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

Abstract

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 we present oxygen K edge and titanium L edge X-ray absorption spectroscopy characterization of TiO2 nanoparticles measured directly in aqueous dispersion. For this purpose, we introduce a new method to probe nanomaterials in liquid using a holey membrane-based flow cell. With this approach, the X-ray transmission of the membrane is increased, especially in the water window, compared to solid membranes.

Water at charged interfaces

“…the application of X-ray spectroscopy techniques to solid and gas phases has a long history 36 , but its use for volatile aqueous phases has been established recently with the introduction of the vacuum liquid microjet technique 261,262 , enabling the acquisition of photoemission spectra from thin aqueous solution films in a ~millibar pressure gas environment. an alternative method that circumvents the exposure of the liquid phase to vacuum uses liquid cells equipped with a few-nanometre-thick membrane to separate the liquid from vacuum 174,[263][264][265] . the membrane is thin enough to transmit the emitted photoelectrons, thus enabling their detection.…”

Enhancement of Ti3C2 MXene Pseudocapacitance after Urea Intercalation Studied by Soft X-ray Absorption Spectroscopy

“…23,24 The high chemical sensitivity of XAS at the Ti L-edge can also be employed in situ in aqueous environments using flow cells with thin X-ray transparent membranes. 20 Probing the MXene Ti chemical environment in different environments is important as electrochemical reactions take place in aqueous media. Nevertheless, XAS in the soft X-ray range has not been applied on MXene so far.…”

“…Furthermore, XAS can be acquired using X-ray photoemission electron microscopy (X-PEEM) to provide XA spectra with 30 nm spatial resolution in vacuum . Pristine Ti 3 C 2 T x MXenes have also been found to be sensitive to oxidation due to a charge transfer that can take place between surface O and Ti atoms. , The high chemical sensitivity of XAS at the Ti L-edge can also be employed in situ in aqueous environments using flow cells with thin X-ray transparent membranes . Probing the MXene Ti chemical bonding in different environments is important as electrochemical reactions take place in aqueous media.…”

Uncovering the Charge Transfer between Carbon Dots and Water by In Situ Soft X-ray Absorption Spectroscopy

“…[10][11][12] However, a major experimental challenge is the apparent contradiction between the generally high vapor pressure of the liquid, especially water, and the vacuum requirement imposed by the short mean free path of photons in the soft X-ray range at ambient conditions. Over the years, various innovative flow cell technologies [13][14][15][16] using membranes to isolate the liquid phase from the vacuum have been devised to enable XAS measurement of liquid samples and nanoparticle dispersions.…”

“…Studying the electronic structure of the liquid environment and aqueous dispersion of nanomaterials under in situ conditions using soft X-ray spectroscopies has attracted substantial attention in recent years. − However, a major experimental challenge is the apparent contradiction between the generally high vapor pressure of the liquid, especially water, and the vacuum requirement imposed by the short mean-free path of photons in the soft X-ray range at ambient conditions. Over the years, various innovative flow cell technologies − using membranes to isolate the liquid phase from the vacuum have been devised to enable XAS measurement of liquid samples and nanoparticle dispersions.…”