Significantly boosted activity for styrene oxidation through simultaneous regulation of porosity and copper sites in microporous metal-organic framework Cu-BTC

As detrimental pollutants to humans and the environment, volatile organic compound (VOC) removal has drawn significantly increasing research attention, among which oxidation of styrene is a hot research topic. Metal-organic frameworks (MOFs) with meso- and macropores, which are important factors for mass transport, are regarded as promising catalysts for heterogeneous catalysis like styrene oxidation. Herein, by in situ doping of 5-aminoisophthalic acid (5-NH₂-H₂ip) with different molar ratios into a microporous Cu-BTC structure, a series of hierarchically porous defect-engineered MOFs (HP-DEMOFs) were prepared. And then they were fully characterized by various techniques including powder XRD, SEM, HAADF-STEM, N₂ physisorption, TG, XPS, and ¹H-NMR. It is worth noting that the additionally created pores (>2 nm) in the parent structure can be systematically regulated from the mesopore to the macropore range by controlling the doping level of 5-NH₂-H₂ip. Simultaneously, a significant amount of Cu⁺ species was generated. These novel HP-DEMOFs were further employed as heterogeneous catalysts for the styrene oxidation reaction, in which HP-DEMOF-4 exhibited more than 20 times higher conversion than that of the microporous Cu-BTC structure after 7 h reaction under the same conditions.