Nozomi Takeuchi

Abstract The establishment of economical and eco-friendly technologies for water treatment is a crucial issue for the realization of a sustainable society. Plasma-based treatments are promising methods for the decomposition of persistent organic compounds. This progress report summarizes recent improvements to plasma-based water treatment technologies by focusing on two types of contaminated solutions: solutions containing high concentrations of acetic acid and solutions containing surfactants,

Perfluorooctanoic acid (PFOA: C7F15COOH) in water was decomposed using either plasma generated inside oxygen bubbles or sulfate radical anions. During the PFOA decomposition processes, perfluorocarboxylic acids (PFCAs: CnF2n+1COOH) with shorter carbon chains were generated. The decomposition processes were deduced based on a zero-dimensional simulation study using experimentally obtained reaction rate constants. During the plasma treatment, the dominant reaction was found to be the direct decomp

Plasmas generated inside oxygen bubbles in water have been developed for water purification. Zero-dimensional numerical simulations were used to investigate the chemical reactions in plasmas driven by dc voltage. The numerical and experimental results of the concentrations of hydrogen peroxide and ozone in the solution were compared with a discharge current between 1 and 7 mA. Upon increasing the water vapour concentration inside bubbles, we saw from the numerical results that the concentration

The production mechanism of liquid-phase H2O2 in dc driven plasma in O2 and Ar with a water electrode was investigated. When a water anode was used, the concentration of H2O2 increased linearly with the treatment time. The production rate was proportional to the discharge current, and there was no dependence on the gap distance. On the other hand, the production rate was much smaller with a water anode. We concluded that the production of gas-phase H2O2 in the cathode sheath just above a water c

Many types of plasma processes have been investigated as potential agents for decomposing persistent organic compounds in water using hydroxyl radicals (OH), and a wide range of energy efficiency in the reduction of total organic carbon (TOC) has been observed. In this study, loss mechanisms of OH that limit the energy efficiency were investigated using a plasma generated over an acetic acid solution. Various experiments, including the analysis of the decomposition process, a parametric study, a

The effect of an insulation cover on a corona wire for a wire-rod type electrohydrodynamic (EHD) gas pump was experimentally investigated and one-dimensional cross sectional averaged analyses were performed. The insulation cover over the corona wire causes a fluctuation of the discharge current, resulting in fluctuations of the EHD gas flow. The insulation cover also changes the EHD force distribution, which is the product of an electric field and ion charge density. The EHD force concentrated a

A wire-rod type electrohydrodynamic (EHD) gas pump was driven by a negative applied voltage with pipes of different inner diameters. An EHD gas flow was generated from a wire electrode to a rod electrode under a negative corona discharge. The flow velocity was proportional to the applied voltage and the square root of the discharge current. Before spark onset, the maximum volumetric flow rate of 43 L/min was achieved with a pipe having an inner diameter 20 mm, and the pump efficiency was higher

Sodium-ion batteries (SiBs) have recently attracted considerable interest due to the plentiful supply of raw materials for their production and their electrochemical behavior, which is similar to that of lithium-ion batteries (LiBs). However, the relatively larger radius of sodium ions than that of lithium ions is not suitable for storage in conventional graphite, which is widely used as the anode. To resolve this issue, in this study, we developed a new harmonized carbon material with a three-d

Perfluorooctane sulfonic acid (PFOS) is an environmentally harmful and persistent substance, and thus, effluent controls have been applied. The decomposition of PFOS in water using plasma attached to the water surface has been successfully performed, and the resulting energy efficiency is relatively high compared to that of other methods such as sonochemical processes. The estimation of the amount of PFOS adsorbing to the plasma-water interface showed much higher mole fraction of PFOS (6.0 ×10 <

An asymmetric surface-barrier discharge induces a unidirectional gas flow of several meters per second near the electrodes. The mechanism of how the discharge induces the gas flow is investigated experimentally by changing the electrode configuration from asymmetric to symmetric. The peak values of the discharge current and the discharge patterns depend on the polarity of the applied voltage in the asymmetric electrode configuration. When the exposed electrode is an anode (negative-going cycle),

Decomposition of acetic acid in water was conducted using multiple plasmas generated within oxygen bubbles. Ballast capacitors were used to control the plasma input power, allowing hydrogen peroxide and ozone to be produced at different rates in each plasma by adjusting the capacitance. By using an ozone absorber connected to the plasma reactor, OH radicals, both generated by the plasmas directly and reproduced from hydrogen peroxide through reactions with ozone, could be effectively utilized fo

A surface dielectric barrier discharge induces a gas flow called an electrohydrodynamic (EHD) flow. Flow velocity measurements with a laser Doppler velocimeter (LDV) have indicated that the driving force of the EHD flow exists within a height of less than 0.3 mm from the dielectric barrier, and therefore, EHD flow generation in a narrow channel of a submillimeter order was attempted by placing a dielectric plate over the discharge. However, a positive charge that accumulated on the inner surface

A surface barrier discharge generated between an exposed and a buried electrode induces a unidirectional gas flow, known as an electrohydrodynamic (EHD) gas flow. The discharge behavior and flow characteristics have been investigated. When the exposed electrode is an anode, several streamers propagate above the buried electrode, whereas when the exposed electrode is a cathode, weak light emission is uniformly observed above the buried electrode. The maximum discharge length increases as both the