Photodegradation of single and mixture of parabens – Kinetic, by-products identification and cost-efficiency analysis

• The presence of H2O2 reduced the time required for total degradation of the pollutants.
• The quantum yields and rate constants (based on time and UV fluence) were determined.
• Main by-products were identified and hydroxylation was identified as major pathway.
• Relatively high mineralization was achieved after UVC/H2O2 treatment of parabens mixture.
• UVC/H2O2 is cost-effective method for photodegradation of single and mixture parabens.

Esters of p-hydroxybenzoic acid, commonly known as parabens are preservatives used in a variety of personal care products, cosmetics, pharmaceutical and food products.This paper presents the results of studies on photochemical degradation of hazardous water contaminants – methyl- (MP), ethyl- (EP), propyl- (PP), butyl- (BuP), benzylparaben (BeP) and p-hydroxybenzoic acid (p-HBA) (individually or in mixture) using ultraviolet C lamps in the presence and absence of hydrogen peroxide. Both systems were very efficient on the degradation of the single parent compounds. Total removal of individual pollutant was achieved after 2 h or 6 min for UVC and UVC/H2O2, respectively. The kinetic constants of hydroxyl radicals reaction and the photolysis quantum yields were obtained for each pollutant. The decomposition of the mixture of the six compounds with the H2O2/UVC system ensures a complete degradation after 30 min with a degree of mineralization of 25%. Whereas only 10% of mineralization was observed after the same time for photolysis. The pseudo-first-order fluence-based rate constants (for UVC and H2O2/UVC) for each paraben in the mixture reaction were calculated for the first time. The analysis using UHPLC/MS/MS technique shows that hydroxylation is the main pathway of the reaction with hydroxyl radicals. In fact, p-hydroxybenzoic acid, 2,4-dihydroxybenzoic acid and 3,4-dihydroxybenzoic acid were identified as a major transformation products. Moreover the mono, di and tri derivatives of parabens were detected as the main intermediates formed during oxidation. The fluence-based experimental data and cost analysis showed that the H2O2/UVC treatment was effective in mineralizing of the parabens mixture.

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