Ryuichi Hayashi

Experimental and theoretical study of acetic-acid decomposition by a pulsed dielectric-barrier plasma in a gas–liquid two-phase flow

Decomposition of acetic acid as a persistent material in water was demonstrated using a pulsed dielectric-barrier plasma in a gas–liquid two-phase flow. The plasma was driven by 35 kV, 200 Hz pulsed voltages and generated in oxygen bubbles in 20 ml solution having a concentration of 10–40 mgTOC l−1. The concentrations of ion species and hydrogen peroxide in the solution were analyzed by ion chromatography and absorptiometry, respectively. After 60 min of operation, the acetic acid was completely decomposed by the plasma. Optical measurements of the emission intensities of OH, H and O radicals suggest that the generated OH radicals are in the ground state in this study. A numerical calculation was carried out to analyze the radical generation processes in the gas phase and decomposition in the liquid phase. O-radical-induced generation of OH radical needed to be considered in the calculation of total organic carbon (TOC) and H2O2 concentrations in the solution. By considering such plasma–water interaction processes, data for the decomposition of acetic acid, which were in good agreement with experimental results, were obtained.

An energy-efficient process for decomposing perfluorooctanoic and perfluorooctane sulfonic acids using dc plasmas generated within gas bubbles

Perfluorooctanoic acid (PFOA) and perfluorooctane sulfonic acid (PFOS) are environmentally harmful and persistent substances. Their decomposition was investigated using dc plasmas generated within small gas bubbles in a solution. The plasma characteristics including discharge voltage, voltage drop in the liquid, plasma shape and the emission spectrum were examined with different gases. The decomposition rate and energy efficiency were evaluated by measuring the concentration of fluoride and sulfate ions released from PFOA/PFOS molecules. The concentration of fluoride ions and energy efficiency in the treatment of a PFOS solution were 17.7 mg l−1 (54.8% of the initial amount of fluorine atoms) and 26 mg kWh−1, respectively, after 240 min of operation. The addition of scavengers of hydroxyl radicals and hydrated electrons showed little effect on the decomposition. The decomposition processes were analyzed with an assumption that positive species reacted with PFOA/PFOS molecules at the boundary of the plasma–solution surface. This type of plasma showed a much higher decomposition energy efficiency compared with energy efficiencies reported in other studies.

Pressure effects on the twisted intramolecular charge transfer (TICT) phenomenon

Abstract Pressure effects on the twisted intramolecular charge transfer (TICT) phenomenon of 4-(N,N-dimethylamino)benzoate bonded to a polymer side chain (copDB) and its low molecular weight model compound (DBAE) were examined in ethyl acetate. The volume change and the activation volume for the formation of the TICT state were determined to be 2.9 cm 3 mol (DBAE) and 5.5 cm 3 mol (copDB), respectively. Although the present results for copDB are reasonably explicable as the viscosity effect on the TICT state formation, the effect could not be described by the normal Stokes-Einstein theory but required the Gierer-Wirtz theory.

EXCIPLEX BY PYRENE‐N,N‐DIMETHYLANILINE PAIR BONDED TO POLYMERS IN AQUEOUS MEDIA

Abstract— Emission spectra of poly[2‐(4‐N,N‐dimethylaminobenzyl)‐2‐(l‐pyrenylmethyl)ethyl methacryl‐ate] (I) and the copolymers with vinyl‐benzyltriethylammonium chloride (II) or sodium p‐styrenesulfo‐nate (III) were studied in extremely polar media such as dimethylformamide (DMF) and water. While the emission by the monomer model compound (2‐(4‐N,N‐dimethylaminobenzyl)‐2‐(l‐pyrenylmethyl)‐ethyl isobutyrate(IV)) scarcely showed exciplex emission in DMF or aqueous DMF, exciplex by I was clearly observed in the same solvents. Furthermore, the ratio of exciplex intensity (Fe) to monomer intensity (Fm) increased by the addition of water to the DMF solution up to 60 vol%. This abnormal spectral behavior of increasing exciplex emission intensity with solvent polarity was interpreted as being due to shrinking of polymer chain. The peaking wavelength of exciplex shifted towards blue in the presence of water, indicating that the solvation of exciplex was hindered and/or the hydrophobic domain was organized. This interpretation was supported by the exciplex emission of II in water. No exciplex was detected from III in water. This is the first example of exciplex emission in homogeneous aqueous solution. In comparison with the published results of micellar systems, the exciplex emission of the polycation indicated that the hydrophobic domain in the polycation was so strong that the solvation of exciplex was considerably hindered. The peaking wavelength of exciplex at 480 nm also lends support to the presence of a non‐polar microenvironment.

Decomposition of perfluorooctane sulfonate in water using atmospheric plasma

Perfluorooctane sulfonate (PFOS) is widely used for industrial and commercial products due to its chemical stability and physical characteristics. Biopersistance and unexpected toxicity however, have raised environmental concerns. In this study, PFOS in water was decomposed using direct plasma methods such as DC plasma generated within oxygen bubbles in water and barrier discharge plasma generated on water surface.