Nanocomposites of polyaniline, its derivatives and platinum prepared using aqueous Pt sol
Introduction
Nanostructured materials exhibit very interesting properties, different from those shown by bulk systems which are characterized by significantly smaller surface-to-volume ratios. Physico-chemical properties of nanometric objects are influenced not only by their size but also by their size distribution. It has been reported, for example, that luminescent spectra of nanocrystalline A(II)B(VI) type semiconductors can be tuned in a wide range by changing the mean size of the nanocrystals. Full width at half maximum of the spectral line is, in turn, a function of the size distribution and it reaches ca. 20 nm for the fractions with this parameter not exceeding 4% [1].
Preparation of nanocrystalline materials is not simple. The process should be conducted in the conditions which limit the growth of the crystals upon their formation and prevent them from subsequent agglomeration. Since the surface of nanocrystals is usually very reactive, it is often necessary to apply stabilizing agents. They coat the particles and thus do not allow their coalescence. In the case of transition metal nanoparticles this stabilization is frequently achieved by using polymers. Poly(N-vinyl-2-pyrrolidone) (PVP) has been widely applied as stabilizer for nanoparticles of e.g. Ag [2], [3], Pt [4], [5], [6], [7], Rh [7], [8], Au [9], [10], Co [11], and Ni [12], [13]. Stabilizing effect of PVP can be attributed to the interactions between its electron donor atoms (nitrogen and oxygen) and surface metal atoms of the nanoparticles. The involvement of PVP carbonyl groups in such interactions has been well documented [7], [13].
Conjugated polymers, whose molecules contain spatially extended π electron system, are extremely promising stabilizers for metal nanoparticles. Therefore intensive research work on the preparation of nanometric metals dispersed in these polymer matrices has been carried out in recent years. Polythiophene–Au [14], Pd [15], polypyrrole–Au [16], Ag [17], polyaniline–Pd [18], [19], and Au [20], [21] nanocomposites have been obtained and their optical [16], sensing [19], [21] and catalytic [15], [18] properties investigated.
Among noble metals, platinum holds a special position since it is a very efficient redox catalyst. Polyaniline (PANI) is, on the other hand, an environmentally stable, easy to prepare conjugated polymer. Hence, a large number of studies presented in the literature concern PANI–Pt composites. In most cases they have been obtained electrochemically, with only a few exceptions describing their chemical preparation [22], [23], [24], [25].
In our previous paper [26] we have shown that Pt nanoparticles embedded in PANI can be prepared chemically using two methods. The first one involves reduction of Pt4+ ions conducted in the presence of the polymer. Another one takes the advantage of basic properties of PANI which make it possible to incorporate Pt-containing anions into the polymer via protonation. Their reduction results in the formation of Pt nanoparticles dispersed in PANI. We have observed, however, that in both methods a strong tendency of the metallic particles towards agglomeration exists. Therefore in the present studies we have chosen a different procedure to obtain Pt nanoparticles dispersed in PANI matrix. First, we have prepared aqueous Pt sol containing small (mainly in the range of 1–3 nm) metallic particles which have been subsequently incorporated into PANI. As it is demonstrated, such procedure allows to obtain PANI–Pt nanocomposites in which metallic nanoparticles whose sizes correspond to those found in the sol are present. Catalytic properties of the obtained PANI–Pt nanocomposites are illustrated by investigations of isopropyl alcohol conversion.
Moreover, in the present work we show that similar procedure can be applied to prepare PANI derivatives, namely poly(o-toluidine) (POT) and poly(o-methoxyaniline) (POMA)–Pt nanocomposites. It should be noted that, in comparison with the parent polymer, significantly less attention has been paid so far to the studies of PANI derivatives–Pt composites. POT–Pt [27] and POMA–Pt [28] composites have been prepared electrochemically and their electrocatalytic properties studied. Due to improved processability of POT and POMA with respect to PANI, application of these polymers as matrices for metallic Pt particles may be advantageous, particularly in the cases when a definite shape of the composite material is needed. Chemical method, on the other hand, allows to prepare large amounts of the material.
It can be postulated that in the composites obtained in the present work, PANI, POMA and POT play the role of the stabilizing agents for metallic Pt nanoparticles.
Section snippets
Experimental
PANI, POMA and POT have been synthesized by oxidation of aniline, o-methoxyaniline and o-toluidine, respectively with ammonium peroxydisulphate carried out according to the similar protocol. Thus, the reactions were performed in 2 mol/dm3 HCl aqueous solution, at 0 °C for 4 h. Molar ratio of the oxidant to aniline or its derivatives in all the systems was equal to 0.25. PANI, POMA and POT hydrochlorides thus obtained were then deprotonated in 0.3 mol/dm3 aqueous ammonia solution for 48 h. The final
Pt sol
For the preparation of Pt sol in the present study the “citrate method” has been chosen since it allows to obtain in a simple way aqueous dispersions of metallic Pt nanoparticles which are stable for a long time [29]. In this procedure, sodium citrate plays a double role. It is a reducing agent for Pt4+ ions initially present in the solution and a stabilizer for metallic Pt particles formed in the reduction process. After the reaction, excess of sodium citrate and other ionic species are
Conclusions
Based on the investigations that have been carried out in the present work the following conclusions can be drawn:
- 1.
PANI, POMA and POT–Pt composites containing metal nanoparticles can be prepared using aqueous Pt sol.
- 2.
The polymers play the role of stabilizers for Pt nanoparticles in the composites. This stabilization is achieved by charge transfer interactions between the polymer backbones and metal nanoparticles resulting in withdrawal of electrons from the polymer chains.
- 3.
Polymer–Pt
References (36)
- et al.
Colloids Surf. A Physicochem. Eng. Aspects
(2007) - et al.
J. Colloid Interf. Sci.
(2000) - et al.
Physica E
(2005) - et al.
Surf. Sci.
(2007) - et al.
J. Colloid Interf. Sci.
(2007) - et al.
Sens. Actuat. B
(2006) - et al.
Biosen. Bioelectron.
(2006) - et al.
J. Electroanal. Chem.
(2005) - et al.
Eur. Polym. J.
(2008) - et al.
Synth. Met.
(1992)
Appl. Surf. Sci.
Synth. Met.
Synth. Met.
J. Phys. Chem.
Photochem. Photobiol. Sci.
Appl. Organometal. Chem.
J. Phys. Chem. C
Chem. Lett.
Cited by (16)
Chemically synthesized poly(o-methoxyaniline): Influence of counterions on the structural and electrical properties
2020, Journal of Molecular StructureProposed mechanisms for the removal of nitrate from water by platinum catalysts supported on polyaniline and polypyrrole
2018, Applied Catalysis B: EnvironmentalCitation Excerpt :Similar ammonium selectivities were obtained and nitrite was not detected in any case. The inherent ability of conducting polymers such as PPy and PANI of switching between different oxidation states imparts them the capability of acting as a source and or a drain of electrons, depending on the redox process in which they are involved [33,34]. Upon reduction of nitrate, some of the metallic platinum is oxidized to Pt2+ (Fig. 4, Table S.5), what is accompanied by a reduction of the oxidation state of the polymeric nitrogen, as evidenced in the recovered polymers (Fig. 3, Table S.5).
Polyaniline-Pt and polypyrrole-Pt nanocomposites: Effect of supporting type and morphology on the nanoparticles size and distribution
2015, Synthetic MetalsCitation Excerpt :PANI-Pt has been prepared using the metallic precursor H2PtCl6 itself as oxidizing agent during the polymerization of aniline monomers [13,14]. Moreover, PANI-Pt nanocomposite with good dispersion of the metallic nanoparticles was obtained by the dissolution of the polymeric matrix in a solution containing Pt nanoparticles synthesized by the reduction of the metallic ions in the presence of sodium citrate. [15] Hirao et al. [16–18] published a series of pioneering work describing the study of different hybrid systems of polyaniline (and polyaniline derivatives, such as poly(2-methoxy-oxyaniline-5-sulfonic acid)) with transition metals (Cu(II), Fe(III), Pd(II) and V(III) and transition metals nanoparticles (Pd and iron oxide).
One-step synthesis and characterization of poly(o-toluidine) nanofiber/metal nanoparticle composite networks as non-enzymatic glucose sensors
2014, Sensors and Actuators, B: ChemicalCitation Excerpt :Additionally, the characteristic peaks from the CC stretching of the quinoid and benzoid rings in POT NF chains can be seen at 1597 cm−1 and 1500 cm−1, respectively [44]. Also, characteristic peaks of CN stretching of secondary aromatic amine at 1315 cm−1 [12,14], CC or CN stretching and in plane CH bending modes at 1210 and 1155 cm−1 [5,14,21], N-quinoid-N at 1107 cm−1 [5,14], and lastly CH in plane vibration of the quinoid rings at 1005 cm−1 [5,14], can be observed from the same spectrum. When the POT-Au/Cu nanocomposites’ spectra are observed; it is easy to realize the broadening/overlapping features, intensity changes [40] and slight shifting [5,14] occurred on the above mentioned characteristic POT peaks.
Synthesis of platinum-polyaniline composite, its evaluation as a performance boosting interphase in the electrode assembly of proton exchange membrane fuel cell
2013, Applied Surface ScienceCitation Excerpt :The unique properties of PANi are its good mechanical strength, tunable electronic and electrical conductivity, high chemical stability for use below 100 °C, large surface area, and simple and low cost manufacturing process. Platinum supported PANi prepared by various methods have been studied for their catalytic properties in redox reactions [14–17]. Composite of PANi and multiwalled carbon nanotube with immobilized Pt particles have been assessed for their redox characteristics [18].
Polyaniline nanostructures and the role of aniline oligomers in their formation
2010, Progress in Polymer Science (Oxford)Citation Excerpt :Polypyrrole can similarly be used for the reduction of silver salts [156,554]. In addition to silver, other noble metals have been produced in combination with PANI or PPy, including: gold [238,284,316,336,340–342,351,464,555,556], palladium [153,436,446,557–559], platinum (Fig. 66) [80,560–562], rhodium [80,555,563], ruthenium [564], etc. Conducting polymers combined with gold [316] or metals of the platinum group find uses in the catalysis of organic reactions [378,446,557] or in fuel-cell electrodes [560,564,565].