Abstract
Purified water supply for human use, agriculture and industry is the major global priority nowadays. The advanced oxidation process based on atmospheric pressure non-thermal plasma (NTP) has been used for purification of wastewater, although the underlying mechanisms of degradation of organic pollutants are still unknown. In this study we employ two needle-type atmospheric pressure non-thermal plasma jets, i.e., indirect (ID-APPJ) and direct (D-APPJ) jets operating at Ar feed gas, for the treatment of methylene blue, methyl orange and congo red dyes, for two different times (i.e., 20 min and 30 min). Specifically, we study the decolorization/degradation of all three dyes using the above mentioned plasma sources, by means of UV-Vis spectroscopy, HPLC and a density meter. We also employ mass spectroscopy to verify whether only decolorization or also degradation takes place after treatment of the dyes by the NTP jets. Additionally, we analyze the interaction of OH radicals with all three dyes using reactive molecular dynamics simulations, based on the density functional-tight binding method. This investigation represents the first report on the degradation of these three different dyes by two types of NTP setups, analyzed by various methods, and based on both experimental and computational studies.
Highlights
The large number of organic dye pollutants cannot be effectively mitigated by conventional wastewater degradation methods, because the molecular structures of these dyes are very stable and do not degrade
In order to understand the mechanisms of the plasma degradation, we studied the generation of reactive oxygen and nitrogen species (RONS) in water after ID-atmospheric pressure plasma jets (APPJs) and D-APPJ treatment for 30 min, as well as the interaction of OH radicals with the dyes using reactive molecular dynamics (MD) simulations
We can conclude from our study that both plasma devices have the potential to degrade all three dyes (MB, methyl orange (MO) and congo red (CR)), and the extent of decolorization/degradation is quite similar for the different dyes
Summary
The large number of organic dye pollutants cannot be effectively mitigated by conventional wastewater degradation methods, because the molecular structures of these dyes are very stable and do not degrade . In this study we apply two needle-type atmospheric pressure plasma jets (APPJs), i.e., an indirect (ID-APPJ) and a direct (D-APPJ) setup, both operating in Ar gas, for the treatment of methylene blue (MB), methyl orange (MO) and congo red (CR) dyes, for two different times (i.e., 20 min and 30 min). We investigate their decolorization/degradation process using UV-Vis spectroscopy, High-performance liquid chromatography (HPLC) as well as a density meter. We study the interaction of OH radicals with the dyes, by means of reactive molecular dynamics (MD) simulations based on the density functional-tight binding (DFTB) method[24]
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