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This article examines the use of molybdenum and tungsten-based polyoxometalates (POMs) for removing methylene blue dye from water. POMs have become popular for water treatment due to their unique properties. The study evaluates the efficiency of two POMs compounds, SiW12 and Mo8, for removing methylene blue. Various factors such as contact time, adsorbent dose, initial dye concentration, pH, and temperature were considered. The results show that both POMs have high adsorption efficiency for methylene blue removal. Additionally, the article discusses the characterization of POMs using FTIR spectroscopy and explores the effects of different parameters on the removal efficiency of methylene blue dye. [Extracted from the article]

A series of (Cu0.5Tl0.5)Ba2Ca2Cu3O10-δ superconducting samples impregnated with different percentage additions of potassium salt {CoSiW11}x nanoparticles (x = 0.00, 0.01, 0.02, 0.04, 0.06, 0.08 and 0.12 wt.%) were prepared using a single-step solid-state reaction technique at ambient pressure. These samples were characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX) to study their structures, construction of the synthesized samples and elemental composition, respectively. XRD studies indicate that the tetragonal structure of (Cu0.5Tl0.5)-1223 phase has not changed by the addition of {CoSiW11} nanoparticles the same as for the values of lattice parameters a and c, where they show a non-remarkable change. The relative volume fraction of (CuTl)-1223 phase record a maximum value for x = 0.02 wt.%. The formation of (CuTl)-1223 phase matches the presence of rectangular-shaped plates seen in SEM images. The enhancement of these plates after the addition of {CoSiW11} nanoparticles up to x = 0.02 wt.% agreed with the measurements of relative volume fraction. The mass percentage of all elements was measured using the EDX technique, which shows the distribution composition of both superconductor and nanoparticle compounds. Vibrational mode analyses of oxygen were accomplished via Fourier transform infrared (FTIR) spectroscopy in (CuTl)-1223 phase impregnated with {CoSiW11} nanoparticles. The Oδ oxygen modes observed are almost unaltered while the other oxygen modes of planar CuO2 are slightly softened and hardened. Superconducting transition temperature (Tc) and critical current density (Jc) were determined from the electrical resistivity and I–V measurements, respectively. The results indicate an increase in the Tc values from 125 K for the pure sample to 132 K for x = 0.02 wt.% impregnated samples, while a decrease in the Jc values is observed upon increasing ‘x’ value from x = 0.00 up to 0.12 wt.%. The suppression of these electrical superconducting parameters for x > 0.02 wt.% may be due to an increase of weak links' connectivity among the grain boundaries and growth of impurity phases that affect the formation of (CuTl)-1223 superconductor phase. The fluctuation-induced conductivity (FIC) analysis has been done in the light of the Aslamasov–Larkin (AL) theory to study the fluctuation conductivity Δσ above Tc as a function of reduced temperature for (CoSiW11)x/(CuTl)-1223 superconductor. The results show four non-identical fluctuation regions that are short-wave (Sw), two-dimensional (2D), three-dimensional (3D) and critical (Cr). The zero-temperature coherence length ( ξ c (0) ), the effective layer thickness of the two-dimensional system (d), inter-layer coupling (I), Fermi velocity (vF) and Fermi energy (EF) were evaluated as a function of ‘x’ addition from FIC analysis of the samples and then correlated to the superconductivity order parameters. The superconducting parameters were increased upon the addition of {CoSiW11} nanoparticles. [ABSTRACT FROM AUTHOR]

Interaction of the mixed-valent 12-manganese coordination complex [MnIII 8Mn IV 4O12(CH3COO)16(H2O)4] with the lacunary 9-tungstoarsenate(V) [A-⎹-AsW9O34]9- resulted in the 10-manganese(III/IV)-containing 36-tungsto-4-arsenate(V), [MnIII 6MnIV 4O4(OH)12(H2O)12(A-α-AsW9O34)4]22- (1).Polyanion 1 was isolated as a hydrated mixed potassium-sodium salt, K14Na8[MnIII 6- MnIV 4O4(OH)12(H2O)12(A-β-AsW9O34)4]104H2O, which crystallizes in the orthorhombic space group Pbcn and was characterized by FT-IR spectroscopy and single-crystal X-ray diffraction, as well as elemental and thermogravimetric analyses. The title polyanion contains a unique [MnIII 6MnIV 4O4(OH)12- (H2O)12]14+ core stabilized within the 36-tungsto-4-arsenate(V) framework. [ABSTRACT FROM AUTHOR]

Interaction of the mixed-valent 12-manganese coordination complex [MnIII 8Mn IV 4O12(CH3COO)16(H2O)4] with the lacunary 9-tungstoarsenate(V) [A-⎹-AsW9O34]9- resulted in the 10-manganese(III/IV)-containing 36-tungsto-4-arsenate(V), [MnIII 6MnIV 4O4(OH)12(H2O)12(A-α-AsW9O34)4]22- (1).Polyanion 1 was isolated as a hydrated mixed potassium-sodium salt, K14Na8[MnIII 6- MnIV 4O4(OH)12(H2O)12(A-β-AsW9O34)4]104H2O, which crystallizes in the orthorhombic space group Pbcn and was characterized by FT-IR spectroscopy and single-crystal X-ray diffraction, as well as elemental and thermogravimetric analyses. The title polyanion contains a unique [MnIII 6MnIV 4O4(OH)12- (H2O)12]14+ core stabilized within the 36-tungsto-4-arsenate(V) framework. [ABSTRACT FROM AUTHOR]

Polyoxometalates (POMs) have been reported as promising electrode materials for energy storage applications due to their ability to undergo fast redox reactions with multiple transferred electrons per polyanion. Here we employ a polyoxovanadate salt, Na6[V10O28], as an electrode material in a lithium-ion containing electrolyte and investigate the electron transfer properties of Na6[V10O28] on long and short timescales. Looking at equilibrated systems, in situ V K-edge X-ray absorption near edge structure (XANES) studies show that all 10 V5+ ions in Na6[V10O28] can be reversibly reduced to V4+ in a potential range of 4–1.75 V vs. Li/Li+. Focusing on the dynamic response of the electrode to potential pulses, the kinetics of Na6[V10O28] electrodes and the dependence of the fundamental electron transfer rate k0 on temperature are investigated. From these measurements we calculate the reorganization energy and compare it with theoretical predictions. The experimentally determined reorganization energy of λ = 184 meV is in line with the theoretical estimate and confirms the hypothesis of small values of λ for POMs due to electrostatic shielding of the redox center from the solvent. [ABSTRACT FROM AUTHOR]