The correlation between photocatalytic oxidation performance and chemical/physical properties of indoor volatile organic compounds

In this study, six species of volatile organic compounds (VOCs), n-hexane, iso-butanol, toluene, p-xylene, m-xylene, and mesitylene, were selected as the target pollutants to investigate how the photocatalytic oxidation (PCO) performance is related to their physical/chemical properties. The PCO kinetics were well fit by a Langmuir–Hinshelwood (L–H) model for bimolecular surface reaction and competitive adsorption at gas flow rate above 1000 mL min−1 (reaction-controlling region), where the gas-phase mass transfer effect was negligible. The rate constants of PCO for toluene, p-xylene, m-xylene, and mesitylene ranged from 1.22 to 4.00 μmol m−2 s−1, and were proportional to VOC-hydroxyl radical rate constant (kOH). The Langmuir adsorption constants of the four aromatic VOCs investigated and water ranged from 0.95 to 1.35 ppm−1 and from 5.61×10−3 to 1.44×10−3 ppm−1, respectively. A strongly linear positive relationship was found between the reciprocal of the Langmuir adsorption constants of the four aromatic VOCs investigated and Henryʹs Law constants. Conversely, the reciprocal of Langmuir adsorption constants of water showed a strong negative relationship with Henryʹs Law constants (in units kPa m3 mol−1) of the four aromatic VOCs investigated. The relationships noted above were not found between different classes of VOCs (n-hexane, iso-butanol, and aromatic VOCs investigated). The percentage of residual intermediates (partially oxidized and incompletely mineralized organic compound from the primary VOCs) decreased as the inlet VOCs concentration decreased.