Highly Selective and Sensitive Detection of PO4 3- Ions in Aqueous Solution by a Luminescent Terbium Metal-Organic Framework

Enhanced phosphate removal from aqueous environments using three-dimensional La-doped carboxylic carbon nanotubes/alginate: Performance and mechanisms

The excessive amounts of phosphorus (P) discharged and usage have caused eutrophication and algal blooms, which seriously jeopardize the environment even the human health. In this study, carbon nanotubes (CNTs) served as carriers to develop a lanthanum-based sodium alginate hydrogel (La-CNT-COOH/SA) aimed at efficiently removing phosphate from wastewater. Characterization results confirmed successful deposition of La(OH)3 nanoparticles onto CNT-COOH. The optimal adsorption efficiency of La-CNT-COOH/SA hydrogels occurred at pH 4, with a maximum adsorption capacity of 54.4 mg/g under an initial phosphate concentration of 60 mg/L. Batch experiments demonstrated that La-CNT-COOH/SA performed well across a favorable pH range and exhibited high tolerance to common coexisting ions during phosphate adsorption. Adsorption isotherms indicated a dominance of both physical and chemical mechanisms in phosphate removal by La-CNT-COOH/SA. At elevated phosphate concentrations, the adsorption process followed quasi-second-order kinetics, primarily driven by chemical adsorption. Multi-instrument characterization emphasized that the substantial loading of La(OH)3 on CNT-COOH significantly contributed to adsorption, alongside crosslinked lanthanum ions on sodium alginate and abundant hydroxyl groups. Mechanisms of adsorption by La-CNT-COOH/SA encompassed electrostatic interactions, surface precipitation, and in-sphere complexation (La-O-P). These findings on fabrication, properties, and adsorption mechanisms of the phosphate-removal hydrogel lay a theoretical foundation for applying biomass-based materials in large-scale remediation practices.

Fluorescent chemosensors facilitate the visualization of plant health and their living environment in sustainable agriculture

Globally, 91% of plant production encounters diverse environmental stresses that adversely affect their growth, leading to severe yield losses of 50-60%. In this case, monitoring the connection between the environment and plant health can balance population demands with environmental protection and resource distribution. Fluorescent chemosensors have shown great progress in monitoring the health and environment of plants due to their high sensitivity and biocompatibility. However, to date, no comprehensive analysis and systematic summary of fluorescent chemosensors used in monitoring the correlation between plant health and their environment have been reported. Thus, herein, we summarize the current fluorescent chemosensors ranging from their design strategies to applications in monitoring plant-environment interaction processes. First, we highlight the types of fluorescent chemosensors with design strategies to resolve the bottlenecks encountered in monitoring the health and living environment of plants. In addition, the applications of fluorescent small-molecule, nano and supramolecular chemosensors in the visualization of the health and living environment of plants are discussed. Finally, the major challenges and perspectives in this field are presented. This work will provide guidance for the design of efficient fluorescent chemosensors to monitor plant health, and then promote sustainable agricultural development.

Turn-off luminescence sensing, white light emission and magnetic studies of two-dimensional lanthanide MOFs

The lanthanide metal organic framework compounds [Ln(BPTA)1.5(Bpy)]·0.5DMF (Ln = Y, Eu, Gd, Tb, Dy; 1a-5a) and [Ln(BPTA)1.5(Phen)]·0.5DMF (Ln = Y, Eu, Gd, Tb, Dy; 1b-5b) were prepared by employing 2,5-bis(prop-2-yn-1-yloxy)terephthalic acid (2,5-BPTA) as the primary ligand and 2,2'-bipyridine (1a-5a) and 1,10-phenanthroline (1b-5b) as the secondary ligands. Single-crystal structural studies on [Gd(BPTA)1.5(Bpy)]·0.5DMF (3a) and [Dy(BPTA)1.5(Phen)]·0.5DMF (5b) indicated that the compounds have a two-dimensional structure. The Y compound exhibits blue emission, and the other compounds exhibit emission in the expected regions (λex = 350 nm). White light emission was achieved by careful mixing of the red (Eu3+) and green (Tb3+) components in the blue emitting Y compound. Thus, Y0.96Tb0.02Eu0.02 (bpy) and Y0.939Tb0.06Eu0.001 (phen) were found to show white emission when excited using a wavelength of 350 nm. The introduction of N-N-containing ancillary ligands (i.e., bpy and phen) increased the overall quantum yield (QY) of white light emission to 31% and 43%, respectively. The high QY observed for the Tb and Eu compounds was found to be sensitive and selective for the fluorometric detection of azinphos-methyl pesticide and trinitrophenol (TNP) in an aqueous medium at the ppb level. The same behaviour was observed when utilising the compounds as onsite paper strip sensors. Their magnetic properties were also studied, revealing for the Tb and Dy derivatives slow relaxation of the magnetisation at low temperature. The present study highlights the usefulness of rigid π-conjugated molecules such as 2,2'-bipyridine and 1,10-phenanthroline in enhancing the many utilities of rare-earth-containing MOFs towards white light emission, the sensing of harmful and dangerous substances and magnetic properties.

Luminescent lanthanide probes for cations and anions: Promises, compromises, and caveats

The long luminescence lifetimes and sharp emission bands of luminescent lanthanide complexes have long been recognized as invaluable strengths for sensing and imaging in complex aqueous biological or environmental media. Herein we discuss the recent developments of these probes for sensing metal ions and, increasingly, anions. Underappreciated in the field, buffers and metal hydrolysis influence the response of many responsive lanthanide probes. The inherent complexities arising from these interactions are further discussed.

Synthesis of a Cd-MOF Fluorescence Sensor and Its Detection of Fe3+, Fluazinam, TNP, and Sulfasalazine Enteric-Coated Tablets in Aqueous Solution

A Cd-based metal-organic framework (Cd-MOF), named after {[Cd(ttc)(H₂O)]·H₂O}_n (ttc = 1-imidazole-1-yl-2,4,6-benzene-tricarboxylic acid), was synthesized using the solvothermal reaction. The single-crystal structure was determined by single X-ray diffraction analysis, and crystalline characteristics and composition were confirmed by powder X-ray diffraction (PXRD) and thermogravimetric analysis (TG), respectively. Structural analysis showed that the Cd²⁺ ion is in the seven-coordinated mode, in which ttc^2- ion adopts the μ₄-η¹-η¹-η²-η² coordination mode. It is worth noting that the Cd²⁺ ion is connected to ttc^2- to form a 2D network, and the adjacent 2D network is expanded into a 3D supramolecular network structure through weak hydrogen bonds. The fluorescence sensing experiments indicated that Cd-MOF could not only be used as a fluorescence sensor for Fe³⁺, fluazinam (FLU), and 2,4,6-trinitrophenolol (TNP) but also for sulfasalazine detection in aqueous solution. To verify the sensitivity of the fluorescent probe, we calculated its detection limit: 5.34 × 10^-8 M (Fe³⁺), 7.8 × 10^-8 M (FLU), 1.21 × 10^-7 M (TNP), and 2.67 × 10^-7 M (SECT). In addition, the quenching mechanism was thoroughly studied.

Design of "turn-off" luminescent Ln-MOFs for sensitive detection of cyanide anions

Two novel 2D lanthanide metal-organic frameworks (Ln-MOFs), namely {[Eu₂(DBTA)₃(DMF)₂]·DMF}_n (1) and {[Tb₂(DBTA)₃(DMF)₂]·DMF}_n (2) (H₂DBTA = 2,5-dibromoterephthalic acid), have been successfully synthesized by the solvothermal method. Single-crystal X-ray diffraction results proved that the complexes possess the same topological structure of a (4²·6)₂(4²·8⁴)(4⁷·6³)₂-connected net. The recognition of CN^- from interfering anions with a low detection limit by "turn-off" luminescence makes them promising candidates for the highly selective and sensitive detection of the cyanide ion. The Ln-MOFs 1 and 2 exhibit excellent chemical sensing properties for CN^- with efficiency, selectivity, and excellent performance in various mixed anions. The evaluation parameters, including the quenching constant and detection limit, have been investigated to obtain the detection performance for CN^-.

Coordination networks for the recognition of oxo-anions

Crystalline coordination networks with an infinite extended framework, also known as coordination polymers (CPs) or metal-organic frameworks (MOFs), have attracted significant attention owing to their tremendous performance in an extensive range of applications. The unique structural features and high stability of coordination networks are responsible for their utilization and potential in diverse fields especially in the area of sensing using luminescent CPs/MOFs. The recognition of toxic oxo-anions present in water is a crucial and first step towards environmental remediation, mainly in the case of water pollution. Accordingly, the utilization of luminescent coordination networks has received significant interest, particularly for the recognition of various toxic oxo-anions, which are considered a threat to aquatic life and the environment. In this frontier article, we summarize recent reports on luminescent CPs/MOFs, their utilization for the sensing of oxo-anions and the chemistry of the interaction of oxo-anions with CPs/MOFs, which is responsible for tuning their optical signals.

Multidimensional Ln-Aminophthalate Photoluminescent Coordination Polymers

The development of straightforward reproducible methods for the preparation of new photoluminescent coordination polymers (CPs) is an important goal in luminescence and chemical sensing fields. Isophthalic acid derivatives have been reported for a wide range of applications, and in addition to their relatively low cost, have encouraged its use in the preparation of novel lanthanide-based coordination polymers (LnCPs). Considering that the photoluminescent properties of these CPs are highly dependent on the existence of water molecules in the crystal structure, our research efforts are now focused on the preparation of CP with the lowest water content possible, while considering a green chemistry approach. One- and two-dimensional (1D and 2D) LnCPs were prepared from 5-aminoisophthalic acid and Sm³⁺/Tb³⁺ using hydrothermal and/or microwave-assisted synthesis. The unprecedented LnCPs were characterized by single-crystal X-ray diffraction (SCRXD), powder X-ray diffraction (PXRD), Fourier transform infrared (FT-IR) spectroscopy and scanning electron microscopy (SEM), and their photoluminescence (PL) properties were studied in the solid state, at room temperature, using the CPs as powders and encapsulated in poly(methyl methacrylate (PMMA) films, envisaging the potential preparation of devices for sensing. The materials revealed interesting PL properties that depend on the dimensionality, metal ion, co-ligand used and water content.

Recent progresses in luminescent metal-organic frameworks (LMOFs) as sensors for the detection of anions and cations in aqueous solution

The discharge of excessive metal ions and anions into water bodies leads to the serious pollution of water and environment, which in turn has a certain impact on industry, agriculture, and human life. Because of the unique advantages of luminescent metal-organic frameworks (LMOFs), they have been successfully explored as various fluorescent probes to quickly and effectively detect these pollutants. This perspective not only introduces the design strategy and classification of LMOFs, especially the construction methods of water-stable LMOFs, but also reports the latest progresses in some LMOFs between 2016 and 2020 as well as expounds the mechanisms of LMOFs for detecting anions and cations. Moreover, the luminescence properties of LMOFs are related to the selection of metal ions, the structure of organic ligands, the pore size, and the interaction of guest molecules. Finally, the further development of LMOFs is summarized and prospected in this field.

Selective and recyclable tandem sensing of PO43- and Al3+ by a water-stable terbium-based metal-organic framework

Herein, a luminescent water-stable terbium-based metal-organic framework (MOF) {[Tb(Cmdcp)(H₂O)₃]₂(NO₃)₂·5H₂O}_n (1, H₃CmdcpBr = N-carboxymethyl-(3,5-dicarboxyl)pyridinium bromide) has been synthesized and used for the recyclable sensing of PO₄^3- and Al³⁺ in tandem. MOF 1 acts as a fluorescent sensor for PO₄^3- by the luminescence "turn-off" mechanism with high selectivity over other anions, such as F^-, Cl^-, Br^-, I^-, NO₃^-, H₂PO₄^-, HSO₄^-, HCO₃^-, HSO₃^-, SO₄^2-, CO₃^2- and HPO₄^2-. The formed PO₄^3-@1 complex further acts as the Al³⁺ sensor with the luminescence "turn-on" mechanism, also with high selectivity over diverse inorganic cations of Fe²⁺, Mn²⁺, Co²⁺, Ni²⁺, Hg²⁺, Na⁺, K⁺, Li⁺, Ag⁺, Mg²⁺, Ca²⁺, Cd²⁺, Pb²⁺, Cu²⁺, and Zn²⁺. The detection process for both PO₄^3- and Al³⁺ can be directly observed with naked eyes under the UV light at 365 nm. The detection limits for PO₄^3- and Al³⁺ are 1.1 μM and 6.6 μM, respectively. Such a sensing cycle is further transferable to urine and serum samples with a satisfactory near-quantitative recovery, highlighting its good potential in biologically relevant applications.

Coordination Polymers Based on Highly Emissive Ligands: Synthesis and Functional Properties

Coordination polymers are constructed from metal ions and bridging ligands, linking them into solid-state structures extending in one (1D), two (2D) or three dimensions (3D). Two- and three-dimensional coordination polymers with potential voids are often referred to as metal-organic frameworks (MOFs) or porous coordination polymers. Luminescence is an important property of coordination polymers, often playing a key role in their applications. Photophysical properties of the coordination polymers can be associated with intraligand, metal-centered, guest-centered, metal-to-ligand and ligand-to-metal electron transitions. In recent years, a rapid growth of publications devoted to luminescent or fluorescent coordination polymers can be observed. In this review the use of fluorescent ligands, namely, 4,4'-stilbenedicarboxylic acid, 1,3,4-oxadiazole, thiazole, 2,1,3-benzothiadiazole, terpyridine and carbazole derivatives, naphthalene diimides, 4,4',4''-nitrilotribenzoic acid, ruthenium(II) and iridium(III) complexes, boron-dipyrromethene (BODIPY) derivatives, porphyrins, for the construction of coordination polymers are surveyed. Applications of such coordination polymers based on their photophysical properties will be discussed. The review covers the literature published before April 2020.

Removal of Phosphorus from an Aqueous Solution by Nanocalcium Hydroxide Derived from Waste Bivalve Seashells: Mechanism and Kinetics

Excessive supply of phosphorus, a vital macronutrient for all organisms, can cause unwanted environmental consequences such as eutrophication. An increase in agricultural and industrial activities has created a considerable imbalance in the phosphorus cycle with continuing adverse effects on sustainability and ecosystem health, thereby stipulating/postulating the significance of phosphorus removal. A unique and sustainable concept for the removal of phosphorus through the utilization of waste bivalve seashells was proposed in the present study. Flat-surfaced and hexagonally shaped nanocalcium hydroxide particles (∼96% purity) with size ranging from 100 to 400 nm have been synthesized, and phosphorus from its aqueous solution is treated via precipitation. An optimization study has been conducted using the Box-Behnken design of response surface methodology, which highlights that with a calcium/phosphorus mass ratio, pH, and temperature of 2.16, 10.20, and 25.48 °C, a phosphorus removal efficiency of 99.33% can be achieved in a residence time of 10 min. Also, under the same conditions, diluted human urine was analyzed and phosphorus removal efficiency of ∼95% was observed. Through experimental results, semiquantitative phase analysis, and transmission electron microscopy, it has been found that the reaction was diffusion-controlled, which was further confirmed through shrinking core diffusion modeling. The present study manifests the promising potential of waste seashell-derived nanocalcium hydroxide for phosphorus treatment and its precipitation in the form of value-added hydroxyapatite.

A luminescent terbium coordination polymer as a multifunctional water-stable sensor for detection of Pb2+ ions, PO43− ions, Cr2O72− ions, and some amino acids

It is the first Ln-CP fluorescence probe for synchronous determination of Tyr and Trp in the presence of other amino acids.