Preparation of hemp-derived activated carbon monoliths. adsorption of water vapor

Activated carbon monoliths have been obtained by the chemical activation of hemp canes with phosphoric acid. The effects of the carbonization temperature and the impregnation ratio on the porous structure and surface chemistry were studied. The porous structure of the activated carbon monoliths was characterized by N-2 adsorption-desorption and CO2 adsorption isotherms. The surface chemistry of the carbons was analyzed by temperature-programmed desorption (TPD) and X-ray photoelectron spectroscopy (XPS), and the surface morphology was analyzed by scanning electron microscopy (SEM). Water vapor adsorption kinetics and capacities of the activated carbon monoliths were studied. The surface properties of the activated carbons were found to be strongly dependent on the carbonization temperature and the impregnation ratio. An activated carbon monolith with an apparent surface area of about 1500 m(2)/g and a significant contribution of mesopores (mesopore volume of 0.6 cm(3)/g) was obtained at 400 degrees C with an impregnation ratio of 2. The water vapor adsorption capacities were found to be comparable to that of silica gel, a material widely used as desiccant, because of the presence of residual phosphates and/or polyphosphates on the surface of the carbons.