Adsorption characteristics of activated carbons obtained from corncobs

Dried, crushed, corncobs were carbonized at 500 degreesC and steam activate d (in one- or two-step schemes), or activated with H3PO4. The products were characterized by N-2 adsorption at 77 K, using the BET. alpha (s) and DR m ethods. Adsorption capacity was demonstrated by the iodine and phenol numbe rs, and the isotherms of methylene blue and Pb2+ ions, from aqueous solutio ns. A distribution of porosity in the carbons was estimated within the vari ous ranges (ultra-, super-, meso- and macropores). Simple carbonization yie lds a poor adsorbing carbon: only its uptake for iodine was high and propos ed to be due to an addition reaction on residual unsaturation of the parent lignocellulosic structures. Enhanced porosity was best associated with che mical activation and:or steam pyrolysis at :700 degreesC. These activated c arbons proved highly porous and rich in mesopores, and showed high adsorpti on capacity for methylene blue and Pb2+ ions. Phenol uptake was found to de pend on surface chemical nature of the carbon rather than its porous proper ties. Corncobs were postulated to be feasible as feedstock to produce good adsorbing carbons, under the one-step activation schemes outlined here. (C) 2001 Elsevier Science B.V. All rights reserved.