Photochemically engineered hierarchical cerium MOFs with amine functionalization for high-performance direct air capture of CO2

Direct air capture (DAC) of CO 2 is a critical negative-emission technology for mitigating climate change. Although amine-functionalized metal-organic frameworks (MOFs) are promising DAC adsorbents, their performance is often constrained by inherently limited microporosity, restricted amine loading, and slow mass transfer. Here, we report a novel strategy to engineer hierarchically porous cerium MOFs Ce-BPY (HP-Ce-BPY) by controllably forming defects through specific photoinduced linker distortion and coordination-bond weakening, generating abundant mesopores while preserving structural crystallinity. Subsequent amine grafting markedly strengthens CO 2 affinity, with HP-Ce-BPY-EDA delivering a CO 2 uptake of 1.35 mmol g⁻ 1 at 1.0 bar and 0.25 mmol g⁻ 1 under DAC conditions (0.4 mbar), over 1000-fold higher than pristine Ce-BPY and HP-Ce-BPY. Remarkably, humidity further enhances dynamic CO 2 adsorption, achieving 0.7 mmol g⁻ 1 at 75% relative humidity, while maintaining over 80% capacity after ten adsorption-desorption cycles. Combined CO 2 -TPD and in-situ DRIFTS analyses reveal a chemisorption-dominated, humidity-dependent adsorption mechanism, shifting from carbamate formation under dry conditions to bicarbonate formation in the presence of water, thereby improving amine utilization efficiency and CO 2 uptake. This work introduces a simple, scalable, and cost-effective photochemical route to hierarchically porous amine-functionalized MOFs, offering a promising material platform for high-performance DAC under realistic ambient environments.