Reversible Crystal Phase Interconversion between Covellite CuS and High Chalcocite Cu₂S Nanocrystals

Abstract

Copper deficient copper sulfides (Cu2–x S, 0 ≤ x ≤ 1) are earth abundant, nontoxic materials with size-, phase-, and composition-dependent localized surface plasmon resonance (LSPR). Although synthesis of Cu2–x S nanocrystals (NCs) has attracted substantial research attention, understanding of the transformations of copper sulfides between their many possible stoichiometries and crystal phases is still lacking. Here, we develop a reversible transformation between CuS, which has a high density of free charge carriers and strong LSPR, and high chalcocite Cu2S with no LSPR. Initial CuS nanoplatelets (NPls) with a diameter of 55 nm and thickness of 4 nm were transformed into round high chalcocite Cu2S NPls with a diameter of 29.2 ± 2.0 nm and a thickness of 10.8 ± 0.7 nm by treatment with 1-dodecanethiol (DDT), which can reduce disulfide bonds in covellite. Treatment with an oleic acid–sulfur complex (OA-S), which serves as a sulfur source, can restore the hexagonal shape of the original CuS NPls during the reverse transformation from Cu2S to CuS, producing hexagonal NPls with a diameter of 43.1 ± 2.0 nm and thickness of 11.2 ± 0.9 nm. We also treated monodisperse, spherical roxbyite (Cu1.78S) NCs with OA-S and obtained hexagonal CuS NPls, showing that the tendency of CuS to form hexagonal NPls is an intrinsic result of its crystal structure. For comparison, we used different sulfur precursors to drive the transformation from Cu2S to CuS, illustrating the different reactivities of S-sources with Cu2S. This interconversion not only provides a better understanding of possible transformations in copper sulfide nanostructures but also provides new possibilities for the well-controlled colloidal synthesis of these nanomaterials with combinations of phase, size, shape, and LSPR energy not previously obtainable.

Electrochemical Fingerprint of CuS-Hexagonal Chemistry from (Bis(N-1,4-Phenyl-N-(4-Morpholinedithiocarbamato) Copper(II) Complexes) as Photon Absorber in Quantum-Dot/Dye-Sensitised Solar Cells

“…Additional XRD peaks emanated from the unreacted ions, but impurities were not observed. There were basically high-intensity diffraction peaks for CuS/HDA at 22 [31]. The presence of these lower intensities and minor phases are usually linked to defect chemistry, and the thermodynamics of the solid and thermal gradient.…”

“…Copper monosulfide (CuS) has distinguished itself among metal sulfides owing to its different band gap and various morphologies. This makes CuS a hot-spot semiconductor material with great potential in the field of photocatalytic and photovoltaic applications [18][19][20][21][22][23][24][25][26]. Hexagonal covellite-CuS with a bandgap of ∼2 eV and a p-type-enhances absorber abilities to cover the entire solar spectrum [18,19].…”

Ultrasmall aqueous starch-capped CuS quantum dots with tunable localized surface plasmon resonance and composition for the selective and sensitive detection of mercury(ii) ions

“…These CuS NSs have been exploited for potential applications such as bioimaging, 26 photocatalysis, 27 nanoelectronics, 28 and theranostics. 29 Currently, there are various methodologies to fabricate CuS NSs, such as sonoelectrochemical, 30 hydrothermal, 30 solventless thermolysis, 30 mechanochemical, 31 microwave, 32 hot-injection, 14 and cationexchange reaction 33 methods. However, in most of these reports CuS NSs were prepared using expensive solvents, strong surfactants, and at high temperature and pressure.…”

One‐Step Transformation from Cu2S Nanocrystal to CuS Nanocrystal with Photocatalytic Properties

“…Liu et al. developed a reversible transformation between CuS and Cu 2 S through 1‐dodecanethiol (DDT) and oleic acid (OA) reaction system, but it is meaningful to design a simple synthesis method to realize the transformation from the Cu 2 S to CuS.…”