One-Step Construction of Hierarchical Porous and Defect-Rich Zn²⁺-Doped NH₂-MIL-125(Ti) to Enhance Photocatalytic Degradation of Tetracycline Hydrochloride

The development of efficient metal-organic framework (MOF) photocatalysts for the degradation of tetracycline hydrochloride (TC) is crucial for environmental and public health. Herein, NH₂-MIL-125(Ti) flakes (namely, Zn_<i>x</i>Ti_1-<i>x</i>-NML), featuring defect-rich and Zn²⁺-doping, were synthesized using a one-step solvothermal method. For the first time, the crystal structure of Zn-doped NML was determined by combining extended X-ray absorption with fine structure spectroscopy. The formation mechanisms of the flake morphology with hierarchical porous structures were thoroughly investigated. Compared to NH₂-MIL-125(Ti), Zn_0.15Ti_0.85-NML achieved a 3.4-fold increase in removal of TC under simulated sunlight. The adjusted electronic structure enhances superoxide radical production, coupled with a flake-like and porous architecture that promotes reaction sites, improved mass transfer, and reduced charge distances. Combined with theoretical calculations of the density of states and electrostatic potential, the ligand-metal-metal charge transfer process was elucidated. The possible pathway for the photocatalytic degradation of TC by Zn_0.15Ti_0.85-NML was further speculated. Moreover, the safety of the photocatalytic pathway was assessed by predicting the toxicity of the degradation intermediates. Our findings link the structure of MOFs to their catalytic efficiency, guiding the creation of sustainable photocatalysts.