A 2D-3D structure transition of gold clusters on CeO2-X(111) surfaces and its influence on CO and O2 adsorption: a comprehensive DFT + U investigation

Unveiling the Structure of Oxygen Vacancies in Bulk Ceria and the Physical Mechanisms behind Their Formation

Understanding the structures of oxygen vacancies in bulk ceria is crucial as they significantly impact the material's catalytic and electronic properties. The complex interaction between oxygen vacancies and Ce3+ ions presents challenges in characterizing ceria's defect chemistry. We introduced a machine learning-assisted cluster-expansion model to predict the energetics of defective configurations accurately within bulk ceria. This model effectively samples configurational spaces, detailing oxygen vacancy structures across different temperatures and concentrations. At lower temperatures, vacancies tend to cluster, mediated by Ce3+ ions and electrostatic repulsion, while at higher temperatures, they distribute uniformly due to configurational entropy. Our analysis also reveals a correlation between thermodynamic stability and the band gap between occupied O 2p and unoccupied Ce 4f orbitals, with wider band gaps indicating higher stability. This work enhances our understanding of defect chemistry in oxide materials and lays the groundwork for further research into how these structural properties affect ceria's performance.

Synergy of Adsorption and Plasmonic Photocatalysis in the Au-CeO2 Nanosystem: Experimental Validation and Plasmonic Modeling

Adsorption-mediated water treatment leaves adsorbents as secondary pollutants in the environment. However, photocatalysis aids in decomposing the contaminant into its nontoxic forms. In this context, we demonstrate an adsorption-photocatalysis pairing in Au-CeO₂ nanocomposites for a total methylene blue (MB) removal from water. We synthesized Au-CeO₂ through the citrate (cit) reduction method at different Au loading and studied its adsorption capacity with kinetics and thermodynamic models. We observe that the high adsorption capacity of Au-CeO₂ is primarily because of the presence of Ce³⁺ states in CeO₂ and citrate ligands on Au NPs. The Ce³⁺ states interact and transfer their electrons to supported Au NPs, rendering a negative charge over Au. The negatively charged Au surface and the carboxyl (-COO^-) group of citrate ligands mediate an electrostatic interaction/adsorption of cationic MB. The total removal of MB is expedited under white light and lasers. A control experiment with Au NPs shows less adsorption-photocatalysis. The size of Au NPs and Au-CeO₂ interfacial interaction is responsible for the surface plasmon resonance spectral position at 550-600 nm. Linear sweep voltammetry (LSV) and plasmonic field simulation show surface plasmon-driven photocatalysis in Au-CeO₂. LSV shows a 3-fold higher photocurrent density in Au-CeO₂ than colloidal Au NPs under white light. The simulated electric field intensity in Au-CeO₂ is maximum at SPR excitation and the closest interfacial separation (d = 0 nm). The plasmon-driven photocatalysis in colloidal Au NPs is mainly due to the interaction of hot electrons with the adsorbed MB molecule. Notably, near-field light concentration, hot electrons, and interfacial charge separation are responsible for excellent MB removal in the Au-CeO₂ nanosystem. The total MB removal through adsorption-photocatalysis pairing is 99.3% (Au-CeO₂), 30.7% (Au NPs), and 13% (CeO₂).

Elucidating Active CO–Au Species on Au/CeO2(111): A Combined Modulation Excitation DRIFTS and Density Functional Theory Study

In this work we elucidate the main steps of the CO oxidation mechanism over Au/CeO2(111), clarifying the course of CO adsorption at a broad variety of surface sites as well as of transmutations of one CO species into another. By combining transient spectroscopy with DFT calculations we provide new evidence that the active centers for CO conversion are single gold atoms. To gain insight into the reaction mechanism, we employ Modulation Excitation (ME) DRIFT spectroscopy in combination with the mathematical tool of Phase Sensitive Detection to identify the active species and perform DFT calculations to facilitate the assignments of the observed bands. The transient nature of the ME-DRIFTS method allows us to sort the observed species temporally, providing further mechanistic insight. Our study highlights the potential of combined transient spectroscopy and theoretical calculations (DFT) to clarify the role of adsorbates observed and to elucidate the reaction mechanism of CO oxidation over supported gold and other noble-metal catalysts.

The dynamic interplay between water and oxygen vacancy at the near-surface of ceria

Water, even at trace concentrations, strongly increases the CO oxidation activities of the reducible metal oxide supported noble-metal catalysts, where the transfer of proton plays a key role. In this paper, we performed a thorough investigation of the interplay between water molecules and the reduced CeO₂(111) surface. It was found that water molecules can induce the migration of oxygen vacancies which in turn results in the formation of surface protons. The proton then entangles with the near-surface polaron to form polaron-proton pair due to their mutual attractive interactions. The hopping of the polaron can easily trigger the long-range or short-range diffusion of protons mediated by water molecules at the CeO₂(111) surface. These findings provide new insights into the key roles of oxygen vacancies and polarons in reducible oxide based heterogeneous catalysis, which is beneficial for the understanding of the increased activity of reducible oxide supported metal nanoparticles in the presence of water.

NO reduction with CO over CuOx/CeO2 nanocomposites: influence of oxygen vacancies and lattice strain

The morphology-dependent population of oxygen vacancies in CuOx/CeO2 nanocomposites used for NO reduction with CO and its pivotal role in the reaction mechanism are examined in this combined experimental and first-principles study.

Stability of AumAgn (m + n = 1-6) clusters supported on a F-center MgO(100) surface

A theoretical study has been performed for deposited AumAgn (m + n = 1-6) clusters. The combined use of the Mexican Enhanced Genetic Algorithm (MEGA) and Density Functional Theory (DFT) calculations allows us to explore the potential energy surface and therefore, find the global minimum configuration for each composition. We have performed calculations of clusters deposited on defects (oxygen vacancies) known as F centers on MgO (100) surfaces. Our results show interesting differences in the geometries of the clusters upon deposition and as a consequence in their electronic properties. The combination of two metals with different electronegativities creates an inhomogeneous charge distribution on their exposed surface producing good conditions for a catalytic process to take place.

Catalytic role of vacancy diffusion in ceria supported atomic gold catalyst

The diffusion of O_v between the surface and subsurface layer is shown to promote the reactivity of CO oxidation

A 3D graphene oxide microchip and a Au-enwrapped silica nanocomposite-based supersandwich cytosensor toward capture and analysis of circulating tumor cells

Determination of the presence and number of circulating tumor cells (CTCs) in peripheral blood can provide clinically important data for prognosis and therapeutic response patterns. In this study, a versatile supersandwich cytosensor was successfully developed for the highly sensitive and selective analysis of CTCs using Au-enwrapped silica nanocomposites (Si/AuNPs) and three-dimensional (3D) microchips. First, 3D microchips were fabricated by a photolithography method. Then, the prepared substrate was applied to bind graphene oxide, streptavidin and biotinylated epithelial-cell adhesion-molecule antibody, resulting in high stability, bioactivity, and capability for CTCs capture. Furthermore, horseradish peroxidase and anti-CA153 were co-linked to the Si/AuNPs for signal amplification. The performance of the cytosensor was evaluated with MCF7 breast cancer cells. Under optimal conditions, the proposed supersandwich cytosensor showed high sensitivity with a wide range of 10(1) to 10(7) cells per mL and a detection limit of 10 cells per mL. More importantly, it could effectively distinguish CTCs from normal cells, which indicated the promising applications of our method for the clinical diagnosis and therapeutic monitoring of cancers.

Electronic storage capacity of ceria: role of peroxide in Aux supported on CeO2(111) facet and CO adsorption

Au adsorbs on CeO₂(111) with an O vacancy to form Au^δ−, which is not favorable for CO adsorption. After peroxide formed on CeO₂(111) with an O vacancy, Au is oxidized to Au^δ+, which improves CO adsorption on Au/CeO₂, where CeO₂ acts as an electron buffer.