Water interactions on the surface of 50 nm rutile TiO2 nanoparticles using in situ DRIFTS

Abstract

Deciphering metal oxide nanoparticle surface chemistry has garnered much interest due to its usage in catalytic systems. Considering the pervasive nature of water, hydroxyl coverage is inherent on nanoparticles and much of the nanoparticle reactivity is owed to this hydroxylation. Herein, we examine the reactivity of water with 50 nm rutile TiO2 nanoparticles via in situ diffuse reflectance Fourier transform infrared spectroscopy (DRIFTS) as a function of both temperature and water vapor pressure. The OH stretching region of the spectrum is used to understand and clarify the native surface chemistry of rutile TiO2 nanopowders. The DRIFT spectrum of the rutile nanoparticles exhibits eight stretching hydroxyl vibrations, each of which are easily exchanged with deuterium signifying they are surface moieties. Furthermore, the frequency of each vibrational feature is reproducible between rounds of annealing and water exposure, indicating the types of surface sites available on the surface remain constant. Our insight into the reactivity between water and TiO2 nanoparticles and the reproducibility of the hydroxylated surface will help to inform process such as photocatalysis or heterogeneous catalysis that benefit from the hydroxylated surface for favorable reaction outcomes.