Preparation Of Metal-Organic Framework Membrane Of Microporous Aromatic Framework For Adsorption Removal Of Iodide In Water

With the rise of nuclear power and the increase of nuclear facilities,and the wide application of radioactive iodine in medicine,industry,agriculture,and scientific research,the risk of contamination of water bodies with radioactive radionuclides has increased,and the problem of water pollution has received widespread attention from people all over the world.The sources of radioactive iodine are mainly nuclear reactors and nuclear fuel reprocessing plants and medical wastewater in the nuclear industry.Since the half-life of the ¹²⁹I isotope of radioactive iodine（1.57×10⁷ years）is very long,it will significantly increase the incidence of thyroid cancer and leukemia.Therefore,it poses a serious threat to human health.Membrane separation technology usually uses selective permeation membranes to effectively separate radioactive iodine from wastewater by using pressure difference,potential difference,concentration difference,or temperature difference as the driving force.The metal-organic framework material is a novel type of porous crystal material formed by the coordinated connection of a metal ion or a cluster of metal ions with a nitrogen-containing heterocycle or an aromatic ring-containing organic ligand,and due to the types of metal ions and organic ligands Diversity,metal-organic framework materials are very rich in composition and topology.Because MOFs have the advantages of high thermal stability,large specific surface area,adjustable pore channels,good selective adsorption performance,and excellent electrical conductivity,they have great application value in many fields,such as:catalysis,adsorption separation,fluorescence,sensing and drug delivery,etc.Therefore,MOFs materials have received great attention from scientific researchers around the world.Membrane separation technology has proven to be very promising in solving energy and environmental challenges.Compared with traditional separation technologies,membrane separation has the advantages of low energy consumption,small carbon footprint,and ease of operation.At present,the membranes used in the field of membrane separation are mainly polymer membranes.However,the polymer membranes have short service life,low thermal and chemical stability,low selectivity,and excellent design and synthesis performance and high stability.Membrane materials become the key to membrane separation technology.Today,zeolite molecular sieve materials have been widely used in the field of membrane separation due to the regular pore structure and high stability.Compared with zeolite molecular sieve materials,MOF materials have the advantages of adjustable pores,good adsorption performance,large specific surface area,and high thermal stability,making them of great application value in the field of membrane separation.The preparation of metal-organic framework membranes with relatively good interactivity has also become a research hot spot for scientific researchers.This dissertation mainly uses the characteristics of high stability and well-regulating dual-π-wall nanopore coordination polymers that can enrich iodine and release iodine in a large amount,and is synthesized by a secondary growth method on a polytetrafluoroethylene（PTFE）carrier.A dual-π-wall nanoporous coordination polymer membrane with good mutuality was developed,and the adsorption and separation performance of the synthesized double-π-wall nanoporous coordination polymer membrane in iodine-containing solution was studied.The specific research content is as follows:The first chapter is the preface,briefly introduces the characteristics and research progress of metal-organic framework materials,the characteristics of metal-organic framework membrane materials,synthetic methods and their research value in the application field.And later introduced the significance of this topic and the main research content.In the second chapter,high-frequency numerically controlled ultrasonic cleaning apparatus is used to first ultrasonically equilibrate dualπ-wall nanopore coordination polymer（hereinafter referred to as lac-Zn）for 12 h to obtain lac-Zn nanocrystals and prepare a seed solution,and then use a solvent filter to pass The filter coating method deposits seed crystals onto the surface of the PTFE support.In the process of seed deposition,poly-4-vinylpyridine（P4VP）was added to enhance the binding force between the seed and the carrier,and then a dual-π-wall nanoporous coordination polymer membrane（lac-Zn composite membrane）with good inter-action was prepared by secondary growth method.The synthetic lac-Zn composite membrane was placed in iodine in cyclohexane solution for iodine adsorption experiments.Static absorption and dynamic adsorption experiments were performed.The concentration of iodine in cyclohexane solution was measured using an ultraviolet-visible spectrophotometer.The kinetics of the lac-Zn composite membrane adsorption process is in accordance with the pseudo-second-order kinetic model.The correlation coefficient of the adsorption isotherm shows that the adsorption is more in line with the Langmuir adsorption,namely monolayer adsorption.The maximum adsorption capacity of iodine in lac-Zn composite membrane was about 755 mg·g^-1.In the third chapter,polydimethylsiloxane（PDMS）was deposited on the lac-Zn composite membrane prepared by the secondary growth method by means of spin-coating,so as to improve the hydrophobicity of the lac-Zn composite membrane,thereby enhancing the water stability of the lac-Zn composite membrane.The contact angle measured by the contact angle meter showed that the contact angle of PDMS hydrophobically modified membranes increased from 58.6°to136.8°.That is,PDMS effectively increased the hydrophobicity of the lac-Zn composite membrane and improved the water stability of the membrane.Through static and dynamic adsorption of iodine experiments,the kinetics of the adsorption process of lac-Zn composite membranes are in accordance with the pseudo-second-order kinetics model,and the membrane has a certain degree of reusability.The correlation coefficient R² of Langmuir adsorption isotherm for adsorption of iodine in iodine aqueous solution of lac-Zn/PDMS membrane is0.9394,and R² of Freundlich adsorption isotherm is 0.9975.The correlation coefficient of the adsorption isotherm shows that the adsorption is more in line with the Freundlich adsorption that is the adsorption of the adsorbent surface heterogeneity.Due to the deposition of PDMS,some adsorption sites on the lac-Zn composite membrane were blocked by PDMS.The maximum adsorption capacity of lac-Zn/PDMS membrane for iodine was only 350 mg·g^-1.