Continuous syntheses of carbon-supported Pd and Pd@Pt core–shell nanoparticles were performed by microwave-assisted flow reactor with frequency synchronized microwave (Symwave) devices. Pd nanoparticles were homogeneously dispersed on the carbon support, and the particle size became larger as the Pd concentration increased. Carbon-supported Pd nanoparticles synthesized by the 915 MHz apparatus suitable for mass production showed the same particle size as those synthesized by the2.45 GHz apparatus. The synthesis of core Pd nanoparticle followed by direct coating of Pt shell was performed, and the core-shell structure was confirmed by TEM-EDS elemental mapping. It was concluded that the homogeneous Pt shell was formed by the evaluation of durability.

View full abstract

Palladium-catalyzed direct C-H arylation polycondensation of 3,4-ethylenedioxythiophene with2,7-dibromo-9,9-dioctylfluorene was carried out under oil bath heating and microwave heating conditions. The polycondensation [Conditions: Pd(OAc)₂ , PivOH, K₂CO₃, DMAc (0.3 M), 1 h] at various temperatures (80-120 o C) gave analternating copolymer, poly(3,4-ethylene-dioxythiophene-alt-9,9-dioctylfluorene-2,7-diyl). Although the microwave heating was effective for the polymer synthesis, we found that the polymerization efficiency depended on the apparatus used. Namely,the molecular weights (the values of M_w and M_n) of resulting polymer from 3,4-ethylenedioxythiophene and2,7-dibromo-9,9-dioctylfluorene were different when the polycondensation was performed at 80-120 o C by CEM (Discover) or Anton Paar (Monowave).

View full abstract

Microwave application technologies such as microwave heating, microwave assisted chemistry, etc. are of the innovative green technologies. In the field of microwave engineering, a waveguide whose sidewalls are replaced with densely arranged metallic posts has been proposed. This guide, called the post-wall waveguide, can easily realize the circuit patterns by arranging metallic posts periodically in a parallel-plate waveguide or a grounded dielectric substrate. In this paper, 5.8 GHz and 2.45 GHz microwave applicators of medium size are proposed based on the post-wall waveguide structure. The 5.8 GHz applicator is allowed to irradiate microwaves to solvent of several milliliters and to flow the heated solvent out continuously. The validity of the 5.8 GHz applicator is examined numerically and experimentally with microwave power sources of about 5 W. Furthermore,the designing of a 2.45 GHz microwave applicator using the same structure is shown.

View full abstract

For theoretical understanding of the microwave and radio frequency heating of water and for comparison to dielectric loss under microwave and radio-frequency irradiation, computational molecular modeling of water hydrogen-bonding aggregates, (H₂O)_3～6 is carried out on the basis of density-functional theory (DFT) using the B3LYP exchange-correlation functional and the 6–31G(d) basis set with Spartan 16 (Wave function, Inc. Irvine,CA) (DFT-based molecular modeling, DFT/MM). The DFT/MM-based IR/FIR spectrum of the water aggregates verifies that all aggregates absorb and dissipate of wide ranges of electromagnetic wave energy, i.e.,giving not only infrared (IR, 4000-500 cm^-1 ) but also far infrared (FIR, 500-0cm^-1) spectra. Absorption peaks inIR can recognize bond vibration, and absorption peaks in FIR recognize intermolecular vibration of aggregated molecules. On the basis of intermolecular vibration of absorption and dissipation spectra at FIR (0～500 cm^-1),which correspond to radio frequency of KHz and MHz, GHz(MW), THz(IR) region, and bond-stretching vibration spectra at IR (500～4000 cm^-1 ), we propose here that the radio and MW frequency heating may be explained as due to thermo-upconversion mechanism, i.e., final thermal dissipation at IR absorption at O-H stretching (3500～3000 cm^-1) caused by up-conversion of radio frequency energy absorbed by (H₂O)_3～6

View full abstract

Carbon felt (CF) is a carbon material composed of graphite fibers with random orientation and heated mainly by conductive heating when subjected to microwave irradiation. Recently, it was found that when two pieces of carbon felts arranged in parallel with a predetermined distance were irradiated with microwave, thermal electrons and thermal radiation were emitted from their surfaces facing with each other and the temperature at the gap between them increased rapidly to reach the thermal equilibrium temperature over 1000 o C. Furthermore, the thermal state was developed to a plasma which we referred to as the carbon felt atmospheric pressure microwave plasma (CF-AMP)when the thermal electrons were sufficiently accelerated to ionize atoms and molecules through collisions under the induced alternative high voltage between carbon felts. In this paper, the spectroscopic observations revealed that the CF-AMP is a non-equilibrium plasma and the properties and some applications of CF-AMP were introduced.

View full abstract