Microwave-Assisted Preparation and Characterization of a Polyoxometalate-Based Inorganic 2D Framework Anode for Enhancing Lithium-Ion Battery Performance

A new route to polyoxometalates via mechanochemistry

Mechanochemistry offers a new route to polyoxometalates (POMs) under mild conditions. The molybdenum isoPOM heptamolybdate and the molybdenum heteroPOMs of the Strandberg- and Keggin-type could be achieved from grinding together molybdenum oxide, potassium or ammonium carbonate and phosphate. The reactions were controlled by the stoichiometric ratio of the starting materials and the liquid used, with reaction times between 30 min and 3 h. In situ investigations of the syntheses reveal the formation of intermediates during the reactions. Their identification helps explaining the mechanism of formation of the intermediates as well as the final POMs.

Under mild conditions, molybdenum POMs could be achieved mechanochemically from simple building blocks, within short reaction times. In situ investigations reveal the formation of intermediates and help explaining the mechanism behind the reaction.

Efficient visible-light-driven reduction of hexavalent chromium catalyzed by conjugated organic species modified hourglass-type phosphomolybdate hybrids

Four conjugated-organic-species modified hourglass-type phosphomolybdate hybrids with a 0-D + 1-D → 3-D supramolecular structure exhibited favorable photocatalytic activity and stability towards Cr(vi) reduction.

Microwave-Assisted Synthesis of Tris-Anderson Polyoxometalates for Facile CO2 Cycloaddition

Four new tris-Anderson polyoxometalates (POMs), (NH₄)₄[ZnMo₆O₁₈(C₄H₈NO₃)(OH)₃]·4H₂O (1), (NH₄)₄[CuMo₆O₁₈(C₄H₈NO₃)(OH)₃]·4H₂O (2), (TBA)₃(NH₄)[ZnMo₆O₁₇(C₅H₉O₃)₂(OH)]·10H₂O (3) (TBA = n-C₁₆H₃₆N), and (NH₄)₄[CuMo₆O₁₈(C₅H₉O₃)₂]·16H₂O (4), were synthesized by a microwave-assisted method. Single-crystal X-ray diffraction revealed that 1 and 2 contained a tris (trihydroxyl organic compounds) ligand grafted on one side, while two tris ligands were grafted on two sides to form χ/δ and δ/δ isomers in 3 and 4, respectively. ¹H and ¹³C NMR spectra of the χ/δ isomer 3 were obtained for the first time, with six methylenes showing six peaks in the ¹H NMR spectrum and only four peaks in the ¹³C NMR spectrum. Mass spectrometry monitoring revealed that during the microwave-assistant process the tris ligand can graft onto POMs to form 1, while tris directly coordinates with metallic heteroatoms to form isopolymolybdates during the conventional reflux synthesis process. In addition, 1-4 can catalyze CO₂ with epoxides into cyclic carbonates with high selectivity and yields at an atmospheric pressure of CO₂, which is lower than the pressure of CO₂ in other catalysis using POMs as catalysts. Furthermore, 1-4 showed good catalytic stability and cycling properties. Mechanism studies substantiated POMs cocatalyzed with Br^- to improve the catalytic yields.

Electromagnetic pollution alert: Microwave radiation and absorption in human organs and tissues

Electromagnetic radiation from communication and electronic devices, networks, systems and base stations has drawn concern due to excessive global usage with increasing power and operating frequency level. Numerous previous researches only focus on how the radiation from certain frequency ranges of particular devices could harm specific human organs and tissues, resulting in distinct symptoms. In this research, electromagnetic propagation and properties in 14 human organs and tissues were analyzed and investigated based on the organs and tissues' electromagnetic and mechanical parameters, and chemical composition. Counting the organs and tissues as electromagnetic materials, their permittivity and conductivity, computed by a 4-Cole-Cole mode, directly respective to the operating frequency, are interrelated to wave behavior and hence influence the organs' response. Tests were conducted in 1 GHz to 105 GHz system settings, covering most microwave frequency uses: 2.4 GHz of 4G-LTE, Wi-Fi, Bluetooth, ZigBee and the 5G ranges: 28 GHz of 5G-mmW and 95 GHz of 5G-IoT. Trial human organs and tissues were placed in the wave propagation direction of 2.4 GHz and 28 GHz dipole antennas, and a waveguide port operating from 95 to 105 GHz. The quantitative data on the effects of 5G penetration and dissipation within human tissues are presented. The absorbance in all organs and tissues is significantly higher as frequency increases. As the wave enters the organ-tissue model, the wavelength is shortened due to the high organ-tissue permittivity. Skin-Bone-Brain layer simulation results demonstrate that both electric and magnetic fields vanish before passing the brain layer at all three focal frequencies of 2.4 GHz, 28 GHz and 100 GHz.

Self-assembly and Li-ion storage performance of three new Nb/W mixed-addendum polyoxometalates based on the {SiNb3W9O40} clusters and transition-metal cations

Three polyoxometalates have been synthesized to be utilized as anode materials for lithium ion batteries.

Ln(iii)-Containing polyoxomolybdates based on β-{Mo8O28}: microwave synthesis and optical and magnetic properties

The reactant mother liquor can be obtained by 600 watt microwave irradiation for 15 minutes. Under ultraviolet irradiation, these two compounds can undergo the photochromic process, and the fading process can occur after the ultraviolet irradiation was turned off.

Proton-Enhanced Dielectric Properties of Polyoxometalates in Water under Radio-Frequency Electromagnetic Waves

Electromagnetic waves, such as microwaves, have been used to enhance various chemical reactions over polyoxometalates. The dielectric properties of catalysts are among the relevant parameters facilitating catalytic reactions under electromagnetic radiation. This study describes the dielectric properties of polyoxometalate catalysts in aqueous and organic solutions to understand the mechanism of interactions between polyoxometalates and electromagnetic waves. Specific loss factors of polyoxometalates were observed at lower frequencies (<1 GHz) by the ionic conduction of the polyoxometalate solution. The evolution of ionic conduction depended strongly on cations rather than anions. Proton-type polyoxometalates exhibited significantly higher loss factors than other cations did. The activation energy for ionic conduction in protonated silicotungstic acid (H₄SiW₁₂O₄₀) was significantly low in water (7.6–14.1 kJ/mol); therefore, the high loss factor of protonated polyoxometalates in water was attributed to the proton relay mechanism (i.e., Grotthuss mechanism). The results suggested that the proton relay mechanism at the radio-frequency band is critical for generating selective interactions of polyoxometalates with applied electromagnetic fields.