Adsorption of benzoic acid and phenol from aqueous solution by activated carbons—effect of surface acidity

Effect of surface acidic groups of activated carbons on their adsorption characteristics for substrates from aqueous solutions were studied. Six kinds of carbons obtained commercially and their heat-treated products were used. Pore-size distribution, BET surface area and surface acidity were measured. Adsorption isotherms for benzoic acid and phenol from aqueous solutions (single or double components) were obtained. Substitution adsorption, i.e. substrate adsorbed preliminarily is substituted by another substrate, was also carried out. It was found that adsorption of benzoic acid is scarcely affected by surface acidity of carbons and the amount adsorbed is almost entirely controlled by the specific surface area of carbons. On the contrary, adsorption of phenol is retarded considerably by the acidity of carbons. In the case of solution of double components, benzoic acid is adsorbed predominatedly. The phenol adsorbed preliminarily is easily substituted by benzoic acid, but the substitution of benzoic acid by phenol scarcely proceeds.