Abstract
Photocatalysis holds promise for the removal of NOx from the air, yet its limited selectivity toward desired products (e.g. nitrate ions) hinders its widespread application. In this study, we synthesized and comprehensively characterized amorphous TiO2 microspheres (ATMS), fluoride-etched TMS (F-TMS), and Al2O3-modified F-TMS (Al2O3/F-TMS) photocatalysts. The photocatalytic NOx abatement tests revealed negligible photoactivity for the ATMS, with significant improvement observed after the fluoride ions etching using the hydrothermal method. However, the selectivity of F-TMS for NOx removal remained lower than that of TiO2 P25. The Al2O3/F-TMS photocatalyst exhibited a substantial increase in selectivity. The analysis of NOx abatement results indicated a 2.7-fold boost in selectivity compared to TiO2 P25. A reasonable correlation between the amount of chemically absorbed water and nitrate selectivity was observed. The electron paramagnetic resonance (EPR) disclosed that the fluoride etching induced the formation of intra-band-gap hole-trapping sites and thus enhanced the photocatalytic activity. Nevertheless, the selectivity improvement was mainly attributed to Al2O3's ability to stabilize the NOx oxidation intermediates at the surface for subsequent oxidation to nitrate ions. This study provides valuable insights for tailoring photocatalysts to enhance both activity and selectivity in photocatalytic NOx abatement.
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