Influence of defect distribution on the reducibility of CeO2-x nanoparticles

Ceria nanoparticles (NPs) are fundamental in heterogeneous catalysis because of their ability to store or release oxygen depending on the ambient conditions. Their oxygen storage capacity is strictly related to the exposed planes, crystallinity, density and distribution of defects. In this work a study of ceria NPs produced with a ligand-free, physical synthesis method is presented. The NP films were grown by a magnetron sputtering based gas aggregation source and studied by high resolution-and scanning-transmission electron microscopy and x-ray photoelectron spectroscopy. In particular, the influence of the oxidation procedure on the NP reducibility has been investigated. The different reducibility has been correlated to the exposed planes, crystallinity and density and distribution of structural defects. The results obtained in this work represent a basis to obtain cerium oxide NP with desired oxygen transport properties.

Synthesis and Characterization of Amphiphilic Gold Nanoparticles

Urszula Beata Cendrowska, Matteo Gasbarri, Zekiye Pelin Güven, Paulo Henrique Jacob Silva, Samuel Thomas Jones, Zhi Luo, Francesco Stellacci

Gold nanoparticles covered with a mixture of 1-octanethiol (OT) and 11-mercapto-1-undecane sulfonic acid (MUS) have been extensively studied because of their interactions with cell membranes, lipid bilayers, and viruses. The hydrophilic ligands make these particles colloidally stable in aqueous solutions and the combination with hydrophobic ligands creates an amphiphilic particle that can be loaded with hydrophobic drugs, fuse with the lipid membranes, and resist nonspecific protein adsorption. Many of these properties depend on nanoparticle size and the composition of the ligand shell. It is, therefore, crucial to have a reproducible synthetic method and reliable characterization techniques that allow the determination of nanoparticle properties and the ligand shell composition. Here, a one-phase chemical reduction, followed by a thorough purification to synthesize these nanoparticles with diameters below 5 nm, is presented. The ratio between the two ligands on the surface of the nanoparticle can be tuned through their stoichiometric ratio used during synthesis. We demonstrate how various routine techniques, such as transmission electron microscopy (TEM), nuclear magnetic resonance (NMR), thermogravimetric analysis (TGA), and ultraviolet-visible (UV-Vis) spectrometry, are combined to comprehensively characterize the physicochemical parameters of the nanoparticles.

JOURNAL OF VISUALIZED EXPERIMENTS2019

Catalytic Fe3+ clusters and complexes in Nafion active in photo-Fenton processes. High-resolution electron microscopy and femtosecond studies

Philippe Buffat, Juan Kiwi, Elena Suvorova Buffat

This study presents the detailed nature of iron clusters formed on Fe3+-Nafion membranes. The catalytic nature of these clusters during immobilized Fenton processes was observed to be a function of the deposition method of Fe ions on the Nafion. The nonbiodegradable azo-dye Orange II and 2-propanol were utilized as convenient organic model compounds in photoassisted Fenton degradation processes. The highest photocatalytic activity was observed when samples were prepared by ion exchange between iron(III) aqua-complexes and H+ or Na+ as counterions of the Nafion SO3- group. Spectroscopic techniques show that iron(III) in the membrane was present mainly as a mononuclear complex of Fe(H2O)(6) and binuclear complexes Fe(H3O2)Fe and Fe-O-Fe. If NaOH or ammonia was added to the former samples prepared by ion exchange, Nafion-Fe membranes with low photocatalytic activity were obtained showing alpha-Fe2O3 and Fe-O-Fe. Detailed high-resolution transmission electron microscopy was carried out for the Nafion-Fe ion-exchariged and also base-treated membranes showing alpha-Fe2O3 nanocrystallites of 3.5-5 nm. Spectral bands were found for iron oxides in the Fe3+-Nafion by femtosecond laser spectroscopy. The alpha-Fe2O3 nanocrystallites in the Nafion exchanged base-treated membranes presented a relaxation dynamics for the excited states close to that observed with alpha-Fe2O3 nanocrystallite colloids taken as reference compounds. Multiexponential transient absorption decay of alpha-Fe2O3 in SO3--water clusters was observed with time constants close to 320 fs, 1.5 ps, and 31 ps after the excitation pulse. Samples of Fe3+-Nafion membranes with-high activity show different transient dynamics relative to the Fe3+-Nafion with low activity. Correlation of the photocatalytic activity of Fe3+-Nafion with UV-vis, Fourier transform infrared, Mossbauer, and X-ray photoelectron spectroscopic results suggests that the photocatalytic activity correlates with the amount of mononuclear Fe(H2O)(6), binuclear complexes Fe(H3O2)Fe and oxo-bridged Fe-O-Fe found in the membranes.

2002

Optical and structural analysis of sol-gel derived Cu-Co-Mn-Si oxides for black selective solar nanocomposite multilayered coatings

Yannik Antonetti, Olivia Valérie Charlotte Bouvard, Thomas Gascou, Marina Aymara González Lazo, Aïcha Hessler-Wyser, Martin Joly, Pierre Loesch, Martin Python, Andreas Schueler

In this paper, we report the preparation of the precursor solutions for the deposition of Cu-Co-Mn-Si oxides by a sot-gel method in order to produce black selective coatings for CSP receiver tubes. Their optical properties were investigated by means of spectroscopic ellipsometry. High Resolution Transmission Electron Microscopy (HRTEM) was used to visualize the microstructure. Time-of-Flight-Secondary-Ion-Mass-Spectroscopy (ToF-SIMS) and X-ray Photoelectron Spectroscopy (XPS) were employed to determine the profile of atomic distribution and their chemical environment in a triple layered coating on a stainless steel (SS) substrate. The studied material shows high potential for the use in multi-layered graded index coatings for solar energy conversion. (C) 2015 Elsevier B.V. All rights reserved.

Elsevier2015

Catalytic Fe3+ clusters and complexes in Nafion active in photo-Fenton processes. High-resolution electron microscopy and femtosecond studies

Philippe Buffat, Juan Kiwi, Elena Suvorova Buffat

2002