A tetrahedron-shaped polyoxoantimotungstate encapsulating a hexanuclear octahedral lanthanide-oxo cluster for an amperometric bromate sensor

An inorganic hexalanthanide-oxo-cluster-encapsulated antimotungstate, K2Na3H43[Nd6(OH)6(H2O)6(B-α-SbW9O33)4]2·67H2O (1), has been successfully synthesized by a facile one-step hydrothermal reaction method. The tetrahedron-shaped two-shell {Nd6(OH)6(H2O)6(B-α-SbW9O33)4}(1a) polyanion is composed of a novel pure lanthanide-oxo {Nd6(μ3-OH)6(H2O)6} octahedron and {(B-α-SbW9O33)4} tetrahedron. After being effectively loaded onto a glassy carbon electrode (GCE) by electrostatic adsorption using polydiallyldimethyl ammonium chloride (PDDA)-functionalized multi-walled carbon nanotubes (MWCNTs), compound 1 exhibits electrochemical activity for the reduction of bromate ions with good selectivity, a high sensitivity of 186 μA mM-1 and a detection limit that has reached 1.9 μM. To the best of our knowledge, this is the first example of an amperometric bromate sensor based on Ln-containing antimotungstates, which will provide new materials for electrochemical sensors.

Organic-Inorganic Hybrid Films of the Sulfate Dawson Polyoxometalate, [S2W18O62]4-, and Polypyrrole for Iodate Electrocatalysis

The Dawson-type sulfate polyoxometalate (POM) [S₂W₁₈O₆₂]^4- has successfully been entrapped in polypyrrole (PPy) films on glassy carbon electrode (GCE) surfaces through pyrrole electropolymerization. Films of varying POM loadings (i.e., thickness) were grown by chronocoulometry. Film-coated electrodes were then characterized using voltammetry, revealing POM surface coverages ranging from 1.9 to 11.7 × 10^-9 mol·cm^-2, and were stable over 100 redox cycles. Typical film morphology and composition were revealed to be porous using atomic force microscopy, scanning electron microscopy, and X-ray photoelectron spectroscopy, and the effects of this porosity on POM redox activity were probed using AC impedance. The hybrid organic-inorganic films exhibited a good electrocatalytic response toward the reduction of iodate with a sensitivity of 0.769 μA·cm^-2·μM^-1.

MOF/POM hybrids as catalysts for organic transformations

Insertion of molecular metal oxides, e.g. polyoxometalates (POMs), into metal-organic frameworks (MOFs) opens up new research opportunities in various fields, particularly in catalysis. POM/MOF composites have strong acidity, oxygen-rich surface, and redox capacity due to typical characteristics of POMs and the large surface area, highly organized structures, tunable pore size, and shape are due to MOFs. Such hybrid materials have gained a lot of attention due to astonishing structural features, and hence have potential applications in organic catalysis, sorption and separation, proton conduction, magnetism, lithium-ion batteries, supercapacitors, electrochemistry, medicine, bio-fuel, and so on. The exceptional chemical and physical characteristics of POMOFs make them useful as catalysts in simple organic transformations with high capacity and selectivity. Here, the thorough catalytic study starts with a brief introduction related to POMs and MOFs, and is followed by the synthetic strategies and applications of these materials in several catalytic organic transformations. Furthermore, catalytic conversions like oxidation, condensation, esterification, and some other types of catalytic reactions including photocatalytic reactions are discussed in length with their plausible catalytic mechanisms. The disadvantages of the POMOFs and difficulties faced in the field have also been explored briefly from our perspectives.

Amphiphilic Polyoxometalate-CNTs Nanohybrid as Highly Efficient Enzyme-free Electrocatalyst for H2O2 Sensing

Hybrid nanomaterials are emerging as a potential platform for the efficient detection of biomolecules, thus, the rational design of such materials has been widely explored. Polyoxometalates (POM) nanoclusters can serve...

Polyoxometalate based ionic crystal: dual applications in selective colorimetric sensor for hydrated ZnCl2 and antimicrobial activity

One-pot synthesis of POM-salt ([Himi]₄[SiMo₁₂O₄₀] (1)) was achieved by mixing silicomolybdic acid and imidazole in acidic conditions and characterized by FTIR, TGA, SEM, EDX, ICP-OES and XPS.

Transition Metal-Substituted Krebs-Type Polyoxometalate-Doped PEDOT Films

The transition metal-substituted Krebs-type polyoxometalates (POMs) [Sb₂W₂₀M₂O₇₀(H₂O)₆]^n-, M = Fe(III), Co(II), or Cu(II), were surface immobilized within the conducting polymer 3,4-ethylenedioxythiophene (PEDOT) on glassy carbon electrode surfaces. The immobilized films of different thicknesses were characterized by electrochemical and surface-based techniques. The inherent redox activity for the Krebs-type POMs, [Sb₂W₂₀M₂O₇₀(H₂O)₆]^n-, M = Fe(III), Co(II), or Cu(II), that were observed in the solution phase were maintained in the polymeric PEDOT matrix. The resulting films were found to be extremely stable toward redox switching between the various POM-based redox states. The films exhibited pH-dependent redox activity and thin layer behavior up to 100 mV s^-1. The films were found to be highly conductive through the employment of electrochemical impedance spectroscopy. Surface characterization of the films was carried out by X-ray photoelectron spectroscopy, atomic force microscopy, and scanning electron microscopy graph.

Nanopillar films with polyoxometalate-doped polyaniline for electrochemical detection of hydrogen peroxide

Design and fabrication of electrodes is key in the development of electrochemical sensors with superior electrochemical performances. Herein, an enzymeless electrochemical sensor is developed for detection of hydrogen peroxide based on the use of highly ordered polyoxometalate (POM)-doped polyaniline (PANI) nanopillar films. The electrodeposition technique enables the entrapment of POMs into PANI during electropolymerization to produce thin coatings of POM-PANI. Electrochemical investigations of the POM-PANI/nanopillar electrode showed well-defined multiple pairs of redox peaks and rapid electron transfer. The nanopillar structure facilitated the diffusion of the electrolyte and thus, enhanced the redox reaction. In particular, the POM-PANI/nanopillar electrode was incorporated into a flow injection biosensor and it demonstrates its electrocatalytic activity to detect hydrogen peroxide with high sensitivity, rapid response time, and low detection limit.

Redox mediated synthesis of hierarchical Bi2O3/MnO2 nanoflowers: a non-enzymatic hydrogen peroxide electrochemical sensor

Redox mediated synthesis of Bi₂O₃/MnO₂ nanoflowers for efficient electrochemical sensing of hydrogen peroxide down to 0.05 μM.

Research progress on polyoxometalate-based transition-metal–rare-earth heterometallic derived materials: synthetic strategies, structural overview and functional applications

This review summarizes the structural types of reported polyoxometalate-based transition-metal–rare-earth heterometallic derived materials (PTRHDMs) together with synthetic strategies, structural motifs and relevant functional applications.

Polyoxometalate-conductive polymer composites for energy conversion, energy storage and nanostructured sensors

The exchange of electric charges between a chemical reaction centre and an external electrical circuit is critical for many real-life technologies. This perspective explores the "wiring" of highly redox-active molecular metal oxide anions, so-called polyoxometalates (POMs) to conductive organic polymers (CPs). The major synthetic approaches to these organic-inorganic hybrid materials are reviewed. Typical applications are highlighted, emphasizing the current bottlenecks in materials development. Utilization of the composites in the fields of energy conversion, electrochemical energy storage, sensors and nanoparticle "wiring" into conductive materials are discussed. The outlook section presents the authors' views on emerging fields of research where the combination of POMs and CPs can be expected to provide novel materials for groundbreaking new technologies. These include light-weight energy storage, high-sensitivity toxin sensors, artificial muscles, photoelectrochemical devices and components for fuel cells.

Enhancement of nitrite and nitrate electrocatalytic reduction through the employment of self-assembled layers of nickel- and copper-substituted crown-type heteropolyanions

Multilayer assemblies of two crown-type type heteropolyanions (HPA), [Cu20Cl(OH)24(H2O)12(P8W48O184)](25-) and Ni4(P8W48O148)(WO2)](28-), have been immobilized onto glassy carbon electrode surfaces via the layer-by-layer (LBL) technique employing polycathion-stabilized silver nanoparticles (AgNP) as the cationic layer within the resulting thin films characterized by electrochemical and physical methods. The redox behaviors of both HPA monitored during LBL assembly with cyclic voltammetry and impedance spectroscopy revealed significant changes by immobilization. The presence of AgNPs led to the retention of film porosity and electronic conductivity, which has been shown with impedance and voltammeric studies of film permeabilities toward reversible redox probes. The resulting films have been characterized by physical methods. Finally, the electrocatalytic performance of obtained films with respect to nitrite and nitrate electrocatalytic reduction has been comparatively studied for both catalysts. Nickel atoms trapped inside HPA exhibited a higher specific activity for reduction.

Polypyrrole-supported membrane proteins for bio-inspired ion channels

Biomedical platforms constructed by immobilizing membrane proteins in matrixes made of synthetic organic polymers is a challenge because the structure and function of these proteins are affected by environmental conditions. In this work, an operative composite that regulates the diffusion of alkali ions has been prepared by functionalizing a supporting matrix made of poly(N-methylpyrrole) (PNMPy) with a β-barrel membrane protein (Omp2a) that forms channels and pores. The protein has been unequivocally identified in the composite, and its structure has been shown to remain unaltered. The PNMPy-Omp2a platform fulfills properties typically associated with functional bio-interfaces with biomedical applications (e.g., biocompatibility, biodegrabadility, and hydrophilicity). The functionality of the immobilized protein has been examined by studying the passive ion transport response in the presence of electrolytic solutions with Na(+) and K(+) concentrations close to those found in blood. Although the behavior of PNMPy and PNMPy-Omp2a is very similar for solutions with very low concentration, the resistance of the latter decreases drastically when the concentration of ions increases to ∼100 mM. This reduction reflects an enhanced ion exchange between the biocomposite and the electrolytic medium, which is not observed in PNMPy, evidencing that PNMPy-Omp2a is particularly well suited to prepare bioinspired channels and smart biosensors.

The nanoporous PdCr alloy as a nonenzymatic electrochemical sensor for hydrogen peroxide and glucose

The nanoporous PdCr alloy fabricated by one-step mild dealloying exhibits superior sensing performance and durability toward H₂O₂ and glucose compared to Pt/C and NP-Pd catalysts.