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Understanding how reaction conditions affect metal-support interactions in catalytic materials is one of the most challenging tasks in heterogeneous catalysis research. Metal nanoparticles and their supports often undergo changes in structure and oxidation state when exposed to reactants, hindering a straightforward understanding of the structure-activity relations using only ex situ or ultrahigh vacuum techniques. Overcoming these limitations, we explored the metal-support interaction between gold nanoparticles and ceria supports in ultrahigh vacuum and after exposure to CO. A combination of in situ methods (on powder and model Au/CeO2 samples) and theoretical calculations was applied to investigate the gold/ceria interface and its reactivity toward CO exposure. X-ray photoelectron spectroscopy measurements rationalized by first-principles calculations reveal a distinctly inhomogeneous charge distribution, with Au+ atoms in contact with the ceria substrate and neutral Au0 atoms at the surface of the Au nanoparticles. Exposure to CO partially reduces the ceria substrate, leading to electron transfer to the supported Au nanoparticles. Transferred electrons can delocalize among the neutral Au atoms of the particle or contribute to forming inert Auδ− atoms near oxygen vacancies at the ceria surface. This charge redistribution is consistent with the evolution of the vibrational frequencies of CO adsorbed on Au particles obtained using diffuse reflectance infrared Fourier transform spectroscopy.

Gadolinium-doped ceria hierarchical gold catalyst shows four-fold TOF increase compared to undoped non-hierarchical system, proving the synergistic effect of doping and structural hierarchy in propane oxidation.

Ru evaporation from the surface of a Ru/CeO2 catalyst is demonstrated.

Functional colloidal nanoparticles capable of converting between various energy types are finding an increasing number of applications. One of the relevant examples concerns light-to-heat-converting colloidal nanoparticles that may be useful for localized photothermal therapy of cancers. Unfortunately, quantitative comparison and ranking of nanoheaters are not straightforward as materials of different compositions and structures have different photophysical and chemical properties and may interact differently with the biological environment. In terms of photophysical properties, the most relevant information to rank these nanoheaters is the light-to-heat conversion efficiency, which, along with information on the absorption capacity of the material, can be used to directly compare materials. In this work, we evaluate the light-to-heat conversion properties of 17 different nanoheaters belonging to different groups (plasmonic, semiconductor, lanthanide-doped nanocrystals, carbon nanocrystals, and metal oxides). We conclude that the light-to-heat conversion efficiency alone is not meaningful enough as many materials have similar conversion efficiencies─in the range of 80-99%─while they significantly differ in their extinction coefficient. We therefore constructed their qualitative ranking based on the external conversion efficiency, which takes into account the conventionally defined light-to-heat conversion efficiency and its absorption capacity. This ranking demonstrated the differences between the samples more meaningfully. Among the studied systems, the top-ranking materials were black porous silicon and CuS nanocrystals. These results allow us to select the most favorable materials for photo-based theranostics and set a new standard in the characterization of nanoheaters.

The thermal stability of Au nanoparticles on ceria support of various morphology (nanocubes, nanooctahedra, and {111}-nanofacetted nanocubes) in oxidizing and reducing atmospheres was investigated by electron microscopy. A beneficial effect of the reconstruction of edges of ceria nanocubes into zigzagged {111}-nanofacetted structures on the inhibition of sintering of Au nanoparticles was shown. The influence of different morphology of Au particles on various ceria supports on the reducibility and catalytic activity in CO oxidation, and CO PROX of Au/ceria catalysts was also investigated and discussed. It was shown, that ceria nanocubes with flat {110} terminated edges are more suitable as a support for Au nanoparticles, used to catalyze CO oxidation, than zigzagged {111}- nanofacetted structures. Graphic Abstract

Control of metal–support interactions is one of the major challenges in heterogeneous catalysis. In this study, we explored the effect of Eu doping on the metal–support interactions in Au/Ce1–xEuxO...

This works presents comprehensive studies on fundamental excitations trapping and the resulting charge destabilization in cubanite AgxS/AgInS2 quantum-confined random alloys. The observed optical activity of defect levels, related to silver alloying, is discussed basing on the femtosecond excited time-resolved photoluminescence spectrograms as well as theoretical predictions obtained via the density functional theory within the reduced cluster model. Impact of the charge trapping on the third-order optical hyper-polarizabilities has also been investigated basing on the two-photon excitation action cross sections. It has been shown that silver induced defects in the AgxS/AgInS2 random alloys are responsible for effective electron/hole trapping and strong temporal charge uncompensation. The silver on indium AgIn, silver interstitials Agi and higher-order defect clusters e.g. (AgIn2--2Agi+) formed effectively due to defect compensation mechanism have been considered in this work as providing possible pathways of defect mediated depopulation of the excited states. The electron/hole trapping mechanism is also discussed as a major mechanism responsible for fast trionic relaxations leading to strong deviation from the first-order decay law and significant temporal red-shifts of the photoluminescence band maximum. Further, it is shown that controlling the silver alloying ratio and the resulting number of defects charge states, it is possible to cause variation of the average photoluminescence decay times by an order of magnitude. The silver alloying was also found as an efficient route for significant increase of the two-photon excitation action cross section.

We demonstrate a low-temperature synthesis of hydrophilic, penicillamine-stabilized hybrid CdS-Au nanoparticles (NPs) utilizing different Au concentrations. The obtained hybrid nanomaterials exhibit photoluminescence quenching and emission lifetime reduction in comparison with their raw semiconductor CdS NPs counterparts. An increase of concentration of Au present at the surface of CdS leads to lower photoluminescence intensity and faster emission decays, suggesting more efficient charge separation when larger Au domains are present. For photocatalysis studies, we performed methylene blue (MB) absorption measurements under irradiation in the presence of CdS-Au NPs. After 1 h of light exposure, we observed the absorbance decrease to about 35% and 10% of the initial value for the CdS-5Au and CdS-7.5Au (the hybrid NPs obtained in a presence of 5.0 and 7.5 mM Au), respectively, which indicates MB reduction caused by electrons effectively separated from holes on metal surface. In further similar photocatalysis experiments, we measured bovine serum albumin (BSA) integrated photoluminescence intensity quenching in the presence of CdS-Au NPs, with a 50% decrease being obtained for CdS-2.5Au NPs and CdS-5Au NPs, with a faster response rate detected for the system prepared with a higher Au concentration. The results suggest hole-driven reactive oxygen species (ROS) production, causing BSA degeneration. Finally, we performed two-photon excited emission (TPEE) measurements for CdS-5Au NPs, obtaining their two-photon absorption (TPA) cross-section values up to 15.8 &times, 103 GM (Goeppert-Mayer units). We conclude that the obtained water-soluble CdS-Au NPs exhibit potential triple functionalities as photocatalysts for reduction and oxidation reactions as well as materials for two-photon absorption applications, so that they may be considered as future theranostics.

Thermally induced reconstruction of ceria nanocubes into {111}-nanofacetted structures was investigated by XRD, TEM and Raman spectroscopy. The beneficial role of reducing atmosphere on the surface reconstruction processes was observed and is discussed. The activity of ceria nanoparticles with various surface morphology in catalytic oxidation of CO was investigated. The order of catalytic activity of the particles: smooth ceria nanocubes > {111}-nanofacetted ceria nanocubes > smooth octahedra correlates with the concentration of Ce3+ - oxygen vacancy pairs determined by Raman spectroscopy.

The effect of Eu doping of ceria nanocubes on the morphology, oxidation state of deposited Au particles and their activity in CO oxidation was studied. The decisive role of doping of ceria support with Eu in the sintering of deposited Au nanoparticles has been established and discussed for the first time. The redispersion of gold nanoparticles is responsible for the formation of small, ca. ~1 nm Au nanoclusters, and as a consequence the increase of the number of active sites participating in CO-oxidation reaction.

Ce1-xEuxO2 nanocubes, with maximum Eu content x = 0.4, were synthesized by a simple hydrothermal method. Application of various experimental techniques (SEM-EDS, STEM-EDS, XPS, ICP-AES) revealed a uniform distribution of Eu and Ce in the nanocubes, but some oxygen depletion near the surface was detected. A model explaining the effect of the Eu doping on the growth of ceria nanocubes by the oriented attachment mechanism is proposed. The oxygen vacancy ordering in high-doped (x [greater-than-or-equal] 0.1) ceria nanoparticles was found, and its effect on the reduction of ceria nanocubes is discussed.

This work presents results of studies on the shape and structural stability of the crystalline ceria-based Ce 1−x Yb x O 2−(x/2) mixed oxides with increasing Yb content (x = 0–0.50). The cube-like, and octahedral nanocrystals of the oxides were synthesized by the hydrothermal method using two different heating methods of the stainless steel Teflon-lined autoclaves — conventional (the heating mantle) and microwave assisted one. It was observed that the predetermined shape of the investigated samples was kept up to x = ~0.2. Above this value, the co-product of synthesis as a rice-like Yb-phosphates have been observed near to octahedron-like Ce 1−x Yb x O 2−(x/2) mixed oxides. In case of cube-like samples, for concentrations of Yb-ions over 20–30%, the shape of crystals starts to be round. Moreover, weaker incorporation of the Yb 3+ -ions into the CeO 2 structure was noticed in case octahedron-like samples than cube-like ones. Additionally, it was found that the mean particle sizes of the octahedral ceria based mixed oxides prepared by the conventional hydrothermal method were larger than the same materials prepared by the microwave assisted method. Thanks to enhanced reducibility at low temperatures and good thermal stability of Ce 1−x Yb x O 2−(x/2) , the investigated oxides are good candidates for catalysts of soot oxidation. For the octahedron-like Ce 0.9 Yb 0.1 O 1.95 the temperature of half oxidation (T 50% = 423 °C) was 154 °C lower than that for non-catalysed oxidation (T 50% = 577 °C). On the other hand, the most stable catalysts were cube-like oxides, both pure and doped ceria (CeO 2 — T Icycle 50% = 438 °C; T IIcycle 50% = 454 °C and Ce 0.9 Yb 0.1 O 1.95 — T Icycle 50% = 435 °C; T IIcycle 50% = 453 °C).