SYNTHESIS AND CHARACTERIZATION OF HIERARCHICAL AL-MOFS FOR CHROMIUM(VI) METAL ION ADSORPTION

• Main Author: Hidayati, Wahyu
• Format: Final Project
• Language: Indonesia
• Subjects: Kimia
• Online Access: https://digilib.itb.ac.id/gdl/view/82822
• Institution: Institut Teknologi Bandung

Metal Organic Frameworks (MOFs) are porous coordination polymers based on metal and organic components that have developed rapidly over the past decades. Due to their adjustable pore sizes, high surface areas, and open active sites, MOFs exhibit versatile properties. However, MOFs with a single pore size face challenges when the analytes have varying sizes. Therefore, hierarchical MOFs have been developed with a wide distribution of pore sizes (heterogeneous) ranging from micropores (less than 2 nm), mesopores (2-50 nm), to macropores (more than 50 nm). The formation of hierarchical MOFs was achieved by mixing solutions of the ligands 2,2’-bipyridine-5,5’-dicarboxylic acid and 4,4’-biphenyl-dicarboxylic acid with solution of Al3+ metal ions with molar ratios of the ligands in the mixture used for synthesis being 0.2 and 0.5. Al-MOFs 0.2 uses a bpydc ligand ratio of 0.2 (bpydc:bpdc = 2:8) while Al-MOFs 0.5 uses a bpydc ligand ratio of 0.5 (bpydc:bpdc = 5:5). Both are synthesized via solvothermal synthesis method for 24 hours at 120 °C. The morphology of the obtained Al-MOFs is flower-like, which is a combined morphology of the reference MOFs, namely MOFs DUT-5 which uses only the 4,4’-biphenyl-dicarboxylic acid ligand and MOFs-253 which uses only the 2,2’-bipyridine-5,5’-dicarboxylic acid ligand. Based on PXRD results, there were two diffractogram dominant peaks at 2???? 6.01° and 12.08°. FTIR results confirmed a changes in the absorption of the C=O functional group, indicating that the ligands were bonded with the Al metal. From the N2 adsorption isotherm results using the BET method, Al MOFs 0.2 had a larger surface area of 64.6242 m2/g compared to Al-MOFs 0.5, which had a surface area of 43.4826 m2/g. Using the BJH method, the pore size distribution was found to be dominated by micropores and mesopores. Hierarchical Al-MOFs were tested for the adsorption of Cr(VI) metal ions in water, which have different species and sizes. These species include Cr2O72-, CrO42-, and HCrO4-. The hierarchical Al-MOFs were tested for the adsorption of Cr(VI) metal ions. The optimal adsorption conditions for Cr(VI) metal ions were found at pH 6 for Al-MOFs with a ratio of 0.2 and at pH 7 for Al-MOFs with a ratio of 0.5, with an optimal contact time of 90 minutes. The obtained adsorption kinetics study fit the pseudo second-order kinetic model. The obtained adsorption isotherm was the Langmuir isotherm model, with maximum adsorption capacities of 79.3857 mg/g for Al-MOFs with a 0.2 ratio and 63.3014 mg/g for Al-MOFs with a 0.5 ratio. Al-MOFs with a 0.2 ratio exhibited better adsorption capabilities compared to Al-MOFs with a 0.5 ratio, but both showed potential for Cr(VI) metal ion adsorption.