Thermal stability of (ZnS)(Ag<sub>2</sub>S)<sub>x</sub> heteronanostructures of zinc and silver sulfides

Heteronanostructures (ZnS)(Ag2S)x with x from 0.002 to 0.50 were synthesized by hydrochemical coprecipitation. The size of ZnS nanoparticles in the resulting heteronanostructures is 2–4 nm. Annealing of synthesized heteronanostructures (ZnS)(Ag2S)x in air at temperatures from 25 to 530°C or more leads to a change in their phase composition due to the oxidation of cubic zinc sulfide to hexagonal zinc oxide. Oxidation begins at a temperature of ~250°C, and the zinc oxide content in them after annealing at 530°C reaches ~26–30 wt.%. The size of nanoparticles of the resulting ZnO ranges from 12 to 17–25 nm. A study of the oxidation of (ZnS)(Ag2S)x heteronanostructures in air showed that the initial mass loss observed upon heating to ~120°C is due to the removal of adsorbed moisture. The subsequent weight loss that occurs upon heating from ~250 to ~430–450°C is associated with the onset of oxidation of ZnS sulfide and the formation of ZnO oxide. The greatest weight loss is observed upon heating from ~450 to ~580°C and is due to an increase in the ZnO content, partial oxidation of sulfur and its removal in the form of SO2. The oxidation stages are confirmed by the presence of maxima in the temperature dependences of ion currents corresponding to H2O, CO2 and SO2. The studied heteronanostructures are thermally stable when heated to ~200–250°C.