Ultrasonic Irradiation: A Novel Approach To Prepare Conductive Polyaniline/Nanocrystalline Titanium Oxide Composites

Abstract

A novel approach, i.e., ultrasonic irradiation, was used to prepare polyaniline/nanocrystalline TiO 2 composite particles. Polymerization of aniline proceeded under ultrasonic irradiation in the presence of nanocrystalline TiO 2 . The aggregation of nano TiO 2 can be reduced under ultrasonic irradiation, and the nanoparticles can be redispersed in the aqueous solution. The polyaniline deposits on the surface of the nanoparticle, which leads to a core−shell structure. The resulting polyaniline/nano TiO 2 composite particles are spherical, and the sizes vary with the content of TiO 2 . The polyaniline/nano TiO 2 composite particles prepared by the conventional stirring method have a “raspberry” aggregate structure, which is different from that obtained through ultrasonic irradiation. The presence of nanocrystalline TiO 2 strengthens the UV absorption of polyaniline and leads to a blue shift of the π-polaron absorption of polyaniline. Ultrasound can enhance the doping level. When polyaniline deposits on the surface of nano TiO 2, the crystalline behavior of polyaniline is hampered and the degree of crystallinity decreases. With increased TiO 2 content, the H-bonding interaction is strengthened and the characteristic peaks of benzoid and quinoid are shifted. X-ray photoelectron spectroscopy (XPS) shows that the ratio of the number of Ti and N atoms (Ti/N) on the surface is lower than that in the bulk. This is strong evidence for a polyaniline-encapsulated nano TiO 2 structure. The conductivity of the composites obtained through ultrasonic irradiation decreases with increasing TiO 2 content. Ultrasonic irradiation contributes to the increase in the conductivity compared with conventional stirring. When the content of polyaniline decreases to ∼10%, the conductivity of composite still remains at 10 - 1 S·cm - 1 . Ultrasonic irradiation provides us a new way to prepare 0−3-dimensional conducting polymer/nanocrystalline particle composites.