Anionic Dye Adsorption on Chemically Modified Ordered Mesoporous Carbons

The surface chemistry of ordered mesoporous carbon CMK-3 was successfully modified by heat treatment in ammonia gas at a temperature of 1173 K, without destroying its hexagonally ordered mesoporous structure significantly. The adsorption kinetics and equilibrium of three commercial anionic dyes, i.e., orange II, reactive red 2 (RR2), and acid black 1(AB1), on the novel functionalized carbon were investigated. It was found that the ammonia-tailored CMK-3 showed a much higher uptake rate than that of a commercial activated carbon, due to its desirable ordered mesoporous structure and the electron-donating effect of the incorporated nitrogen-containing functional groups, particularly for the adsorption of the large molecule dye with a long chain, AB1. The dye initial concentration and adsorption temperature had little influence on the adsorption rate, while the size and spatial structure of dye molecules and the shaking speed played an important role during the adsorption process. The adsorption of AB1 which has a long chain required the longest time to reach equilibrium. Film mass transfer (the mass transport between the carbon surface and the flowing dye fluid) might be the rate-controlling step. This novel fiinctionalized adsorbent could enhance the adsorption capacity of the three anionic dyes by 90-200% and 40-60% compared to the commercial activated carbon and unmodified CMK-3, respectively. This significant improvement was attributed to the enhanced dispersive forces between the carbon surface and the dye molecules induced by the nitrogen-containing functional groups. The Freundlich isotherm showed better correlation with the experimental adsorption data in all cases than the Langmuir isotherm as a result of the functional groups induced energetic heterogeneous surface. Slow desorption rate and low desorption efficiency of RR2 indicated that the adsorption of RR2 on the modified CMK-3 was extremely favorable, tending to be weakly reversible.