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

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.