Grafting of precoordinated Cu(2+)-N-(2-aminoethyl)aminopropylsilane complexes onto mesoporous silicas and the adsorption of aqueous selenate on them.

N-(2-Aminoethyl)aminopropylsilane (AeAptes) was coordinated with Cu(2+) with Cu:AeAptes ratios of 1:1 and 1:2. These were then grafted onto MCM-41 [the products being denoted as Cu(en)-MCM-41 and Cu(en)2-MCM-41, respectively] and SBA-15 [the products being denoted as Cu(en)-SBA-15 and Cu(en)2-SBA-15, respectively]. The periodic structures of these mesoporous silica frameworks were well-retained after grafting. UV-visible and EPR spectroscopies were used to analyze the coordination structure of Cu(2+), revealing the structure expected from the ratio of Cu(2+) to silane. We also prepared Cu(en)- and Cu(en)2-M7D by the same procedure using Cab-O-sil M7D silica. In contrast to the complexes grafted onto the mesoporous silicas, no significant differences were found in the d-d transition band positions, the g-tensor, and hyperfine coupling constants between Cu(en)-M7D and Cu(en)2-M7D. The structural parameters of these were almost the same as those of Cu(en)-MCM-41 and Cu(en)-SBA-15, suggesting that the grafting onto M7D resulted in the transformation of coordination structure of Cu(2+)(AeAptes)2. The adsorption of selenate was analyzed using the Langmuir equation. The adsorption capacities for Cu(en)- and Cu(en)2-mesoporous silicas were Se/Cu = 0.5 and 1.0, respectively, while the Langmuir coefficients for Cu(en)2-mesoporous silicas were more than twice those for Cu(en)-mesoporous silicas. However, no significant differences in these two parameters were found between Cu(en)- and Cu(en)2-M7D; Se/Cu = 0.53-0.56 at saturation and the Langmuir coefficients were the same. The decomposition of the coordinated Cu complex after grafting onto M7D is discussed with respect to the structure of the silica surface. The electronic state of Cu in Cu(en)- and Cu(en)2-mesoporous silicas was analyzed by XANES spectroscopy before and after the adsorption of selenate.