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Chemical Engineering of Functional Stable Metal-Organic Frameworks: Porous Crystals and Thin Film Devices

Periodic Reporting for period 4 - chem-fs-MOF (Chemical Engineering of Functional Stable Metal-Organic Frameworks: Porous Crystals and Thin Film Devices)

Okres sprawozdawczy: 2021-07-01 do 2022-12-31

Regarding chemically demanding processes, MOFs still need to fulfil critical requirements like time-on-stream behaviour and leaching stability. Though high-temperature heterogeneous catalysis is likely to be dominated by inorganic solids like zeolites, MOFs display adequate thermal stability for low-temperature processes and unique chemical/structural control for an unlimited range of materials. However, except for particular cases, MOFs generally lack the chemical stability and structural robustness required due to to weak coordination bonds that hydrolyse with moisture or chemical decomposition in presence of acid or base. This is arguably limiting the incorporation of MOFs into a broader range of practical applications nowadays. Besides chemical stability, the insulating character of MOFs is another key limitation. Provided combination of high surface areas with good charge mobility, MOFs could become a game changer and make significant contributions to applications of environmental relevance as photovoltaics, photocatalysis, electrocatalysis, supercapacitors or sensing (transduction of electrical signal), to cite a few. Assembly of 2D nanosheets with atomic thickness of layered MOFs also represents an interesting technological avenue. This would enable fabrication of solid-supported devices in which function would be reduced to a single/few layers whilst retaining most of the properties of the bulk alongside integration into a useful platform (direct contact with another materials).
The project has covered most of the goals originally proposed and create new and exciting opportunities built on the control gained on the assembly of porous, ultrastable molecular frameworks.

New synthetic platforms in Reticular Chemistry: we have implemented high-throughput synthetic methodologies for the systematic preparation of titanium-organic frameworks. These families of MOFs – labelled as MUV (Materials of University of Valencia)– are based on earth abundant metals and combine sizeable porosities with exceptional chemical stabilities. These synthetic routes have led to new strategies for the chemical engineering of photocatalytic activity of porous solids (Angew. Chem. Int. Ed. 2018, 57, 8453–8457), the introduction of siderophore-type linkers as alternative metal connectors for engineering photocatalytic performance (J. Am. Chem. Soc. 2019, 141, 13124–13133), the assembly of photoactive mesoporous solids with surface areas beyond 2000 m2·g-1 (Chem. Sci. 2019, 10, 4313–4321), or the design of the first family of permanently porous titanium-organic cages (J. Am. Chem. Soc. 2021, 143, 21195–21199). We have also introduced new concepts to enable dual-metal synergistic catalysis in heterometallic MOFs (Chem 2020, 6, 3118–3131) or the use of cluster chemistry for selective implantation of amines for cooperative catalysis in porous solids (Angew. Chem. Int. Ed. 2021, 60, 11868–11873).
Chemical complexity for targeted function: we have also set focus in advancing our understanding on how the composition or spatial arrangement of MOF components or defects can determine their function. In this context, we have developed new methodologies for the synthesis of heterometallic titanium-organic frameworks by unprecedented metal-induced dynamic topological transformations (J. Am. Chem. Soc. 2020, 142, 6638–6648), or demonstrated the effect of linker distribution in the photocatalytic activity of multivariate mesoporous crystals (J. Am. Chem. Soc. 2021, 143, 1798–1806). We have also pioneered alternative routes for controlling the introduction of defects in titanium MOFs by using modulators with varying connectivity (Chem. Sci. 2020, 12, 2586–2593) or sub-stochiometric linker concentrations (Chem. Sci. 2021, 12, 11839–11844), and have demonstrated the advantages offered by fine control of the metal distribution in mixed-metal MOFs for accessing unprecedented mixed oxide catalysts (Chem Catal. 2021, 1, 364–382).

Processing at the nanoscale for device integration: conductive MOFs and bi-stable coordination polymers are carving a niche for themselves in the world of molecular electronics. The tunability and processability of these materials alongside with the combination of electrical conductivity with porosity or spin transition offers unprecedented opportunities from their integration into functional devices. We have achieved the fabrication of MOF ultrathin films for the design of electronically active interfaces (J. Am. Chem. Soc. 2016, 138, 2576–2584), study of the electrical response of MOF devices featuring films as thin as 10 nm (Adv. Mater. 2018, 30, 1704291), or the development of instrumentation for demonstrating the origin of the chemo resistive response of MOF films to changes in the environment (Angew. Chem. Int. Ed. 2018, 57, 15086–15090). In the context of spin transition, we have has also demonstrated the influence of pillaring linkers on the vertical charge transport of ultrathin films of 2D Hofmann-type clathrates (Chem. Mater. 2019, 31, 7277–7287), or the effect of nanostructuration on their spin crossover transition (Chem. Sci. 2019, 10, 4038–4047). Most of our contributions in this context have been covered in a topical review of the area (Chem. Soc. Rev. 2020, 49, 5601–5638).

Exploitation of results: Some of the technologies and materials created during the project have led to the creation of 2 start-ups: Porous Materials for Advanced Applications S. L. (2018) and Porous Materials in Action S. L. (2021), to accelerate the transfer of these results into products and services. These entrepreneurial platforms have licensed one of the patents filed during the project to approach the high-scale synthesis of MOFs with optimal cost and reduced environmental impact to enable their commercialization. This has already facilitated the signature of transfer contracts with several technological centers and companies.
Most developments in the chemistry and applications of Metal-Organic Frameworks (MOFs) have been made possible thanks to the value of reticular chemistry in guiding the unlimited combination of organic connectors and secondary building units (SBUs) into targeted architectures. However, the development of new titanium-frameworks remained still limited by the difficulties in controlling the formation of persistent Ti-SBUs with predetermined directionality amenable to the isoreticular approach. We have implemented new synthetic methodologies (high-throughput exploration of the chemical space) to accelerate the discovery of new materials and optimize their synthesis at high-scale regardless the precursor of choice. Our approach has also included exploration of unexplored metal binders rather than more conventional carboxylate or azolate linkers.
We have also established new methodologies to access MOF ultrathin films of sufficient quality for application in photocatalytic devices. Besides their processing, we have developed the techniques required for evaluating charge transport in nanometric thick films.

Built upon the unlimited conceptual opportunities offered by Reticular Chemistry to tailor porosity and chemical composition, now combined with the tools developed to control the assembly of ultrastable frameworks, we expect the knowledge gained with Chem-fs-MOF to assist in the creation of advanced porous materials for more efficient capture and valorization of post-combustion gases.
Graphical abstract summarising main results for this period