Synthesis and characterisation of acid/basic modified adsorbents. Application for chlorophenols removal.

A commercial activated carbon was modified with acid and basic reagents -an acidic one via treatment with sulphuric acid and a basic via treatment with pentaethylenehexamine- to yield adsorbents with different surface acid/base character. These modified adsorbents were characterised by elemental and immediate analysis, N2 adsorption, XPS and point zero charge measurements. The new adsorbents were tested for chlorophenols removal in water (4-chlorophenol, 3,5-dichlorophenol, 2,4,6-trichlorophenol, 2,3,4,6-tetrachlorophenol and pentachlorophenol) at different temperatures. Although the calculated process enthalpy was positive for all cases, indicating an endothermic process, the entropy was positive, resulting in a negative Gibbs free energy and spontaneous process. The adsorption capacity increases with temperature and decreases when the phenols' number of substituents increases. The modified acid-activated carbon demonstrated an exciting higher adsorbing capacity from 426.9 to 742.3 mg g-1 for 2,4,6-trichlorophenol, whereas the adsorption capacity for the basic ranged between 142.9 and 238.0 mg g-1. The Langmuir model satisfactorily fitted the adsorption equilibrium data for all chlorophenol contaminants.