Preparation and photochromism of nanocomposite thin film based on polyoxometalate and polyethyleneglycol

A photochromic nanocomposite based on Keggin structure phosphomolybdic acid (PMoA) well dispersed in polyethyleneglycol (PEG) was fabricated. TEM image showed that PMoA nanoparticles with narrow size distribution were finely dispersed in polymer matrix. FT-IR results showed that the Keggin geometry of polyoxometalates was still preserved inside the composites and strong coulombic interaction was built between PMoA and polymer matrix. Under UV irradiation, the film was reduced photochemically to yield a blue species, which was in accordance with a charge-transfer mechanism.     

Synthesis, characterization, and crystal structures of two new polyoxomolybdate wheel clusters

Two new polyoxomolybdates Na₅(NH₄)₁₆[Mo₅₇Mn₆(NO)₆O₁₇₄ (OH)₃(H₂O)₂₄] · 44H₂O (1) and (NH₄)₂₁[Mo₅₇Cu₆(NO)₆O₁₆₈(OH)₃(H₂O)₂₄] · 53H₂O (2) were synthesized in aqueous solution and characterized by elemental analysis, IR, TG analysis and single-crystal X-ray diffraction. They represent interesting examples of integrating and embedding magnetic 3d metal ions into the diamagnetic polyoxomolybdate host structure.     

Anodic photodissolution of n-InP, under electroless conditions

In the presence of α-SiMo₁₂O₄₀⁴⁻ ions dissolved in acidic solution and under laser irradiation, the electroless photoetching of n-type InP is achieved. At the laser impact, the semiconductor is oxidized while SiMo₁₂O₄₀⁴⁻ species are reduced. The shape of the pit formed, due to the photoanodic dissolution of the material, depends on the experimental conditions, notably on the presence or not of Cl⁻ ions in the medium. It can have either a Gaussian shape or a flat bottom. To specify the charge transfer which occurs at the n-InP/solution illuminated interface, some electrochemical studies were performed on n- and p-type InP electrodes. In fact, the reduction of SiMo₁₂O₄₀⁴⁻ ions occurs by capture of electrons from the InP conduction band. Considering the energetic situation at the InP/electrolyte interface and some electrochemical results, it is concluded that the electron transfer from InP to SiMo₁₂ is mediated by surface states. The influence of Cl⁻ ions on the n-InP photodissolution process is also discussed.     

Polyoxometalate modified inorganic–organic nanocomposite materials for energy storage applications: A review

Modification of organic substrates with inorganic polyoxometalate (POM) clusters can be used to engineer nanocomposite materials with improved properties and diverse functionalities. This review will outline concepts and methodologies for fabricating POM based inorganic–organic composite materials with a special focus on the electrochemical functionality of these composites for energy storage applications. The strengths and limitations of three different fabrication techniques, chemisorption to a carbon surface, immobilization in a polymer matrix, and layer-by-layer self-assembly will be assessed. Furthermore, the latest developments in the use of POM nanocomposite materials in energy storage applications like electrochemical capacitors (ECs) and lithium ion batteries will be presented. This review will highlight the issues and challenges that need to be addressed to achieve inorganic–organic POM nanocomposites able to support high performance energy storage applications.     

A modified composite film electrode of polyoxometalate/carbon nanotubes and its electrocatalytic reduction

Keggin-type polyoxometalate (H₄SiMo₁₂O₄₀) and carbon nanotubes (CNTs) coated by poly(allylamine hydrochloride) (PAH) were alternately deposited on glassy carbon (GC) electrodes by an electrochemical growth method in acidic aqueous solution. The preparation of the film electrode was simple and convenient. Thus-prepared multilayer films and the electrochemical behavior of the composite film modified electrode were characterized by UV–vis spectroscopy and cyclic voltammetry. It was shown that the multilayer films are uniform and stable. The resulting multilayer film modified electrode behaves as an electrochemical sensor because of its low overpotential for the catalytic reduction of S₂O₈ ²⁻ and NO₂ ⁻ in acidic aqueous solution.     

Multicolor electrochromic and pH-sensitive nanocomposite thin film based on polyoxometalates and polyviologen

A multiple-colored electrochromic composite film of polyoxometalates (P₂W₁₈) and poly(hexyl viologen) (PXV) is fabricated by layer-by-layer (LbL) self-assembly method. The P₂W₁₈/PXV composite film exhibits a linear increase in film thickness with assembly processing, and undergoes a colorless to blue to violet transition over the potential range from +0.1 to −0.9 V. The optical contrast, response time and stability for the as-prepared films are carefully investigated. These results show the validation of an LbL method based intermixing strategy for the design of tunable-color electrochromic thin films. The composite film can also be used as a pH sensor because of the pH dependence of its electrochemical response.     

Increased in vitro Anti-HIV Activity of Caffeinium-Functionalized Polyoxometalates

Polyoxometalates (POMs), molecular metal oxide anions, are inorganic clusters with promising antiviral activity. Herein we report increased anti-HIV-1 activity of a POM when electrostatically combined with organic counter-cations. To this end, Keggin-type cerium tungstate POMs have been combined with organic methyl-caffeinium (Caf) cations, and their cytotoxicity, antiviral activity and mode of action have been studied. The novel compound, Caf₄K[β₂-CeSiW₁₁O₃₉]×H₂O, exhibits sub-nanomolar antiviral activity and inhibits HIV-1 infectivity by acting on an early step of the viral infection cycle. This work demonstrates that combination of POM anions and organic bioactive cations can be a powerful new strategy to increase antiviral activity of these inorganic compounds.     

Preparation and Electrocatalytic Application of Composites Containing Gold Nanoparticles Protected with Rhodium-Substituted Polyoxometalates

Substitution of a metal center of phosphomolybdate, PMo₁₂O₄₀³⁻ (PMo₁₂), or its tungsten analogue with dirhodium(II) and subsequent stabilization of gold nanoparticles, AuNPs, with Rh₂PMo₁₁ are demonstrated. The AuNP-Rh₂PMo₁₁ mediates oxidations but adsorbs too weakly for direct modification of electrode materials. Stability in quiescent solution was achieved by modifying glassy carbon (GC) with 3-aminopropyltriethoxysilane (APTES) and then electrostatically assembling AuNP-Rh₂PMo₁₁. At GC|APTES|AuNP-Rh₂PMo₁₁, cyclic voltammetry showed the expected set of three reversible peak-pairs for PMo₁₁ in the range −0.2 to 0.6 vs. (Ag/AgCl)/V and the reversible Rh^II,III couple at 1.0 vs. (Ag/AgCl)/V. The presence of AuNPs increased the current for the reduction of bromate by a factor of 2.5 relative to that at GC|Rh₂PMo₁₁, and the electrocatalytic oxidation of methionine displayed characteristics of synergism between the AuNP and Rh^II. To stabilize AuNP-Rh₂PMo₁₁ on a surface in a flow system, GC was modified by electrochemically assisted deposition of a sol–gel with templated 10-nm pores prior to immobilizing the catalyst in the pores. The resulting electrode permitted determination of bromate by flow-injection amperometry with a detection limit of 4.0 × 10⁻⁸ mol dm⁻³.     

Carbon nanotubes-assisted polyoxometalate nanocomposite film with enhanced electrochromic performance

A nanocomposite film containing polyoxometalates (POMs) cluster K₆P₂W₁₈O₆₂·14H₂O (P₂W₁₈), carbon nanotubes (CNTs) and chitosan (CS) was fabricated by layer-by-layer (LbL) methods. The composite material displays enhanced electrochromic performance, with the optical contrast of 20.3% and coloration efficiency of 91.5 cm² C⁻¹ at 620 nm. Furthermore, the composite material displays the increased thickness and surface roughness by incorporation of CNTs into the P₂W₁₈ film. Obviously, the presence of CNTs has the strong influence on the multilayer structure, leading to high optical contrast and coloration efficiency. The results demonstrate the essential role of CNTs in enhancing functionality on POMs for applications of electrochromic devices.