Fabrication And Characterization Of Monovalent Ion Permselective Membranes(MIPMs)

In this thesis,the fundamental goal was the development of cost-effective and efficient monovalent ion permselective membranes and their utilization for selective ion separation applying membrane-based technology.The existing membranes-based technologies,such as electrodialysis,reverse osmosis,ultrafiltration,and Donnan dialysis process,have been extensively used by many industries to address the overbearing problems in the separation processes.Among these processes,electrodialysis is convenient for specific industrial applications.This technology is more competent when combined with the monovalent ion permselective membranes to segregate ions.Moreover,it is more reasonable in terms of high recovery efficiency and low energy consumption for various ions separation systems.During the selective ion separation,the existence of multivalent ions such as Fe2+,Mg2+,and SO42-causes severe issues in the practical process,which significantly affects the process efficiency.Therefore,it is indispensable to induce new capability in the membrane's architecture for anticipated applications.For membranes synthesis,we used commercial polymers,such as polyvinyl alcohol,bromo-methylated poly(phenylene oxide),and sulfonated poly(2,6-dimethyl-1,4-phenylene oxide),respectively.In the present work,novel procedures have been acquired to prepare low-cost and highly perm-selectivity membrane for desired applications as described in the following chapters.In the 1nd case,efficient monovalent cation permselective membranes(MCPMs)were prepared via layer by layer(LbL)approach and tested for cations separation via ED.A base cation exchange membrane(CEM)was prepared by mixing di-ethylenetriaminepentaacetic acid(DTPA)in PVA(5%)solution at 60?.The obtained membrane was crosslinked through heat treatment,and then decorated with a cationic layer composed of quaternized poly(2,6-dimethyl-1,4-phenylene oxide),and an anionic layer made up of sulfonated poly(2,6-dimethyl-1,4-phenylene oxide).The LbL assembled membranes exhibited high perm-selectivity of 5.16 for 0.1 mol L-1 Li+/Mg2+system via ED at 2.12 mA cm-2 current density.In the 2nd activity,we reported highly stable cation permselective membranes composed of SPVA and a positively charged surface layer.SPVA was prepared by mixing SPPO and PVA in an appropriate ratio(5:2.5)in DMSO solvent and then crosslinked with GA at 25?.The prepared CEM was then coated with a positively charged layer(QPPO).The thickness of the selective layer was precisely controlled using various concentrations of the QPPO solution.The prepared membranes were tested for cation fractionations via ED at a current density of 2.12 mA cm-2.The influence of the selective barrier(thickness)endows MCPMs with high a perm-selectivity up to 12.7 for 0.1 mol L-1 Li+/Mg2+ system,which is very satisfactory for the polymeric membranes.In our 3rd activity,we focused our study on the synthesis of zwitterion membrane for the separation of various monovalent cations via ED.Firstly,a QPPO polymer was prepared with two hydrophilic linkages.The membrane backbone was then supplemented with-COOH groups using amino isophthalic acid(AIPA).The cation exchange segment was then strengthened,employing a crosslinker tetraethyl orthosilicate(TEOS).The amount of AIPA was tuned(various concentration)by considering the flux and perm-selectivity of the membrane towards the monovalent cation.Amongst the prepared membranes,QAIPA-20 had shown best perm-selectivity for various cation systems,such as Li+/Mg2+,Na+/Mg2+,K+/Mg2+,and H+/Fe2+via ED.The QAIPA-20 membrane can be applied effectively for different separation processes,such as brackish water desalination and acid recovery.In the 4th activity,we prepared monovalent anion permselective membranes(MAPMs)using the in-situ interfacial polymerization(IP).The QPPO membrane with-OH groups were transformed with trimesoyl chloride(TMC)into surface-crosslinked structure.The integration of MDEA into the PPO backbone provided a precise step for the first degree of IP.The surface crosslinking with TMC reduced the Wu and supplemented the membrane's surface with repulsive hubs(-COOH)to advance the perm-selectivity.The optimization of MDEA content inferred that a high-Wu is not profitable for high perm-selectivity of the membranes.The best membrane(TMQ-2),conferred high Cl-flux up to 6.303 × 10-8 mol cm-2 s-1 with perm-selectivity of 60 for Cl-/SO42-system.The membranes showed a high limiting current density with low surface resistance.The membrane ED performance,such as stability,flux,and perm-selectivity are superior as compared with the recent reported MAPMs.Relatively high limiting current density of TMQ-2 provides a large window to obtain effective desalination in relatively high applied current density.