Photochemical degradation of 4-chlorophenol in the aqueous phase using peroxyacetic acid (PAA)

UV/Peracetic Acid for Degradation of Pharmaceuticals and Reactive Species Evaluation

Peracetic acid (PAA) is a widely used disinfectant, and combined UV light with PAA (i.e., UV/PAA) can be a novel advanced oxidation process for elimination of water contaminants. This study is among the first to evaluate the photolysis of PAA under UV irradiation (254 nm) and degradation of pharmaceuticals by UV/PAA. PAA exhibited high quantum yields (Φ_254 nm = 1.20 and 2.09 mol·Einstein^-1 for the neutral (PAA⁰) and anionic (PAA^-) species, respectively) and also showed scavenging effects on hydroxyl radicals (k_{^•OH/PAA⁰} = (9.33 ± 0.3) × 10⁸ M^-1·s^-1 and k_^•OH/PAA^- = (9.97 ± 2.3) × 10⁹ M^-1·s^-1). The pharmaceuticals were persistent with PAA alone but degraded rapidly by UV/PAA. The contributions of direct photolysis, hydroxyl radicals, and other radicals to pharmaceutical degradation under UV/PAA were systematically evaluated. Results revealed that ^•OH was the primary radical responsible for the degradation of carbamazepine and ibuprofen by UV/PAA, whereas CH₃C(═O)O^• and/or CH₃C(═O)O₂^• contributed significantly to the degradation of naproxen and 2-naphthoxyacetic acid by UV/PAA in addition to ^•OH. The carbon-centered radicals generated from UV/PAA showed strong reactivity to oxidize certain naphthyl compounds. The new knowledge obtained in this study will facilitate further research and development of UV/PAA as a new degradation strategy for water contaminants.

Investigation of the Photodegradation of Reactive Blue 19 on P-25 Titanium Dioxide: Effect of Experimental Parameters

The photocatalytic decolorization and degradation of an anthraquinone-based reactive dye, C.I. Reactive Blue 19, was carried out in laboratory-scale experiments with the systematic variation of several operational parameters, including electron acceptor (hydrogen peroxide) concentration, initial pH, use of buffer solution, aeration, and the specific chemical nature of the buffer solution. Photodegradation was performed under simulated natural light, and conditions were chosen to mimic those found in industry. Mineralization and decolorization were monitored by UV-vis spectroscopy and total organic carbon analysis, and kinetics were modelled using an in-series first-order combination mechanism. Reaction products were examined and monitored by high-resolution mass spectrometry. Under the conditions explored, the reaction rate was found to depend not only on pH and electron acceptor concentration, but also on the specific chemical nature of the buffer used.