Preparation Of Nano-ZnO Particles Using Hollow Fiber Membranes Dispersion Technology

The nano-ZnO which has been widely used in various fields has excellent properties. It is the hot spot that using membrane dispersion technology to prepare nano-materials in the field of materials study in recent years. When micro-porous membrane or micro-filtration membrane is used as dispersion medium, the solution through the membrane will be dispersed into droplets of pore-scale level under the pressure difference, which enhance the mass-transfer. In this paper, a membrane dispersion technology was submerged to prepare nano-particles that using hollow fiber membrane to make membrane modules. Taking ZnCl2 and NaOH as raw materials, the nano-ZnO particles were prepared by dispersion method using single hollow fiber membrane dispersion technology and double hollow membranes dispersion respectively.The effects of different factors such as the concentration of ZnCl2 solution, molar ratio of NaOH and ZnCl2, membrane model and other conditions were investigated by orthogonal test while prepared ZnO by single hollow fiber membranes dispersion technology, and the optimum process conditions selected were found as follows:the concentration ZnCl2 was 0.14mol/L, molar ratio of NaOH and ZnCl2 was 2, using the membrane as dispersion medium, taking NaOH as the dispersed phase, adding surfactant, controlling the flow rate at 20mL/min, and water bath aging for 2h. Under the conditions above mentioned, we can obtain nano-ZnO, the average particles size of which was 60nm with narrow distribution.In the preparation of nano-ZnO by the double hollow fiber membranes dispersion technology, ZnO with different morphology could be prepared by controlling the concentration ratio of reactants. With the increase of the molar ratio of NaOH and ZnCl2, the product changes from particles to flower clusters, and we could get nano-ZnO particles in the molar ratio of 2. Through the study of other operating conditions, we prepared nano-ZnO by a mean particle size of about 40nm with narrow distribution when the membrane length was 2.5cm, dispersed phase flow rate was at 15mL/min, stirring speed was 1000rpm and the aging time was 2h. Compared with the single-membrane dispersion technology, this method spread the two reactants into the reactor at the same time and is suitable for continuous operationIn the double membrane dispersion technology, the addition of surfactants can not only reduce the average particle size, but also maintain the average particle size essentially unchanged with reaction time continued. When the flow rate of dispersed phase was 70mL/min, the average size about 45nm of zinc oxide particles could be obtained. If instead solvent system of pure ethanol, in the, the average size of about 49nm of the ZnO particles could be obtained while the flow rate of dispersed phase was kept at 20mL/min. It shows that the surfactant and organic solvent ethanol can both play a good role in inhibiting aggregation.