Optimization of p-Type Cu₂O Nanocube Photocatalysts Based on Electronic Effects

Abstract

The size effect in semiconductor photocatalysis has been widely investigated but still remains elusive. Herein, employing p-type Cu 2 O nanocubes as the heterogeneous photocatalysts, we propose a feasible size optimization strategy to enhance the photocatalytic performance of semiconductors. With the size of Cu 2 O increasing from 2.5 nm (exciton Bohr radius) to 5 nm (twice the exciton Bohr radius), the corresponding calculated band gap of Cu 2 O decreases from 3.39 to 2.41 eV, indicating that controlling the size to above twice the exciton Bohr radius is vital for retaining the visible-light response of Cu 2 O. Based on the theoretical calculations and experimental measurements of the charge carrier dynamics, we found that the synthesized 30 nm Cu 2 O nanocubes have an electron diffusion length of 191 nm, while 229 nm Cu 2 O nanocubes show an electron diffusion length of 45 nm. An electron diffusion length larger than the semiconductor particle size lowers the electron−hole recombination, resulting in a visible-light CO generation rate 23.4 times higher for the smaller Cu 2 O nanocubes than that for the larger ones. These results verify that confining Cu 2 O size to within the minority carrier diffusion length and above twice the exciton Bohr radius is a promising way to enhance Cu 2 O photocatalytic activity.

Thickness dependence of the room-temperature ethanol sensor properties of Cu2O polycrystalline films

“…The observed effect can be attributed to the reduced radii of the Cu 2 O nanocrystals, which decrease from 12 to 4.5 nm with increasing Z. These dimensions are close to the Bohr exciton radius of 2.5 nm [31], suggesting a likely confinement effect. This phenomenon aligns with prior literature, which has documented confinement effects in Cu 2 O nanoparticles ranging from 5 to 12.5 nm [32].…”

“…Figure 4(b) shows the obtained bandgap energy as a function of the mean crystallite size (〈D〉), determined from the XRD data analysis. Additionally, figure 4(c) also includes data points from Lin et al [34], for comparison purposes. From the curve fitting (solid red line) the bandgap energy of the bulk 2.16 ± 0.02eV and the reduced effective mass (μ) of ∼0.194m 0 were found, being this value in fairly good agreement with the effective mass of the electron (0.83m 0 ) and hole (0.20m 0 ), previously reported in the literature, giving a reduced mass of μ = 0.161m 0 .…”