Water-Resistant Fluoro-Switchable MOF and Reconfigurable Bio-Composite for Nanomolar Level Ultra-Fast Monitoring of Organo-Arsenic and Antibiotic Feed-Additives

A mixed-ligand-based novel 3D Cd(II)-based metal-organic framework (MOF) is devised from π-electron-rich organic struts that shows two-fold interpenetrated bilayer-pillar structure. The strong luminescence of the MOF gets remarkably quenched by roxarsone (ROX) organo-arsenic in water. The material further exemplifies one-of-a-kind fluoro-switchable probe for antibiotics and exhibits massive turn-off emission by tetracycline (TTC), whereas sulfamethazine (SMZ) triggers an unprecedented 120% emission enhancement. Apart from regenerative, fast-responsive, and selective fluoro-detection of all three feed-additives, particularly significant is nanomolar limits of detection (LOD) of ROX (48.9 nm), whereas LOD for SMZ (33.9 nm) ranks lowest, and that of TTC (22.8 nm) stands second lowest among reported sensory MOFs. Besides varying degrees of energy transfer contribution for turn-off detection by ROX and TTC, density functional theory calculations manifest changes in MOF energy levels by individual organo-aromatics and additionally describe framework-analyte supramolecular interactions. The MOF sensor works equally well in different wastewater specimens and a wide pH range with good recovery percentage. To broaden the practical scope of the material, cheap MOF@paper strip as well as reconfigurable MOF@chitosan@paper bio-composite is developed and successfully employed for the instantaneous turn-off detection of ROX and fluoro-switchable monitoring of both the antibiotics at their low concentrations.

Lanthanide-Based Metal-Organic Frameworks Offering Hydrogen Bonding Cavities: Luminescent Characteristics and Sensing Applications

This work presents the synthesis and characterization of three isomorphous lanthanide-based metal-organic frameworks (Ln-MOFs) (Ln3+=Eu (1), Tb (2), and Sm (3)) supported by a pyridine-2,6-dicarboxamide-based linker offering appended arylcarboxylate groups. Single crystal X-ray diffraction studies highlight that these Ln-MOFs present three-dimensional porous architectures offering large cavities decorated with hydrogen bonding (H-bonding) groups. These Ln-MOFs display noteworthy luminescent characteristics. The mixed-metal strategy affords a series of Ln-MOFs exhibiting color-tunable emissions. The Eu-MOF was utilized for the nanomolar sensing of both nitrobenzene and 4-nitrophenol. The critical role of H-bonding in detecting these analytes is validated through multiple spectroscopic, ξ potential, and molecular docking studies. The Eu-MOF illustrated notable anticounterfeiting as well as practical sensing applications.

Design and preparation of a multi-responsive Cd-based fluorescent coordination polymer for smart sensing of nitrobenzene and ornidazole

The improper utilization of nitrobenzene (NB) and ornidazole (ORN) has resulted in irreversible effects on the environment. By combining experimental investigation, density functional theory (DFT) calculations, and machine learning, an effective green strategy for detecting NB and ORN in aqueous solutions can be developed. In this study, a one-dimensional Cd-based coordination polymer (Cd-HCIA-3) was designed and synthesized using 5-((4-carboxybenzyl)oxy)isophthalic acid and rigid 2,2'-bipyridine under solvothermal reaction conditions. Cd-HCIA-3 exhibits excellent fluorescence properties and stability in aqueous solutions. DFT calculations were performed to predict the fluorescence sensing performance of Cd-HCIA-3, revealing that photoinduced electron transfer is the key mechanism for inducing fluorescence quenching in the presence of NB and ORN, with weak molecular interactions promoting electron transfer. Fluorescence sensing experiments were conducted to verify the DFT results, showing that Cd-HCIA-3 can selectively detect NB and ORN in aqueous solutions with limits of detection of 7.22 × 10-8 and 1.31 × 10-7 mol/L, respectively. This study's findings provide valuable insights into the design and synthesis of fluorescent coordination polymers for target analytes.

Preparation of Functionalized Ethylene-Vinyl-Alcohol Nanofibrous Membrane Filter for Rapid and Cyclic Removing of Organic Dye from Aqueous Solution

A functionalized ethylene-vinyl-alcohol (EVOH) nanofibrous membrane (NFM) was fabricated via co-electrospinning H4SiW12O40 (SiW12) and EVOH first, and then grafting citric acid (CCA) on the electrospun SiW12@EVOH NFM. Characterization with FT-IR, EDX, and XPS confirmed that CCA was introduced to the surface of SiW12@EVOH NFM and the Keggin structure of SiW12 was maintained well in the composite fibers. Due to a number of carboxyl groups introduced by CCA, the as-prepared SiW12@EVOH-CCA NFM can form a high number of hydrogen bonds with CR, and thus can be used to selectively absorb congo red (CR) in aqueous solutions. More importantly, the CR enriched in the NFM can be rapidly degraded via photocatalysis. SiW12 in the NFM acted as a photocatalyst, and the hydroxyl groups in the NFM acted as an electron donor to accelerate the photodegradation rate of CR. Meanwhile, the SiW12@EVOH-CCA NFM was regenerated and then exhibited a relatively stable adsorption capacity in five cycles of filtration-regeneration. The bifunctional nanofibrous membrane filter showed potential for use in the thorough purification of dye wastewater.

A smartphone-integrated test paper sensing platform for visual and intelligent detection of nitrofurantoin in honey samples

The development of a rapid and convenient detection method for nitrofurantoin (NFT) residual is of great significance for food safety. Herein, a new fluorescent probe (Eu-TDCA-Phen) was developed for the visual and sensitive assay of NFT through the fluorescence quenching effect of inner filter effect (IFE) and photo-induced electron transfer (PET). The probe suspension demonstrates a wide linear range (0-0.16 mM), low detection limit (90 nM), high sensitivity, and rapid response time (2 min) in the "turn-off" process. To quantify the visual detection process, a smartphone-assisted test paper sensing platform was established and was applied for NFT determination in real honey samples, achieving satisfactory recovery rate ranges from 98.04 % to 105.04 %. Furthermore, a logic gate device was integrated with the sensing platform to streamline the visual detection process. The sensing platform offers several merits, including simpleness, quantification, portability and cost-effectiveness, making it highly suitable for real-time and on-site detection of antibiotics in food samples.

Recyclable adsorption removal and fluorescent monitoring of hexavalent chromium by electrospun nanofibers membrane derived from Tb3+ coordinating polyarylene ether amidoxime

Emerging technologies or advanced materials which can simultaneously adsorb and detect highly toxic Cr(VI) are urgently in demand for environmental remediation. Herein, we have designed and synthesized a functional polyarylene ether with aromatic main chain and pendent carboxyl groups along with amidoxime group that can be coordinated with different metal ions. Thanks to its versatile activation of the lanthanide ions' inherent fluorescence and good processability, the fluorescent nanofiber membranes with competitive Cr(VI) adsorption and detection performance have been fabricated via one-step electrospinning of mixed solution containing synthesized polymer and terbium salt. More specifically, the optimized nanofiber membrane exhibits a maximal Cr(VI) adsorption of 278.2 mg/g and specific detection for hexavalent chromium down to 11.76 nM. More importantly, the prepared fluorescent nanofiber membranes can be easily re-generated and re-used for both Cr(VI) adsorption and detection for five times. Given the unique advantages of easy fabrication, competitive dual functionalities as well as good reusability of electrospun fluorescent nanofiber membranes, the present work basically opens up new insight in the design of multifunctional recyclable material for the remediation of heavy metal pollution.

Recent advances in determination applications of emerging films based on nanomaterials

Sensitive and facile detection of analytes is crucial in various fields such as agriculture production, food safety, clinical diagnosis and therapy, and environmental monitoring. However, the synergy of complicated sample pretreatment and detection is an urgent challenge. By integrating the inherent porosity, processability and flexibility of films and the diversified merits of nanomaterials, nanomaterial-based films have evolved as preferred candidates to meet the above challenge. Recent years have witnessed the flourishment of films-based detection technologies due to their unique porous structures and integrated physical/chemical merits, which favors the separation/collection and detection of analytes in a rapid, efficient and facile way. In particular, films based on nanomaterials consisting of 0D metal-organic framework particles, 1D nanofibers and carbon nanotubes, and 2D graphene and analogs have drawn increasing attention due to incorporating new properties from nanomaterials. This paper summarizes the progress of the fabrication of emerging films based on nanomaterials and their detection applications in recent five years, focusing on typical electrochemical and optical methods. Some new interesting applications, such as point-of-care testing, wearable devices and detection chips, are proposed and emphasized. This review will provide insights into the integration and processability of films based on nanomaterials, thus stimulate further contributions towards films based on nanomaterials for high-performance analytical-chemistry-related applications.

Relative capability demonstration of luminescent Al-MOFs for ideal detection of nitroaromatic explosives

Here, we have synthesised three luminescent Al MOFs i.e., Al-NTP, Al-FDA, and Al-TDA, using common metal ions (AlCl₃·6H₂O) with different carboxylic acid organic linkers (5-nitroisophthalic acid, 2,5-furan dicarboxylic acid, and 2,5-thiophenedicarboxylic acid) in a semi-aqueous medium. The structural analysis of Al-MOFs has been confirmed through powder X-ray diffraction (PXRD), Fourier transform infrared spectroscopy and absorption spectroscopy. Afterward, the optical properties of all three Al-MOFs were confirmed using photoluminescence spectroscopy and demonstrated for the detection of nitroaromatic explosives. We have observed host-guest interaction through a quenching mechanism. Among the three synthesised Al-MOFs, Al-NTP MOF exhibit 0.014 ppm lowest limit of detection in chloroform at room temperature. Our comparative study results reveal that the selection of the organic linker and solvent plays a critical role in MOF based sensing applications.

Asymmetric Activation of the Nitro Group over a Ag/Graphene Heterointerface to Boost Highly Selective Electrocatalytic Reduction of Nitrobenzene

The electrocatalytic reduction of nitrobenzene to aniline normally faces high overpotential and poor selectivity because of its six-electron redox nature. Herein, a Ag nanoparticles/laser-induced-graphene (LIG) heterointerface was fabricated on polyimide films and employed as an electrode material for an efficient nitrobenzene reduction reaction (NBRR) via a one-step laser direct writing technology. The first-principles calculations reveal that Ag/LIG shows the lowest activation barriers for the NBRR, which could be attributed to the optimum adsorption of the H atom realized by the appropriate interaction between Ag/LIG heterointerfaces and nitrobenzene. As a result, the overpotential of the NBRR is reduced by 217 mV after silver loading, and Ag/LIG shows a high aniline selectivity of 93%. Furthermore, an electrochemical reduction of nitrobenzene in tandem with an electrochemical oxidative polymerization of aniline was designed to serve as an alternative method to remove nitrobenzene from the aqueous solution. This strategy highlights the significance of heterointerfaces for efficient electrocatalysts, which may stimulate the development of novel electrocatalysts to boost the electrocatalytic activity.

Facile fabrication of Tb3+-functionalized COF mixed-matrix membrane as a highly sensitive platform for the sequential detection of oxolinic acid and nitrobenzene

A novel Tb³⁺-functionalized covalent organic framework-based polymer mixed-matrix membrane (Tb³⁺@COF MMM) has been successfully fabricated by incorporating the highly stable Tb³⁺@PI-COF as filler into polyvinylidene fluoride (PVDF) solution. Compared with pure COF membrane, MMM exhibits its good flexibility, processability and high detection sensitivity. The obtained Tb³⁺@COF-MMM (M) can be employed as a highly sensitive sensing platform for the sequential detection of oxolinic acid (OA) and nitrobenzene (NB) based on a "off-on-off" process. M has performed its great selectivity, high sensitivity, and low detection limit for detecting OA with "turn-on" mechanism. Moreover, owing to the good chemical stability and anti-interference of M sensor, it is prospective to efficiently detect residues of OA in serum or river water. After the detection of M-15 toward OA, the obtained fluorescent M-15/OA exhibits the rapid quenching, facile manipulation, cycling utility and low detection limits for sensing NB solution and vapor. This work has proposed a typical case of developing flexible Ln³⁺-functionalized COF-based polymer mixed-matrix membrane as a highly sensitive sensing platform for detecting OA and NB, simultaneously revealed the applied potentiality of M for monitoring animal health and environmental pollution.

Recent advances in molecular logic gate chemosensors based on luminescent metal organic frameworks

Luminescent metal-organic frameworks (LMOFs) as chemosensors, can sense various analytes, such as heavy metal ions, antibiotics, pesticides, and small biological molecules. Based on the fluorescence characteristics of LMOFs, a variety of logic gates have been developed. In this review, we mainly discuss some common logic systems based on LMOFs, and then summarize the strategies of constructing logic gates from two perspectives. One is based on superior characteristics of MOFs, which can be synthesized from Ln3+ based MOFs (Ln-MOFs) or form hybrids by encapsulating different materials, including metal ions, dyes, and quantum dots (QDs). The other is to control the presence of inputs by reactions between different reactants and then further control switches of logic gates. Additionally, the common sensing mechanisms of LMOFs in logic gates are discussed. In the end, we have envisioned MOFs that possess a promising future in logic computing areas.

Single-atom niobium doped BCN nanotubes for highly sensitive electrochemical detection of nitrobenzene

Herein, single-atom niobium-doped boron-carbon-nitrogen nanotubes (SANb-BCN) were synthesized and utilized to fabricate an electrochemical sensor for the detection of nitrobenzene (NB), an environmental pollutant. SANb-BCN were characterized through scanning transmission electron microscopy, scanning electron microscopy, transmission electron microscopy, X-ray diffraction analysis, and Raman spectroscopy. The Nb-BNC material modified on a glassy carbon electrode (GCE) showed an excellent electrochemical response behavior toward NB. The SANb-BCN-modified GCE (SANb-BCN/GCE) gave rise to a prominent NB reduction peak at -0.6 V, which was positively shifted by 120 mV from the NB reduction peak of the bare GCE. Furthermore, the NB peak current (55.74 μA) obtained using SANb-BCN/GCE was nearly 42-fold higher than that using the bare GCE (1.32 μA), indicating that SANb-BCN/GCE is a highly sensitive electrochemical sensor for NB. An ultralow limit of detection (0.70 μM, S/N = 3) was also achieved. Furthermore, the SANb-BCN/GCE sensor was found to possess favorable anti-interference ability during NB detection; thus, the presence of various organic and inorganic coexisting species, including Mg2+, Cr6+, Cu2+, K+, Ca2+, NH4+, Cd2+, urea, 1-bromo-4-nitrobenzene, 3-hydroxybenzoic, terephthalic acid, 1-iodo-4-nitrobenzene, and toluene, minimally affected the NB detection signal. Notably, the SANb-BNC sensor material exhibited high sensitivity and specificity toward detection of NB in environmental samples. Thus, the use of the proposed sensor will serve as an effective alternative method for the identification and treatment of pollutants.

A Stable Cd(II)-Based Metal-Organic Framework: Synthesis, Structure, and Its Eu3+ Functionalization for Ratiometric Sensing on the Biomarker 2-(2-Methoxyethoxy) Acetic Acid

A novel two-dimensional Cd-based metal-organic framework (MOF), [Cd(pddb)H₂O]_n (Cd-MOF), has been hydrothermally synthesized using the V-shaped ligand 4,4'-(pyridine-2,6-diyl)-dibenzoic acid (H₂pddb) and structurally characterized. The framework exhibits fascinating one-dimensional in-plane channels functionalized with active pyridine-N sites. The as-synthesized Cd-MOF exhibits excellent water and chemical stability. Furthermore, a simple and nondestructive coordinated postsynthetic modification method has been applied to Cd-MOF to obtain a class of MOF hybrids functionalized by lanthanide ions. More interestingly, Eu³⁺@Cd-MOF can act as a dual-emissive ratiometric fluorescent probe for 2-(2-methoxyethoxy) acetic acid (MEAA), a metabolite of 2-(2-methoxyethoxy) ethanol, which could result in DNA damage and teratogenic and developmental toxicity. During the sensing process, the fluorescence sensor exhibits notable water tolerance, reusability, and a low detection limit (8.5 μg mL^-1). In addition, the chemical substances in human urine and serum do not interfere with the fluorescence quenching process, which makes it possible for the fluorescent probe to be applied in the detection of MEAA in human urine and serum systems. The possible sensing mechanism is also studied and discussed in detail.

Postsynthesis Strategy of Functional Zn-MOF Sensors for the Detection of ClO- and DPA

Active species were introduced into MOFs to prepare multifunctional fluorescent probes by a stepwise postsynthetic modulation strategy. First, two-dimensional HPU-16 (HPU = Henan Polytechnic University; HPU-16 = Zn(L)₂(H₂O); HL = 2-(5-pyridin-4-yl-5H-[1,2,4]triazol-3-yl)-pyrazine) was transformed into three-dimensional HPU-17 ({Zn₃(L)₂(btc)₂(H₂O)}_n) through a crystal dissolution-recrystallization process. Second, linker replacement was used to introduce -NH₂ into the HPU-17 to generate functional NH₂-HPU-17 via a single-crystal to single-crystal transformation. The functional amino groups caused NH₂-HPU-17 to show a significant response to ClO^-. Because of the interaction of amino groups and ClO^-, the fluorescence of NH₂-HPU-17 gradually changed from blue to yellow-green. More interestingly, NH₂-HPU-17 could encapsulate Tb³⁺ and sensitize the visible-emitting characteristic fluorescence of Tb³⁺ in aqueous solution. Then, newly generated Tb³⁺@NH₂-HPU-17 could serve as an effective probe for the determination of DPA. This work paves a new way for the design and modulation of ratiometric fluorescence probes for the selective and sensitive detection of special molecules.

A Trinuclear Cobalt-Organic Framework: Solvatochromic Sensor towards CH2 Cl2 , and its Derivative as an Anode of Lithium-Ion Batteries with High Performance

Here, a porous cobalt-organic framework with pillared layer structures, namely [Co₃ OBA₃ PTD(H₂ O)₂ ⋅ 2 DMA⋅H₂ O]_n (1, H₂ OBA=4,4'-oxybis(benzoic acid); PTD=6-(pyridin-4-yl)-1,3,5-triazine-2,4-diamine), was fabricated by using cobalt trinuclear nodes, low-cost carboxylic linker, and accessible nitrogen heterocyclic ligands. This compound exhibited a highly efficient solvatochromism towards CH₂ Cl₂ within one minute and can be used 200 times at least. The corresponding dropper detector was assembled as a practical sensor. Meanwhile, the porous Co₃ O₄ was obtained by a simple but effective annealing treatment. Electrochemical measurements confirm that this Co₃ O₄ material derived from compound 1 shows high and stable lithium storage capabilities (1081.75 mA h g^-1 at 200 mA g^-1 after 115 cycles) and excellent rate properties.

Nickel nanoparticles embedded in porous carbon nanofibers and its electrochemical properties

Flexible porous carbon nanofibers containing nickel nanoparticles were synthesized by direct carbonization of electrospun Ni-MOFs/polyacrylonitrile fibers. The as-synthesized composite nanofibers were employed as binder-free electrodes, and exhibit high specific capacitance (up 672 F g^-1 at current density of 2 A g^-1) and superior rate capability (57% capacitance retention from current density of 2-10 A g^-1), which may be attributed to their binder-free nature, unique one-dimensional (1D) structure and highly dispersed electrochemically active nickel nanoparticles. Furthermore, a symmetric supercapacitor was assembled using the fiber electrodes in 6 M KOH, and the energy density of 17.8 Wh kg^-1 was achieved in a potential window of 1.5 V. This self-standing fiber with abundant mesopores and macropores is expected to become a promising electrode material for high-performance supercapacitors.

Preparation of a DNA-Tb-MOF conjugate as a time-resolved probe for the detection of SO2 derivatives through an off-on effect

Herein we synthesize a DNA-sensitized Tb-MOF conjugate (DNA-Tb-MOF) as a time-resolved luminescent probe to sensitively and selectively assay SO₂ and their derivatives (i.e., HSO₃^-) through a photoluminescence off-on effect. The charge and energy transfer mechanism enables the demonstration of the effect of the photoluminescence turn-on which results from the reaction between the amino group of the DNA-Tb-MOF conjugate and SO₂/HSO₃^-. The results demonstrate that the DNA-Tb-MOF conjugate probe can sense SO₂ and their derivatives (i.e., HSO₃^-) with a detection limit of 0.02 ppm. Moreover, the photoluminescence off-on effect can be observed even by the naked eye.

Dual-Functional Proton-Conducting and pH-Sensing Polymer Membrane Benefiting from a Eu-MOF

Porous metal-organic frameworks (MOFs) have demonstrated a great potential in proton conduction and luminescence sensing due to functionalized nodes, ligands and channels, or pores. Herein, we prepared a hydrothermally stable Eu-MOF that also resisted acid and base using a bifunctional organic ligand containing carboxylic acid groups, which are easily coordinated to Eu ions, and Eu-phobic tetrazolyl groups as potential proton-hopping sites. The hydrogen bond network, which was constructed by the uncoordinated anionic tetrazolium and the coordinated and free water molecules, endowed this Eu-MOF with the highest proton conductivity of 4.45 × 10^-2 S/cm at 373 K and 93% relative humidity. The proton conductivity of the Nafion membrane containing this Eu-MOF increased 1.74 times. More interestingly, the hybrid membrane displayed luminescence pH sensing because the changeable protonation levels of uncoordinated tetrazolium groups along with the pH tuned the emission of embedded Eu-MOFs. Such a dual-functional MOF-based hybrid membrane including proton conduction and pH sensing is reported for the first time, which could open an avenue to the more practical application for functional MOFs.

Enhanced proton conduction of imidazole localized in one-dimensional Ni-metal-organic framework nanofibers

Metal-organic frameworks (MOFs) show possibilities to be potential candidates for proton exchange membranes (PEMs). However, the poor flexibility and processability of MOFs due to their crystalline nature limit their applications significantly. An efficient approach to overcome this limitation is to combine MOFs with polymers. In this work, novel lightweight and flexible Ni-MOFs/polyacrylonitrile nanofibers were fabricated by electrospinning. The nanofibers consisted of one-dimensional proton conduction channels for imidazole and show enhanced proton conductivity. A proton conductivity of 6.04 × 10^-5 Scm^-1 was achieved at 363 K and 90% RH. Furthermore, the proton transport dynamics of the fibers were investigated using the AC impedance technique.

Recent advances in the shaping of metal–organic frameworks

In this review, the recent advances in the shaping of MOFs are overviewed, and some promising strategies recently developed are highlighted, including templated shaping, self-shaping, shaping on substrates, and shaping with sacrificial materials.

Solvent triggering structural changes for two terbium-based metal–organic frameworks and their photoluminescence sensing

TbPDBA-8 and TbPDBA-9 have been obtained based on the same ligand, and have different structures and luminescence properties.

Fabrication of silver chalcogenolate cluster hybrid membranes with enhanced structural stability and luminescence efficiency

The present study reports the fabrication of a silver chalcogenolate cluster hybrid membrane (SCC membrane) through self-assembly of SCCs, and then covalent cross-linking of the modified SCC assembled materials. This strategy provides access to silver clusters with superior chemical stability and enhanced luminescence efficiency for practical applications.