Photocatalytic degradation of ammonia with TiO2 as photocatalyst in the laboratory and under the use of solar radiation

A laboratory set-up for the photocatalytic degradation of NH3/NH4+ was designed. It includes a tube reactor (volume 12.3 ml) and a Xe-lamp (lambda > 300 nm) as irradiation source. Suspended TiO2 powder was used as photocatalyst. For the on-line determination of NH3 a gas-sensing probe was shown to be useful down to the lower mg/l level (detection limit: 2.2 . 10(-6) mol/l). After optimization a breakdown of NH3/NH4+ at the 5 . 10(4) mol/l level for up to 70 % after 6 h if irradiation could be realized. The influence of the pH, the TiO2 concentration, the temperature and the flow rate on the degradation of NH3/NH4+ was examined. The anionic degradation products, which were found to occur beside the N-2 itself, were determined by single column ion chromatography (SCIC). As a function of the pH and the concentration of TiO2 variable concentrations of NO2- and NO3- were found (optimum: 9.9 % and 19.0 % of the decomposed NH3/NH4+ or 4.0 and 7.3 % of the NH3/NH4+ originally present). Experiments with solar radiation were carried out in a parabolic trough reactor at pilot plant-scale and were found to give degradation rates and reaction products similar to those obtained with the laboratory set-up. (C) 1997 Elsevier Science Ltd.