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

Hg(II), Pb(II), Ag(I) and Cu(II) cations have been adsorbed onto a new thick-walled form of mesoporous silica having a minor amount of microporosity and then voltammetrically reduced after the fabrication of a carbon paste–mesoporous silica composite electrode which has been placed in an aqueous acidic electrolyte medium. The following well-defined voltammetric responses are observed for the systems studied:Hg(II)⇌e− Hg(I)⇌e− Hg(0)Pb(II)⇌2e− Pb(0)Ag(I)⇌e− Ag(0)Cu(II)⇌e− Cu(I)⇌e− Cu(0)Notable features relative to voltammograms obtained when the metal ions are reduced directly in the solution phase are the stabilization of the mercury(I) oxidation state, the linear dependence of peak heights on acid concentration in the molar concentration region and the absence of metal stripping characteristics when metal is reoxidised. The dependence of the voltammetric responses on the amount of material adsorbed on the mesoporous silica and the dependence on acid concentration have been examined in detail and have led to a mechanism being proposed. The voltammetric reduction of metal ions adsorbed onto this new form of mesoporous silica is superior to that observed when chromatography grade silica is used.