Retention of heavy metal ions on SBA-15 mesoporous silica functionalised with carboxylic groups
Three samples of SBA-15 functionalised with -(CH 2 ) 3 COOH groups have been prepared by co-condensation, starting from solutions of TEOS and 4-(triethoxysilyl)butyronitrile, acting as -(CH 2 ) 3 COOH precursor, of different molar compositions. Materials were characterised by X-ray diffraction, nitrogen adsorption, and FT-IR spectroscopy. The pK a 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 pK a (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 + , Cd 2+ , Fe 3+ , Cu 2+ , Zn 2+ ) 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.