Eggshell membrane derived nitrogen rich porous carbon for selective electrosorption of nitrate from water.

Nitrate (NO) is a ubiquitous contaminant in water and wastewater. Conventional treatment processes such as adsorption and membrane separation suffer from low selectivity for NO removal, causing high energy consumption and adsorbents usage. In this study, we demonstrate selective removal of NO in an electrosorption process by a thin, porous carbonized eggshell membrane (CESM) derived from eggshell bio-waste. The CESM possesses an interconnected hierarchical pore structure with pore size ranging from a few nanometers to tens of micrometers. When utilized as the anode in an electrosorption process, the CESM exhibited strong selectivity for NO over Cl, SO, and HPO. Adsorption of NO by the CESM reached 2.4 × 10 mmol/m, almost two orders of magnitude higher than that by activated carbon (AC). More importantly, the CESM achieved NO/Cl selectivity of 7.79 at an applied voltage of 1.2 V, the highest NO/Cl selectivity reported to date. The high selectivity led to a five-fold reduction in energy consumption for NO removal compared to electrosorption using conventional AC electrodes. Density function theory calculation suggests that the high NO selectivity of CESM is attributed to its rich nitrogen-containing functional groups, which possess higher binding energy with NO compared to Cl, SO, and HPO. These results suggest that nitrogen-rich biomaterials are good precursors for NO selective electrodes; similar chemistry can also be used in other materials to achieve NO selectivity.