Quaternary nitrogen functionalized carbonaceous adsorbents to remove nitrate from aqueous phase

Abstract

Quaternary nitrogen (N-Q) functionalized porous carbon could be prepared from thermally stabilized polyacrylonitrile (PAN) fiber (PYR) by ZnCl2 activation (PYR-7Z4) and consecutive heat treatment at 950 °C (PYR-7Z4-9.5HT10). The prepared carbonaceous adsorbents could effectively remove nitrate anion from water by 0.6 mmol/g or more in the wide range of equilibrium solution pH (pHe) 3–8. Although the adsorption amounts on the materials derived from PYR were about a half of ion-exchange resin (HP555), fairly good adsorption performance could be realized as carbonaceous materials compared with the other carbon based adsorbents containing nitrogen species. This is caused by the presence of the equivalent N-Q sites on the prepared porous PAN carbon surface. Examining adsorption isotherms of nitrate, PYR-7Z4-9.5HT10 exhibited a little better performance than PYR-7Z4. Comparing adsorption performance of nitrogen-doped rayon based activated carbon fiber (ACF) prepared in our previous study, N-Q sites could be dominantly introduced on carbon surface for the materials derived from PYR. In addition, post heat treatment at 950 °C also seems to be effective to reduce unexpected negatively charged carboxy groups leading to the increase in both adsorption capacity and affinity of nitrate on the carbon surface.