X-Ray Absorption Spectroscopy of TiO₂ Nanoparticles in Water Using a Holey Membrane-Based Flow Cell

Many applications of TiO₂ nanoparticles, such as photocatalytic water splitting or water remediation, occur in aqueous environment. However, the impact of solvation on TiO₂ electronic structure remains unclear because only few experimental methods are currently available to probe nanoparticle–water interface. Soft X-ray absorption spectroscopy has been extensively used to characterize the electronic structure of TiO₂ materials, but so far only in vacuum conditions. Here, oxygen K edge and titanium L edge X-ray absorption spectroscopy characterization of TiO₂ nanoparticles measured directly in aqueous dispersion is presented. For this purpose, a new method to probe nanomaterials in liquid using a holey membrane-based flow cell is introduced. With this approach, the X-ray transmission of the membrane is increased, especially in the water window, compared to solid membranes.