Study On The Preparation Of ZIF-8 Membrane By Contra-diffusion Method And Its Performance Of Removed Iodine From Aqueous Solution

If radioactive nuclides(such as ¹²⁹I and ¹³¹I)are released into the environment,they will cause serious damage to the environment and organisms.Efficient and safe removal of radioiodides in water has become one of the leading topics in the field of radioactive wastewater treatment.Metal-Organic Frameworks?MOFs?,as a new kind of ordered porous crystalline materials,have shown great potential in the application of adsorption and removal of radioiodides in liquids.MOFs materials can be adjusted for their porosity,specific surface area and pore size by selecting appropriate metal centers and organic ligands.In addition,selecting organic ligands rich in electron-donating groups and?-conjugated aromatic rings as building blocks,using electron-donating groups to form charge transfer complexes with iodine can also increase the amount of MOFs to adsorb iodine.However,the fragility,difficulty of forming and poor water stability of MOFs have restricted their development in the field of water treatment.At present,guided by the effective removal of iodine nuclide in water,the continuous construction of MOFs membrane with directional density is constructed,revealing the structure change law of MOFs membrane in the process of filtering iodine aqueous solution,clarifying the mechanism of MOFs membrane removing iodide ions in water,and becoming MOFs Membranes are the key scientific problems that need to be solved urgently in the application of radioactive wastewater treatment.In view of the above problems,this thesis proposes to prepare a uniform and dense ZIF-8membrane on the surface of polyvinylidene fluoride by Contra-diffusion method,explores the performance of ZIF-8 membrane to remove iodide ions in water,and focuses on the initial concentration of iodide ions and the pH value of the solution The effect of coexisting anions in the solution on the performance of ZIF-8 membrane to remove iodide ions.In order to improve the hydrolysis resistance of ZIF-8 membranes,we tried to hydrophobically modify ZIF-8membranes through post-synthesis ligand exchange strategy and in-situ polymerization strategy,and studied the hydrophobically modified ZIF-8 membranes to remove iodide ions in water Performance.The specific research content mainly includes the following four aspects:?1?In order to prepare homogeneous and dense ZIF-8 membrane on PVDF microporous membrane,the surface of PVDF microporous membrane needs to be functionalized first.In this thesis,PVDF microporous membrane was modified by spin coating and suction filtration,and ZIF-8 membrane was prepared by Contra-diffusion on the surface of P4VP modified PVDF membrane.The results show that:under the same concentration of P4VP solution,the ZIF-8membrane prepared by the Contra-diffusion method of PVDF film deposited by spin coating method with P4VP is continuous,dense and uniform;When the concentration of the P4VP solution is 0.8×10^-3 mol/L,the thickness of the prepared ZIF-8 membrane is about 10?m.?2?ZIF-8 has the advantages of large specific surface area,high porosity and high pore volume,and has good adsorption capacity for iodine.This article systematically studied the static adsorption and dynamic filtration performance of ZIF-8 membrane for iodine ions in water,and discussed the effects of solution pH,initial concentration of iodide ions and coexisting anions in the solution on the performance of ZIF-8 membrane dynamic filtration of iodide ions in aqueous solution.The ZIF-8 membrane with a mass of 0.0045 g and a membrane area of 8.05 cm² has a maximum adsorption capacity of 602.86 mg/g during static adsorption in 200 mL of 0.246mmol/L iodine solution;In the experiment of dynamic filtration of iodine aqueous solution,the curve changes of rejection rate and permeate water flux show that the decrease of iodide ion concentration in the solution mainly depends on the retention effect of ZIF-8 membrane;the I₂@ZIF-8 membrane after dynamic filtration of iodine aqueous solution released iodine completely after 156 hours in ethanol,and the maximum iodine released was about 10.96?g/mL;after five cycles of dynamic filtration of iodine water,the iod ine removal efficiency of ZIF-8membrane remained 63.69%;Adsorption method was used to study the water flux recovery rate?FR_W?,Rir?irreversible protein?and Rr?reversible protein?anti-fouling performance of ZIF-8membrane.After being contaminated with protein,it still has a high flux.?3?ZIF-8 membrane is prone to hydrolysis when dynamically filtering iodine aqueous solution.In this thesis,first,the post-synthesis ligand method is used to improve the water stability of ZIF-8.The benzimidazole partially replaces the 2-methylimidazole ligand in the ZIF-8 framework.After the synthesis,the ZIF-8/DMBIM membrane obtained by the ligand exchange reaction has a rejection rate of 77%for iodide ions in water,and the rejection rates of ZIF-8/ABT membrane and ZIF-8/2-Methylbenzimidazole membrane for iodide ions in water are both less than 60%.ATR-FTIR,PXRD and FE-SEM results show that the hydrolysis resistance of the ZIF-8 membrane is improved after ligand exchange,and the original crystal structure is retained after static and dynamic filtration experiments,but it is still possible to stay in the aqueous phase for a long time.This led to the disintegration of the ZIF-8 framework.?4?This thesis also explores the hydrophobic modification of ZIF-8 membrane with in-situ polymerized pyrrole.Through the comparison of ATR-FTIR and Raman patterns before and after the reaction,it was found that after chemical oxidation polymerization,polypyrrole was formed on the surface of ZIF-8 membrane.In this thesis,a ZIF-8 membrane was prepared on the PVDF microporous membrane modified by P4VP deposition by Contra-diffusion method,and it was used for static adsorption and dynamic filtration to remove iodide ions in aqueous solution.Aiming at the problem of ZIF-8 membrane being hydrolyzed during dynamic filtration,two strategies of ligand exchange and in-situ surface polymerization after synthesis were proposed to hydrophobically modify the ZIF-8 membrane,improving the hydrolysis resistance stability of the ZIF-8 membrane The research results have positive significance for promoting the practical application of ZIF-8membrane in the field of radioactive wastewater treatment.