A green approach to magnetically-hard electrically-conducting polyaniline/CoFe2O4 nanocomposites

Magnetically-hard, electrically-conducting polyaniline/CoFe2O4 nanocomposites were prepared by oxidative polymerization of N-(4-aminophenyl)aniline using molecular oxygen or hydrogen peroxide as the oxidants and magnetic CoFe2O4 nanoparticles, both uncoated and oleic acid-coated, with the double role of polymerization catalyst and magnetic filler. Oleic acid-coated nanoparticles showed higher catalytic activity than uncoated ones, especially under aerobic conditions. The size of the nanoparticles did not undergo significant changes during the polymerization process. The nanocomposites are magnetically hard with large remanence/saturation ratio, very large coercivity (8-15 kOe at 5 K) and do not display superparamagnetic effects even at RT. The addition of Fe3+ as a further oxidant allowed to tune the electroconductive properties of the materials, with conductivity ranging from 7.3 ⋅ 10−5 S/cm to 5.5 ⋅ 10−3 S/cm.