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

## TL;DR

This paper describes a new method to transform copper oxide nanooctahedra into copper sulfide quantum-dot superstructures using a thiol compound, and explores their optical and electrochemical properties.

## Contribution

A novel approach to synthesize Cu2S quantum-dot superstructures using β-mercaptoethanol as both sulfur source and stabilizer.

## Key findings

- Cu2O nanooctahedra are transformed into Cu2S superstructures composed of 4–5 nm quantum dots.
- The superstructures exhibit p-type semiconductor behavior and generate negative photocurrent under UV light.
- Au nanograins enhance the photocurrent and demonstrate the potential for photofunctional nanomaterials.

## Abstract

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.