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 •O2–, •OH, 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

Electrosorption-promoted Photodegradation of Opaque Wastewater on A Novel TiO₂/Carbon Aerogel Electrode

A novel electrosorption-photocatalysis synergistic electrode of TiO2/carbon aerogel (TiO2/CA) is prepared. The thermal stability and dispersion of the anatase TiO2 particles are well facilitated by the porous and discontinuous microstructure of CA. The degradation experiments show that the TiO2/CA material is not only a good photocatalyst but also an excellent electrosorptive electrode. The TiO2/CA is easily molded to an agglomerate electrode. The opaque wastewater with dyestuff is degraded effectively by the electrosorption-promoted photocatalytic process on this electrode. For the simulated methylene blue (MB) wastewater (150 mg L−1), the rate constant of MB degradation in the electro-assisted photocatalytic process with the conventional ITO-supported TiO2 (TiO2/ITO) is 0.55 × 10−3 min−1 and that the electrosorption-promoted photocatalysis with TiO2/CA is 10.27 × 10−3 min−1, which is 18 times the former. In the electrosorption-promoted photocatalytic process with TiO2/CA, the energy consumption removing per unit TOC is only 15% of that in the electro-assisted photocatalysis with TiO2/ITO, because the electrosorption is a nonfaradic process irrelative to any electron transfer and requires very low consumption. This study provides a new method for exploring highly efficient electrosorption-promoted photocatalytics technology in the treatment of opaque wastewater

Modular Construction of an MIL-101(Fe)@MIL-100(Fe) Dual-Compartment Nanoreactor and Its Boosted Photocatalytic Activity toward Tetracycline

Iron-based metal–organic frameworks (MOFs) have aroused extensive concern as prospective photocatalysts for antibiotic (e.g., tetracycline, TC) degradation. However, efficiencies of single and simple Fe-based MOFs still undergo restricted light absorption and weak charge separation. Assembly of different iron-based MOF building blocks into a hybrid MOF@MOF heterostructure reactor could be an encouraging strategy for the effective capture of antibiotics from the aqueous phase. This paper reports a new-style MIL-101­(Fe)@MIL-100­(Fe) photocatalyst, which was groundbreakingly constructed to realize a double win for boosting the performances of adsorption and photocatalysis. The optical response range, surface open sites, and charge separation efficiency of MIL-101­(Fe)@MIL-100­(Fe) can be regulated through accurate design and alteration. Attributed to the synergistic effects of double iron-based MOFs, MIL-101­(Fe)@MIL-100­(Fe) exhibits an excellent photocatalytic activity toward TC degradability compared to MIL-101­(Fe) and MIL-100­(Fe), which is even superior to those reported previously in the literature. Furthermore, the main active species of •O2– and h+ were proved through trapping tests of the photocatalytic process. Additionally, MIL-101­(Fe)@MIL-100­(Fe) possesses remarkable stability, maintaining more than 90% initial photocatalytic activity after the fifth cycle. In brief, MIL-101­(Fe)@MIL-100­(Fe) was highly efficient for TC degradation. Our work offers a new strategy for visible-light photodegradation of TC by exploring the double Fe-based MOF composite