Photocatalytic degradation of citric acid under different conditions: TiO sub(2) heterogeneous photocatalysis against homogeneous photolytic processes promoted by Fe(III) and H sub(2)O sub(2)

• Published in: Applied catalysis. B, Environmental Vol. 71; no. 3-4; pp. 117 - 124
• Main Authors: Quici, Natalia, Morgada, Maria E, Gettar, Raquel T, Bolte, Michele, Litter, Marta I
• Format: Journal Article
• Language: English
• Published: 01.02.2007
• Subjects: Indexing in process; Q1
• ISSN: 0926-3373
• DOI: 10.1016/j.apcatb.2006.09.001

Degradation of citric acid (Cit) at relatively high concentrations by photocatalysis over TiO sub(2) under air bubbling and near UV-light was tested under different conditions. The reaction was improved by addition of H sub(2)O sub(2), Fe(III) or both. Minor amounts of H sub(2)O sub(2) were effective to enhance the oxidation and the mineralization. H sub(2)O sub(2) addition impacts more on the initial rate, while the effect of Fe(III) is more important after prolonged irradiation. The kinetic profiles were analyzed and compared, and the best ratio of reagents was found (1:1:1 H sub(2)O sub(2)/Cit/Fe molar ratio). However, a lower amount of Fe (1:1:0.2 H sub(2)O sub(2)/Cit/Fe ratio) was also effective. Similar experiments under the optimal conditions in the absence of TiO sub(2) were performed for comparison. When both H sub(2)O sub(2) and Fe(III) were present, the behavior with and without TiO sub(2) was very similar. So far, 3-oxoglutaric acid was detected as a reaction intermediate. A mechanistic analysis is initiated to explain some features of these complex systems.