Construction of an S-scheme Ce/Ti-MOFs heterojunction with abundant Oxygen vacancies (Ovs) for efficient charges separation: Performance and mechanism insight

The S-scheme heterojunction in the semiconductors can effectively enhance the photocatalytic activity by retaining strong light-generated electrons (e−) and holes (h+) while recombining meaningless charge carriers. In this work, a Ce/Ti-MOFs (CT-MOFs) heterojunction material with plentiful oxygen vacancies (Ovs) was synthesized via the hydrothermal method. The catalysts were employed for the degradation of Tetracycline (TC) in the aquatic environment under simulated sunlight. The Ce/Ti-MOFs (CT 1–4) sample exhibited the best photocatalytic activity, with a rate constant of 0.01243 min−1, which is 7.49 times greater than that of Ce-MOF, and 2.40 times higher than that of MIL-125 (Ti), respectively. The experimental results show that the constructed CT-MOFs can increase the density of Ovs, accelerate charge transfer, and improve photocatalytic performance. Furthermore, the Ti4+/Ti3+ variable valence metal cycle in CT 1–4 compensates for charge balance and promotes rapid carrier separation. The difference between the Fermi energy level and work function drives the electron transfer from the MIL-125(Ti) side to the Ce-MOF side. The above results indicate that the successful establishment of the S-scheme heterojunction preserves the strong redox effects of e− and h+, prolongs the electron lifetime, and facilitates the carrier's separation.