Ultrasonic synthesis: Structural, optical and electrical correlation of TiO₂ nanoparticles

Sonochemical synthesis of nanometric anatase phase has been successfully produced at room temperature by using a simple and environment-friendly method. The effect of the heat treatment on the structural properties of the as-prepared sample has been evaluated and discussed in this research by X-ray powder diffraction and transmission electron microscopy techniques. The structural properties are expected to be strongly correlated with the optical band gap and electrical properties. The results show that the average size of nanocrystallites is in the order of 5 nm with large surface area, where as the system presents pores at the junctions of crystallites. Optical band gap of as-prepared sample has a blue shift, which could be attributed to a quantum size effect. The heat-treated reveals structural changes from anatase to rutile structure at 550 °C. Crystal size increase from 5 to 35 nm, in which anatase and rutile phases coexist. However, by electrochemical technique the high current-charge magnitude is observed in samples with crystallite size of 17 nm but if anatase and rutile are simultaneously present the conductivity decreased. This phenomenon is observed if the difference between anatase and rutile is about 36% in size, indicating that the conduction and valence bands could be further away in the sample.