The anion effect was investigated for the copper adsorption on NH2-MCM-41 from Cu(NO3)(2) and CuSO4 solutions. The copper adsorption was higher and faster in the presence Of SO42- anion compared to NO3-. 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 NH2-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 Cu2+ adsorption. The remaining sites were only accessible in the presence of SO42-. Evidence showed that the SO42- anion affects the adsorption by interacting with the dissolved copper to form [CuSO4](0) species, coadsorbing with Cu2+ to form stable complexes, and may even indirectly react with the weakly acidic silanol groups to liberate aminopropyls for more Cu2+ adsorption.