Dual modifications of sensitizers and lanthanide ions on a two-dimensional zirconium-based metal–organic framework for photoluminescent detection

Abstract

A two-dimensional (2D) zirconium-based metal–organic framework (Zr-MOF) with abundant terminal –OH/–OH₂ groups on its nodes, ZrBTB (BTB = 1,3,5-tris(4-carboxyphenyl)benzene), is utilized as a platform for dual post-synthetic modifications (PSM) to immobilize both the benzophenone-based photosensitizer (benzophenone-4,4′-dicarboxylate, bzpdc) and terbium ions onto the 2D Zr-MOF molecular sheets. Terbium ions are installed on the 2D Zr-MOF at various temperatures to adjust the loading of terbium ions on the 2D Zr-MOF while preserving the loading of the photosensitizer. The crystallinity, morphology, porosity, and loadings of both bzpdc ligands and terbium ions are characterized for each material, and the coordinating locations of terbium ions in the Zr-MOF structure are investigated. The photoluminescence (PL) properties of these materials are then examined. Since the installed bzpdc ligand can induce a highly efficient energy transfer to the neighbouring terbium ion upon excitation, the obtained material after dual PSM (ZrBTB-bzpdc-Tb-120) can show strong PL emissions of terbium ions upon the excitation of the bzpdc ligand at 355 nm, with a PL quantum yield of 5.04%. It is more advantageous than the 2D Zr-MOF solely functionalized with terbium ions, which can only exhibit similar emissions upon the excitation of the BTB linker at a less friendly wavelength of 310 nm, with a lower PL quantum yield of 2.94%. Owing to the high chemical stability as well as good dispersity of the luminescent ZrBTB-bzpdc-Tb-120 in water, its performances in selective PL sensing of Fe(III) ions present in aqueous solutions are investigated.