Preparation And Performance Of L-tryptophan Molecularly Imprinted Membrane By Microemulsion Polymerization

The molecularly imprinted membrane (MIM) was prepared by microemulsionpolymerization. L-tryptophan was used as the template molecule and the bicontinuousmicroemulsion as the precursor systems to synthesize microstructure-controllable MIM.A new method of preparation of MIM, the microemulsion template polymerization, wasproposed. The imprinting microemulsion system as well as the the specificity adsorptionproperty and pore structure of MIM were investigated. The morphology and themechanism of separation process of MIM were observed and studied.Firstly, pseudo-ternary phase diagram of imprinting microemulsion systemMMA-BA/AA-L-trp/H2O and the electrical conductivity were studied. The resultsshowed that L-trp and AM have emulsifying effect on the system, and L-trp also has thecontribution to the formation of bicontinuous microemulsion. The MMA/BA ratio hadno significant impact on bicontinuous microemulsion. The MIM was synthesized fromthe imprinting microemulsion system initiated by redox initiator system KPS/TMEDA.The factors affecting specificity adsorption property and water flux of MIM wereanalyzed. The results indicated that the EGDMA maintains the shape of imprintedcavities and improves the stability of pore structure of MIM. The water phase of systemprovided favorable conditions for formation of pore structure and imprinting layer. Butthe high water fraction in the polymerization process is prone to inducing microphaseseparation, leading to the cavities and pore structure damaged. The AA content isclosely related to pore size and binding sites. The excessive AA affects the non-specificadsorption and pore structure of MIM. MMA had met the need of rigid structure ofcavities, but the high MMA content will affect the configuration of the cavities. As theL-trp content increased, the water flux of MIM improved, but excessive L-trp causedutilization declined. When the EGDMA content was2.0%, water fraction was40%, theAA/MMA-BA mass ratio was2.5, the MMA/BA mass ratio was2.0and L-trp contentwas0.9%, the specificity adsorption property and the pore structure in a better level. The surface morphology of MIM was observed by SEM, it retained continuouspore structure from the bicontinuous microemulsions. The pore size and thepermeability for L-trp of MIM were improved with the water fraction increased. Theadsorption speed of MIM reached equilibrium within120minutes. Combiningpermeation with infrared spectrum analysis, it was found that the recognizing processwas achieved by hydrogen bonding between functional groups and template molecule.The permeation of L-trp was considered as preferential adsorption then diffusionthrough the MIM. The MIM had good acid resistance, but was poor in alkaline solution.MIM has a good thermal stability. Being treated in water at20~50℃will cause theMIM densification and reduction of permeability, but being treated at60℃will damagethe membrane pore structure.