A Zr-Based Metal–Organic Framework with a DUT-52 Structure Containing a Trifluoroacetamido-Functionalized Linker for Aqueous Phase Fluorescence Sensing of the Cyanide Ion and Aerobic Oxidation of Cyclohexane

• Published in: Inorganic chemistry 2021-04, Vol.60 (7), p.4539-4550
• Main Authors: Gogoi, Chiranjib, Nagarjun, Nagarathinam, Roy, Shubasis, Mostakim, SK, Volkmer, Dirk, Dhakshinamoorthy, Amarajothi, Biswas, Shyam
• Format: Article
• Language: English
• ISSN: 0020-1669; 1520-510X
• DOI: 10.1021/acs.inorgchem.0c03472

A zirconium (Zr) metal–organic framework having a DUT-52 (DUT stands for Dresden University of Technology) structure with face-centered cubic topology and bearing the rigid 1-(2,2,2-trifluoroacetamido) naphthalene-3,7-dicarboxylic acid (H2NDC-NHCOCF3) ligand was prepared, and its solid structure was characterized with the help of the X-ray powder diffraction (XRPD) technique. Other characterization methods like thermogravimetric analysis (TGA) and Fourier transform infrared (FT-IR) spectroscopy were applied to verify the phase purity of the compound. In order to get the solvent-free compound (1′), 1 was stirred with methanol for overnight and subsequently heated at 100 °C overnight under vacuum. As-synthesized (1) and activated (1′) compounds are thermally stable up to 300 °C. The Brunsuer Emmett-Teller (BET) surface area of 1′ was found to be 1105 m2 g–1. Fluorescence titration experiments showed that 1′ exhibits highly selective and sensitive fluorescence turn-on behavior toward cyanide (CN–) anion. The interference experiments suggested that other anions did not interfere in the detection of CN–. Moreover, a very short response time (2 min) was shown by probe 1′ for CN– detection. The detection limit was found to be 0.23 μM. 1′ can also be effectively used for CN– detection in real water samples. The mechanism for the selective detection of CN– was investigated systematically. Furthermore, the aerobic oxidation of cyclohexane was performed with 1′ under mild reaction conditions, observing higher activity than the analogous DUT-52 solid under identical conditions. These experiments clearly indicate the benefits of hydrophobic cavities of 1′ in achieving higher conversion of cyclohexane and cyclohexanol/cyclohexanone selectivity. Catalyst stability was proved by two consecutive reuses and comparing the structural integrity of 1′ before and after reuses by the XRPD study.