Preparation of biochar from walnut shells and iodine capture
Using agricultural waste to prepare biochar for iodine capture possess the ecological function of treating waste with waste.The biochar prepared from waste walnut shell has rich pore structure and good thermal stability in this study,and the pore size distribution was dominated by micropores,supplemented by mesopores and macropores.Static adsorption experiments showed that the amount of gaseous iodine captured by biochar could reached 2027mg/g.In aqueous solution,iodine capture experiments showed that 0.1g/L biochar could remove more than 97％of iodine from 20mg/L and 100mg/L elemental iodine within 90minutes at pH=5.0.4g/L biochar could remove more than 99％of iodine from 20mg/L in cyclohexane within 90minutes.The above properties were better than those of commercial nuclear grade activated carbon under the same conditions.The mechanism study showed that the iodine capture by walnut shell biochar was physical adsorption,and the adsorbed iodine formed polyiodide ions through charge transfer.Pore structure was proved to be an important factor for the high iodine capture performance of walnut shell biochar.Micropores played a leading role in iodine capture.Hierarchical pores contributed to the migration and transfer of iodine inside and outside the biochar structure.The calculation results of density functional theory supported the experimental conclusion that iodine molecules are more easily adsorbed in the pore size matching their own kinetic size for monolayer adsorption.
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