Ion-selective sensors based on molybdenum bronzes

Abstract.

New pH- and sodium ion-sensitive metal-oxide-type sensors have been developed and tested with a direct solid state contact method. Performance was demonstrated at ambient temperature with single crystals of several molybdenum bronzes (i.e. Na_0.9Mo₆O₁₇, Li_0.9Mo₆O₁₇, Li_0.33MoO₃ and K_0.3MoO₃). The pH sensors with Na-molybdenum-oxide bronzes show near ideal Nernstian behavior in the pH range 3–9. The response is not affected by the direction of the pH change. The response time of most molybdenum bronze pH sensors is less than 5 s for 90% response. The sodium molybdenum bronze sensor responded reproducibly and fast to changes of Na⁺ concentration in the range 1–10^–4 mol dm^–3. Cross sensitivity tests to other ions such as H⁺ or K⁺ have shown that the new sodium ion sensor may be used when the concentration of other ions is an order of magnitude smaller than the Na⁺ concentration. pH sensors with single crystals of molybdenum oxide bronzes can be used to follow pH titrations.