Nozomi Takeuchi - Academia.edu (original) (raw)

Papers by Nozomi Takeuchi

IEEE Transactions on Plasma Science, Dec 1, 2007

Japanese Journal of Applied Physics, Oct 16, 2020

The transactions of the Institute of Electrical Engineers of Japan.A, 2012

The transactions of the Institute of Electrical Engineers of Japan.A, 2007

Japanese Journal of Applied Physics, May 4, 2023

As a plasma-based method, diaphragm discharge plasma, an underwater discharge, exhibits a relativ... more As a plasma-based method, diaphragm discharge plasma, an underwater discharge, exhibits a relatively high production rate and efficiency of hydrogen peroxide (H2O2). This study aimed to characterize the energetic state of plasma and the H2O2 production mechanism by optical emission spectroscopy, evaluating the excitation temperature, gas temperature, electron density, and their temporal variations. The excitation temperature was approximately 3000 K, which was also presumed to almost coincide with the electron temperature in the plasma. The gas temperature was approximately 2500 K, and the electron density was approximately 6 × 1022 m−3 at maximum. The electron density sustained higher values under the condition of better H2O2 production performance, whereas the other two parameters exhibited almost no difference and variation. The reaction rate calculation based on the observation results indicated that the thermal dissociation of H2O is a more crucial reaction path for H2O2 production in our plasma than expected.

The transactions of the Institute of Electrical Engineers of Japan.A, 2018

ABSTRACT form only given. Perfluorooctane sulfonic acid (PFOS) can be decomposed efficiently by p... more ABSTRACT form only given. Perfluorooctane sulfonic acid (PFOS) can be decomposed efficiently by plasmas generated in gas bubbles. However, mass balance during the degradation of PFOS is not fully understood. Mass balance is quite important for commercial applications. Thus, the purpose of this study is to clarify the value of the mass balances of fluorine, carbon, and sulfur, and to understand the degradation process of PFOS. PFOS in water was decomposed by dc plasma generated in argon gas bubbles. The reactor was made of acrylic. A ceramics plate, which was 0.3 mm in thickness and had a micro hole of 0.3 mm diameter at the center, was attached on the bottom of the reactor. Argon gas was supplied through the hole to PFOS solution at a flow rate of 100 sccm. A stainless steel mesh (SUS304, 30mesh) was used as a high voltage electrode and attached on the back side of the ceramics plate. A grounded electrode was put into the reactor and immersed in the solution. High voltage was applied to the high voltage electrode through a ballast resister (250 kΩ) and plasma was generated in argon gas bubbles. A resister (1 kΩ) was used to measure the electric current, which was regulated at 10 mA. The concentration of carbon dioxide (CO2) in the gas released from the plasma reactor was measured using gas chromatography. Other components in the gas were analyzed using Fourier transform infrared spectroscopy (FT-IR). The solution was analyzed using liquid chromatography-mass spectroscopy (LC-MS) and ion chromatography. During the degradation of PFOS, the concentrations of PFOS, perfluorocarboxylic acids (PFCAs: CnF2n+1COOH) with shorter carbon chains (n = 1-7), fluoride ion, and sulfate ion in the solution, and CO2 in the gas were quantified. The mass balances of fluorine, carbon and sulfur were calculated using these concentrations, and were 59.1%, 44.6%, and 83.2% respectively after 365 min treatment. Tetrafluoro methane (CF4- ub>), trifluoro methane (CHF3), hexafluoro ethane(C2F6), and carbon monoxide (CO) were detected in the gas using FT-IR but the concentrations of them were not quantified yet. By the quantification of the concentrations of the gas components, it will be possible for the mass balances to amount to 100%.

Summary form only given. Water-treatment processes utilizing OH radicals (*OH) to decompose persi... more Summary form only given. Water-treatment processes utilizing OH radicals (*OH) to decompose persistent organic compounds are called advanced oxidation processes (AOPs). *OH can be produced by the reaction of hydrogen peroxide (H₂O₂) with ozone (O₃). When O₃ was passed through a plasma-treated, highly concentrated solution of organic compounds, the processing speed and efficiency of the decomposition of the organic compounds was improved. When using a DC-voltage plasma, the production rate of H₂O₂ was high with a high energy input, whereas that of O₃ was high with a low energy input1. Multiple plasmas could be generated in parallel using an AC voltage with ballast capacitors². In this manner, if the selective production of H₂O₂ or O₃ in each plasma is achieved, AOPs can be realized without generating O₃ using an ozonizer. In this study, we investigated the characteristics of H₂O₂ and O₃ production driven by an AC voltage. The plasma reactor consisted of a high-voltage needle electrode and a ceramic plate containing a hole of 0.3 mm diameter for the generation of oxygen (O₂) gas bubbles and plasma. In addition, the reactor had a grounded electrode, immersed in Na₂SO₄ solution (40 mL) with a conductivity of 1.5 mS/cm. A square-wave AC voltage was applied through a ballast capacitor of 15-100 pF, and the plasma was generated between the needle electrode and the bubble surface. The concentrations of H₂O₂ in the solution and O₃ in the exhaust gas were measured. The power input to the reactor was increased in proportion to the frequency and the capacitance. When the source voltage was 4 kV and the frequency was 2 kHz, the power was 1.2 W at a capacitance of 15 pF; at 100 pF, the power was 5.9 W. The concentration of H₂O₂ increased, and that of O₃ decreased, as the input power increased. The molar ratio of the reactive species produced (H₂O₂/O₃) was 0.28 at a power of 1.2 W, and 4.1 at 5.9 W. Therefore, the plasma power, as well as the amounts of H₂O₂ and O₃ produced and their ratio could be controlled by varying the ballast capacitor in AC-plasma operation. AOPs with a reactor utilizing ballast capacitors to produce multiple plasmas will thus be possible.

The Japan Society of Applied Physics, Jul 17, 2015

The Japan Society of Applied Physics, Jul 4, 2013

Electrical Engineering in Japan, Apr 21, 2014

SUMMARYPerfluorooctanoic acid (PFOA: C7F15COOH) in water is effectively decomposed by plasma gene... more SUMMARYPerfluorooctanoic acid (PFOA: C7F15COOH) in water is effectively decomposed by plasma generated at a gas–liquid interface. During the decomposition of PFOA, perfluorocarboxylic acids (PFCAs: ) with shorter carbon chains (n = 1–6) are generated as by‐products. Since these PFCAs are surfactants, they are adsorb onto the gas–liquid interface and show high surface concentrations. This study investigated the relationship between the adsorbed amount of PFCA and the rate of decomposition by a direct current plasma. The adsorbed amount of PFCA at the gas–liquid interface increased as the length of the carbon chain increased, resulting in a higher rate of decomposition. However, the reaction rate reached saturation at a certain adsorption amount, depending on the discharge current.

Journal of Physics D, May 26, 2022

Although sulfonated carbon catalysts are considered promising solid acid catalysts for cellulose ... more Although sulfonated carbon catalysts are considered promising solid acid catalysts for cellulose conversion, most carbon sulfonation processes require concentrated sulfuric acid (18 M) at elevated temperatures. This work investigates a novel sulfonation mechanism for carbon acid catalysts via a gas–liquid interfacial plasma sulfonation system under atmospheric pressure conditions with a dilute sulfuric acid solution (1 M) at 38 °C, and the by-products of the plasma sulfonation process were investigated by in-situ and ex-situ diagnosis. The results show that a high gas temperature (>1050 K) around the plasma allows H2SO4 droplet decomposition, and active species (•OH, SO3, and HOSO2•) generated at the gas–liquid interface were grafted on the defects of the carbon materials and subsequently formed sulfonic acid groups (0.36 mmol g−1) and total acid groups (4.16 mmol g−1) on the carbon network. This study aimed to provide significant insight into the understanding of the sulfonation mechanisms of an emerging plasma-based process for carbon acid catalysts, which is important for the further development of an environmentally friendly sulfonation process for acid catalysts for biomass conversion.

The transactions of the Institute of Electrical Engineers of Japan.A, Mar 1, 2022

Electrochimica Acta, Sep 1, 2021

Abstract Carbon-based materials have been widely studied as promising energy conversion materials... more Abstract Carbon-based materials have been widely studied as promising energy conversion materials that can replace noble metal catalysts. In addition, the plasma-in-liquid process has recently been used to synthesize heteroatom-doped carbon materials for oxygen reduction reactions, such as nitrogen-, boron-, and halogen-doped carbon. However, there has been a lack of insight into pristine carbon, which is the base material for such reactions. In this study, pristine carbon materials (Cx-P) were synthesized using a plasma-in-liquid process, and the material properties and oxygen reduction reaction (ORR) performance were analyzed with respect to heat treatment. Cx-P was successfully synthesized as a carbon nanoparticle and redesigned as partially crystallized carbon with various pore-size distributions using heat treatment. The 2-electron-transfer ORR pathway was identified as the intrinsic reduction route. On the other hand, the electrochemical activity increased with heat treatment, showing an unexpectedly superior kinetic current density of ~18.30 mA cm−2 (at 0.5 V vs. RHE). Our results are expected to provide an important reference to the ORR performance of the relevant carbon materials, including insights into the basic material properties of partially crystallized porous carbon synthesized using the plasma-in-liquid process.

Electronics and Communications in Japan, Nov 19, 2015

SUMMARYOne‐ and zero‐dimensional (0D) numerical models of plasma generated over a solution were e... more SUMMARYOne‐ and zero‐dimensional (0D) numerical models of plasma generated over a solution were established. Gas‐ and liquid‐phase reactions and mass transfer through a gas–liquid interface for OH radical, hydrogen peroxide, and HO2 radical were considered, and the decomposition of acetic acid in water was evaluated. In a 1D model with a small diffusion coefficient (10−9 m2/s) in liquid phase, the diffusion rate was the rate‐limiting factor of the decomposition of acetic acid. With such a small diffusion coefficient, the concentrations of OH radical and acetic acid in the 0D model showed large differences from those in the 1D model. When the time scale of diffusion in the liquid phase was shorter than that of the decomposition reaction between OH radical and acetic acid, reasonable results were obtained in the 0D model.

Japanese Journal of Applied Physics, Oct 31, 2017

IEEE Transactions on Dielectrics and Electrical Insulation, Apr 1, 2009

2016 IEEE International Conference on Plasma Science (ICOPS), 2016

Summary form only given. Water-treatment processes utilizing OH radicals (*OH) to decompose persi... more Summary form only given. Water-treatment processes utilizing OH radicals (*OH) to decompose persistent organic compounds are called advanced oxidation processes (AOPs). *OH can be produced by the reaction of hydrogen peroxide (H₂O₂) with ozone (O₃). When O₃ was passed through a plasma-treated, highly concentrated solution of organic compounds, the processing speed and efficiency of the decomposition of the organic compounds was improved. When using a DC-voltage plasma, the production rate of H₂O₂ was high with a high energy input, whereas that of O₃ was high with a low energy input1. Multiple plasmas could be generated in parallel using an AC voltage with ballast capacitors². In this manner, if the selective production of H₂O₂ or O₃ in each plasma is achieved, AOPs can be realized without generating O₃ using an ozonizer. In this study, we investigated the characteristics of H₂O₂ and O₃ production driven by an AC voltage. The plasma reactor consisted of a high-voltage needle electrode and a ceramic plate containing a hole of 0.3 mm diameter for the generation of oxygen (O₂) gas bubbles and plasma. In addition, the reactor had a grounded electrode, immersed in Na₂SO₄ solution (40 mL) with a conductivity of 1.5 mS/cm. A square-wave AC voltage was applied through a ballast capacitor of 15-100 pF, and the plasma was generated between the needle electrode and the bubble surface. The concentrations of H₂O₂ in the solution and O₃ in the exhaust gas were measured. The power input to the reactor was increased in proportion to the frequency and the capacitance. When the source voltage was 4 kV and the frequency was 2 kHz, the power was 1.2 W at a capacitance of 15 pF; at 100 pF, the power was 5.9 W. The concentration of H₂O₂ increased, and that of O₃ decreased, as the input power increased. The molar ratio of the reactive species produced (H₂O₂/O₃) was 0.28 at a power of 1.2 W, and 4.1 at 5.9 W. Therefore, the plasma power, as well as the amounts of H₂O₂ and O₃ produced and their ratio could be controlled by varying the ballast capacitor in AC-plasma operation. AOPs with a reactor utilizing ballast capacitors to produce multiple plasmas will thus be possible.

IEEJ Transactions on Fundamentals and Materials, 2022

IEEE Transactions on Plasma Science, Dec 1, 2007

Japanese Journal of Applied Physics, Oct 16, 2020

The transactions of the Institute of Electrical Engineers of Japan.A, 2012

The transactions of the Institute of Electrical Engineers of Japan.A, 2007

Japanese Journal of Applied Physics, May 4, 2023

As a plasma-based method, diaphragm discharge plasma, an underwater discharge, exhibits a relativ... more As a plasma-based method, diaphragm discharge plasma, an underwater discharge, exhibits a relatively high production rate and efficiency of hydrogen peroxide (H2O2). This study aimed to characterize the energetic state of plasma and the H2O2 production mechanism by optical emission spectroscopy, evaluating the excitation temperature, gas temperature, electron density, and their temporal variations. The excitation temperature was approximately 3000 K, which was also presumed to almost coincide with the electron temperature in the plasma. The gas temperature was approximately 2500 K, and the electron density was approximately 6 × 1022 m−3 at maximum. The electron density sustained higher values under the condition of better H2O2 production performance, whereas the other two parameters exhibited almost no difference and variation. The reaction rate calculation based on the observation results indicated that the thermal dissociation of H2O is a more crucial reaction path for H2O2 production in our plasma than expected.

The transactions of the Institute of Electrical Engineers of Japan.A, 2018

ABSTRACT form only given. Perfluorooctane sulfonic acid (PFOS) can be decomposed efficiently by p... more ABSTRACT form only given. Perfluorooctane sulfonic acid (PFOS) can be decomposed efficiently by plasmas generated in gas bubbles. However, mass balance during the degradation of PFOS is not fully understood. Mass balance is quite important for commercial applications. Thus, the purpose of this study is to clarify the value of the mass balances of fluorine, carbon, and sulfur, and to understand the degradation process of PFOS. PFOS in water was decomposed by dc plasma generated in argon gas bubbles. The reactor was made of acrylic. A ceramics plate, which was 0.3 mm in thickness and had a micro hole of 0.3 mm diameter at the center, was attached on the bottom of the reactor. Argon gas was supplied through the hole to PFOS solution at a flow rate of 100 sccm. A stainless steel mesh (SUS304, 30mesh) was used as a high voltage electrode and attached on the back side of the ceramics plate. A grounded electrode was put into the reactor and immersed in the solution. High voltage was applied to the high voltage electrode through a ballast resister (250 kΩ) and plasma was generated in argon gas bubbles. A resister (1 kΩ) was used to measure the electric current, which was regulated at 10 mA. The concentration of carbon dioxide (CO2) in the gas released from the plasma reactor was measured using gas chromatography. Other components in the gas were analyzed using Fourier transform infrared spectroscopy (FT-IR). The solution was analyzed using liquid chromatography-mass spectroscopy (LC-MS) and ion chromatography. During the degradation of PFOS, the concentrations of PFOS, perfluorocarboxylic acids (PFCAs: CnF2n+1COOH) with shorter carbon chains (n = 1-7), fluoride ion, and sulfate ion in the solution, and CO2 in the gas were quantified. The mass balances of fluorine, carbon and sulfur were calculated using these concentrations, and were 59.1%, 44.6%, and 83.2% respectively after 365 min treatment. Tetrafluoro methane (CF4- ub>), trifluoro methane (CHF3), hexafluoro ethane(C2F6), and carbon monoxide (CO) were detected in the gas using FT-IR but the concentrations of them were not quantified yet. By the quantification of the concentrations of the gas components, it will be possible for the mass balances to amount to 100%.

Summary form only given. Water-treatment processes utilizing OH radicals (*OH) to decompose persi... more Summary form only given. Water-treatment processes utilizing OH radicals (*OH) to decompose persistent organic compounds are called advanced oxidation processes (AOPs). *OH can be produced by the reaction of hydrogen peroxide (H₂O₂) with ozone (O₃). When O₃ was passed through a plasma-treated, highly concentrated solution of organic compounds, the processing speed and efficiency of the decomposition of the organic compounds was improved. When using a DC-voltage plasma, the production rate of H₂O₂ was high with a high energy input, whereas that of O₃ was high with a low energy input1. Multiple plasmas could be generated in parallel using an AC voltage with ballast capacitors². In this manner, if the selective production of H₂O₂ or O₃ in each plasma is achieved, AOPs can be realized without generating O₃ using an ozonizer. In this study, we investigated the characteristics of H₂O₂ and O₃ production driven by an AC voltage. The plasma reactor consisted of a high-voltage needle electrode and a ceramic plate containing a hole of 0.3 mm diameter for the generation of oxygen (O₂) gas bubbles and plasma. In addition, the reactor had a grounded electrode, immersed in Na₂SO₄ solution (40 mL) with a conductivity of 1.5 mS/cm. A square-wave AC voltage was applied through a ballast capacitor of 15-100 pF, and the plasma was generated between the needle electrode and the bubble surface. The concentrations of H₂O₂ in the solution and O₃ in the exhaust gas were measured. The power input to the reactor was increased in proportion to the frequency and the capacitance. When the source voltage was 4 kV and the frequency was 2 kHz, the power was 1.2 W at a capacitance of 15 pF; at 100 pF, the power was 5.9 W. The concentration of H₂O₂ increased, and that of O₃ decreased, as the input power increased. The molar ratio of the reactive species produced (H₂O₂/O₃) was 0.28 at a power of 1.2 W, and 4.1 at 5.9 W. Therefore, the plasma power, as well as the amounts of H₂O₂ and O₃ produced and their ratio could be controlled by varying the ballast capacitor in AC-plasma operation. AOPs with a reactor utilizing ballast capacitors to produce multiple plasmas will thus be possible.

The Japan Society of Applied Physics, Jul 17, 2015

The Japan Society of Applied Physics, Jul 4, 2013

Electrical Engineering in Japan, Apr 21, 2014

SUMMARYPerfluorooctanoic acid (PFOA: C7F15COOH) in water is effectively decomposed by plasma gene... more SUMMARYPerfluorooctanoic acid (PFOA: C7F15COOH) in water is effectively decomposed by plasma generated at a gas–liquid interface. During the decomposition of PFOA, perfluorocarboxylic acids (PFCAs: ) with shorter carbon chains (n = 1–6) are generated as by‐products. Since these PFCAs are surfactants, they are adsorb onto the gas–liquid interface and show high surface concentrations. This study investigated the relationship between the adsorbed amount of PFCA and the rate of decomposition by a direct current plasma. The adsorbed amount of PFCA at the gas–liquid interface increased as the length of the carbon chain increased, resulting in a higher rate of decomposition. However, the reaction rate reached saturation at a certain adsorption amount, depending on the discharge current.

Journal of Physics D, May 26, 2022

Although sulfonated carbon catalysts are considered promising solid acid catalysts for cellulose ... more Although sulfonated carbon catalysts are considered promising solid acid catalysts for cellulose conversion, most carbon sulfonation processes require concentrated sulfuric acid (18 M) at elevated temperatures. This work investigates a novel sulfonation mechanism for carbon acid catalysts via a gas–liquid interfacial plasma sulfonation system under atmospheric pressure conditions with a dilute sulfuric acid solution (1 M) at 38 °C, and the by-products of the plasma sulfonation process were investigated by in-situ and ex-situ diagnosis. The results show that a high gas temperature (>1050 K) around the plasma allows H2SO4 droplet decomposition, and active species (•OH, SO3, and HOSO2•) generated at the gas–liquid interface were grafted on the defects of the carbon materials and subsequently formed sulfonic acid groups (0.36 mmol g−1) and total acid groups (4.16 mmol g−1) on the carbon network. This study aimed to provide significant insight into the understanding of the sulfonation mechanisms of an emerging plasma-based process for carbon acid catalysts, which is important for the further development of an environmentally friendly sulfonation process for acid catalysts for biomass conversion.

The transactions of the Institute of Electrical Engineers of Japan.A, Mar 1, 2022

Electrochimica Acta, Sep 1, 2021

Abstract Carbon-based materials have been widely studied as promising energy conversion materials... more Abstract Carbon-based materials have been widely studied as promising energy conversion materials that can replace noble metal catalysts. In addition, the plasma-in-liquid process has recently been used to synthesize heteroatom-doped carbon materials for oxygen reduction reactions, such as nitrogen-, boron-, and halogen-doped carbon. However, there has been a lack of insight into pristine carbon, which is the base material for such reactions. In this study, pristine carbon materials (Cx-P) were synthesized using a plasma-in-liquid process, and the material properties and oxygen reduction reaction (ORR) performance were analyzed with respect to heat treatment. Cx-P was successfully synthesized as a carbon nanoparticle and redesigned as partially crystallized carbon with various pore-size distributions using heat treatment. The 2-electron-transfer ORR pathway was identified as the intrinsic reduction route. On the other hand, the electrochemical activity increased with heat treatment, showing an unexpectedly superior kinetic current density of ~18.30 mA cm−2 (at 0.5 V vs. RHE). Our results are expected to provide an important reference to the ORR performance of the relevant carbon materials, including insights into the basic material properties of partially crystallized porous carbon synthesized using the plasma-in-liquid process.

Electronics and Communications in Japan, Nov 19, 2015

SUMMARYOne‐ and zero‐dimensional (0D) numerical models of plasma generated over a solution were e... more SUMMARYOne‐ and zero‐dimensional (0D) numerical models of plasma generated over a solution were established. Gas‐ and liquid‐phase reactions and mass transfer through a gas–liquid interface for OH radical, hydrogen peroxide, and HO2 radical were considered, and the decomposition of acetic acid in water was evaluated. In a 1D model with a small diffusion coefficient (10−9 m2/s) in liquid phase, the diffusion rate was the rate‐limiting factor of the decomposition of acetic acid. With such a small diffusion coefficient, the concentrations of OH radical and acetic acid in the 0D model showed large differences from those in the 1D model. When the time scale of diffusion in the liquid phase was shorter than that of the decomposition reaction between OH radical and acetic acid, reasonable results were obtained in the 0D model.

Japanese Journal of Applied Physics, Oct 31, 2017

IEEE Transactions on Dielectrics and Electrical Insulation, Apr 1, 2009

2016 IEEE International Conference on Plasma Science (ICOPS), 2016

Summary form only given. Water-treatment processes utilizing OH radicals (*OH) to decompose persi... more Summary form only given. Water-treatment processes utilizing OH radicals (*OH) to decompose persistent organic compounds are called advanced oxidation processes (AOPs). *OH can be produced by the reaction of hydrogen peroxide (H₂O₂) with ozone (O₃). When O₃ was passed through a plasma-treated, highly concentrated solution of organic compounds, the processing speed and efficiency of the decomposition of the organic compounds was improved. When using a DC-voltage plasma, the production rate of H₂O₂ was high with a high energy input, whereas that of O₃ was high with a low energy input1. Multiple plasmas could be generated in parallel using an AC voltage with ballast capacitors². In this manner, if the selective production of H₂O₂ or O₃ in each plasma is achieved, AOPs can be realized without generating O₃ using an ozonizer. In this study, we investigated the characteristics of H₂O₂ and O₃ production driven by an AC voltage. The plasma reactor consisted of a high-voltage needle electrode and a ceramic plate containing a hole of 0.3 mm diameter for the generation of oxygen (O₂) gas bubbles and plasma. In addition, the reactor had a grounded electrode, immersed in Na₂SO₄ solution (40 mL) with a conductivity of 1.5 mS/cm. A square-wave AC voltage was applied through a ballast capacitor of 15-100 pF, and the plasma was generated between the needle electrode and the bubble surface. The concentrations of H₂O₂ in the solution and O₃ in the exhaust gas were measured. The power input to the reactor was increased in proportion to the frequency and the capacitance. When the source voltage was 4 kV and the frequency was 2 kHz, the power was 1.2 W at a capacitance of 15 pF; at 100 pF, the power was 5.9 W. The concentration of H₂O₂ increased, and that of O₃ decreased, as the input power increased. The molar ratio of the reactive species produced (H₂O₂/O₃) was 0.28 at a power of 1.2 W, and 4.1 at 5.9 W. Therefore, the plasma power, as well as the amounts of H₂O₂ and O₃ produced and their ratio could be controlled by varying the ballast capacitor in AC-plasma operation. AOPs with a reactor utilizing ballast capacitors to produce multiple plasmas will thus be possible.

IEEJ Transactions on Fundamentals and Materials, 2022