Apart from syngas, woody biomass gasification process also generates significant amount of carbon residues (char) and ashes as by-products, which usually contain high concentration of harmful compounds, hence causing health and environmental problems during disposal. In view of this, it is essential to develop beneficial uses of these solid residual wastes. In this work, carbon residue obtained from wood gasification was employed as a precursor for preparing adsorbent via physical activation. The effect of activating agents and temperature was examined in order to obtain the optimal conditions for the activation stage. The obtained activated carbon was characterized and tested as an adsorbent for dye (Rhodamine B) removal, and the influence of adsorption time, initial concentration and pH were also studied. Kinetics and isotherm analysis were also performed.
From BET analysis, the surface area of unprocessed char was less than 200 m2 per gram and it was greatly increased to 776.46 m2 per gram after steam activation at 900°C. Moreover, the FTIR spectra also showed the abundance of hydroxyl (-OH) and carboxyl (-COOH) groups on the surface of activated carbon obtained from steam activation. The activated carbon produced at the optimal conditions was used for dye adsorption and it exhibited high dye adsorption capability. This can be attributed to the increase in surface area as well as the abundance of hydroxyl and carboxyl groups on the activated carbon surface. Moreover, it was found that the dye adsorption capability was significantly increased at basic condition. This can be attributed to the increased electrostatic interaction between the deprotonated (negatively charged) activated carbon and dye molecules. Furthermore, kinetics showed that the dye adsorption data follow the pseudo-second-order adsorption model, whereas the isotherm analysis indicated that the dye adsorption data can be represented by the Langmuir model. Our results clearly showed that the activated carbon prepared from steam activation of carbon residue from wood gasification can be effectively used as an adsorbent for dye removal.
The use of carbon residues produced from wood gasification as a source of absorbent materials not only provides a cost-effective and environmental friendly way of recycling those residual wastes, reducing its negative environmental effects, but also produces high-value products, offering the economic benefits for woody biomass gasification process.
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