Radicals and Ions Formed in Plasma-Treated Organic Solvents: A Mechanistic Investigation to Rationalize the Enhancement of Electrospinnability of Polycaprolactone.

This paper reports and discusses the beneficial effects on the quality of electrospun polycaprolactone nanofibers brought about by pretreatment of the solvent with non-thermal plasma. Chloroform/dimethylformamide 9:1 (CHCl3:DMF 9:1) and pure chloroform were pretreated by a few minute exposure to the plasma generated by an atmospheric pressure plasma jet (APPJ). Interestingly, when pure chloroform was used, the advantages of plasma pretreatment of the solvent were way less pronounced than found with the CHCl3:DMF 9:1 mixture. The chemical modifications induced by the plasma in the solvents were investigated by means of complementary analytical techniques. GC-MS revealed the formation of solvent-derived volatile products, notably tetrachloroethylene (C2Cl4), 1,1,2,2-tetrachloroethane (C2H2Cl4), pentachloroethane (C2HCl5), hexachloroethane (C2Cl6) and, in the case of the mixed solvent, also N-methylformamide (C2H5NO). The chlorinated volatile products are attributed to reactions of ·Cl and Cl-containing methyl radicals and carbenes formed in the plasma-treated solvents. ·Cl and ·CCl3 radicals were detected and identified by EPR spectroscopy analyses. Ion chromatography revealed the presence of Cl-, NO 3 - , and HCOO- (the latter only in the presence of DMF) in the plasma-treated solvents, thus accounting for the observed increased conductivity and acidification of the solvent after plasma treatment. Mechanisms for the formation of these solvent derived products induced by plasma are proposed and discussed. The major role of radicals and ions in the plasma chemistry of chloroform and of the chloroform/dimethylformamide mixture is highlighted. The results provide insight into the interaction of plasma with organic solvents, a field so far little explored but holding promise for interesting applications.

Air non-thermal plasma treatment of Irgarol 1051 deposited on TiO2.

The herbicide 2-(methylthio)-4-(tert-butylamino)-6-(cyclopropylamino)-s-triazine (tradename Irgarol 1051, abbreviated here as Irg), widely used in antifouling paints as biocide inhibiting seaweeds growth, is found in coastal waters in the vicinity of ports and harbors. In this work, Irg was subjected to air non-thermal plasma (NTP) treatment, alone and in the presence of TiO2. A dielectric barrier discharge reactor was used, powered by AC voltage (18 kV, 50 Hz) to produce air-NTP directly above the surface of the aqueous Irg solution to be treated. Due to the very fast degradation of Irg occurring under the experimental conditions used, the results of kinetic experiments failed to detect any rate enhancement due to titania induced photodegradation. We show, however, that pre-adsorption of Irg on titania provides a means to significantly increase Irg NTP-induced degradation throughput, a result which might have useful practical consequences. It is concluded that this phenomenon is due to the acidic character of TiO2 which brings more Irg in solution by increasing the value of the ionization ratio, [IrgH+]/[Irg]. Product analysis, performed by LC/ESI-MSn, allowed us to detect and identify numerous intermediates of Irg degradation and to propose different competing reaction pathways for the investigated NTP induced Irg advanced oxidation process. The extent of mineralization to CO2 was assessed by Total Carbon analysis. It was found to reach 95% after 5 h treatment of Irg solutions with an initial concentration of 5·10-6 M. These results confirm the capability of our NTP prototype reactor to mineralize persistent organic pollutants.