Structural diversity and applications of Ce(III)-based coordination polymers

A Coordination-Derived Cerium-Based Amorphous-Crystalline Heterostructure with High Electrocatalytic Oxygen Evolution Activity

The rational design of heterogeneous catalysts is crucial for achieving optimal physicochemical properties and high electrochemical activity. However, the development of new amorphous-crystalline heterostructures is significantly more challenging than that of the existing crystalline-crystalline heterostructures. To overcome these issues, a coordination-assisted strategy that can help fabricate an amorphous NiO/crystalline NiCeOx (a-NiO/c-NiCeOx) heterostructure is reported herein. The coordination geometry of the organic ligands plays a pivotal role in permitting the formation of coordination polymers with high Ni contents. This consequently provides an opportunity for enabling the supersaturation of Ni in the NiCeOx structure during annealing, leading to the endogenous spillover of Ni from the depths of NiCeOx to its surface. The resulting heterostructure, featuring strongly coupled amorphous NiO and crystalline NiCeOx, exhibits harmonious interactions in addition to low overpotentials and high catalytic stability in the oxygen evolution reaction (OER). Theoretical calculations prove that the amorphous-crystalline interfaces facilitate charge transfer, which plays a critical role in regulating the local electron density of the Ni sites, thereby promoting the adsorption of oxygen-based intermediates on the Ni sites and lowering the dissociation-related energy barriers. Overall, this study underscores the potential of coordinating different metal ions at the molecular level to advance amorphous-crystalline heterostructure design.

Cerium(III) and 5-methylisophthalate-based MOFs with slow relaxation of magnetization and photoluminescence emission

Two novel Ce(III) metal organic frameworks (MOFs) with formulas [Ce(5Meip)(H-5Meip)]nGR-MOF-17 and [CeCl(5Meip)(DMF)]nGR-MOF-18 (5Meip = 5-methylisophthalate, DMF = N,N-dimethylformamide) have been synthesized, forming 3-dimensional frameworks. Magnetic measurements show that both compounds present field-induced slow magnetic relaxation under a small applied dc field. For GR-MOF-17, the temperature dependence of relaxation times is best described by a Raman mechanism, whereas for GR-MOF-18, relaxation occurs through a combination of Raman and local-mode pathways. Moreover, when avoiding short Ce⋯Ce interactions by magnetic dilution in GR-MOF-17@La and GR-MOF-18@La, only the local-mode mechanism is responsible for magnetic relaxation. Photophysical studies show the occurrence of ligand-centred luminescence in both compounds and phosphorescence emission at low temperature for GR-MOF-17.

Wearable, Biocompatible, and Dual-Emission Ocular Multisensor Patch for Continuous Profiling of Fluoroquinolone Antibiotics in Tears

The abuse or misuse of antibiotics in clinical and agricultural settings severely endangers human health and ecosystems, which has raised profound concerns for public health worldwide. Trace detection and reliable discrimination of commonly used fluoroquinolone (FQ) antibiotics and their analogues have consequently become urgent to guide the rational use of antibiotic medicines and deliver efficient treatments for associated diseases. Herein, we report a wearable eye patch integrated with a quadruplex nanosensor chip for noninvasive detection and discrimination of primary FQ antibiotics in tears during routine eyedrop treatment. A set of dual-mode fluorescent nanoprobes of red- or green-emitting CdTe quantum dots integrated with lanthanide ions and a sensitizer, adenosine monophosphate, were constructed to provide an enhanced fluorescence up to 45-fold and nanomolar sensitivity toward major FQs owing to the aggregation-regulated antenna effect. The aggregation-driven, CdTe-Ln(III)-based microfluidic sensor chip is highly specific to FQ antibiotics against other non-FQ counterparts or biomolecular interfering species and is able to accurately discriminate nine types of FQ or non-FQ eyedrop suspensions using linear discriminant analysis. The prototyped wearable sensing detector has proven to be biocompatible and nontoxic to human tissues, which integrates the entire optical imaging modules into a miniaturized, smartphone-based platform for field use and reduces the overall assay time to ∼5 min. The practicability of the wearable eye patch was demonstrated through accurate quantification of antibiotics in a bactericidal event and the continuous profiling of FQ residues in tears after using a typical prescription antibiotic eyedrop. This technology provides a useful supplement to the toolbox for on-site and real-time examination and regulation of inappropriate daily drug use that might potentially lead to long-term antibiotic abuse and has great implications in advancing personal healthcare techniques for the regulation of daily medication therapy.

Ultrasound-assisted synthesis of a Eu3+-functionalized ZnII coordination polymer as a fluorescent dual detection probe for highly sensitive recognition of HgII and L-Cys

A new ZnII coordination polymer (CP) based on 2,3-pyrazine dicarboxylic acid (H2pzdc) and 4,4'-bipyridine (bpy) (ZCP) was synthesized using a facile slow evaporation method. Single-crystal X-ray diffraction revealed that ZCP is a two-dimensional porous CP, [Zn2(pzdc)2(bpy)(H2O)2]n, with van der Waals forces as the dominant interaction within its layers forming a 63 network. Employing energetic ultrasound irradiation, nanoscale ZCP (nZCP) was successfully synthesized and Eu3+ ions were incorporated within its host lattice (Eu@nZCP). The resulting platform exhibits superior fluorescence characteristics and demonstrates notable optical durability. Therefore, it was used as a dual detection fluorescent sensing platform for the detection of mercury and L-cysteine (L-Cys) in aqueous media through a turn-off/on strategy. In the turn-off process, the fluorescence emission of Eu@nZCP progressively quenches by the addition of HgII via a photo-induced electron transfer (PET) mechanism. The fluorescence of Eu@nZCP is quenched to establish a low fluorescence background through the incorporation of HgII. This devised turn-on fluorescent system is suitable for the recognition of L-Cys (based on the strong affinity of L-Cys to the HgII ion) through a quencher detachment mechanism. This method attained a relatively wide linear range, spanning from 0.001 to 25 µM, with the low detection limit of 5 nM for the sensing of HgII. Also, the corresponding limit of detection (LOD) for L-Cys is 8 nM in a relatively wide linear range, spanning from 0.001 to 40 µM.

Isomorphic Insertion of Ce(III)/Ce(IV) Centers into Layered Double Hydroxide as a Heterogeneous Multifunctional Catalyst for Efficient Meerwein-Ponndorf-Verley Reduction

The development of highly active acid-base catalysts for transfer hydrogenations of biomass derived carbonyl compounds is a pressing challenge. Solid frustrated Lewis pairs (FLP) catalysis is possibly a solution, but the development of this concept is still at a very early stage. Herein, stable, phase-pure, crystalline hydrotalcite-like compounds were synthesized by incorporating cerium cations into layered double hydroxide (MgAlCe-LDH). Besides the insertion of well-isolated cerium centers surrounded by hydroxyl groups, the formation of hydroxyl vacancies near the aluminum centers, which were formed by the insertion of cerium centers into the layered double hydroxides (LDH) lattice, was also identified. Depending on the initial cerium concentration, LDHs with different Ce(III)/Ce(IV) ratios were produced, which had Lewis acidic and basic characters, respectively. However, the acid-base character of these LDHs was related to the actual Ce(III)/Ce(IV) molar ratios, resulting in significant differences in their catalytic performance. The as-prepared structures enabled varying degrees of transfer hydrogenation (Meerwein-Ponndorf-Verley MPV reduction) of biomass-derived carbonyl compounds to the corresponding alcohols without the collapse of the original lamellar structure of the LDH. The catalytic markers through the test reactions were changed as a function of the amount of Ce(III) centers, indicating the active role of Ce(III)-OH units. However, the cooperative interplay between the active sites of Ce(III)-containing specimens and the hydroxyl vacancies was necessary to maximize catalytic efficiency, pointing out that Ce-containing LDH is a potentially commercial solid FLP catalysts. Furthermore, the crucial role of the surface hydroxyl groups in the MPV reactions and the negative impact of the interlamellar water molecules on the catalytic activity of MgAlCe-LDH were demonstrated. These solid FLP-like catalysts exhibited excellent catalytic performance (cyclohexanol yield of 45%; furfuryl alcohol yield of 51%), which is competitive to the benchmark Sn- and Zr-containing zeolite catalysts, under mild reaction conditions, especially at low temperature (T = 65 °C).

Bacterial Cellulose-Based MOF Hybrid as a Sensitive Switch Off-On Luminescent Sensor for the Selective Recognition of l-Histidine

In this study, a stable and luminescent UiO-66-NH2 (UN) and its derivative Cu2+@UN were prepared and utilized successfully as an Off-On luminescent sensing platform for effective, selective, as well as rapid (5 min) detection of l-Histidine (l-His). The UN reveals efficient quenching in the presence of Cu2+ ions through photoinduced electron transition (PET) mechanism as a dynamic quenching process (in the range of 0.01-1 mM) forming Cu2+@UN sensing platform. However, due to the remarkable affinity between l-His and Cu2+, the luminescence of Cu2+@UN is recovered in the presence of l-His indicating Turn-On behavior via a quencher detachment mechanism (QD). A good linear relationship between the l-His concentration and luminescence intensity was observed in the range of 0.01-40 μM (R2 = 0.9978) with a detection limit of 7 nM for l-His sensing. The suggested method was successfully utilized for l-His determination in real samples with good recoveries and satisfying consequences. Moreover, the result indicates that only l-His induces a significant luminescence restoration of Cu2+@UN and that the signal is significantly greater than that of the other amino acids. Also, the portable test paper based on bacterial cellulose (BC) as the Cu2+@UNBC sensing platform was developed to conveniently evaluate the effective detection of l-His.

Atomic / Molecular Layer Deposition of Cerium (III) Hybrid Thin Films using Rigid Organic Precursors

Atomic / molecular layer deposition (ALD/MLD) process for the fabrication of cerium-based metal-organic hybrid films is demonstrated for the first time. The highly reactive cerium (III) guanidinate precursor [Ce(dpdmg)3] was...

Novel Lanthanide (III) Complexes Derived from an Imidazole-Biphenyl-Carboxylate Ligand: Synthesis, Structure and Luminescence Properties

A series of neutral mononuclear lanthanide complexes [Ln(HL)₂(NO₃)₃] (Ln = La, Ce, Nd, Eu, Gd, Dy, Ho) with rigid bidentate ligand, HL (4'-(1H-imidazol-1-yl)biphenyl-4-carboxylic acid) were synthesized under solvothermal conditions. The coordination compounds have been characterized by infrared spectroscopy, thermogravimetry, powder X-ray diffraction and elemental analysis. According to X-ray diffraction, all the complexes are a series of isostructural compounds crystallized in the P2/n monoclinic space group. Additionally, solid-state luminescence measurements of all complexes show that [Eu(HL)₂(NO₃)₃] complex displays the characteristic emission peaks of Eu(III) ion at 593, 597, 615, and 651 nm.

Oxygen Vacancy-Rich Mixed-Valence Cerium MOF: An Efficient Separator Coating to High-Performance Lithium-Sulfur Batteries

Mixed-valence metal-organic frameworks (MOFs) have exhibited unique potential in fields such as catalysis and gas separation. However, it is still an open challenge to prepare mixed-valence MOFs with isolated Ce(IV, III) arrays due to the easy formation of Ce^III under the synthetic conditions for MOFs. Meanwhile, the performance of Li-S batteries is greatly limited by the fatal shuttle effect and the slow transmission rate of Li⁺ caused by the inherent characteristics of sulfur species. Here, we report a mixed-valence cerium MOF, named CSUST-1 (CSUST stands for Changsha University of Science and Technology), with isolated Ce(IV, III) arrays and abundant oxygen vacancies (OVs), synthesized as guided by the facile and elaborate kinetic stability study of UiO-66(Ce), to work as an efficient separator coating for circumventing both issues at the same time. Benefiting from the synergistic function of the Ce(IV, III) arrays (redox couples), the abundant OVs, and the open Ce sites within CSUST-1, the CSUST-1/CNT composite, as a separator coating material in the Li-S battery, can remarkably accelerate the redox kinetics of the polysulfides and the Li⁺ transportation. Consequently, the Li-S cell with the CSUST-1/CNT-coated separator exhibited a high initial specific capacity of 1468 mA h/g at 0.1 C and maintained long-term stability for a capacity of 538 mA h/g after 1200 cycles at 2 C with a decay rate of only 0.037% per cycle. Even at a high sulfur loading of 8 mg/cm², the cell with the CSUST/CNT-coated separator still demonstrated excellent performance with an initial areal capacity of 8.7 mA h/cm² at 0.1 C and retained the areal capacity of 6.1 mA h/cm² after 60 cycles.

Luminescence response mode and chemical sensing mechanism for lanthanide-functionalized metal–organic framework hybrids

This comprehensive review systematically summarizes the luminescence response mode and chemical sensing mechanism for lanthanide-functionalized MOF hybrids (abbreviated as LnFMOFH).

The chemistry of Ce-based metal-organic frameworks

Metal-organic frameworks (MOFs) have gained widespread attention due to their modular construction that allows the tuning of their properties. Within this vast class of compounds, metal carboxylates containing tri- and tetravalent metal ions have been in the focus of many studies due to their often high thermal and chemical stabilities. Cerium has a rich chemistry, which depends strongly on its oxidation state. Ce(iii) exhibits properties typically observed for rare earth elements, while Ce(iv) is mostly known for its oxidation behaviour. In MOF chemistry this is reflected in their unique optical and catalytic properties. The synthetic parameters for Ce(iii)- and Ce(iv)-MOFs also differ substantially and conditions must be chosen to prevent reduction of Ce(iv) for the formation of the latter. Ce(iii)-MOFs are usually reported in comprehensive studies together with those constructed with other RE elements and normally they are isostructural. They exhibit a greater structural diversity, which is reflected in the larger variety of inorganic building units. In contrast, the synthesis conditions of Ce(iv)-MOFs were only recently (2015) established. These lead selectively to hexanuclear Ce-O clusters that are well-known for Zr-MOFs and therefore very similar structural and isoreticluar chemistry is found. Hence Ce(iv)-MOFs exhibit often high porosity, while only a few porous Ce(iii)-MOFs have been described. Some of these show structural flexibility which makes them interesting for separation processes. For Ce(iv)-MOFs the redox properties are most relevant. Thus, they are intensively discussed for catalytic, photocatalytic and sensing applications. In this perspective, the synthesis, structural chemistry and properties of Ce-MOFs are summarized.