Sono-Photocatalytic Degradation of 4-Clorophenol in Aqueous Solutions

Abstract

The kinetic patterns of oxidative processes involving highly reactive oxygen-containing radicals generated in situ in the aqueous medium affected by acoustic cavitation of the megahertz range (1.7 MHz) and UV radiation (254 nm) are established using 4-chlorophenol as an example. The results indicate the substantial activation of 4-chlorophenol oxidation processes upon both UV irradiation and the combined influence of high-frequency ultrasound of the megahertz range and UV irradiation in the Fenton-like iron-persulfate system Fe²⁺/\({{{\text{S}}}_{{\text{2}}}}{\text{O}}_{8}^{{2 - }}\). Full conversion of 4-chlorophenol in the hybrid oxidative system US/UV/Fe²⁺/\({{{\text{S}}}_{{\text{2}}}}{\text{O}}_{8}^{{2 - }}\) is attained after 60 min of treatment, while the mineralization of the organic substance after 180 min of treatment is 83.2%. The activation of a coupled radical-chain mechanism in the oxidative systems US/UV/Fe²⁺/\({{{\text{S}}}_{{\text{2}}}}{\text{O}}_{8}^{{2 - }}\) and UV/Fe²⁺/\({{{\text{S}}}_{{\text{2}}}}{\text{O}}_{8}^{{2 - }}\) is confirmed by high values of the synergic indices in both cases for the conversion of 4-chlorophenol (φ₁ > 1) and the mineralization of dissolved organic matter (φ₂ ≫ 1). The considered sono- and/or photoinduced oxidative systems can be arranged in the following order according to the effectiveness of the oxidative degradation of 4-chlorophenol US/UV/Fe²⁺/\({{{\text{S}}}_{{\text{2}}}}{\text{O}}_{8}^{{2 - }}\) > UV/Fe²⁺/\({{{\text{S}}}_{{\text{2}}}}{\text{O}}_{8}^{{2 - }}\) ≫ US/Fe²⁺/\({{{\text{S}}}_{{\text{2}}}}{\text{O}}_{8}^{{2 - }}\) > Fe²⁺/\({{{\text{S}}}_{{\text{2}}}}{\text{O}}_{8}^{{2 - }}\) > US/UV.