Synthesis of High-Quality Mg-MOF-74 Thin Films via Vapor-Assisted Crystallization

Ki-Joong Kim; Jeffrey T Culp; Paul R Ohodnicki; Praveen K Thallapally; Jinhui Tao

doi:10.1021/acsami.1c12000

Synthesis of High-Quality Mg-MOF-74 Thin Films via Vapor-Assisted Crystallization

ACS Appl Mater Interfaces. 2021 Jul 28;13(29):35223-35231. doi: 10.1021/acsami.1c12000. Epub 2021 Jul 13.

Authors

Ki-Joong Kim^{1

2}, Jeffrey T Culp^{1

2}, Paul R Ohodnicki¹, Praveen K Thallapally³, Jinhui Tao³

Affiliations

¹ National Energy Technology Laboratory, 626 Cochrans Mill Road, P.O. Box 10940, Pittsburgh, Pennsylvania 15236-0940, United States.
² NETL Support Contractor, 626 Cochrans Mill Road, P.O. Box 10940, Pittsburgh, Pennsylvania 15236-0940, United States.
³ Pacific Northwest National Laboratory, Richland, Washington 99352, United States.

PMID: 34254786
DOI: 10.1021/acsami.1c12000

Abstract

The unique features of metal-organic frameworks (MOFs), such as their large surface areas and diversity of structures, make them suitable for a broad range of applications including storage, separation, and sensing of gases. Among all the MOFs, Mg-MOF-74 with the highest CO₂ uptake at 1 bar and 25 °C would be particularly beneficial for CO₂-related applications. One of the most critical enabling technologies for implementing Mg-MOF-74 is the preparation of dense and continuous films that would maximize the sorption behaviors. However, Mg-MOF-74 thin films present significant challenges in demonstrating large-scale coatings. Herein, we demonstrate for the first time high-quality Mg-MOF-74 films synthesized via a vapor-assisted crystallization (VAC) process. The VAC process described herein provides dense and highly crystalline layers of the Mg-MOF-74 thin film with a low coefficient of variation of film thickness below 7%. By minimizing the solvent use, the VAC process is also more environmentally friendly than conventional techniques. In this work, we first optimized a precursor solution for the VAC process and then investigated the effects of synthesis temperature, time, and droplet volume on the growth, crystallinity, and thickness of VAC Mg-MOF-74 films. The porosity of the MOF film was assessed by measuring the CO₂ uptake at room temperature and 1 bar. The obtained VAC Mg-MOF-74 films possess a well-defined microporosity, as deduced from CO₂ adsorption studies via quartz crystal microbalance (QCM) and comparison with bulk Mg-MOF-74 reference data. Furthermore, CO₂ cyclic adsorption-desorption experiments on the VAC Mg-MOF-74 films showed scaled uptakes to a wide range of CO₂ concentration without showing significant variations in the baseline. We specifically demonstrate how the film's quality of the MOF affects adsorption behavior of CO₂ on VAC Mg-MOF-74 and drop-cast Mg-MOF-74 films.

Keywords: CO2 uptake; Mg-MOF-74; metal-organic framework thin films; quartz crystal microbalance; vapor-assisted crystallization.