Photoassisted Chemical Transformation of Cu2O Nanooctahedra into Cu2S Quantum-Dot Superstructures: Structural and Photoelectrochemical Properties.

Copper sulfides represent a broad range of chemical compounds, including naturally occurring minerals and wet-chemically synthesized nanoparticles. Tailoring the size, shape, and chemical composition of Cu2‑x S nanoparticles enables the tuning of their optical and electronic properties allowing the switch between semiconducting and plasmonic characteristics. While the sulfidation of metals and metal oxides can even occur spontaneously under ambient storage conditions, the targeted synthesis of Cu2‑x S nanoparticles mostly relies on the use of inorganic sulfur compounds. Inspired by the natural sulfidation reactions, a novel approach is developed in this paper to transform sacrificial Cu2O nanooctahedra by a short-chain organic thiol (β-mercaptoethanol) into spherical Cu2S superstructures consisting of phase-pure Cu2S quantum dots. The optical and photoelectrochemical properties are thoroughly investigated and supplemented by advanced electron microscopy analysis to identify the phase of the superstructure building blocks. Structural and surface analyses reveal that the superstructures are composed of small (4-5 nm) Cu2S quantum dots spatially separated by a thin amorphous ligand layer. The results highlight the dual role of β-mercaptoethanol serving both as a sulfur source and as a stabilizing ligand upon superstructure formation. To synthesize semiconductor/metal multicomponent nanostructures, the surface of the superstructures is decorated with Au nanograins initiated by the photoreduction of aqueous Au3+ ions. Upon the fabrication of working electrodes from the developed superstructures, the p-type nature of the Cu2S is demonstrated by open-circuit potentiometry. Superstructures supply negative photocurrent under UV irradiation, which can be further enhanced by the presence of Au nanograins. Using the developed synthetic method, phase-pure photofunctional nanomaterials can be prepared by the sulfidation of cuprous oxide in a controlled manner.