Construction of g–C3N4/PDI–g–C3N4 homojunction for enhancing the photocatalytic degradation of SMX under visible light

g–C 3 N 4 / PDI–g–C 3 N 4 homojunction (CPCN–X) was prepared to effectively remove sulfamethoxazole (SMX) from water under visible light. The band of CPCN–X bent and the new flat band potential resulted in the generation of a built–in electric field at the contact interface between PDI–g–C 3 N 4 (CNPDI) and g–C 3 N 4 (CN). This facilitated interlayer charge migration, optimized the transportation efficiency of photoinduced electron pairs, and thereby boosted photocatalytic activity. CPCN–6 photocatalyst prepared with a mass ratio of 1:6 (CNPDI to CN) exhibited the highest photocatalytic activity, which can degrade 97.0 % of SMX after 90 min of visible light irradiation. The related degradation rate constant was calculated as 0.0371 min −1 , which was a 2.3 and 4.7 fold increase in comparison to CNPDI and CN, respectively. Free radical scavenging experiments revealed that ·O 2 − and h + were the predominant active materials for the photocatalytic decomposition of SMX by CPCN–6, while ·OH and 1 O 2 exhibited a relatively negligible contribution. It was found that CPCN–6 exhibited the potential to degrade sulfonamide antibiotics and the limited ability to remove atrazine and phenol in the visible light region due to the difference of redox properties and molecular structure.