Ligand-mediated band structure engineering and physiochemical properties of UiO-66 (Zr) metal-organic frameworks (MOFs) for solar-driven degradation of dye molecules

Abstract

In this study, Zr-based metal organic frameworks (Zr-MOFs) with different ligands such as terephthalic acid (UiO-66), 2-aminoterephthalic (UiO-66-NH2) and 2-methylimidazole (UiO‐66‐2M) are synthesized using hydrothermal method in order to investigate their ligand-dependent properties towards photocatalytic degradation of dyes molecules under solar light. The structural analysis by XRD revealed the fundamental cubic-topology of the UiO-66 structure for all the synthesized MOFs, and the presence of respective functional groups is confirmed via their ART-IR spectra. A spherical morphology with average size of ~80 and 200 nm are observed for UiO-66 and UiO-66-NH2 MOFs, respectively, whereas, bricks-like morphology is observed for UiO‐66‐2M, which is attributed to the binding habit of the respective ligands. Band gap energy of the synthesized UiO-66, UiO-66-NH2 and UiO‐66‐2M is estimated to be ~3.85, 2.92 and 2.77 eV, respectively. Among the synthesized MOFs, the photocatalytic degradation efficiency of UiO-66-NH2 MOFs is found to be greater towards the cationic rhodamine B (RhB) dye (~95% in 120 min), while it is relatively less efficient in degrading the anionic Congo red (CR) dye, (~64% in 120 min). The insights gained from the fundamental characterizations, Mott-Schottky, scavenger and electrochemical impedance analysis revealed that the amino-groups in UiO-66-NH2 MOFs offered the band edge potentials suitable for the effective generation of energetic radical species with the improved carrier delocalization, recombination resistance and charge transfer properties in the MOFs. The further parametric studies revealed that the UiO-66-NH2 MOFs can be effectively scaled-up and used for dye degradation applications in real-time.