Diffusion mediated selective adsorption of Zn2+ from artificial seawater by MCM-41

• Calcined MCM-41 (Pristine-MCM-41) was used for the adsorption of metal ions.
• The materials were found to be 100% selective for Zn2+ from artificial seawater.
• Detailed adsorption mechanism was studied for the selective adsorption of Zn2+.

MCM-41 can play a pivotal role as a host material for adsorption applications. In this work, MCM-41 was found to be 100% selective for Zn2+ from artificial seawater containing Ni2+, Li+, Co2+, Cd2+ and Zn2+ as hetero ions. The pristine and Zn2+ ions adsorbed MCM-41 (Zn@MCM-41) were well characterized by various spectroscopic techniques. The selective Zn2+ ion adsorption property of MCM-41 remained intact irrespective of the concentration of Zn2+ ions. The adsorption property of MCM-41 was unaffected by the synthesis strategy of MCM-41. SBA-15 exhibited 85 and 15% mole selectivity for Zn2+ and Cd2+ ions, respectively, under similar experimental conditions. This highlights the unique property of MCM-41 for the selective adsorption of Zn2+ ions from artificial seawater. TEM, FTIR and XPS analysis confirmed the presence of Zn2+ ions in Zn@MCM-41. The protection using methyl group on the outer/both surfaces of MCM-41 (Me-MCM-41/MeS-MCM-41) disclosed the necessity of interaction between silica surface and metal ion for selective adsorption of Zn2+ ions. The detailed investigation of adsorption mechanism postulates that the selective adsorption of Zn2+ ions by MCM-41 was achieved only in the presence of sodium chloride, which is the major component of artificial seawater. An adsorbed amount of 12 mg g−1 was observed for Zn2+ ions even in presence of Cd2+ ions, while both of the ions possess similar chemical characteristics.

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