Chemisorption of lanthanide ions on succinate-functionalized mesoporous silica: An in situ characterization by fluorescence

Chemisorption of Eu³⁺ and Tb³⁺ on SBA-15 functionalized with succinic groups has been studied by in situ steady-state fluorescence measurements. The enhancement of the emission sensitive bands indicates that both ions adsorb forming inner-sphere surface complexes. Adsorption is a fast process that attains equilibrium in about 5min. The variation of the peaks maxima (I₅₉₂ and I₆₁₆, for europium, and I₄₉₀ and I₅₄₅, for terbium) with the total ion concentration is accounted for by the sum of the contributions due to the adsorbed and free ions. The former contribution is langmuirian. At pH 4.5, the respective adsorption constants are 5×10⁵ and 3×10⁵M^-1, and the maximum adsorption capacities are 5.10×10^-4 and 5.23×10^-4molg^-1. The mismatch between the latter values and the number of attached carboxylic groups is discussed. Comparison with other functionalized mesoporous silicas indicates that the anchored succinic groups are very efficient for removing lanthanide ions from aqueous solutions.