Acetaldehyde and acetic acid adsorption on TiO2 under dry and humid conditions

Abstract

Adsorption plays a key role in the volatile organic compound (VOC) photocatalytic oxidation performance and kinetic behavior. It can lead to VOC mixture sequential treatment or even photocatalyst deactivation. The aim of this work is to determine qualitative and quantitative data regarding VOC adsorption on P25 TiO2. Acetaldehyde and acetic acid adsorption on TiO2 have been studied under both dry and humid conditions. Three experimental methods have been used: breakthrough curves, room temperature desorptions and temperature-programmed desorptions. First, acetaldehyde and acetic acid adsorptions are studied individually. Dry and humid experiments provide complementary pieces of information to identify the adsorption modes, in accordance with literature. The Langmuir model parameters (adsorption constant (K), reversible and irreversible maximum adsorbed amounts (qm,rev and qm,irr), and adsorption enthalpy ΔH) are determined for each VOC. Based on experimental results, a model for acetaldehyde and water co-adsorption is proposed, taking into account the specific interaction between acetaldehyde and water molecule. Regarding acetic acid, a reactive adsorption pathway is proposed and a kinetic model is developed to describe the reactive adsorption. Finally, in order to understand multi-VOC interaction on TiO2 surface, the sequential adsorption of acetaldehyde and acetic acid is investigated and confronted with the single-VOC data. As a result, single VOC adsorption parameters are useful to understand and predict multi-VOC photocatalytic oxidation.