A Water-Stable Dual-Channel Luminescence Sensor for UO2 2+ Ions Based on an Anionic Terbium(III) Metal-Organic Framework

Three coordination polymers based on 4,4'-bis(2-methylimidazol-1-yl)diphenyl ether: Synthesis, structure and selective fluorescent sensing properties

Three CPs [Zn2(PDA)2(BMIOPE)2·3H2O]n (1), [Co(Br-BDC)(BMIOPE)]n (2) and [Co(MIP)(BMIOPE)]n (3) were synthesized by solvothermal method based on dual-ligand strategy (H2PDA, Br-H2BDC, BMIOPE and H2MIP are 1,3-phenylenediacetic acid, 5-bromo-isophthalic acid, 4,4'-bis(2-methylimidazol-1-yl)diphenyl ether and 5-methylisophthalic acid, respectively). Complexes 1 and 3 exhibit twofold parallel interwoven sql nets. Complex 2 is 2D layer structure. The luminescence property investigations showed that complexes 1-3 could act as multi-responsive fluorescent sensors to detect UO22+, Cr2O72- and CrO42- and nitrofurantoin (NFT) through fluorescence turn-off process, presenting excellent sensitivity and selectivity. Finally, the possible fluorescent quenching mechanisms of complexes 1-3 toward the above pollutants are also further investigated by employing spectroscopic methods and quantum chemical calculations. The fluorescence lifetime measurements manifest the mechanism of fluorescence quenching is static quenching process.

Distinguishing nitroimidazoles from nitrofurans via luminescence sensing

Similarity of nitroimidazole and nitrofuran antibiotics in molecular structure and photophysical properties makes them difficult to distinguish via luminescence sensing technology. Herein, this is solved by a dye-encapsulated lanthanide metal-organic framework luminescent sensor.

Fluorescent Eu-MOF@nanocellulose-based nanopaper for rapid and sensitive detection of uranium (Ⅵ)

Radioactive uranium leaks into natural water bodies mainly in the form of uranyl ions (UO22+), posing ecological and human health risks. Fluorescent europium-based metal-organic frameworks (Eu-MOFs) have been demonstrated to be effective fluorescent sensors for UO22+, but the large size, powder state and poor dispersity limit their further application. In this work, fluorescent Eu-MOFs were in-situ grown on TEMPO-oxidized cellulose nanofibers (TOCNFs), which is the first time that spherical Eu-MOF crystals with sizes below 10 nm were prepared. Fluorescence spectral analysis revealed a nine-fold increase in the fluorescence intensity of TOCNF@Eu-MOF compared to Eu-MOF. The nanocomposites achieved rapid and sensitive fluorescence quenching to UO22+ through the "antenna effect" and unsaturated Lewis basic sites on the ligands binding with UO22+. Moreover, TOCNF@Eu-MOF demonstrated excellent selectivity and anti-interference for UO22+ detection. For the nanopaper-based sensor made from TOCNF@Eu-MOF, the Stern-Volmer quenching constant (KSV) was calculated as 8.21 × 104 M-1, and the lowest limit of detection (LOD) was 6.6 × 10-7 M, significantly lower than the 1.32 × 10-6 M of Eu-MOFs. In addition, the nanopaper exhibited good fluorescence stability and cyclic detection performance, enabling the rapid and convenient detection of UO22+ in the aqueous phase within 30 s by simple dipping.

On-Site Ratiometric Analysis of UO22+ with High Selectivity

Uranyl ions (UO22+) are recognized as important indicators for monitoring sudden nuclear accidents. However, the interferences coexisting in the complicated environmental matrices impart serious constraints on the reliability of current on-site monitoring methods. Herein, a novel ratiometric method for the highly sensitive and selective detection of UO22+ is reported based on a [Eu(diaminoterephthalic acid)] (Eu-DATP) metal-organic framework. Benefiting from the unique chemical structure of Eu-DATP, energy transfer from DATP to UO22+ was enabled, resulting in the up-regulated fluorescence of UO22+ and the simultaneous down-regulated fluorescence of Eu3+. The limit of detection reached as low as 2.7 nM, which was almost 2 orders of magnitude below the restricted limit in drinking water set by the United States Environmental Protection Agency (130 nM). The Eu-DATP probe showed excellent specificity to UO22+ over numerous interfering species, as the intrinsic emissions of UO22+ were triggered. This unprecedentedly high selectivity is especially beneficial for monitoring UO22+ in complicated environmental matrices with no need for tedious sample pretreatment, such as filtration and digestion. Then, by facilely equipping a Eu-DATP-based sampler on a drone, remotely controlled sampling and on-site analysis in real water samples were realized. The concentrations of UO22+ were determined to be from 16.5 to 23.5 nM in the river water of the Guangzhou downtown area, which was consistent with the results determined by the gold-standard inductively coupled plasma mass spectrometry. This study presents a reliable and convenient method for the on-site analysis of UO22+.

A Ni(II) Coordination Polymer as a Multifunctional Luminescent Sensor for Detection of UO22+, Cr2O72-, CrO42- and Nitrofurantoin

A new Ni coordination polymer [Ni(MIP)(BMIOPE)]_n (1) was constructed (BMIOPE = 4,4'-bis(2-methylimidazol-1-yl)diphenyl ether, and H₂MIP = 5-methylisophthalic acid), possessing two-dimensional (2D) twofold parallel interwoven net structure with a 4⁴∙6² point symbol. Complex 1 has been successfully obtained based on mixed-ligand strategy. The fluorescence titration experiments revealed that complex 1 could act as multifunctional luminescent sensor to simultaneously detect UO₂²⁺, Cr₂O₇^2- and CrO₄^2-, and NFT (nitrofurantoin). The limit of detection (LOD) values for complex 1 are 2.86 × 10^-5, 4.09 × 10^-5, 3.79 × 10^-5 and 9.32 × 10^-5 M for UO₂²⁺, Cr₂O₇^2-, CrO₄^2- and NFT. The K_sv values are 6.18 × 10³, 1.44 × 10⁴, 1.27 × 10⁴ and 1.51 × 10⁴ M^-1 for NFT, CrO₄^2-, Cr₂O₇^2- and UO₂²⁺. Finally, the mechanism of its luminescence sensing is studied in detail. These results manifest that complex 1 is a multifunctional sensor for sensitive fluorescent UO₂²⁺, Cr₂O₇^2-, CrO₄^2- and NFT detection.

Nanoscale carbon dot-embedded metal-organic framework for turn-on fluorescence detection of water in organic solvents

An easy-to-use, highly selective, and real-time organic solvent quality assessment is desirable to detect water contamination in organic solvents. Herein, a one-step procedure using ultrasound irradiation was used for encapsulating nanoscale carbon dots (CDs) into metal-organic framework-199 (HKUST-1) to form CDs@HKUST-1 composite. The CDs@HKUST-1 exhibited very weak fluorescence due to photo-induced electron transfer (PET) from the CDs to the Cu²⁺ centers, acting as a fluorescent sensor in its off-state. The designed material can detect and discriminate water from other organic solvents, driven by turn-on fluorescence. This highly sensitive sensing platform could be applied for the detection of water in ethanol, acetonitrile, and acetone with wide linear detection ranges of 0-70% v/v, 2-12% v/v, and 10-50% v/v and limits of detection of 0.70% v/v, 0.59% v/v, and 1.08% v/v, respectively. The detection mechanism is attributed to the interruption of the PET process due to the release of fluorescent CDs after treatment with water. A smartphone-based quantitative test was successfully developed to monitor the water content in organic solvents utilizing CDs@HKUST-1 and a phone color processing application, thus making it possible to develop an on-site, real time and easy-to-use sensor for water detection.

"Two-in-one" dual-function luminescent MOF hydrogel for onsite ultra-sensitive detection and efficient enrichment of radioactive uranium in water

In consideration of the severe hazards of radioactive uranium pollution and the growing demand of uranium resources, the novel sensor/adsorbent composite was creatively developed to integrate the dual functions for on-site detection of uranium contamination and efficient recovery of uranium resources. By hybridizing the luminescent 3D terbium (III) metal-organic framework (Tb-MOF) with sodium alginate (SA) gel using terbium (III) as cross-linker, the Tb-MOF/Tb-AG was fabricated with multi-luminescence centers and sufficient binding sites for uranium. Notably, the ultra-high sensitivity with detection limit as low as 1.2 ppt was achieved, which was 4 orders of magnitude lower than the uranium contamination standard in drinking water (USEPA) and even comparable to the sensitivity of the ICP-MS. Furthermore, the very wide quantification range (1.0 ×10^-9-5.0 ×10^-4 mol/L), remarkable adsorption capacity (549.0 mg/g) and outstanding anti-interference ability have been achieved without sophisticated sample preparation procedures. Applied in complex natural water samples from Uranium Tailings and the Pearl River, this method has shown good detection accuracy. The ultra high sensitivity and great adsorption capacity for uranium could be ascribed to the synergistic coordination, hydrogen bonding and ion exchange between uranium and Tb-MOF/Tb-AG. The mechanisms were explored by infrared spectroscopy, batch experiments, X-ray photoelectron studies and energy dispersive spectroscopic studies. In addition, the Tb-MOF/Tb-AG can be reused for uranium adsorption.

Integration of quantum dots with Zn2GeO4 nanoellipsoids to expand the dynamic detection range of uranyl ions in fluorescent test strips

Fluorescent colorimetric test strips normally have a narrow dynamic detection-range due to the limited responsive range from single responsive materials, which cannot meet the wide detection requirement in practical applications. Herein, we developed an approach to detect uranyl ions (UO₂²⁺) with a broad detection range using the synthesized ZnS:Mn quantum dots (QDs) modified Zn₂GeO₄ nanoellipsoids (Zn₂GeO₄ @ZnS:Mn NEs), containing two responsive materials with the opposite signal responses at different UO₂²⁺ concentrations. Specifically, a red to chocolate color change was observed at low analyte concentrations (0.01-100 μM) resulting from the photoinduced electron transfer effect from ZnS:Mn QDs to UO₂²⁺. A sequentially olive drab to green color change has been observed when further increasing the UO₂²⁺ concentration (100-1000 μM) as a result of the antenna effect between Zn₂GeO₄ nanoellipsoids and UO₂²⁺. In addition, a low-cost and portable fluorescent test strip has been further fabricated through embedding Zn₂GeO₄ @ZnS:Mn NEs on a microporous structure membrane, demonstrating a facile yet effective colorimetric response to UO₂²⁺ in lab water, lake water, and seawater with a wide dynamic range. Therefore, it is potentially attractive for real-time and on-site detection of UO₂²⁺ in sudden-onset situations.

Hydrolytically Stable Zr-Based Metal-Organic Framework as a Highly Sensitive and Selective Luminescent Sensor of Radionuclides

Effective detections of radionuclides including uranium and its predominant fission products, for example, iodine, are highly desired owing to their radiotoxicity and potential threat to human health. However, traditional analytical techniques of radionuclides are instrument-demanding, and chemosensors targeted for sensitization of radionuclides remain limited. In this regard, we report a sensitive and selective sensor of UO₂²⁺ and I^- based on the unique quenching behavior of a luminescent Zr-based metal-organic framework, Zr₆O₄(OH)₄(OH)₆(H₂O)₆(TCPE)_1.5·(H₂O)₂₄(C₃H₇NO)₉ (Zr-TCPE). Immobilization of the luminescent tetrakis(4-carboxyphenyl)ethylene (TCPE^4-) linkers by Zr₆ nodes enhances the photoluminescence quantum yield of Zr-TCPE, which facilitates the effective sensing of radionuclides in a "turn-off" manner. Moreover, Zr-TCPE can sensitively and selectively recognize UO₂²⁺ and I^- ions with the lowest limits of detection of 0.67 and 0.87 μg/kg, respectively, of which the former one is much lower than the permissible value (30 μg/L) defined by the U.S. EPA. In addition, Zr-TCPE features excellent hydrolytic stability and can withstand pH conditions ranging from 3 to 11. To facilitate real-world applications, we have further fabricated polyvinylidene fluoride-integrating Zr-TCPE as luminescence-based sensor membranes for on-site sensing of UO₂²⁺ and I^-.

Metal-Organic Framework-Based Materials for Adsorption and Detection of Uranium(VI) from Aqueous Solution

The steady supply of uranium resources and the reduction or elimination of the ecological and human health hazards of wastewater containing uranium make the recovery and detection of uranium in water greatly important. Thus, the development of effective adsorbents and sensors has received growing attention. Metal-organic frameworks (MOFs) possessing fascinating characteristics such as high surface area, high porosity, adjustable pore size, and luminescence have been widely used for either uranium adsorption or sensing. Now pertinent research has transited slowly into simultaneous uranium adsorption and detection. In this review, the progress on the research of MOF-based materials used for both adsorption and detection of uranium in water is first summarized. The adsorption mechanisms between uranium species in aqueous solution and MOF-based materials are elaborated by macroscopic batch experiments combined with microscopic spectral technology. Moreover, the application of MOF-based materials as uranium sensors is focused on their typical structures, sensing mechanisms, and the representative examples. Furthermore, the bifunctional MOF-based materials used for simultaneous detection and adsorption of U(VI) from aqueous solution are introduced. Finally, we also discuss the challenges and perspectives of MOF-based materials for uranium adsorption and detection to provide a useful inspiration and significant reference for further developing better adsorbents and sensors for uranium containment and detection.

Dye functionalized lanthanide metal-organic framework as a multifunctional luminescent hybrid material for visual sensing of biomarker 2-methoxyaceticacid and sulfide anion

Based on the anionic Slug-47 [Gd(bpdc)₂^-] [NH₂(CH₃)₂⁺], a multifunctional fluorescent material with ultra-high stability has been fabricated successfully. Firstly, Eu_0.04Tb_39.96Gd₆₀ with white light emission is prepared by adjusting the doping ratio of Eu³⁺ ions and Tb³⁺ ions. Then, the dye acriflavine (ACF) is further introduced into the framework of Eu@ Slug-47 (1) via cation exchange to obtain ACF@1, which can be used as a ratio fluorescence sensor to detect 2-methoxyaceticacid (Maa), a toxic metabolite of glycol monomethyl ether, with the limit of detection (LOD) as low as 0.27 μg/mL. It is impressive that the emissions of ACF and biphenyl-4,4'-dicarboxylicacid ligands are gradually enhanced with the gradual weakening of the emission of Eu³⁺ ions during the detection of Maa. Under the superposition of three different colors, the sensing process undergoes a distinct color change from red to white and then to blue. These rich and colorful colors provide conditions for accurate visual detection of Maa. In addition, the material can also respond well to the pollutant S^2- ions and the LOD can reach 11.3 μmol /L. It is worth mentioning that the available quenching effect can be observed even if Maa and S^2- ions are detected in urine and tap water respectively, indicating that the multifunctional material has a brilliant application prospect. Finally, the quenching mechanism of Maa, S^2- ions toward ACF@1 is discussed in detail.

Preparation of Eu0.075Tb0.925-Metal Organic Framework as a Fluorescent Probe and Application in the Detection of Fe3+ and Cr2O72

Luminescent Ln-MOFs (Eu0.075Tb0.925-MOF) were successfully synthesised through the solvothermal reaction of Tb(NO3)3·6H2O, Eu(NO3)3·6H2O, and the ligand pyromellitic acid. The product was characterised by X-ray diffraction (XRD), TG analysis, EM, X-ray photoelectron spectroscopy (XPS), and luminescence properties, and results show that the synthesised material Eu0.075Tb0.925-MOF has a selective ratio-based fluorescence response to Fe3+ or Cr2O72-. On the basis of the internal filtering effect, the fluorescence detection experiment shows that as the concentration of Fe3+ or Cr2O72- increases, the intensity of the characteristic emission peak at 544 nm of Tb3+ decreases, and the intensity of the characteristic emission peak at 653 nm of Eu3+ increases in Eu0.075Tb0.925-MOF. The fluorescence intensity ratio (I653/I544) has a good linear relationship with the target concentration. The detection linear range for Fe3+ or Cr2O72- is 10-100 μM/L, and the detection limits are 2.71 × 10-7 and 8.72 × 10-7 M, respectively. Compared with the sensor material with a single fluorescence emission, the synthesised material has a higher anti-interference ability. The synthesised Eu0.075Tb0.925-MOF can be used as a highly selective and recyclable sensing material for Fe3+ or Cr2O72-. This material should be an excellent candidate for multifunctional sensors.

Metal-Organic-Framework Based Functional Materials for Uranium Recovery: Performance Optimization and Structure/Functionality-Activity Relationships

Uranium recovery has profound significance in both uranium resource acquisition and pollution treatment. In recent years, metal-organic frameworks (MOFs) have attracted much attention as potential uranium adsorbents owing to their tunable structural topology and designable functionalities. This review explores the research progress in representative classic MOFs (MIL-101, UiO-66, ZIF-8/ZIF-67) and other advanced MOF-based materials for efficient uranium extraction in aqueous or seawater environments. The uranium uptake mechanism of the MOF-based materials is refined, and the structure/functionality-property relationship is further systematically elucidated. By summarizing the typical functionalization and structure design methods, the performance improvement strategies for MOF-based adsorbents are emphasized. Finally, the present challenges and potential opportunities are proposed for the breakthrough of high-performance MOF-based materials in uranium extraction.

Temperature-robust and ratiometric G-quadruplex proximate DNAzyme assay for robustly monitoring of uranium pollution and its microbial biosorbents screening

Uranium pollution in environment and food chain is a serious threat to public security and human health. Herein, we proposed a temperature-robust, ratiometric, and label-free bioassay based on G-quadruplex proximate DNAzyme (G4DNAzyme), accommodating us to precisely monitor uranium pollution and biosorption. The proximity of split G-quadruplex probes was proposed to sense UO₂²⁺-activated DNAzyme activity, thus eliminating the use of chemically labeled nucleic acid probes. And the simultaneous monitoring of G-quadruplex and double-stranded structures of DNAzyme probes contributed to a ratiometric and robust detection of UO₂²⁺. Particularly, the separation of enzymatic digestion and fluorescence monitoring endued a robust and highly responsive detection of UO₂²⁺ upon the temperature of enzymatic digestion process ranged from 18° to 41 °C. Consequently, G4DNAzyme assay allowed a robust, label-free and ratiometric quantification of uranium. We demonstrated the feasibility of G4DNAzyme assay for estimating uranium pollution in water and aquatic product samples. Ultimately, G4DNAzyme assay was adopted to serve as the platform to screen bacterial species and conditions for uranium biosorption, promising its roles in uranium associated biosafety control.

Polymer Ligand-Sensitized Lanthanide Metal-Organic Frameworks for an On-Site Analysis of a Radionuclide

Herein, a new strategy to increase the sensitivity of a lanthanide metal-organic framework (Ln-MOF) to UO₂²⁺ was proposed by using polymeric ligands. By utilizing [Tb(1,3,5-benzenetrisbenzoate)]n (Tb-TBT) MOF as the host, preloaded 2-vinyl terephthalic acid (VTP) was polymerized in situ, which produced a novel fluorescent composite denoted as PVTP⊂Tb-TBT. Benefiting from the coordination of PVTP to the Tb nodes, the polymeric chains performed both as molecular scaffolds that improved the water stability of the framework and as additional antennae that sensitized the photoluminescence of the Tb nodes. More importantly, the detection sensitivity and selectivity of PVTP⊂Tb-TBT to UO₂²⁺ were much improved compared to those of Tb-TBT. Detailed characterizations indicated that the incorporation of PVTP efficiently enriched UO₂²⁺ in the probe, which promoted the energy dissipation to UO₂²⁺. Besides, UO₂²⁺ was also supposed to release PVTP from PVTP⊂Tb-TBT and, thus, exposed the open metal sites to water molecules, which interrupted the sensitization effect of PVTP and induced a nonradiative energy dissipation. A limit of detection (LOD) as low as 0.75 nm was recorded by suspending the PVTP⊂Tb-TBT probe in a water sample, far below the limit in drinking water set by the United States Environmental Protection Agency (130 nm). Furthermore, a remotely controlled sampling and an on-site analysis of real water samples were realized by facilely loading PVTP⊂Tb-TBT on thin films (TFs). The LOD for UO₂²⁺ was 2.5 nm by using the TFs. This study reports a new strategy for boosting the sensitivity and selectivity of Ln-MOF to monitor UO₂²⁺ and expands the application of the strategy to an on-site analysis.

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.

Epoxy Functional Composites Based on Lanthanide Metal-Organic Frameworks for Luminescent Polymer Materials

The integration of metal-organic frameworks (MOF) into organic polymers represents a direct and effective strategy for developing innovative composite materials that combine the exceptional properties of MOFs with the robustness of organic polymers. However, the preparation of MOF@polymer hybrid composites requires an efficient dispersion and interaction of MOF particles with polymer matrices, which remains a significant challenge. In this work, a new simple and direct approach was applied for the development of Ln-MOF@polymer materials. A series of Ln-MOF@TGIC composites {Ln-MOF = [Ln(μ₃-BTC)(H₂O)₆]_n (Ln-BTC), where Ln = Eu, Tb, Eu_0.05Tb_0.95; H₃BTC = 1,3,5-benzenetricarboxylic acid; TGIC = triglycidyl isocyanurate} were successfully obtained by applying a grinding method via the chemical bonding between uncoordinated carboxylate groups in Ln-BTC and epoxy groups in TGIC. The Ln-BTC@TGIC materials possess significant fluorescence characteristics with superior emission lifetimes and quantum yields if compared to parent Ln-MOFs. Interestingly, under the UV irradiation, a considerable color change from yellow in Eu_0.05Tb_0.95-BTC to red in Eu_0.05Tb_0.95-BTC@TGIC was observed. The energy-transfer mechanism was also rationalized by the density functional theory (DFT) calculations. The developed Ln-BTC@TGIC composites were further applied as functional fluorescent coatings for the fabrication, via a simple spraying method, of the flexible polyimide (PI) films, Ln-BTC@TGIC@PI. Thus, the present work unveils a new methodology and expands its applicability for the design and assembly of stable, multicomponent, and soft polymer materials with remarkable fluorescence properties.

Exploiting a new europium(III) coordination polymer based on a zwitterionic ligand as a fluorescent probe for uranyl cations

Two new isostructural lanthanide(III) coordination polymers based on an unreported zwitterionic ligand, namely, [Ln(ox)(L)]n (ox = oxalate, HL = N,N'-dipropionic acid imidazolium, Ln = Eu or La), are synthesized under hydrothermal conditions and characterized by single-crystal X-ray diffraction, infrared spectroscopy, powder X-ray diffraction, and thermogravimetric analysis. The fluorescence properties of the europium coordination polymer are investigated. In addition, the europium-based coordination polymer is utilized for specific sensing of UO22+ ions, showing high selectivity, a fast response time (8 min) and high sensitivity with noticeable quenching ( Ksv = 6.19 × 104 M−1) and limit of detection of 1.95 µM.

Water and Metal-Organic Frameworks: From Interaction toward Utilization

The steep stepwise uptake of water vapor and easy release at low relative pressures and moderate temperatures together with high working capacities make metal-organic frameworks (MOFs) attractive, promising materials for energy efficient applications in adsorption devices for humidity control (evaporation and condensation processes) and heat reallocation (heating and cooling) by utilizing water as benign sorptive and low-grade renewable or waste heat. Emerging MOF-based process applications covered are desiccation, heat pumps/chillers, water harvesting, air conditioning, and desalination. Governing parameters of the intrinsic sorption properties and stability under humid conditions and cyclic operation are identified. Transport of mass and heat in MOF structures, at least as important, is still an underexposed topic. Essential engineering elements of operation and implementation are presented. An update on stability of MOFs in water vapor and liquid systems is provided, and a suite of 18 MOFs are identified for selective use in heat pumps and chillers, while several can be used for air conditioning, water harvesting, and desalination. Most applications with MOFs are still in an exploratory state. An outlook is given for further R&D to realize these applications, providing essential kinetic parameters, performing smart engineering in the design of systems, and conceptual process designs to benchmark them against existing technologies. A concerted effort bridging chemistry, materials science, and engineering is required.

In-situ synthesis of metal nanoparticles@metal-organic frameworks: Highly effective catalytic performance and synergistic antimicrobial activity

M-NP@Zn-BIF (M-NP = Ag or Cu nanoparticle; Zn-BIF is a zinc-based boron imidazolate framework, Zn₂(BH(2-mim)₃)₂(obb); 2-mim = 2-methylimidazole; obb = 4,4'-oxybis(benzoate)) composites were successfully in-situ synthesized by utilizing the reducing ability of the BH bond contained in the Zn-BIF at room temperature without any additional chemical reduction reagents. These composites (225 μg/mL) exhibited excellent catalytic activity to convert 4-nitrophenol to 4-aminophenol in 2.5 min and 6 min with a conversion rate of 99.9 %, respectively. In addition, Ag@Zn-BIF (50 μg/mL) showed highly synergistic antibacterial activity against both Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) with a bactericidal rate of approximately 99.9 %. An antibacterial mechanism was proposed for the generation of intracellular reactive oxygen species (ROS) levels. Superoxide radicals (O^2-) and hydroxyl radicals (OH) formed during the antibacterial process were shown to accelerate the death of bacteria. They also exhibited highly photocatalytic activity for Rhodamine B (RhB). When the concentration of the composites is 1000 μg/mL, the photocatalytic efficiency of Ag@Zn-BIF and Cu@Zn-BIF increased by 31.62 and 18.13 times compared with Zn-BIF, respectively. All in all, this study developed a simple and versatile integrated platform for the removal of nitrophenols, organic dyes, and the effective inactivation of bacteria in water.

Rational Construction of Porous Metal-Organic Frameworks for Uranium(VI) Extraction: The Strong Periodic Tendency with a Metal Node

Although metal-organic frameworks (MOFs) have been reported as important porous materials for the potential utility in metal ion separation, coordinating the functionality, structure, and component of MOFs remains a great challenge. Herein, a series of anionic rare earth MOFs (RE-MOFs) were synthesized via a solvothermal template reaction and for the first time explored for uranium(VI) capture from an acidic medium. The unusually high extraction capacity of UO₂²⁺ (e.g., 538 mg U per g of Y-MOF) was achieved through ion-exchange with the concomitant release of Me₂NH₂⁺, during which the uranium(VI) extraction in the series of isostructural RE-MOFs was found to be highly sensitive to the ionic radii of the metal nodes. That is, the uranium(VI) adsorption capacities continuously increased as the ionic radii decreased. In-depth mechanism insight was obtained from molecular dynamics simulations, suggesting that both the accessible pore volume of the MOFs and hydrogen-bonding interactions contribute to the strong periodic tendency of uranium(VI) extraction.

The utilization of biomineralization technique based on microbial induced phosphate precipitation in remediation of potentially toxic ions contaminated soil: A mini review

In recent years, many studies have been devoted to investigate the application of microbial induced phosphate precipitation (MIPP) process for potentially toxic element polluted soil remediation. MIPP biomineralization technique exhibits a great potential to efficiently remediate polluted soil considering its low cost, green and ecofriendly process, and simple in operation. This paper represented a review on the state of the art of polluted soil remediation based on MIPP technique. Briefly, certain defined criteria on targeted microbe selection was discussed; an overall review on the utilization of MIPP process for toxic ions biomineralization in soil was provided; influencing factors reported in the literature, such as pH, temperature, humic substances, coexisting ions, effective microbial population, and enzyme activity, were then comprehensively reviewed; finally; a special emphasis was given to enhance MIPP remediation performance in soil in future research.

Unexpected structural complexity of thorium coordination polymers and polyoxo cluster built from simple formate ligands

A simple synthetic approach with [HCOOH]/[Th(iv)] and water controls the yield of six thorium formates with unexpected structural complexity.

From IR to x-rays: gaining molecular level insights on metal-organic frameworks through spectroscopy

This topical review focuses on the application of several types of spectroscopy methods to a class of solid state materials called metal organic frameworks (MOFs). MOFs are self-assembled, porous crystalline materials composed of metal cluster nodes linked through coordination bonds with organic or organometallic molecular constituents. Their unique host-guest properties make them attractive for many adsorption-based applications such as gas storage and separation, catalysis, sensing and others. While much research focuses on the development and application of these materials, fundamental studies of MOF properties and molecular level host-guest interactions behind their functionality have become a significant research direction on its own. Spectroscopy methods are now ubiquitous tools in this pursuit. This review focuses on the application of three classes of spectroscopy methods to MOF materials: vibrational, optical electronic and x-ray spectroscopies. Following brief introductions to each method that include pertinent theory and experimental considerations, we present a broad overview of the types of MOF systems that have been studied, with specific examples and important new molecular level insights highlighted along the way. The current status of spectroscopic studies of MOFs is presented at the end along with some perspectives on the future directions in this area of research.

A quencher-free DNAzyme beacon for fluorescently sensing uranyl ions via embedding 2-aminopurine

DNAzyme-based fluorescent probes have provided valuable protocols for detecting uranium, one of the most common radioactive contaminants in the environment, with ultra-high selectivity and sensitivity. Designing novel DNAzyme beacons to update the mode of fluorescence reporting and/or quenching will continuously enhance "turn-on" sensing performance as well as promote actual application of the biological probes. In this work, we developed a novel quencher-free DNAzyme beacon by embedding fluorescent 2-aminopurine for rapid detection of uranyl ion. 2-aminopurine is able to substitute adenine and keep strong fluorescence in single-stranded DNA whereas being quenched in the hybridized double-stranded DNA by the base-stacking interaction. The combination of such trait of 2-aminopurine and cleavage reaction of DNAzyme in the presence of target co-factors possesses two main advantages for ion sensing: simplicity for avoidance of extra quencher groups and high performance because of superiority of DNAzyme essence. The experimental conditions including embedding site, pH and salt concentration of buffer solutions, and the amount ratio of enzyme strand to substrate strand used to form DNAzymes were systematically optimized to inspire the highest performance of the biological beacon. Thus, a detection limit of 9.6 nM, a wide linear range from 5 nM to 400 nM (R² = 0.997), and selectivity of more than 400 000-fold over other metal ions were achieved by the novel DNAzyme probes. The highly sensitive, selective and quencher-free DNAzyme probes accommodated a simple and cost-efficient alternative to current fluorescent counterparts, holding a great potential for further application in practical ion assay.

Detection of inorganic phosphor in environmental water samples using a lanthanide and nanoparticle chemosensor based on Fӧrster resonance energy transfer

A novel chemosensor is presented for the detection of inorganic phosphate (Pi) in environmental water samples. The sensing solution is comprised of terbium (Tb³⁺) chelated to ethylenediaminetetraacetic acid (EDTA) acid and cetyltrimethylammonium bromide (CTAB)-capped gold nanoparticles (Au NPs). Upon mixing, Tb-EDTA and Au NPs undergo Fӧrster resonance energy transfer (FRET) in which the luminescence from the lanthanide ion is quenched. Upon the addition of Pi, Au NPs aggregate and precipitate out of solution. The aggregation of Au NPs results in the restoration of the Tb-EDTA luminescence signal, which correlates linearly to the Pi concentration in the matrix of analysis. The limit of detection (LOD) of the luminescence sensor (83 ng·mL^-1) is within the range of LODs previously reported for on-site monitoring of Pi. Quantitative analysis carried out via the multiple standard additions method provides accurate determination of Pi concentrations in heavily contaminated environmental waters.

A Pillar-Layered Zn-LMOF with Uncoordinated Carboxylic Acid Sites: High Performance for Luminescence Sensing Fe3+ and TNP

By using the mixed-linker strategy, a new pillar-layered luminescence Zn-LMOF (JLU-MOF71) ([Zn₂Na₂(TPHC)(4,4-Bipy)(DMF)]·8H₂O) (TPHC = [1,1':2',1″-terphenyl]-3,3″,4,4',4″,5'-hexacarboxylic acid, 4,4-bipy = 4,4-bipyridine, DMF = N, N-dimethylformamide) was successfully synthesized and structurally characterized. JLU-MOF71 is constructed by the 4,4-bipy pillars and 2D layers which consist of Zn²⁺ and TPHC ligands, and displays a rare fsh topology. Benefiting from the uncoordinated carboxylate sites in the framework, JLU-MOF71 not only can sensitively detect trace amounts of individual Fe³⁺ and 2,4,6-trinitrophenol (TNP) through luminescence quenching but also exhibits high selectivity when other competing analytes exist. Besides, TNP can also be effectively monitored with the help of the shifting direction of luminescent spectra (red shift) which has rarely been reported before. On the basis of the aforementioned, JLU-MOF71 can be considered as a potential luminescence sensor for detecting Fe³⁺ and TNP.

A dual-responsive luminescent metal–organic framework as a recyclable luminescent probe for the highly effective detection of pyrophosphate and nitrofurantoin

Luminescent ZTMOF-1 can discriminately detect PPi and NFT with high selectivity, sensitivity and stability.

Terbium Oxalatophosphonate as Efficient Multiresponsive Luminescent Sensors for Chromate Anions and Tryptophan Molecules

A stable 2D terbium oxalatophosphonate with green luminescence, namely, [Tb2(H3L)(C2O4)3(H2O)4]·2H2O (1), has been hydrothermally obtained by using (4-carboxypiperidyl)-N-methylenephosphonic acid (H3L) and oxalate ligand. The luminescent investigation indicates that the emission behavior of compound 1 shows high water and pH stabilities. It can be applied as a multiresponsive luminescent probe with high selectivity, high sensitivity, recycling capability, and fast sensing of CrO4 2-, Cr2O7 2- anions and tryptophan (Trp) molecules in aqueous solution through the luminescence quenching effect. Moreover, the sensing results can be distinguished by the naked eye under the irradiation of UV light of 254 nm. In addition, the probable mechanisms for the quenching behavior are also discussed, which can be mainly attributed to the competitive absorption of excitation energy between compound 1 and the analytes.

Multifunctional Ln-MOF Luminescent Probe for Efficient Sensing of Fe3+, Ce3+, and Acetone

A new series of five three-dimensional Ln(III) metal-organic frameworks (MOFs) formulated as [Ln₄(μ₆-L)₂(μ-HCOO)(μ₃-OH)₃(μ₃-O)(DMF)₂(H₂O)₄] _n {Ln³⁺ = Tb³⁺ (1), Eu³⁺ (2), Gd³⁺ (3), Dy³⁺ (4), and Er³⁺ (5)} was successfully obtained via a solvothermal reaction between the corresponding lanthanide(III) nitrates and 2-(6-carboxypyridin-3-yl)terephthalic acid (H₃L). All of the obtained compounds were fully characterized, and their structures were established by single-crystal X-ray diffraction. All products are isostructural and possess porous 3D networks of the fluorite topological type, which are driven by the cubane-like [Ln₄(μ₃-OH)₃(μ₃-O)(μ-HCOO)]⁶⁺ blocks and μ₆-L^3- spacers. Luminescent and sensing properties of 1-5 were investigated in detail, revealing a unique capability of Tb-MOF (1) for sensing acetone and metal(III) cations (Fe³⁺ or Ce³⁺) with high efficiency and selectivity. Apart from a facile recyclability after sensing experiments, the obtained Tb-MOF material features a remarkable stability in a diversity of environments such as common solvents, aqueous solutions of metal ions, and solutions with a broad pH range from 4 to 11. In addition, compound 1 represents a very rare example of the versatile Ln-MOF probe capable of sensing Ce³⁺ or Fe³⁺ cations or acetone molecules.

Novel double layer lanthanide metal–organic networks for sensing applications

Two isostructural lanthanide-based 2D coordination polymers were synthesized under hydrothermal conditions and fully characterized. The obtained compounds display notable sensing ability for p-phenylenediamine, benzidine, and acetone analytes.