Enhanced Selective Electrosorption of Nitrate from Wastewater by Controllably Doping Nitrogen into Porous Carbon with Micropores

The biological NO3– removal process might be accompanied by high CO2 emissions and operation costs. Capacitive deionization (CDI) has been widely studied as a very efficient method to purify water. Here, a porous carbon material with a tunable nitrogen configuration was developed. Characterization and density functional theory calculation show that nitrogenous functional groups have a higher NO3– binding energy than Cl–, SO42–, and H2PO4–. In addition, the selectivity of NO3– is improved after the introduction of micropores by using the pore template. The NO3– ion removal and selectivity of MN-C-12 are 4.57 and 3.46–5.42 times that of activated carbon (AC), respectively. The high NO3– selectivity and electrosorption properties of MN-C-12 (the highest N content and micropore area) are due to the synergistic effect of the affinity of nitrogen functional groups to NO3– and microporous ion screening. A CDI unit for the removal of nitrogen from municipal wastewater was constructed and applied to treat wastewater meeting higher discharge standards of A (N: 15 mg L–1) and B (N: 20 mg L–1) ((GB18918–2002), China). This work provides new insights into enhanced carbon materials for the selective electrosorption of wastewater by CDI technology.