Microemulsion route to the synthesis of nanoparticles

Abstract

Nanoparticles of several titanates and zirconates in the range of 20-60 nm have been obtained using the reverse micellar route. Important oxides like CeO₂ (mixture of nanorods; 7 nm diameter and 30 nm length and nanoparticles; 10 nm), ZrO₂ (3-4 nm) and SnO₂ (8 nm) have also been synthesized. Nanorods and nanoparticles of CaCO₃ in all three forms (aragonite, vaterite, and calcite) have been obtained using reverse micelles as nanoreactors. The specific reactions vary depending on the nature of the target nanomaterial. For synthesis of ternary oxides like BaTiO₃, a modified and convenient route using microemulsions (avoiding Ba-alkoxide) has evolved. Monophasic tin dioxide (SnO₂) was obtained when liquid NH₃ was used as precipitating agent. Transmission electron microscopy (TEM) studies show that the SnO₂ nanoparticles are highly uniform and particle size was found to be 6-8 nm at 500°C. The gas sensing characteristics of SnO₂ have also been investigated using n-butane, which shows high sensitivity and fast recovery time. Reverse micelles have been used, for the first time, to mimic the conditions suitable for the room-temperature synthesis of the high-temperature and -pressure orthorhombic phase of calcium carbonate (aragonite). Other forms of calcium carbonate (vaterite and calcite) could be obtained by varying the atmospheric conditions. At a lower temperature (5°C), homogeneous and monodisperse spheres of vaterite are obtained. The spherical particles aggregate after longer aging (168 h) to form nanorods, and the self-assembly is clearly seen at various stages by electron microscopy images. The samples were well characterized using powder X-ray diffraction (PXRD), line-broadening studies, TEM, variation in the dielectric properties with frequency and temperature, were measured on disks sintered at high temperature.