Surface-decorated porphyrinic zirconium-based metal–organic frameworks (MOFs) using post-synthetic self-assembly for photodegradation of methyl orange dye

Abstract

We report herein the surface decoration of a water-soluble free-base porphyrin, namely, 5,10,15,20-tetrakis(1-methyl-4-pyridinio)porphyrin-tetra(p-toluenesulfonate) (H₂TMPyP), over three different zirconium-based metal–organic frameworks of different linker structure and functionality; namely UiO66, UiO66-NH₂, and MIP-202, via self-assembly. The synthesized MOFs along with the resulting complexes have been characterized via spectroscopic and analytical techniques (XRD, FT-IR, TEM, N₂ adsorption/desorption, and laser scanning confocal microscopy). The self-assembly of H₂TMPyP with the examined three MOFs was observed by using the steady-state absorption and fluorescence, as well as the fluorescence lifetime studies. It was evident that the highest complex interaction was recorded between porphyrin and UiO-66-NH₂ compared with the lowest interactions between porphyrin and MIP-202. This is in good agreement with the high surface area and pore volume of UiO-66 (1100 m² g⁻¹ and 0.68 cm³ g⁻¹) and compared to that of MIP-202 (94 m² g⁻¹ and 0.26 cm³ g⁻¹). The photocatalytic activities of the three porphyrin entities immobilized zirconium-based MOFs were compared toward methyl orange dye degradation from aqueous solution under visible light irradiation (λ_ex = 430 nm). The photocatalytic studies render the fabrication of the self-assembled H₂TMPyP@UiO-66-NH₂ composite as a promising material for dye degradation from polluted wastewater.