Synthesis of ZnO Particles by Ammonia-Catalyzed Hydrolysis of Zinc Dibutoxide in Nonionic Reversed Micelles

Ultrafine ZnO particles were synthesized by ammonia-catalyzed hydrolysis of zinc di- n -butoxide (ZDB) in polyoxyethylene (6) nonylphenyl ether (NP-6)/cyclohexane solutions in both the reversed and swollen micelle regions of the solubilization diagram of aqueous NH 3 . In all micelle regions, rodlike ZnO particles were produced which were determined to be hexagonal single crystals having a wurtzite structure. The effects of changing R w (the molar ratio of water to surfactant = [H 2 O]/[NP-6]), R a (the molar ratio of ammonia to surfactant = [NH 3 ]/[NP-6]), and ZDB on the length (〈 P L 〉) and width (〈 P W 〉) of the ZnO particles were examined. The values of both 〈 P L 〉 and 〈 P W 〉 increased slowly from about R w = 4. This increase reflected a change in the system, from reversed micelles with water bound to the polar groups of the surfactants to swollen micelles with semibound water interacting with hydrated polar groups. At a constant R w ( R w = 6.0), as R a was increased, both 〈 P L 〉 and 〈 P W 〉 slowly decreased. The 〈 P L 〉 and 〈 P W 〉 profiles of the ZnO particles at various R w or R a values were similar to the micellar droplet size profile at various R w or R a values, respectively. These facts indicate that the particle size of ZnO is controlled by both the solubilized states of water and the size of the micellar droplets. However, the 〈 P L 〉 and 〈 P W 〉 of the synthesized particles were independent of the ZDB. The 〈 P L 〉 and 〈 P W 〉 values also correlated to the average crystallite sizes of the (002) and (110) faces of the particles as determined by X-ray diffraction measurements. The long side of the rodlike particle was also found to be parallel to the c -axis of the hexagonal system.