Dawson-type Polyoxometalate Research Articles

Enhanced Electrical Conductivity of Polyoxometalates by Bridging with Mixed-Valent Multinuclear Platinum Complexes.

Polyoxometalates (POMs) are nanosized molecular metal oxide anion clusters with tuneable structures and functionalities, and they exhibit a redox chemistry and catalytic activity in multielectron redox processes. These are typically poor electrical conductors (<10-10 Scm-1), which is attributed to negligible electronic interactions among anions in the solid state. Since the reduced electrons on the d0 metals in POMs are delocalized, electrical conductivity was improved when judicious pathways for the electrons were created by bridging the POMs. Utilized with the electronic interactions between bridging oxygen atoms with the highest occupied molecular orbital in the POMs and the metal dz2 orbitals in the multinuclear platinum complexes, and three mixed-valent assemblies were synthesized and characterized. Simply mixing Keggin-type or Dawson-type POMs with tetranuclear or trinuclear platinum complexes in solution afforded three single crystals, and all three compounds were paramagnetic with mixed oxidation states and better conductivities at room temperature than the parent compounds.

Electrochemical behaviour of layer-by-layer constructed of silver nanoparticles and Dawson-type polyoxometalates

Dawson-type polyoxometalate (POM), [(n-C3H7)4N]4S2W18O62 [S2W18], was co-assembled with silver nanoparticles (AgNps) into a multilayer film on the surface of a glassy carbon electrode by using a layer-by-layer approach. The systematic growth of the multilayer film was monitored by cyclic voltammetry and electrochemical impedance spectroscopy (EIS). The [S2W18]- AgNps multilayers exhibited excellent redox activity and good stability towards multiple redox cycling and thin layer behaviour up to 100 mV/s. CV of the multilayer film showed two redox peaks corresponding to the W units present in the POM structure. The slope values of the pH plot suggesting ca. 0.2 and 0.6 protons were related to processes I (one electron transfer) and II (two electron transfer), respectively. The multilayers were found to be highly conductive due to the presence of the nanoparticles as inferred by EIS and resulting charge transfer resistance values obtained for the layers.

Self-assembly of Dawson-type H6P2W18O62@[Cu6O(TZI)3(H2O)6]4 for high-performance aerobic oxidation desulfurization of fuel.

Because global sulfur emission has escalated, the development of high-efficiency deep desulfurization techniques has become imperative. Herein, to design a high-activity heterogeneous catalyst for the aerobic oxidation desulfurization (AODS) of fuel, Dawson-type polyoxometalate (H6P2W18O62 abbreviated as D-P2W18), characterized by its high activity and strong oxidative capacity, was applied to react with CuCl2·2H2O and H3TZI via a one-pot hydrothermal method. Consequently, blue crystalline H6P2W18O62@[Cu6O(TZI)3(H2O)6]4 (abbreviated as D-P2W18@rht-MOF-1; rht-MOF-1 = [Cu6O(TZI)3(H2O)6]4·nH2O) was afforded. X-ray diffraction analysis indicated that D-P2W18 was successfully encapsulated in two different cages of rht-MOF-1, which is distinct from the crystal structure of Keggin-type POMs@rht-MOF-1. It represents the first crystal structure of Dawson-type POMs@rht-MOF-1. When D-P2W18@rht-MOF-1 was employed as a catalyst for AODS under ambient oxygen pressure with the assistance of surfactant dioctadecyl dimethyl ammonium chloride (DODMAC), it demonstrated remarkable catalytic capability and recyclability for both model fuel and commercial diesel. Further, the AODS reaction mechanism, identified as a free radical oxidation-reduction process, was verified by way of radical quenching experiments, EPR and XPS analysis. This approach offers a feasible route for the synthesis of new Dawson-type POMs@MOFs of heterogeneous catalysts for highly active AODS of fuel.

K6[P2Mo18O62] as DNase-Mimetic Artificial Nucleases to Promote Extracellular Deoxyribonucleic Acid Degradation in Bacterial Biofilms.

In the current study, the DNase-like activity of the Dawson-type polyoxometalate K6[P2Mo18O62] was explored. The obtained findings demonstrated that K6[P2Mo18O62] could effectively cleave phosphoester bonds in the DNA model substrate (4-nitrophenyl phosphate) and result in the degradation of plasmid DNA. Moreover, the application potential of this Dawson-type polyoxometalate as a DNase-mimetic artificial enzyme to degrade extracellular DNA (eDNA) in Escherichia coli (E. coli) bacterial biofilm was explored. The results demonstrated that K6[P2Mo18O62] exhibited high cleavage ability toward eDNA secreted by E. coli and thus eradicated the bacterial biofilm. In conclusion, Dawson-type polyoxometalate K6[P2Mo18O62] possessed desirable DNase-like activity, which could serve as a bacterial biofilm eradication agent by cleaving and degrading eDNA molecules.

Ionic liquid-mediated PEO-based solid-state electrolyte membrane modified with Dawson-type polyoxometalates

Ionic liquid-mediated PEO-based solid-state electrolyte membrane modified with Dawson-type polyoxometalates

Polyoxometalates-modified and facets-engineered TiO2 nanocomposites for selective photocatalytic cleavage of C–C bond of lignin models

Selective cleavage of C-C bond of lignin derivatives and models via oxidation is vital to realize value-added utilization of lignocellulosic biomass. Herein, based on the strategy of facet engineering and pseudo-heterojunction construction, a series of P2W17V/{001}-TiO2 heterogenous photocatalysts were constructed by loading monovanadium-substituted Dawson-type polyoxometalates P2W17V onto TiO2 with exposed {001} facets. The morphologies, structures, photoelectrical properties, and photocatalytic performances of the nanocomposites were researched. P2W17V/{001}-TiO2 could effectively photocatalyze the transformation of 2-phenoxy-1-phenylethanol, the lignin model compound with characteristic β-O-4 structure, to benzaldehyde and phenol. Photogenerated electrons and O2•- were disclosed critical to lignin model conversion that could induce C-C bond cleavage, with a selectivity above 85%, through a Cβ-centered radical. Neither pure O2 nor precious metal was required in the photocatalysis. P2W17V acted as electron pools. The engineered facets of TiO2 and the pseudo-heterojunction between P2W17V and TiO2 suppressed electron-hole recombination, facilitated charge transfer, and promoted photocatalytic performance. This work paved a new avenue to convert lignin and lignin derivatives to high-value chemicals by selectively breaking C-C bond under mild conditions.

Polyoxometalate/MXene hybrid film with a 3D porous structure for high-performance electrochromic supercapacitors

MXenes (2D transition metal carbides, nitrides, and carbonitrides) are attractive pseudocapacitive electrode materials for electrochemical energy conversion and storage applications. The layered structure of MXenes provides intercalation pseudocapacitance properties and numerous reaction sites; however, nanosheet agglomeration and stacking reduce the reaction site availability and limit the electrochemical reaction dynamics of the interlayer ions. In this study, a unique electrochromic-energy storage hybrid film (NW/P2W17Ni/Ti3C2Tx), based on a Ni mono-substituted Dawson-type polyoxometalate (P2W17Ni) and a 2D transition metal carbide (Ti3C2Tx), was produced by the combination of a hydrothermal process and layer-by-layer self-assembly method. With positively charged polyelectrolyte polyetherimide (PEI) as a linker, negatively charged Ti3C2Tx layered sheets and P2W17Ni polyanions were deposited on a TiO2 nanowire (NW) array to form a 3D porous structure which prevented the stacking of nanoparticles and sheets, provided more ion transmission paths, and enhanced the ion transfer kinetics. The NW/P2W17Ni/Ti3C2Tx hybrid film demonstrated elevenfold higher areal capacitance (16.1 mF cm−2, 0.6 mA cm−2) than a pure Ti3C2Tx film (1.4 mF cm−2, 0.6 mA cm−2), and the retention rate reached 100% after 1000 cycles. The asymmetric electrochromic supercapacitor (ECSC) assembled with the NW/P2W17Ni/Ti3C2Tx film as the cathode exhibited a high capacity with significant dual-band regulation in the visible and near-infrared regions. The ECSC illuminated a light-emitting diode and achieved high-speed color switching between olive green and dark azure blue during the charging and discharging processes, demonstrating the energy storage status. These results could lead to considerable advances in the development of MXene-based ECSCs.

Supramolecular Aggregation Control in Polyoxometalates Covalently Functionalized with Oligoaromatic Groups.

CLICK-chemistry has become a universal route to covalently link organic molecules functionalized with azides and alkynes, respectively. Here, we report how CLICK-chemistry can be used to attach oligoaromatic organic moieties to Dawson-type polyoxometalates. In step one, the lacunary Dawson anion [α2 -P2 W17 O61 ]6- is functionalized with phosphonate anchors featuring peripheral azide groups. In step two, this organic-inorganic hybrid undergoes microwave-assisted CLICK coupling. We demonstrate the versatility of this route to access a series of Dawson anions covalently functionalized with oligoaromatic groups. The supramolecular chemistry and aggregation of these systems in solution is explored, and we report distinct changes in charge-transfer behavior depending on the size of the oligoaromatic π-system.

A pH and voltage dual-adjustment of electrochromic material achieves multicolor change based on alizarin red and Dawson-type polyoxometalate

A novel material can realize multicolor change process based on polyoxometalate and dye with pH and voltage dual-adjustment.

A sensing platform based on Cu-MOF encapsulated Dawson-type polyoxometalate crystal material for electrochemical detection of xanthine

A promising sensing platform based on polyoxometalate-based metal-organic framework (POMOF) was established for sensitive electrochemical detection of xanthine (XA). In the unique structure of POMOF, the Dawson polyoxoanions P2W18 were encapsulated into 3D open copper-mixed ligand nanotube framework Cu-MOF, in which the cavity of the metal-organic framework provides a specific shelter to prevent the aggregation and loss of polyoxometalate in electrocatalytic reactions; meanwhile, unsaturated Cu(II) active sites of Cu-MOF can also serve as electrocatalytic active center. The POMOF-based sensor (CuMOFP2W18/XC-72R) was fabricated by using acetylene black (XC-72R) as a support material to enhance the conductivity of POMOF. The performances of the POMOF-based sensor were studied by using different electrochemical testing methods. The composite displayed remarkable electrocatalytic activity for the oxidation of XA due to the synergistic effect of polyoxometalate (POM) and metal-organic framework (MOF). The electrochemical sensor demonstrated a wide linear range (0.5μM-240μM), low detection limit (0.26μM), and excellent selectivity for detecting XA. Furthermore, the composite further demonstrated excellent reproducibility and great stability. More importantly, the proposed sensor was utilized to detect XA in real samples, which may provide a new way for early disease diagnosis.

Grafting of Anionic Decahydro-Closo-Decaborate Clusters on Keggin and Dawson-Type Polyoxometalates: Syntheses, Studies in Solution, DFT Calculations and Electrochemical Properties.

Herein we report the synthesis of a new class of compounds associating Keggin and Dawson-type Polyoxometalates (POMs) with a derivative of the anionic decahydro-closo-decaborate cluster [B10H10]2- through aminopropylsilyl ligand (APTES) acting as both a linker and a spacer between the two negatively charged species. Three new adducts were isolated and fully characterized by various NMR techniques and MALDI-TOF mass spectrometry, notably revealing the isolation of an unprecedented monofunctionalized SiW10 derivative stabilized through intramolecular H-H dihydrogen contacts. DFT as well as electrochemical studies allowed studying the electronic effect of grafting the decaborate cluster on the POM moiety and its consequences on the hydrogen evolution reaction (HER) properties.

Synthesis of {P2W18}-based coated structured nano materials with supercapacitors and H2O2 sensing

The combination of metal-organic frameworks (MOFs) with large specific surface area and high stability and Dawson-type polyoxometalates (POMs) with excellent electron transfer ability to build a new inorganic-organic hybrid as energy storage materials can give full play to the advantages of both. Therefore, the inorganic organic hybrid nano material {Ag4K2P2W18O62}@[Ag3(μ-Hbtc)(μ-H2btc)]n (which became {Ag4K2P2W18O62}@Ag-BTC, where BTC = 1,3,5-benzenetricarboxylic acid) was synthesized by liquid-assisted grinding. The XRD, SEM, TEM characterization show that {Ag4K2P2W18O62}@Ag-BTC is a coating structure. The specific capacitance is 378.9 F g−1 at a current density of 1 A g−1, with a retention rate of 93.5 % for 5000 cycles. An energy density of 7.8 Wh kg−1 and the power density of 500.0 W kg−1 are obtained in water-based symmetric two-electrode supercapacitor system. In addition, when used as an H2O2 sensor, it has a broad detection range of 1.5 μM to 1.5 mM and the small detection limit of 0.206 μM, also offers excellent interference immunity and stability. Moreover, by applying this nano material to the detection of H2O2 in human serum, results are acceptable. The above result shows that the composite material synthesized by the liquid-assisted grinding method adequately combines properties of both parent materials is a viable strategy for achieving performance enhancement.

Dawson-type polyoxometalate modified separator for anchoring/catalyzing polysulfides in high-performance lithium-sulfur batteries

Considering ultrahigh energy density as well as the cost-effectiveness of lithium-sulfur batteries (Li-S, LSBs), it is considered the most outstanding battery. However, the shuttling behavior and sluggish conversion of polysulfides (LiPSs), and the dendrite formation seriously impede the practical applications of LSBs. The modified separator is an effective method to solve the above problems. Herein, we propose a Dawson-type polyoxometalate (K6P2W18O62, P2W18) modified polypropylene membrane (P2W18/PVDF/PP) with multiple functions for inhibiting the diffusion of LiPSs, promoting the redox kinetics of LiPSs conversion, avoiding the dendrite formation, and promoting Li+ rapid transfer. Based on spectroscopic techniques as well as electrochemical dates, it was confirmed that P2W18 can effectively adsorb LiPSs and accelerate LiPSs conversion kinetics to improve the electrochemical performance of LSBs. As a result, LSBs with P2W18/PVDF/PP separator show an initial specific capacity of 724 mAh g–1 at 3.0 C with excellent cycling stability over 400 cycles. The result offers a new perspective for exploring the role of Dawson-type polyoxometalate in extending cycling life and increasing specific capacity in LSBs.

Vanadium-Substituted Dawson-Type Polyoxometalate-TiO2 Nanowire Composite Film as Advanced Cathode Material for Bifunctional Electrochromic Energy-Storage Devices.

Polyoxometalates (POMs) demonstrate potential for application in the development of integrated smart energy devices based on bifunctional electrochromic (EC) optical modulation and electrochemical energy storage. Herein, a nanocomposite thin film composed of a vanadium-substituted Dawson-type POM, i.e., K7[P2W17VO62]·18H2O, and TiO2 nanowires were constructed via the combination of hydrothermal and layer-by-layer self-assembly methods. Through scanning electron microscopy and energy-dispersive spectroscopy characterisations, it was found that the TiO2 nanowire substrate acts as a skeleton to adsorb POM nanoparticles, thereby avoiding the aggregation or stacking of POM particles. The unique three-dimensional core−shell structures of these nanocomposites with high specific surface areas increases the number of active sites during the reaction process and shortens the ion diffusion pathway, thereby improving the electrochemical activities and electrical conductivities. Compared with pure POM thin films, the composite films showed improved EC properties with a significant optical contrast (38.32% at 580 nm), a short response time (1.65 and 1.64 s for colouring and bleaching, respectively), an excellent colouration efficiency (116.5 cm2 C−1), and satisfactory energy-storage properties (volumetric capacitance = 297.1 F cm−3 at 0.2 mA cm−2). Finally, a solid-state electrochromic energy-storage (EES) device was fabricated using the composite film as the cathode. After charging, the constructed device was able to light up a single light-emitting diode for 20 s. These results highlight the promising features of POM-based EES devices and demonstrate their potential for use in a wide range of applications, such as smart windows, military camouflage, sensors, and intelligent systems.

Electrochemical Studies of LbL Films With Dawson Type Heteropolyanion Glassy Carbon Electrode Sensor Modified for Methyl Parathion Detection

Rapid methyl parathion detection was measured using a fabricated glassy carbon electrode (GCE) sensor designed using the layer-by-layer (LBL) method. Multilayer assemblies were developed on the glassy carbon electrode by alternating depositions of anions and cations in which a Dawson Type Polyoxometalate β-K6[(P2W18O62·H2O)]·14H2O (∼P2W18 POM) and polyethyleneimine (PEI) stabilized silver nanoparticles (∼PEI-AgNPs) acted as anions and cations, respectively. The redox behavior of P2W18 POM within LBL assembly was carried out via cyclic voltammetry. This LBL assembly was thoroughly characterized by UV-Visible, FT-IR, XRD, AFM, and SEM techniques. The fabricate GCE sensor was investigated for the electrocatalytic activity to detect methyl parathion. The results clearly showed that the fabricated GCE sensor was successfully synthesized. More interestingly, the current response for detecting methyl parathion was found to be less than 1 ppm, proving that this fabricated GCE sensor may exhibit potential applications in the detection of targeted pesticide.

Front Cover: Syntheses, Polymorphic Transformations, and Functions of Ionic Crystals Based on Mononuclear Bismuth(III) Complexes and Polyoxometalates (ChemNanoMat 5/2022)

Polyoxometalates (POMs) have been a popular motif in crystal engineering. In this work, seven ionic crystals based on Keggin- or Dawson-type POMs and mononuclear Bi(III) complexes were synthesized. The Bi(III) center exhibited triangular dodecahedron, square antiprism, or pseudo-cubic eight-coordination geometries, with DMSO or DMF as ligands. The ionic crystals showed polymorphic transformations, and high proton conductivities depending on the structure. More information can be found in the Research Article by Sayaka Uchida et al.

Oxidation of cyclohexanone and/or cyclohexanol catalyzed by Dawson-type polyoxometalates using hydrogen peroxide

Oxidation of cyclohexanone and/or cyclohexanol catalyzed by Dawson-type polyoxometalates using hydrogen peroxide

Efficient Preparation of a Nonenzymatic Nanoassembly Based on Cobalt-Substituted Polyoxometalate and Polyethylene Imine-Capped Silver Nanoparticles for the Electrochemical Sensing of Carbofuran.

The ever-growing exploitation of pesticides and their lethal effects on living beings have made it a dire need of the day to develop an accurate and reliable approach for their monitoring at trace levels. The designing of an enzyme-free electrocatalyst to electrochemically detect the pesticide residues is currently gaining much importance. In this study, a novel redox-sensing film was constructed successfully based on cobalt-substituted Dawson-type polyoxometalate [P2W17O61 (Co2+·OH2)]7– (Co-POM) and polyethylene imine (PEI)-capped silver nanoparticles (AgNPs). A nanohybrid assembly was fabricated on a glassy carbon electrode’s surface by alternately depositing Co-POM and PEI-AgNPs using the layer-by-layer self-assembly method. The surface morphology of the immobilized CoPOM/AgNP multilayer nanoassembly was analyzed through scanning electron microscopy along with energy-dispersive spectroscopy for elemental analysis. The redox properties and surface morphologies of fabricated assemblies were evaluated by cyclic voltammetry and electrochemical impedance spectroscopy. The practicability and feasibility of the proposed sensing layer was tested for the detection of a highly toxic insecticide, that is, carbofuran. The fabricated sensor exhibited a limit of detection of 0.1 mM with a sensitivity of 13.11 μA mM–1 for carbofuran. The results depicted that the fabricated nonenzymatic hybrid film showed excellent electrocatalytic efficiency for the carbofuran oxidation. Furthermore, the obtained value of “apparent Km”, that is, 0.4 mM, illustrates a good electro-oxidation activity of the sensor for the detection of carbofuran. The exceptionally stable redox activity of Co-POM, high surface area and greater conductivity of AgNPs, and the synergistic effect of all components of the film resulted in an excellent analytical performance of the proposed sensing assembly. This work provides a new direction to the progress and designing of nonenzymatic electrochemical sensors for pesticide determination in real samples.

Ultrasensitive photochromic and Raman dual response to ethylenediamine gas through polyoxometalate–viologen crystalline hybrid

A new crystalline complex is successfully synthesized based on Dawson type polyoxometalate and amino substituted viologen. It exhibits ultrasensitive photochromic and Raman dual response to ethylenediamine gas.

Injectable hydrogel platform with biodegradable Dawson-type polyoxometalate and R848 for combinational photothermal-immunotherapy of cancer.

Photothermal therapy (PTT) is a powerful strategy for cancer treatment with minimal invasiveness but still limited by lack of long-term efficacy against tumor recurrence and toxicity concerns about the slow biodegradability of the PTT agents. Herein, an injectable hydrogel platform (R848/POM@GG) of gellan gum co-loaded with Dawson-type {P2Mo18} polyoxometalate (POM) and Toll-like receptors agonist resiquimod (R848) is developed for combinational photothermal-immunotherapy of cancer. The POM-based gellan gum hydrogel (POM@GG) exhibits high photothermal conversion efficiency (63.1%) at a safe power density of 0.3 W cm-2 and good photostability during five cycles. By further incorporation of R848, the obtained R848/POM@GG exerts synergetic photothermal-immunotherapy on solid tumors, giving a high tumor inhibition rate of 99.3% and negligible lung metastases in the breast cancer mice models. A strong antitumor immune system with significantly elevated TNF-α, IL-2, and IL-6 levels is activated by R848. Additionally, the POM clusters gradually degrade to nontoxic molybdate in the physiological environment. Overall, the injectable hydrogel platform of R848/POM@GG has great translational potential for localized antitumor treatments.