Study on the internal electric field in the Cu2O/g-C3N4 p–n heterojunction structure for enhancing visible light photocatalytic activity

Abstract

Study of the degradation mechanism of the Cu₂O/g-C₃N₄ p–n heterojunction is very challenging and important for the preparation and practical applications of the g-C₃N₄ photocatalyst in controlling water pollution. Therefore, the Cu₂O/g-C₃N₄ p–n heterojunction was designed and prepared successfully and the mechanism of enhanced visible-light photocatalytic activity was proposed. The morphology and structure of the synthesized materials were characterized by using SEM, TEM, FT-IR and XPS. And the optical and electrical properties of the materials were studied by measuring DRS, the photocurrent density and the Mott–Schottky curve. The results showed that the g-C₃N₄ photocatalyst is coated on the surface of Cu₂O to form a tight heterojunction, which facilitates the separation and migration of photogenerated carriers, and the quantum yield of the Cu₂O/g-C₃N₄ composite photocatalyst was 3–7 times higher than that of the single component. It has been shown that the built-in electric field formed at the heterojunction interface can effectively separate photogenerated electrons and holes. The photocatalytic performance of the material was evaluated by the photocatalytic degradation of tetracycline (TC) under visible light. The maximum degradation rate of Cu₂O/g-C₃N₄ for TC could reach over 90% in 90 min, and the degradation rate of the single component is more than doubled. Simultaneously, the TOC tests monitored the mineralization of TC up to 83.4%, and the active substances in the reaction process were determined to be ˙O₂⁻ and h⁺ through free radical trap experiments and ESR tests. This work shows that the construction of an internal electric field has greatly improved the photocatalytic performance of g-C₃N₄. The Cu₂O/g-C₃N₄ p–n heterojunction has good degradation ability toward tetracycline and is a good tetracycline-type wastewater treatment material.