Direct synthesis of sulfonic acid functionalized zirconium metal-organic framework

This study successfully develops a direct synthesis protocol for sulfonic acid functionalized four carbons (C4) based Zr-Metal-Organic Frameworks (MOFs), resulting in the formation of two MOFs one with a defective UiO-type and a new structure named as UiS-1 (Universitetet i Stavanger). The new phase is formed in presence of modulators and at the excess linker to metal ratio (L:M) of 4:1. The synthesis with 40 equivalences of acetic acid and L:M ratio of 4:1 exhibits a similar pH, highlighting the role of H⁺ and, consequently pH of the reaction. The tuning of pH plays a crucial role in determining the formation of these distinct MOF structures, emphasizing the importance of precise control over synthetic conditions. The ZrSSA MOF (without modulator) aligns with the well-known UiO-type MOF, while UiS-1-40AA forms UiS-1 structure. UiS-1 is a tetragonal structure, previously unreported, is further elucidated in this research. This UiS-1 structure is characterized by lattice parameters a = b = 13.5233(4) Å, c = 16.3543(9) Å and angles α = β = γ = 90°. The UiS-1 structure is characterized using in-situ techniques and compositional analysis to assess, its properties and structural integrity, additional methods employed to verify the physical, chemical, and mechanical stability of UiS-1. These analyses demonstrate that UiS-1 maintains its structural integrity under various conditions, making sulfosuccinic acid a robust building block for designing of MOFs. Furthermore, the study explores the potential applications of the synthesized MOFs in gas adsorption. The adsorption capabilities of the MOFs were tested using CO₂, H₂O, and NH₃ gases, showcasing the material's efficiency and selectivity in capturing these molecules. The CO₂ adsorption results indicate that the functionalized Zr-MOFs, particularly ZrSSA and UiS-1-40AA shows 1.79 mmol g⁻¹ (7.88 wt%), and 1.46 mmol g⁻¹ (6.42 wt%), respectively at 1 bar and 273 K. This high CO₂ uptake per m² could be attributed to the high number of functional groups present in the structures.