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To exploit the size dependent properties of nanoparticles, it is essential to control the particle size. We show that injection of octanethiol into suspensions of ZnO particles can be used to quench particle growth. X-ray photoelectron spectroscopy studies of the adsorption of octanethiol on ZnO single crystals indicate relatively weak adsorption of thiolate and sulfonate species dependent on the crystal orientation. These results suggest that adsorption of thiolate and sulfonate groups on ZnO particles in suspension prevent dissolution of the solid phase. Furthermore, the octanethiol is adsorbed sufficiently strongly to quench growth but can be easily removed for subsequent surface functionalization.

In this communication, we reported for the first time an ultrasensitive nanostructrued sensor that can detect 50 ppt of NH 3 gas in air. Specifically, nanograins of a p-type conductive polymer, polyaniline (PANI), are enchased on an electrospun n-type semiconductive TiO 2 fiber surface. The resistance of the p-n heterojunctions combining with the bulk resistance of PANI nanograins can function as electric current switches when NH 3 gas is absorbed by PANI nanoparticles. As a result, the sensor sensitivity can be significantly improved. The sensor fabricated in this work is 1000 times more sensitive than the best PANI sensor reported in the literature.* To whom the correspondence should be addressed, yulin.deng@ chbe.gatech.edu (Y. Deng).

In solution phase synthesis of nanoparticles, processes such as coarsening and aggregation can compete with nucleation and growth in modifying the particle size distribution in the system. We report on the synthesis of ZnO nanoparticles from Zn(CH3CO2)2, ZnBr2, and Zn(ClO4)2 in 2-propanol. For synthesis from Zn(CH3CO2)2 and ZnBr2, nucleation and growth are fast and are followed by diffusion-limited coarsening. For synthesis from Zn(ClO4)2, diffusion-limited coarsening is observed at shorter times whereas at longer times the particle size increases more rapidly. The rate constant for coarsening at constant temperature increases in the order Br- < CH3CO2 - < ClO4 - indicating that the rate is dependent on anion adsorption. The temperature dependence of the rate constant for coarsening is due to the temperature dependence of the solvent viscosity and the temperature dependence of the bulk solubility of ZnO.