Adsorption of tannic acid and phenol on mesoporous carbon activated by CO2

Abstract

Ordered mesoporous carbon CMK-3 was synthesized and further activated using CO2 at 1173K for 2h (C1173-2). Batch experiments were conducted to access the adsorption properties of C1173-2 towards aqueous phenol and tannic acid. Nonporous graphite, the pristine CMK-3, and a commercial microporous activated carbon (AC) were also included as comparative adsorbents. The adsorption affinity of C1173-2 for both phenol and tannic acid was much higher than that of CMK-3, resulting from the enhanced specific surface area of C1173-2. After normalizing for adsorbent surface area, phenol adsorption on the three porous carbons was comparable. However, tannic acid adsorption on C1173-2 was similar to that on CMK-3, but prominently higher than that on AC. N2 adsorption results of the porous adsorbents with tannic acid loaded reflected that the pore volume, especially micropore volume of C1173-2 and CMK-3, was effectively utilized by tannic acid, which was different from the poor occupation of pore volumes for AC. Phenol and tannic acid adsorption over C1173-2, CMK-3 and AC followed the pseudo-second order model and the adsorption rate of C1173-2 was the highest. Moreover, adsorption of the two solutes on C1173-2, CMK-3 and AC was affected by external mass transfer and intraparticle diffusion. To our knowledge, it is the first study on the adsorption of aqueous organic contaminants on mesoporous carbon activated by CO2. The findings highlight the significance of CO2 activation method to improve the adsorption properties of ordered mesoporous carbon for aqueous organic contaminants.