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

Abstract

Three novel porous transition-metal–organic frameworks (TM-OFs), formulated as [Co3(DCPN)2­(μ2-OH2)4­(H2O)4]­(DMF)2 (1), [Cd3(DCPN)2­(μ2-OH2)4­(H2O)4]­(DMF)2 (2), and [CdK­(DCPN)­(DMA)] (3), have been successfully prepared via solvothermal conditions based on a 5-(3′,6′-dicarboxylic phenyl) nicotinic carboxylic acid (H3DCPN) ligand. 1 and 2 both have the same porous 3D network structure with the point symbol of {410·614·84}·{45·6}2 based on trinuclear ({Co3} or {Cd3}) clusters, indicating a one-dimensional porous channel, and possess excellent water and thermal stability; 3 also displays a porous 3D network structure with a 4-connected sra topology based on the heteronuclear metal cluster {CdK}. Complex 1 can be used to load Pd nanoparticles (Pd NPs) via a wetness impregnation strategy to obtain Pd@1. The reduction of nitrophenols (2-NP, 3-NP, 4-NP) by Pd@1 in aqueous solution shows outstanding conversion, excellent rate constants (k), and remarkable cycling stability due to the synergistic effect of complex 1 and Pd NPs. Luminescence sensing tests confirmed that 2 is a reliable multifunctional chemical sensor with high selectivity and sensitivity for low concentrations of Fe3+, Cr2O7 2–, CPFX, and NFX. Specifically, 2 shows a fluorescence enhancement behavior toward fluoroquinolone antibiotics (CPFX and NFX), which has not been reported previously in the literature. Moreover, the rational mechanism of fluorescence sensing was also systematically investigated by various detection means and theoretical calculations.

Two-Dimensional Lanthanide Metal–Organic Frameworks as a Platform for Sensing Pollutant and Nitrophenols Reduction

“…In addition, the lowest record limit of detection (LOD) of LCUH-105 for sensing NFX was calculated to be 0.375 μM by using the equation 3σ/ k (σ is the standard deviation of ten blank tests for the fluorescence intensity of LCUH-105 , k is the slope of the linear relationship between fluorescence intensity and concentration). Except for extraordinary high selectivity, LCUH-105 also indicated high detection sensitivity for sensing NFX, which is equivalent approximately to the sensing ability of other reported MOFs. − It is worth noting that the fluorescence sensor LCUH-105 can realize the naked eye detection of trace NFX in water.…”

“…Thus, the Pd NPs@ LCUH-104 catalytic activity for NPs followed the order of 3-NP > 2-NP > 4-NP, which can be ascribed to their different electron cloud densities of nitro groups in different NP molecules. Because the distance between −OH and −NO 2 is shorter for 2-NP than that of 4-NP, the inductive effect of 2-NP is stronger than that of 4-NP, so 2-NP shows higher reactivity than 4-NP . In contrast, there exist inductive effect without conjugation effect in the 3-NP molecule, which made it easier to gain electrons.…”

“…The emission peak of LCUH-105 is slightly different in different solvents, which might be attributed to the solvent effects. There exist abundant tetrazole rings, carboxyl, and aromatic rings in the frameworks, so many weak interactions between the MOF skeleton and different solvents can be formed including hydrogen bonding and π···π stacking, which may lead to obvious changes in emission spectra . Meanwhile, due to the structure of LCUH-105 is extremely stable in aqueous solution, it can be utilized to detect of harmful substances in actual wastewater.…”

“…Among the fluorescent sensing materials, porous luminescent MOFs (LMOFs) is one of prevalent and efficient material and they have been used for fluorescence sensing applications because of their superior fluorescence properties. , The lanthanide-based MOFs (Ln-MOFs) have an excellent sensing performance during the detection process, and thereby, they have become unique luminescence materials for the significant application in the detection of water pollutant. − Herein, LCUH-105 exhibits an excellent fluorescence behavior due to its high selectivity and sensitivity for the detection of NFX, especially its fluorescence response mode is fluorescence enhancement (turn-on) during the detection process. As we well known, most of MOFs indicated fluorescence quenching mode during the process of detecting antibiotics, − while few fluorescence enhancement examples are used to detect antibiotics. − All the nitrogen atoms of TZI 3– in LCUH-105 did not participate in the coordination with metal ions; meanwhile, the tetrazole group has one negative charge, which made it to easily form hydrogen bonds with antibiotics. Therefore, the characteristic of ligand TZI 3– in LCUH-105 make the fluorescence resonance energy transfer easy to complete from antibiotics to ligand, resulting in the fluorescence enhancement (turn on) behavior toward norfloxacin (NFX).…”

Metal–organic framework (MOF)-based fluorescence “turn-on” sensors

“…MOFs have also been used for the detection of antibiotic molecules. [121][122][123] With the increase in the population globally, the intake of antibiotics has significantly increased, which has a negative effect on the environment. 124 Also, the side effects associated with antibiotics negatively impact human health and cause several diseases.…”