Selective dye sorption and metal ion sensing behaviours of a new Cd-based MOF

Abstract

A Cd(II)-based metal–organic framework (MOF), [Cd(PDA)(L)₂] (PDA = 1,4-phenylenediacetate and L = 2,4,5-tri-4-pyridyl-1H-imidazole), 1, was synthesized by a solvothermal method and characterized by single-crystal X-ray diffraction, powder X-ray diffraction, Fourier transform infrared (FTIR) spectroscopy and thermogravimetric analysis (TGA). The single-crystal X-ray studies showed that the connectivity among Cd²⁺ ions, PDA and 2,4,5-tri-4-pyridyl-1H-imidazole ligands forms two-dimensional structures. The two-dimensional structures are arranged in an AAA….fashion to form a three-dimensional packing arrangement. Compound 1 showed selective and efficient sorption of the large anionic dye remazol brilliant blue R (RBBR) in aqueous medium, whereas it exhibited low sorption towards orange G (OG), methyl orange (MO), methylene blue (MB) and rhodamine B (RhB). Compound 1 also exhibited photoluminescence-based sensing behaviors towards Fe³⁺, Cr³⁺ and Al³⁺ ions in aqueous medium based on the luminescence quenching effect. However, photoluminescence studies in the presence of other common metal ions such as Cd²⁺, Cu²⁺, Mg²⁺, Ca²⁺, Co²⁺, K⁺, Mn²⁺, Pb²⁺, Zn²⁺, and Na⁺ in aqueous medium showed a negligible turn-on effect. The limits of detection for Fe³⁺, Cr³⁺, and Al³⁺ ions were 75, 257 and 107 ppb, respectively. Compound 1 also showed comparable gas sorption capacity towards CO₂ (64.5 cm³ g⁻¹), N₂ (72.25 cm³ g⁻¹) and H₂ (45.30 cm³ g⁻¹) at 1 bar.