Synthesis, characterization and examination of photocatalytic performance of hexagonal covellite CuS nanoplates

Copper sulphide (CuS) powder was prepared in a large-scale by precipitation of Cu2+ cations in aqueous solution by gaseous hydrogen sulphide (H2S). XRD and Raman analyses confirmed that precipitated CuS particles possess single crystal phase structure corresponding to mineral covellite with the metallic-like conductivity 3.6 × 103 S cm−1. The powder consisted of non-porous hexagonal nanoplates with specific surface area 19.4 m2 g−1, which can be mainly accounted to {110} crystal plane. In order to shed light into ambiguous reports, covellite photocatalytic effectivity was re-examined. It was revealed, that CuS nanoplates exhibit relatively high adsorption capacity of cationic dye tested, while rate of photocatalytic decomposition of model dye under UV light is negligible if any at all. On the other hand, addition of small amount of H2O2 greatly enhanced the rate of degradation reaction. Furthermore, the reaction proceeds at the same rate even in the dark condition, thus the light is not prerequisite for the dye degradation. From this point of view, the covellite CuS cannot be considered as photocatalyst, but rather as an oxidation catalyst. Moreover, covellite powder exposed to dilute peroxide solution was fully oxidized to Posnjakite Cu4(SO4)(OH)6(H2O) at room temperature in 24 h.