Surface Modification Of Hydrophobic PVDF Membrane By SiO₂ Nanoparticles And Its Application

The development of human society has increased its dependence on natural resources,which oftentimes leads to sever environmental pollution,thus making people so eager for a sustainable development path.One of the major issues is to improve human's efficient utilization on water resources.Composite membrane separation technology tries to separate dyes molecule and water molecule from dyes wastewater using selective separation function of membrane.The technology,taking separation membrane as the basic material and ceramic membrane as separation membrane,houses both obdurability of basic membrane and functionality of composite bed,has become a research hotspot for various scholars.The research uses ultra-thin hydrophobic PVDF membrane as matrix membrane to prepare composite membrane through nano-SiO₂ sol dip-coating and deposition method,and explores the impact of the ethyl silicate,ammonia,peptization temperature and time on SiO₂ particles.It has obtained the best data parameters through the exploration on the technological conditions of SiO₂/PVDF composite membrane.Through the filtration experiment of ink dye and lake water by using composite membrane,this paper studies the application and functionality of composite membrane and makes a brief introduction on its recycling.Main research conclusions are as follows:SiO₂ sol is the precondition for the production of composite membrane.The research uses ethyl silicate as precursor,deionized water as the main solvent and alkali solvent as peptizer to make nano-SiO₂ particles through Colloidal Gel Route.Experiments indicates that the optimum production conditions are that the molar concentration ratio TEOS:H2O:EtOH:NH4OH=1:53.6:40.1:0.64,the reaction temperature 60? and that peptizing time 6h.Through the production technology research of SiO₂/PVDF composite membrane,the research concludes that the PVDF membrane,dip-coating in the nano-SiO₂ sol of 0.047mol/L concentration for 4 minutes and undergoing 140?heat treatment,can form the best SiO₂/PVDF composite membrane.The composite membrane in the best production condition is of below 30?m thick,with average pore size 3.045nm and porosity rate 30.17%,and the flux is 116.5 L/?m2·h?when filtering ink dye under 0.1 MPa,and removal rate above 98%.By observation of morphology and cross-section,the coating layer is sponge-like with aperture size of about 20-30nm,which is in the scope of ultra-filtration.In the end,this paper also probes into the recycling of composite membranes.Through the method of forward and backward flushing,ultrasonic oscillation cleaning,chemical cleaning to process the contaminated composite membrane will make the composite membrane valuable of recycling.The cleaning of composite membrane should consider the actual pollution situation,choosing a proper method to recover the flux of membrane.