Degradation of short-chain alkyl- and alkanolamines by TiO2- and Pt/TiO2-assisted photocatalysis

The photooxidation of C2H5NH2, (C2H5)2NH, HOC2H4NH2, (HOC2H4)2NH and (HOC2H4)3N using TiO2 and Pt/TiO2 as photocatalysts has been investigated. A laboratory set up was designed and a study on the influence of the concentration of the photocatalyst, the pH-value and the structure of the amine performed. The photocatalytic process was optimized with respect to the concentrations of the model substances during degradation. The decrease of the amine concentrations was found to be maximum at a pH of 10. The time-dependence of the formation of cationic breakdown products, such as NH3/NH+4 and short-chain alkyl- and alkanolamines was studied by analyses with single column ion chromatography. The experimental data show that the photodegradation follows a Langmuir–Hinshelwood kinetic. The mineralization of the model substances also was monitored by measurements of the decrease of the TOC and of the formation of NO−2 and NO−3. The different mineralization efficiencies for the model substances studied are discussed with regard to their structure and adsorption behaviour on the photocatalyst. A possible breakdown mechanism involving the electrophilic attack of the hydroxyl radical is given. The applicability of the TiO2-assisted photocatalytic degradation of C2H5NH2 and (C2H5)2NH was tested at the pilot plant-scale with real solar radiation. The degradation rates and products obtained were similar to those found in the laboratory experiments.