title: In Situ Investigations of Laser-Generated Ligand-Free Platinum Nanoparticles by X-ray Absorption Spectroscopy: How Does the Immediate Environment Influence the Particle Surface?
abstract: Pulsed laser ablation in liquid (PLAL) has proven its usefulness as a nanoparticle (NP) synthesis method alternative to traditional chemical reduction methods, where the absence of any molecular ligands or residual reactants makes laser-generated nanoparticles ideal reference materials for charge-transfer experiments. We synthesized additive-free platinum nanoparticles by PLAL and in-situ characterized their interaction with H2O, sodium phosphate buffer, and sodium citrate as well as a TiO2 support by X-ray absorption fine structure (XAFS), i.e., X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS). Differences in the white-line intensity among the colloidal particles in the three liquids indicate that the respective NP-solvent interaction varies in strength. The ions added ex situ diffuse through the particles' electric double layer and interact electrostatically with the Stern plane. Consequently, these ions weaken the interaction of the functional OH groups that are bound to the partially oxidized platinum surfaces and cause their partial reduction. Comparing XAFS spectra of laser-generated Pt NPs in citrate with wet-chemically synthesized ones (both ligand-covered) indicates different types of Pt-O bonds: a Pt(IV)O2 type in the case of wet-chemical NPs and a Pt(II)O type in the case of laser-generated NPs. A comparison of unsupported laser-generated platinum NPs in H2O with TiO2-supported ones shows no white-line intensity differences and also an identical number of Pt-O bonds in both cases. This suggests that in the deposition process at least part of the double-layer coating stays intact and that the ligand-free Pt particle properties are preserved in the TiO2-supported Pt particles, relevant for heterogeneous catalysis.
authors.affiliation: Physikalisches Institut der Universitaet Bonn , Nußallee 12, 53115 Bonn, Germany.|Canadian Light Source, 44 Innovation Boulevard, Saskatoon, SK S7N 2 V3, Canada.
authors.forename: Mathias
authors.initials: M
authors.lastname: Fischer
authors.affiliation: Physikalisches Institut der Universitaet Bonn , Nußallee 12, 53115 Bonn, Germany.|Center for Advanced Microstructures and Devices, Louisiana State University , 6980 Jefferson Highway, Baton Rouge, Louisiana 70806, United States.
authors.forename: Josef
authors.initials: J
authors.lastname: Hormes
authors.affiliation: Technical Chemistry I and Center for Nanointegration Duisburg-Essen (CENIDE) and NanoEnergieTechnikZentrum (NETZ), University of Duisburg-Essen , Universitaetsstr. 7, 45141 Essen, Germany.
authors.forename: Galina
authors.initials: G
authors.lastname: Marzun
authors.affiliation: Technical Chemistry I and Center for Nanointegration Duisburg-Essen (CENIDE) and NanoEnergieTechnikZentrum (NETZ), University of Duisburg-Essen , Universitaetsstr. 7, 45141 Essen, Germany.
authors.forename: Philipp
authors.initials: P
authors.lastname: Wagener
authors.affiliation: Interdisciplinary Center for Analytics on the Nanoscale (ICAN) and Center for Nanointegration Duisburg-Essen (CENIDE) and NanoEnergieTechnikZentrum (NETZ), University of Duisburg-Essen , Carl-Benz-Str. 199, 47057 Duisburg, Germany.
authors.forename: Ulrich
authors.initials: U
authors.lastname: Hagemann
authors.affiliation: Technical Chemistry I and Center for Nanointegration Duisburg-Essen (CENIDE) and NanoEnergieTechnikZentrum (NETZ), University of Duisburg-Essen , Universitaetsstr. 7, 45141 Essen, Germany.
authors.forename: Stephan
authors.initials: S
authors.lastname: Barcikowski