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Retention of heavy metal ions on SBA-15 mesoporous silica functionalised with carboxylic groups

Bruzzoniti, Maria Concetta, Prelle, Ambra, Sarzanini, Corrado, Onida, Barbara, Fiorilli, Sonia, Garrone, Edoardo
Journal of separation science 2007 v.30 no.15 pp. 2414-2420
X-ray diffraction, adsorption, cadmium, cation exchange, chromatography, copper, heavy metals, iron, metal ions, nitrogen, pH, silica, silver, spectroscopy, titration, zinc
Three samples of SBA-15 functionalised with -(CH₂)₃COOH groups have been prepared by co-condensation, starting from solutions of TEOS and 4-(triethoxysilyl)butyronitrile, acting as -(CH₂)₃COOH precursor, of different molar compositions. Materials were characterised by X-ray diffraction, nitrogen adsorption, and FT-IR spectroscopy. The pKa and the acidic capacity were measured for all samples by potentiometric titration. The acidic capacity increases with increasing amount of -COOH precursor in the synthesis mixture only up to 10% molar of total alkoxysilane. The value for the pKa (4.75) is independent of the acidic capacity of the material. The sample prepared starting from an amount of -COOH precursor equal to 10% molar of total alkoxysilane was chosen to test selective interactions with heavy metals of environmental importance (Ag⁺, Cd²⁺, Fe³⁺, Cu²⁺, Zn²⁺) at different pH values and ionic strengths. The significant and selective adsorption exhibited by the material has been exploited in a preliminary cation-exchange chromatographic application showing the possibility of eluting the metal ions at different retention times.