Ultrasonic irradiation: A novel approach to prepare conductive polyaniline/nanocrystalline titanium oxide composites

A novel approach, i.e., ultrasonic irradiation, was used to prepare polyaniline/nanocrystalline TiO2 composite particles. Polymerization of aniline proceeded under ultrasonic irradiation in the presence of nanocrystalline TiO2. The aggregation of nano TiO2 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 coreshell structure. The resulting polyaniline/nano TiO2 composite particles are spherical, and the sizes vary with the content of TiO2. The polyaniline/nano TiO2 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 TiO2 strengthens the UV absorption of polyaniline and leads to a blue shift of the pi-polaron absorption of polyaniline. Ultrasound can enhance the doping level. When polyaniline deposits on the surface of nano TiO2, the crystalline behavior of polyaniline is hampered and the degree of crystallinity decreases. With increased TiO2 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 TiO2 structure. The conductivity of the composites obtained through ultrasonic irradiation decreases with increasing TiO2 content. Ultrasonic irradiation contributes to the increase in the conductivity compared with conventional stirring. When the content of polyaniline decreases to similar to10%, 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.