Enhancing Removal of Cu(II) from Aqueous Solution by Walnut Shell-Based Activated Carbon with Pyrolusite Modification

Pyrolusite modified carbon was prepared from walnut shell for enhancing removal of Cu(II) from aqueous solution. 1% pyrolusite addition was proved to be efficient and economic on adsorption capacity improvement of the produced carbon. Cu(II) removal rate on the modified walnut shell-based carbon was ca. 20% higher than the unmodified one, while the adsorption capacity for the modified carbon was high up to 34.4 mg/g. Within weakly acidic pH range (pH = 5 similar to 6), it was suitable for Cu(II) adsorption with larger than 97% removal rate on the produced carbon. SEM and BET analysis showed that pyrolusite played an important role on pore formation of the produced carbon. The specific surface area, mesopore and micropore volume of the modified carbon were 27.2%, 39.5%, 17.5%, respectively, higher than those of the unmodified one. After modification, oxygen-containing functional groups, especially phenol and carbonyl groups, were remarkably increased on the produced carbon, which were helpful for Cu(II)'s adsorption. FTIR showed that a large amount of organic carbon was decomposed into inorganic carbon skeleton during the carbonisation process, thus forming a large number of pores, and was conducive to adsorbing copper ions. This work is expected to be helpful for an effective agricultural residue management and innovative modification of walnut shell-based adsorbent as low-cost precursors for heavy metal treatment.