Electrochemically-mediated adsorption systems for selective nitrate recovery: agriculture and the water-energy nexus

DR. XIAO SU, STEPHEN COTTY, UNIVERSITY OF ILLINOIS


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We developed a hybrid structure which consists of an electrically-conductive support framework (carbon black and carbon nanotubes (CNTs)) with the coating of redox-responsive polymeric films (polyvinylferrocene (PVF), poly-TEMPO-methacrylate (PTMA), polyaniline (PANI), Poly(3-hexylthiophene-2,5-diyl) (P3HT). In our preliminary result using density-functional theory (DFT), it was shown that nitrate binds strongly to oxidized ferrocene group. In our lab-scale preliminary tests, PVF-CNT electrode showed fast adsorption kinetics (reaching equilibrium within 1 h), and the highest uptake up to 200 mg/g. This model polymer allowed electrochemically-controlled capture and release of nitrate, like on/off switches, exhibiting >95 % regeneration efficiencies and thus demonstrating fully reversible, electrochemically modulated nature of our process. In addition, we found that PANI revealed the higher adsorption uptake than any other materials tested (45 mg/g for PANI and 10 mg/g PVF at 1 mM nitrate). We hypothesize that hydrogen bonding with protonated amine group (-NH 2 + ) site is responsible for selective separation. Redox-mediated operation allows adsorption and desorption via simple electrical swings with minimal pH, temperature or other changes in solution conditions, and combines the inherent advantages of electrochemical methods, including high capacity, fast kinetics and modularity, without the selectivity limitations present in traditional capacitive deionization. Thus, this energetically-efficient, point-of-source system for nitrate recovery will be expected to strongly increase community resilience to nutrient problems, and provide a techno-economic motivation to agricultural stakeholders to employ these technologies on the long-term. Continuation of the efforts are being pursued by PI Su and co-PI Cotty.

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