Fe–O–Zr Bond-Mediated MOF-on-MOF Heterojunction on Polymer-Carbonized Wood for Efficient Water Purification

Heterojunction photocatalysts offer a promising strategy for peroxymonosulfate (PMS) activation toward pollutant degradation, yet conventional heterojunctions with weak physical contact suffer from interfacial charge recombination and inefficient charge transfer. Herein, a novel MOF-on-MOF heterojunction (UA-Y) bridged by Fe–O–Zr linkages was fabricated via an in situ hydrothermal method. The optimized UA-3 achieved 94.3% degradation of bisphenol A (BPA, 100 mg L–1) within 50 min, with a rate 1.6 and 34.0 times higher than those of MIL-88A (88A) and Fe3+-doped UiO-67 (UiO-35), respectively. Furthermore, a self-floating immobilized photocatalytic system (CP-UA-3) was developed by embedding UA-3 in a polymer-carbonized wood (CW) matrix. This design preserves the BPA degradation efficiency (93.8% within 50 min), reduces Fe ion leaching (0.42 mg L–1), mitigates the light-shielding effect, and maintains reusability (>79% after 14 cycles). Finally, this work analyzes the potential degradation mechanism of UA-3 for BPA and proposes a “chemical bond-mediated and orbital relaxation-driven” charge transfer mechanism based on density functional theory (DFT) calculations. By immobilizing a novel chemical bond-mediated heterojunction on a polymer-CW carrier, this design provides an effective strategy for accelerating charge transfer and developing recyclable photocatalysts.