(595e) A Polypyrrole-Based Asymmetric System for Electrochemically Mediated Separations of Organics from Water

Authors: 
Ren, Y., Massachusetts Institute of Technology
Mao, X., Massachusetts Institute of Technology
Hatton, T. A., Massachusetts Institute of Technology
Water contamination by neutral organic species, including industrial chemicals, pesticides, and pharmaceuticals, and personal care products is a long-standing issue globally. Adsorption is one of the most widely used technologies for mitigating uncharged organic contaminants in the aquatic system. However, conventional adsorbent materials such as activated carbons suffer from costly regeneration and high attrition rates. Polymeric adsorbents have shown great potential to overcome the challenges around regeneration and replace activated carbons for removing a wide range of toxic pollutants. We use electrochemical stimuli to modulate the affinity between target hydrophobic organic molecules and polymeric adsorbents as an energetically efficient and environmentally friendly means of regenerating the adsorbents. We choose polypyrrole (PPy), an intrinsically conducting polymer, as the primary component of the electrochemically regenerable adsorbent. We have developed two approaches to electrochemically modulate the hydrophobicity in PPy, by incorporating redox-responsive ferrocene moieties, and by doping PPy with amphiphilic surfactant anions. We functionalize the two types of PPy onto conductive carbon fibers and assemble the two electrodes into an asymmetric system for treating water contaminated with organics. Both electrodes have high affinities for organics when the asymmetric system is uncharged while their affinities can be lowered upon applying a mild potential (1.5V) to render the polymer hydrophilic. We can therefore apply an electrical potential to drive the desorption of organics from the electrodes when the polymer is saturated. Because the reactivation of the two electrodes in the asymmetric system is spontaneous, the asymmetric system improves the efficiencies of the separation by avoiding water splitting. We demonstrate experimentally that the asymmetric system can be used reversibly for removing model organic contaminants from water in a cyclic fashion with minimal decay in capacity over a number of cycles. We also design and simulate a multi-stage separation process using the asymmetric PPy-based system to further enhance the efficiency with careful choice of process parameters.