Oxidative decomposition and mineralization of caffeine by advanced oxidation processes: The effect of hybridization

Abstract

The study consists of a detailed investigation of the degradability of the emerging water contaminant-caffeine by homogeneous and heterogeneous Advanced Oxidation Processes (AOP’s), estimation of a synergy index for each hybrid operation thereof, and proposing the most plausible reaction mechanisms that are consistent with the experimental data. It also encompasses evaluation of the effect of the water matrix represented by carbonate species and humic acids, as strong scavengers of hydroxyl radicals. The results showed that single AOP’s such as sonolysis (577 kHz) and photolysis with H 2 O 2 provided complete caffeine elimination, but they were insufficient for the mineralization of the compound. Hybrid AOP’s were considerably more effective, particularly when operated at a heterogeneous mode using commercial TiO 2 . The most effective hybrid process was UV-H 2 O 2 /TiO 2 , which provided more than 75% TOC decay at the minimum test doses of the reagent and catalyst. While the addition of ultrasound to the process significantly increased the rate of caffeine decomposition, it reduced the overall degradation of the compound to 64% in terms of TOC decay. The antagonistic effect was attributed to the formation of excess H 2 O 2 , and the presence of cavity clouds and/or high density layers that inhibited the transmission of UV light. The effect of natural water ingredients was found to reduce the reaction rates, signifying the major contribution of hydroxyl radicals to the destruction of caffeine. The proposed reaction mechanisms based on OH radical attack and the calculated energy barriers were in good agreement with the experimentally detected reaction byproducts.

Preparation of high-crystalline and non-metal modified g-C3N4 for improving ultrasound-accelerated white-LED-light-driven photocatalytic performances

“…The enhancement temperature could accelerate the heat-dependent reaction (Eqs. ( 3 ), ( 4 ) and ( 12 )) 71 – 73 .…”

Degradation of pollutants in water by Fenton-like oxidation over LaFe-catalysts: Optimization by experimental design

“…A high performance liquid chromatograph (HPLC), equipped with an isocratic pump (Jasco PU-980 Intelligent HPLC Pump) and a double on-line detection including an UVvis detector (Jasco Intelligent), was used for quantifying Caf at 272 nm, i.e. at the maximum of Caf absorption reported in the literature [21,30,31]. An ion exchange column (Aminex HPX-87H by Biorad) and a mobile phase consisting of 1.8x10 -3 M sulfuric acid with a flow of 0.8 mL/min were used for the separation of reaction products.…”

Special Issue on “Ultrasound hybridized technologies: A new breathing for sonochemistry”

“…Ziylan-Yavas et al describe in detail the decomposition and mineralization of caffeine, a substance commonly found in wastewater [3] . The authors have employed two well-known oxidative processes affording OH radicals, such as sonolysis (at 577 kHz) and UV-photolysis with H 2 O 2 .…”