Photoluminescent multilayer film based on polyoxometalate and tris(2,2-bipyridine)ruthenium

A photoluminescent multilayer film based on Keggin-type polyoxometalate PMo₁₂O₄₀³⁻ (PMo₁₂) and transition metal complex tris(2,2-bipyridine) ruthenium [Ru(bpy)₃]²⁺ (Ru(bpy)) was prepared by using layer-by-layer assembly(LBL). The formation of multilayer film was monitored by ultraviolet absorption spectra. The absorption intensity of characteristic peaks increase with a four-layer cycle, indicating that the LBL assembly film grow linearly and reproducibly from layer to layer. The composition of the film was measured by X-ray photoelectron spectrum (XPS). The data of XPS confirmed the presence of the expected elements. The film exhibited photoluminescence arising from π^*−t_2g ligand-to-metal transition of Ru(bpy) and redox activity attributing to molybdenum-centered redox processes of PMo₁₂. The surface morphology of multilayer film was characterized by atomic force microscopy (AFM). The result shows that the film had a smooth surface with root-mean-square (rms) roughness ca. 1.363 nm for {PEI/(PSS/PEI/PMo₁₂/Ru(bpy))₃}. The grains are homogeneously dispersed in the substrate and have a rather narrow diameter size distribution.     

A Simple and Novel Electrochemical Sensor Based on Phosphomolybdic‐Polypyrrole Film Modified Electrode for Highly Sensitive Detection of Cholic Acid

A simpe electrochemical sensor for detection of cholic acid (CA) was designed by modifying phosphomolybdate (PMo₁₂) doped polypyrrole (PPy) film on glassy carbon electrode (PMo₁₂‐PPy/GCE). The electrochemical behavior of CA on PMo₁₂‐PPy/GCE was investigated by cyclic voltammetry and 0.5 order differential voltammetry. The results indicated that CA had high inhibitory activity toward the peak currents of PMo₁₂‐PPy/GCE. The reduction peak currents were linearly related to the logarithmic value of the concentration of CA from 1.0×10^?7 to 1.0×10^?3 mol/L with a low detection limit of 1.0×10^?8 mol/L. The developed sensor exhibited excellent sensitivity, selectivity and stability for detection of CA, and it could be successfully applied to detect the level of CA in the urine samples. Moreover, the response mechanism of CA on the PMo₁₂‐PPy/GCE was discussed in detail.     

Phosphomolybdic acid functionalized graphene loading copper nanoparticles modified electrodes for non-enzymatic electrochemical sensing of glucose

A sensitive non-enzymatic glucose electrochemical biosensor (Cu/PMo₁₂-GR/GCE) was developed based on the combination of copper nanoparticles (CuNPs) and phosphomolybdic acid functionalized graphene (PMo₁₂-GR). PMo₁₂-GR films were modified on the surface of glassy carbon electrode (GCE) through electrostatic self-assembly with the aid of poly diallyl dimethyl ammonium chloride (PDDA). Then CuNPs were successfully decorated onto the PMo₁₂-GR modified GCE through electrodeposition. The morphology of Cu/PMo₁₂-GR/GCE was characterized by scanning electron microscope (SEM). Cyclic voltammetry (CV) and chronoamperometry were used to investigate the electrochemical performances of the biosensor. The results indicated that the modified electrode displayed a synergistic effect of PMo₁₂-GR sheets and CuNPs towards the electro-oxidation of glucose in the alkaline solution. At the optimal detection potential of 0.50 V, the response towards glucose presented a linear response ranging from 0.10 μM to 1.0 mM with a detection limit of 3.0 × 10⁻² μM (S/N = 3). In addition, Cu/PMo₁₂-GR/GCE possessed a high selectivity, good reproducibility, excellent stability and acceptable recovery, which indicating the potential application in clinical field.     

Electrochemical Characterization and Application of Carbon Ionic Liquid Electrodes Containing 1 : 12 Phosphomolybdic Acid

1 : 12 Phosphomolybdic acid (PMo₁₂) and graphite powder were homogeneously dispersed into an n‐octylpyridinum hexafluorophosphate base carbon ionic liquid electrode (CILE). The cyclic voltammograms of the PMo₁₂ modified CILE showed three well‐defined pairs of redox peaks due to the PMo₁₂ system. Formal potentials and electrochemical characteristics including electron transfer rate constant and transfer coefficient were evaluated. Additionally, PMo₁₂ modified CILE exhibited good electrocatalytic activity toward iodate reduction. The kinetic of catalytic reduction of iodate on PMo₁₂ modified CILE was investigated in detail. The modified electrode was used for amperometric determination of iodate in commercial table salt.     

Differential pulse voltammetric determination of P(V) following adsorptive accumulation of alpha-[PMo(12)O(40)](3-) on a polypyrrole-modified glassy carbon electrode

On the basis of the formation and pre-concentration of an α-Keggin-type [PMo₁₂O₄₀]³⁻ complex, a novel voltammetric method was developed for the determination of trace levels of P(V). The α-[PMo₁₂O₄₀]³⁻ complex was formed by heating a 5×10⁻⁴ M Mo(VI)-0.2 M HCl-40% (v/v) CH₃CN system containing a trace amount of P(V) at 70 °C for 30 min. During the electrochemical polymerization of pyrrole in the α-[PMo₁₂O₄₀]³⁻ solution, the α-[PMo₁₂O₄₀]³⁻ complex was accumulated into the polypyrrole film on a glassy carbon electrode. The differential pulse voltammetric peak current due to the α-[PMo₁₂O₄₀]³⁻ complex incorporated in the polypyrrole film was linearly dependent on the P(V) concentration in the range of 5×10⁻⁹-5×10⁻⁷ M; a detection limit of 2×10⁻⁹ M was achieved.     

A novel bacterial cellulose-based carbon paste electrode and its polyoxometalate-modified properties

A novel bacterial cellulose nanofiber-based carbon paste electrode (BCPE) was fabricated. It was characterized by scanning electron microscopy, cyclic voltammetry and electrochemical impedance spectroscopy. Compared with traditional carbon paste electrode, BCPE exhibited better electrochemical reversibility with the enhancement of the redox currents and decrease of peak potential separation as well as lower charge transfer resistance in Fe(CN)₆^3?/4? redox system. Keggin-type sodium phosphopolyoxomolybdate, PMo₁₂, was successfully assembled on BCPE via cyclic voltametric scan, and the obtained PMo₁₂/BCPE possessed not only a good electrochemical behavior but also an excellent electrocatalytic activity toward the reduction of nitrite. Because of its nano-dimension, lower cost and prominent electrochemical properties, bacterial cellulose-based carbonaceous materials would be a candidate of graphite for the preparation of novel carbon paste electrode.     

磷钼酸修饰铂电极的电化学行为及对甲醇氧化的电催化作用

通过循环伏安扫描法制备了PMo₁₂修饰Pt/Pt电极,并研究了该修饰电极在硫酸溶液中的电化学行为。研究结果表明:虽然磷钼酸具有较大的分子尺寸,但在Pt/Pt电极上仍能发生吸附作用,并且由于PMo₁₂在电极上的吸附,降低了Pt/Pt电极上氢区和氧区的荷电量,另外在0.02V左右还观察到磷钼酸的氧化-还原峰。通过稳态极化曲线和循环伏安曲线研究了PMo₁₂修饰Pt/Pt电极对甲醇氧化的电催化作用。测试结果表明:PMo₁₂修饰铂基电极不但对甲醇的电氧化具有较高的活性,而且还有一定的抗CO中毒性。该修饰电极还具有较高的稳定性。     

Electrochemical charging and electrocatalysis at hybrid films of polymer-interconnected polyoxometallate-stabilized carbon submicroparticles

Using the layer-by-layer technique, carbon submicroparticles, that have been modified and stabilized with monolayers of Keggin-type phosphododecamolybdate (PMo₁₂O₄₀³⁻), can be dispersed in multilayer films of organic polymers, poly(3,4-ethylenedioxythiophene), i.e., PEDOT, or poly(diallyldimethylammonium) chloride, i.e., PDDA, deposited on glassy carbon or indium-tin oxide conductive glass electrodes. The approach involves alternate treatments in the colloidal suspension of PMo₁₂O₄₀³⁻-covered carbon submicroparticles in the solution of monomer, 3,4-ethylenedioxythiophene or in solution of PDDA polymer. Electrostatic attractive interactions between anionic phosphomolybdate-modified carbon submicroparticles and cationic polymer layers permit not only uniform and controlled growth of the hybrid organic–inorganic film but also contribute to its overall stability. The system composed of PMo₁₂O₄₀³⁻-covered carbon submicroparticles dispersed in PEDOT is characterized by fast dynamics of charge transport and has been used to construct symmetric microelectrochemical redox capacitor. The PDDA-based system has occurred to be attractive for electrocatalytic reduction of hydrogen peroxide.     

Preparation, characterization, and electrocatalytic properties of hybrid coatings of hexacyanometalate-doped-cationic films

Electrochemically active hybrid coatings based on cationic films, didodecyldimethylammonium bromide (DDAB), and poly(diallyldimethylammonium chloride) (PDDAC) are prepared on electrode surface by cycling the film-covered electrode repetitively in a pH 6.5 solution containing Fe(CN)₆ ³⁻ and Ru(CN)₆ ⁴⁻ anions. Modified electrodes exhibited stable and reversible voltammetric responses corresponding to characteristics of Fe(CN)₆ ^3−/4− and Ru(CN)₆ ^4−/3− redox couples. The cyclic voltammetric features of hybrid coatings resemble that of electron transfer process of surface-confined redox couple. Electrochemical quartz crystal microbalance results show that more amounts of electroactive anionic complexes partitioned into DDAB coating than those doped into PDDAC coating from the same doping solution. Peak potentials of hybrid film-bound redox couples showed a negative shift compared to those at bare electrode and this shift was more pronounced in the case of DDAB. Finally, the advantages of hybrid coatings in electrocatalysis are demonstrated with sulfur oxoanions.     

The Electrochemical Properties of 12-Molybdophosphoric Acid Modified Ionic Liquid Carbon Paste Electrode

A [C₈mim]₃PMo₁₂O₄₀-modified ionic liquid carbon paste electrode ([C₈mim]₃PMo₁₂O₄₀-ILCPE, C₈mim = 1-methyl-3-octylimidazolium) was successfully fabricated. Its electrochemical properties were carried out on the cyclic voltammograms. The results of the cyclic voltammograms indicated that [C₈mim]₃PMo₁₂O₄₀-ILCPE exhibited remarkable electrocatalytic activities toward the reduction of BrO₃ ⁻ and good stability. The value of I_pc was as a function with the concentration of bromate from 2 × 10⁻⁶ to 1 × 10⁻⁴ M, which indicated that the [C₈mim]₃PMo₁₂O₄₀-ILCPE can be a candidate for electrochemical sensor.     

Nanohybridization of CoS2/MoS2 Heterostructure with Polyoxometalate on Functionalized Reduced Graphene Oxide for High-Performance LIBs

To address the poor cycling stability and low rate capability of MoS₂ as electrode materials for lithium-ion batteries (LIBs), herein, the CoS₂/MoS₂/PDDA-rGO/PMo₁₂ nanocomposites are constructed via a simple hydrothermal process, combining the advantages of all three, namely, CoS₂/MoS₂ heterojunction and polyoxometalates (POMs) provide abundant catalytically active sites and increase the multi-electron transfer ability, and the positively charged poly(diallyldimethylammonium chloride) modified reduced graphene oxide (PDDA-rGO) improve electronic conductivity and effectively prevent the aggregation of MoS₂, meanwhile stabilize the negatively charged [PMo₁₂O₄₀]³⁻. After the electrochemical testing, the resulting CoS₂/MoS₂/PDDA-rGO/PMo₁₂ nanocomposite achieved 1055 mA h g⁻¹ initial specific capacities and stabilized at 740 mA h g⁻¹ after 150 cycles at 100 mA g⁻¹ current density. And the specific capacities of MoS₂, MoS₂/PDDA-rGO, CoS₂/MoS₂, and CoS₂/MoS₂/PDDA-rGO were 201, 421, 518, and 589 at 100 mA g⁻¹ after 150 cycles, respectively. The fact of the greatly improving capacity of MoS₂-based nanocomposites suggests its potential for high performance electrode materials of LIBs. Moreover, the lithium storage mechanism of CoS₂/MoS₂/PDDA-rGO/PMo₁₂ has been discussed on the basis of cyclic voltammetry with different scan rates.     

Double-Shelled Hollow SiO2@N-C Nanofiber Boosts the Lithium Storage Performance of [PMo12O40]3−

Polyoxometalates (POMs)-based materials, with high theoretical capacities and abundant reversible multi-electron redox properties, are considered as promising candidates in lithium-ion storage. However, the poor electronic conductivity, low specific surface area and high solubility in the electrolyte limited their practical applications. Herein, a double-shelled hollow PMo₁₂−SiO₂@N−C nanofiber (PMo₁₂−SiO₂@N−C, where PMo₁₂ is [PMo₁₂O₄₀]³⁻, N−C is nitrogen-doped carbon) was fabricated for the first time by combining coaxial electrospinning technique, thermal treatment and electrostatic adsorption. As an anode material for LIBs, the PMo₁₂−SiO₂@N−C delivered an excellent specific capacity of 1641 mA h g⁻¹ after 1000 cycles under 2 A g⁻¹. The excellent electrochemical performance benefited from the unique double-shelled hollow structure of the material, in which the outermost N−C shell cannot only hinder the agglomeration of PMo₁₂, but also improve its electronic conductivity. The SiO₂ inner shell can efficiently avoid the loss of active components. The hollow structure can buffer the volume expansion and accelerate Li⁺ diffusion during lithiation/delithiation process. Moreover, PMo₁₂ can greatly reduce charge-resistance and facilitate electron transfer of the entire composites, as evidenced by the EIS kinetics study and lithium-ion diffusion analysis. This work paves the way for the fabrication of novel POM-based LIBs anode materials with excellent lithium storage performance.     

PMo<Subscript>11</Subscript>V@N-CNT electrochemical properties and its application as electrochemical sensor for determination of acetaminophen

A polyoxometalate-nanocarbon composite, PMo₁₁V@N-CNT, was prepared by a simple procedure which consisted of the immobilization of phosphovanadomolybdate (PMo₁₁V) onto N-doped carbon nanotubes (N-CNT). The FTIR and XPS characterizations confirmed its successful synthesis. The cyclic voltammograms of glassy carbon electrode (GCE) modified with PMo₁₁V and PMo₁₁V@N-CNT showed four Mo-centred redox processes (Mo^VI/V) and a vanadium redox process (V^V/IV). All were surface-confined redox processes. Additionally, PMo₁₁V@N-CNT/GCE showed good stability and well-resolved redox peaks with high current intensities. The electrocatalytic sensing properties of PMo₁₁V@N-CNT/GCE towards acetaminophen (AC) in the presence of tryptophan (TRP) were evaluated by square wave voltammetry. Under the conditions used, the peak current increased linearly with AC concentration in the presence of TRP, with a linear range from 1.5 × 10^?6 to 3.9 × 10^?4 mol dm^?3 and a detection limit of 1.0 × 10^?6 mol dm^?3.     

Electrochemical behavior of α-Keggin-type nanoparticles,Co(en)<Subscript>3</Subscript>(PMo<Subscript>12</Subscript>O<Subscript>40</Subscript>), in polyethylene glycol

The electrochemical behavior of α-Keggin-type nanoparticles, Co(en)₃(PMo₁₂O₄₀) (abbreviated as PMo₁₂-Co), have been studied in poly(ethylene glycol) for four different molecular weights (PEG, average MW 400, 600, 1000, and 2000 g mol^–1) and containing LiClO₄ (O/Li=100/1) supporting electrolyte. The diffusion coefficients of the PMo₁₂-Co nanoparticles were determined using a microelectrode by chronoamperometry for PEG of different molecular weights that were used to describe the diffusion behavior of PMo₁₂-Co nanoparticles in different phase states. Moreover, the conductivity of the composite system increases upon addition of PMo₁₂-Co nanoparticles, which was measured by an a.c. impedance technique. FT-IR spectra and DSC were used to follow the interactions of PEG-LiClO₄-PMo₁₂-Co, and well described the reason that the PMo₁₂-Co nanoparticles could promote the conductivity of the PEG-LiClO₄-PMo₁₂-Co system. Electronic Publication     

12-Molybdophosphoric Acid as an Analytical Reagent for Greater Celandine (Celadonium) Alkaloids

The conditions for determining the total greater celandine alkaloids resulting from a plant by acid infusion were studied. The interaction between the organic cations of alkaloids and the heteropoly anion PMo₁₂O^3- ₄₀ with the formation of a sparingly soluble stable associate of total celandine alkaloids was examined using UV and IR spectroscopy and quantum-chemical calculations. The associate composition (Alk)₃PMo₁₂O₄₀ was found by amperometric titration, and the ionic solubility product was calculated to be equal to (3.0 ± 0.2) × 10^–27 at P = 0.95 and n = 5. The synthesized associate was used as an electrode-active substance in the development of an ion-selective electrode with a plasticized membrane that is reversible and selective for the organic cations of greater celandine alkaloids. Procedures for determining total alkaloids in extracts, infusions, and medicinal forms were developed using potentiometry with ion-selective electrodes and amperometric titration.     

An ionic liquid-type carbon paste electrode and its polyoxometalate-modified properties

The replacement of a non-conductive organic binder with a conductive room temperature ionic liquid in fabricating carbon paste electrode has been made. This new electrode due to its enhanced conductivity presented very large current response from electroactive substrates. The novel carbon paste electrode was bulk-modified via the uniform dispersion of Keggin-type phospho polyoxomolybdate (PMo₁₂) in bulky carbons, which possessed excellent electrocatalytic activity for the reduction of nitrite. The pronounced multi-electron catalytic ability was ascribed to the used hydrophobic ionic liquid which constructed an excellent charge-transfer bridge in the bulk of carbon paste electrode, thus facilitated the intake of electrons from reduced PMo₁₂ mediators. In view of their prominent properties, the carbon paste electrode using ionic liquid binder and its bulk-modified electrode take on good prospects of the application in physical chemistry and electroanalytical chemistry fields.     

Facilitated electron transfer from an electrode to horseradish peroxidase in a biomembrane-like surfactant film

Direct electron transfer was found to be greatly facilitated for horseradish peroxidase (HRP) in a didodecyldimethylammonium bromide (DDAB) biomembrane-like film at a pyrolytic graphite (PG) electrode involving the Fe^III Fe^II couple. The heterogeneous electron transfer rate constant k_s was fitted as 9.0 s⁻¹ using the non-linear regression analysis of the square wave voltammograms at a series of frequencies and pulse heights. The pH dependence of the formal potential for HRP in DDAB film at medium pH environments suggested one-proton transfer coupled with a one-electron transfer reaction. Scanning electron microscopy (SEM) showed different film morphology for HRP and HRP---DDAB films. UV–vis and reflectance absorption infrared (RAIR) spectra inferred that the heme state of HRP in DDAB film was similar to that in its native state. Circular dichroism (CD) results indicated slight perturbation of DDAB on the second structure of HRP. Thus, the embedded HRP in the biomembrane-like DDAB film showed nearly native structural properties and improved electrochemical characteristics. This has potential value for the basic and applied bioelectrochemistry of enzymes.     

Three-Dimensional Carbon Framework Anchored Polyoxometalate as a High-Performance Anode for Lithium-Ion Batteries

Recently, it has become very important to develop cost-effective anode materials for the large-scale use of lithium-ion batteries (LIBs). Polyoxometalates (POMs) have been considered as one of the most promising alternatives for LIB electrodes owing to their reversible multi-electron-transfer capacity. Herein, Keggin-type [PMo₁₂O₄₀]³⁻ (donated as PMo₁₂) clusters are anchored onto a 3D microporous carbon framework derived from ZIF-8 through electrostatic interactions. The PMo₁₂ clusters can be immobilized steadily and uniformly on the carbon framework, which provides enhanced electrical conductivity and high stability. Compared with PMo₁₂ itself, the as-prepared novel 3D Carbon-PMo₁₂ composite displays a significantly improved Li-ion storage performance as an LIB anode, with excellent reversible specific capacity and rate capacity, as well as high cycling performance (discharge capacity of 985 mA h g⁻¹ after 200 cycles), which are superior to other POM-based anode materials reported so far. The high performance of the Carbon-PMo₁₂ composite can be attributed to the 3D conductive network with fast electron transport, high ratio of pseudocapacitive contribution, and evenly distributed PMo₁₂ clusters with reversible 24-electron transfer capacity. This work offers a facile way to explore novel LIB anodes consisting of electroactive molecule clusters.     

pH-dependent assembly of two polyoxometalate-based coordination polymers: structures and electrocatalytic properties

Two new polyoxometalate-based coordination polymers have been synthesized at different pHs under identical hydrothermal conditions, (Hbib)[Cu₂(bib)₂(PMo₁₂O₄₀)] (1) and (Hbib)₂[Cu(bib) (PMo₁₂O₄₀)]·2H₂O (2) (bib = 4-bis(imidazol-1-yl) benzene). Their structures were determined by single crystal X-ray diffraction analyses and characterized by routine methods. When the pH was adjusted to 2.0???2.5, 1 was obtained, which exhibits a 1-D rail-like chain. Compound 2 was obtained at pH of 2.5???3.2 and exhibits a 2-D layer with (4⁴) sql net. The pH of the reaction plays a key role in the assembly of the polyoxometalate-based coordination polymer. The electrochemical experiments indicate that 2-based carbon paste electrode possesses high catalytic efficiency and high stability towards reduction of iodate and oxidation of ascorbic acid.     

Characterization and Electrocatalytic Properties of Composite Poly(new fuchsin) and Phosphomolybdate Films

Organic/inorganic hybrid films of poly(new fuchsin) and phosphomolybdate (PMo₁₂O ) have been prepared in acidic aqueous solutions. These new combination films are stable, electrochemically active, and can be produced on glassy carbon, platinum, gold, and transparent semiconductor tin oxide electrodes. An electrochemical quartz crystal microbalance along with cyclic voltammetry and UV‐visible absorption spectroscopy were used to study the in situ growth of the hybrid films. The hybrid poly(new fuchsin) and PMo₁₂O films showed four obvious redox couples, and when transferred to various acidic aqueous solutions, the formal potentials of the four redox couples were found to be pH dependent. The electrocatalytic reduction of ClO , BrO , IO , SO , S₂O , H₂O₂, and NO by the hybrid poly(new fuchsin) and PMo₁₂O films was achieved in acidic aqueous solutions. In an aqueous solution at pH 1.5, a hybrid poly(new fuchsin) and PMo₁₂O film showed a higher electrocatalytic reduction activity of IO than BrO or ClO , and the order of electrocatalytic activity was IO >BrO >ClO . The order of electrocatalytic reduction of SO , S₂O , H₂O₂, and NO by hybrid poly(new fuchsin) and PMo₁₂O films in an aqueous solution at pH 1.5 was NO >H₂O₂>S₂O and SO . The electrocatalytic reactions of the poly(new fuchsin) and PMo₁₂O films were investigated using the rotating ring‐disk electrode method.