Mechanochemistry of copper sulfides: Characterization, surface oxidation and photocatalytic activity

In the present study, the mechanochemically prepared covellite, CuS and chalcocite, Cu2S nanocrystals are compared in detail. Concretely, the SEM, EDS, N2 adsorption, UV-Vis, PL, FTIR, ZP measurement, PCCS, XPS and DTA/TG were used. SEM, EDS and elemental mapping have shown that the agglomerates containing nanoparticles of the corresponding phases were formed as a result of milling. The nitrogen adsorption method has documented richer surface properties in the case of CuS sample. The specific surface area values were 2.7 m2 g−1 and 1.4 m2 g−1 for CuS and Cu2S, respectively. UV-Vis and PL measurements have shown that these materials might be suitable for optoelectronic applications, as the optical bandgaps were 1.92 eV and 3 eV for CuS and Cu2S, respectively. FTIR spectrum of CuS exhibited a peak at 621 cm−1, which is characteristic for this material. ZP values were more negative in the case of CuS and PCCS has confirmed the finer character of this sample (x50 values were 680 nm and 617 nm for Cu2S and CuS, respectively). XPS method documented the surface oxidation of the prepared Cu2S. The thermal stability measurement up to 550 °C has shown that Cu2S does not undergo significant changes (only 1.4% weight loss was observed), whereas CuS is losing sulfur and is transformed into digenite and chalcocite (14.3% weight loss was observed). The mechanochemically synthesized copper sulfides show high activities in photodecolorization of Methyl Orange dye under visible light irradiation, as Cu2S was able to completely decompose the dye in 150 min and CuS caused 80% decomposition after the same time of treatment.