Cu2O as an emerging semiconductor in photocatalytic and photoelectrocatalytic treatment of water contaminated with organic substances: a review

Abstract

A wide range of semiconductor photocatalysts have been used over the years in water treatment to eliminate toxic organic substances from wastewater. The quest for visible or solar light driven photocatalysts with striking merits such as wide range of applications, ease of preparation, tailored architecture that gives rise to improved performance, ability of dual existence as both p type or n type semiconductor, among others, presents copper(i) oxide as a promising photocatalyst. This paper reviews the recent applications of Cu₂O in photocatalytic and photoelectrocatalytic treatment of water laden with organic pollutants such as dyes and pharmaceuticals. It covers the various modes of synthesis, morphologies and composites or heterostructures of Cu₂O as found in the literature. Concluding remarks and future perspectives on the application of Cu₂O are presented.

Fig. 1. Scheme showing the synthesis of Cu₂O and CuO by sol–gel method.

Fig. 2. SEM images of the Cu₂O nanocrystals with various morphologies with vol. of NH₂OH·HCl added (in parenthesis): (a) cubes (0.15 mL), (b) truncated cubes (0.25 mL), (c) cuboctahedra (0.35 mL), (d) type I truncated octahedra (0.45 mL), (e) type II truncated octahedra (0.55 mL), (f) octahedra (0.65 mL), (g) short hexapods (0.95 mL), and (h) extended hexapods (0.76 mL). Scale bar = 1 μm (this figure has been adapted/reproduced from ref. 53 with permission from AMERICAN CHEMICAL SOCIETY, copyright 2009).

Fig. 3. Representation of the (a) Cu₂O unit cell, and (b–d) Cu₂O crystal structure (100), (111) and (110) facet respectively.

Fig. 4. (A) Schematic diagram of photo-induced electron–hole pairs separated process in PEC system based on Cu₂O/α-Fe₂O₃. (B) A mechanism for the changes of Cu₂O/α-Fe₂O₃ after PEC treatment (this figure has been adapted/reproduced from ref. 89 with permission from ELSEVIER, copyright 2018).

Fig. 5. Schematic diagram of the PEC degradation process on n-CdS/p-Cu₂O/n-ZnO NRAs and a magnified view of the proposed working mechanism (this figure has been adapted/reproduced from ref. 93 with permission from AMERICAN CHEMICAL SOCIETY, copyright 2017).

Babatunde A. Koiki

Omotayo A. Arotiba