Molecular Dynamic Study And Preparation Of Novel Polyamide Reverse Osmosis Membranes

The lack of fresh water resources has become one of the greatest challenges for mankind in the 21^st century.Membrane separation technology has attracted extensive attention in many fields such as desalination of seawater and zero emission of industrial wastewater due to its unique advantages in recent years.Preparation of novel membrane material is the key to break through the trade-off limit.In this paper,the ultrafiltration membrane modified by diazonium-induced anchoring process（DIAP）was used as the research basis.From the perspectives of new membrane material preparation,novel polyamide reverse osmosis（RO）membranes with high separation performance were prepared,providing important theoretical foundations for the development of novel membrane materials.In advance of experimental research,this paper utilized Molecular Dynamics（MD）to explore the process of layer-by-layer assembly preparing novel polyamide RO membrane and membrane separation process at molecular level.It proved the fesibility of preparing reverse osmosis（RO）membrane through layer-by-layer assembly by utilizing 3,5-bis（trifluoroacetamido）benzoyl chloride（AB₂）and 5-（trifluoroacetamido）isophthaloyl chloride（A₂B）.On the other hand,during the research of mass transfer process,retention rate was found to have an acceleration phenomenon when the membrane layer exceeds threshold value,which corresponds to the experimental results well.The molecular simulation provided more scientific and rigorous data to guide the experiments afterwards.For the preparation of novel polyamide composite membranes,this paper designed and synthesized two monomers AB₂ and A₂B containing both acid chloride groups and amino protecting groups.By demonstrating the feasibility of amino deprotection process on membrane surface and exploring the optimal conditions for deprotection（15%N₂H₄,50^oC,5min）,the reaction of dendrimer polymers in the solution was transferred to membrane surface successfully,and the polyamide separation layer with dendritic structure was successfully prepared.In order to further optimize the separation performance of the above novel polyamide composite membrane,the monomer 5-（N-sulfonamide）isophthaloyl chloride（A₂B-NSO）containing another amino protecting group was synthesized to replace A₂B,further reacting with AB₂ to prepare polyamide membrane M_PAP-AB₂-（A₂B-NSO）.The resulted salt rejections of Na₂SO₄,Mg SO₄,Na Cl and Ca Cl₂ were 98.9±0.41%,99.4±0.61%,89.4±1.17%,98.5±1.02%,respectively,and the pure water flux was 10.6±1.04 L/m²/h,thus achieving better separation and permeation performance.At the same time,M_PAP-AB₂-（A₂B-NSO）membrane has lower flux decay rate and higher flux recovery rate in the pollution resistance test compared with the commercial RO membrane,therefore showing better anti-fouling performance during 600hours of testing and indicating a broader application prospect.