Surface and adsorptive properties of carbons prepared from biomass

A number of activated carbons were prepared from a locally available by-product, corncobs, under currently established activation schemes. Obtained carbons were characterized by N2 adsorption at 77 K and the isotherms were analyzed by BET and αs methods. Steam-activation at 900 °C produced a microporous carbon having the highest Sα of 788 m2 g−1, whereas activation with air at 350 °C produced a carbon of Sα = 321 m2/g and possess wider pores. KOH impregnation with char in ratio 1:1 (w/w) and impregnated in the same ratio with the raw material prior to pyrolysis at 700 °C for 1 h, gave CK700, K700 respectively. An additional sample was obtained by oxidizing part of K700 with conc. HNO3. All three KOH carbons show pore structures much close to char itself which may be due to potassium salt left in pores and is not easily leached with repeated water washings. In addition, KOH is more effective on the precursor itself than on its char of already developed porosity. FT-IR spectra show an increase in oxygen functionalties on the carbon surface as a result of activation process and the bands become stronger in the spectra of the acid-treated sample. The oxidized carbon sample showed relatively higher uptake of Pb2+ and MB and its surface chemistry plays the key role in their adsorption, while sharp decrease was observed in the uptake of phenol and mono-nitrophenols from aqueous solutions. An SEM study showed that air activation produce obvious voids reflecting its erosive effect on the external carbon surface.