Adsorption of p-Nitrophenol on Activated Carbon Prepared from Phosphoric Acid-treated Apricot Stone Shells

The effect of temperature on the adsorption of p-nitrophenol (PNP) from aqueous solution has been determined at various initial phenol concentrations. Eight activated carbons were tested, being laboratory-prepared from apricot stone shells impregnated with H 3 PO 4 and carbonized at 300–500°C. The adsorption capacity increased as a function of the percentage of activating acid added as well as the temperature of carbonization. The PNP surface areas evaluated were generally lower than the nitrogen BET surface areas due to restricted adsorption inside certain pores. Enthalpies of adsorption of 20–24 kJ/mol were estimated in all cases, except for one carbon which exhibited 'activated', diffusion-controlled adsorption. Greater than 90% desorption was observed at 100 ppm levels of PNP, but this decreased considerably at higher phenol levels.