Chemistry PhD – Final Defense — Jiahong Li, Graduate Student

About the event

Speaker:  Jiahong Li

Group: Qiang Zhang

Title: Carboxylate-based Metal–organic frameworks: Synthesis, Thermodynamic Analysis, and Catalytic Activity

Abstract: Metal-organic frameworks (MOFs) are a class of coordination polymers composed of inorganic metal ions or clusters and organic linkers. Such materials became popular due to their distinctive properties, including large surface areas, high porosities, high adaptabilities, and diverse functionalities, which allows them to have potential applications across many different fields.

Over the last three decades, more than 90,000 MOFs were created. The preparation methods of MOFs evolved from the initial stages of simply obtaining the material to realizations of more sustainable syntheses. However, obtaining phase-pure products remains a challenge. In our work, a solvent-free, green synthetic method was developed for the aluminum trimesates (Al-BTCs) system which generates three distinct phases, MIL-96, MIL-100, and MIL-110, from the same metal and ligand precursors. We then conducted a series of experiments to investigate the formation of Al-BTCs from an energetic perspective. The results showed that the linker stabilization of the Al-polyhedra is an important factor driving the formation of the Al-BTC frameworks, with higher coordinative metal-polyhedra attaining more enthalpic stabilization from the coordinated ligands.

Furthermore, solvent-free synthesized MIL-96 was selected as a support for Mn²⁺ dopant creating a simple and affordable catalyst, Mn(Ⅱ)@MIL-96(Al). The catalytic value of Mn(Ⅱ)@MIL-96(Al) was assessed with the aerobic olefin epoxidation reaction under mild conditions. The results demonstrated high selectivity and efficiency and of the catalyst toward the production of epoxides.

Finally, an up-scaling modulator-free synthetic approach was utilized to produce functionalized hierarchically porous UiO-66 (HP-UiO-66) materials. The defect sites, mesopores, and different ratios of mixed ligands were introduced to enhance the catalytic activity of the HP-UiO-66s. To evaluate the catalytic performance of seven prepared X:Y-HP-UiO-66 (X:Y = molar ratio of NH₂BDC:BDC) derivatives with different Lewis acid-base functionalities, we employed CO₂ cycloaddition with organic epoxide as a model reaction. The results showed excellent catalytic performance, which provides promising insight for the rational design of MOFs via linker functionalization for more effective catalytic applications.