Plasma Chemistry and Plasma Processing (v.33, #6)

Decomposition of aqueous dichlorophenols and trichlorophenols was investigated by means of contact glow discharge electrolysis. With the decay of chlorophenols (CPs), the amount of total organic carbon (TOC) in water also decreased smoothly, indicating that carbon atoms of benzene nucleus could be eventually converted to inorganic carbons. And, it was found that chlorine atoms in the CPs were released as chloride ions. As the by-products, oxalate and formate were formed. The chlorine derivatives of 1,4-hydroquinone and 1,4-benzoquinone were detected as the primary intermediates in the initial stage of decomposition of each of CPs. The decay of both CPs and TOC obeyed the first-order rate law, respectively. The apparent rate constants for the decay of CPs increased with the decrease in pKa values of CPs, while those for the decay of TOC were substantially unaffected.
Keywords: Chlorophenols; Decomposition; Contact glow discharge electrolysis; First-order rate law; pKa

p-Nitrophenol Enhanced Degradation in High-Voltage Pulsed Corona Discharges Combined with Ozone System by Hongai Zheng; Yi Guo; Hui Zhu; Dazhao Pan; Lili Pan; Jianshe Liu (1053-1062).
Degradation of p-nitrophenol (PNP) in aqueous solution by high-voltage pulse corona discharges (HVPD) combined with ozone was investigated in this study. Experimental results showed that 96 % of PNP (380 mg/L) can be degraded within 30 min using a combined technology. Additionally, the effects of initial concentration of PNP, synergistic effect of both techniques, and pH of the aqueous solution on PNP degradation were evaluated. This combined technology achieved better results than using two mineralization techniques in series which indicates that synergistic effect of HVPD and ozone promoted pollutant decomposition. On the other hand, weak alkalinity was favorable for PNP removal. In the end, intermediate products resulting from PNP degradation processes were analyzed by ion chromatography and high performance liquid chromatography-tandem mass spectrometry. Main intermediate products, including p-benzoquinone, nitro benzoquinone, trans-muconic acid, maleic acid, acetic acid, formic acid, NO2 and NO3 were identified. It was proposed a possible reaction pathway.
Keywords: High-voltage pulse corona discharges (HVPD); Ozone; Synergistic; p-Nitrophenol (PNP); Degradation; Plasma

The degradation of aqueous solutions containing azo dyes (ortho-, meta-, and para-methyl red) was carried out by means of atmospheric pressure plasma treatment. As evidenced by optical emission spectroscopy, the metastable argon in the discharge is responsible for initiating reactions in dye solutions. The bleaching of aqueous solutions is attributed to the destruction of dye molecules as observed in the UV–visible absorption spectra. We found that the degradation pathways of methyl red critically depend on the pH values in aqueous solutions as well as isomeric structures. The reaction pathways are entirely different in basic (pH = 11), near-neutral (pH = 6), and acidic conditions (pH = 2). Kinetic analysis shows that acidic condition gives the fastest degradation rates of methyl red isomers with removal rate: ortho > meta > para among all conditions. At basic condition, the degradation rates are equally slow for all methyl red isomers.
Keywords: Atmospheric pressure plasma; Methyl red; UV–visible absorption

The performance of NiO, MnO2, CeO2, Fe2O3, and CuO catalysts on alumina in removing toluene from a gas stream was studied in a plasma catalysis system. The NiO catalyst performed better than the other catalysts, generating more toluene-destroying oxygen species by decomposing ozone. The optimum nickel loading in the NiO/γ-Al2O3 catalyst was approximately 5 wt%, close to the monolayer dispersion threshold of NiO on γ-Al2O3. The presence of water vapor had a negative effect on catalytic performance due to its quenching of high speed electrons and its competition with toluene for adsorption sites. Water vapor also reduced the outlet ozone concentration by inhibiting the production of key intermediate in the ozone formation process.
Keywords: Nickel oxide; Plasma catalysis; Toluene conversion; Monolayer dispersion threshold; Water vapor

Ozone-Assisted Catalysis of Toluene with Layered ZSM-5 and Ag/ZSM-5 Zeolites by Hyun-Ha Kim; Masami Sugasawa; Hiroshi Hirata; Yoshiyuki Teramoto; Katsunori Kosuge; Nobuaki Negishi; Atsushi Ogata (1083-1098).
This paper presents a new type of ozone-assisted catalysis for toluene decomposition. The different catalytic activities of ZSM-5 and Ag/ZSM-5 were incorporated into a layered catalyst with a tandem configuration. Instead of increasing the amount of metal catalyst, the layered catalyst was formed, which had an equal amount of bare ZSM-5 and Ag/ZSM-5 and could achieve both high toluene conversion and CO2 selectivity concurrently. The properties of each catalyst were evaluated with respect to toluene conversion, formation of intermediates, CO2 selectivity and ozone demand factor. The bare ZSM-5 exhibited higher toluene conversion than the Ag/ZSM-5, while its activity toward deep oxidation was limited. However, the Ag/ZSM-5 was found to be effective for the deep oxidation of reaction intermediates (HCOOH and CO). Separate oxidation tests with HCOOH and CO revealed that the ZSM-5-supported Ag nanoparticles could oxidize the HCOOH and CO in the absence of ozone, which was not possible with the bare ZSM-5. Plausible pathways for the oxidation of toluene with O3 over ZSM-5 and Ag/ZSM-5 were proposed based on the experimental evidence.
Keywords: Ozone-assisted catalysis; VOC; Layered catalyst; Ag/ZSM-5

Decomposition of Trimethylamine by an Electron Beam by Youn-Suk Son; Pillheon Kim; Jun Hyung Park; Junghwan Kim; Jo-Chun Kim (1099-1109).
To identify the decomposition characteristics of trimethylamine (TMA) by electron beam (EB), we conducted an experiment based on process parameters, including absorbed dose (2.5–10 kGy), background gas (air, O2, N2 and He), water content (1,200, 14,300, and 27,500 ppm), initial concentration (50, 100, and 200 ppm) and reactor type (batch or continuous flow system). Air background gas showed a maximum TMA removal efficiency of 86 % at 10 kGy and that was the highest efficiency of all background gases. Energy efficiencies were higher when the absorbed dose was lower (e.g., 2.5 kGy). Decomposition efficiencies of all initial TMA concentrations were approximately >90 % at 10 kGy. Removal efficiencies increased up to 30 % as water vapor increased. As a by-product, it is observed that CH3 radical formed by EB irradiation was converted into CH4 by reaction with residual TMA, (CH3)2NH, and H. These results suggest that EB technology can be applied for TMA treatment under low concentration and high flow rate conditions.
Keywords: Electron beam; Trimethylamine; By-products; Odorous compounds; CH3 radical

A new in-flight glass melting technology with induction thermal plasmas was developed to reduce the energy consumption and the emissions of greenhouse gases for glass production. The effects of carrier gas on the in-flight melting behavior of granulated alkali-free raw material were investigated by various modern analyses. Results show that the particles have smooth spherical surface and compact structure after heat treatment. As the carrier gas flow rate increases, the vitrification degree decreases and the average diameter increases. Higher vitrification results in more shrinkage of particle. The carbonates in raw material decompose completely during in-flight melting. The highest volatilization of B2O3 is attributed to more heat transferred from plasmas to particles at the lowest carrier gas flow rate.
Keywords: Induction thermal plasmas; In-flight melting; Heat transfer; Alkali-free glass

We present numerical simulation of the nitrogen atmospheric pressure plasma jet (APPJ) using three fluid models—namely, laminar model, modified laminar model, and turbulent (k-ε) model—coupled with gas-phase reaction kinetics. The spatial profiles of the light emission intensities, gas temperature, and NO density predicted by the turbulent model show a better agreement with the experimental observations, compared with laminar and modified laminar models. We have demonstrated that the turbulent model shows more oxygen entrainment, more mixing with the ambient air, and a lower axial velocity at the downstream. These allow the turbulent model to more precisely capture the APPJ characteristics than the laminar and modified laminar models do.
Keywords: Atmospheric pressure plasma; Nitrogen plasma; Turbulent and laminar jet; Numerical simulation

Surface Modification of Absorbable Magnesium Stents by Reactive Ion Etching by E. Galvin; M. M. Morshed; C. Cummins; S. Daniels; C. Lally; B. MacDonald (1137-1152).
The surface texture and chemistry of WE43 absorbable magnesium stents (AMS) and tube specimens processed by chemical and reactive ion etching (RIE) were investigated. Tube specimens were produced in three different conditions, namely as-received, chemically etched and plasma etched. The results of scanning electron microscopy, atomic force microscopy and energy dispersive X-ray spectroscopy studies showed that plasma etching and cleaning reduced surface roughness by 10 % compared to chemical etching alone, and completely removed surface deposits remaining from the chemical etch process. The same combination of chemical and plasma etching processes was employed to produce AMS. Expansion tests demonstrated uniform stent expansion characteristics and confirmed the viability of the device. The results of this study show that RIE is an effective surface modification technique for absorbable magnesium devices.
Keywords: Reactive ion etching (RIE); Plasma etching; Chemical etching; Magnesium alloy WE43; Absorbable stents

To improve the biocompatibility of poly(tetrafluoroethylene-co-hexafluoropropylene) (FEP) film, a technique based on Ar plasma pretreatment and UV-induced grafting polymerization was used to immobilize carboxymethyl chitosan (CMCS) on the FEP film surfaces. Initially Ar plasma was used to treat FEP film. Then, plasma treated FEP film was modified via UV-induced grafting polymerization with hydrophilic acrylic acid (AAc) monomer. The following immobilization of CMCS on the FEP-pAAc surface was carried out via an amidation reaction. The change of chemical composition and surface morphology of FEP film were characterized by attenuated total reflectance Fourier transform infrared (ATR-FTIR), X-ray photoelectron spectroscopy (XPS), scanning electronic microscopy (SEM) and atomic force microscopy (AFM). Results of water contact angles measurement showed that the hydrophilicity of the surface has improved significantly after surface modification. Furthermore, methyl thiazolyl tetrazolium (MTT) assay and cell morphology analysis confirmed that mouse fibroblasts (L929 cells) attachment and proliferation were improved remarkably on the modified FEP surface. These results suggest that CMCS were successfully employed to surface engineering FEP film, and enhanced its cell biocompatibility. The approach presented here may be exploited for surface modification of biomaterials.
Keywords: Plasma treatment; UV-induced grafted polymerization; Carboxymethyl chitosan; Amidation reaction; Cytocompatibility

Laser Based Optical Emission Studies of Zinc Oxide (ZnO) Plasma by M. Hanif; M. Salik; M. A. Baig (1167-1178).
We present the optical emission characteristics of the zinc oxide (ZnO) plasma produced by the first (1,064 nm) and second (532 nm) harmonics of a Q switched Nd: YAG laser. The target material was placed in front of laser beam in air (at atmospheric pressure).The experimentally observed line profiles of neutral zinc (Zn I) have been used to extract the electron temperature using the Boltzmann plot method, whereas, the electron number density has been determined from the Stark broadening. The electron temperature is calculated by varying distance from the target surface along the line of propagation of plasma plume and also by varying the laser irradiance. Beside we have studied the variation of number density as a function of laser irradiance as well as its variation with distance from the target surface. It is observed that electron temperature and electron number density increases as laser energy is increased.
Keywords: Zinc oxide plasma; Laser ablation; Optical emission spectroscopy; Electron temperature; Electron number density