Abstract

Treatment of CuS films with AgNO₃ solutions gave CuS/Ag₂S films with concentration ratios Cu/Ag of 0.08–0.15. These materials were characterized by scanning electron microscopy and X-ray powder diffraction, and their Cu²⁺-detecting capabilities were studied by a potentiometric method. A uniform secondary-electron image was observed for a CuS/Ag₂S film prepared from a CuS film having a high crystallinity. An electrode constructed with the resulting mixed-sulfide film was capable of detecting Cu²⁺ ions down to a concentration as low as 10⁻⁷ mol dm⁻³. A CuS/Ag₂S film obtained from amorphous CuS had a heterogeneous surface and as an electrode was inactive towards Cu²⁺. The rate of reaction between CuS and Ag⁺ is dependent on the crystallinity of CuS, with CuS films of a high crystallinity being resistant to the attack of Ag⁺ so that the reaction is slow enough to provide a uniform and well-adhering CuS/Ag₂S film.