Influence of surface characteristics on liquid-phase adsorption of phenol by activated carbons prepared from bituminous coal

Liquid-phase adsorption of phenol by activated carbons prepared from a bituminous coal was investigated. The carbon preparation consisted of carbonization of the oxidized or the unoxidized coal followed by activation in CO2 to various extents of burnoff. It was observed from the experimental results that BET surface area and pore volume are important factors in determining the adsorptive capacity of the activated carbons. The Langmuir model yields a fairly good fit to the adsorption isotherms, indicating a monolayer adsorption of phenol onto these carbons. The amount of phenol adsorbed per unit surface area, corresponding to complete coverage of the adsorptive sites, decreases with the extent of burnoff and with the particle size of the carbon. The decrease can be attributed to the increase in diffusion path. It was found that the adsorptive capacity decreases with the temperature for the carbon prepared from the unoxidized coal, while it increases for the carbons from the oxidized coal. This difference can be attributed to different populations of oxygen functional groups on the carbon surfaces. According to the Langmuir model, the adsorption of phenol on these carbons was found to be to an endothermic process.