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Photocatalytic degradation of benzenesulfonate on colloidal titanium dioxide
Authors:Szabó-Bárdos Erzsébet  Markovics Otília  Horváth Ottó  Töro Norbert  Kiss Gyula
Affiliation:a University of Pannonia, Institute of Chemistry, Department of General and Inorganic Chemistry, H-8200 Veszprém, POB. 158, Hungary
b University of Pannonia, Institute of Environmental Sciences, H-8200 Veszprém, POB. 158, Hungary
c Air Chemistry Group of Hungarian Academy of Sciences at University of Pannonia, H-8201 Veszprém, POB. 158, Hungary
Abstract:Titanium dioxide-mediated photocatalyzed degradation of benzenesulfonate (BS) was investigated by monitoring chemical oxygen demand (COD), total organic carbon (TOC) content, sulfate concentration, pH as well as the absorption and emission spectral changes in both argon-saturated and aerated systems. Liquid chromatography-mass spectrometry analysis was utilized for the detection of intermediates formed during the irradiation in the UVA range (λmax = 350 nm). The results obtained by these analytical techniques indicate that the initial step of degradation is hydroxylation of the starting surfactant, resulting in the production of hydroxy- and dihydroxybenzenesulfonates. These reactions were accompanied by desulfonation, which increases H+] in both argon-saturated and aerated systems. In accordance with our previous theoretical calculations, the formation of ortho- and meta-hydroxylated derivatives is favored in the first step. The main product of the further oxygenation of these derivatives was 2,5-dihydroxy-benzesulfonate. No decay of the hydroxy species occurred during the 8-h irradiation in the absence of dissolved oxygen. In the aerated system much more efficient desulfonation and hydroxylation, moreover, a significant decrease of TOC took place at the initial stage. Further hydroxylation led to cleavage of the aromatic system, due to the formation of polyhydroxy derivatives, followed by ring fission, resulting in the production of aldehydes and carboxylic acids. Total mineralization was achieved by the end of the 8-h photocatalysis. It has been proved that in this photocatalytic procedure the presence of dissolved oxygen is necessary for the cleavage of the aromatic ring because hydroxyl radicals photochemically formed in the deaerated system too alone are not able to break the C-C bonds.
Keywords:Benzenesulfonate  Photocatalysis  Titanium dioxide  Oxidative degradation  Intermediates  Oxygenation
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