Anion Effect on Cu²⁺ Adsorption on NH₂-MCM-41

The anion effect was investigated for the copper adsorption on NH 2 -MCM-41 from Cu(NO 3 ) 2 and CuSO 4 solutions. The copper adsorption was higher and faster in the presence of SO 4 2− anion compared to NO 3 − . The MCM-41 possesses well-ordered mesopores that are readily accessible and a uniform surface that is amenable to the attachment of the chemical moieties for creating tailored adsorption sites. The adsorption sites on NH 2 -MCM-41 were created by grafting aminopropyls on MCM-41, and the random deposition resulted in a site distribution best described by the Freundlich equation. The majority of the adsorption sites (i.e., up to 70%) are readily accessible to Cu 2+ adsorption. The remaining sites were only accessible in the presence of SO 4 2− . Evidence showed that the SO 4 2− anion affects the adsorption by interacting with the dissolved copper to form [CuSO 4 ] 0 species, coadsorbing with Cu 2+ to form stable complexes, and may even indirectly react with the weakly acidic silanol groups to liberate aminopropyls for more Cu 2+ adsorption.