Sustainable N-doped lignin-derived porous carbon showing ion selectivity in capacitive deionization applications

Abstract

As a green material, we presented a highly ion-selective N-doped lignin-derived porous carbon (NLC) material treated with urea. The synthetic reaction occurred through self-assembly of a low toxicity crosslinking agent (glyoxal), a triblock copolymer template (Pluronic F127), and urea as a non-toxic N precursor. The NLC product had a higher BET surface area and increased active sites with a N content of 4.19 at%. Furthermore, structural N (pyridinic, pyrrolic, and graphitic N types) facilitated electron transfer and increased hydrophilicity in the carbon matrix. We investigated the ion selectivity of NLC for capacitive deionization (CDI) in different single-salt solutions and in a competitive ion environment. A significant improvement in electrosorption was detected due to more active sites of NLC as a Lewis base, compared to unmodified lignin-derived porous carbon (LC). The results revealed that the cation adsorption capacity strongly relied on the ionic charge, hydrated radii, and initial concentration of the salt solution. The divalent cation selectivity was achieved by high local electrostatic attraction between the N atom and divalent cations. Finally, this study provided a promising electrode material for CDI applications to enable high adsorption for brackish water and high selectivity for softening water.