Conducting polypyrrole silicotungstate deposited on macroporous melamine sponge for electromagnetic interference shielding

Abstract

Macroporous melamine/formaldehyde sponge was coated in situ during the oxidation of pyrrole with iron(III) chloride hexahydrate in aqueous medium. The reaction mixture contained a heteropolyacid, silicotungstic acid, which protonated polypyrrole. Polypyrrole/silicotungstate deposits were prepared either in globular form or as nanotubes. The resulting hybrid composites thus combine an organic conducting polymer with inorganic component known, e.g., for its proton conductivity and electrocatalytic activity. The specific surface area of all materials was of the order of tens m2g−1. The molecular structure is discussed on the basis of FTIR and Raman spectra. The resistivity of the sponges was recorded as a function of compression to 10 MPa and it decreased from the order of 10 Ω cm to 0.1 Ω cm. The sponges were tested in electromagnetic interference shielding and absorbed over 80% of 9 GHz radiation frequency. The shielding is based mainly on the radiation absorption efficiency, −8.2 dB for globular polypyrrole and −13.1 dB for nanotubes, afforded by silicotungstic component. Hybrid composite sponges were subsequently carbonized at 650 °C in inert atmosphere when they converted to a sponge-like macroporous carbons enriched with nitrogen atoms. Their resistivity increased by two orders of magnitude after this process. The absorption of electromagnetic radiation, however, fell below 10%. Original and carbonized hybrid sponges may be of interest in the construction of macroporous electrodes.