In Situ Assembly of Ti-Zr Bimetallic Organic Cages towards High-Performance Photocatalytic Degradation of Tetracycline Hydrochloride

This study reports one-pot microwave-assisted solvothermal synthesis of Ti-Zr bimetallic organic cages (TiZrT-BTC-α, where α denotes the actual Ti molar percentage and T represents the tetrahedral cage structure). The reaction employed zirconocene dichloride (Cp 2 ZrCl 2 , Cp =  η 5 -C 5 H 5 ), titanocene dichloride (Cp 2 TiCl 2 ) and 1,3,5-benzenetricarboxylic acid (H 3 BTC) as solid precursors to form a V 4 F 4 (V = vertex and F = face) coordination tetrahedron. The presence of the characteristic Ti-O vibration band at 420 cm -1 in the FT-IR spectrum, along with the characteristic Ti 4+ band signal at 458.6 eV in the XPS spectrum, collectively demonstrates the successful incorporation of titanium into the molecular cage structure. Notably, the introduction of titanium endowed the material with visible light absorption capability and modulates its electronic structure, reducing the band gap value from 3.73 eV (ZrT-BTC) to 2.48 eV (TiZrT-BTC-7.9). The photocatalytic activities of TiZrT-BTC-α were evaluated using tetracycline hydrochloride (TC) as a target pollutant under visible light illumination. Among the series, TiZrT-BTC-7.9 demonstrated excellent photocatalytic activity, achieving 92.17% degradation efficiency for TC (20 mg/L) within 3 hours. Electron spin resonance (ESR) spectroscopy combined with radical trapping experiments identified superoxide radicals (·O 2 - ) served as the dominant reactive species. This work paves the way for developing cage-based photocatalysts with tunable optoelectronic properties.