Highly luminescent Ln-MOFs based on 1,3-adamantanediacetic acid as bifunctional sensor

Abstract

A series of lanthanide metal-organic-frameworks (Ln-MOFs) are synthesized under mild hydrothermal condition by introducing the ligand of 1,3-adamantanediacetic acid (H2ADA). They are three dimentional (3D) structures and have the formula of [Ln(ADA)1.5(phen)]n (Ln3+=Eu3+1a, Gd3+1b, Tb3+1c, La3+1d, Ce3+1e, Pr3+1f, Nd3+1g, Y3+1h; phen=1,10-phenanthroline). These Ln-MOFs are fully characterized by single-crystal X-ray diffraction, PXRD, TGA, EA and FT-IR. Luminescence properties, including luminescence spectra, luminescence decay lifetimes and luminescence quantum yields (QYs) are analyzed in detail. Eu3+ complex of 1a shows highly luminescence QYs of 58.61%, which due to that the triplet state of phen competes well with the excited emission state of Eu3+. Further investigation reveals that 1a is a bifunctional sensor, which can be used as a turn-off luminescence sensor for detecting Ni2+ and turn-on luminescence sensor for probing Val at the same time. Interestingly, the limit of detect (LOD) for sensing Ni2+ is an ultrahigh sensitive value of 1.0×10−9M (5.9×10−5mg/L), which is lower than the Chinese environmental quality standard (0.5mg/L of total Ni2+ content, GB25467-2010), and it is the most sensitive chemosensor for detecting Ni2+, to the best of our knowledge. Investigation also reveals there is a good linear relationship between luminescence intensity and the concentration of Ni2+ in 0.2–0.6μM. The sensing mechanism for detecting Ni2+ and Val are also discussed.