(337m) Clarifying the Stability and Reactivity of Metal-Organic Frameworks Constructed from Zirconium and Iron in Aqueous Pollutant Degradation

Increased water consumption with concomitant rise in water pollution drives a continued effort to enhance the efficacy of wastewater treatment processes. Metal-organic frameworks (MOFs), consisting of highly tunable networks of organic linkers coordinated to metal-containing nodes, possess potential in both adsorptive and (photo)catalytic removal of aqueous pollutants. MOFs made from relatively low cost metals, such as zirconium(Zr)- and iron(Fe)-based structures, are attractive and have demonstrated water pollutant degradation.[1] However, their regimes of stability in wastewater treatment remain less well defined. This work focuses on hydrogen peroxide oxidation of methylene blue (MB), a medication and dye, to probe connections between structure and function of Zr- and Fe-MOFs in the catalytic removal of pollutants pertinent to industrial effluent.

Under excess oxidant conditions, MIL-101(Fe) demonstrates a lumped first order rate constant (normalized by total Fe) over three times that of MOF-235, a contrasting Fe-terephthalate with the same secondary building units in different crystallographic arrangement (MTN zeotype vs. acs topology, respectively), [2,3] possibly as a result of differences in the ligands coordinated to their metal nodes. However, significant structural changes are evident, including loss in crystallinity and apparent iron leaching. Moreover, the dominant role of solvent interactions in causing these changes is implicated by leaching occurring when catalyst is exposed to water alone. In contrast, Zr-based UiO-67 retains its long-range order after exposure to water with appropriate exchange with low surface tension solvent. This work shows that addition of Fe-oxide nanoparticles to UiO-67 via incipient wetness impregnation decreases the material band gap energy, allowing for enhanced photocatalytic degradation of MB at lower energy wavelengths. Continued development of hybrid structures using earth-abundant metal source MOFs demonstrates a promising route forward in refining their structure for use in wastewater treatment applications.

Research Interests

Focusing on MOF synthesis and use on this and a related project for small molecule drug transformations, I have formed a strong skillset in materials characterization and kinetic evaluation of catalysts over the course of my graduate career. This builds off the experience I gained in process design and construction for the food and beverage industry at the Dennis Group prior to graduate school, which has helped ground my research perspective in long-term application outlook. In the future, I aim to harness these skills in the development of greener chemical products and processing methods in industry.

1. https://doi.org/10.1021/acsami.7b02563
2. https://doi.org/10.1021/cm051870o
3. https://doi.org/1039/d1mh01663f