Mechanism studies on lead ion-selective chalcogenide glass sensors

Abstract

The lead ion-sensing mechanism of PbSAs 2S 3, AgAsS 2 and PbSAg 2SAs 2S 3 chalcogenide glass sensors has been studied. The following principal methods have been chosen: (i) a study of the sensitivity of Ag-free PbSAs 2S 3 glasses to lead ions in solution; (ii) an investigation of induced exchange-site formation using XPS, AES and SIMS; (iii) 212Pb tracer measurements to obtain information about lead ion exchange. It has been shown that Ag-free PbSAs 2S 3 glasses are sensitive to Pb 2+ ions in solution; their standard potentials are close to those of Ag-containing vitreous alloys. The formation of induced exchange sites governing the lead-ion sensitivity of Pb-free AgAsS 2 glass sensors has been confirmed by surface spectroscopies. Evidence for direct Pb 2+ ion exchange at the membrane/solution interface for both PbSAg 2SAs 2S 3 and AgAsS 2 glasses has been obtained by tracers. All these experiments indicate that the ion response of lead ion-selective chalcogenide glass sensors can be completely described within the framework of the modified surface-layer model.