CuS nanoparticles in humid environments: adsorbed water enhances the transformation of CuS to CuSO4

摘要

Covellite copper sulfide nanoparticles (CuS NPs) have attracted immense research interest due to their widespread use in a range of biological and energy applications. As such, it is crucial to understand the transformations of these nanomaterials and how these transformations influence the behavior of these nanoparticles in environmental and biological systems. This study specifically focuses on understanding the role of water vapor and adsorbed water in the transformation of CuS NP surfaces to CuSO(4)in humid environments. Surface sulfide ions are oxidized to sulfate by oxygen in the presence of water vapor, as detected by atomic force microscopy based photothermal infrared spectroscopy (AFM-PTIR) andin situattenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy. These results show that the transformation of CuS to CuSO(4)is highly dependent on relative humidity (RH). While sulfide to sulfate conversion is not observed to a great extent at low RH (80%). X-ray photoelectron spectroscopy (XPS) analysis confirms that sulfide is irreversibly oxidized to sulfate. Furthermore, it shows that initially, the Cu ions possess the original oxidation state similar to the original covellite,i.e.Cu+, but they are oxidized to Cu(2+)at higher RH. The formation of CuSO(4)has also been confirmed by HRTEM. These analyses show that adsorbed water on the NP surfaces enhances the conversion of sulfide to sulfate and the oxidation of Cu(+)to Cu(2+)in the presence of molecular oxygen.