Preparation And Properties Of Poly (Vinylidene Fluoride) Membrane With Inverse Opal Structure

Poly（vinylidene fluoride）（PVDF）membranes are widely applied to purify the printing and dyeing wastewater in textile owing to their good heat resistance,mechanical properties and chemical stability.However,the membrane performance is inevitably limited by the“trade-off”effect between its permeation flux and separation efficiency.With adequate mechanical properties,improving the membrane’s interconnectivity,pore size uniformity and porosity simultaneously is one of the solutions to overcome the limitation of the“trade-off”effect.Inspired by inverse opal,one typical architecture of photonic crystals,which presents high porosity and interconnectivity,great uniformity of pore size and easy modulation,this study combined PVDF membranes and inverse opal structure to produce PVDF membranes with inverse opal structure,providing supports theoretically and practically for the fabrication of high-performance PVDF membranes.The research content of this paper mainly includes the following two aspects:（1）Preparation and properties of inverse opal-structured PVDF membrane made by the three-step method.SiO₂ microspheres with controllable particle size and good monodispersity was prepared via changing the synthesis parameters and their morphologies were characterized.Self-assembly parameters（self-assembly solution concentration and assembly temperature）were optimized.Filling parameters（polymer molecular weight（Mn）and solution concentration）were optimized.The formation mechanism of SiO₂/PVDF composite photonic crystals during filling was analyzed.The microporous structure,mechanical properties,separation performance and antifouling properties of PVDF membranes obtained from different particle size microspheres were discussed.（2）Preparation and properties of inverse opal-structured PVDF membrane made by the two-step method.Co-assembly parameters（polymer concentration and co-assembly temperature）were optimized.The co-assembly process of SiO₂and PVDF was described,and the corresponding formation mechanism was explored.The properties of PVDF membrane under different mass ratios of SiO₂ microspheres to PVDF resin were analyzed.The performance of the membranes made by the three-step method and the two-step method respectively was compared.The results showed that:（1）the particle size of SiO₂ microspheres increased with the augmentation of NH₃·H₂O and TEOS,respectively.The obtained SiO₂ microspheres are of good sphericity and monodispersity.The optimal assembly concentration and temperature were 1 wt%and 60°C,respectively.The molecular weight（Mn）and solution concentration of the polymer were preferably 20 w and 9 wt%,respectively.During filling,PVDF is uniformly solidified in the interstice between SiO₂microspheres initially,and then the interstice is full of PVDF with continuous filling,and finally SiO₂/PVDF composite photonic crystal is formed.PVDF membranes with inverse opal structure are realized from SiO₂ microspheres of different particle size.With the decrease of the particle size of microspheres,the pore size distribution becomes wider and macropores increases,the porosity augments and the mechanical properties turn weaker,the pure water flux increases and the antifouling performance decreases.（2）The optimal polymer concentration and co-assembly temperature are 8wt%and 120°C,respectively.In the co-assembly process,the polymer and SiO₂microspheres first gather near the gas-liquid interface and assemble into a regular layer,and then the thickness of the regular layer increases,and finally SiO₂/PVDF composite photonic crystals are achieved.With the increase of the mass ratio of SiO₂ to PVDF,the pure water flux of the membrane increases,the average pore size and porosity increase.the pore size of the obtained membranes is uniform,the rejection rate is high,and the fouling resistance is excellent.The membranes via the three-step method exhibit a regular structure,high porosity and pure water flux,but easily present macropores.Although the structural regularity of the membranes by the two-step method decreases,they show high pore size uniformity,high rejection rate and excellent antifouling performance.