Phase Stability of High Entropy (Mg,Ni,Co,Cu,Zn)O from Temperature-Resolved Synchrotron Diffraction: Tetragonal Distortion and Guggenite Phase.

The temperature-resolved structure evolution of quinary and quaternary equimolar oxides containing Mg, Ni, Zn, Co, and Cu is investigated by in situ synchrotron diffraction. Important structural modifications occur already at mild temperatures and depend on the elements involved. All quaternary compounds with χ(Cu) = 0.

In Situ X-ray Absorption Spectroscopy Study of the Deactivation Mechanism of a Ni-SrTiO Photocatalyst Slurry Active in Water Splitting.

We used in situ X-ray absorption spectroscopy (XAS) to investigate the composition-performance correlation of Ni-SrTiO photocatalysts active for water splitting. After preparation and exposure to ambient conditions, the Ni particles on SrTiO consist of Ni(0) and Ni(II) phases, with a 4:1 at % ratio, in a metal/oxide core/shell configuration, as confirmed by XPS and TEM-EDX. In situ XAS experiments using an aqueous slurry of the Ni-SrTiO photocatalyst and simultaneous continuous exposure to 365 nm light with a power density of 100 mW cm and the X-rays do not reveal significant changes in oxidation state of the Ni particles.

Accurate prediction of the optical properties of nanoalloys with both plasmonic and magnetic elements.

The alloying process plays a pivotal role in the development of advanced multifunctional plasmonic materials within the realm of modern nanotechnology. However, accurate in silico predictions are only available for metal clusters of just a few nanometers, while the support of modelling is required to navigate the broad landscape of components, structures and stoichiometry of plasmonic nanoalloys regardless of their size. Here we report on the accurate calculation and conceptual understanding of the optical properties of metastable alloys of both plasmonic (Au) and magnetic (Co) elements obtained through a tailored laser synthesis procedure.

Single-Atoms on Crystalline Carbon Nitrides for Selective C─H Photooxidation: A Bridge to Achieve Homogeneous Pathways in Heterogeneous Materials.

Single-atom catalysis is a field of paramount importance in contemporary science due to its exceptional ability to combine the domains of homogeneous and heterogeneous catalysis. Iron and manganese metalloenzymes are known to be effective in C─H oxidation reactions in nature, inspiring scientists to mimic their active sites in artificial catalytic systems. Herein, a simple and versatile cation exchange method is successfully employed to stabilize low-cost iron and manganese single-atoms in poly(heptazine imides) (PHI).

Metastable Ni(I)-TiO Photocatalysts: Self-Amplifying H Evolution from Plain Water without Noble Metal Co-Catalyst and Sacrificial Agent.

Decoration of semiconductor photocatalysts with cocatalysts is generally done by a step-by-step assembly process. Here, we describe the self-assembling and self-activating nature of a photocatalytic system that forms under illumination of reduced anatase TiO nanoparticles in an aqueous Ni solution. UV illumination creates a Ni/TiO/Ti photocatalyst that self-activates and, over time, produces H at a higher rate.

Full Spectroscopic Characterization of the Molecular Oxygen-Based Methane to Methanol Conversion over Open Fe(II) Sites in a Metal-Organic Framework.

Iron-based enzymes efficiently activate molecular oxygen to perform the oxidation of methane to methanol (MTM), a reaction central to the contemporary chemical industry. Conversely, a very limited number of artificial catalysts have been devised to mimic this process. Herein, we employ the MIL-100(Fe) metal-organic framework (MOF), a material that exhibits isolated Fe sites, to accomplish the MTM conversion using O as the oxidant under mild conditions.

Capabilities of Grazing Incidence X-ray Diffraction in the Investigation of Amorphous Mixed Oxides with Variable Composition.

X-ray Diffraction has been fully exploited as a probe to investigate crystalline materials. However, very little research has been carried out to unveil its potentialities towards amorphous materials. In this work, we demonstrated the capabilities of Grazing Incidence X-ray Diffraction (GIXRD) as a simple and fast tool to obtain quantitative information about the composition of amorphous mixed oxides.

Structural and mechanistic insights into low-temperature CO oxidation over a prototypical high entropy oxide by Cu L-edge operando soft X-ray absorption spectroscopy.

High entropy oxides (HEOs) are an emerging class of materials constituted by multicomponent systems that are receiving special interest as candidates for obtaining novel and desirable properties. In this study we present a detailed investigation of the relevant intermediates arising at the surface of the prototypical HEO MgCoNiCuZnO during low-temperature CO oxidation. By combining Cu L-edge operando soft X-ray absorption spectroscopy (soft-XAS) with density functional theory simulations and FT-IR spectroscopy, we propose that upon HEO exposure to CO at 235 °C reduced Cu(I) sites arise mostly coordinated to activated CO molecules and partly to bidentate carbonate species.

The Missing Piece: The Structure of the TiCT MXene and Its Behavior as Negative Electrode in Sodium Ion Batteries.

The most common MXene composition TiCT (T = F, O) shows outstanding stability as anode for sodium ion batteries (100% of capacity retention after 530 cycles with charge efficiency >99.7%). However, the reversibility of the intercalation/deintercalation process is strongly affected by the synthesis parameters determining, in turn, significant differences in the material structure.

Understanding Solid-Gas Reaction Mechanisms by Operando Soft X-Ray Absorption Spectroscopy at Ambient Pressure.

Ambient-pressure operando soft X-ray absorption spectroscopy (soft-XAS) was applied to study the reactivity of hydroxylated SnO nanoparticles toward reducing gases. H was first used as a test case, showing that the gas phase and surface states can be simultaneously probed: Soft-XAS at the O K-edge gains sensitivity toward the gas phase, while at the Sn M-edges, tin surface states are explicitly probed. Results obtained by flowing hydrocarbons (CH and CHCHCH) unequivocally show that these gases react with surface hydroxyl groups to produce water without producing carbon oxides and release electrons that localize on Sn to eventually form SnO.

Dielectric Effects in FeO -Coated Au Nanoparticles Boost the Magnetoplasmonic Response: Implications for Active Plasmonic Devices.

Plasmon resonance modulation with an external magnetic field (magnetoplasmonics) represents a promising route for the improvement of the sensitivity of plasmon-based refractometric sensing. To this purpose, an accurate material choice is needed to realize hybrid nanostructures with an improved magnetoplasmonic response. In this work, we prepared core@shell nanostructures made of an 8 nm Au core surrounded by an ultrathin iron oxide shell (≤1 nm).

Lithiation Mechanism in High-Entropy Oxides as Anode Materials for Li-Ion Batteries: An Operando XAS Study.

High-entropy oxides based on transition metals, such as MgCoNiCuZnO (TM-HEO), have recently drawn special attention as potential anodes in lithium-ion batteries due to high specific capacity and cycling reversibility. However, the lithiation/delithiation mechanism of such systems is still controversial and not clearly addressed. Here, we report on an operando XAS investigation into TM-HEO-based anodes for lithium-ion cells during the first lithiation/delithiation cycle.

Operando X-ray Absorption Spectroscopy (XAS) Observation of Photoinduced Oxidation in FeNi (Oxy)hydroxide Overlayers on Hematite (α-FeO) Photoanodes for Solar Water Splitting.

An FeNi (oxy)hydroxide cocatalyst overlayer was photoelectrochemically deposited on a thin-film hematite (α-FeO) photoanode, leading to a cathodic shift of ∼100 mV in the photocurrent onset potential. Operando X-ray absorption spectroscopy (XAS) at the Fe and Ni K-edges was used to study the changes in the overlayer with potential in the dark and under illumination conditions. Potential or illumination only had a minor effect on the Fe oxidation state, suggesting that Fe atoms do not accumulate significant amount of charge over the whole potential range.

Dewetting of PtCu Nanoalloys on TiO Nanocavities Provides a Synergistic Photocatalytic Enhancement for Efficient H Evolution.

We investigate the co-catalytic activity of PtCu alloy nanoparticles for photocatalytic H evolution from methanol-water solutions. To produce the photocatalysts, a few-nanometer-thick Pt-Cu bilayers are deposited on anodic TiO nanocavity arrays and converted by solid-state dewetting via a suitable thermal treatment into bimetallic PtCu nanoparticles. X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) results prove the formation of PtCu nanoalloys that carry a shell of surface oxides.

Role of Synthetic Parameters on the Structural and Optical Properties of N,Sn-Copromoted Nanostructured TiO: A Combined Ti K-Edge and Sn L-Edges X-ray Absorption Investigation.

Sn-modification of TiO photocatalysts has been recently proposed as a suitable strategy to improve pollutant degradation as well as hydrogen production. In particular, visible light activity could be promoted by doping with Sn species, which are, however, thermally unstable. Co-promotion with N and Sn has been shown to lead to synergistic effects in terms of visible light activity, but the underlying mechanism has, so far, been poorly understood due to the system complexity.

Stabilization by Configurational Entropy of the Cu(II) Active Site during CO Oxidation on MgCoNiCuZnO.

The mechanisms of CO oxidation on the MgCoNiCuZnO high-entropy oxide were studied by means of operando soft X-ray absorption spectroscopy. We found that Cu is the active metal and that Cu(II) can be rapidly reduced to Cu(I) by CO when the temperature is higher than 130 °C. Co and Ni do not have any role in this respect.

Nanoaggregates of iron poly-oxo-clusters obtained by laser ablation in aqueous solution of phosphonates.

Laser ablation in liquid (LAL) emerged as a versatile technique for the synthesis of nanoparticles with various structures and compositions, although the control over products remains challenging in most cases. For instance, it is still difficult to drive the size of metal oxide crystalline domains down to the level of few atom clusters with LAL. Here we demonstrate that laser ablation of a bulk iron target in aqueous solution of phosphonates gives phosphonate-grafted iron oxo-clusters polymerized into nanoaggregates with Fe:ligand ratio of 2:1, instead of the usual nanocrystalline iron oxides.

Structure and Stability of a Copper(II) Lactate Complex in Alkaline Solution: a Case Study by Energy-Dispersive X-ray Absorption Spectroscopy.

Energy-dispersive X-ray absorption spectroscopy was applied, aimed at solving the problem of the structure and stability of a copper(II) lactate complex in alkaline solution, used as a precursor for the electrodeposition of CuO. The application of multiple scattering calculations to the simulation of the X-ray absorption near-edge structure part of the spectra allowed an accurate resolution of the structure: the copper(II) cation is surrounded by four lactate ions in a distorted tetrahedral environment, with the lactate anions acting as monodentate ligands. This results in an atomic arrangement where copper is surrounded by four oxygen atoms located at quite a short distance (ca.

Correction: Dependence of the Ce(iii)/Ce(iv) ratio on intracellular localization in ceria nanoparticles internalized by human cells.

Correction for 'Dependence of the Ce(iii)/Ce(iv) ratio on intracellular localization in ceria nanoparticles internalized by human cells' by Daniela Ferraro, et al., Nanoscale, 2017, 9, 1527-1538.

Observation of charge transfer cascades in α-FeO/IrO photoanodes by operando X-ray absorption spectroscopy.

Electrochemical devices for energy conversion and storage are central for a sustainable economy. The performance of electrodes is driven by charge transfer across different layer materials and an understanding of the mechanistics is pivotal to gain improved efficiency. Here, we directly observe the transfer of photogenerated charge carriers in a photoanode made of hematite (α-FeO) and a hydrous iridium oxide (IrO) overlayer, which plays a key role in photoelectrochemical water oxidation.

Structural and Thermodynamic Properties of Nanoparticle-Protein Complexes: A Combined SAXS and SANS Study.

We propose a novel method for determining the structural and thermodynamic properties of nanoparticle-protein complexes under physiological conditions. The method consists of collecting a full set of small-angle X-ray and neutron-scattering measurements in solutions with different concentrations of nanoparticles and protein. The nanoparticle-protein dissociation process is described in the framework of the Hill cooperative model, based on which the whole set of X-ray and neutron-scattering data is fitted simultaneously.

Dependence of the Ce(iii)/Ce(iv) ratio on intracellular localization in ceria nanoparticles internalized by human cells.

CeO nanoparticles (CNPs) have been investigated as promising antioxidant agents with significant activity in the therapy of diseases involving free radicals or oxidative stress. However, the exact mechanism responsible for CNP activity has not been completely elucidated. In particular, in situ evidence of modification of the oxidative state of CNPs in human cells and their evolution during cell internalization and subsequent intracellular distribution has never been presented.