期刊
ENVIRONMENTAL TECHNOLOGY
卷 42, 期 4, 页码 609-617出版社
TAYLOR & FRANCIS LTD
DOI: 10.1080/09593330.2019.1639830
关键词
Caffeine; dissolved oxygen; ferrous ion; hydrogen peroxide; photo-Fenton
资金
- Department of Environmental and Chemical Engineering of the University of the Basque Country UPV/EHU
The formation of oxygen in caffeine aqueous solutions happens through self-decomposition reactions of hydrogen peroxide, used as an oxidant in photo-Fenton treatment. Oxygen is not released at concentrations lower than a specific value. As the concentration of catalyst increases, the rate of oxygen generation increases until reaching a peak and then starts to decrease.
Formation of oxygen in the caffeine aqueous solutions occurs through self-decomposition reactions of the hydrogen peroxide, used as an oxidant in the photo-Fenton treatment. The total concentration of hydrogen peroxide used in the treatment would be the contribution of the stoichiometric concentration that reacts with the organic matter ([H2O2](0) = 2.0 mM) and the excess of oxidant that decomposes to oxygen, through radical mechanisms, according to a ratio of 0.8164 mmol H2O2 mg(-1) O-2. When operating at concentrations lower than [H2O2](0) = 2.0 mM, oxygen is not released because there is no excess of oxidant. Moreover, it is verified that the ferrous ion catalyst is oxidized to ferric ion and its subsequent regeneration to ferrous ion. Working at concentrations higher than [H2O2](0) = 2.0 mM, oxygen is released in the water, verifying that the catalyst remains as ferric species, which does not regenerate. The reaction time in which oxygen evolution happpens depends on the concentration of catalyst used in the oxidation, verifying that the highest oxygen generation rates are obtained when applying [Fe](0) = 10.0 mg L-1. Once generated in the water, the maximum concentration of oxygen begins to decrease as the hydrogen peroxide is consumed, until reaching a constant value. The stages of formation and decrease of oxygen are adjusted to zero-order kinetics, estimating the kinetics constants as a function of the catalyst concentration: k(f) = 29.48 [Fe](0)(-1.25) (mg O-2 L-1 min(-1)) and k(d) = -0.006 [Fe](0) (2.0) + 0.244 [Fe](0)-3.69 (mg O-2 L-1 min(-1)). [GRAPHICS] .
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