Control Of The Pore Size Of Acylhydrazone-based COF Membranes And Their Study On Dye Separation Performance

Covalent organic framework materials（COFs）are a new class of crystalline porous materials,which are widely used in gas storage,catalysis,photoelectric sensor and separation fields,with open and regular pore structure,low density,high specific surface area and easy structural design.Most of the pore sizes of COF membranes reported at present are within the technical parameters of nanofiltration membranes（0.001-0.01μm）,so COF nanofiltration membranes are widely used.However,its application in the field of membrane separation has certain limitations.On the one hand,the reaction of synthesize COFs is generally reversible dehydration condensation reaction,which makes the regular frame structure of COFs material collapse in a humid atmosphere.On the other hand,the common method is to synthesize COF powder material and then use it as filler to prepare mixed matrix membrane under strict conditions.It is a technical difficulty to prepare COF membrane material directly.In view of existing problems,in this thesis,2,5-diethoxy p-benzoyl hydrazine（DTH）and 1,3,5-trialdehyde phloroglucinol（Tp）were selected as reaction monomers to prepare water-stable COF composite membrane materials with enolone tautomerism through interfacial polymerization,and different Bronsteric acid（B-acid）was added in the regulation reaction.The pore size of the membrane is regulated by different replacement monomers and polymers.The specific research is as follows:（1）Tp DTH/CPAN composite membranes with good stability were prepared by interfacial polymerization of Tp and DTH on modified polyacrylonitrile（CPAN）porous ultrafiltration membranes.By adding four types of B-acids（AA acetate,N-hexanoic acid NHA,n-octanoic acid NOA and n-decanoic acid NDA）to control the reaction rate of membrane formation.The COF composite membrane with an average pore size distribution of about 2.54 nm was finally obtained when NOA was used as catalyst.The dye separation experiments showed that,the pore structure of Tp DTH COF can be used as a water channel and has the role of pore-sieving mechanism.The water flux is 29.51 L/（m²·h·bar）.（2）Two small molecules of COF with different structures were used to construct monomer melamine（Me）or hydrazine hydrate（Hz）.After Tp DTH/CPAN composite membrane was prepared using NOA as catalyst,the original amine monomer DTH was replaced with Me or Hz.The pore structure,hydrophilicity and dye rejection of the membrane were studied by adjusting the concentration of the replacement monomer.When the concentration of Me is 6 times that of DTH equivalent-NH₂group,Tp DTH@Me（6）/CPAN composite membrane with pore size about 1.6 nm is successfully prepared,and the rejection of Coomath bright blue-R250 is 98.72%and water flux is 27.22 L/（m²·h·bar）.When the Hz concentration is 4 times of the DTH equivalent-NH₂group,the Tp DTH@Hz（4）/CPAN composite membrane whose pore size is about 1.4 nm has been successfully prepared.The rejection of Coomath bright blue-R250 is more than 99%,and the rejection of Congo red and chrome-black T is more than 95%.And the water flux is 30.24 L/（m²·h·bar）.Because the pore size of Tp DTH@Hz（4）/CPAN composite membrane surface separation layer is smaller than Tp DTH@Me（6）/CPAN composite membrane surface separation layer,it has better interception effect.（3）The poly DTH-400_X/CPAN composite membrane containing PEG-400 was prepared by interfacing polymerization of DTH,DTH-400 and Tp.The effects of DTH-400 and DTH addition ratio on the mechanical properties and rejection performance of the membrane were investigated.The experimental results show that the introduction of polymer chain can effectively reduce the pore size of the separation layer COF,and the flexibility of the polymer chain segment improves the mechanical properties of the membrane and makes the membrane have better stability.When the mass of d TH-400 and DTH was 1:2,the prepared polymer membrane poly DTH-400_1/3/CPAN had the best performance,with the rejection rate of Coomath bright blue-R250 greater than 99%and the pure water flux of 25 L/（m²·h·bar）.