(610d) Overview of Iron-Functionalized Oxidative Membrane Platforms for Water Treatment
Membrane-based separation processes have been used extensively for drinking water purification, wastewater treatment, and numerous other applications. Modification of the membrane pores allows such membranes to be used in areas from tunable separations to catalysis. Reactive membranes synthesized through such methods offer enhanced reactivity due to increased surface area and low diffusion limitations. Oxidative techniques utilizing free radicals have proven effective for the destruction of toxic organics as well as various other environmental applications. Many free radical generating processes rely on the reaction of Fenton-like processes using ferrous iron and hydrogen peroxide to form hydroxyl radicals.
A functionalized membrane consisting of a support membrane coated with a polyelectrolyte offers an excellent platform for iron capture by ion exchange and subsequent oxidation (such as with hydrogen peroxide). Our group has performed in-situ polymerization of poly(acrylic acid) (PAA) inside the pores of a polyvinylidene fluoride (PVDF) membrane for Fe(II) capture. By convectively passing hydrogen peroxide through the membrane, we are able to generate hydroxyl radicals which can be used for contaminant degradation. As Fe(II) is converted to Fe(III), it is recaptured in the PAA matrix, where it continues to react with hydrogen peroxide. Steady-state hydrogen peroxide degradation in a PAA/PVDF membrane containing Fe(III) showed first order reaction kinetics (modeled as a continuous stirred-tank reactor). In order to better understand the mechanism by which hydroxyl radicals are generated by the reaction of the ion-exchanged iron and hydrogen peroxide, it is important to quantify their production. This was accomplished through the use of a radical probe, such as benzoic acid. By varying hydrogen peroxide concentration and residence time, the rate of hydroxyl radical production can be altered, therefore determining both the extent and rate of benzoic acid oxidation.
Using these membrane-immobilized systems, we have demonstrated successful degradation of model water contaminants, such as trichlorophenol (TCP). Using the same PVDF/PAA membranes, we have shown controlled synthesis of iron oxide nanoparticles within the membrane domain for the generation of free radicals in the presence of hydrogen peroxide. To our knowledge, this is the first study demonstrating controlled free radical generation within a PAA/PVDF membrane. Support of this research has been provided by NSF-IGERT, NIEHS-SRP, and DOE-KRCEE.