Enhanced photocatalytic degradation of organic contaminants over a CuO/g-C 3 N 4 p–n heterojunction under visible light irradiation

results from the built-in electric field close to the formed p-n heterojunction, which switches the electron transfer mechanism from a double-charge transfer mechanism to a Z-scheme mechanism. In addition, the formed p-n heterojunction favors charge transfer, and thus the photocatalytic performance is significantly improved.