Luminescent lanthanide mixed N-phthaloylglycinate and terephthalate coordination polymers: Structural and optical properties.

A new class of lanthanide mixed-carboxylate ligands compounds with formula {[Ln2 (phthgly)4 (bdc)(H2 O)6 ]·(H2 O)4 }∞ , labelled as Ln3+ : Eu (1) and Gd (2) coordination polymers (CP) were synthesized under mild reaction conditions between lanthanide nitrate salts and a solution of N-phthaloylglycine (phthgly) and terephthalic (bdc) ligands. The (1) and (2) coordination polymers were formed by symmetric binuclear units, in which phthgly and bdc carboxylate ligands are coordinated to the lanthanide ions by different coordination modes. Surprisingly, all organic ligands participate in hydrogen bonding interactions, forming an extremally rigid crystalline structure. The red narrow emission bands from the 5 D0 →7 FJ transitions of the Eu3+ ion show a high colour purity. The intramolecular energy transfer process from L→Eu3+ ion has been discussed. The experimental intensity parameters (Ω2,4 ) reflect lower angular distortion and polarizability of the chemical environment around the metal ion compared with other Eu3+ compounds reported in the literature. This novel class of coordination polymer offers a more attractive platform for developing luminescent functional materials for different applications.

Synthesis and Nanostructure Investigation of Hybrid ß-Ga2 O3 /ZnGa2 O4 Nanocomposite Networks with Narrow-Band Green Luminescence and High Initial Electrochemical Capacity.

The material design of functional "aero"-networks offers a facile approach to optical, catalytical, or and electrochemical applications based on multiscale morphologies, high large reactive area, and prominent material diversity. Here in this paper, the synthesis and structural characterization of a hybrid ß-Ga2 O3 /ZnGa2 O4 nanocomposite aero-network are presented. The nanocomposite networks are studied on multiscale with respect to their micro- and nanostructure by X-ray diffraction (XRD) and transmission electron microscopy (TEM) and are characterized for their photoluminescent response to UV light excitation and their electrochemical performance with Li-ion conversion reaction. The structural investigations reveal the simultaneous transformation of the precursor aero-GaN(ZnO) network into hollow architectures composed of ß-Ga2 O3 and ZnGa2 O4 nanocrystals with a phase ratio of ≈1:2. The photoluminescence of hybrid aero-ß-Ga2 O3 /ZnGa2 O4 nanocomposite networks demonstrates narrow band (λem  = 504 nm) green light emission of ZnGa2 O4 under UV light excitation (λex  = 300 nm). The evaluation of the metal-oxide network performance for electrochemical application for Li-ion batteries shows high initial capacities of ≈714 mAh g-1 at 100 mA g-1 paired with exceptional rate performance even at high current densities of 4 A g-1 with 347 mAh g-1 . This study provides is an exciting showcase example of novel networked materials and demonstrates the opportunities of tailored micro-/nanostructures for diverse applications a diversity of possible applications.

Magnetism and Afterglow United: Synthesis of Novel Double Core-Shell Eu2+ -Doped Bifunctional Nanoparticles.

Afterglow-magnetic nanoparticles (NPs) offer enormous potential for bioimaging applications, as they can be manipulated by a magnetic field, as well as emitting light after irradiation with an excitation source, thus distinguishing themselves from fluorescent living cells. In this work, a novel double core-shell strategy is presented, uniting co-precipitation with combustion synthesis routes to combine an Fe3 O4 magnetic core (≈15 nm) with an afterglow SrAl2 O4 :Eu2+ ,Dy3+ outer coat (≈10 nm), and applying a SiO2 protective middle layer (≈16 nm) to reduce the luminescence quenching caused by the Fe core ions. The resulting Fe3 O4 @SiO2 @SrAl2 O4 :Eu2+ ,Dy3+ NPs emit green light attributed to the 4f6 5d1 →4f7 (8 S7/2 ) transition of Eu2+ under UV radiation and for a few seconds afterwards. This bifunctional nanocomposite can potentially be applied for the detection and separation of cells or diagnostically relevant molecules.

A Scandium MOF with an Unprecedented Inorganic Building Unit, Delimiting the Micropore Windows.

A new scandium metal-organic framework (Sc-MOF) with the composition of [Sc(OH)(OBA)], denoted as Sc-CAU-21, was prepared under solvothermal reaction conditions using 4,4'-oxidibenzoic acid (H2OBA) as the ligand. Single-crystal structure determination revealed the presence of the new inorganic building unit (IBU) {Sc8(µ-OH)8(O2C)16}. It is composed of cis-connected ScO6 polyhedra forming an eight-membered ring through bridging µ-OH groups. The connection of the IBUs leads to a 3D framework, containing 1D pores with a diameter between 4.2 and 5.6 Å. Pore access is limited by the size of the IBU, and in contrast to the isoreticular aluminum compound Al-CAU-21 [Al(OH)(OBA)], which is nonporous toward nitrogen at 77 K, Sc-CAU-21 exhibits a specific surface area of 610 m2 g-1. The title compound is thermally stable in air up to 350 °C and can be employed as a host for photoluminescent ions. Sc-CAU-21 exhibits a ligand-based blue emission, and (co)substituting Sc3+ ions with Ln3+ ions (Eu3+, Tb3+, and Dy3+) allows the tuning of the emitting color of the phosphor from red to green. Single-phase white-light emission with CIE color coordinates close to the ideal for white-light emission was also achieved. The luminescence property was utilized in combination with powder X-ray diffraction to study in situ the crystallization process of Sc-CAU-21:Tb and Sc-CAU-21:Eu. Both studies indicate a two-step crystallization process, with a crystalline intermediate, prior to the formation of Sc-CAU-21:Ln.

Facile Ionic Liquid-Assisted Strategy for Direct Precipitation of Eu2+ -Activated Nanophosphors under Ambient Conditions.

This work describes a novel ionic liquid (IL)-assisted synthesis strategy for a direct and easy production of Eu2+ -doped nanoparticles (NPs), where ILs are also used as fluoride sources to avoid the use of elemental fluorine or toxic hydrofluoric acid. Up to now, the direct synthesis of Eu2+ -doped nanophosphors consisted of an enormous challenge, due to the oxidation to Eu3+ observed in hydrous solution, which is commonly used for the preparation of NPs, generating lattice defects and undesired particle growth or agglomeration by additional reducing steps at high temperatures. In contrast, ILs, unless containing ClO4- or NO3- anions, do not present an oxidizing character, allowing the direct precipitation of NPs, e.g., using Eu2+ containing starting materials. Here, the undoped and Eu2+ -doped BaFCl NPs have been prepared under atmospheric conditions for the first time using ILs as solvents and also as fluoride source, applying sonochemical and microwave-assisted approaches. In general, this method bears an enormous potential for an easy synthesis of fluoride materials compared to inconvenient solid-state methods. In addition, the IL plays the role of a strongly attached protecting shell which represents ≈7-8% of the total NPs weight.

Development of a new in situ analysis technique applying luminescence of local coordination sensors: principle and application for monitoring metal-ligand exchange processes.

Here, we introduce the principle of the novel in situ luminescence analysis of coordination sensor (ILACS) approach for monitoring the formation of solid materials, recording information from the formed solid compounds as well as from the surrounding solutions. This technique utilizes as a main tool the sensitivity of luminescence properties of lanthanide (Ln) ions on the coordination environment, being incorporated as local sensors by the investigated material during synthesis. The luminescence spectra and their environment-dependent developments are monitored in situ from the early stages of the reaction until the final product formation under real conditions with a high time resolution. The ILACS principle is demonstrated here for monitoring the formation of [Eu(phen)2(NO3)3] (phen = 1,10-phenanthroline) and further metal-ligand exchange processes during its conversion to [Sn(phen)Cl4]. These reactions were followed, for instance, analyzing the antenna effect, shift of the (5)D0→(7)F4 Eu(3+) transition and quenching effects. In addition, these results have been validated by comparison with other in situ techniques. The results demonstrate that ILACS is a new powerful, fast, broadly available in situ characterization method, which is applicable for liquids, amorphous samples, and very small crystallites besides for large crystals.

Towards High-Performance Photo-Fenton Degradation of Organic Pollutants with Magnetite-Silver Composites: Synthesis, Catalytic Reactions and In Situ Insights.

In this study, Fe3O4/Ag magnetite-silver (MSx) nanocomposites were investigated as catalysts for advanced oxidation processes by coupling the plasmonic effect of silver nanoparticles and the ferromagnetism of iron oxide species. A surfactant-free co-precipitation synthesis method yielded pure Fe3O4 magnetite and four types of MSx nanocomposites. Their characterisation included structural, compositional, morphological and optical analyses, revealing Fe3O4 magnetite and Ag silver phases with particle sizes ranging from 15 to 40 nm, increasing with the silver content. The heterostructures with silver reduced magnetite particle aggregation, as confirmed by dynamic light scattering. The UV-Vis spectra showed that the Fe:Ag ratio strongly influenced the absorbance, with a strong absorption band around 400 nm due to the silver phase. The oxidation kinetics of organic pollutants, monitored by in situ luminescence measurements using rhodamine B as a model system, demonstrated the higher performance of the developed catalysts with increasing Ag content. The specific surface area measurements highlighted the importance of active sites in the synergistic catalytic activity of Fe3O4/Ag nanocomposites in the photo-Fenton reaction. Finally, the straightforward fabrication of diverse Fe3O4/Ag heterostructures combining magnetism and plasmonic effects opens up promising possibilities for heterogeneous catalysis and environmental remediation.

In situ Investigations of the Formation Mechanism of Metastable γ-BiPd Nanoparticles in Polyol Reductions.

Synthesizing intermetallic phases containing noble metals often poses a challenge as the melting points of noble metals often exceed the boiling point of bismuth (1560 °C). Reactions in the solid state generally circumvent this issue but are extremely time consuming. A convenient method to overcome these obstacles is the co-reduction of metal salts in polyols, which can be performed within hours at moderate temperatures and even allows access to metastable phases. However, little attention has been paid to the formation mechanisms of intermetallic particles in polyol reductions. Identifying crucial reaction parameters and finding patterns are key factors to enable targeted syntheses and product design. Here, we chose metastable γ-BiPd as an example to investigate the formation mechanism from mixtures of metal salts in ethylene glycol and to determine critical factors for phase formation. The reaction was also monitored by in situ X-ray diffraction using synchrotron radiation. Products, intermediates and solutions were characterized by (in situ) X-ray diffraction, electron microscopy, and UV-Vis spectroscopy. In the first step of the reaction, elemental palladium precipitates. Increasing temperature induces the reduction of bismuth cations and the subsequent rapid incorporation of bismuth into the palladium cores, yielding the γ-BiPd phase.

Eu3+ doped ZnAl layered double hydroxides as calibrationless, fluorescent sensors for carbonate.

The photoluminescence properties (PL) of Eu3+ hosted in the hydroxide layers of layered double hydroxides (LDHs) enables calibrationless quantification of anions in the interlayers. The concept is demonstrated during the nitrate-to-carbonate ion exchange in Zn2+/Al3+/Eu3+ LDHs and can be implemented as a remote optical sensor to detect intrusion of anions such as Cl- or CO32-.

In situ investigation of the formation mechanism of α-Bi2Rh nanoparticles in polyol reductions.

The synthesis of intermetallic phases formed from elements with very different melting points is often time and energy consuming, and in extreme cases the evaporation of a reactant may even prevent formation completely. An alternative, facile synthesis approach is the reduction of metal salts in the polyol process, which requires only moderate temperatures and short reaction times. In addition, the starting materials for this procedure are readily available and do not require any special treatment to remove or prevent passivation layers, for example. Although the formation of intermetallic particles via the polyol process is an established method, little attention has been paid to the mechanism behind it. However, it is precisely a deeper understanding of the underlying mechanisms that would enable better and more targeted synthesis planning and product design. Taking the well-known formation of Bi2Rh particles from Bi(NO3)3 and various rhodium salts in ethylene glycol as an example, we studied the chemical process in detail. We investigated the effects of anion type and pH on the polyol reaction. The reaction was also probed by in situ X-ray diffraction using synchrotron radiation. Products, intermediates and solutions were characterized by X-ray and electron diffraction, electron microscopy and optical spectroscopy. In the first step, co-reduction of the metal cations leads to BiRh. Only with increasing reaction temperature, the remaining bismuth cations in the solution are reduced and incorporated into the BiRh particles, leading to a gradual transition from BiRh to α-Bi2Rh.

Superior Sodium Storage Properties in the Anode Material NiCr2 S4 for Sodium-Ion Batteries: An X-ray Diffraction, Pair Distribution Function, and X-ray Absorption Study Reveals a Conversion Mechanism via Nickel Extrusion.

The pseudo-layered sulfide NiCr2 S4 exhibits outstanding electrochemical performance as anode material in sodium-ion batteries (SIBs). The Na storage mechanism is investigated by synchrotron-based X-ray scattering and absorption techniques as well as by electrochemical measurements. A very high reversible capacity in the 500th cycle of 489 mAh g-1 is observed at 2.0 A g-1 in the potential window 3.0-0.1 V. Full discharge includes irreversible generation of Ni0 and Cr0 nanoparticles embedded in nanocrystalline Na2 S yielding shortened diffusion lengths and predominantly surface-controlled charge storage. During charge, Ni0 and Cr0 are oxidized, Na2 S is consumed, and amorphous Ni and Cr sulfides are formed. Limiting the potential window to 3.0-0.3 V an unusual nickel extrusion sodium insertion mechanism occurs: Ni2+ is reduced to nanosized Ni0 domains, expelled from the host lattice, and is replaced by Na+ cations to form O3-type like NaCrS2 . Surprisingly, the discharge and charge processes comprise Na+ shuttling between highly crystalline NiCr2 S4 and NaCrS2 enabling a superior long-term stability for 3000 cycles. The results not only provide valuable insights for the electrochemistry of conversion materials but also extend the scope of layered electrode materials considering the reversible nickel extrusion sodium insertion reaction as new concept for SIBs.

Formation of Bi2Ir nanoparticles in a microwave-assisted polyol process revealing the suboxide Bi4Ir2O.

Intermetallic phases are usually obtained by crystallization from the melt. However, phases containing elements with widely different melting and boiling points, as well as nanoparticles, which provide a high specific surface area, are hardly accessible via such a high-temperature process. The polyol process is one option to circumvent these obstacles by using a solution-based approach at moderate temperatures. In this study, the formation of Bi2Ir nanoparticles in a microwave-assisted polyol process was investigated. Solutions were analyzed using UV-Vis spectroscopy and the reaction was tracked with synchrotron-based in situ powder X-ray diffraction (PXRD). The products were characterized by PXRD and high-resolution transmission electron microscopy. Starting from Bi(NO3)3 and Ir(OAc)3, the new suboxide Bi4Ir2O forms as an intermediate phase at about 160 °C. Its structure was determined by a combination of PXRD and quantum-chemical calculations. Bi4Ir2O decomposes in vacuum at about 250 °C and is reduced to Bi2Ir by hydrogen at 150 °C. At about 240 °C, the polyol process leads to the immediate reduction of the two metal-containing precursors and crystallization of Bi2Ir nanoparticles.