Photo-catalytic properties of doped or substituted polyaniline-coated Fe₃O₄ nanoparticles

In this work, doped and substituted polyaniline (PANI)-coated Fe₃O₄ nanoparticles were synthesized. The diameter of Fe₃O₄ core was ~430 nm, and the thickness of PANI shell was ~20 nm. Their photo-catalytic properties for methyl orange were investigated under natural light illumination. The photo-catalytic activity sequence of three doped PANI/Fe₃O₄ nanoparticles is as follows: iodine doping > without doping > graphite powder doping. This should be due to the difference of structure, conductivity, and band gap resulting from the dopants. The photo-catalytic activity of five substituted PANI/Fe₃O₄ nanoparticles followed the order of poly(1,2-diaminobenzene) > poly(o-toluidine) > poly(1,3-diaminobenzene) > PANI > polydiphenylamine. The effects of steric hindrance, activated ability, and conjugation of the substituents on the photo-catalytic properties were discussed. The ESR results suggested that O₂ and H₂O₂ dissolved in the solutions were important factors on the photo-degradation, and the ·OH generated via h⁺-mediated pathway was the key oxidizing substance.