The Influence of Surface Properties of Activated Carbon on the Adsorption of Nitrate Ion

The adsorption mechanisms of nitrate ion on chemically and physically treated activated carbon (AC) were investigated. The commercial activated carbon (NORIT R1 EXTRA) was first de-ashed with both acids of HCl and H2F2. The de-ashed AC was then treated with nitric acid to introduce acidic functional groups on the surface, subsequently outgassed at different temperatures of 600, 800 and 1000 °C in helium flow to eliminate acidic functional groups. Also, the out-gassing treatment at different temperatures of 500, 700 and 1000 °C was conducted for the de-ashed AC to increase Cπ electon site on the graphene layer. The results obtained in this study showed that the introduction of acidic functional groups on the surface of AC could be achieved through acid treatment with nitric acid. Carboxylic and lactonic groups could be completely removed by out-gassing under the temperature over 800 °C. Also, Cπ electron site was increased accompanying to higher temperature in the process of out-gassing. The surface acidic functional groups such as carboxylic and lactonic groups prevented the adsorption of nitrate ion, while no interruption for the adsorption of nitrate ion by phenolic hydroxyl group was observed contrastive to carboxylic and lactonic groups. The amount of nitrate ion adsorbed on the carbon could be increased with the expansion of basic site.