Adsorption of Humic Acid from Water Using Metal-Organic Frameworks (MOFs): An Effective Removal Strategy

Abstract

The escalating presence of humic acid (HA) in aquatic systems poses significant ecological and potable water treatment challenges, altering the color, taste, and odor of water and fueling algal blooms that deplete oxygen levels to the detriment of aquatic life. Traditional techniques like coagulation-flocculation, membrane filtration, oxidation fall short in efficiency due to its small fraction of HA, Humic acids (HAs) can interact with various organic and inorganic substances, affecting their characteristics and behavior in water. These interactions can influence the efficiency of water treatment processes like adsorption and coagulation. Specifically, HAs may compete with other contaminants for treatment sites or alter the chemical conditions of the treatment processes, impacting their effectiveness. This thesis confronts the pervasive issue of HA contamination by leveraging the advanced properties of metal-organic frameworks (MOFs). In this work, four representative MOFs are synthesized and well characterized. Then, their capability to enhance coagulation processes in water for HA and HA-kaolin treatment are detailed evaluated. The findings from this research extend beyond academic curiosity, offering actionable insights for water treatment facilities and environmental management agencies. The synthesis of MOFs which are UiO-66(Zr), MIL-100(Fe), ZIF-8, and Al-fum. Each MOFs have been applied to remove HA by adsorption under different condition, effect of contact time, effect of initial pH, effect of adsorbent dosage. After adsorption experiment, MOF samples prepared to dry and went through characterization. Removal of HA by MOF adsorption showed UiO-66(Zr) and MIL-100(Fe) examined shortest reaching equilibrium state with 10-15 min, however, ZIF-8 and Al-fum gradually reached equilibrium state after 60 min. Among various pH conditions, UiO-66(Zr) and MIL-100(Fe) showed the highest adsorption capacity under acidic conditions, while ZIF-8 excelled at neutral pH, and Al-fum exhibited the highest adsorption capacity under both acidic and basic conditions. ZIF-8 has the highest adsorption capacity among the MOFs with capacity of 754 mg/g. MOF after adsorption samples went through characterizations and their remained characteristics indicating the adsorption not affected the structure of the MOFs.