Influence of carbon-oxygen surface groups on the adsorption of phenol by activated carbons

Abstract

Adsorption isotherms of phenol from its aqueous solutions on four samples of activated carbons having different surface areas and associated with varying amounts of carbon-oxygen surface groups have been determined in the concentration range 20-1000 mgIL. The adsorption of phenol does not depend upon surface area alone but is also influenced by the presence of carbon-oxygen surface groups. The amount of these surface groups was enhanced by oxidation with nitric acid, ammonium persulphate and hydrogen peroxide and was decreased by degassing the activated carbons at gradually increasing temperatures of 400, 650° and 950°C. The oxidation of the carbons decreases the adsorption of phenol, the extent of decrease depending upon the nature of the oxidative treatment. The adsorption increases on degassing of the carbon samples, the increase depending upon the nature of the carbon­ oxygen surface groups being eliminated at that temperature on degassing. The results indicate that while the presence of acidic carbon-oxygen surface groups which are evolved as COl suppresses the adsorption of phenol, the presence of non-acidic surface groups which are evolved as CO tends to enhance the adsorption of phenol. Phenols and their derivatives are invariably present in th e effluents from industries engaged in the manufacture of a variety of chemicals such as plastics, dyes and in plants used for thermal processing of coal. Many of these phenols are carcinogenic even when present in low concentrations. The presence of phenols in water also produces foul smelling chlorophenols during chlorination treatment of water for domestic supply. Thus, investigations relating to the removal of phenols from water have engaged the attention of a large number of investigators. Activated carbons, because of their large surface area and a high degree of surface reactivity, are potential adsorbents for the removal of organics in general and have been found to have a high efficiency for the removal of phenols from waste waters. laroniec and co-workers,,2, Enrique et at. 3 , Worch and Zakke 4 and Magne and WalkerS studied the adsorption of several phenols from aqueous solutions and found that the adsorption was partly physical and pal11y chemical in characte r. Aytekin 6 , Chaplin7 and Kiselev and Krasilinkov 8 observed that the adsorption isotherms of phenol from aqueous solution were step wise suggestin g the possibility of re arrangement of