Optical characterization of non-thermal plasma jet energy carriers for effective catalytic processing of industrial wastewaters.

An argon plasma jet was sustained in open air and characterized for its chemical composition. The optically characterized plasma jet was used to treat industrial wastewater containing mixed textile dyes and heavy metals. Since plasma jet produces UV-radiations, the photocatalytic TiO2 was used to enhance plasma treatment efficiency especially for degradation of dyes. Mixed anatase and rutile phases of TiO2 (5.2–8.5 nm) were produced through surfactant assisted sol–gel approach. The emission spectrum confirmed the presence of excited argon, OH, excited nitrogen, excited oxygen, ozone and nitric oxide in the plasma jet. The spectral lines of excited Ar, NO, O3, OH−, N2, $${\mathrm{N}}_{2}^{+}$$ , O, $${\mathrm{O}}_{2}^{+}$$ and O+ species were observed at wavelength of 695–740 nm, 254.3 nm, 307.9 nm, 302–310 nm, 330–380 nm, 390–415 nm, 715.6 nm, 500–600 nm and 400–500 nm. These reactive species decompose the organic pollutants and separate the heavy metals from the water samples. The conductivity of plasma exposed water samples increased while pH and hardness decreased. The atomic absorption spectrophotometry analysis confirmed the presence of heavy metals in the samples, which were effectively removed through plasma treatment. Finally, the effect of plasma treatment on Staphylococcus aureus strains was more pronounced than Escherichia coli strains.