Nonclassical Growth Mechanism of Double-Walled Metal-Oxide Nanotubes Implying Transient Single-Walled Structures

The formation of imogolite nanotubes is reported to be a kinetic process involving intermediate roof-tile nanostructures. Here, the structural evolution occurring during the synthesis of aluminogermanate double-walled imogolite nanotubes is in situ monitored, thanks to an instrumented autoclave allowing the control of the temperature, the continuous measurement of pH and pressure, and the regular sampling of gas and solution. Chemical analyses confirm the completion of the precursor's conversion with the release of CO2 , ethanol, and dioxane as main side products. The combination of microscopic observations, infrared, and absorption spectroscopies with small and wide-angle X-ray scattering experiments unravel a unique growth mechanism implying transient single-walled nanotubes instead of the self-assembly of stacked proto-imogolite tiles. The growth formation of these transient nanotubes is followed at the molecular level by Quick-X-ray absoprtion specotrscopy experiments. Multivariate data analysis evidences that the near neighboring atomic environment of Ge evolves from monotonous to a more complex one as the reaction progresses. The following transformation into a double-walled nanotube takes place at a nearly constant mean radius, as demonstrated by the simulation of X-ray scattering diagrams. Overall, transient nanotubes appear to serve for the anchoring of a new wall, corresponding to a mechanism radically different from that proposed in the literature.

Mechanism of formation of Co-Ru nanoalloys: the key role of Ru in the reduction pathway of Co

The chemical synthesis of alloy nanoparticles requires adequate conditions to enable co-reduction instead of separate reduction of the two metal cations. The mechanism of formation of bimetallic cobalt-ruthenium nanoalloys by reducing metal salts in an alcohol medium was explored to draw general rules to extrapolate to other systems. The relative kinetics of the reduction of both metal cations were studied by UV-visible and in situ Quick-X-ray absorption spectroscopies as well as H2 evolution. The addition of Co(II) ions does not influence the reduction kinetics of Ru(III) but adding Ru(III) to a Co(II) solution promotes the reduction of cobalt cations. Indeed, while CoO is formed when reaching the boiling temperature of the solvent for the monometallic system, a direct reduction of Co is observed at this temperature without formation of the oxide for the bimetallic one. The co-reduction of the metal cations results in the formation of bimetallic nanoplatelets, the size of which can be tuned by changing the Ru content.

Development of a custom-made 2.8 T permanent-magnet dipole photon source for the ROCK beamline at SOLEIL

In August 2021, the SOLEIL storage ring was restarted after the summer shutdown with a new bending magnet made entirely of permanent magnets. Producing a magnetic field of 2.8 T, it replaced one of the 32 electromagnetic dipoles (magnetic field of 1.7 T) of the ring to allow the ROCK beamline to exploit more intense photon fluxes in the hard X-ray range, thus improving the time resolution performances of the beamline for experiments carried out above 20 keV. The reduction of the new dipole magnetic gap required to produce the higher field has led to the construction and installation of a new vacuum vessel. The realization of the new dipole with permanent magnets was a technological feat due to the very strong magnetic forces. The permanent-magnet assembly required dedicated tools to be designed and constructed. Thanks to accurate magnetic measurements, a precise modelization of the new dipole was performed to identify its effects on the electron beam dynamics. The first measurements carried out on the ROCK beamline have highlighted the expected increase in photon flux, and the operation performances remain unchanged for the other beamlines. Here, the major developments and results of this innovative project are described in terms of technology, electron beam dynamics and photon beam performance on the ROCK beamline.

In situ study of the evolution of NiFe nanocatalysts in reductive and oxidative environments upon thermal treatments

The conversion of biomass as a sustainable path to access valuable chemicals and fuels is very attractive for the chemical industry, but catalytic conversions still often rely on the use of noble metals. Sustainability constraints require developing alternative catalysts from abundant and low-cost metals. In this context, NiFe nanoparticles are interesting candidates. In their reduced and supported form, they have been reported to be more active and selective than monometallic Ni in the hydrogenation of the polar functions of organic molecules, and the two metals are very abundant. However, unlike noble metals, Ni and Fe are easily oxidized in ambient conditions, and understanding their transformation in both oxidative and reductive atmospheres is an important though seldom investigated issue to be addressed before their application in catalysis. Three types of NiFe nanoparticles were prepared by an organometallic approach to ensure the formation of ultrasmall nanoparticles (<3.5 nm) with a narrow size distribution, controlled composition and chemical order, while working in mild conditions: Ni2Fe1 and Ni1Fe1, both with a Ni rich core and Fe rich surface, and an alloy with a Ni1Fe9 composition. Supported systems were obtained by the impregnation of silica with a colloidal solution of the preformed nanoparticles. Using advanced characterization techniques, such as wide-angle X-ray scattering (WAXS) and X-ray absorption spectroscopy (XAS) in in situ conditions, this study reports on the evolution of the chemical order and of the oxidation state of the metals upon exposure to air, hydrogen, and/or increasing temperature, all factors that may affect their degree of reduction and subsequent performance in catalysis. We show that if oxidation readily occurs upon exposure to air, the metals can revert to their initial state upon heating in the presence of H₂ but with a change in structure and chemical ordering.

Green synthesis of water splitting electrocatalysts: IrO2 nanocages via Pearson's chemistry

Highly porous iridium oxide structures are particularly well-suited for the preparation of porous catalyst layers needed in proton exchange membrane water electrolyzers. Herein, we report the formation of iridium oxide nanostructured cages, via a water-based process performed at room temperature, using cheap Cu2O cubes as the template. In this synthetic approach, based on Pearson's hard and soft acid-base theory, the replacement of the Cu2O core by an iridium shell is permitted by the difference in hardness/softness of cations and anions of the two reactants Cu2O and IrCl3. Calcination followed by acid leaching allow the removal of residual copper oxide cores and leave IrO2 hierarchical porous structures with outstanding activity toward the oxygen evolution reaction. Fundamental understanding of the reaction steps and identification of the intermediates are permitted by coupling a set of ex situ and in situ techniques including operando time-resolved X-ray absorption spectroscopy during the synthesis.

Advanced design of a x-ray absorption spectroscopy setup for measuring transition metals speciation in molten carbonates, hydroxides and hydrogenosulfates

Battery recycling is currently becoming a crucial issue. One possible treatment path involves the use of molten salts. A mechanistic understanding of the underlying processes requires being able to analyze in situ speciation in molten salts at various temperatures. This can be advantageously achieved using x-ray absorption spectroscopy, the use of Quick-EXAFS facilities being particularly appropriate. Consequently, this paper presents the design and development of a new setup allowing carrying out Quick-EXAFS experiments in oxidizing molten salts at high temperatures. We describe the different components of a cell and the performance of the heating device. We illustrate the capabilities of the setup by analyzing the temperature evolution of Co speciation upon dissolution of LiCoO₂, a typical battery electrode material, in molten carbonates, hydroxides, and hydrogenosulphates.

Insights into the Preparation of Copper Catalysts Supported on Layered Double Hydroxide Derived Mixed Oxides for Ethanol Dehydrogenation

Acetaldehyde is an important chemical commodity and a building block for producing several other high-value products in the chemical industry. This has motivated the search for suitable, efficient, stable, and selective catalysts, as well as renewable raw materials such as ethanol. In this work, supported copper catalysts were prepared from CuZnAl layered double hydroxides (LDHs) with different copper contents (5, 10, and 20 wt %) for application in the ethanol dehydrogenation reaction (EDR). The samples were thoroughly characterized by a series of techniques, which allowed for analysis of all of the copper and zinc species involved in the different catalyst preparation steps and during the EDR. The results obtained by in situ quick extended X-ray absorption fine structure (EXAFS) measurements, combined with multivariate data analysis, showed that the copper content in the pristine LDH influenced the phase composition of the mixed oxide support, which consequently affected the dispersion of copper nanoparticles. The higher the copper content, the higher are the ZnAl₂O₄ and zinc tetrahedral prenuclei (TPN) contents, to the detriment of the ZnO content. All the samples showed high selectivity (>97%) and stability in the catalytic reactions at 300 and 350 °C, with no observed deactivation during 6 h on-stream. Although the samples with lower copper content presented higher copper dispersion and reactivity, the sample containing 20 wt % of copper outperformed the others, with greater conversion and higher activity toward acetaldehyde.

How crucial is the impact of calcium on the reactivity of iron-organic matter aggregates? Insights from arsenic

Environmental iron-organic matter (Fe-OM) aggregates play a major role in the dynamic of pollutants. Nowadays, there is a lack of information about the control exerted by their structural organization on their reactivity towards metal(loid)s and in particular, the impact of major ions, such as calcium. The sorption capacity of mimetic environmental Fe-OM-Ca aggregates was investigated relative to the Fe/organic carbon (OC) and Ca/Fe ratios using As as a probe. It was shown that Fe speciation is the key factor controlling the reactivity of Fe-OM-Ca aggregates regarding the high affinity of Fe(III)-oligomers towards As and the high sorption capacity of ferrihydrite-like nanoparticles. Moreover, when it occurs at high concentration, Ca competes with Fe for OM binding leading to an increase in the amount of ferrihydrite-like nanoparticles and binding site availability. As a consequence, Ca not only impacts the ionic strength but it also has a dramatic impact on the structural organization of Fe-OM aggregates at several scales of organization, resulting in an increase of their sorption capacity. In the presence of high amounts of Ca, Fe-OM-Ca aggregates could immobilize pollutants in the soil porous media as they form a micrometric network exhibiting a strong sorption capacity.

Quick-EXAFS and Raman monitoring of activation, reaction and deactivation of NiCu catalysts obtained from hydrotalcite-like precursors

The understanding of phase transformation upon activation, reaction and deactivation of catalysts is of prime importance for tailoring catalysts with better performances. Herein we combined Quick-EXAFS and Raman spectroscopies in operando conditions through the monitoring of reaction products by mass spectrometry in order to study in depth active species and deactivating ones for Ethanol Steam Reforming reaction. Quick-EXAFS data analyzed by multivariate analysis allows one to determine the nickel and copper species involved during the activation of a Ni-Cu hydrotalcite-like precursors. Upon reaction and regeneration monitoring, Raman spectroscopy combined with mass spectrometry highlights the side products formed upon ESR leading to the formation of amorphous coke species encapsulating active metallic species and inducing catalyst deactivation. The coke encapsulation of active species was demonstrated by the simultaneous observation of oxidation of nickel and copper as soon as the amorphous coke was burnt by the oxidative regeneration treatment. Formation of filamentous coke species is also confirmed as causing little impact in catalyst deactivation.

Unveiling the Local Structure of Palladium Loaded into Imine-Linked Layered Covalent Organic Frameworks for Cross-Coupling Catalysis

Layered covalent organic frameworks (2D-COFs), composed of reversible imine linkages and accessible pores, offer versatility for chemical modifications towards the development of catalytic materials. Nitrogen-enriched COFs are good candidates for binding Pd species. Understanding the local structure of reacting Pd sites bonded to the COF pores is key to rationalize interactions between active sites and porous surfaces. By combining advanced synchrotron characterization methods with periodic computational DFT modeling, the precise atomic structure of catalytic Pd sites attached to local defects is resolved within an archetypical imine-linked 2D-COF. This material was synthesized using an in situ method as a gel, under which imine hydrolysis and metalation reactions are coupled. Local defects formed in situ within imine-linked 2D-COF materials are highly reactive towards Pd metalation, resulting in active materials for Suzuki-Miyaura cross-coupling reactions.

Multivariate Analysis of Coupled Operando EPR/XANES/EXAFS/UV-Vis/ATR-IR Spectroscopy: A New Dimension for Mechanistic Studies of Catalytic Gas-Liquid Phase Reactions

Operando EPR, XANES/EXAFS, UV‐Vis and ATR‐IR spectroscopic methods have been coupled for the first time in the same experimental setup for investigation of unclear mechanistic aspects of selective aerobic oxidation of benzyl alcohol by a Cu/TEMPO catalytic system (TEMPO=2,2,6,6‐tetramethylpiperidinyloxyl). By multivariate curve resolution with alternating least‐squares fitting (MCR‐ALS) of simultaneously recorded XAS and UV‐Vis data sets, it was found that an initially formed (bpy)(NMI)Cu^I‐ complex (bpy=2,2′‐bipyridine, NMI=N‐methylimidazole ) is converted to two different Cu^II species, a mononuclear (bpy)(NMI)(CH₃CN)Cu^II‐OOH species detectable by EPR and ESI‐MS, and an EPR‐silent dinuclear (CH₃CN)(bpy)(NMI)Cu^II(μ‐OH)₂⋅Cu^II (bpy)(NMI) complex. The latter is cleaved in the further course of reaction into (bpy)(NMI)(HOO)Cu^II‐TEMPO monomers that are also EPR‐silent due to dipolar interaction with bound TEMPO. Both Cu monomers and the Cu dimer are catalytically active in the initial phase of the reaction, yet the dimer is definitely not a major active species nor a resting state since it is irreversibly cleaved in the course of the reaction while catalytic activity is maintained. Gradual formation of non‐reducible Cu^II leads to slight deactivation at extended reaction times.

Effectiveness of Ligand Denticity-Dependent Oxidation Protection in Copper MOD Inks

The recent cost-driven transition from silver- to copper-based inks for printing on flexible substrates is connected with new key challenges. Given the high oxidation sensitivity of copper inks before, during, and after the curing process, the conductivity and thereby the device performance can be affected. Strategies to limit or even avoid this drawback include the development of metal organic decomposition (MOD) inks with selected "protective" ligands. In this study, the influence of the ligand on the oxide formation during the ink decomposition process is described using a wide variety of in situ characterization techniques. It is demonstrated that bidentate ligands provide an improved oxidation barrier, although the copper preservation mechanism has its limits: oxygen can interfere in every reduction pathway depending on the curing duration and atmospheric conditions. The generated insights can be applied in the further evolution toward ambient-curable copper MOD inks.

Aggregating ability of ferric chloride in the presence of phosphate ligand

Complexing anions such as phosphate or silicate play an ambivalent role in the performance of hydrolyzing metal coagulants: On one hand, they significantly interfere with the hydrolytic pathway of conventional iron or aluminum coagulants, the associated destabilization mechanism remaining rather elusive; on the other hand, they have been shown to be key ingredients in the formulation of innovative coagulant solutions exhibiting improved removal efficiency, their action mechanism at the molecular scale being presently poorly understood. In this paper, we explore the effect of small additions of phosphate ligand on the chemical coagulation of silica nanoparticles with ferric chloride. Transmission Electron Microscopy-Energy Dispersed X-ray Spectroscopy (TEM-EDXS) combined with Extended X-ray absorption Fine Structure Spectroscopy (EXAFS) at the Fe K-edge are used to provide an insight into the nature of coagulant species, whereas jar-tests, laser diffraction, Small Angle X-ray Scattering (SAXS), and electrophoretic mobility, are used to investigate the aggregation dynamics of silica particles in the presence of phosphate ligand. We show that, in spite of a slight increase in the consumption of iron coagulant, the addition of phosphate significantly improves the formation of silica aggregates provided that the elemental Fe/P ratio remains above 7. Such effects originate from both a large increase in the overall number of coagulant species, the binding of a phosphate ligand terminating the growth of polymeric chains of edge-sharing Fe octahedra, and a change in the nature of the coagulant species that evolves with the Fe/P ratio, small polycations built-up from Fe-oligomers linked by phosphate tetrahedra being eventually formed. Those non-equilibrium nanosize Fe-P coagulant species assemble the silica nanoparticles to form hetero-aggregates whose structure is consistent with a Diffusion-Limited Cluster Aggregation mechanism.

In situ QXAS study of sulfidation/oxidative regeneration reactions of zinc molybdate (ZnMoO4) and ZnO–MoO3 materials

QXAS combined to multivariate data analysis enabled to follow sulfidation and oxidative regeneration kinetics of Zn and Mo based materials, with a description of the evolution of the several intermediate phases.

A phase transformable ultrastable titanium-carboxylate framework for photoconduction

Porous titanium oxide materials are attractive for energy-related applications. However, many suffer from poor stability and crystallinity. Here we present a robust nanoporous metal-organic framework (MOF), comprising a Ti₁₂O₁₅ oxocluster and a tetracarboxylate ligand, achieved through a scalable synthesis. This material undergoes an unusual irreversible thermally induced phase transformation that generates a highly crystalline porous product with an infinite inorganic moiety of a very high condensation degree. Preliminary photophysical experiments indicate that the product after phase transformation exhibits photoconductive behavior, highlighting the impact of inorganic unit dimensionality on the alteration of physical properties. Introduction of a conductive polymer into its pores leads to a significant increase of the charge separation lifetime under irradiation. Additionally, the inorganic unit of this Ti-MOF can be easily modified via doping with other metal elements. The combined advantages of this compound make it a promising functional scaffold for practical applications.

The Critical Role of Thioacetamide Concentration in the Formation of ZnO/ZnS Heterostructures by Sol-Gel Process

ZnO/ZnS heterostructures have emerged as an attractive approach for tailoring the properties of particles comprising these semiconductors. They can be synthesized using low temperature sol-gel routes. The present work yields insight into the mechanisms involved in the formation of ZnO/ZnS nanostructures. ZnO colloidal suspensions, prepared by hydrolysis and condensation of a Zn acetate precursor solution, were allowed to react with an ethanolic thioacetamide solution (TAA) as sulfur source. The reactions were monitored in situ by Small Angle X-ray Scattering (SAXS) and UV-vis spectroscopy, and the final colloidal suspensions were characterized by High Resolution Transmission Electron Microscopy (HRTEM). The powders extracted at the end of the reactions were analyzed by X-ray Absorption spectroscopy (XAS) and X-ray diffraction (XRD). Depending on TAA concentration, different nanostructures were revealed. ZnO and ZnS phases were mainly obtained at low and high TAA concentrations, respectively. At intermediate TAA concentrations, we evidenced the formation of ZnO/ZnS heterostructures. ZnS formation could take place via direct crystal growth involving Zn ions remaining in solution and S ions provided by TAA and/or chemical conversion of ZnO to ZnS. The combination of all the characterization techniques was crucial to elucidate the reaction steps and the nature of the final products.

Thermal stability of PMMA–LDH nanocomposites: decoupling the physical barrier, radical trapping, and charring contributions using XAS/WAXS/Raman time-resolved experiments

In-depth understanding of the thermal stability of polymer–clay nanocomposites requires the use of advanced time-resolved techniques combined with multivariate data analysis, as well as the preparation of layered nanofillers with well-defined composition. The layered double hydroxide (LDH) compounds Zn₂Al(OH)₆·nH₂O, Zn₂Al_0.75Fe_0.25(OH)₆·nH₂O, ZnCuAl(OH)₆·nH₂O, and ZnCuAl_0.5Fe_0.5(OH)₆·nH₂O were prepared, each designed to specifically identify the physical barrier, radical trapping, and char formation contributions to the thermal stability of the PMMA–LDH nanocomposites. The unique combination of conventional methods (TG, DSC, and Raman spectroscopy) and synchrotron radiation techniques (XAS and WAXS), applied during PMMA–LDH heating, revealed the synergetic (of iron) and antagonist (of copper) effects of the LDH layers transformations on the three main endothermic steps of mass loss of the polymer. The diffusion barrier effect was proved by the downshift of the PMMA thermal decomposition temperature caused by the decrease of the LDH edifice thermostability when divalent cations were substituted in the LDH (passing from PMMA–Zn₂Al(OH)₆·nH₂O to PMMA–ZnCuAl(OH)₆·nH₂O). For PMMA–Zn₂Al_0.75Fe_0.25(OH)₆·nH₂O, a cooperative contribution of iron reduction, stabilisation of layered edifice, and radical trapping effects was observed for the thermal stability of the nanocomposite. LDH also acted as a diffusion barrier to the efflux and evaporation of depolymerized species, favouring the charring which exerts an additional contribution to thermal stability of the PMMA–LDH nanocomposites.

Thermal stability of polymer-double layered hydroxides nanocomposites: concurrent contributions from physical barrier, char formation and radical trapping.

Molecular approach to prepare mixed MoW alumina supported hydrotreatment catalysts using H4SiMonW12−nO40 heteropolyacids

Higher catalytic conversions and different selectivity ratios are explained by the formation of the mixed (MoW)S₂ active phase when using mixed MoW heteropolyacid as starting material.

Operando XAS/Raman/MS monitoring of ethanol steam reforming reaction–regeneration cycles

The catalyst regeneration leads to the redispersion of smaller cobalt particles leading to a similar conversion along successive reaction–regeneration cycles.

Controlling the atomic distribution in PtPd nanoparticles: thermal stability and reactivity during NO abatement

In situ X-ray absorption spectroscopy and mass spectrometry measurements were employed to simultaneously probe the atom specific short range order and reactivity of Pd and PtPd nanoparticles towards NO decomposition at 300 °C. The nanoparticles were synthesized by a well controlled, eco-friendly wet chemical reduction of metal salts and later supported on activated carbon. Particularly for the bimetallic PtPd samples, distinct atomic arrangements were achieved using a seeding growth method, which allowed producing a random nanoalloy, or nanoparticles with Pt- or Pd-rich core. X-ray photoelectron spectroscopy, transmission electron microscopy, and X-ray diffraction provided additional insights on their electronic, morphological and long range order structural properties. The results revealed that the higher the thermal induced atomic migration observed within the nanoparticles during thermal treatments, the least were their reactivity for NO abatement.

Time-resolved XAS/MS/Raman monitoring of mutual copper self-reduction and ethanol dehydrogenation reactions

The most active copper species for ethanol dehydrogenation to H₂, acetaldehyde and ethyl acetate on a hierarchical porous Cu/Al₂O₃ catalyst is described.

High surface area hierarchical porous Al2O3 prepared by the integration of sol–gel transition and phase separation

Mechanism of gelation process and phase separation for production of hierarchical porous alumina with high surface area.

A thorough spectroscopic study of luminescent precursor solution of Y3Al5O12:Tb3+: influence of acetylacetone

Upon blue excitation, acac-modified solutions present significantly higher luminescence compared to unmodified ones due to the presence of pre-nuclei of YAG:Tb structure which is very interesting for using them for optical applications.

Site-selective formation of an iron(iv)-oxo species at the more electron-rich iron atom of heteroleptic μ-nitrido diiron phthalocyanines

A combination of MS and computation on μ-nitrido bridged diiron complexes reveals H₂O₂ binding to the complex and generates an oxidant capable of oxidizing methane.

Iron(iv)–oxo species have been identified as the active intermediates in key enzymatic processes, and their catalytic properties are strongly affected by the equatorial and axial ligands bound to the metal, but details of these effects are still unresolved. In our aim to create better and more efficient oxidants of H-atom abstraction reactions, we have investigated a unique heteroleptic diiron phthalocyanine complex. We propose a novel intramolecular approach to determine the structural features that govern the catalytic activity of iron(iv)–oxo sites. Heteroleptic μ-nitrido diiron phthalocyanine complexes having an unsubstituted phthalocyanine (Pc1) and a phthalocyanine ligand substituted with electron-withdrawing alkylsulfonyl groups (PcSO₂R) were prepared and characterized. A reaction with terminal oxidants gives two isomeric iron(iv)–oxo and iron(iii)–hydroperoxo species with abundances dependent on the equatorial ligand. Cryospray ionization mass spectrometry (CSI-MS) characterized both hydroperoxo and diiron oxo species in the presence of H₂O₂. When m-CPBA was used as the oxidant, the formation of diiron oxo species (PcSO₂R)FeNFe(Pc1) Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> O was also evidenced. Sufficient amounts of these transient species were trapped in the quadrupole region of the mass-spectrometer and underwent a CID-MS/MS fragmentation. Analyses of fragmentation patterns indicated a preferential formation of hydroperoxo and oxo moieties at more electron-rich iron sites of both heteroleptic μ-nitrido complexes. DFT calculations show that both isomers are close in energy. However, the analysis of the iron(iii)–hydroperoxo bond strength reveals major differences for the (Pc1)FeN(PcSO₂R)Fe^IIIOOH system as compared to (PcSO₂R)FeN(Pc1)Fe^IIIOOH system, and, hence binding of a terminal oxidant will be preferentially on more electron-rich sides. Subsequent kinetics studies showed that these oxidants are able to even oxidize methane to formic acid efficiently.

Surface modified Mg-doped ZnO QDs for biological imaging

Nanocrystals of ZnO are currently attracting great interest as potential labels for biological applications, such as theranostic devices, due to their luminescent properties and low toxicity in vivo. It has been reported that doping with Mg