Preparation and characterization of activated carbons from coconut shell impregnated with phosphoric acid

Abstract

A series of activated carbons was prepared from coconut shell impregnated with phosphoric acid using a one-step carbonization procedure and varying conditions in order to optimize preparation parameters. The mode and nature of gaseous flow during carbonization were found to affect the surface area and yield, suggesting that oxygen derived from the gas phase may play an important role in activation, and that coking of volatiles could be contributing to the building of the porous structure. The optimum activation temperature for a higher surface area was 450°C. Higher surface area and mesoporosity were favored by increasing the acid concentration of the impregnating solution. Infrared spectra showed bands corresponding to surface oxygen complexes and a band assigned to P-O groups. Temperature-programmed reduction and desorption spectra showed two signals ascribed also to surface oxygen complexes, and other higher-temperature signals corresponding to hydrogen desorption. These were all significantly more intense in the carbons prepared with phosphoric acid as compared with a standard prepared using high-temperature activation.