Adsorptive activity of activated carbon for urea in aqueous solutions

For the application of activated carbons as adsorbents for removal of urea in blood, adsorption properties of urea were examined in aqueous solution. The adsorptive activity or adsorptive capacity was found to be nearly constant for most kinds of commercial products of activated carbon (0.13-0.15 g of urea per g of activated carbon) (Table 1). The activity was enhanced by oxidation with conc. HNO3. The enhanced activity was, however, reduced by heat-treatment at higher temperatures; it decreased linearly with temperature, and became to half after heat-treatment at 800°C. On the other hand, the activity of non-oxidized activated carbon was not changed by heat-treatment up to 900°C (Fig.2). As compared to the non-oxidized sample, the conc. HNO3-treated sample showed stronger solid acidity (Fig.4), and evolved much more amounts of CO2 during heat-treatment in N2 atmosphere at tempera. tures lower than 400°C (Fig.3). The results of urea adsorption carried out in Ringer solution showed that the activity of the oxidized sample was somewhat suppressed by coexistence of alkaline metal ions, although that of the non-oxidized sample was not affected (Table 3). These facts suggested that the active sites for the urea adsorption on the conc. HNO3-treated sample was dicarboxylic groups on the surface, while those on the non-oxidized sample might be lactone or related groups on the surface.