Tuning the Structural Properties of Zirconium-Based Metal-Organic Framework Crystals for Environmental Applications

Abstract

The superior activity and properties of zirconium UiO-66 frameworks including their intriguing structural tunability, high porosity, and outstanding chemical and thermal stability have rendered them as epitome of metal-organic frameworks. In our study, we describe various synthesis and structural engineering techniques used for the construction of UiO-66 frameworks with an enhanced surface and adsorptive activities in addition to embellished nucleation and growth processes. In the first project, we report for the first time a novel method to synthesize one member of the UiO-66 family, namely UiO-66-(OH)2, via a reaction diffusion framework (RDF) process at room temperature. This method, known to be scalable, safe, rapid, climate friendly, and cost efficient provides control over the size and morphology of the UiO-66-(OH)2 crystals obtained which were never achieved nor reported before. Furthermore, several experimental parameters are explored and their effect on the particles’ size distribution and morphology is studied. In the second part of this thesis work, we report a systematic study that was done for the first time to examine the adsorption sites in UiO-66 frameworks for cationic and anionic contaminants found in water. For this reason, different structural engineering techniques were used to alter the properties of Zr-MOFs such as linker functionalization with different groups and defects creation to increase the density of active sites. Lead and cadmium are used as cationic contaminants whereas arsenate and selenite are used as anionic pollutants. As a result, the functionalization of the UiO-66 based structures with carboxylate groups increases the removal efficiency of Pb(II) cations by more than 70% and that of Cd(II) cations by more than 60%. Moreover, the defects created are demonstrated to be the preferred adsorption sites of the anion pollutants, As(V) and Se(IV), but diffusion limitations were encountered when using the functionalized structure indicating that unfunctionalized and defected UiO-66 framework is superior adsorbent for anions. Moreover, chemical adsorption is considered to be the predominant type of interaction between the adsorbents and the UiO-66-based adsorbents based on the isotherm data that were fitted into adsorption and kinetics models. This study helps give a comprehensive conclusion on the type of engineering for both the cluster and linker in order to maximize the performance of these materials for the decontamination of water from highly toxic materials.