What was the inspiration for this cover design? The catalyst-modified MOF thin filmi sg rown on al eaf-like electrode conductive substrate. The "leaf" electrochemically oxidizesw ater,o ne of the half reactions required for natural photosynthesis.
The dominant charge transfer mechanism in a vast number of metal-organic frameworks (MOFs) is that of redox hopping, a process best explained through the motion of electrons via self-exchange reactions between redox centers coupled to the motion of counter-balancing ions. Mechanistic studies of redox hopping transport in MOFs reveal characteristics that recall pioneering studies in linear redox polymers. When MOFs are employed as electrocatalysts, consideration must be given to both the catalytic properties - turn-over frequency (TOF) and energetic requirements (overpotential, TON) - and the charge transport properties - rate of charge hopping, measured via an apparent diffusion coefficient (Dapp). Herein, we provide a mathematical framework to provide constraints to MOF catalyst development by relating Dapp, TOF, and film thickness in the context of providing 10 mA cm-2 of catalytic current. Lastly with the mechanistic studies discussed as a foundation, design rules for future MOF electrocatalysts are provided and the challenges to the community to optimize MOF charge transport are laid out.
Metal-organic frameworks (MOFs) have shown great promise in catalysis, mainly due to their high content of active centers, large internal surface areas, tunable pore size, and versatile chemical functionalities. However, it is a challenge to rationally design and construct MOFs that can serve as highly stable and reusable heterogeneous catalysts. Here two new robust 3D porous metal-cyclam-based zirconium MOFs, denoted VPI-100 (Cu) and VPI-100 (Ni), have been prepared by a modulated synthetic strategy. The frameworks are assembled by eight-connected Zr clusters and metallocyclams as organic linkers. Importantly, the cyclam core has accessible axial coordination sites for guest interactions and maintains the electronic properties exhibited by the parent cyclam ring. The VPI-100 MOFs exhibit excellent chemical stability in various organic and aqueous solvents over a wide pH range and show high CO uptake capacity (up to ∼9.83 wt% adsorption at 273 K under 1 atm). Moreover, VPI-100 MOFs demonstrate some of the highest reported catalytic activity values (turnover frequency and conversion efficiency) among Zr-based MOFs for the chemical fixation of CO with epoxides, including sterically hindered epoxides. The MOFs, which bear dual catalytic sites (Zr and Cu/Ni), enable chemistry not possible with the cyclam ligand under the same conditions and can be used as recoverable stable heterogeneous catalysts without losing performance.
Ruthenium(ii) polypyridyl-doped metal–organic framework sensitized films on TiO2 for photovoltaics reveal that the preparative method of dye doping/incorporation into the MOF is integral to the total solar cell efficiency.
We report the photo-induced degradation of and cargo release from a nanoscale metal-organic framework (nMOF) incorporating photo-isomerizable 4,4'-azobenzenedicarboxylate (AZB) linkers. The structure matches a UiO-type framework where 12 4,4'-azobenzenedicarboxylate moieties are connected to a ZrO(OH) cluster, referred to as UiO-AZB. Due to the incorporation of photo-isomerizable struts, the degradation of UiO-AZB is accelerated by irradiation with white light (1.3 ± 0.1% h under dark conditions vs. 8.4 ± 0.4% h when irradiated). Additionally, we show slow release of Nile Red (NR) which is triggered by irradiation (0.04 ± 0.01% h under dark conditions vs. 0.36 ± 0.02% h when irradiated).
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