Structure–activity relationship of surface hydroxyl groups during NO2 adsorption and transformation on TiO2 nanoparticles

Abstract

The role of hydroxyl groups (OH) is significant in understanding the surface reactions on oxides. Here we combined spectroscopic experiments and theoretical calculations to reveal the role of OH in the heterogeneous reactions of NO₂ on TiO₂ nanoparticles with various crystal structures. The interaction between OH and NO₂ was determined to be a critical step, giving rise to the formation of surface HNO₃. HNO₃ was found to be either a stable product on amorphous TiO₂, or an important intermediate of nitrate on anatase due to its further reaction with nearby OH. The lack of surface OH on rutile limited its reactivity toward NO₂. This study presents clear evidence that the reactivity of TiO₂ toward NO₂ greatly depends on the surface OH as well as the crystalline form. Considering the ubiquitous presence of TiO₂ nanoparticles in catalysts and in natural environments, our results could provide insights helpful to future research in both environmental catalysis and atmospheric chemistry.