  Nitrate is an important pollutant in drinking water worldwide, and a number
of methods exist for the removal of nitrate from water including ion exchange
and reverse osmosis. However, these approaches suffer from a variety of
disadvantages including requirements for supply and disposal of brine used for
regeneration in ion exchange and low water recovery ratio for reverse osmosis.
Here, we demonstrate the use of high surface area activated carbon electrodes
functionalized with moieties having high affinity for adsorption of nitrate
from aqueous solution, such as those used in ion exchange. Adsorption of
surfactant molecules having a quaternary amine ionic group to the activated
carbon surfaces provides functionalization of the surfaces without complex
chemistries. The functionalized electrodes have adsorption capacities of about
80 mg NaNO$_3$ per gram of activated carbon material. Unlike a traditional ion
exchanger, the functionalized surfaces can be repeatedly regenerated by the
application of an electrostatic potential which displaces the bound NO$_3^-$
while leaving an excess of electronic charge on the electrode. The cell is
completed by an inert counter electrode where Faradaic reactions occur during
regeneration. Up to approximately 40% of the initial capacity of the electrode
is accessible following electrical regeneration.
