Heon Lee

Rapid destruction of the rhodamine B using TiO2 photocatalyst in the liquid phase plasma

BackgroundRhodamine B (RhB) is widely used as a colorant in textiles and food stuffs, and is also a well-known water tracer fluorescent. It is harmful to human beings and animals, and causes irritation of the skin, eyes and respiratory tract. The carcinogenicity, reproductive and developmental toxicity, neurotoxicity and chronic toxicity toward humans and animals have been experimentally proven. RhB cannot be effectively removed by biological treatment due to the slow kinetics. Therefore, RhB is chosen as a model pollutant for liquid phase plasma (LPP) treatment in the present investigation.ResultsThis paper presents experimental results for the bleaching of RhB from aqueous solutions in the presence of TiO2 photocatalyst with LPP system. Properties of generated plasma were investigated by optical emission spectroscopy methods. The results of electrical-discharge degradation of RhB showed that the decomposition rate increased with the applied voltage, pulse width, and frequency. The oxygen gas addition to reactant solution increases the degradation rate by active oxygen species. The RhB decomposition rate was shown to increase with the TiO2 particle dosage.ConclusionThis work presents the conclusions on the photocatalytic oxidation of RhB, as a function of plasma conditions, oxygen gas bubbling as well as TiO2 particle dosage. We knew that using the liquid phase plasma system with TiO2 photocatalyst at high speed we could remove the organic matter in the water.

Facile synthesis of iron-ruthenium bimetallic oxide nanoparticles on carbon nanotube composites by liquid phase plasma method for supercapacitor

Iron-ruthenium bimetallic oxide nanoparticles were precipitated on carbon nanotubes by liquid-phase plasma method. We also evaluated the physicochemical and electrochemical properties of prepared composite for supercapacitor electrode. Polycrystalline about 10 to 25 nm-sized bimetallic nanoparticles were evenly precipitated on the carbon nanotube (CNT) and consisted of Fe3+ and Ru4+. Bimetallic oxide nanoparticles’ composition depended on the ratio of the metal precursor concentration and standard reduction potential. The C-V area and specific capacitance of iron-ruthenium oxide nanoparticle/carbon nanotube (IRCNT) composite electrodes was higher than that of untreated CNT electrode, and increased with increasing ruthenium content. The cycling stability of IRCNT composite electrode was higher than untreated CNT electrode, especially iron element was more stable.

Electrical Properties of Low-Dielectric-Constant SiOC(–H) Films Prepared by Plasma-Enhanced Chemical Vapor Deposition from Methyltriethoxysilane and O2

SiOC(–H) films were deposited on a p-type Si(100) substrate by plasma-enhanced chemical vapor deposition (PECVD) from methyltriethoxysilane (MTES) and oxygen precursors. The MTES/O2 flow rate ratio was varied from 40 to 100% to investigate its effect on the properties of the films. Film thickness and refractive index were measured by field-emission scanning electron microscopy (FESEM) and ellipsometry, respectively. The chemical structures of the SiOC(–H) films were characterized by Fourier transform infrared spectroscopy (FTIR) in the absorbance mode. The bonding configurations of the SiOC(–H) films remained the unchanged upon annealing, showing their good thermal stability. The electrical properties of the films were measured using a metal–insulator–semiconductor (MIS) Al/SiOC(–H)/ p-Si structure. The experimental lowest dielectric constant of the SiOC(–H) film was found to be 2.38 at an annealing temperature 500 °C and the film has excellent thermal stability up to 500 °C. The SiOC(–H) films deposited by MTES and O2 precursors are a promising material for next-generation Cu-interconnect technology.

Liquid phase plasma synthesis of iron oxide/carbon composite as dielectric material for capacitor

Iron oxide/carbon composite was synthesized using a liquid phase plasma process to be used as the electrode of supercapacitor. Spherical iron oxide nanoparticles with the size of 5-10 nm were dispersed uniformly on carbon powder surface. The specific capacitance of the composite increased with increasing quantity of iron oxide precipitate on the carbon powder up to a certain quantity. When the quantity of the iron oxide precipitate exceeds the threshold, however, the specific capacitance was rather reduced by the addition of precipitate. The iron oxide/carbon composite containing an optimum quantity (0.33 atomic %) of iron oxide precipitate exhibited the smallest resistance and the largest initial resistance slope.

Photo-catalytic destruction of ethylene using microwave discharge electrodeless lamp

A double tube type microwave discharge electrodeless lamp was employed to investigate the photo-catalytic decomposition of ethylene gas, an important VOC species. The anatase TiO2 film photo-catalyst balls prepared by a low pressure metal organic chemical vapor deposition method were used. In addition, the advantages of microwave/UV/TiO2 photo-catalysts hybrid process were analyzed. The removal performance was examined under different conditions with different initial ethylene concentrations, gas residence times and oxygen concentrations. At all microwave powers tested, UV-C exhibited much larger irradiance than UV-A and UV-B. The degradation efficiency of ethylene increased with increasing microwave intensity, with decreasing inlet concentration, and with decreasing reaction gas flow rate. Taking the energy cost into account, residence time should be determined considering inlet concentration, volume of degradation, capacity of devices, and admitted costs. Microwave intensity was shown to be a critical operation variable for the photo-catalytic degradation of ethylene, required to be determined depending on initial ethylene concentration.

Contribution of Dissolved Oxygen to Methylene Blue Decomposition by Hybrid Advanced Oxidation Processes System

Experimental results of photocatalysis under high dissolved oxygen (DO) concentration conditions are reported. Methylene blue was used as the organic pollutant to be degraded by a novel microwave/UV/DO/TiO2 photocatalyst hybrid system. The degradation rate increased with TiO2 nanoparticle dosages and DO concentration. However, inhibition of photocatalysis due to bubbles produced by DO generator was also observed. When the DO generator was used to increase the DO concentration in the pollutant solution treated by the microwave-assisted UV-TiO2 photocatalysis, the decomposition rate constant was highest among all the experimental conditions tested in this study. This result demonstrated that high concentration of DO can enhance the photocatalytic reaction rate by causing a synergistic effect of constituent techniques.

Characterization of Bimetallic Fe-Ru Oxide Nanoparticles Prepared by Liquid-Phase Plasma Method.

The bimetallic Fe-Ru oxide nanoparticles were synthesized in the liquid-phase plasma (LPP) method which employed iron chloride and ruthenium chloride as precursors. The active species (OH·, Hα, Hβ, and OI) and the iron and ruthenium ions were observed in the plasma field created by the LPP process. The spherical-shaped bimetallic Fe-Ru oxide nanoparticles were synthesized by the LPP reaction, and the size of the particles was growing along with the progression of the LPP reaction. The synthesized bimetallic Fe-Ru oxide nanoparticles were comprised of Fe2O3, Fe3O4, RuO, and RuO2. Ruthenium had a higher reduction potential than iron and resulted in higher ruthenium composition in the synthesized bimetallic nanoparticles. The control of the molar ratio of the precursors in the reactant solution was found to be employed as a means to control the composition of the elements in bimetallic nanoparticles.

Application of recycled zero-valent iron nanoparticle to the treatment of wastewater containing nitrobenzene

Zero-valent iron (ZVI) was synthesized using iron oxide, a byproduct of pickling line at a steel work. ZVI with a mean particle size of 500 nm was synthesized. The reaction activity of the synthesized ZVI was much higher than commercial ZVI. When applied to the decomposition of nitrobenzene (NB), the ZVI particles underwent corrosion and passivation oxide film formation, resulting in particle size decrease. The NB decomposition rate increased with increasing ZVI dosage level and with decreasing pH. The solution pH increased monotonously with increasing reaction duration, whereas the aniline concentration showed a maximum at 50 min. Based on the GC/MS analysis, NB is presumed to be reduced into aniline via reductive intermediates such as azobenzene and azoxybenzene. When combined with a subsequent biological process, the synthesized ZVI will be able to decompose NB in wastewater effectively.

Contribution of Dissolved Oxygen to Methyl Orange Decomposition by Liquid Phase Plasma Processes System

Degradation of methyl orange (MO) in liquid phase plasma (LPP) was investigated. A bipolar pulsed power supply was used to generate discharges in the aqueous solution. Properties of generated plasma were investigated by electrical and optical emission spectroscopy methods. The MO decomposition rate increased with increasing levels of applied voltage, pulse width and frequency. The concentrations of activated species, including OH• radicals, were increased by the supply of DO. The concentration of OH• increased with increasing DO concentration up to 50 ppm. Further increase in the DO concentration, however, reduced the OH• concentration because of recombination of OH• radicals. The trend of MO decomposition rate with varying DO concentration was the same as that observed for the OH• concentration, suggesting that OH• radicals play a critical role in the decomposition of MO. Therefore, the LPP process for MO decomposition should be operated with an optimum DO concentration where the OH• radical concentration becomes highest.

Synthesis Process of Cobalt Nanoparticles in Liquid-Phase Plasma

In this work, the liquid phase plasma reduction method was applied to prepare cobalt nanoparticles from the cobalt chloride solution. A bipolar pulsed power supply was used to generate discharges in aqueous solutions. The excited states of atomic hydrogen and atomic oxygen as well as the molecular bands of the hydroxyl radical OH were detected in emission spectra. The duration of plasma treatment affected not only size and number of produced particles but also the particle shape. Many spots could be seen in the Electron diffraction pattern of polycrystalline particles.