Metal-organic frameworks (MOFs) have received a great deal of interest because they exhibit significantly greater porosity, diversity and multiplicity compared with traditional porous materials. Moreover, they have unique catalytic properties and chemical moieties, which expand the horizons of their possible application. Already, MOFs have shown promise in applications such as drug delivery, sensing and separations; however, nanoscale MOF dispersion can be challenging. It is widely acknowledged that MOF dispersion is important: in drug delivery, MOF size is critical in determining drug transport and cell uptake; in sensing, making high-quality optical films via coating techniques enables rapid photometric detection; and in separation, non-selective defect formation from MOF aggregates is an Achilles heel for mixed matrix membrane fabrication. To date, many authors have either found a simple dispersion method that suited their study via trial-and-error or ignored the aggregation problem altogether. However, applying a theoretical framework would expedite the trial-and-error approach and enable applications that are impeded by MOF aggregation. This work explored such a theoretical framework by first taking a look at the classic DLVO interactions of a MOF, MIL-101, for the first time. Optical-quality, sub-micron films of MIL-101 were synthesized via dip coating and characterized with environmental spectroscopic ellipsometry to obtain Hamaker constants of MIL-101 in select solvents. These data were combined with zeta potential and dielectric constant data to develop a correlation between the critical point of aggregation and the classic DLVO interactions of MIL-101 in select solvents. The assumptions, successes and limitations of this approach will be discussed. One practical limitation revealed by this work was that MIL-101 suspension in low dielectric constant solvents was impossible. To ameliorate this challenge, MIL-101 was post-synthetically modified to enhance its suspension by at least tenfold in such environments by adding steric repulsion, which can be described by an extended DLVO model. This technique is advantageous over the use of surfactants because it enables the dry storage and transportation of facilely suspended MIL-101 particles. These modified particles were thoroughly characterized to determine the impacts to MIL-101’s structure and the uniformity of the modification.

Extended DLVO interactions of a metal-organic framework: Implications on colloidal dispersion

256th National Meeting (2018)

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