A robust Zr-MOF (LIFM-28) containing replaceable coordination sites for additional spacer installation has been employed to demonstrate a swing- or multirole strategy for multifunctional MOFs. Through reversible installation/uninstallation of two types of spacers with different lengths and variable functional groups, different tasks can be accomplished using the same parent MOF. An orthogonal optimizing method is applied with seven shorter (L) and six longer (L) spacers to tune the functionalities, achieving multipurpose switches among gas separation, catalysis, click reaction, luminescence, and particularly, ultrahigh methane storage working capacity at 5-80 bar and 298 K.
We demonstrate herein a facile strategy
to engineer versatile catalytically
active coordination interspace in the same primitive metal–organic
framework (MOF) for variable heterogeneous catalysis. Different functional
ligands can be reversibly inserted into and removed from proto-LIFM-28 individually or successively to bring in single or binary
catalytic sites for specific reactions and switch the parent MOF to
multipurpose catalysts. Alcohol-oxidation, Knoevenagel-condensation,
click, acetal, and Baylis–Hillman reactions are achievable
through simple exchange of a single catalytic spacer, while sequential
or stepwise reactions are designable via selective combination of
two catalytic spacers with different functionalities, thus making proto-LIFM-28 a multivariate MOF for multiuse and economic
catalysis.
To combine flexibility and modifiability towards a more controllable complexity of MOFs, a post-synthetic variable-spacer installation (PVSI) strategy is used to implement kinetic installation/ uninstallation of secondary ligands into/from a robust yet flexible proto-Zr-MOF. This PVSI process features precise positioning of spacers with different length, size, number, and functionality, enabling accurate fixation of successive breathing stages and fine-tuning of pore surface. It shows unprecedented synthetic tailorability to create complicated MOFs in a predictable way for property modification, for example, CO2 and R22 adsorption/separation, thermal/chemical stability, and extended breathing behavior.
Isophthalic acid (IPA), a feedstock linker, has been considered so far to build series of topical metal-organic frameworks (MOFs) of diverse structures with various di-and trivalent metal ions, such as CAU-10(Al), owing to its facile availability, unique connection angle/mode and a wide scope of functional groups attached. Constructing MOFs from IPA and tetravalent metals, typically Group 4 metals, would be of a great interest due to expected higher chemical stability. In particular, titanium-IPA frameworks possessing photoresponse is alluring, in relation to the known challenge of synthesizing new Ti-MOFs. Here, we have synthesized the first Ti-IPA MOF, denoted as MIP-208, via a solvothermal process that efficiently combines the use of preformed Ti 8 oxoclusters and in situ acetylation of 5-NH 2 -IPA linker. MIP-208 has helical chains of cis-connected corner-sharing TiO 6 polyhedra as the inorganic building units, which are interconnected to each other leading to a 3D ultramicroporous framework. Solid-solution mixed linkers strategy was then successfully applied resulting in a series of multivariate MIP-208 structures with tunable chemical environment and sizable porosity. Finally, the excellent thermal and hydrolytic stabilities of MIP-208 allowed its use for the photocatalytic carbon dioxide (CO 2 ) methanation, showing the best result among the pure MOF catalysts. Ruthenium oxide nanoparticles were further photodeposited on MIP-208 forming a highly active and selective composite catalyst, MIP-208@RuO x , to largely improve the photocatalytic performance, which features a notable visible light response, an excellent stability and recycling ability.
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