Highly selective and sensitive detection of Hg2+, Cr2O72−, and nitrobenzene/2,4-dinitrophenol in water via two fluorescent Cd-CPs
Two novel luminescent cadmium coordination polymers (Cd-CPs), [Cd(TPA)(DIB)]n (1) and [Cd(TPA)(BIYB)]n (2), have been successfully designed and synthesized using Cd2+, deprotonated 3,3′-thiodipropionic acid (H2TPA), and 4,4-bis(imidazol-1-ylmethyl)biphenyl (BIYB) or 1,4-di(1H-imidazol-1-yl)benzene (DIB). CP 1 has a 3D structure with a new topology. CP 2 possesses a double layer 2D structure with two types of 1D tunnel. The fluorescence property application and mechanisms of the two Cd-CPs for detecting Hg2+, Cr2O72−, nitrobenzene (NB), or 2,4-dinitrophenol (2,4-DNP) have been researched. CPs 1–2 demonstrate good chemical stability, high sensitivity and selective responsive detection of Hg2+, Cr2O72−, NB, or 2,4-DNP. The high quenching percentages in dilute aqueous solutions were 98.5% (Hg2+, 1), 96.2% (Hg2+, 2), 98.5% (Cr2O72−, 1), 96.4% (Cr2O72−, 2), 99.6% (NB, 1) and 99.2% (2,4-DNP, 2). The detection limits were 2.1 × 10−7 (Hg2+, 1), 1.1 × 10−6 (Cr2O72−, 1), 2.7 × 10−7 (NB, 1), 1.9 × 10−7 (Hg2+, 2), 2.4 × 10−7 (Cr2O72−, 2), and 1.3 × 10−7 (2,4-DNP, 2) and are similar to the permissible limits set by the USEPA. The mechanism of Hg2+ luminescence quenching involves an interaction with the free thio sites of the CPs. The Cr2O72−, NB, and 2,4-DNP quenching mechanism involves the overlap of the absorption bands of the recognition materials with the excitation or emission bands of CPs 1–2. To the best of our knowledge, these are the best examples of CPs as probes for sensing Hg2+, Cr2O72−, NB, or 2,4-DNP.