2D and 3D printing of MOF nanocrystals using DLP

Metal-Organic Frameworks (MOFs) are nano- to microscopic crystalline powder materials formed by the coordination of metal-containing units and organic linkers, exhibiting a porosity that outperforms classical materials such as zeolites and carbons. Over the last three decades, MOFs have been considered among the principal materials of interest due to their exceptional sorption capacities and versatility, displaying potential for a wide range of applications including gas storage, catalysis, separation, and sensing. Although several important milestones have been achieved, there is still a significant delay in transforming this basic science into real industrial applications. This bottleneck is mostly due to the lack of techniques for the processing of MOF powders into both high-density 3D structures and robustly surface-anchored films and patterns, while preserving their physicochemical properties. The objective of this project consists of developing a general approach for the covalent assembly of MOFs into surface patterns and 3D architectures with unprecedented control of the crystal characteristics using digital-light processing (DLP). The first specific aim will consist of the transformation of nanoscopic MOFs (nMOFs) crystals into core- shell photoreactive building-blocks. Second, the functionalized nMOFs, acting like molecules in solution, will be photo-immobilized on silicon using a 3D printer. The integration of a flow-through system into the DLP printer will enable the multiplexing of different MOFs. A miniaturized multiplexed luminescent sensor for the quantification of four gases will demonstrate the potential of this approach. Finally, a systematic exploration of formulations for the 3D printing of the functionalized nMOFs will be deployed, with the aim of minimizing the binding agents and integrating strategies for the post-printing consolidation into dense monoliths. The completion of the objectives of this project will enable surface multiplexed MOFs patterning for the fabrication of multi-sensors, lab-on-a-chip devices, micro-separators, and MOF-based electronics, as well as the 3D printing of MOFs and MOFs composites for their densification and shaping - facilitating their use in myriad industrial applications, by using commercially available and cost-effective 3D printers and reagents. Primary Researchers Involved. Dr. Carlos Carbonell, Prof. Paolo Falcaro, and Prof. Georg Gescheidt-Demner

The most significant results of the project are compiled in a study recently published in Advanced Materials (https://doi.org/10.1002/adma.202408770) addressing the growing need for accessible and affordable micropatterning technologies that enable multi-MOF micropatterning, preserve pore accessibility, offer complete design flexibility, and are applicable to a wide range of MOFs for electronics, photonics, sensing, and encryption applications. The work introduces a novel patterning approach named DLP-flow, that meets all these requirements by combining Digital Light Processing (DLP), microfluidics, and an oligomer-based MOF-ink formulation. Our method, enables spatially controlled photopolymerization of the MOF-ink, achieving 20-m feature sizes and allowing the arbitrary micropatterning of a 20 cm surface with four different MOFs under 10 minutes. We have successfully printed ZIF-8, MIL-88A, MOF-74 (Co), HKUST-1, Pyr@ZIF-8, ZIF-67, and PCN-224 and, in addition, we have demonstrated three proof-of-concept applications: (1) a luminescence oxygen sensor based on pyrene (Pyrene@ZIF-8), that proves pore accessibility to oxygen. (2) A dual encryption system obtained by printing combinations of optically active inks based on pyrene, Pyrene@ZIF-8, and ZIF-67. (3) A zirconium porphyrinic MOF (PCN-224) as amines colorimetric indicator, to evidence that molecules as large as aniline can penetrate the patterned MOF, and that pores as large as 1.9 nm (PCN-224) remain accessible upon patterning. This work represents the first demonstration of rapid, arbitrary, cost-effective, and pore- accessible multi-MOF micropatterning. We believe that our strategy will accelerate the design-to-application cycle of MOF-based devices and we anticipate that new MOF-inks incorporating advanced functional polymers, and nanomaterials, and the adoption of our approach to multi-MOF 3D printing of hierarchical porous architectures, will find transformative applications in health, energy, and environment.