Voltammetric reduction of mercury(II), silver(I), lead(II) and copper(II) ions adsorbed onto a new form of mesoporous silica

Hg(II), Pb(II), Ag(I) and Cu(II) cations have been adsorbed onto a new thic k-walled form of mesoporous silica having a minor amount of microporosity a nd then voltammetrically reduced after the fabrication of a carbon paste-me soporous silica composite electrode which has been placed in an aqueous aci dic electrolyte medium. The following well-defined voltammetric responses a re observed for the systems studied: [GRAPHICS] Notable features relative to voltammograms obtained when the metal ions are reduced directly in the solution phase are the stabilization of the mercur y(I) oxidation state, the linear dependence of peak heights on acid concent ration in the molar concentration region and the absence of metal stripping characteristics when metal is reoxidised. The dependence of the voltammetr ic responses on the amount of material adsorbed on the mesoporous silica an d the dependence on acid concentration have been examined in detail and hav e led to a mechanism being proposed. The voltammetric reduction of metal io ns adsorbed onto this new form of mesoporous silica is superior to that obs erved when chromatography grade silica is used. (C)1999 Elsevier Science B. V. All rights reserved.