Polypyrrole–Palladium
Nanocomposite Coating
of Micrometer-Sized Polymer Particles Toward a Recyclable Catalyst
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Abstract
A range of near-monodisperse, <i>multimicrometer-sized</i> polymer particles has been coated with ultrathin overlayers of polypyrrole–palladium
(PPy–Pd) nanocomposite by chemical oxidative polymerization
of pyrrole using PdCl<sub>2</sub> as an oxidant in aqueous media.
Good control over the targeted PPy–Pd nanocomposite loading
is achieved for 5.2 μm diameter polystyrene (PS) particles,
and PS particles of up to 84 μm diameter can also be efficiently
coated with the PPy–Pd nanocomposite. The seed polymer particles
and resulting composite particles were extensively characterized with
respect to particle size and size distribution, morphology, surface/bulk
chemical compositions, and conductivity. Laser diffraction studies
of dilute aqueous suspensions indicate that the polymer particles
disperse stably before and after nanocoating with the PPy–Pd
nanocomposite. The Fourier transform infrared (FT-IR) spectrum of
the PS particles coated with the PPy–Pd nanocomposite overlayer
is dominated by the underlying particle, since this is the major component
(>96% by mass). Thermogravimetric and elemental analysis indicated
that PPy–Pd nanocomposite loadings were below 6 wt %. The conductivity
of pressed pellets prepared with the nanocomposite-coated particles
increased with a decrease of particle diameter because of higher PPy–Pd
nanocomposite loading. “Flattened ball” morphologies
were observed by scanning/transmission electron microscopy after extraction
of the PS component from the composite particles, which confirmed
a PS core and a PPy–Pd nanocomposite shell morphology. X-ray
diffraction confirmed the production of elemental Pd and X-ray photoelectron
spectroscopy studies indicated the existence of elemental Pd on the
surface of the composite particles. Transmission electron microscopy
confirmed that nanometer-sized Pd particles were distributed in the
shell. Near-monodisperse poly(methyl methacrylate) particles with
diameters ranging between 10 and 19 μm have been also successfully
coated with PPy–Pd nanocomposite, and stable aqueous dispersions
were obtained. The nanocomposite particles functioned as an efficient
catalyst for the aerobic oxidative homocoupling reaction of 4-carboxyphenylboronic
acid in aqueous media for the formation of carbon–carbon bonds.
The composite particles sediment in a short time