(54d) Functionalized Responsive Membranes for Environmental Applications (invited paper)
The functionalization of microfiltration membrane pores with macromolecules undergoing conformational changes provides nano-scale interactions in a confined domain. The development of these types of biomimetic, tunable, nanocomposite membranes with stimuli-responsive properties provide opportunities in flux tunability and separation selectivity control. Depending on the types of functionalized groups (such as, chain length, charge of groups, biomolecule, etc.), these membranes could be used in applications ranging from metal (or oxyanions) separation to enzymatic catalysis. The use of microfiltration membrane-based sorbents containing polypeptides which provides nano-scale interaction is a novel technique to achieve very high (1 – 1.5 g/g sorbent) metal sorption and selective separations under convective flow conditions. In addition to toxic metal separations, one can reduce the sorbed metals directly to nanoparticles for environmental catalysis. These membranes (with functionalized polypeptides or other polyelectrolytes) are also used for obtaining nanofiltration type separations at pressure < 3 bar. For example, we have demonstrated 90 % separations of arsenic oxyanions with high water flux at pressure of about 1 bar. By taking advantage of helix-coil transitions one can get tunable separations by altering pH. In addition, electrostatic self assembly in pores (layer-by-layer, LBL) can also be achieved through alternate adsorption of cationic and anionic poly-aminoacids or polyelectrolytes under convective flow conditions. Non-stoichiometric immobilization of charged multilayers within a confined pore geometry leads to an enhanced volume density of ionizable groups in the membrane phase leading highly tunable separations. Multilayer assemblies of polyelectrolytes provide excellent platform for protein/enzyme immobilization by providing reusability and high reactivity. Our results with Glucose oxidase enzyme with glucose as substrate showed very high (70 to 80% of homogeneous activity) activity, and continuous synthesis of hydrogen peroxide and gluconic acid. The presentation will include the role of nano-domain interactions for selective separations, full-scale synthesis aspects, stimuli responsive permeability, polypeptide assembly in membrane pores, and integrated enzyme-nanoparticle systems for environmental applications. This research has been supported by NIEHS and NSF-IGERT program.