Study Of The Modified Ceramic Microfiltration Membrane With Nano ZnO Coating By Sol-gel Method

Composite ceramic membrane for microfiltration has a prosperous future of application in fields of liquid separation, biological chemicals, environmental protection, etc. And it is still an important topic of membrane research because of its high price and low separation efficiency. Modified by metal oxide, their physical and chemical properties proved to be improved, meanwhile, the separation efficiency of inorganic membrane were also enhanced significantly.Therefore, the research on the modification and regulation of composite ceramic membrane for microfiltration will provide a solid technological platform for their applications.In this thesis, the sol-gel method to prepare modified ZnO sol was first used with Zn(OAc)2 as precursor, ethylene glycol monomethyl ether as solvent, and ethanolamine as the stabilizer. Its inner wall modification was done with Al2O3 microfiltration membrane (pore sizeφ= 0.89μm) as substrate. The pocess factors influencing the modification of ZnO sol, such as reaction temperature, reaction concentration and sol aging time, were fully discussed in detail. Also, the changes of pore size and water flux before and after the modification of Al2O3 micro-membrane were detected and analyzed using TEM, SEM, Zeta potential, etc. The results show that: in a water bath of 65℃, the concentration of Zn2+modified sol was 0.2mol / I, pH was 3, sol aging time was 72 hours. The modified sample calcined at 600℃could form a thin layer of nano-ZnO grain, with size of 5 to 15nm and thickness of about 15nm. When membrane pore size was decreased of 7%, the water flux of modified micro-membrane increased significantly, reaching the largest value of 151.8%.To regulate the performance of modified ZnO layer, the Ag ions doping was done on the basis of the studies on the optimal conditions for sol-gel method to prepare ZnO modified sol. The changes of pore size, water flux and Zeta potential caused by Ag ions of different molar ratio were tested. This paper mainly focused on the relationship between the flux microfiltration and Zeta potential. When the PH value of distilled water, as filtration medium, was 7, and the doping ratio of Ag was 0.2 (Ag+:Zn2+), the highest Zeta potential and the largest water flux of ZnO particles were achieved. It was found that the modified layer constituted of Ag doped ZnO nanocrystals also has the function of improving membrane water flux, 187.96%( max.) more than the unmodified one, better than that modified with ZnO alone.