Non-uniform spatial distribution of tin oxide (SnO<sub>2</sub>) nanoparticles at the air–water interface

Jordan, Inga; Redondo, Amaia Beloqui; Brown, Matthew A.; Fodor, Daniel; Staniuk, Malwina; Kleibert, Armin; Wörner, Hans Jakob; Giorgi, Javier B.; Bokhoven, Jeroen A. van

doi:10.1039/c4cc00720d

Cited by 19 publications

(22 citation statements)

References 27 publications

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“…6–8, 10–14 The ID for a semi-infinite, structureless slab (a bulk liquid with no structure at the interface) of pure liquid water was calculated from Eq. (1) and is shown in Figure 1 for an emission angle α = 0°.…”

Section: Resultsmentioning

confidence: 99%

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Quantitative interpretation of molecular dynamics simulations for X-ray photoelectron spectroscopy of aqueous solutions

Olivieri

Parry

Powell

et al. 2016

The Journal of Chemical Physics

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Over the past decade, energy-dependent ambient pressure X-ray photoelectron spectroscopy (AP-XPS) has emerged as a powerful analytical probe of the ion spatial distributions at the vapor (vacuum)-aqueous electrolyte interface. These experiments are often paired with complementary molecular dynamics (MD) simulations in an attempt at to provide a complete description of the liquid interface. There is, however, no systematic protocol that permits a straightforward comparison of the two sets of results. XPS is an integrated technique that averages signals from multiple layers in a solution even at the lowest photoelectron kinetic energies routinely employed, whereas MD simulations provide a microscopic layer-by-layer description of the solution composition near the interface. Here we use the National Institute of Standards and Technology database for the Simulation of Electron Spectra for Surface Analysis (SESSA) to quantitatively interpret atom-density profiles from MD simulations for XPS signal intensities using sodium and potassium iodide solutions as examples. We show that electron inelastic mean free paths calculated from a semi-empirical formula depend strongly on solution composition, varying by up to 30 % between pure water and concentrated NaI. The XPS signal thus arises from different information depths in different solutions for a fixed photoelectron kinetic energy. XPS signal intensities are calculated using SESSA as a function of photoelectron kinetic energy (probe depth) and compared with a widely employed ad hoc method. SESSA simulations illustrate the importance of accounting for elastic scattering events at low photoelectron kinetic energies (< 300 eV) where the ad hoc method systematically underestimates the preferential enhancement of anions over cations. Finally, some technical aspects of applying SESSA to liquid interfaces are discussed.

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Section: Resultsmentioning

confidence: 99%

“…5 In liquids, more specifically in aqueous solutions, consensus remains elusive and several publications report substantially different values for the electron IMFP. 6–10 This poor understanding of the electron IMFP limits the ability to quantitatively interpret XPS signal intensities from aqueous solutions.…”

Section: Introductionmentioning

confidence: 99%

Quantitative interpretation of molecular dynamics simulations for X-ray photoelectron spectroscopy of aqueous solutions

Olivieri

Parry

Powell

et al. 2016

The Journal of Chemical Physics

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“…40 (Figure 3c), a solid/liquid (as well as vapor) interface was investigated. 48,49 This work led to the understanding of tin oxide nanoparticles spatial distribution at the water/air interface, 48 as well as the influence of silica colloid nanoparticles surface charge densities ability to regulate its adsorption to the interface. 49 A similar approach can also be used to investigate gas phase reactions with solid aerosol particles through the combination of an aerodynamic lens with APXPS.…”

Section: In Situ/operando Operando Liquid/vapor and Solid/liquid Intementioning

confidence: 99%

X-ray spectroscopy of energy materials under in situ/operando conditions

Crumlin

Liu

Bluhm

et al. 2015

Journal of Electron Spectroscopy and Related Phenomena

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A perspective and brief review of in situ/operando X-ray spectroscopic techniques with focus on energy materials is presented, including discussion on current status, choice of cells and suitable X-ray energy range. Initial discussion focuses on the scientific advancement achieved using ambient pressure X-ray photoelectron spectroscopy (APXPS) at the solid/gas interface, and then progresses through the techniques evolution to probe the liquid/vapor and the emerging solid/liquid interface. This is followed by an overview of soft X-ray adsorption spectroscopy (sXAS) for energy science using both window and windowless cell configurations. Concluding remarks provide a future outlook for where the authors believe these techniques and class of science will progress towards.

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“…On the one hand this complexity originates from our poor understanding of the electron inelastic mean free path (IMFP) in aqueous solution [41][42][43], which in turn limits our ability to quantify the probe depth of the experiment. On the other hand it comes from the complex spatial distributions of NPs at the vacuum-liquid interface [34,35,41,44,45]. Probing deeper into solution not only probes deeper into the NP (like in UHV) but also samples additional NPs whose distributions keep them further below the interface.…”

Section: Xps Depth-profilingmentioning

confidence: 99%

Structure of a Core–Shell Type Colloid Nanoparticle in Aqueous Solution Studied by XPS from a Liquid Microjet

Olivieri

Brown

2016

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With the developments of near ambient pressure photoemission and the liquid microjet, X-ray photoelectron spectroscopy (XPS) measurements at the liquidnanoparticle interface are now possible. This significant advance allows soft matter physicists working in the field of colloid nanoscience the opportunity to perform surface science experiments long deemed impossible. Here we use XPS in conjunction with a liquid microjet to study the electronic and geometric structures of a core-shell type nanoparticle, Al x O y @SiO 2 , suspended in aqueous solution. The Al 2p spectrum is consistent with two unique electronic structures that we assign to neutral sites,[Al-OH, at higher kinetic energy (KE) and to protonated species, [Al-OH 2 ? , at lower KE. The presence of excess positive charge on the nanoparticles surface is additionally confirmed by electrophoretic mobility experiments (positive zeta-potentials). Taking advantage of the quantitative nature of XPS we find *35 % of the Al x O y monolayer is protonated at the pH of the experiment. Finally, we perform additional experiments as a function of photoelectron kinetic energy (depth profiling) and qualitatively determine the Si 2p/Al 2p ratios. We discuss the quantitative limitations to such an experiment in aqueous solution.Keywords X-ray photoelectron spectroscopy Á Near ambient pressure photoemission (NAPP) Á Surface structure Á Solid-liquid interface Á Acid-base equilibrium

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Non-uniform spatial distribution of tin oxide (SnO₂) nanoparticles at the air–water interface

Cited by 19 publications

References 27 publications

Quantitative interpretation of molecular dynamics simulations for X-ray photoelectron spectroscopy of aqueous solutions

Quantitative interpretation of molecular dynamics simulations for X-ray photoelectron spectroscopy of aqueous solutions

X-ray spectroscopy of energy materials under in situ/operando conditions

Structure of a Core–Shell Type Colloid Nanoparticle in Aqueous Solution Studied by XPS from a Liquid Microjet

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Non-uniform spatial distribution of tin oxide (SnO2) nanoparticles at the air–water interface

Cited by 19 publications

References 27 publications

Quantitative interpretation of molecular dynamics simulations for X-ray photoelectron spectroscopy of aqueous solutions

Quantitative interpretation of molecular dynamics simulations for X-ray photoelectron spectroscopy of aqueous solutions

X-ray spectroscopy of energy materials under in situ/operando conditions

Structure of a Core–Shell Type Colloid Nanoparticle in Aqueous Solution Studied by XPS from a Liquid Microjet

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Product

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Non-uniform spatial distribution of tin oxide (SnO₂) nanoparticles at the air–water interface