Postoxidation of Zr-MOFs for Gas-Solid Photocatalytic Reduction of Dilute CO2

Photocatalytic conversion of diluted CO2 into CO offers a sustainable route to mitigate greenhouse effects while producing renewable fuels. However, industrial flue gas typically contains low CO2 concentration (∼15 vol %), with N2 as the predominant component, leading to competitive adsorption that severely limits CO2 capture and the subsequent photoreduction kinetics. Here, we report a postoxidation strategy to introduce polar sulfoxide and sulfone groups into a zirconium-based metal-organic framework material (DUT-67). The resulting DUT-67-O exhibits significantly enhanced CO2/N2 selectivity (31.14 versus 27.27 for pristine DUT-67) under diluted gas (15% CO2 in N2). In a closed system containing CO2 and water vapor without any photosensitizer or sacrificial agent, DUT-67-O achieves a CO production rate of 39.37 μmol g-1 h-1 under pure CO2, 2.35 times that of pristine DUT-67. Notably, under 15% CO2 balanced with N2, DUT-67-O still delivers a CO production rate of 28.35 μmol g-1 h-1, 3.64 times higher than DUT-67. Mechanistic studies reveal that the introduction of S═O groups narrows the band gap, enhances light absorption, promotes electron delocalization, and facilitates photogenerated charge carrier separation and migration. This work provides an effective strategy for boosting photocatalytic conversion of diluted CO2 via electronic structure modulation through sulfone functionalization.