(183v) Tuning Uio-66 Particle Size, Defectiveness, and Fluorescence Via Modulation of Water and Ligand Equivalents

UiO-66 is a zirconium(IV)-based metal-organic framework (MOF) comprised of six-metal clusters and six terephthalic acid ligands that has shown great promise for many applications because of its notable thermal and chemical stability. Because of this stability, as well as its high adsorption capacity, applications of UiO-66 range from gas storage to drug delivery. Current approaches for the synthesis of UiO-66 frequently utilize acid as a modulator to control the size of yielded nanoparticles; however, incorporation of this modulator results in missing terephthalic acid linkers in the UiO-66 structure, i.e. increased “defectiveness.” To date, there are no effective means to decouple UiO-66 nanoparticle size from defectiveness, limiting the tunability of this MOF for desired applications. To address this need for simultaneous control of size and defectiveness, we utilized an acid-free synthetic approach that modulated the molar amounts of water and ligand relative to the amount of zirconium(IV) metal present during synthesis. Use of these facile synthetic handles yielded highly crystalline UiO-66 nanoparticles with average particle diameters ranging from 20 to 120 nm and defectiveness ranging from 0 to 12%. Variation in particle defectiveness led to an over-estimation of particle size measurements obtained via dynamic light scattering (DLS). To correct for this over-estimation, we developed correlations between the hydrodynamic diameter determined via DLS and the geometric diameter determined via scanning electron microscopy (SEM). This correlation, the first of its kind for UiO-66, allows for estimation of geometric diameter knowing only the hydrodynamic diameter and defectiveness. Lastly, we observed fluorescence of non-functionalized UiO-66, which exhibits peak fluorescence at 390 nm following excitation at 280 nm. The peak fluorescence is maximized in larger, lower-defect particles. Overall, our synthetic approach utilizing quantified water content and molar equivalents of terephthalic acid ligand allow for a high degree of tunability of UiO-66 particle size, defectiveness, and fluorescence, which will expand and improve the applications of this MOF.