Relationship between mineralization kinetics and mechanistic pathway during malic acid photodegradation

The photocatalytic degradation of malic acid was studied under ambient conditions in an aqueous TiO2 suspension. The results demonstrated the presence of four distinct mineralization rate variations over the course of its degradation. Differences in the mineralization rate were governed by the dominant intermediate present in the solution at that time. Initial mineralization was rapid (∼175 μg C/min) resulting from the swift extraction of a carbon from strongly adsorbed malic acid via the photo-Kolbe mechanism. The mineralization rate then slowed down (∼50–70 μg C/min) with the continued formation of an intermediate product (believed to be malonaldehydic acid), malonic acid and acetic acid in the solution. The findings provide greater insight into the photocatalytic degradation mechanism, illustrating the importance of intermediates and their attributes in relation to the overall rate of organic removal.

. Changes in the malic acid mineralization rate during photooxidation illustrate the importance of intermediates and their attributes in relation to the overall organic removal rate.Figure optionsDownload high-quality image (124 K)Download as PowerPoint slideResearch highlights▶ Malic acid mineralization profile possesses varying mineralization rates. ▶ The mineralization rates depend on the dominant intermediate present in the solution. ▶ The affinity of the intermediates to TiO2 surface together with their structure affect the mineralization kinetics.