Four agriculture residues, including raw wheat husk, bio-treated wheat husk, rice husk, and pistachio shell, were used as starting materials to produce activated carbons with diverse physical and chemical properties. The adsorption behavior of volatile organic compounds (VOCs) for resulting adsorbents was tested with toluene as an adsorbate. Results showed that with adequate steam activation time, activated carbons with a surface area between 360 and 950 m2/g were developed. Further increases in the activation time destroyed the pore structure of activated carbons, which resulted in a decrease in the surface area and pore volume. Elemental analyses and X-ray photoelectron spectroscopy examination suggested that the oxygen content of activated carbons increased with increasing activation time. Furthermore, the amounts of oxygen-containing functional groups, including hydroxyl, carbonyl, and carboxyl groups also increased. These results indicate that H2O molecules react with the carbon surface to form those oxygen-containing acidic functional groups. Results from adsorption of toluene (inlet concentrations between 50 and 600 ppmv) at 40 to 80℃ showed that the adsorption capacities increased as the inlet toluene concentration increases, and decreased with increasing adsorption temperatures. Furthermore, these results were successfully fitted with Freundlich and Dubinin-Radushkevich (DR) isotherms (R2 > 0.96). The obtained Freundlich and DR constants can then be used to predict equilibrium adsorption capacities at various adsorption conditions and to calculate other important thermodynamic constants, such as heat of adsorption.

Activated carbon, Wheat husk, Adsorption