Preparation and characterization of magnetic Fe3O 4-polypyrrole nanoparticles

A novel approach to synthesize core-shell nanoparticles with Fe ₃O₄ as the magnetic core and PPY as the conducting shell was investigated. The Fe₃O₄ nanoparticles primarily prepared by precipitation-oxidation method, and the Fe₃O ₄-PPY nanoparticles with core-shell structure was synthesized via an in-situ polymerization of pyrrole monomer in an aqueous solution containing well-dispersed Fe₃O₄ nanoparticles and surfactant NaBS. The particles are almost spherical with diameters ranging from 20-30 nm. These particles are polydisperse and some of them agglomerated due to magneto-dipole interactions between particles. 70% to 80% of the Fe₃O ₄-PPY particles are ranged from 30-40 nm in diameter. The core-shell structure of nanoparticles was evidenced by TEM observations. The Fe ₃O₄ content was found to affect significantly both the conductivity and the magnetization of the resulting PPY composites. When 9% Fe₃O₄ was incorporated into PPY, the conductivity of PPY composite was greatly reduced from 6.52 × 10^-3 to 1.94 × 10^-4 S/cm. Further increasing of Fe₃O₄ content from 8.2% to 28.2 wt%, resulted in slight reduction of the conductivity at room temperature. The decrease in conductivity of Fe₃O₄-PPY composites with increasing Fe₃O₄ content was due to a decrease in the doping degree, assigned as S/N ratio. The S/N ratios decrease from 0.34 to 0.19 with increasing Fe₃O₄ content from 0 to 28.2%. The magnetic properties of the Fe₃O₄-PPY nanocomposites depend on the Fe₃O₄ content too. Increasing Fe₃O₄ content from 0 to 28.2% considerably increased both the saturated magnetization (Ms) and the coercive force (Hc) from 0 to 23.42 emu/g and 0 to 45.2 Oe, respectively. Since PPY powder is not magnetic, the ferromagnetic properties of the composites are attributed to the magnetic Fe₃O₄ nanoparticles. The magnetic Fe ₃O₄ nanoparticles can improve the thermal stability of Fe₃O₄-polypyrrole nanocomposites due to interaction between Fe₃O₄ particles and PPY chains.