Utilization of ethanol to enhance photocatalytic NOx oxidation and storage on TiO2

Abstract

Nitrogen oxides (NOx), especially nitric oxide (NO) and nitrogen dioxide (NO2) severely affect human health. In this regard, semiconductor photocatalysis present an appealing approach, since the only requirements for this procedure are sunlight, water and oxygen which are naturally abundant. Despite its favorable properties like chemical inertness, long-term stability and low cost, titania (TiO2) has a lower NOx abatement performance due to its low selectivity towards nitrites/nitrates as final product. In this work, we report a simple monohydric alcohol impregnation protocol at mild temperature range to synthesize colored TiO2 nanoparticles for efficient photocatalytic NOx oxidation and storage (PHONOS) application under UVA illumination. The ethanol induced coloration of commercial benchmark TiO2 (P25) and photocatalytic activity for NOx abatement were observed to be dependent on heat-treatment temperature; the highest activity was obtained at 150 °C. Comprehensive analyses of the optimized photocatalyst suggest the presence of surface functionalities of adsorbed formic acid and acetate. The doping of TiO2 with these in situ generated impurities results in the generation of Ti3+ and oxygen vacancies (Vos) (intrinsic defects) which are aimed to be observed using X-Ray Photoelectron Spectroscopy (XPS), Raman Spectroscopy and Diffuse Reflectance UV Visible Spectroscopy (DR-UV-Vis). These fine-tuned materials demonstrated superior photocatalytic performance surpassing conventional P25 benchmark in short (1 h) and long term (15 h) evaluation studies. Special attention has been paid to the selectivity of the designed photocatalyst toward nitrate/nitrite formation and CaO was introduced as NOx storage domains to further improve the stability of best performing photocatalysts for extended time period.