Room temperature synthesis of aqueous soluble covellite CuS nanocrystals with high photothermal conversion

Near-infrared plasmonic binary copper-based chalcogenides have found promising applications in photovoltaics and photothermal therapy. Here, we report a facile synthetic protocol for aqueous soluble covellite (CuS) nanocrystals (NCs) at room temperature. In contrast to previously reported routes, the present method involves the reaction of Cu precursors (e.g. CuCl2, Cu(NO3)2, Cu(Ac)2) with sulphur precursors (e.g. Na2S and (NH4)2S) under ambient conditions in the presence of various ligands, requiring neither high temperature and high pressure nor an inert atmosphere. The as-synthesized CuS NCs, without any further ligand exchange, can be readily dispersed in water and exhibit well-defined near-infrared (NIR) plasmon absorbance. The scalability and reproducibility of the present procedure allow for the gram-scale production of CuS NCs in a one-pot reaction, which is elaborated by upscaling the amounts of precursors and solvents/ligands. In particular, when excited with an 806 nm laser (1.2 W cm−2), the aqueous soluble covellite NCs produce significant photothermal heating with a photothermal transduction efficiency of 20.3%, comparable to previously reported binary copper chalcogenides. Combined with good photothermal transduction properties, photostability and synthesis scalability, the present work provides a general and cost-effective synthetic protocol for not only Cu2−xS but also other copper chalcogenides for promising photothermal applications.