A novel nanotubular TiO2-based Plug-Flow reactor for gas phase photocatalytic degradation of toluene

In this study, a novel annular plug flow reactor (PFR) with built-in nanotubular TiO2 obtained via anodizing was tested for the photocatalytic degradation of toluene. The oxide was grown directly on a titanium substrate by anodizing, as this method implies no risk of nanoparticles release in the environment during or after the photocatalytic process. Experiments were carried out in presence of an UV-A light source by modulating relative humidity, gas concentration and flow rate, to evaluate possible applications in indoor and industrial environments. The photocatalytic system demonstrated high photodegradation efficiency up to 90% for an inlet toluene concentration of 10 ppm, thus showing potential applications in mildly polluted environments, such as homes, offices and up to more severely polluted ones like offset printing plants, automobile manufacturing industries or even professional kitchens, where the exposure to cooking oil fumes is significant. In case of high toluene concentration, the initial degradation percentage falls in a range between 60 and 70%; subsequently, the instant degradation shows a gradual decrease ascribed to photocatalyst deactivation, which occurred due to the accumulation of recalcitrant by-products on the adsorption sites, thus highlighting some limitations for industrial applications when selected VOCs are present; nonetheless, the photocatalyst regained its initial activity through a simple photocatalyst reactivation process, leading to a maximum instant degradation percentage up to 90% for an inlet toluene concentration of 20 ppm.