Search Results (136)

In this work, the synthesis and structural characterization of the smallest possible member of the family of bis-functionalized {MnMo₆O₂₄} Anderson–Evans polyoxometalates (POMs) is reported. The synthesis of the title compound TBA₃{[HC(CH₂O)₃]₂MnMo₆O₁₈} (1) was accomplished by using trimethylolmethane as the capping unit (TBA: tetra(n-butyl)ammonium, n-B_u4N⁺). The molecular structure of the organic–inorganic POM gave rise to yet undisclosed ¹H-NMR features, which are discussed thoroughly. Single-crystal X-ray diffraction (XRD) analysis revealed a highly regular 3D packing of the polyoxoanions within a matrix of TBA cations. The hybrid POM is of particular interest regarding potential applications in photocatalysis (i.e., hydrogen evolution) and energy storage. Thus, the electrochemical and thermal properties of 1 are also analyzed. Full article

Polyoxometalate (POM)-type supramolecular materials have unique structures and hold immense potential for development in the fields of biomedicine, information storage, and electrocatalysis. In this study, (NH₄)₃ [AlMo₆O₂₄H₆]·7H₂O was employed as a polyacid anion template, pentacyclic imidazole molecules served as organic ligands, and the moderate-temperature hydrothermal and natural evaporation methods were used in combination for the design and synthesis of two octamolybdenum-oxo cluster (homopolyacids containing molybdenum-oxygen structures as the main small-molecular structures)-based organic–inorganic hybrid compounds, [(C₃N₂H₅)(C₃N₂H₄)][(β-Mo₈O₂₆H₂)]_0.5 (1) and {Zn(C₃N₂H₄)₄}{[(γ-Mo₈O₂₆)(C₃N₂H₄)₂]_0.5}·2H₂O (2). Structural and property characterization revealed that both compounds crystallized in the P-1 space group with relatively stable three-dimensional structures under the action of hydrogen bonding. Upon temperature stimulation, the [Zn(C₃N₂H₄)₄]²⁺ cation and water molecules in 2 exhibited obvious oscillations, leading to significant dielectric anomalies at approximately 250 and 260 K when dielectric testing was conducted under heating conditions. Full article

Polyoxometalates (POMs) surrounded by organic cations and related systems composed of POMs immobilized on functionalized Merrifield resin (MR) were synthesized, characterized and tested as catalysts for the oxidation of two natural terpenes, β-myrcene and β-caryophyllene, using H₂O₂ and TBHP as green oxidants. The ionic immobilization enabled easy catalyst recovery and reuse. The results showed high conversion and selectivity, with some catalysts maintaining their efficiency for at least three runs without leaching. The catalytic performances of both homogeneous and heterogeneous systems, along with the necessary characterizations, are discussed. Full article

Water, the source of life, is undeniably essential to all living beings in nature. However, the process of industrialization has led to the pollution of water resources. Photocatalytic water treatment technology can convert solar energy into environmentally friendly and renewable chemical energy, effectively degrading organic pollutants in water. This offers a promising solution for the purification of water environments. The development of high-performance photocatalysts is crucial for photocatalytic reactions. Polyoxometalates (POMs) are anionic metal oxide clusters that come in various sizes and shapes. Their unique electronic properties, tunable structures, and photocatalytic activity make them highly promising materials for the efficient degradation of organic pollutants in water. This review summarizes the recent advances in emerging POM-based photocatalytic materials for water treatment, elaborating on their mechanisms of action. Finally, the current development prospects and the future challenges of POM-based photocatalytic materials are envisioned. Full article

Polyoxometalates are a promising family of compounds for the development of new catalyst materials, although up to now they have mainly been applied in acid catalysis and oxidative processes. In this study, we present the synthesis and characterisation of two new Keggin-type phosphomolybdates, H₆[PRuMo₁₁O₄₀] and H₉[PRu₂Mo₁₀O₄₀]. The successful synthesis was confirmed with ICP-OES (elemental composition) and infrared spectroscopy (structure). Furthermore, the molecular structure of H₆[PRuMo₁₁O₄₀] was determined by electron diffraction. The new compounds were comprehensively characterised using ³¹P-NMR spectroscopy, UV-Vis spectroscopy, and electrochemical methods. Square-Wave-Voltammetry revealed an additional RedOx peak for the Ru-substituted POMs compared to the unsubstituted phosphomolybdate at around 825 mV. In a test reaction, the new compounds showed promising catalytic activity for the hydrogenation of lactic acid. Full article

Solid electrolytes, including polymer electrolytes, are a promising option for improving the performance of environmentally friendly batteries such as rechargeable lithium-ion batteries or fuel cells. Hydrogen–oxygen fuel cells producing only water under power generation are attracting widespread attention, and they need proton conductors as electrolytes. Fluoropolymer electrolytes such as Nafion^® have been utilized for hydrogen–oxygen fuel cells below 100 °C; however, they are not applicable over the working temperature. Therefore, other types of polymer electrolytes are demanded for hydrogen–oxygen fuel cells. Polyoxometalate (POM) inorganic clusters are known as proton conductors and are utilized to prepare POM–polymer composites for solid electrolyte application. In such POM–polymer composites, distinct compositions and structures are significant for improving the performance of proton conductivity. Recently, POM–polymer composites with distinct compositions and structures have been synthesized to obtain high proton conductivity. The key factor is to use single-crystalline compounds. Here, several examples are overviewed by classifying them into three categories: (i) single-crystalline POM–polymer composites, (ii) organically modified POM (org-POM) polymers, and (iii) POM hybrid polymers using polymerizable cations. The application of proton-conductive solid electrolytes is focused on. Full article

Redox Flow Batteries (RFBs) are promising large-scale Energy Storage Systems, which support the integration of renewable energies into the current electric grid. Emerging chemistries for electrolytes, such as Polyoxometalates (POMs), are being studied. POMs have attracted great interest because of their reversible multi-electron transfers and the possibility of tuning their electrochemical properties. Recently, the cobalt-containing Keggin-type species [CoW₁₂O₄₀]⁶⁻ (CoW₁₂) has been successfully implemented in a symmetric RFB, and its further implementation calls for new materials for the membrane to enhance its cell performance. In this work, different types of ion exchange membranes (Nafion™-NR212, FAPQ-330 and Amphion™) were tested. The electrolyte uptake, swelling, conductivity and permeability of the membranes in the CoW₁₂ electrolyte, as well as a detailed cell performance study, are reported herein. Better performance results ascribed to the robustness, efficiency and energy density of the system were found for Nafion™-NR212, with 88.5% energy efficiency, 98.9% capacity retention and 3.1 Wh L⁻¹ over 100 cycles at 20 mA cm⁻². FAPQ-330 and Amphion membranes showed large capacity fade (up to 0.2%/cycle). Crossover and the low conductivity of these membranes in the mild pH conditions of the electrolyte were revealed to be responsible for the reduced cell performance. Full article

Modern research technology’s goal is to produce multifunctional materials that require low energy. In this work, we have applied polypyrrole (PPy) doped with dodecyl benzenesulfonate (DBS-) with the addition of polyoxometalates (POM) such as phosphotungstic acid (PTA) forming PPyDBS-PT composites. Two different PTA concentrations (4 mM and 8 mM) were used to form PPyDBS-PT4 and PPyDBS-PT8. The higher concentration of PTA created a highly dense and compact film which can be observed from scanning electron microscopy (SEM cross-section image), and also contains fewer phosphotungstate anions (PT³⁻) inclusion (via energy-dispersive X-ray spectroscopy, EDX). Three different aqueous electrolytes, LiCl (lithium chloride), NaCl (sodium chloride), and KCl (potassium chloride), were applied to investigate how those alkali metal ions perform as typical cation-driven actuators. Cyclic voltammetry with linear actuation revealed the tendency LiCl > NaCl > KCl in view of better strain, charge density, electronic conductivity, and Young’s modulus of PPyDBS-PT4 outperformed PPyDBS-PT8. Chronopotentiometric measurements showed high specific capacitance for PPyDBS-PT4 at 260.6 ± 21 F g⁻¹ with capacity retention after 5000 cycles of 88.5%. The sensor calibration of PPyDBS-PT4 revealed that the alkali cations (Li⁺, Na⁺, and K⁺) can be differentiated from each other. The PPyDBS-PT4 has multifunctional applications such as actuators, sensors, and energy storage. Full article

The efficient utilization of lignin, a pivotal component of lignocellulosic biomass, is crucial for advancing sustainable biorefinery processes. However, optimizing lignin valorization remains challenging due to its intricate structure and susceptibility to undesirable reactions during processing. In this study, we delve into the impact of various pretreatment agents on birch lignin, aiming to enhance its catalytic oxidation and depolymerization under polyoxometalates (POMs) catalysis. Our results reveal that pretreatment with formaldehyde effectively safeguards aryl ether linkages in lignin, leading to a notable increase in aromatic compound yields under POMs catalysis. Furthermore, gel permeation chromatography (GPC) analysis underscores the inhibition of aryl ether linkage hydrolysis upon formaldehyde addition. Gas chromatography–mass spectrometry (GC–MS) analysis demonstrates that formaldehyde pretreatment boosts lignin monomer yield by 2 to 3 times compared to untreated lignin, underscoring the effectiveness of tailored pretreatment strategies. This research underscores the significance of adopting rational pretreatment methods to advance lignin valorization pathways catalyzed by POMs, thereby contributing to the evolution of sustainable biomass conversion technologies. Full article

Reticular and cluster materials often feature complex formulas, making a comprehensive overview challenging due to the need to consult various resources. While datasets have been collected for metal-organic frameworks (MOFs), covalent organic frameworks (COFs), and zeolites, among others, there remains a gap in systematically organized information for polyoxometalates. This paper introduces a carefully curated dataset of 1984 polyoxometalate (POM) and related cluster metal oxide formula instances, currently connecting over 2500 POM material instances. These POM instances incorporate 75 different chemical elements, with compositions ranging from binary to octonary element clusters. This dataset not only enhances accessibility to polyoxometalate data but also aims to facilitate further research and development in the study of these complex inorganic compounds. Full article

In this work, TiO₂ and Anderson-type polyoxometalates (Ni, Co, and Fe) thin-film composites were fabricated. The composites were characterized by FTIR and Raman spectroscopy, diffuse reflectance, and scanning electronic microscopy. The methylene blue (MB) photocatalytic degradation on the composites under UV irradiation was studied. Spectroscopic results verified the modification of TiO₂ thin films. Optical and morphological properties changed after TiO₂ modification. The largest change in the optical band gap was observed for the FePOM/TiO₂ system, which reported a value of 3.05 eV. The POM/TiO₂ systems were more efficient in methylene blue (MB) adsorption than bare TiO₂. Furthermore, the modified films were more efficient than bare TiO₂ during MB photodegradation tests. The NiPOM/TiO₂ and the CoPOM/TiO₂ were the most efficient in the MB adsorption, reaching ~20%. The NiPOM/TiO₂ and the CoPOM/TiO₂ composites were the most efficient in the photodegradation process, reaching ~50% of MB removal. The stability tests indicated that composite films were moderately stable after the three performed reusability cycles. Thus, these results suggest that POM modification of TiO₂ can improve the adsorption and photodegradation capacity of semiconductors. Full article

An organic–inorganic hybrid polyoxometalate (POM) CoPMoV [PMo^VI₈V^IV₄V^V₂O₄₂][Co(Phen)₂(H₂O)]₂[TEA]₂•H₃O•3H₂O (Phen = 1,10-phenanthroline, TEA = triethylamine) prepared by hydrothermal synthesis was explored as a heterogeneous catalysts to remove methylene blue (MB) through Fenton-like reaction and catalytic reduction. X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray (EDX), Fourier transform infrared spectroscopy (FT-IR), and X-ray photoelectron spectroscopy (XPS) were employed to characterize CoPMoV. The MB removal rates for the Fenton-like reaction and the catalytic reduction were 91.6% (120 min) and 97.5% (2 min), respectively, under optimum conditions. CoPMoV demonstrated excellent stability and recyclability in the Fenton-like reaction and catalytic reduction, which was confirmed by 5 cycle tests. Plausible mechanisms for MB degradation and reduction have also been proposed. Benefiting from the excellent redox properties of cobalt and [PMo^VI₈V^IV₄V^V₂O₄₂]⁵⁻ anion, CoPMoV could act as a Fenton-like and reductive catalyst for the removal of MB. This study provides a green and facile strategy to design POM-based organic–inorganic material for dye wastewater treatment via oxidation and reduction. Full article

Polyoxometalate (POM)-based ionic liquids (POM-ILs) are gaining increasing attention due to their diverse structures and functionalities. POMs in POM-ILs not only act as essential structural building blocks but also play a crucial role in their functional performance. With the incorporation of POMs, POM-ILs find applications in various fields such as chemical catalysis, energy science, materials science, sensors, and more. The abundant availability of POMs and other building blocks in POM-ILs, along with their versatile combination possibilities, present promising opportunities for the future. Rather than focusing solely on discovering new structures of POM-ILs, current developments in this field emphasize exploring their functions, leading to the emergence of numerous new applications. Summarizing these advancements aids in understanding the latest trends and facilitates rapid evolution. This review examines the recent five years’ worth of results to analyze the new functions of POM-ILs, categorizing them based on their unique characteristics. Full article

Polyoxometalates (POMs) with transition metals (Co, Cu, Fe, Mn, Ni) of Keggin structure and lamellar-stacked multi-layer morphology were synthesized. They were subsequently explored as bifunctional electrocatalysts for oxygen electrodes, i.e., oxygen reduction (ORR) and evolution (OER) reaction, for aqueous rechargeable metal-air batteries in alkaline media. The lowest Tafel slope (85 mV dec⁻¹) value and the highest OER current density of 93.8 mA cm⁻² were obtained for the Fe-POM electrocatalyst. Similar OER electrochemical catalytic activity was noticed for the Co-POM electrocatalyst. This behavior was confirmed by electrochemical impedance spectroscopy, where Fe-POM gave the lowest charge transfer resistance of 3.35 Ω, followed by Co-POM with R_ct of 15.04 Ω, during the OER. Additionally, Tafel slope values of 85 and 109 mV dec⁻¹ were calculated for Fe-POM and Co-POM, respectively, during the ORR. The ORR at Fe-POM proceeded by mixed two- and four-electron pathways, while ORR at Co-POM proceeded exclusively by the four-electron pathway. Finally, capacitance studies were conducted on the synthesized POMs. Full article

Lanthanide elements such as europium exhibit distinctive emissions due to the transitions of inner-shell 4f electrons. Inorganic materials containing lanthanide elements have been widely used as phosphors in conventional displays. The hybridization of lanthanide ions with organic components enables to control of the material’s shapes and properties and broadens the possibility of lanthanide compounds as inorganic–organic materials. Lanthanide ion-containing polyoxometalate anions (Ln-POM) are a promising category as an inorganic component to design and synthesize inorganic–organic hybrids. Several inorganic–organic Ln-POM systems have been reported by hybridizing with cationic surfactants as luminescent materials. However, single-crystalline ordering has not been achieved in most cases. Here, we report syntheses and structures of inorganic–organic hybrid crystals of lanthanide-based POM and bolaamphiphile surfactants with two hydrophilic heads in one molecule. An emissive decatungstoeuropate ([EuW₁₀O₃₆]⁹⁻, EuW₁₀) anion was employed as a lanthanide source. The bolaamphiphile counterparts are 1,8-octamethylenediammonium ([H₃N(CH₂)₈NH₃]²⁺, C₈N₂) and 1,10-decamethylenediammonium ([H₃N(CH₂)₁₀NH₃]²⁺, C₁₀N₂). Both hybrid crystals of C₈N₂-EuW₁₀ and C₁₀N₂-EuW₁₀ were successfully obtained as single crystals, and their crystal structures were unambiguously determined using X-ray diffraction measurements. The photoluminescence properties of C₈N₂-EuW₁₀ and C₁₀N₂-EuW₁₀ were investigated by means of steady-state and time-resolved spectroscopy. The characteristic emission derived from the EuW₁₀ anion was retained after the hybridization process. Full article