Synthesis Of ZnO Nanoparticles In Continuous Microreactor By Microemulsion

ZnO is an important semiconductor material with extensive applications in electrons, photoelectronics, sensors, and optical devices. The quality of ZnO is highly dependent on its morphology, particle size and particle size distribution. Therefore, new methods which facilitate the nucleation, growth, and particle size distribution in the synthesis of ZnO nanoparticles are highly desirable for researchers. Microemulsion method, as a mild, easily controlled method, has been widely used in nanomaterial synthesis areas. Nanomaterials produced by microemulsion method are influenced by many factors, such as, the way of materials adding, temperature distribution, the diffusion rate of reactant between phase interface, strength of phase interface, stirring rate, etc. The continuous flow type microrchannel reactors are able to intensify the transfers of both mass and heat as well as the mixing due to its small size and high surface-to-volume ratio.In this paper, ZnO nanoparticles were synthesized by mixing the Zn2+containing water-in-oil microemulsion with the NaOH-containing one in a micromixer followed by subsequent reaction in the relay tube, and the ZnO nanomaterials were produced in the regular mixed tank reactor for comparision. Firstly, the phase behavior of the microemulsion system of CTAB as surfactant was studied and obtained the proper microemulsion system for preparation of ZnO nanoparticles. The study showed that when choose N-octane as oil-phase, N-butanol as alcohol-phase and the mass ratio of CTAB:N-octane:N-butanol is1.2:4.4:1, the system has wide area of microemulsion region and high water solubility. Secondly, Villermaux-Dushman fast parallel competitive reaction system was brought into measuring the micromixing efficiency of the microreactor, in purpose of optimizing the experimental conditions. The last, Zinc oxide (ZnO) nanoparticles were synthesized from CTAB/N-octane/N-butanol microemulsions in a microchannel reactor system. The microemulsions provide confined space for the reactants, which is favorable for controllable reaction and nucleation, avoiding the formation of large particles. In addition, the microemulsions prevent the deposition of ZnO particles on the wall of the microchannels of the reactor. Three Zn2+sources (Zn(NO3)2, ZnSO4, and ZnCl2) were tested in the synthesis of ZnO nanoparticles. Among them, Zn(NO3)2showed best performance in the synthesis. The effects of Zn2+concentration, reaction temperature, and feed flow rate on the average particle size of ZnO nanoparticles were investigated. At optimal conditions, the water content at15%, feed flow speed at3mL/min, reaction temperature at50℃, reaction pressure at2.0MPa, ZnO nanoparticles with average size of10-20nm were obtained. The UV-visible absorption spectroscopy indicated that the material synthesis in microchannel reactors shows certain blue shift.