堀越 智

This study addresses challenges in recycling electronic waste (e-waste) by developing a self-degrading electrical wire coating material using graphitic carbon nitride (g-C3N4). Two types, melamine-derived carbon nitride (MCN) and urea-derived carbon nitride (UCN), were synthesized and evaluated for their photocatalytic activity by measuring the decolorization rate of rhodamine-B (RhB). UCN demonstrated superior photocatalytic performance compared to the widely used TiO2. When incorporated into PVC film, UCN achieved a maximum weight loss of 68% in photodegradation tests after 40 days of irradiation, contributing to reduced environmental impact. A UCN-mixed coating for a vinyl-insulated cable prototype showed that photodecomposition in water facilitated copper wire separation. The study also indicated that water is vital for the decomposition process, while UCN enhanced stiffness and tensile strength of the material without compromising elongation and electrical insulation properties.

Although positive effects of microwave irradiation on plants have been reported, their underlying mechanisms remain unknown. In this study, we investigated the effects of low microwave irradiation on Arabidopsis thaliana. Interestingly, we found low output (23 W) with oscillating condition (not continuous irradiation) promoted plant growth. The microwave irradiation neither raised the plants' temperature nor induced heat responsive gene expression. Furthermore, overall transcriptome profile in microwave irradiation treated plants were significantly different from heat treated plants, suggesting that growth promotion might be attributed to non-thermal effects of microwave. Transcriptome and metabolome analysis indicated that microwave irradiation altered circadian clock as well as hormonal response especially in auxin and gibberellin, which promoted plant growth by inducing amino acid biosynthesis and stress tolerance, and reducing cell wall thickness. This finding potentially contributes to develop new approach to increase food production through accelerating crop yield in environmentally friendly way.

In a ground-breaking recent study, we unveiled the remarkable cellular uptake of 60 nm ZnO and TiO2 nanoparticles by NIH/3T3 mouse skin fibroblasts under microwave irradiation. Even more stimulating is our current demonstration of the potent ability of Ag nanoparticles (147 nm) and Au nanoparticles (120 nm) to stifle the growth of Escherichia coli (E. coli-a prokaryote whose cells lack a membrane-bound nucleus and other membrane-bound organelles), vastly smaller than the NIH/3T3 cells, when exposed to significantly optimized low-power microwave irradiation conditions. Our rigorous assessment of the method's effectiveness involved scrutinizing the growth rate of E. coli bacteria under diverse conditions involving silver and gold nanoparticles. This indisputably underscores the potential of microwave-nanoparticle interactions in impeding bacterial proliferation. Furthermore, our noteworthy findings on the uptake of fluorescent organosilica nanoparticles by E. coli cells following brief, repeated microwave irradiation highlight the bacteria's remarkable ability to assimilate extraneous substances.

This study investigated the impact of a 10 kHz amplitude-modulation (AM) wave from a semiconductor microwave generator on the heating of ultrapure water and electrolyte aqueous solutions containing NaCl. It also examined the effects of AM waves on the yields of 4-methylbiphenyl (4-MBP) in the heterogeneous Suzuki-Miyaura coupling reaction, which was conducted in the presence of palladium nanoparticles supported on activated carbon (Pd/AC), as well as their influence on the growth rate during silver nanoparticle synthesis. Applying AM waves, typically used in telecommunications, enhanced heating efficiencies and improved product yields in both the chemical reaction and nanoparticle growth. Irradiating with microwaves under AM conditions allowed it to reduce power output while still achieving target yields and growth rates, even at the same temperatures without AM. This indicates the potential for highly efficient and energy-saving microwave processes in chemical reactions and material synthesis.

This study utilized a microwave-induced in-liquid plasma (MILP) device to treat water contaminated with microplastics (MPs) and metal ions. The performance of the device was initially assessed using a rhodamine-B (RhB) aqueous dye solution in a circulation-type reactor, yielding a greater degradation efficiency compared to conventional batch treatments. Polyethylene (PE) particles (diameter, 20 μm; average molecular weight, 1.8 million) served as a model for MPs to evaluate their disposal and degradation under continuous circulation treatment. A plasma-induced polymer gel synthesis method was employed to remove metal ions, achieving over 80% removal of copper, tin, lead, and mercury within 5 minutes. These findings highlight the significant potential of MILP technology for innovative advanced water treatment applications.

Recycling e-wastes using a VVF power cable through a rapid pyrolytic mechanism by microwave radiation is reported, and it is possible to produce copper wire and carbon resources without going through highly toxic intermediates.

Abstract Variable Frequency Microwave (VFM) radiation provides a solution to the inhomogeneity of the electric field in the cavity, which has long led to a decline in the reliability of microwave chemical data and its industrial utilization. Herein, we report in-situ three-dimensional experimental measurements of the electric field’s uniform distribution of VFMs within a multimode cavity under high power conditions, and their subsequent comparison to Fixed Frequency Microwaves (FFM) that could only be assessed earlier through theoretical analysis. We also examine the consequences of changes in VFM irradiation conditions and elucidate the threshold at which VFM irradiation might prove beneficial in syntheses. With an ultimate focus on the use of VFM microwave radiation toward industrial applications, we carried out an effective synthesis of 4-methylbyphenyl (4-MBP) in the presence of palladium (the catalyst) supported on activated carbon particulates (Pd/AC), and revisited two principal objectives: (a) the effective suppression of discharge phenomena (formation of hot spots), and (b) synthesis scale-up using a 5-fold increase in sample quantity and a 7.5-fold larger reactor size (diameter) than otherwise used in earlier studies.

Abstract The microwave vulcanization of tire rubber was investigated by monitoring the dielectric properties of the rubber polymer and other components of the formulation (including carbon filler, antioxidant, and vulcanization agents) as functions of frequency and temperature. The effect of the vulcanization reaction on the dielectric properties during heating was also assessed. The physical interaction between the crosslinked structure and the carbon black significantly favors the responsiveness to microwaves during the vulcanization reaction. Based on these basic data, microwave irradiation conditions were determined, and model tire samples were microwave vulcanized in a PTFE mold. It has achieved a shorter time of heating and 65% energy saving, but on the other hand, it has become clear that the vulcanization produces very poor physical quality compared to vulcanization by electric furnace heating. To solve this problem, we performed microwave irradiation using variable frequency microwave (VFM; 5.85 ~ 6.65 GHz) using glass fiber on polyetherketoneketone (PEEK/GF) mold. In VFM, compared to conventional fixed frequency microwave (FFM), successfully synthesized high‐quality tire rubber because it showed 4.2, 1.1, 2.0, 1.2, and 1.8 times higher values in terms of cross‐linking density value, hardness value, tensile strength, elongation at break, and 200% modulus, respectively.

<p>The discovery of a water-soluble polymer that cross-links to form a gel using a novel green gelation method: the microwave-induced in-liquid-plasma method that requires neither a cross-linking agent nor an initiator as are required in the conventional chemical method.</p>

This study used controlled microwaves to elucidate the response of adhesive components to microwaves and examined the advantages of microwave radiation in curing epoxy adhesives. Curing of adhesives with microwaves proceeded very rapidly, even though each component of the adhesive was not efficiently heated by the microwaves. The reason the adhesive cured rapidly is that microwave heating was enhanced by the electrically charged (ionic) intermediates produced by the curing reaction. In contrast, the cured adhesive displayed lower microwave absorption and lower heating efficiency, suggesting that the cured adhesive stopped heating even if it continued to be exposed to microwaves. This is a definite advantage in the curing of adhesives with microwaves, as, for example, adhesives dropped onto polystyrene could be cured using microwave heating without degrading the polystyrene base substrate.

The heptyl butanoate ester was synthesized from butanoic acid and heptanol in a heterogeneous medium in the presence of sulfonated activated carbon (AC-SO3H) catalyst particles subjected to microwave irradiation, which led to higher conversion yields (greater product yields) than conventional heating with an oil bath. The advantage of the microwaves appeared only when the moisture content in the butanoic acid batch(es) was high, suggesting that, unlike conventional heating, the reverse reaction caused by the moisture content and/or by the byproduct water was suppressed by the microwaves. This contrasted with the results that were found when carrying out the reaction in a homogeneous medium in the presence of the 2,4,6-trimethylpyridinium-p-toluene sulfonate (TMP-PTS) catalyst, as product yields were not improved by microwave heating relative to conventional heating. The removal of moisture/water content in the reaction solution was more pronounced when the reactor was cooled, as the reaction yields were enhanced via selective heating of the heterogeneous catalyst. A coupled electromagnetic field/heat transfer analysis gave credence to the selective heating of the AC-SO3H catalyst, which was further enhanced by cooling the reactor. It was deduced that unforeseen impurities and local high-temperature fields generated on the surface of small fine catalyst particles may have had an effect on the microwave chemistry such that the associated phenomena could be mistaken as originating from a nonthermal effect of the microwaves. Accordingly, it is highly recommended that impurities and selective heating be taken into consideration when examining and concluding the occurrence of a microwave nonthermal effect.

We report on the low-temperature steam reforming and water–gas shift processes to generate H₂ efficiently from water passed through MW-heated activated carbon (AC) particles, contrary to the inefficient conventional steam reforming at T ≈ 600 °C.

The application and advantages of variable frequency microwaves (VFM; range, 5.85–6.65 GHz) are reported for the first time in microwave chemistry, particularly when carrying out reactions catalyzed by metallic conductive catalysts so as to avoid the formation of arc discharges, and especially when using a strong microwave absorber such as activated carbon (AC) particulates as supports of metal-based catalysts. Two model reactions performed in low boiling point nonpolar solvents are described wherein arc discharges easily occur under the more conventional fixed frequency microwave (FFM) approach: (i) the synthesis of 4-methylbiphenyl (4MBP) by the Suzuki-Miyaura cross-coupling process catalyzed by Pd particles supported on AC particulates (Pd/AC), and (ii) the synthesis of toluene via the dehydrogenation of methylcyclohexane (MCH) catalyzed by Pt particles dispersed on AC particulates (Pt/AC). Contrary to the usage of fixed frequency microwaves (5.85 GHz and 6.65 GHz), the use of VFM microwaves increased the chemical yields of 4MBP {49% versus 5–8% after 60 min} and toluene {89% versus 24% after 10 min} by suppressing the formation of discharges that otherwise occur on the catalyst/AC surface with FFM microwaves. Consequently, relative to the latter approach, the VFM technology is significantly advantageous, especially in reactions with solid conductive catalysts, not least of which are the reduction in power consumption, thus energy savings, and the prevention of potential mishaps.