Enhanced carbon dioxide adsorption performance of UiO-66-SO3H with a mixed ligand strategy

In this work, a sulfonated UiO-66 was synthesized and modified with a mixed ligand strategy using 2-amino terephthalic acid as a second linker. The X-ray diffraction (XRD) diffractogram shows a transition from an amorphous to a crystalline pattern with the addition of a second linker. The Fourier transforms infrared spectroscopy spectra show the presence of new peaks at 1255, 1382, and 1426 cm-1, which refer to N-H and C-N stretching. All the mixed ligand samples showed stable thermal stability as the pristine UiO-66-SO3H sample. The field emission scanning electron microscopy analysis also showed a morphological change from a round-like shape (UiO-66-SO3H) to a triangular-based pyramid shape (UiO-66-SO3H-NH2-0.85). The nitrogen physisorption analyses showed a significant increase in the BET surface area of UiO-66-SO3H-NH2-0.85 (706 m2/g) from UiO-66-SO3H (16 m2/g). The CO2-TPD results demonstrated that the greater formation of medium basic sites (monodentate carbonate and bidentate carbonate species) is due to the increase in the amount of the second linker. Furthermore, the UiO-66-SO3H-NH2-0.85 showed CO2 adsorption of 2.17 mmol/g, five times higher than UiO-66-SO3H (0.43 mmol/g). Both samples also showed excellent recyclability up to ten cycles. After being reused for ten cycles, the sample preserved the characteristics of the XRD pattern and crystallinity, functional groups, and thermal stability. For the water and pH stability studies, UiO-66-SO3H and UiO-66-SO3H-NH2-0.85 maintained the original XRD patterns, a high BET surface area, and good CO2 adsorption in water and acid environments.