(6gb) Metal-Organic Framework (MOF) Thin Films for Functional Materials Enabled By Atomic Layer Deposition

Metal-organic frameworks are crystalline porous materials that consist of metal ions/clusters and organic linkers. MOFs typically exhibit high surface area, good adsorption capacity and opportunity for post-synthetic modification. While thousands of MOFs have been reported in the past decade, the insoluble MOF powders typically obtained through conventional solvothermal methods may not be the ideal configuration for applications like gas filters, chemical sensors and smart membranes etc.¹Growing MOF thin films onto various functional substrates, however, could expand the material set of MOF-based composites and enable new applications.

    Atomic layer deposition (ALD) enables precise control of thin film coatings and surface functionality on a variety of substrates at low processing temperature. Using a lab-designed ALD reactor system, I have successfully grown conformal Cu-BTC MOF thin films on to Al₂O₃-coated polypropylene (PP) fibers using both solvothermal and layer-by-layer methods.^1,2 Compared to previous reports, my approach significantly enhances MOF mass loading and greatly improves the growth uniformity of MOF thin films. MOF functionality is fully maintained after integration, as indicated by high BET surface area and large adsorption capacity for hazardous gases such as NH₃ and H₂S. I have also demonstrated the wide applicability of this process scheme to other MOFs and substrate materials.

    Though an extensive investigation for the effect of different ALD metal oxide nucleation layers, I found an ultra-fast reaction path for Cu-BTC formation at room temperature using ZnO. I achieved a space-time-yield up to 2.9×10⁴ kg∙m^-3∙d^-1for producing Cu-BTC powder, which is more than 10× larger than previously reported. Same synthesis strategy has also been applied to MOF thin films and MOF patterns using ALD ZnO seed layers. The results indicate my method dramatically improves Cu-BTC production rates and widely expand the material set of MOF-functionalized composites.

    In addition to the research progress highlighted above, I have also applied ALD to the synthesis of ZnO nanostructures, designed and built an automated reactor that realizes fast layer-by-layer deposition of MOF thin films (>8x faster than manual processes), and investigated UiO-66-NH₂ growth on different ALD surfaces and its photocatalytic activity towards organic dye degradation. In the future, I will actively apply my research findings to application-oriented device configurations, and continue the effort of scaling up processes for MOF and MOF-based composite materials.

1.  Zhao, J. et al. Conformal and highly adsorptive metal–organic framework thin films via layer-by-layer growth on ALD-coated fiber mats. J. Mater. Chem. A 3,1458–1464 (2015).

2.  Zhao, J. et al. Highly Adsorptive, MOF-Functionalized Nonwoven Fiber Mats for Hazardous Gas Capture Enabled by Atomic Layer Deposition. Adv. Mater. Interfaces 1, (2014). doi: 10.1002/admi.201400040