Metal-Organic Framework (MOF) Derived Recyclable, Superhydrophobic Composite of Cotton Fabrics for the Facile Removal of Oil Spills.

Marine oil spill cleanup is one of the major challenges in recent years due to its detrimental effect on our ecosystem. Hence, the development of new superhydrophobic oil absorbent materials is in high demand. The third-generation porous materials, namely metal-organic frameworks (MOFs), have drawn great attention due to their fascinating properties. In this work, a superhydrophobic MOF with UiO-66 (SH-UiO-66) topology was synthesized strategically with a new fluorinated dicarboxylate linker to absorb oil selectively from water. The fully characterized superhydrophobic MOF showed extreme water repellency with an advancing water contact angle (WCA) of 160° with a contact angle hysteresis (CAH) of 8°. The newly synthesized porous MOF (SBET = 873 m2 g-1) material with high WCA found its promising application in oil/water separation. The superhydrophobic SH-UiO-66 MOF was further used for the in-situ coating on naturally abundant cotton fiber to make a superhydrophobic MOF@cotton composite material. The MOF-coated cotton fiber composite (SH-UiO-66@CFs) showed water repellency with a WCA of 163° and a low CAH of 4°. The flexible superhydrophobic SH-UiO-66@CFs showed an oil absorption capacity more than 2500 wt % for both heavy and light oils at room temperature. The superoleophilicity of SH-UiO-66@CFs was further exploited to separate light floating oil as well as sedimentary heavy oil from water. SH-UiO-66@CFs material can also separate oil from the oil/water mixture by gravity-directed active filtration. Hence, the newly developed MOF-based composite material has high potential as an oil absorbent material for marine oil spill cleanup.

An acetoxy functionalized Al(III) based metal-organic framework showing selective "turn on" detection of perborate in environmental samples.

Here, we have described the design, preparation and detailed characterization of a new acetoxy functionalized aluminium based metal-organic framework (MOF) called CAU-10-OCOCH3 (1) (CAU stands for Christian-Albrechts-University). The desolvated compound was employed for the detection of perborate in a pure aqueous environment. The presented MOF based perborate sensing probe (1) was synthesized by employing 5-acetoxyisophthalic acid and AlCl3·6H2O as the linker molecule and metal salt source, respectively, in DMF/H2O medium at 120 °C for 12 h. The material (1') showed a very selective fluorescent turn-on response towards perborate in aqueous medium with the coexistence of several competitive analytes. A dramatic increment (65 fold) in emission intensity of the probe was observed within 5 min of the addition of perborate. A chemo-selective reaction between perborate and the acetoxy functionality and subsequent hydrolysis of the acetoxy group to the hydroxy group is the main cause of the turn-on nature of detection. The material showed a detection limit of 1.19 µM. The probe was also applied for the recognition of perborate in several environmental water samples. The material is the first ever MOF based probe for selective detection of perborate.

Rapid switch-on fluorescent detection of nanomolar-level hydrazine in water by a diacetoxy-functionalized MOF: application in paper strips and environmental samples.

Here, we present a new diacetoxy-functionalized UiO-66 metal-organic framework (MOF) for the trace level detection of hydrazine in water. The MOF material (1) was solvothermally prepared by the reaction between ZrOCl2·8H2O and 2,5-diacetoxy-1,4-benzenedicarboxylic acid (H2BDC-(OCOCH3)2). The desolvated material (1') showed a highly selective fluorescent turn-on signal towards hydrazine in water, which can be visualized by the naked eye under a UV lamp. Within 1 min of hydrazine addition, there was 14-fold fluorescence enhancement. The probe can detect hydrazine up to the nanomolar level (detection limit = 78.8 nM) in water. This detection limit is the lowest among MOF-based fluorescent probes for hydrazine. The material was also utilized for the sensing of hydrazine in paper strips and environmental water samples. Hydrazine-selective deprotection of ester groups anchored with the ligand is the principal reason behind the switch-on nature of sensing.

Post-synthetic modification of a metal-organic framework with a chemodosimeter for the rapid detection of lethal cyanide via dual emission.

A new Hf(iv) based metal-organic framework with the UiO-66 (UiO = University of Oslo) topology was prepared via a standard modulated solvothermal reaction. The weakly emissive MOF material was well characterized via various analytical techniques. The parent MOF was then post-synthetically modified with a highly emissive pyrene based chemodosimeter probe without altering the parent framework structure. The incorporation of the chemodosimeter in the modified MOF material was successfully confirmed by using FT-IR and 1H NMR spectroscopy. The emission behaviour of the parent MOF was changed drastically with a noticeable colour change after post-synthetic modification. After modification, the MOF material showed a very selective colorimetric and fluorometric dual-emissive response towards lethal cyanide ions. A large blue shift (Δλ = 127 nm) was observed in the emission spectra which can be also visualized with the naked eye under a hand held UV lamp. The presence of a vinyl functional group in the chemodosimeter can serve as a potential nucleophilic reaction centre, which was also confirmed by the DFT calculations. The reaction based sensing mechanism of the MOF material was successfully confirmed by 1H NMR spectroscopy. Furthermore, to apply the modified MOF material in real life, the test strip based sensing of cyanide in drinking water was demonstrated.

A phthalimide-functionalized UiO-66 metal-organic framework for the fluorogenic detection of hydrazine in live cells.

Here, we demonstrated the synthesis, characterization and application of a phthalimide-functionalized UiO-66 metal-organic framework, which showed an intrinsic detection capability for hydrazine. The MOF material (1) was solvothermally prepared by the reaction between ZrCl4 and 2-(1,3-dioxoisoindolin-2-yl)benzene-1,4-dioic acid (H2L) ligand in DMF solvent in the presence of benzoic acid for 48 h at 120 °C. The guest molecule free material (1') was used as a turn-on fluorescent sensor for the selective detection of hydrazine under biological conditions. The phthalimide group anchored in the structure of 1' is converted to the amine group by reaction with hydrazine and this free amine is accountable for the turn-on fluorescence behavior. The probe exhibited an extraordinary detection limit towards hydrazine (0.87 µM). The cellular imaging ability of the MOF probe for hydrazine was also demonstrated with MDAMB-231 breast cancer cells. The probe-loaded cells didn't show considerable cellular cytotoxicity and morphological deformities. They responded towards hydrazine solution by giving an intense blue fluorescent signal. Hence, 1' is capable of monitoring hydrazine in both the aqueous phase and living cells.

A recyclable post-synthetically modified Al(iii) based metal-organic framework for fast and selective fluorogenic recognition of bilirubin in human biofluids.

Herein, we report the fast and selective detection of bilirubin by a recyclable Al(iii) based post-synthetically modified MIL-53 metal-organic framework (MOF) (1-NH2@THB). Post-synthetic modification was achieved by the aldimine condensation reaction between MIL-53-NH2 and 2,3,4-trihydroxy benzaldehyde. The post-synthetically modified compound was successfully characterized by Fourier transform infrared (FT-IR) spectroscopy, thermogravimetric (TG) analysis and X-ray powder diffraction (XRPD) experiments. The material has huge potential to detect bilirubin in HEPES buffer medium (pH = 7.4) by a fluorescence "turn-off" mechanism. The drastic quenching in the fluorescence emission intensity of the MOF material in the presence of bilirubin is due to the inner filter effect as well as molecular interactions between the MOF material and bilirubin. The probe displayed ultra-fast response (30 s), low detection limit (1.26 pM) and high selectivity towards bilirubin with the co-existence of several metal ions and biomolecules. Moreover, the real field application of the probe was thoroughly investigated in human bio-fluids (blood serum and urine samples) by the standard addition method. Furthermore, the quenching ability of the MOF material by bilirubin was also explored on a portable paper strip device. All the above discussions indicate that the probe is a potential candidate for the clinical detection of jaundice.

Metal-Organic Framework Showing Selective and Sensitive Detection of Exogenous and Endogenous Formaldehyde.

In this work, we report a new hydrazine-functionalized Al(III)- based metal-organic framework having MIL-53 (MIL = Material of Institute Lavoisier) framework topology for the sensitive and selective detection of formaldehyde (FA). The phase purity of the thermally activated and as-synthesized forms of the material was examined by X-ray powder diffraction experiments, Fourier transform infrared spectroscopy, and thermogravimetric analysis. The desolvated material (1') showed great potential for the selective sensing of FA in the existence of other potentially competitive aldehydes in both aqueous and 10 mM HEPES buffer (pH = 7.4) media. The fluorescence "turn-on" behavior of the reaction-based probe can be ascribed to the inhibition of the photoinduced electron transfer process (from the hydrazine group to the phenyl ring) because of the formation of the hydrazone moiety. The detection limit of the probe toward FA in HEPES buffer is 8.37 µM (0.25 ppm), which lies below the intracellular concentration of FA (100-400 µM). A very short response time (1 min) has been displayed by 1' for FA sensing. Moreover, a remarkable enhancement in the emission intensity (sevenfold and fourfold in aqueous and HEPES buffer media, respectively) of 1' was observed after 1 min of FA addition. Furthermore, the ability of the probe to detect FA in the vapor phase was demonstrated. Interestingly, the material is also capable to detect endogenous FA in cancer cells. All the above discussed features clearly reveal that the present material has a huge potential for selective recognition of FA in both real water and biological samples.

Selective Sensing of Peroxynitrite by Hf-Based UiO-66-B(OH)2 Metal-Organic Framework: Applicability to Cell Imaging.

The first boronic acid functionalized Hf-based UiO-66 (UiO = University of Oslo) metal-organic framework (MOF) having the ability to detect both extracellular and intracellular peroxynitrite is presented. The Hf-UiO-66-B(OH)2 material (1) was synthesized under solvothermal conditions from a mixture of HfCl4 and 2-borono-1,4-benzenedicarboxylic acid [H2BDC-B(OH)2] ligand in DMF in the presence of formic acid (modulator) at 130 °C for 48 h. The desolvated material (1') was utilized as a fluorescent turn-on probe for the rapid sensing of extracellular peroxynitrite (ONOO-) under conditions mimicking those of biological medium (10 mM HEPES buffer, pH 7.4). Selective sensing of ONOO- over other ROS/RNS was also achieved by 1'. The oxidative cleavage of attached boronic acid groups forming corresponding hydroxy-functionalized ligands can be accounted for the fluorescent increment phenomenon in the presence of ONOO-. The probe showed extraordinary sensitivity (detection limit = 9.0 nM) toward ONOO- in 10 mM HEPES buffer at pH 7.4. Probe-loaded cells did not exhibit cytotoxicity and morphological deformities. It is remarkable that the probe inside the cells responded toward the peroxynitrite solution to give an intense blue fluorescent signal. The fluorescence microscopy study with J774A.1 macrophage cells unambiguously demonstrated that probe 1' is suitable to image peroxynitrite in living cells.

A dinitro-functionalized metal-organic framework featuring visual and fluorogenic sensing of H2S in living cells, human blood plasma and environmental samples.

Here, we describe a new dinitro-functionalized Zr(iv) MOF (MOF = metal-organic framework) having a UiO-66 (UiO = University of Oslo) framework topology called UiO-66-(NO2)2 (1). It shows fluorescence turn-on behavior towards H2S in simulated biological medium (HEPES buffer, pH = 7.4). By employing solvothermal conditions, 1 was successfully synthesized by reacting ZrCl4, H2BDC-(NO2)2 [H2BDC-(NO2)2 = 2,5-dinitro-1,4-benzenedicarboxylic acid] ligand and benzoic acid with a molar ratio of 1 : 1 : 10 in DMF (DMF = N,N-dimethylformamide) at 130 °C for 24 h. The material was characterized by infrared spectroscopy, X-ray powder diffraction (XRPD) and thermogravimetric (TG) analyses. The compound not only displays highly sensitive fluorometric sensing of H2S but also exhibits a visually detectable colorimetric change towards H2S in daylight. Moreover, the high selectivity of 1' towards H2S is retained even when several other biologically intrusive species co-exist in the sensing medium. The limit of detection (LOD) of the compound is 14.14 µM which lies in the range of the H2S concentration found in biological systems. Fluorescence microscopy studies on J774A.1 cells revealed the efficacy of the probe for imaging H2S in living cells. Moreover, this material can detect H2S in human blood plasma (HBP) and monitor the sulfide concentration in real water samples. All these features clearly demonstrate that the material has huge potential for highly selective sensing of both extracellular and intracellular H2S.

Rapid and highly sensitive detection of extracellular and intracellular H2S by an azide-functionalized Al(iii)-based metal-organic framework.

A new, azide-functionalized Al(iii)-based metal-organic framework (MOF) denoted as CAU-10-N3 (1, CAU = Christian-Albrechts-University) and consisting of the 5-azido-isophthalic acid (H2IPA-N3) ligand was employed as a reaction-based fluorescent turn-on probe for the detection of H2S. The activated compound (1') showed fast, selective and highly sensitive sensing properties for extracellular H2S in HEPES buffer (10 mM, pH = 7.4). The material retained its high selectivity even in the presence of possibly competing biological species. The limit of detection of 1' for H2S is 2.65 µM, which is lower than the earlier reports on MOFs for H2S sensing. The material displayed a short response time (420 s) and a significant increase (20-fold and 26-fold after 1 and 7 min of addition of Na2S, respectively) in the fluorescence intensity towards H2S. Macrophage cells loaded with probe 1' exhibited blue fluorescence with a response time of 15 min after Na2S addition, indicating the suitability of the probe for intracellular H2S detection. Moreover, CAU-10-N3 featured excellent detection performance (quick response and 32-fold increment in fluorescence intensity after 7 min of Na2S addition) in water. Hence, it can be utilized to regulate the H2S level in aqueous samples collected from the environment.