| AVS 63rd International Symposium & Exhibition | |
| In-Situ and Operando Spectroscopy and Microscopy for Catalysts, Surfaces, & Materials Focus Topic | Thursday Sessions |
| Session IS-ThA |
| Session: | Ambient Pressure Photoelectron Spectroscopy and Scanning Probe Techniques |
| Presenter: | Randima Galhenage, University of California, Irvine |
| Authors: | R.P. Galhenage, University of California, Irvine M.J. Makowski, University of California, Irvine J.M. Langford, University of California, Irvine J.C. Hemminger, University of California, Irvine |
| Correspondent: | Click to Email |
To our knowledge, this is the first attempt to understand a true colloidal titania nanoparticle/water interface using Ambient Pressure X-ray Photoelectron Spectroscopy (AP-XPS). Titania has attracted a significant amount of research interest due to its broad catalytic applications, many of which involve titania nanoparticles in aqueous solution. Therefore, understanding the titania nanoparticle/water interface is critical for the rational development of such systems. Here, we have employed liquid-jet Ambient Pressure X-ray Photoelectron Spectroscopy (AP-XPS) to investigate the solid/liquid interface of 20 nm diameter TiO2 nanoparticles in 0.1M aqueous nitric acid solution. Liquid-jet AP-XPS experiments were conducted at beamline 11.0.2 of the Advanced Light Source at the Lawrence Berkeley National Laboratory. The temperature controlled liquid jet system generates a 25 um diameter liquid beam at a constant flow rate. The jet is irradiated by x-rays of variable photon energies which, therefore, enables us to probe different depths of the solution. Ejected electrons travel through a small aperture and are analyzed by a deferentially pumped electrostatic analyzer. A combination of the Ti2p line shape and the absolute binding energies of Ti2p and O1s reflect a stoichiometric titania lattice and no indication of oxygen vacancies (Ti3+). Further, by increasing the x-ray excitation energy, the difference in O1s binding energies between that of liquid water (O1sliq) and the titania lattice (O1slat) oxygen was measured over an increasing experimental probe depth into the particle. The titania lattice, O1slat, binding energy decreases by 250 meV when probing from the surface into the bulk of the particle. This binding energy difference cannot be accounted for by any other interfacial species as they should have a larger binding energy shifts with respect to the lattice oxygen. Moreover, due to the lack of characteristic Ti3+ signal, it is clear that further dissociation of water does not occur on the colloidal particles during the course of our XPS study. The observed change in binding energy is interpreted as downward band bending at the surface, resulting from accumulated charge on the surface of the titania nanoparticle.