Synthesis and characterization of zirconium-based metal-organic gel/metal-organic framework for chromium removal

• Main Author: Anis Muneerah Shaiful Bahari, Ms.
• Format: text::Thesis
• Language: English
• Published: 2023
• Subjects: Zirconium-based metal-organic gel/metal-organic framework

Metal-Organic Framework materials (MOFs) are famous for their unique structure, large chemical variation, high surface area and tunable pores. Nevertheless, MOF has a significant drawback, such as it came in the form of microcrystalline powder. MetalOrganic Gel (MOG) came as a new strategy to overcome MOFs' disadvantage as microcrystalline powder. However, the synthesis method in producing MOF and MOG usually uses toxic chemicals that can be dangerous to the environment and humans. Human exposure to dimethylformamide and strong acid such as hydrochloric acid (HCl) can irritate the eyes, lungs and skin. This study is an initiative in producing green MOF and MOG. Zr-MOG and Zr-MOF (UiO-66) without HCl were synthesized in this research. Zirconium nitrate oxyhydrate and dicarboxylic acid were used to form a soft supramolecular structure in a sol–gel-like processing method. Amorphous ZrMOG were successfully synthesized without chloride ion and toxic modulators for the first time to develop a sustainable and green approach. On the other hand, UiO-66 with 12-connected [Zr6O6(OH)4]12+ secondary building block forming octahedral structure was successfully synthesized for the first time without using chloride ions (Cl-) at room temperature in a facile approach. The as-synthesized Zr-MOG and UiO-66 were characterized to elucidate the resulting physical structure and elemental bondings. Synthesized Zr-MOG xerogel exhibited three different X-ray diffraction (XRD) patterns categories: fully amorphous, 1:1 ratio and 1:4 ratio of amorphous and crystalline structure. At the same time, all UiO-66 exhibited the XRD peaks corresponding to (111), (002) and (022) reflection planes suggesting the successful formation of UiO-66. XPS characterizations suggested that the Zr atoms and organic linker bonding in Zr-MOG were intact, forming an amorphous MOG network. The characterizations results suggested that the new Zr-MOG synthesized using nitratebased Zr salt (Zr(NO3)2) and green sol-gel method without using HCl as modulator was successful. Furthermore, the performance of UiO-66 and Zr-MOG were investigated. The result suggested that high relative crystallinity (RC) in UiO-66 values decrease the overall active sites for photoreduction reaction to occur, resulting in less photoreduction efficiency. On the other hand, hybrid structure Zr-MOG (ZrMOG 5) shows the highest Cr(VI) ion reduction with 87% removal in 120 min due to two different phases (amorphous and crystalline) in the structure.