Plasma Chemistry and Plasma Processing (v.34, #6)

Titanium and its alloys are currently considered as successful biocompatible materials because titanium made implants become easily, structurally and functionally, connected to biological systems. As far as biological systems is concerned, antibacterial activity for medical implants are worth of interest to prevent inflammation at implant site. In this study RF cold plasma is employed as potential technology to prevent or reduce bacterial activity on Ti samples. Several plasma parameters are investigated for finding the best antibacterial process conditions against Escherichia coli 32. Main results of this investigation show that high antibacterial activity is exhibited by Ti samples in several experimental set-ups. In addition, the antibacterial activity detected at same level of previous, 16 days after the treatment suggests the effectiveness of the plasma surface modification. Finally, an attempt is made to correlate antibacterial effect with plasma treated titanium surface energy and plasma parameters.
Keywords: Antibacterial effect; Cold plasma; Titanium

Plasma-Initiated DT Graft Polymerization of Acrylic Acid on Surface of Porous Polypropylene Membrane for Pore Size Control by Saijie Shi; Yue Zhou; Xiao Lu; Yuansong Ye; Jian Huang; Xiaolin Wang (1257-1269).
A plasma-initiated degenerative transfer (DT) graft polymerization (PDTGP) was carried out on the surface of porous polypropylene membrane, with acrylic acid as monomer and iodoform as transfer agent. The polymerization rate was found to increase linearly with time. Well-defined poly(acrylic acid), with a narrow polydispersity (1.31), were obtained. Less solvent effect was observed in the PDTGP, whereas stronger solvent occurred in the plasma-initiated polymerization without iodoform. It was speculated that the unconventional radical induced by plasma should behave similarly in forming the dormant species as the conventional radical did. The polymerization is proposed to undergo via a DT mechanism. For modified membranes, graft amounts were indicated to increase linearly with conversions, i.e., proportional to molecular weights of graft chains. The PDTGP was proved a desirable method for controlling pore sizes of porous membranes.
Keywords: Plasma-initiated polymerization; Degenerative transfer polymerization; Graft polymerization; Surface modification; Porous membrane

Fertilization of Radishes, Tomatoes, and Marigolds Using a Large-Volume Atmospheric Glow Discharge by Alex Lindsay; Brandon Byrns; Wesley King; Asish Andhvarapou; Jeb Fields; Detlef Knappe; William Fonteno; Steven Shannon (1271-1290).
A large-volume atmospheric glow discharge has been used to incorporate nitrogen species into aqueous solution that is subsequently used to fertilize radishes, marigolds, and tomatoes. Treatment with plasma activated water (PAW) was compared to a tap water control. Water application began immediately after seeding and continued for 4 weeks. At the conclusion of the experiment, PAW treated plants had shoot masses 1.7–2.2 times larger than controls. Subsequent research has focused on optimizing the amount of nitrogen in solution by varying discharge power, air flow, air–water interface, and water alkalinity. When the discharge hovers over a stationary water phase, nitrate concentrations increase with decreasing power and increasing air flow. When water droplets are injected directly into the plasma, nitrate concentrations increase with increasing power and decreasing air flow. These contrasting trends are believed to depend on the balance between hydroxyl and electron concentrations in the discharge. Adding NaHCO3 to water before plasma treatment affects both the amount of nitrogen present in solution as well as the ratio between oxidized and reduced species. Concentrated NaHCO3 solution had 2.9 times more total nitrogen, 59 times more nitrite, and 27 % less nitrate after plasma treatment than a solution with no NaHCO3. Two factors could contribute to the spike in nitrite and decrease in nitrate: reaction of nitric and nitrous oxides with bicarbonate to form nitrite, and a decrease in disproportionation of nitrate that occurs readily at acidic pH but negligibly under neutral conditions.
Keywords: Large-volume glow; Atmospheric pressure plasma; Fertilization; Reactive nitrogen and oxygen species

The aim of this study was to evaluate the effect of oxygen plasma treatment on the surface roughness, morphology, chemical surface structure, crystallinity and tensile properties of wool fiber yarn. The wool fibers were treated with oxygen plasma at a different treatment time. The morphological surface characterization of wool fibers was realized at sub-micro scale by means of high-resolution scandisk confocal microscopy and scanning electron microscopy. The chemical structure of untreated and plasma treated wool fiber surface was analyzed by Attenuated Total Reflectance Fourier Transform Infrared spectrometry. In addition, the percentage of crystallinity and the size of the crystals were investigated using an X-ray diffractometer. The results showed that oxygen plasma treatment leads to the removal of surface lipids and oxidizes the cysteine in the exocuticle and increases the surface roughness.
Keywords: Wool fiber; Oxygen plasma; Roughness; Structure; Crystalinity

Effect of Ozone Addition to Lean NOx Trap Method Using Plasma-Catalyst System by Masato Nagata; Yasunari Hanaki; Atsushi Ikeda; Yasushi Sekine (1303-1315).
Although diesel vehicles have high energy efficiency, the removal of emitted NOx at low temperature persists as an important issue. This report presents an examination of low-temperature NOx removal using ozone injection and a plasma-lean NOx trap (LNT) catalyst system. Ozone is readily producible by a dielectric barrier discharge reactor using oxygen in air, and its injection to emitted NO enables oxidation to NO2 even at low temperatures. Results show that synergetic effects of ozone injection and plasma-LNT catalyst system enable low-temperature NOx removal.
Keywords: Dielectric barrier discharge; Ozone injection; Lean NOx trap; Plasma-catalyst; Automobile exhaust gas cleaning

Plasma-Enhanced Methane Direct Conversion over Particle-Size Adjusted MOx/Al2O3 (M = Ti and Mg) Catalysts by Palraj Kasinathan; Sunyoung Park; Woon Choon Choi; Young Kyu Hwang; Jong-San Chang; Yong-Ki Park (1317-1330).
Non-oxidative methane activation over particle-size adjusted alumina catalysts loaded with metal oxide (Al2O3, MgO/Al2O3, and TiO2/Al2O3) was investigated with a dielectric barrier discharge reactor using 10 % CH4 in Ar at plasma induced temperature. Plasma-assisted catalytic activity for direct conversion of methane over the catalysts was compared with that using plasma only. Catalyst hybrid reaction in a non-thermal discharge showed that MgO/Al2O3 had the highest activity for methane conversion. C2, C3, and C4 hydrocarbons were formed as products; ethane, ethylene, and acetylene were predominant over all catalysts. The effect of varying particle size of the MgO/Al2O3 catalyst was also examined. The conversion of methane over MgO/Al2O3 dramatically increased with decreasing catalyst particle size from 1.70 to 0.25 mm. It is interesting to note that distribution of C2 hydrocarbons was tuned by changing the particle size of the catalyst. It was also observed that the gas flow rate, frequency, and power supplied affected direct conversion of methane and selectivity of products significantly.
Keywords: Non-oxidative methane activation; DBD reactor; Metal oxide; Particle size

Non-thermal plasmas can be used for water treatment system because they allow free radical generation without heating. Advanced oxidation processes using non-thermal plasmas have been developed to decompose persistent organic pollutants. In this study, a water treatment method that involves spraying a solution into a coaxial dielectric barrier discharge (DBD) tube using an air, argon or oxygen carrier gas was investigated. The alumina DBD tube had an inner high-voltage electrode and an outer ground electrode. Acetic acid was used as the decomposition target because acetic acid is a known persistent organic material. An acetic acid solution, diluted 10,000 times in purified water, was atomized by an ultrasonic atomizer unit and introduced into the DBD tube. The residence time of the droplets sprayed into the discharge area was almost 7 ms. Acetic acid was effectively decomposed and the decomposition ratio reached almost 80 % when Ar was employed as the carrier gas. This is due to the very fine droplets in the sprayed mist having a large specific surface area and OH radicals being able to react directly in solution. Furthermore, the results suggest that the chemical processes involved in acetic acid decomposition can be controlled by varying the carrier gas composition.
Keywords: Water treatment; Non-thermal plasma; Mist flow; Organic compounds

Matrix IR Study of Benzene Transformations in a Pulsed Glow Discharge in the Absence and the Presence of Oxygen by Sergey E. Boganov; Sergey V. Kudryashov; Andrey Yu. Ryabov; Alexey I. Suslov; Stanislav S. Rynin; Mikhail P. Egorov; Oleg M. Nefedov (1345-1370).
Matrix FTIR study of products of benzene transformations in a pulsed glow discharge at low pressure in highly diluted mixtures of benzene with argon in the presence and absence of small oxygen additions has been carried out. Formation of the following hydrocarbon species has been established: acetylene, butadiyne, fulvene, benzvalene, methane, ethylene, phenyl, ethynyl and butadiynyl radicals. It has been shown that oxygen additions mainly result in deep oxidation of benzene to CO2, CO and H2O, although some products of intermediate oxidation have been detected. Those are formaldehyde, formyl radical, ketene, ketenyl radical, propadiene-1,3-dione, propadien-3-on-1-ilyden and hydroperoxyl radical. At the same time, it has unexpectedly been found that oxygen additions strongly increase the yield of butadiyne. Possible pathways, leading to formation of the listed species have been discussed on the basis of the obtained data and results reported in the literature.
Keywords: Glow discharge; Matrix FTIR spectroscopy; Benzene; Fulvene; Butadiyne; Phenol

Influence of N2/O2 Mixtures on Decomposition of Naphthalene in Surface Dielectric Barrier Discharge Based Reactor by Ayman A. Abdelaziz; Takafumi Seto; M. Abdel-Salam; Yoshio Otani (1371-1385).
The decomposition of naphthalene in surface dielectric barrier discharge (SDBD) based reactor is investigated in different carrier gases (air, nitrogen, and oxygen) in order to understand the reaction mechanism of the decomposition process. The decomposition efficiency of naphthalene is determined at different oxygen content (from 0 to 10 vol%) and different input power. The highest decomposition efficiency is obtained in nitrogen at low input power, due to the role played by the nitrogen excited species in the decomposition process. In addition, the decomposition efficiency is decreased with increasing the oxygen content at a low input power. At a relatively high input power, the decomposition efficiency reached its maximum value in pure oxygen. Moreover, the decomposition efficiency decreases with the increase of the oxygen content reaching minimum value at a small content of oxygen (~3 vol% O2) and relatively high input power, and then increases at higher oxygen content. The results show that the decomposition of naphthalene in the present reactor could be treated as a first order reaction with respect to the concentration of naphthalene.
Keywords: Surface discharge; Decomposition efficiency; Naphthalene; Oxygen content

Benzene Removal Using Non-thermal Plasma with CuO/AC Catalyst: Reaction Condition Optimization and Decomposition Mechanism by Ning Xu; Weina Fu; Chi He; Lianfang Cao; Xiaohe Liu; Jinglian Zhao; Hua Pan (1387-1402).
Non-thermal plasma (NTP) technology in synergy with adsorption catalysts was used to decompose volatile organic compounds. The obtained results indicated that the non-thermal plasma-assisted catalytic system (NTP-C) resulted in higher benzene removal capability and system energy efficiency. The CuO/AC (AC: active carbon) catalysts were prepared by incipient-wetness impregnation method, and effect of CuO loading on benzene destruction was tested. The effect of reaction conditions such as inlet benzene concentration, reaction space velocity, reaction humidity and energy density were also studied. Additionally, the reaction conditions were optimized by the multi-factor orthogonal experiment, and the highest benzene removal efficiency achieved 96.5 %. The influence degree of various factors for benzene elimination was: reaction space velocity ≫ CuO loading > energy density > inlet benzene concentration ≫ reaction humidity. Furthermore, the benzene decomposition mechanism was discussed by analyses of the reaction exhaust, the coke substance inside the reactor, and the surface property of the used catalyst. The oxidation byproducts primarily consisted of phenol and substitutions of phenol. We propose that the radical reactions play a significant role in benzene removal on the surface of catalysts.
Keywords: Non-thermal plasma; Benzene; CuO/active carbon; Reaction conditions; Decomposition mechanism

Enhanced Degradation of Acid Orange 7 Solution by Non-thermal Plasma Discharge with TiO2 by Ya-na Liu; Hang Xu; Shu-fa Zhu; Ming Zhou; Juan Miao (1403-1413).
The combination of TiO2 photocatalyst with non-thermal gliding arc discharge for the degradation of organic pollutant Acid Orange 7 (AO7) was studied in aqueous solution. The effects of different parameters including initial concentration of TiO2, carrier gas source and initial pH value were studied. The variations of H2O2, O3 and OH· active species and catalytic performance of reusing TiO2 were also investigated. It was shown that the optimum conditions for AO7 were TiO2 concentration of 1.0 g/L, oxygen as the carrier gas, and the initial pH value at acidic or basic. The crystal type of TiO2 didn’t changed after repeated three times.
Keywords: Acid Orange 7 (AO7); Titanium dioxide (TiO2); Organic pollutant; Non-thermal plasma discharge

Characterization of a Plasma Jet Produced by Spark Discharges in Argon Air Mixtures at Atmospheric Pressure by Ruggero Barni; Ilaria Biganzoli; Dario Tassetti; Claudia Riccardi (1415-1431).
A stark difference in the electrical, optical and thermal properties of an atmospheric pressure plasma jet source exploiting spark discharges in a gas stream was reported when argon is used instead of air in the flow. Electrical probe results are discussed together with optical ones in order to investigate the discharge properties and the temporal structure of the different pulses of electrical current. If air-argon mixtures are used as feeding gas for the discharge, a sharp transition from a hot plume to a cold plasma jet is observed when argon content exceeds 90 %. Characteristics of the source are examined from the point of view of their utility as a tool for plasma treatment of materials. In this respect, a 10 % air in argon mixture corresponds to a promising oxidizing condition, as revealed by the pronounced peak in atomic oxygen emission intensity.
Keywords: Plasma discharges; Spark discharges; Atmospheric pressure plasmas; Plasma diagnostics; Chemical kinetics; Optical emission spectroscopy

Nanostructured ZnO thin films have been deposited on glass substrate at low substrate temperature (200 °C) using the Spray Plasma technique. The zinc nitrate or zinc chloride precursors (droplets) are injected in a low-pressure Ar/O2 radio-frequency inductive discharge. The O2 fraction and the distance between the inductive coil and the substrate holder were varied, and the resulting effect on the deposited film properties was investigated by means of X-ray diffraction, atomic force microscopy, transmittance electron microscopy and UV–visible spectroscopy. It was shown that the c-axis orientation growth depends on these two parameters but not on the precursor nature. The quality of the deposited film is optimal for 5 % O2 in argon when the inductive coil-substrate distance is small. The Ar/O2 plasma was also diagnosed by optical emission spectroscopy. The oxygen atom relative concentration was monitored by optical emission actinometry and the rotational spectrum of OH was recorded to estimate the gas temperature.
Keywords: Zinc oxide; Spray Plasma deposition; Inductively coupled argon–oxygen plasma; Optical emission spectroscopy; X-ray diffraction