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Automated on-line monitoring of the TiO2 based photocatalytic degradation of dimethyl phthalate and diethyl phthalate

Abstract

A fully automated on-line system for monitoring the TiO2 based photocatalytic degradation of dimethyl phthalate (DMP) and diethyl phthalate (DEP) using sequential injection analysis (SIA) coupled to liquid chromatography (LC) with UV detection was proposed. The effect of type of catalyst (sol-gel, Degussa P25 and Hombikat), amount of catalyst (0.5, 1.0 and 1.5 g L-1), and the solution pH (4, 7 and 10) were evaluated through a three-level fractional factorial design (FFD) to verify the influence of the factors on the response variable (degradation efficiency, %). As a result of FFD evaluation, the main factor that influences the process was type of catalyst. Degradation percentages close to a 100 % under UV-vis radiation were reached using two commercial TiO2 materials, which present mixed phases (anatase/rutile), Degussa P25 (82 %/18 %) and Hombikat (76 %/24 %). A 60 % of degradation was obtained using the laboratory-made pure anatase crystalline TiO2 phase. The pH and amount of catalyst showed minimum significant effect on the degradation efficiencies of DMP and DEP. The greater degradation efficiency was achieved using Degussa P25 at pH 10 with 1.5 g L-1 catalyst dosage. Under these conditions a complete degradation and 92 % mineralization was achieved after 300 min of reaction. Additionally, a drastic decrease in the concentration of BOD5 and COD was observed, which results in significant enhancement of its biodegradability obtaining after the photocatalytic treatment a BOD5/COD index of 0.66. The main intermediate products found were dimethyl 4-hydroxyphthalate, 4-hydroxy-diethyl phthalate, phthalic acid and phthalic anhydride indicating that the photocatalytic degradation pathway involved hydrolysis reaction of the aliphatic chain and hydroxylation of the aromatic ring, obtaining products with lower toxicity than the initial molecules.

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Publication details

The article was received on 13 Jul 2018, accepted on 10 Sep 2018 and first published on 11 Sep 2018


Article type: Paper
DOI: 10.1039/C8PP00307F
Citation: Photochem. Photobiol. Sci., 2018, Accepted Manuscript
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    Automated on-line monitoring of the TiO2 based photocatalytic degradation of dimethyl phthalate and diethyl phthalate

    D. Salazar-Beltrán, L. Hinojosa-Reyes, F. Maya, G. Turnes Palomino, C. Palomino Cabello, A. Hernandez-Ramirez and J. L. Guzmán-Mar, Photochem. Photobiol. Sci., 2018, Accepted Manuscript , DOI: 10.1039/C8PP00307F

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