Synthesis and Thermal Decomposition of High-Entropy Layered Rare Earth Hydroxychlorides

The synthesis of multicomponent and high-entropy compounds has become a rapidly developing field in advanced inorganic chemistry, making it possible to combine the properties of multiple elements in a single phase. This paper reports on the synthesis of a series of novel high-entropy layered rare earth hydroxychlorides, namely, (Sm,Eu,Gd,Y,Er)2(OH)5Cl, (Eu,Gd,Tb,Y,Er)2(OH)5Cl, (Eu,Gd,Dy,Y,Er)2(OH)5Cl, and (Eu,Gd,Y,Er,Yb)2(OH)5Cl, using a homogeneous hydrolysis technique under hydrothermal conditions. Elemental mapping proved the even distribution of rare earth elements, while luminescence spectroscopy confirmed efficient energy transfer between europium and other rare earth cations, thus providing additional evidence of the homogeneous distribution of rare earth elements within the crystal lattice. The average rare earth cation radii correlated linearly with the unit cell parameters (0.868 < R2 < 0.982) of the high-entropy layered rare earth hydroxychlorides. The thermal stability of the high-entropy layered rare earth hydroxychlorides was similar to that of individual hydroxychlorides and their binary solid solutions.

Noncovalent Self-Assembly of Single-Layer MoS2 Nanosheets and Zinc Porphyrin into Stable SURMOF Nanohybrids with Multimodal Photocatalytic Properties

A noncovalent integration of nanosheets of molybdenum disulfide (MoS2) and the zinc porphyrin complex Zn(II) 5,10,15,20-tetrakis(4-carboxyphenyl)porphine (ZnTCPP) through coordination bonding with metal clusters of zinc acetate (Zn[OAc]2) was applied for synthesis of stable hybrid nanomaterial avoiding surface prefunctionalization. The X-ray powder diffraction in combination with the BET nitrogen adsorption method confirms formation of a ZnTCPP-based surface-attached metal-organic framework (SURMOF) with micropores of 1.63 nm on the MoS2 nanosheets. Fluorescence spectroscopy confirmed Forster resonance energy transfer (FRET) between MoS2 and ZnTCPP without contact quenching. Fluorescent trapping with terephthalic acid for hydroxyl radicals and Sensor Green for singlet oxygen was applied for studying the pathways of photodegradation of model organic pollutant 1,5-dihydroxynaphthalene (DHN) in the presence of SURMOF/MoS2. Visible light initiates sensitization through the excitation of ZnTCPP generating singlet oxygen, whereas UV-light promotes either aerobic FRET-mediated "Z scheme" or anaerobic "Type II heterojunction" mechanisms. Owing to its multimodal photochemistry, the SURMOF/MoS2 hybrid showed comparatively high photocatalytic activity in UV-assisted degradation of DHN (keffUV = 4.0 × 10-2 min-1) as well as the antibacterial activity confirmed by E. coli survival test under visible light. Noncovalent self-assembly utilizing coordination bonding in SURMOFs as supramolecular adhesive to avoid surface premodification provides a basis for new types of multicomponent nanosystems with switchable functionalities by combining different 2D materials and chromophores in one hybrid structure.

Cinnamate-Intercalated Layered Yttrium Hydroxide: UV Light-Responsive Switchable Material

In recent years, there has been an increasing interest in stimuli-responsive host-guest materials due to the high potential for their application in switchable devices. Light is the most convenient stimulus for operating these materials; a light-responsive guest affects the host structure and the functional characteristics of the entire material. UV-transparent layered rare earth hydroxides intercalated with UV-switchable anions are promising candidates as stimuli-responsive host-guest materials. The interlayer distance in the layered rare earth hydroxides depends on the size of the intercalated anions, which could be changed in situ, e.g., via anion isomerisation. Nevertheless, for layered rare earth hydroxides, the possibility of such changes has not been reported yet. A good candidate anion that is capable of intercalating into the interlayer space is the cinnamate anion, which undergoes UV-assisted irreversible trans-cis isomerisation. In this work, both trans- and cis-cinnamate anions were intercalated in layered yttrium hydroxide (LYH). Upon UV-irradiation, the interlayer distance of trans-cinnamate-intercalated layered yttrium hydroxide suspended in isopropanol changed from 21.9 to 20.6 Å. For the first time, the results obtained demonstrate the possibility of using layered rare earth hydroxides as stimuli-responsive materials.

High-Entropy Layered Rare Earth Hydroxides

New high-entropy layered rare earth hydroxides ─ (Y,Eu,Gd,Er,Sm)₂(OH)₅NO₃, (Y,Eu,Gd,Er,Tb)₂(OH)₅NO₃, (Y,Eu,Gd,Er,Yb)₂(OH)₅NO₃, (Y,Eu,Gd,Er,Nd)₂(OH)₅NO₃, and (Y,Eu,Gd,Er,Nd,Sm,Tb)₂(OH)₅NO₃ ─ were obtained using a hydrothermal microwave method. The annealing of layered rare earth hydroxides at 900 °C resulted in the corresponding high-entropy rare earth oxides. Based on inductively coupled plasma atomic emission spectroscopy data, the values for configurational entropy for both rare earth hydroxides and oxides were estimated, confirming the formation of high-entropy compounds. Energy-dispersive X-ray spectroscopy mapping, including mapping in the scanning transmission microscopy mode, showed no signs of chemical segregation and confirmed uniform rare earth elements' distribution both in the particles of high-entropy layered basic nitrates and in the particles of high-entropy oxides. The ratios of rare earth cations in the initial aqueous solutions of mixed nitrates were close to the ratios of cations in the resulting high-entropy layered rare earth basic nitrates and high-entropy rare earth oxides.

Layered Gadolinium-Europium-Terbium Hydroxides Sensitised with 4-Sulfobenzoate as All Solid-State Luminescent Thermometers

Ternary layered gadolinium-europium-terbium basic chlorides were synthesised using a facile hydrothermal-microwave technique. A continuous series of solid solutions was obtained in a full range of rare earth concentrations. To sensitise the luminescence of Eu3+ and Tb3+, a 4-sulfobenzoate anion was intercalated in the ternary layered rare earth hydroxides using one of two methods—a high-temperature ion exchange or a single-stage synthesis. The luminescent colour of the materials was governed by the gadolinium content: at low and medium gadolinium concentrations (0–70%), layered Gd-Eu-Tb basic sulfobenzoate exhibited a bright red europium luminescence; at high gadolinium content (70–90%), a bright green terbium luminescence was observed. The colour coordinates of layered Gd-Eu-Tb basic sulfobenzoate luminescence depended on the temperature in the physiological range (20–50 °C). The relative thermal sensitivity of the obtained materials was up to 2.9%·K−1.

89Y chemical shift anisotropy: a sensitive structural probe of layered yttrium hydroxides revealed by solid-state NMR spectroscopy and DFT calculations

Anion-exchangeable Y₂(OH)₅X·nH₂O (LYH-X, X = monovalent anions, n ≈ 1.5) materials are an ideal platform for incorporating the unique properties of layered metal hydroxides and rare-earth (RE) ions, and thus have exhibited promising prospects for various applications. To further improve the performance of LYH-X and related functional materials, their structure-property relationships must be explored. However, due to the intrinsic felxibility, extracting the local structural details of these materials is particularly challenging. In this work, we utilized a combined approach of ⁸⁹Y solid-state NMR (ssNMR) spectroscopy and density functional theory (DFT) calculations to reveal the response of ⁸⁹Y chemical shift anisotropy (CSA) in LYH-X to the structural changes including a small displacement of cationic yttrium hydroxide layers and intercalated anions. Such subtle structural changes are often associated with dehydration/rehydration, anion-exchange, exfoliation, and the self-assembly process of LYH-X and related functional materials, which are exceedingly difficult to detect using other techniques. The principal components of ⁸⁹Y CSA show a larger variation range than isotropic chemical shifts, making CSA a more sensitive probe. In addition, it is found that the response of ⁸⁹Y CSA to structural changes is distinct for Y sites with different local coordination environments, opening great opportunities to analyze each Y site within these materials. All these observations suggest that the strategy involving both experimental (⁸⁹Y ssNMR) and theoretical (DFT) approaches can be utilized to extract previously unavailable ultrafine structural information of LYH-X and related materials, and provide fruitful insights into their thorough structure-property relationships.

Eu-Doped layered yttrium hydroxides sensitized by a series of benzenedicarboxylate and sulphobenzoate anions

A series of new Eu-doped layered yttrium hydroxides intercalated with various organic dianions having similar molecular structure (dicarboxylates and sulphobenzoates) were synthesized.

Synthesis of Y2O3:Bi3+,Yb3+ nanosheets from layered yttrium hydroxide precursor and their photoluminescence properties

Morphologies, photoluminescence properties, and photostability were characterized for Y₂O₃:Bi³⁺,Yb³⁺ fluorescent nanosheets prepared through calcining solvothermally synthesized layered yttrium hydroxide precursors.

Synthesis of Y2O3:Bi3+,Eu3+ nanosheets from layered yttrium hydroxide precursor and their photoluminescence properties

Morphologies, photoluminescence properties, and photostability were characterized for Y₂O₃:Bi³⁺,Eu³⁺ fluorescent nanosheets prepared through calcining solvothermally synthesized layered yttrium hydroxide precursors.