Ion exchange and ion exchange voltammetry with functionalized mesoporous silica materials

Ordered mesoporous silicas prepared by the surfactant template route can be readily used as effective ion exchangers when they are functionalized with organic groups bearing either positive or negative charges. This is illustrated here on the basis of sulfonic acid- and/or quaternary ammonium-functionalized silica spheres obtained by the sol–gel process in the presence of cetyltrimethylammonium as a template. Various materials have been synthesized at several functionalization levels and their physico-chemical characteristics (especially their porosity) have been discussed with respect to the amount of functional groups in the porous solids. Their ion exchange behavior was then studied from batch experiments (determination of cation and anion exchange capacities) and by electrochemistry at carbon paste electrodes (CPE) modified with these solids (ion exchange voltammetry). The preconcentration efficiency was discussed on the basis of the organic group content in the materials as well as their structure and porosity. The series of materials containing both sulfonic acid and quaternary ammonium moieties displayed zwitterionic surfaces and thus both cation and anion exchange properties.