Aqueous-Phase Nanomolar Detection of Dichromate by a Recyclable Cd(II) Metal–Organic Framework

Abstract

A new Cd­(II)–organic framework with a quinoline-2,6-dicarboxylic acid (H2QDA) ligand having the formula {[Cd­(QDA)]·DMF·0.5H2O}n (1) was synthesized by heating a mixture of Cd­(ClO4)2·6H2O, H2QDA, concentrated HNO3, and DMF (N,N′-dimethylformamide) at 120 °C for 72 h. A single-crystal X-ray diffraction analysis confirmed that 1 has a rare ptr topology and Cd2+ attains highly distorted trigonal prismatic geometry with a CdO5N configuration. The as-synthesized compound 1 was activated by solvent exchange and drying at 100 °C for 24 h. By using analytical methods such as X-ray powder diffraction (XRPD), Fourier transform infrared (FT-IR), and thermogravimetric analysis (TGA), both 1 and its activated form (1′) were characterized. Compound 1′ exhibits good thermal stability, high water stability, and easy regeneration ability. The compound was used for the selective and sensitive detection of dichromate (Cr2O7 2–) in water via fluorescence quenching. The K SV and detection limit values for Cr2O7 2– in water for 1′ were found to be 9.65 × 104 M–1 and 81.6 nM (linear range: 0–1.2 μM), respectively. The compound also showed good recyclability and structural stability after the sensing experiment. Moreover, the quenching process was fast (30 s) in the presence of 3 mM aqueous Cr2O7 2– solution. The possible mechanism for the quenching effect of 1′ was also investigated. The compound is a promising fluorescent sensor by virtue of its great detection efficiency, reusability, and fast response rate.

Diamino group-functionalized Zr-based metal–organic framework for fluorescence sensing of free chlorine in the aqueous phase and Knoevenagel condensation

“…This non-linearity with the increase in concentration indicates the presence of both the static and dynamic quenching behaviour of DUT-52-(NH 2 ) 2 -1′ towards ClO − . 41 The reason behind this deviation may be due to the self-absorption or an energy-transfer process. 45 The calculated K SV value is 5.13 × 10 4 M −1 , which is comparable with the previously reported ClO − sensors based on MOF materials.…”

“…The fluorescence quenching efficiencies were calculated with the help of a well-established formula (1- I f / I i ) × 100%, where I i is the initial fluorescence emission intensity before inclusion of any analyte and I f is the final (after inclusion of an analyte) fluorescence emission intensity. 41…”

“…To develop any kind of sensing system, selectivity is an important criterion that needs to be maintained. To examine the sensing selectivity towards ClO − , the fluorescence responses of DUT-52-(NH 2 ) 2 -1′ towards various potentially interfering metal ions (5 mM) and common anionic species (5 mM) including Fe 3+ , Co 2+ , Na + , Ni 2+ , Cd 2+ , Cu 2+ , Zn 2+ , Cr 3+ , Mg 2+ , K + , Hg 2+ , Al 3+ , Pb 2+ , Mn 2+ , F − , I − , Cl − , CO 41 The reason behind this deviation may be due to the self-absorption or an energy-transfer process. 45 The calculated K SV value is 5.13 × 10 4 M −1 , which is comparable with the previously reported ClO − sensors based on MOF materials.…”

Series of TM-OFs as a Platform for Efficient Catalysis and Multifunctional Luminescence Sensing

“…On comparison with the maximum emission peak of H 3 DCPN, the emission peak positions red-shifted 58 nm (2) and 61 nm (3), respectively, which may be attributed to the additional metalto-ligand charge transfer states. 31,32 After they were dispersed in DMF solvent, the emission peaks of 2 and 3 were at 430 and 434 nm (λ = 327 nm), respectively, which might attributed to an intraligand π* → n or π* → π electronic transition within the deprotonated ligand DCPN 3− from compounds 2 and 3 (Figure S14). The fluorescence emission intensity of 2 was enhanced about 1.4 times compared with H 3 DCPN ligands, which may be attributed to the electron transfer within the ligand.…”

“…However, the poor water stability of Cd-MOFs greatly limits their application for the detection of contaminants in water. Although researchers have taken many measures to enhance the chemical stability of Cd-MOFs, few stable Cd-MOFs have been successfully obtained. − Therefore, the synthesis of Cd-MOFs with high chemical stability in water is a challenging task.…”