Analysis of Energetic Species Caused by Contact Glow Discharge Electrolysis in Aqueous Solution

Contact glow discharge electrolysis is a non-Faradaic electrochemical process with an abnormal relationship between the current and voltage. Hydroxyl radicals, hydrogen radicals and hydrogen peroxide can be produced under the glow discharge, which are often used to degrade organic contaminants in aqueous solution. In this study, with 4-nitrophenol taken as an example of contaminants and tert-butanol as a scavenger of hydroxyl radicals, the role of energetic species in degrading organic compounds was examined in detail. Moreover, the effects of the applied voltage, solution conductivity and pH on the formation of three energetic species were also observed. The formation rate constants of the three energetic species were calculated based on the experimental data.

Oxidative Degradation of o-Chlorophenol with Contact Glow Discharges in Aqueous Solution

Contact glow discharge electrolysis (CGDE) of o-chlorophenol (2-CP) was investigated under different pH, voltages and initial concentrations. And the mechanism of the oxidation was explored. The results suggested that the degradation followed the first order kinetic law; Fe2+ had a remarkable catalytic effect on the removal rate of o-chloropenol. In the presence of Fe2+, 2-CP underwent an exhaustive degradation, from which the major intermediates included o-dihydroxybenze, p-hydroxybenze, p-benzoquione and carboxlic acids.

Degradation of Chloroanilines in Aqueous Solution by Contact Glow Discharge Electrolysis

Contact glow discharge electrolysis of some chloroanilines in sodium sulfate was investigated in different initial concentrations. Each of them underwent the dechlorination, deam-ination through oxidative degradation, and were eventually decomposed into hydrogen carbonate and carbon dioxide. It was testified that the chlorine atom and amidogen could be transformed into chloride ion and nitrite ion, respectively. Fe2+ has a remarkable catalytic effect on the degradation of them. On the basis of the detailed analysis of the intermediate products and kinetic behaviors, the reaction pathway was proposed, in which the attack of hydroxyl radical on the benzene ring of starting material might be a key step.

Degradation of Methyl Orange in Water by Contact Glow Discharge Electrolysis

The degradation of methyl orange in a neutral phosphate buffer solution was investigated by means of contact glow discharge electrolysis （CGDE）. The methyl oranges were degraded and eventually decomposed into inorganic carbon when CGDE was conducted under the applied DC voltage of 480 V and current of ca. 80 mA. As the intermediate products, some phenolic compounds were detected as well as carboxylic acids. Experimental results showed that the oxidation process followed the first-order reaction law. Based on the analysis of the ultraviolet （UV） spectra of the solution and the intermediate products from High Pressure Liquid Chromatography-Mass Spectrum （HPLC-MS）, the reaction pathway was proposed. The attack of hydroxyl radicals was considered to be a key step to start the whole oxidation process.

The Role of Fe(Ⅱ)in the Contact Glow Discharge Electrolysis

In this paper, we use methyl violet as a model organic substrate in wastewater to study the effect of Fe（Ⅱ） ion on the contact glow discharge electrolysis （CGDE）. The decoloration rate and the COD （Chemical Oxygen Demand） value have been examined. It is found that the presence of Fe（Ⅱ） ion can accelerate obviously the degradation of methyl violet, because it reacts with H2O2 in the CGDE process to yield hydroxyl radical, just acting as a Fenton-like reagent. Moreover, the optimal conditions for decoloring methyl violet were obtained, by means of an orthogonal experiment, to be [Fe^2＋] =1×10^-3 mol/L, applied voltage of 700 V of and pH = 9.0.

Mineralization of aqueous pentachlorophenolate by anodic contact glow discharge electrolysis

Exhaustive mineralization of pentachlorophenolate ion（PCP） in phosphate buffer was carried out using anodic contact glow discharge electrolysis（CGDE）,in which plasma was sustained between the electrolyte and anode.During CGDE,PCP degraded smoothly.The amount of total organic carbon decreased significantly,indicating the eventual conversion of the carbon atoms of benzene nucleus to inorganic carbons.Furthermore,chlorine atoms in PCP were liberated as chloride ions.As a primary intermediate product,2,3,5,6tetrachloro-1,4-benzoquinone was detected,and oxalate and formate as byproducts were also found.It was revealed that disappearance of PCP obeyed first-order kinetics.The reaction rate was generally unaffected by both O2 and inert gases in the cell,although it decreased by raising initial pH of solution.In addition,a plausible reaction pathway involving hydroxyl radical was proposed.

Destruction of 4-phenolsulfonic acid in water by anodic contact glow discharge electrolysis

Destruction of 4-phenolsulfonic acid （4-PSA） in water was carded out using anodic contact glow discharge electrolysis. Accompanying the decay of 4-PSA, the amount of total organic carbon （TOC） in water correspondingly decreased, while the sulfonate group of 4- PSA was released as sulfate ion. Oxalate and formate were obtained as minor by-products. Additionally, phenol, 1,4-hydroquinone, hydroxyquinol and 1,4-benzoquinone were detected as primary intermediates in the initial stages of decomposition of 4-PSA. A reaction pathway involving successive attacks of hydroxyl and hydrogen radicals was assumed on the basis of the observed products and kinetics. It was revealed that the decay of both 4-PSA and TOC obeyed a first-order rate law. The effects of different Fe ions and initial concentrations of 4-PSA on the degradation rate were investigated. It was found that the presence of Fe ions could increase the degradation rate of 4-PSA, while initial concentrations lower than 80 mmol/L had no significant effect on kinetic behaviour. The disappearance rate of 4-PSA was significantly affected by pH.

Study on Glow Discharge Plasma Used in Polyester Surface Modification

To achieve an atmospheric pressure glow discharge（APGD）in air and modify the surface of polyester thread using plasma,the electric field distribution and discharge characteristics under different conditions were studied.We found that the region with a strong electric field,which was formed in a tiny gap between two electrodes constituting a line-line contact electrode structure,provided the initial electron for the entire discharge process.Thus,the discharge voltage was reduced.The dielectric barrier of the line-line contact electrodes can inhibit the generation of secondary electrons.Thus,the transient current pulse discharge was reduced significantly,and an APGD in air was achieved.We designed double layer line-line contact electrodes,which can generate the APGD on the surface of a material under treatment directly.A noticeable change in the surface morphology of polyester fiber was visualized with the aid of a scanning electron microscope（SEM）.Two electrode structures-the multi-row line-line and double-helix line-line contact electrodes-were designed.A large area of the APGD plasma with flat and curved surfaces can be formed in air using these contact electrodes.This can improve the efficiency of surface treatment and is significant for the application of the APGD plasma in industries.