Abstract

Electrochemical deposition of p-type Cu₂O films on transparent conducting glass from a Cu₂SO₄ solution was conducted at different temperatures. The films were examined for H₂ evolution from photoelectrolysis of water under visible light illumination. Using Pt as the counter electrode, photocurrents with corresponding H₂ evolution could be observed for the deposited Cu₂O films in a Na₂SO₄ solution under a cathodic bias. The Cu₂O films obtained at different deposition temperatures were in the cubic phase, but showed different out-of-plane crystalline orientations. An incident monochromatic photon-to-current conversion efficiency of 26% at 400 nm was achieved for a Cu₂O film with a [1 1 1] out-of-plane orientation, while an efficiency of only 17% was obtained for a film with a [1 1 0] orientation. The [1 1 1]-oriented film exhibited a higher electronic conductivity, which might have led to a higher charge delocalization rate. By coupling with an n-type WO₃ film to promote charge transport, the photocurrent for the Cu₂O films was significantly improved.

Abstract

A novel fabrication of Cu₂O nanoparticles was successfully achieved through the reduction of Cu²⁺ in the interlayer of montmorillonite (denoted as MT). The Cu₂O nanoparticles formed in the clay interlayer (denoted as Cu₂O/MT) had a lamellate shape of 20–100 nm in width and ca. 0.39 nm in thickness, and thus, the Cu₂O/MT exhibited a higher specific surface area than neat Cu₂O. The Cu₂O/MT was applied to a photocatalyst, and its photocatalytic activity was examined in terms of water reduction (i.e., H₂ evolution) in the presence of methanol (electron donor). The Cu₂O/MT showed a high photocatalytic activity in comparison with neat Cu₂O; moreover, the photocatalytic activity was improved by loading a Pt catalyst onto the surface of Cu₂O. Based on the dependencies of photocatalytic activity on light intensity as well as methanol concentration, it was revealed that the H₂ evolution from water on Cu₂O/MT is the rate-determining step. Thus, the active and efficient photocatalysis of Cu₂O/MT was associated with an increase in specific surface area corresponding to the number of active sites.

Graphical abstract

Abstract

Single-crystalline micrometer-sized Cu₂O cubes with concave planes were synthesized via γ-irradiation reducing reaction under ambient conditions without any surfactant. Selected area electron diffraction (SAED) investigation reveals that these cubes are single crystals. The powder X-ray diffraction (XRD) and scanning electron microscopy (SEM) are used to investigate the nucleation and crystal growth process of Cu₂O cubes. The UV–vis absorption spectrum is used to estimate the band gap energies of the Cu₂O cubes. The band gap of the products calculated from the UV–vis spectrum corresponds to 2.53 eV, which is larger than the direct band gap (2.17 eV) of the bulk Cu₂O. Another value of 1.97 eV hints excitonic discrete energy level in forbidden band, arising from the crystal defects of as-prepared Cu₂O single crystal.

Graphical abstract

Single-crystalline micrometer-sized Cu₂O cubes with concave planes were synthesized through nucleation and anisotropic crystal growth processes via gamma-irradiation under ambient conditions without using any surfactant. Unlike most of other methods, our experiments are carried out under mild conditions, hydrated electrons generated through γ-radiolysis of water act as reducing agent. The band gap of the as-prepared products calculated from the UV–vis spectrum corresponds to 2.53 eV, another value of 1.97 eV hints excitonic discrete energy level in forbidden band of as-prepared Cu₂O material.