Decomposition of carbon tetrachloride in air plasma using glow discharge atomic emission spectrometry†

Abstract

Gas-jet glow discharge atomic emission spectrometry was developed to eliminate toxic contaminants or harmful gases in air flows at low pressure in a low temperature plasma. To find the optimum conditions for removing pollutants from air effectively, the voltage–current relationship, the background spectrum and the spectrum of air with CCl₄ were investigated. In this study, CCl₄ was chosen as an air pollutant owing to its similar molecular structure with respect to the final target toxic gases such as phosgene, diphosgene and CCl₄ itself, which show serious toxicity effects. It was found that the emission spectrum from a glow discharge with CCl₄ in an air flow contains a series of Cl atomic lines in the range from 400 to 500 nm and molecular bands of Cl₂ at 256.4, 307.4 and 510 nm. The emission intensity of each line was investigated with respect to discharge voltage, gas flow and pressure. The spectrum of air under similar conditions was studied for comparison. The emission intensity of each line increases with increase in the discharge current, showing that CCl₄ was effectively decomposed with this kind of discharge. The level of decomposition measured by GC with flame ionization detection before and after the discharge was >96 ± 4%. Also, the emission intensity of the Cl I 452.6 nm line might be used to monitor the decomposition of CCl₄ on a real time basis since the emission intensity of Cl increased linearly as the concentration of CCl₄ increased.