Oxidative degradation of 2,4-xylidine by photosensitization with 2,4,6-triphenylpyrylium: homogeneous and heterogeneous catalysis

• Published in: Chemosphere (Oxford) Vol. 57; no. 9; pp. 1123 - 1130
• Main Authors: Amat, Ana M., Arques, Antonio, Bossmann, Stefan H., Braun, André M., Göb, Sabine, Miranda, Miguel A., Oliveros, Esther
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier Ltd 01-12-2004; Elsevier
• Subjects: 2,4,6-Triphenylpyrylium; 2,4-Dimethylaniline; Aniline Compounds - chemistry; Applied sciences; Benzene Derivatives - chemistry; Catalysis; Chromatography, High Pressure Liquid; Doehlert matrix; Exact sciences and technology; Fluorescence; General purification processes; Heterogeneous photocatalysis; Oxidation-Reduction; Photochemistry; Photodegradation; Pollution; Waste Disposal, Fluid; Wastewaters; Water Purification - methods; Water treatment and pollution; Y-zeolite; Zeolites - chemistry; 2,4-Dimethylaniline; Photodegradation; Wastewaters; Doehlert matrix; Heterogeneous photocatalysis; 2,4,6-Triphenylpyrylium; Y-zeolite; Electron transfer; Modeling; Supported catalyst; Amine; Model compound; Aromatic compound; Oxidation; Photochemical degradation; Radical cation; Photocatalysis; Zeolite; Empirical model; Y- zeolite; Heterogeneous catalysis; Homogeneous catalysis; Physicochemical purification; Kinetics; Waste water purification; Photooxidation
• ISSN: 0045-6535; 1879-1298
• DOI: 10.1016/j.chemosphere.2004.08.029

The possibility of using zeolites containing the 2,4,6-triphenylpyrylium cation as photocatalysts for the degradation of pollutants has been tested on aqueous xylidine (2,4-dimethylaniline) solutions as models for contaminated wastewaters. The influence of the photocatalyst and substrate concentrations on xylidine oxidation has been investigated in homogeneous solution, by performing a series of experiments chosen according to the experimental design methodology (Doehlert uniform array). The empirical models and the corresponding response surfaces obtained from data analysis have been used for simulating and predicting degradation efficiency. The results have shown that conversion increases with increasing amounts of photocatalyst and decreasing concentration of the model pollutant. The fluorescence of 2,4,6-triphenylpyrylium was quenched by xylidine with a rate constant
k
q
of 3.1
×
10
9
M
−1
s
−1. This result suggests a direct electron transfer between the excited pyrylium salt and xylidine. Because of the limited stability of the photocatalyst in homogeneous media, a pyrylium containing Y-zeolite has been tested for the photocatalytic oxidation of xylidine under heterogeneous conditions. The results suggest that the supported catalyst has a much improved stability and that xylidine oxidation rates remain nearly constant during the whole reaction time. An additional advantage of the pyrylium containing zeolite photocatalyst is that it can be recycled and used for further experiments.