investigation, Writing – review & editing. Jiřina Hromádková: Investigation, Writing – review & editing. Patrycja Bober:
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgment
The authors wish to thank the Czech Science Foundation (21–01401S) for the financial support. Ms. Zuzana Walterova and Ms. Markéta Karbusická are acknowledged for performing elemental analysis and TGA measurements, respectively.
Notes
The authors declare no competing financial interest.
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