Preparation Of UiO-66 Membrane And Its Separation Of Iodide Ions From Water

Radioactive iodine nuclides,such as ¹²⁹I,¹³¹I,and ¹²³I,of which emit radiation can directly damage cells and tissue structures,Furthemore,because of its radioactive iodine’s long-half life and fluidity,which can enriched in organisms through the accumulation of water and cause serious damage.Metal-Organic Frameworks（MOFs）porous materials have the characteristics of large specific surface area and high porosity,If MOFs powder is directly applied to the field of water treatment,there are still disadvantages of small volume,low efficiency and poor circulation of pollutants.The preparation of MOFs membrane materials can not only overcome the above shortcomings,but also adjust the pore size and membrane thickness to achieve a screening effect.Therefore,guided by the efficient complementation of iodide ions in radioactive wastewater,MOFs are used as membrane separation materials to prepare separation membrane materials that have separation characteristics and stability for iodide ions in aqueous solutions,in aqueous solutions explore the seperation performance and mechanism of MOFs membranes which have important research significance and value for the treatment of iodine-containing radioactive waste water.The reason why UiO-66 MOFs materials is selected in this paper is that,it’s good water and thermal stability,as well as it’s size of 0.7 nm is very close to the size of the iodine ion in aqueous solution.Therefore secondary growth method is used to construct the continuous and dense UiO-66 membrane on the outer surface of the ceramic tube,studying the effect of the controllable preparation of UiO-66 nano seed crystals,the deposition method of the seed crystals on the outer wall of the ceramic tube and the preparation conditions of the secondary growth method on the microstructure of the UiO-66 membrane during the preparation process.At the same time,the influence of iodide ion concentration,solution p H value,and mixed anions on the separation performance of UiO-66 membrane for iodide ions was explored.Furthermore,the preliminary study on recyclability of UiO-66 membrane was carried out.In order to further improve the separation performance of UiO-66 membrane for iodide ions,we adopted a post-synthesis modification strategy to modify the surface of UiO-66 membrane with poly-4-vinylpyridine and polypyrrole polymer materials.The specific research content is divided into the following three parts:（1）The surface of the tubularα-Al₂O₃membrane is oriented to synthesize a continuous and dense UiO-66 membrane.The controllable preparation of UiO-66 nanocrystals in the hydrothermal method,the functional modification of the surface of tubular ceramic membranes,the deposition conditions of UiO-66 nanocrystals and the secondary growth method to prepare UiO-66 membranes.Experimental research found that,compared to PVP,acetic acid is used as a deprotonation reagent during the preparation can obtain smaller-sized UiO-66 crystals;the dipping-lifting method is more suitable for the secondary growth method to prepare UiO-66.During the process of secondary growth,hydrofluoric acid is used as a deprotonation reagent to obtain a UiO-66 membrane with better crystal intergrowth.At the same time,the carrier obtained by using 3-isocyanatopropyl as the functional modifier is thinner than the carrier obtained by using 3-aminopropylethoxysilane as the functional modifier,and the thickness of the UiO-66menbrane is about 20μm.（2）The separation performance of UiO-66 membrane for iodide ions in aqueous solution was studied.The filtration performance test with 0.5 Mpa of filtration operating pressure of and a filtration time is up to 4 hours was conducted in an aqueous solution of KI and I₂.The dynamic filtration performance of the UiO-66 membrane and rease performance were studiedrespectively.In addition the initial concentration of iodide ions in the filtrate,the p H value of the filtrate,and the mixed anions contained in the filtrate are filtration environment variables to study their influence on the filtration performance of the UiO-66 membrane.Futhermore,studied about the preliminarily mechanism of UiO-66 membrane is used to separate the iodide ions in water was conducted through the penetration test.The UiO-66 membrane with a filtration area of?18.85cm²has a stable rejection rate of 87%under dynamic filtration with an operating pressure of 0.5Mpa,and the separation performance data is dropped to 76%after five cycles of use.（3）Post-synthetic modification improves the separation performance of UiO-66 membrane for iodide ions in aqueous solution.Use poly-4-vinylpyridine（P4VP）and polypyrrole（PPy）with nitrogen-rich aromatic ring polymer to repair the intercrystalline pores of UiO-66 membrane.The UiO-66 membrane coated with P4VP is quaternized to form a charge transfer with iodide ions to improve the trapping performance of the UiO-66 membrane.Experimental studies have found that the in-situ chemical polymerization of polypyrrole has uncontrollable reaction and cannot well repair the intercrystalline pores of UiO-66 membrane.The UiO-66 membrane surface is coated with aromatic ringcontaining polytetravinylpyridine（P4VP）,and the UiO-66membrane containing Quaternary ammonium salt is obtained by the quaternization reaction on it,which can optimize the defects of the UiO-66 membrane to a certain extent.As the amount of P4VP coating increases,the iodine water filtration performance of the modified P4VP@UiO-66membrane will also increase.When using the maximum coating concentration(3×10^-3mmol/L P4VP solution)the rejection rate reached 92.61%,and the rejection rate after the quaternization reaction of the P4VP@UiO-66 membrane with the maximum coating concentration would further increase to 94.20%.