Abstract:

Activated carbons were prepared from walnut shell by H₃PO₄ activation and the effects of adding different kinds and contents of additives to H₃PO₄ solution on the properties of activated carbons were investigated. The adsorption property was characterized by methylene blue and iodine adsorption values. The pore structure parameters, mechanical strength and graphite microcrystalline of activated carbon were tested. When the activated carbons were prepared by walnut shell immersed in H₃PO₄ solution with the addition of citric acid, sodium citrate, boric acid and saccharin, respectively, the methylene blue adsorption values increased, and the iodine adsorption values and the mechanical strength decreased. This meant the additives promoted the expansion of micropores of activated carbons to mesopores. Adding 0.5% sodium citrate in H₃PO₄ solution, the activated carbon with the maximum methylene blue and iodine adsorption values was gained, which were 236.5 and 744.1 mg/g, respectively. In addition, the structure of activated carbon obtained by adding 1% boric acid into H₃PO₄ solution contained microcrystalline carbon, which was hard and played a role in enhancing pore structure and the mechanical strength was 85.8%. However, the microcrystalline carbon in the activated carbon obtained by adding 1% saccharin almost transformed graphitization transformation, resulting in soft graphite, thus the strength decreased to 80.1%. The activated carbon with 0.5% sodium citrate had low strength(82.5%) because of its rich pore structure without microcrystalline reinforcement.

Key words: walnut shell, activated carbon, additive, microcrystalline carbon