Synthesis Of Covalent Organic Frame-works Water Treatment Membranes Via Schiff-base Reaction

Covalent organic frameworks(COFs)as a kind of porous material with crystal morphology received increasing interests since 2005.At present,the research on COFs mainly focuses on two topics:constructing novel COFs morphology and extending their applications into other fields.Until now,COFs materials have been gradually applied in gas storage,catalysis,opoelectronic devices and water treatment.Because of their open and regular pore structure,COFs are regarded as an ideal new type of water treatment membrane material.However,their powder form and instability in water highly challenge to the preparation of separation membranes.In order to solve this problem,we will realize stable and highly efficient water-treatment membranes by selecting the type of COFs and optimal synthetic conditions.We utilized graphene oxide or layer-by-layer method to fabricate continuous COFs membranes and studid their performance in organic dye separation,the primary contents are as follows:(1)Synthesis and adsorption properties of water-stable COFs materials:Two water-stable Schiff base COFs with similar structure but different pore sizes were prepared by in-situ growth at room temperature.Their dye adsorption performance shows that the saturation absorptive capacity is almost 96 mg/g for a cationic dye,methylene blue,and 18 mg/g for an anionic dye,the Congo red,at 25? and pH=7 by electrostatic interaction force.(2)Synthesis and separation properties of GO-COFs membranes:Continuous GO-COFs membranes were formed by the excellent film-forming property of graphene oxide via vacuum filtration and applied to the separation of three anionic dyes with different molecular sizes.The rejection of Congo Red,Black T and Sunset Yellow is 99%,88%,and 0%,and the flux is 136 Lh-1m-2bar-1,175 Lh-1m-2bar-1 and 204 Lh-1m-2bar-1,respectively.The threshold size of the COFs membranes should be between 0.65nm?0.75nm.(3)Synthesis and characterization of pure COFs membrane:Continuous COFs membranes were prepared by Layer-by-Layer stratergy,where COFs building units were grown successively on the surface of modified porous substrates.However,due to their low crystallinity,the dye rejection is very low.In conclusion,two kinds of membranes based on water stable Schiff-base COFs materials were fabricated.And their dyes separation performance was studied.The result shows that COFs membranes with unique pore channel structure can separate dyes precisely.This research extended COFs application into water treatment.