Stepwise Engineering the Pore Aperture of a Cage-like MOF for the Efficient Separation of Isomeric C4 Paraffins under Humid Conditions.

The separation of isomeric C4 paraffins is an important task in the petrochemical industry, while current adsorbents undergo a trade-off relationship between selectivity and adsorption capacity. In this work, the pore aperture of a cage-like Zn-bzc (bzc=pyrazole-4-carboxylic acid) is tuned by the stepwise installation methyl groups on its narrow aperture to achieve both molecular-sieving separation and high n-C4 H10 uptake. Notably, the resulting Zn-bzc-2CH3 (bzc-2CH3 =3,5-dimethylpyrazole-4-carboxylic acid) can sensitively capture n-C4 H10 and exclude iso-C4 H10 , affording molecular-sieving for n-C4 H10 /iso-C4 H10 separation and high n-C4 H10 adsorption capacity (54.3 cm3 g-1 ). Breakthrough tests prove n-C4 H10 /iso-C4 H10 can be efficiently separated and high-purity iso-C4 H10 (99.99 %) can be collected. Importantly, the hydrophobic microenvironment created by the introduced methyl groups greatly improves the stability of Zn-bzc and significantly eliminates the negative effect of water vapor on gas separation under humid conditions, indicating Zn-bzc-2CH3 is a new benchmark adsorbent for n-C4 H10 /iso-C4 H10 separation.

Simultaneous introduction of oxygen vacancies and hierarchical pores into titanium-based metal-organic framework for enhanced photocatalytic performance.

Photo-generated radicals play an important role in photocatalytic reactions, yet numerous radicals undergo self-quenching before contact with the substrate because of their ultrafast lifetimes and limited diffusion distances, which decreases the utilization of free radicals and reduces the activity of photocatalysts. Herein, both hierarchical pores and oxygen vacancies (OVs) were successfully introduced into a titanium-based metal-organic framework (MOF), namely MIL-125-NH2 (MIL for Materials of Institut Lavoisier), via a simple and controllable acid etching method. The generation of OVs increased the yield of photogenerated radicals, while the hierarchical pore structure conferred a pore enrichment effect, thus enhancing the utilization of photogenerated radicals. Owing to the synergistic effect of the hierarchical pores and OVs, the obtained single-crystal nanoreactor, H-MIL-125-NH2-VO, showed much higher catalytic activity for rhodamine (RhB) degradation than pristine MIL-125-NH2. In fact, the rate constant for catalytic RhB degradation in H-MIL-125-NH2-VO was approximately eight times that of MIL-125-NH2. This work highlights the significant contribution of both hierarchical pores and OVs to enhancing the photocatalytic performance of MOFs.