Comparison of Direct and Indirect Effect of Spark Discharge Plasma and UV Lamp Radiation on Water and an Aqueous Solution of Methyl Orange

The oxidation of methyl orange (MO) under the influence of radiation from spark discharge plasma in air and a low-pressure mercury lamp is studied. Two modes of sample processing are compared: the action of radiation on an aqueous solution of MO (mode 1, direct action) and the action of radiation on water, after which the water is mixed with a solution of MO (mode 2, indirect action). The radiation energy of the mercury lamp is ten times greater than the energy of radiation from spark discharge, but the yield of MO oxidation under the action of the mercury lamp is 100 times lesser than the yield under the action of spark discharge radiation. This is due to the difference in the spectrum of radiation and the operating regime (continuous and pulsed). The yields of MO oxidation under the action of spark discharge plasma radiation for modes 1 and 2 are the same and amount to 1.2-1.3 1/(100 eV). This means that active species are first produced in water and then interact with the dissolved substance, indirect mechanism takes place. Under the action of radiation from a mercury lamp, the oxidation yield in mode 2 is zero within the limits of experimental errors, direct mechanism takes place.