Relationship between mineralization kinetics and mechanistic pathway during malic acid photodegradation

Abstract

a b s t r a c tThe photocatalytic degradation of malic acid was studied under ambient conditions in an aqueous TiO 2 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 g 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 g 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.

Photocatalytic degradation of malic acid using a thin coated TiO2‐film: Insights on the mechanism of photocatalysis

“…Malonic acid appeared as the main intermediate species formed during malic acid photoconversion. This is in agreement with other research studies published in the literature …”

“…The Langmuir–Hinshelwood (L–H) approach provides a well‐known model to describe the catalytic conversion of chemical species involving adsorption at equilibrium. Several authors have used L–H to represent the heterogeneous photoconversion kinetics of organic species photodegradation onof(check) TiO 2 catalysts . L–H has the advantage of considering not only the model compounds but also the intermediates formed during the photocatalytic conversion.…”

Enhancing the catalytic oxidation capacity of Pt/TiO2 using a light pre-treatment approach

“…Pre-illumination is regularly used to prime the surface of TiO 2 and other semiconductors prior to assessing photocatalytic performance. That is, pre-illumination is often used to oxidise adsorbed carbon species originally present on the semiconductor surface which may interfere with its photocatalytic activity during assessment [15]. To evaluate the impact of light pre-treatment on surface carbon on Pt/TiO 2 , XPS spectra depicting the C 1s core levels before and after illumination are compared in Fig.…”

Overview on oxidation mechanisms of organic compounds by TiO2 in heterogeneous photocatalysis

“…The photocatalytic degradation of malic acid was studied under ambient conditions in an aqueous TiO 2 suspension [32][33][34]. Photogenerated holes and hydroxyl radicals are the oxidizing agents.…”