(342a) Adsorptive and Reactive MF Membranes for Environmental Applications (invited paper)
Traditional adsorptive and/or reactive materials rely on high surface area materials which often lead to diffusion resistance limitations. Our approach involved the creation of open structured membrane materials with various surface functionalities, such as, polyelectrolytes, polypeptides, thiol derivatives, etc. These types of novel, adsorptive materials find applications in environmental remediation, affinity-based separations, sensors, catalysis, etc. The presentation will include two types of applications for adsorptive and reactive materials development: (1) Functionalized MF membranes for toxic and valuable metal capture from aqueous solutions at very high capacity, and for NF type separations with MF membranes, (2) incorporation of reactive enzymes in polyelectrolyte (LBL assembly) functionalized membranes The development of adsorptive and reactive separation processes with reduced energy consumption and minimal environmental impact is critical for sustainable operation. The questions are: Can we make membranes which can capture toxic metals at high capacity? Can we add functional moiety in pores which can go through conformation changes resulting in tunable sorption and desorption behavior? Can we entrap enzymes in MF membrane pores for catalysis? These are indeed possible if one can integrate life sciences field with synthetic membranes to make tunable (in terms of separations) and functionalized adsorptive materials. If the selected macromolecule for surface functionalization is a biomolecule, such as, polypeptide (for ex., poly-glutamic or poly-aspartic acid) then in addition to creating a highly charged field in the membrane pores, conformational changes (such as, helix-coil) can be utilized to conduct tunable separations and metal capture at high capacity with macroporous membranes at low pressures. The use of microfiltration (PVDF, Cellulose, polycarbonate, etc..) membrane-based sorbents containing polypeptides which provides nano-scale interaction is a novel technique to achieve high metal sorption under convective flow (not possible with conventional adsorbents) conditions. This was achieved by attachment of various polyamino acids (MW 2,500-20,000) directly on the membrane pore surfaces. The dependence of conformation properties of polyelectrolytes on pH also provides tunable separation and membrane flux control. Layer-by-layer (LBL) assembly technique, most commonly conducted by intercalation of positive and negative polyelectrolytes or polypeptides, is a powerful, versatile and simple method for assembling supramolecular structures. Multilayer assemblies of polyelectrolytes can also be created within the membrane pore domain for enzyme immobilization without covalent attachment. Our work with glucose oxidase (GOX) enzyme showed excellent product formation rates (H2O2) and stability under convective flow operations through the LBL assembly in pores. The in-situ generation of H2O2 and gluconic acid by enzyme catalysis is a powerful technique for green chemical synthesis, and for advanced oxidations for detoxification of water. The authors would like to acknowledge the research support of US EPA, Huber Corporation, and NIEHS-SRP Program.