CdS Nanoparticles Supported on a Dual Metal-Organic Framework as a Catalyst for the Photodegradation of Tetracycline

The photocatalytic activity of individual metal-organic frameworks (MOFs) such as UiO-66-NH2 and MIL-101(Fe) is less satisfactory due to the disappointing separation rate of electron-hole pairs and weak solar energy utilization efficiency. In this context, we develop hierarchical dual Z-scheme heterostructured photocatalysts prepared via an in situ hydrothermal synthesis method anchoring cadmium sulfide (CdS) nanoparticles onto the (UiO-66-NH2)-(MIL-101(Fe)) (UM) dual metal-organic frameworks. Attributed to the synergistic effects of CdS, UiO-66-NH2, and MIL-101(Fe), the (UiO-66-NH2)-(MIL-101)(Fe)-CdS (UM-CdS) exhibits outstanding degradation activities toward TC degradability. Typically, 10 mg of UM-CdS achieved an 87% degradation rate of TC within 140 min, which is 8.7, 2.4, and 1.4 times than those of UiO-66-NH2, MIL-101(Fe), and CdS, which achieved higher photocatalytic degradation rate with a less dosage of catalysts compared with previous reports. The outstanding photocatalytic activity of UM-CdS is primarily attributed to its hierarchical structure, which provides numerous active sites. Additionally, the special heterostructure not only exhibits a dual Z-scheme migration mechanism for charge carriers, which facilitates the efficient separation and migration of photoinduced electrons and holes, but also promotes the redox capability of UM-CdS. Furthermore, the trapping tests demonstrated that O-center dot(2)-, (OH)-O-center dot, and h(+) were the main active species during the photocatalytic process. The degradation products or intermediates were also studied in-depth through the liquid chromatography-mass spectrometry (LC-MS) technique. Besides, the UM-CdS possesses excellent stability, retaining more than 90% initial photocatalytic activity after the fifth cycle. This work provides a double MOF-supported CdS strategy to prepare recyclable dual Z-scheme heterojunction photocatalysts for the degradation of refractory antibiotics (e.g., TC) in sewage.