Preparation Of Hydrogen-Bonded Organic Framework Membranes And Separation Of Alkali/Alkaline Earth Metal Ions In Aqueous Phase

With the prominent problems of resource consumption and environmental pollution,the sustainable development and utilization of resources has been widely concerned.The demand for the separation of alkali/alkaline earth metal ions in marine lakes and ore resources becomes fairly urgent.Due to the fact that alkali/alkaline earth metal ions are located in adjacent main groups and have similar properties,traditional separation methods such as extraction,foam flotation and electrochemical methods face challenges with high separation difficulty,energy consumption and low selectivity.Membrane separation has the advantages of green,high efficiency,energy saving and emission reduction,and is often used in gas separation,solution separation and purification.In recent years,crystalline porous materials（CPMs）have been favored by researchers for their superior characteristics such as tunable pore size,permanent porosity,and high specific surface area.Among them,hydrogen-bonded organic frameworks（HOFs）stand out for their solution processability,high crystalline structure,good recyclability,and non-metallic toxicity.Therefore,this paper focuses on material synthesis,membranes preparation,water phase ion separation performance test and optimization,and studies the mechanism of ion selective separation by theoretical calculation,aiming to prepare HOFs separation membrane materials with good alkali/alkaline earth metal ion selectivity.（1）Synthesis of organic monomer molecules for constructing crystalline porous HOFs materials:organic molecules containing multiple hydrogen bond building groups were selected as basic building units to obtain sufficient hydrogen bond density per unit volume and enhance the stability of the materials.In this monomer,the pyrene ring with conjugate effect is mainly used as the parent,and the carboxylic acid is used as the hydrogen bond building group to regulate the size of the molecular arm through the benzene ring and the naphthalene ring.The monomers 1,3,6,8-tetracarboxylic acid pyrene（H₄TCPy）,1,3,6,8-tetra（4-carboxylphenyl）pyrene（H₄TBAPy）,6,6’,6’’,6’’’-（pyrene-1,3,6,8-tetradecyl）tetrakis（2-naphthalenecarboxylic acid）（H₄PTNA）monomers were prepared in high purity and high yield by controlling the feeding amount during the monomer synthesis and isolation and purification by recrystallization.The crystal structures of different sizes were cultivated by vapor diffusion and other methods,and performance tests were carried out.（2）Preparation of crystalline porous membranes of HOFs and performance testing of alkali/alkaline earth metal ion separation in aqueous solution:spherical alumina membranes（05S-Al₂O₃）and anodic alumina membranes（AAO）were used as substrates to prepare crystalline porous membranes by interfacial growth,vapor diffusion,and vacuum filtration method.According to the characterization results of scanning electron microscopy,a large number of crystals were grown in the hydroxyl-rich spherical alumina channels,which formed strong hydrogen bonding interactions with water molecules.The experimental results of ion selective separation show that different hydrated metal ions show significant transport differences in the channels,The selectivity of Ca²⁺/Li⁺reached 13.82.（3）Mechanistic study of the separation performance of HOFs crystalline porous membranes for alkali/alkaline earth metal ions:in this paper,theoretical exploration will be carried out by simulation calculations to further investigate the transport mechanism of hydrated ions in HOFs pore channels.For ions with higher charge density,their stronger attraction to oxygen atoms in the hydrated layer makes the hydrogen atoms in the hydrated layer exhibit greater hydrogen bonding activity and form stronger hydrogen bonding interactions with the hydrogen bonding sites in the nanochannels of crystalline porous membranes,thus exhibiting a lower transport rate.