Highly Luminescent MOF and Its In Situ Fabricated Sustainable Corn Starch Gel Composite as a Fluoro-Switchable Reversible Sensor Triggered by Antibiotics and Oxo-Anions

Frequent use of antibiotics and the growth of industry lead to the pollution of several natural resources which is one of the major consequences for fatality to human health. Exploration of smart sensing materials is highly anticipated for ultrasensitive detection of those hazardous organics. The robust porous hydrogen bonded network encompassing a free-NH₂ moiety, Zn(II)-based metal-organic framework (MOF) (1), is used for the selective detection of antibiotics and toxic oxo-anions at the ppb level. The framework is able to detect the electronically dissimilar antibiotic sulfadiazine and nitrofurazone via fluorescence "turn-on" and "turn-off" processes, respectively. The antibiotic-triggered reversible fluoro-switching phenomena (fluorescence "on-off-on") are also observed by using the fluorimetric method. An extensive theoretical investigation was performed to establish the fluoro-switching response of 1, triggered by a class of antibiotics and also the sensing of oxo-anions. This investigation reveals that the interchange of the HOMO-LUMO energy levels of fluorophore and analytes is responsible for such a fluoro-switchable sensing activity. Sensor 1 showed the versatile detection ability which is reflected by the detection of a carcinogenic nitro-group-containing drug "roxarsone". In view of the sustainable environment along with quick-responsive merit of 1, an in situ MOF gel composite (1@CS; CS = corn starch) is prepared using 1 and CS due to its useful potential features such as biocompatibility, toxicologically innocuous, good flexibility, and low commercial price. The MOF composite exhibited visual detection of the above analytes as well as antibiotic-triggered reversible fluoro-switchable colorimetric "on-off-on" response. Therefore, 1@CS represents a promising smart sensing material for monitoring of the antibiotics and oxo-anions, particularly appropriate for the real-field analysis of carcinogenic drug molecule "roxarsone" in food specimens.

A Dihydrotetrazine-Functionalized Metal-Organic Framework as a Highly Selective Luminescent Host-Guest Sensor for Detection of 2,4,6-Trinitrophenol

Pore decoration of metal-organic frameworks (MOFs) with functional groups is a useful strategy to attain high selectivity toward specific analytes, especially in the presence of interfering molecules with similar structures and energy levels, through selective host-guest interactions. In this work, we applied a dihydrotetrazine-decorated MOF, TMU-34, with the formula [Zn(OBA)(H₂DPT)_0.5]_n·DMF, where H₂OBA is 4,4'-oxybis(benzoic acid) and H₂DPT is 3,6-bis(pyridin-4-yl)-1,4-dihydro-1,2,4,5-tetrazine, for the highly selective detection of phenolic NACs, especially TNP (94% quenching efficiency, detection limit 8.1 × 10^-6 M, K_SV = 182663 mol L^-1), in the presence of other substituted NACs especially -NH₂-substituted NACs. Investigations reveal that the quenching mechanism is dominated by photoinduced MOF-to-TNP electron transfer through possible hydrogen-bonding interactions between the phenolic hydroxyl group of TNP and dihydrotetrazine functions of TMU-34. Despite extensive publications on the detection of TNP in the presence of other NACs, the significance of this work will be elucidated if attention is paid to the fact that TMU-34 is among the rare and highly selective MOF-based TNP sensors in the presence of -NH₂-substituted NACs as the serious interferers.

Fluorescence sensing of nitrophenol explosives using a two-dimensional organic-metal chalcogenide fully covered with functional groups

A new 2D fluorescent organic-metal chalcogenide (OMC), CdClHT (HT = 4-hydroxythiophenol), evenly covered with phenol groups is reported. CdClHT represents unparalleled selectivity and the highest sensitivity towards 2,4,6-trinitrophenol (TNP) (K_SV = 2.16 × 10⁷ m^-1, experimental LOD = 2 nM), among all reported 2D conjugated polymer (CP) luminescent detectors.

Anthracene-Tagged UiO-67-MOF as Highly Selective Aqueous Sensor for Nanoscale Detection of Arginine Amino Acid

In the present paper, new functionalized UiO-67 metal-organic frameworks (MOF) which contain aromatic tagged groups such as phenyl, naphthyl, and anthracene have been synthesized, characterized, and used for sensing water-soluble amino acids. The results show that anthracene-tagged UiO-67-MOF is shown to act as a highly efficient and selective aqueous sensor for arginine over other water-soluble amino acids in nanoscale. Upon adding an increasing amount of arginine, PL bands of the anth-UiO-67 MOF quenched completely, while there is no perturbation in the PL bands for other amino acid observed. This MOF allows a selective ratiometric detection of arginine without any interference from other amino acids.

Design and synthesis of aryl-functionalized carbazole-based porous coordination cages

A subset of coordination cages have garnered considerable recent attention for their potential permanent porosity in the solid state. Herein, we report a series of functionalized carbazole-based cages of the structure type M₁₂(R-cdc)₁₂ (M = Cr, Cu, Mo) where the functional groups include a range of aromatic substituents. Single-crystal X-ray structure determinations reveal a variety of intercage interactions in these materials, largely governed by pi-pi stacking. Density functional theory for a subset of these cages was used to confirm that the nature of the increased stability of aryl-functionalized cages is a result of inter-cage ligand interactions.

Novel syntheses of carbazole-3,6-dicarboxylate ligands and their utilization for porous coordination cages

A benzyl-protecting strategy affords access to large quantities of carbazole-based ligands or molecular adsorbents with tunable inter-cage interactions.

Sensing organic analytes by metal–organic frameworks: a new way of considering the topic

In this review, our goal is comparison of advantageous and disadvantageous of MOFs about signal-transduction in different instrumental methods for detection of different categories of organic analytes.

A carbazole-functionalized metal–organic framework for efficient detection of antibiotics, pesticides and nitroaromatic compounds

A carbazole-functionalized Cd-MOF exhibits highly selective and sensitive fluorescence detection towards antibiotics, pesticides and nitroaromatic compounds.

Photoactive metal-organic framework as a bifunctional material for 4-hydroxy-4'-nitrobiphenyl detection and photodegradation of methylene blue

Environmental pollution resulting from organic pollutants is becoming an overwhelming problem throughout the world, and how to efficiently detect or eliminate these organic pollutants remains an important issue for environmental protection. Herein, a cadmium(ii)-based MOF, Cd-TCAA, was successfully prepared by the hydrothermal reaction of 4,4',4''-tricarboxyltriphenylamine (H3tca), (E)-1,2-di(pyridin-4-yl)diazene (abp) and cadmium nitrate. Because the H3tca moiety is a typically versatile functional material that exhibits good hole-transporting capabilities, efficient light harvesting, and excellent electron-donating properties, this novel photoactive metal-organic framework operates as a bifunctional material for the detection and degradation of organic pollutants. It exhibits excellent selectivity and sensitivity towards 4-hydroxy-4'-nitrobiphenyl (HNBP) with a detection limit of 50 nM in solution, and represents the first example of a MOF-based sensor for the detection of HNBP. The photocatalytic activity of Cd-TCAA was also determined by investigating the photo-induced degradation of methylene blue (MB). Cd-TCAA has the advantages of excellent catalytic activity, stability, and recyclability.

Size-Selective Detection of Picric Acid by Fluorescent Palladium Macrocycles

This work presents the synthesis and characterization of two palladium-based fluorescent macrocycles offering hydrogen-bonding cavities of contrasting dimensions. Both palladium macrocycles function as chemosensors for the detection of nitroaromatics, whereas the larger macrocycle not only illustrates nanomolar detection of picric acid but also transports its significant amount from an aqueous to an organic phase.

A supramolecular Tröger's base derived coordination zinc polymer for fluorescent sensing of phenolic-nitroaromatic explosives in water

A V-Shaped 4-amino-1,8-napthalimide derived tetracarboxylic acid linker (L; bis-[N-(1,3-benzenedicarboxylic acid)]-9,18-methano-1,8-naphthalimide-[b,f][1,5]diazocine) comprising the Tröger's base (TB) structural motif was rationally designed and synthesised to access a nitrogen-rich fluorescent supramolecular coordination polymer. By adopting the straight forward precipitation method, a new luminescent nanoscale Zn(ii) coordination polymer (TB-Zn-CP) was synthesized in quantitative yield using Zn(OAc)2·2H2O and tetraacid linker L (1 : 0.5) in DMF at room temperature. The phase-purity of as-synthesised TB-Zn-CP was confirmed by X-ray powder diffraction analysis, infra-red spectroscopy, and elemental analysis. Thermogravimetric analysis suggests that TB-Zn-CP is thermally stable up to 330 °C and the morphological features of TB-Zn-CP was analysed by SEM and AFM techniques. The N2 adsorption isotherm of thermally activated TB-Zn-CP at 77 K revealed a type-II reversible adsorption isotherm and the calculated Brunauer-Emmett-Teller (BET) surface area was found to be 72 m2 g-1. Furthermore, TB-Zn-CP displayed an excellent CO2 uptake capacity of 76 mg g-1 at 273 K and good adsorption selectivity for CO2 over N2 and H2. The aqueous suspension of as-synthesized TB-Zn-CP showed strong green fluorescence (λmax = 520 nm) characteristics due to the internal-charge transfer (ICT) transition and was used as a fluorescent sensor for the discriminative sensing of nitroaromatic explosives. The aqueous suspension of TB-Zn-CP showed the largest quenching responses with high selectivity for phenolic-nitroaromatics (4-NP, 2,4-DNP and PA) even in the concurrent presence of other potentially competing nitroaromatic analytes. The fluorescence titration studies also provide evidence that TB-Zn-CP detects picric acid as low as the parts per billion (26.3 ppb) range. Furthermore, the observed fluorescence quenching responses of TB-Zn-CP towards picric acid were highly reversible. The highly selective fluorescence quenching responses including the reversible detection efficiency make the nanoscale coordination polymer TB-Zn-CP a potential material for the discriminative fluorescent sensing of nitroaromatic explosives.

Chemical Sensors Based on Metal-Organic Frameworks

Metal-organic frameworks (MOFs) as chemical sensors have developed rapidly in recent years. There have been many papers concerning this field and interest is still growing. The reason is that the specific merits of MOFs can be utilized to enhance sensitivity and selectivity by various energy/charge transfers occurring among different ligands, ligand, and metal centers, such as from ligands to metal centers or metal centers to ligands, as well as from MOF skeletons to guest species. This review intends to provide an update on recent progress in various applications of different MOF-based sensors on the basis of their luminescent and electrochemical responses towards small molecules, gas molecules, ions (cations and anions), pH, humidity, temperature, and biomolecules. MOF-based sensors function by utilizing different mechanisms, including luminescent responses of "turn-on" and "turn-off", as well as electrochemical responses.

Highly Stable Zr(IV)-Based Metal-Organic Frameworks for the Detection and Removal of Antibiotics and Organic Explosives in Water

Antibiotics and organic explosives are among the main organic pollutants in wastewater; their detection and removal are quite important but challenging. As a new class of porous materials, metal-organic frameworks (MOFs) are considered as a promising platform for the sensing and adsorption applications. In this work, guided by a topological design approach, two stable isostructural Zr(IV)-based MOFs, Zr6O4(OH)8(H2O)4(CTTA)8/3 (BUT-12, H3CTTA = 5'-(4-carboxyphenyl)-2',4',6'-trimethyl-[1,1':3',1″-terphenyl]-4,4″-dicarboxylic acid) and Zr6O4(OH)8(H2O)4(TTNA)8/3 (BUT-13, H3TTNA = 6,6',6″-(2,4,6-trimethylbenzene-1,3,5-triyl)tris(2-naphthoic acid)) with the the-a topological structure constructed by D4h 8-connected Zr6 clusters and D3h 3-connected linkers were designed and synthesized. The two MOFs are highly porous with the Brunauer-Emmett-Teller surface area of 3387 and 3948 m(2) g(-1), respectively. Particularly, BUT-13 features one of the most porous water-stable MOFs reported so far. Interestingly, these MOFs represent excellent fluorescent properties, which can be efficiently quenched by trace amounts of nitrofurazone (NZF) and nitrofurantoin (NFT) antibiotics as well as 2,4,6-trinitrophenol (TNP) and 4-nitrophenol (4-NP) organic explosives in water solution. They are responsive to NZF and TNP at parts per billion (ppb) levels, which are among the best performing luminescent MOF-based sensing materials. Simultaneously, both MOFs also display high adsorption abilities toward these organic molecules. It was demonstrated that the adsorption plays an important role in the preconcentration of analytes, which can further increase the fluorescent quenching efficiency. These results indicate that BUT-12 and -13 are favorable materials for the simultaneous selective detection and removal of specific antibiotics and organic explosives from water, being potentially useful in monitoring water quality and treating wastewater.

A Zn-MOF constructed from electron-rich π-conjugated ligands with an interpenetrated graphene-like net as an efficient nitroaromatic sensor

A π-electron conjugated ligand has been employed in a Zn-MOF efficient fluorescent sensor for determining electron-deficient nitroaromatics.

Two luminescent Zn(ii) metal–organic frameworks for exceptionally selective detection of picric acid explosives

Two luminescent thiophene-containing Zn–MOFs exhibit very highly sensitive and selective detection of picric acid compared to other nitroaromatic explosives.

Water-induced phase transformation of a CuII coordination framework with pyridine-2,5-dicarboxylate and di-2-pyridyl ketone: synchrotron radiation analysis

Water-induced reversible phase transformation in the Cu^II–PDC–(py)₂C(OH)₂ system.

Aggregates of a hydrazono-sulfonamide adduct as picric acid sensors

A sensitive and selective sensor for picric acid was developed using aggregates of a novel hydrazono-sulfonamide adduct.

Protonation and axial ligation intervened fluorescence turn-off sensing of picric acid in freebase and tin(iv) porphyrins

Protonation and axial ligation: selective sensing of picric acid using freebase and tin(iv) meso-tetraarylporphyrins occurs through protonation and axial ligation which is evident from UV-visible, fluorescence, ¹H NMR titrations and X-ray crystallography.