In response to compounding challenges to global water-energy systems, researchers are investigating advanced membrane structures to reduce the energy costs associated with separations and fluid manipulations. Combining the morphologies and scaled production of polymeric membranes with the functional properties of metal oxides (MOs) enables novel hybrid materials that improve performance characteristics and introduce wholly new capabilities in water applications. We integrate inorganic metal oxides into polymeric materials by two closely related techniques. The first, atomic layer deposition (ALD), is a technique for the conformal growth of MOs consisting of alternating pulses of metal-organic precursor and oxygen-containing co-reactant – and enables the growth of MOs covalently bonded on the outer surface of polymers. The second, sequential infiltration synthesis (SIS), utilizes the same precursors as ALD but relies on longer exposure periods to allow diffusion within the polymer bulk. SIS relies on non-covalent interactions between precursors and polar polymeric functional groups to promote prolonged residence within the polymer film, and can be exploited for selective growth in polar domains of block copolymers. Wide processing latitudes present in ALD and SIS enable precision tuning of properties. First, the choice of MO deposited opens a range of different surface chemistries. This is relevant to the ubiquitous problem of membrane fouling. The surface charge density of MO dictates the hydration layer at the membrane/water interface, and tightly hydrated MO-coated membranes can repel crude oil, whereas loosely hydrated MO membranes are easily fouled. By controlling the vapor transport during deposition, spatial gradients in the MO coating can be realized. Starting with hydrophobic polypropylene membranes and using hydrophilic aluminum oxide ALD, Janus membranes are fabricated with a tunable density gradient of aluminum oxide from top to bottom of the membrane. These Janus membranes showed more efficient aeration performance compared to pristine polymer membranes. Control over MO materials and spatial gradients can be extended with SIS to isoporous block copolymer-derived membranes with nanometer-precise pores spanning from ultrafiltration to nanofiltration regimes.

Combining polymeric structures with metal oxides for advanced water treatment

2019 Fall National Meeting

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