Synergistic Lewis Acid Photocatalysis Over Cluster-Defect-Engineered UiO-66 for Efficient Liquid Biomass Upgrading

Defect engineering provides new opportunities to overcome the intrinsic limitations of metal-organic frameworks (MOFs) in photocatalysis. Herein, a cluster-defect engineering (CDE) strategy is employed to modify the pristine UiO-66 framework, wherein Zn incorporation followed by selective acid etching yields defect-rich A/(Zn,Zr)UiO-66 catalysts featuring hierarchical porous architectures and abundant Lewis (L) acid sites. Optical and photoelectrochemical analyses confirm that CDE broadens visible-light harvesting, narrows the bandgap, and prolongs carrier lifetimes. The synergistic interplay between L acid sites and photocatalysis over A/(Zn,Zr)UiO-66 results in an excellent photocatalytic performance in biodiesel production via oleic acid (OA) esterification with methanol (CH₃OH) under mild reaction conditions, outperforming pristine UiO-66. Notably, the optimized A/(Zn,Zr)UiO-66-0.2 achieves a remarkable 99.3% biodiesel yield under mild conditions, alongside superior stability and reusability. Further, in situ spectroscopic investigations and density functional theory (DFT) calculations disclose that CDE lowers the coupling barrier of OA and CH₃O• radicals by strengthening OA adsorption and activation as well as facilitating charge stabilization at unsaturated Zr sites. This work highlights CDE as an ingenious strategy for tailoring the electronic configuration and interfacial chemistry of MOFs, offering a versatile platform for visible-light-driven biomass upgrading and sustainable fuel production.