An insight into the KOH activation mechanism through the production of microporous activated carbon for the removal of Pb2+ cations

Chemical activation was used through direct mixing of KOH with maize stalks in the smallest amount of water to provide KOH-to-stalk ratios of 33, 50, 66 and 75% by weight. The KOH-treated stalks were carbonized at 700 degrees C to produce a series of four activated carbons, besides a non-activated sample that was prepared and carbonized at 550 degrees C. The porous properties of these carbons were characterized by the Langmuir, BET and Dubinin-Radushkevich linear equations as well as both alpha(s) (alpha-s) and t methods based on nitrogen adsorption isotherms. The chemical reactions involved during the impregnation and the carbonization processes for these hydroxide/lignocellulose mixtures have been proposed. Deep insight has been obtained concerning the possible reactions mechanism. The results showed that the KOH ratio was found to be the basic indicator of micoporosity development. The increase in the concentration of KOH much increased the S-alpha values of the resulting carbons reaching a maximum limit at 66 wt% KOH with S-alpha of 1684 m(2)/g and micropore ratio of similar to 85% displaying an inverse correlation thereafter. The thermal behaviour and the surface microstructure in addition to the surface functional groups of the maize stalks and their prepared carbons were investigated by TGA, SEM and FTIR. The investigated carbons took up significant amounts of Pb2+ ions from aqueous solutions, which are ascribed to both the porosity and surface chemical nature of the adsorbents. (C) 2008 Elsevier B.V. All rights reserved.