Piezocatalytic MOF-based heterojunctions as a new paradigm: Sub-minute Cr(VI) reduction via fluorine-engineered ZnO/UiO-66-F4

First piezo-responsive MOF heterostructure for mechanical Cr(VI) reduction. • F-modified MOF and ZnO loading synergistically boost piezoelectric response. • Efficient piezo-catalytic interface enables ultrafast Cr(VI) reduction. • 10 ppm Cr(VI) completely reduced to undetectable level within only 15 s. Hexavalent chromium (Cr(VI)) is highly toxic and carcinogenic; its reduction to Cr(III) remains the most viable remediation strategy. Piezoelectric catalysis, which converts mechanical energy into chemical energy via built-in electric fields, offers a sustainable route for pollutant degradation. However, the application of piezoelectric Metal-Organic Frameworks (MOFs) in heavy metal reduction remains largely unexplored. Herein, we report a strategy of fluorination combine with ZnO loading to construct piezoelectric MOF heterostructures for ultrafast Cr(VI) reduction. The optimized ZnO/UiO-66-F 4 completely reduced 10 ppm Cr(VI) to below detection limits within merely 30 s under sonication, substantially outperforming pristines. Systematic characterizations and DFT calculations revealed that fluorination depresses the conduction band to −0.91 V vs. NHE, establishing a type-II staggered band alignment with ZnO that synergizes with the piezoelectric field to drive vectorial charge separation, as corroborated by markedly reduced charge-transfer resistance and prolonged fluorescence lifetime with enhanced quantum yield. Mechanistic investigations further identified the interfacial Zn Zr dual-atom site as the true catalytic center, exhibiting the strongest Cr(VI) adsorption affinity and the lowest activation energy barrier for the rate-determining step. The catalyst demonstrated exceptional durability, retaining 98.2% removal efficiency after five cycles with negligible metal leaching. This work pioneers the application of piezoelectric MOFs in heavy metal remediation and establishes a molecular-level electronic modulation strategy for mechanical-energy-driven water purification. Piezoelectric ZnO/UiO-66-F 4 heterostructure was constructed via fluorine modification coupled with ZnO loading, demonstrating superior piezocatalytic performance for Cr(VI) reduction under ultrasonic vibration. Download: Download high-res image (138KB) Download: Download full-size image