Combined X-ray Absorption Spectroscopy Research Articles

Out-of-equilibrium supported Pt-Co core-shell nanoparticles stabilized by kinetic trapping at room temperature

The chemical stability of supported CoPt nanoparticles in out-of-equilibrium core-shell configurations was investigated mainly by anomalous grazing incidence small angle X-ray scattering (AGISAXS) in association with combined transmission electron microscopy and X-ray absorption spectroscopy. CoPt nanoparticles were prepared at room temperature by ultrahigh vacuum atom beam deposition using two different routes: simultaneous deposition of the two metals (CoPt) or sequential deposition. In this last case, Co deposition on a Pt-core (Pt@Co) and the reverse configuration (Co@Pt) are explored. In the Pt@Co case, our experimental analysis of 2.5 nm particles shows the stability of a Pt rich-core (80% Pt) surrounded by a two-monolayers-thick Co shell. In the reverse case, the core-shell structure is also stabilized, while the codeposited sample leads to an alloyed structure. These results suggest that the growth kinetics can trap the thermodynamically non-favorable core-shell structure even for this system which has a high alloying tendency. Besides the lack of atom mobility at room temperature, this stabilization can also be associated with core strain effects. Post thermal treatment of core-shell samples induces a structural transition from the core-shell configuration to the equilibrium alloyed configuration. This study demonstrates that the element-selective scattering technique, AGISAXS is highly efficient for the extraction of chemical segregation information from multi-component supported nanoparticles, such as core-shell structures, up to ultimate small sizes.

Involvement of 5f Orbitals in the Covalent Bonding between the Uranyl Ion and Trialkyl Phosphine Oxide: Unraveled by Oxygen K-Edge X-ray Absorption Spectroscopy and Density Functional Theory.

Monodentate organophosphorus ligands have been used for the extraction of the uranyl ion (UO22+) for over half a century and have exhibited exceptional extractability and selectivity toward the uranyl ion due to the presence of the phosphoryl group (O═P). Tributyl phosphate (TBP) is the extractant of the world-renowned PUREX process, which selectively recovers uranium from spent nuclear fuel. Trialkyl phosphine oxide (TRPO) shows extractability toward the uranyl ion that far exceeds that for other metal ions, and it has been used in the TRPO process. To date, however, the mechanism of the high affinity of the phosphoryl group for UO22+ remains elusive. We herein investigate the bonding covalency in a series of complexes of UO22+ with TRPO by oxygen K-edge X-ray absorption spectroscopy (XAS) in combination with density functional theory (DFT) calculations. Four TRPO ligands with different R substituents are examined in this work, for which both the ligands and their uranyl complexes are crystallized and investigated. The study of the electronic structure of the TRPO ligands reveals that the two TRPO molecules, irrespective of their substituents, can engage in σ- and π-type interactions with U 5f and 6d orbitals in the UO2Cl2(TRPO)2 complexes. Although both the axial (Oyl) and equatorial (Oeq) oxygen atoms in the UO2Cl2(TRPO)2 complexes contribute to the X-ray absorption, the first pre-edge feature in the O K-edge XAS with a small intensity is exclusively contributed by Oeq and is assigned to the transition from Oeq 1s orbitals to the unoccupied molecular orbitals of 1b1u + 1b2u + 1b3u symmetries resulting from the σ- and π-type mixing between U 5f and Oeq 2p orbitals. The small intensity in the experimental spectra is consistent with the small amount of Oeq 2p character in these orbitals for the four UO2Cl2(TRPO)2 complexes as obtained by Mulliken population analysis. The DFT calculations demonstrate that the U 6d orbitals are also involved in the U-TRPO bonding interactions in the UO2Cl2(TRPO)2 complexes. The covalent bonding interactions between TRPO and UO22+, especially the contributions from U 5f orbitals, while appearing to be small, are sufficiently responsible for the exceptional extractability and selectivity of monodentate organophosphorus ligands for the uranyl ion. Our results provide valuable insight into the fundamental actinide chemistry and are expected to directly guide actinide separation schemes needed for the development of advanced nuclear fuel cycle technologies.

Uranium (VI) Adsorbate Structures on Portlandite [Ca(OH)2] Type Surfaces Determined by Computational Modelling and X-ray Absorption Spectroscopy

Portlandite [Ca(OH)2] is a potentially dominant solid phase in the high pH fluids expected within the cementitious engineered barriers of Geological Disposal Facilities (GDF). This study combined X-ray Absorption Spectroscopy with computational modelling in order to provide atomic-scale data which improves our understanding of how a critically important radionuclide (U) will be adsorbed onto this phase under conditions relevant to a GDF environment. Such data are fundamental for predicting radionuclide mass transfer. Surface coordination chemistry and speciation of uranium with portlandite [Ca(OH)2] under alkaline groundwater conditions (ca. pH 12) were determined by both in situ and ex situ grazing incidence extended X-ray absorption fine structure analysis (EXAFS) and by computational modelling at the atomic level. Free energies of sorption of aqueous uranyl hydroxides, [UO2(OH)n]2–n (n = 0–5) with the (001), (100) and (203) or (101) surfaces of portlandite are predicted from the potential of mean force using classical molecular umbrella sampling simulation methods and the structural interactions are further explored using fully periodic density functional theory computations. Although uranyl is predicted to only weakly adsorb to the (001) and (100) clean surfaces, there should be significantly stronger interactions with the (203/101) surface or at hydroxyl vacancies, both prevalent under groundwater conditions. The uranyl surface complex is typically found to include four equatorially coordinated hydroxyl ligands, forming an inner-sphere sorbate by direct interaction of a uranyl oxygen with surface calcium ions in both the (001) and (203/101) cases. In contrast, on the (100) surface, uranyl is sorbed with its axis more parallel to the surface plane. The EXAFS data are largely consistent with a surface structural layer or film similar to calcium uranate, but also show distinct uranyl characteristics, with the uranyl ion exhibiting the classic dioxygenyl oxygens at 1.8 Å and between four and five equatorial oxygen atoms at distances between 2.28 and 2.35 Å from the central U absorber. These experimental data are wholly consistent with the adsorbate configuration predicted by the computational models. These findings suggest that, under the strongly alkaline conditions of a cementitious backfill engineered barrier, there would be significant uptake of uranyl by portlandite to inhibit the mobility of U(VI) from the near field of a geological disposal facility.

Operando bulk and interfacial characterization for electrochemical energy storage: Case study employing isothermal microcalorimetry and X-ray absorption spectroscopy

The global shift to electricity as the main energy carrier will require innovation in electrochemical energy storage (EES). EES systems are the key to the “electron energy economy,” minimizing losses and increasing reliability between energy supply and demand. However, steep challenges such as cost, cycle/calendar life, energy density, material availability, and safety limit widespread adoption of batteries for large-scale grid and vehicle applications. Battery innovation that meets today’s challenges will require new chemistries, which can originate from understanding charge transport phenomena at multiple time and length scales. The advancement of operando characterization can expedite this progress as changes can be observed during battery function. This article highlights progress in bulk and interfacial operando characterization of batteries. Specifically, a case study involving Fe3O4 is provided demonstrating that combining X-ray absorption spectroscopy and isothermal microcalorimetry can provide real-time characterization of productive faradaic redox processes and parasitic interfacial reactions during (de)lithiation.Graphic abstract

Local Structure of Ga85:8In14:2 Eutectic Alloy and Its Pressure–Temperature Melting Line

The structure of the eutectic liquid alloy is investigated both under ambient conditions and at high pressure/high temperature using X‐ray absorption spectroscopy (XAS) and X‐ray diffraction (XRD) techniques. The local structure of the liquid alloy at ambient conditions is analyzed using double‐edge refinements of the XAS data. Solid–liquid phase transitions under high‐pressure and high‐temperature conditions are monitored by combined XAS and XRD measurements along several quasi‐isobaric heating runs, allowing to draw a melting line up to 10 GPa. The established melting line is found to be slightly below the one of pure gallium (Ga) and to follow its trend as expected from the eutectic nature of the compound. A series of Ga K‐edge X‐ray absorption fine structure (XAFS) spectra measured at different pressures indicates the absence of large structural modifications at local Ga sites in the liquid within the investigated pressure and temperature range.

Planar triangular S=3/2 magnet AgCrSe2 : Magnetic frustration, short range correlations, and field-tuned anisotropic cycloidal magnetic order

Single crystals of the hexagonal triangular lattice compound AgCrSe2 have been grown by chemical vapor transport. The crystals have been carefully characterized and studied by magnetic susceptibility, magnetization, specific heat, and thermal expansion. In addition, we used Cr-electron spin resonance and neutron diffraction to probe the Cr 3d3 magnetism microscopically. To obtain the electronic density of states, we employed x-ray absorption and resonant photoemission spectroscopy in combination with density functional theory calculations. Our studies evidence an anisotropic magnetic order below TN=32K. Susceptibility data in small fields of about 1 T reveal an antiferromagnetic (AFM) type of order for H⊥c, whereas for H∥c the data are reminiscent of a field-induced ferromagnetic (FM) structure. At low temperatures and for H⊥c, the field-dependent magnetization and AC susceptibility data evidence a metamagnetic transition at H+=5T, which is absent for H∥c. We assign this to a transition from a planar cycloidal spin structure at low fields to a planar fanlike arrangement above H+. A fully ferromagnetically polarized state is obtained above the saturation field of H⊥S=23.7T at 2 K with a magnetization of Ms=2.8μB/Cr. For H∥c, M(H) monotonically increases and saturates at the same Ms value at H∥S=25.1T at 4.2 K. Above TN, the magnetic susceptibility and specific heat indicate signatures of two dimensional (2D) frustration related to the presence of planar ferromagnetic and antiferromagnetic exchange interactions. We found a pronounced nearly isotropic maximum in both properties at about T*=45K, which is a clear fingerprint of short range correlations and emergent spin fluctuations. Calculations based on a planar 2D Heisenberg model support our experimental findings and suggest a predominant FM exchange among nearest and AFM exchange among third-nearest neighbors. Only a minor contribution might be assigned to the antisymmetric Dzyaloshinskii-Moriya interaction possibly related to the noncentrosymmetric polar space group R3m. Due to these competing interactions, the magnetism in AgCrSe2, in contrast to the oxygen-based delafossites, can be tuned by relatively small, experimentally accessible magnetic fields, allowing us to establish the complete anisotropic magnetic H-T phase diagram in detail.9 MoreReceived 4 August 2021Revised 3 September 2021Accepted 20 September 2021DOI:https://doi.org/10.1103/PhysRevB.104.134410Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI. Open access publication funded by the Max Planck Society.Published by the American Physical SocietyPhysics Subject Headings (PhySH)Research AreasFrustrated magnetismMagnetic susceptibilityThermal expansionTechniquesElectron spin resonanceNeutron diffractionPhotoemission spectroscopySpecific heat measurementsCondensed Matter & Materials Physics

Tunable one-dimensional inorganic perovskite nanomeshes library for water splitting

Perovskites are highly promising candidates in future energy conversion and storage due to their rich diversities and readily tunable electronic properties. However, the poor morphology controllability and limited surface areas have severely limited their applications. We present a generalizable synthesis strategy to fabricate a library of one-dimensional (1D) inorganic perovskite nanomeshes via pyrolysis of metal salt-polymer fibers. Within the evaluated perovskite nanomeshes, La 0.5 Ba 0.5 Co 0.8 Ni 0.2 O 3 delivers the most remarkable performance for the oxygen evolution reaction (OER). Combined X-ray absorption spectroscopy experiments and density functional theory calculations reveal that introduction of additional metals endows more flexible electronic structures to realize the electron transfer in 1D perovskite nanomeshes. This work demonstrates a scalable and retrosynthetic route to easily synthesize the inorganic perovskite nanomaterials with tunable compositions. • Establish the multicomponent 1D perovskite nanomesh library up to six dissimilar metal elements. • The optimized La 0.5 Ba 0.5 Co 0.8 Ni 0.2 O 3 (LBCNO) exhibits a superior OER performance than most reported perovskites. • Demonstrate a scalable and retrosynthetic route to perovskite nanomaterials with tunable composition.

Validating the Electronic Structure of Vanadium Phosphate Cathode Materials.

Investigation of the electronic structure of contending battery electrode materials is an essential step for developing a detailed mechanistic understanding of charge-discharge properties. Herein, we use synchrotron soft X-ray absorption spectroscopy (XAS) in combination with complementary experiments and density functional theory calculations to map the electronic structure, band positioning, and band gap of prototype vanadium(III) phosphate cathode materials, Na3V2(PO4)3, Li3V2(PO4)3, and K3V3(PO4)4·H2O, for alkali-ion rechargeable batteries. XAS fluorescence yield and electron yield measurements reveal substantial variation in surface-to-bulk atomic structure, vanadium oxidation states, and density of oxygen hole states across all samples. We attribute this variation to an intrinsic alkali metal surface depletion identified across these alkali metal vanadium(III) phosphates. We propose that an alkali-depleted surface provides a beneficial interface with the bulk structure(s) that raises the Fermi level and improves surface charge transfer kinetics. Furthermore, we discuss how this effect can play a significant role in reducing the electronic and ionic diffusion limitations of alkali vanadium phosphates in alkali-ion rechargeable batteries. These findings clarify the electronic structure and properties of alkali metal vanadium phosphates and offer guidance on future strategies to improve vanadium phosphate battery performance.

Anionic Redox Investigation of Na2Mn3O7 Electrode Material for Sodium-Ion Batteries

NaxMeyOz oxides have attracted wide attention as promising cathode materials for sodium-ion batteries because of their potential high capacity and rate capability (1). The stable cycling performance, usually obtained within a low voltage range, drastically decrease when cycled at high voltage range despite the large initial charge capacity. Thus, it has been suggested that besides storing charge on the transition metal ions, oxygen ions can also participate in the charge compensation mechanisms at high voltage which induces an oxygen loss from the lattice when charging which is the reason behind the poor cycling stability (2).In this work, the aim is to investigate the anionic redox reactions of Na2Mn3O7 cathode material, within the voltage window of 1.5 – 4.5 V using combined soft X-ray absorption spectroscopy (XAS) and resonant inelastic X-ray scattering (RIXS) which allow us to study the electronic structure of this material. Keywords: Energy, Storage, Sodium-ion, Cathode, layered oxide, anionic redox, oxygen activity.

Recent Applications of X-ray Absorption Spectroscopy in Combination with High Energy Resolution Fluorescence Detection

X-ray absorption spectroscopy (XAS) has grown as one of the essential tools to analyze electronic and geometric structure of a target element in chemistry over the course of a half-century. X-ray e...

In-situ investigation of ethanol steam reforming on Ni and Cr doped ferrites using combined X-ray absorption spectroscopy, mass spectrometry, and gas chromatography

An ethanol steam reforming (ESR) reaction is a H2-production process that the fuel reacts with water in the presence of catalysts. The catalyst structures and active phase compositions have a role in ethanol conversion and hydrogen-production selectivity. The Fe3O4 catalysts with Ni and Cr dopants were prepared and used for the ESR. The morphology and structural property of prepared catalysts were determined by FESEM-EDS, XRD, and XAS techniques. The spinel structures were observed in Fe3O4, Ni/Cr@Fe3O4, and NiFe2O4 while the CrFe2O4 exhibited a mixture between Fe2O3 and Cr2O3 phases. The combined X-ray absorption spectroscopy, mass spectrometry, and gas chromatography was applied to investigate the performance of prepared catalysts during temperature-programmed reduction and ESR processes. The NiFe2O4 exhibited the highest catalytic activity and stability for hydrogen production. The Ni-incorporation in spinel ferrite structure enhanced reduction efficiency of iron compounds at low temperatures and improves its catalytic activity and stability to the ESR process. Furthermore, the NiFe2O4 catalyst also exhibited the ability to regenerate during ESR process as evidenced by X-ray absorption spectrum.

Correlations in the Electronic Structure of van der Waals NiPS3 Crystals: An X-ray Absorption and Resonant Photoelectron Spectroscopy Study.

The electronic structure of high-quality van der Waals NiPS3 crystals was studied using near-edge X-ray absorption spectroscopy (NEXAFS) and resonant photoelectron spectroscopy (ResPES) in combination with density functional theory (DFT) approach. The experimental spectroscopic methods, being element specific, allow one to discriminate between atomic contributions in the valence and conduction band density of states and give direct comparison with the results of DFT calculations. Analysis of the NEXAFS and ResPES data allows one to identify the NiPS3 material as a charge-transfer insulator. Obtained spectroscopic and theoretical data are very important for the consideration of possible correlated-electron phenomena in such transition-metal layered materials, where the interplay between different degrees of freedom for electrons defines their electronic properties, allowing one to understand their optical and transport properties and to propose further possible applications in electronics, spintronics, and catalysis.

Chemical gradients in automotive Cu-SSZ-13 catalysts for NOx removal revealed by operando X-ray spectrotomography

Nitrogen oxide (NOx) emissions are a major source of pollution, demanding ever-improving performance from catalytic after-treatment systems. However, catalyst development is often hindered by limited understanding of the catalyst at work, exacerbated by widespread use of model catalysts rather than technical catalysts, and by global rather than spatially resolved characterization tools. Here we combine operando X-ray absorption spectroscopy with microtomography to perform three-dimensional chemical imaging of the chemical state of copper species in a Cu-SSZ-13 washcoated monolith catalyst during NOx reduction. Gradients in copper oxidation state and coordination environment, resulting from an interplay of NOx reduction with adsorption–desorption of NH3 and mass transport phenomena, were revealed at micrometre spatial resolution while simultaneously determining catalytic performance. Crucially, direct three-dimensional visualization of complex reactions on non-model catalysts is feasible only by the use of operando X-ray spectrotomography, which can improve our understanding of structure–activity relationships, including the observation of mass and heat transport effects. Obtaining spatially resolved spectroscopic information for catalysts under working conditions remains challenging. Here, an approach that combines X-ray absorption spectroscopy with microtomography is introduced and showcased for the selective catalytic reduction of NOx with ammonia over a Cu-SSZ-13 washcoated monolith catalyst.

P.191 The impact of physical activity and fitness on resilience to modern-life stress and the role of brain-derived neurotrophic factor (BDNF)

Although zinc is ubiquitous in ambient particulate matter (PM), exposure to size fractionated residual oil fly ash (ROFA) PM is of particular concern due to several studies implicating particle zinc in mortality, adverse respiratory and cardiac effects. The lack of zinc speciation data is an impediment to our understanding of the biological mechanism of Zn induced toxicity. ROFA PM2.5+ samples (i.e. particle with aerodynamic diameter >2.5 μm) are prepared in a small 732 kW practical fire tube boiler by combusting one No. 5 and three No. 6 residual oil(s) of varying sulfur and ash contents. The combined X-ray absorption spectroscopy and selective extraction method is used to determine the Zn speciation in PM2.5+ samples. The Zn speciation in ROFA PM2.5 (i.e. particle with aerodynamic diameter <2.5 μm) samples, reported earlier, is included here for comparison purposes. The data show that zinc sulfate is predominant in both fractions. In addition, an appreciable amount of zinc phosphate was detected in the PM2.5 fraction. The insoluble zinc forms in both the fractions are identified as Zn-sorbed-ferrihydrite and zinc sulphide. The variation of Zn speciation across different size fractions has implication on the bioavailability and toxicity of Zn. Such source specific speciation data are needed for developing source inventories, and for amending existing regulations/framing new regulations for different size fractions.

Correlating the phase evolution and anionic redox in Co-Free Ni-Rich layered oxide cathodes

Abstract Current trend of high-capacity Ni-rich layered cathode is to develop high-Ni and low-Co or Co-free oxides. The high Ni content layered oxides provide great advantages in capacity, cost and environmental benignity, similar to LiNiO2 parent compound. But they also inherit drawbacks in structural and chemical instability at high voltages upon cycling. Elemental substitution plays a profound role in addressing these challenges. This work elucidates the roles of Al doping in cationic redox and anionic oxygen activity in LiAlxNi1-xO2 using combined X-ray absorption spectroscopy (XAS), resonant inelastic X-ray scattering (RIXS) as well as operando differential electrochemical mass spectrometry (DEMS). Using synchrotron wide-angle X-ray scattering (WAXS), we extrapolate a general principle of phase transition and its coupling with lattice anionic oxygen redox. These findings shed light on the advancement of high-capacity, stable-cycling and safe-operating Ni-rich cathode materials for next generation Li-ion batteries.

Peculiarities of electronic structure and composition in ultrasound milled silicon nanowires

The combined X-ray absorption and emission spectroscopy approach was applied for the detailed electronic structure and composition studies of silicon nanoparticles produced by the ultrasound milling of heavily and lowly doped Si nanowires formed by metal-assisted wet chemical etching. The ultrasoft X-ray emission spectroscopy and synchrotron based X-ray absorption near edges structure spectroscopy techniques were utilize to study the valence and conduction bands electronic structure together with developed surface phase composition qualitative analysis. Our achieved results based on the implemented surface sensitive techniques strongly suggest that nanoparticles under studies show a significant presence of the silicon suboxides depending on the pre-nature of initial Si wafers. The controlled variation of the Si nanoparticles surface composition and electronic structure, including band gap engineering, can open a new prospective for a wide range Si-based nanostructures application including the integration of such structures with organic or biological systems.

Reversible control of magnetic and transport properties of NdNiO3–δ epitaxial films

Rare-earth nickelates possess intrinsic charge order, orbital order, and electron-lattice coupling, which make them very interesting for applications in oxide-based electronic devices. In this study, we grew NdNiO3–δ (NNO) films with oxygen pressures changing from 27 to 10−5 Pa. With decreasing oxygen pressure, the antiferromagnetic state of the NNO film becomes a ferromagnetic state, and the resistance increases significantly. According to combined X-ray absorption spectroscopy and X-ray linear dichroism measurements, the ratio of Ni2+-ions increases with decreasing oxygen-pressure, and the preferred orbital occupation changes from x2-y2 to 3z2-r2. In addition, using the ionic-liquid gating method to control the migration of oxygen vacancies, both the magnetic properties and resistance of NNO films can be modulated reversibly. The oxygen vacancy induces a valence in the Ni ions and the orbital occupation changes, which alters the magnetic properties and the electronic transport in these NNO films. This study describes a novel tunable method for electronic devices that use NdNiO3–δ films, and opens new doors for future improvements and functionalities.

The structural and magnetic characterization of ironstone-derived magnetite ceramic nanopowders

This paper demonstrates how magnetite (Fe3O4) nanopowders with a controlled crystallite size are successfully synthesized from Indonesian ironstone by employing a co-precipitation method. The variation of acidic environments (i.e., pH 9, 10, and 11) during precipitation revealed the influences on their structure, magnetic and microwave absorption properties. The characterization of materials included a combined synchrotron X-ray diffraction (XRD) and X-ray absorption spectroscopy (XAS), high-resolution transmission electron microscope (HRTEM), and selected area electron diffraction (SAED) techniques. The magnetic and microwave absorption properties were characterized by vibrating sample magnetometer (VSM) and vector network analyzer (VNA), respectively. The structural characterization of the materials confirmed the formation of a single-phase magnetite which showed sphere-like agglomerated particles with a decreased average crystallite size with precipitation pH. The powders exhibited crystallite sizes of 9.8–13.4 nm. Additionally, the linear combination fitting (LCF) analysis of the XANES data showed a Fe2+/Fe3+ varying composition with pH. We found that, through the EXAFS fitting analysis on the first and second shells, interatomic distance decreased with increasing pH. Moreover, the M–H hysteresis loop demonstrated a ferrimagnetic behavior where the magnetization increased from 51.75 to 77.79 emu/g with decreasing crystallite size. Finally, the microwave absorption properties showed a significant change in reflection loss value from – 4.42 to – 23.11 dB with decreasing crystallite size.

Strain and electric field control of the orbital and spin order in multiferroic $$\hbox {BiMnO}_3$$

The new frontier for spintronics is the realization of devices in which the spin can be controlled by electric fields. Multiferroics, materials exhibiting strong interplay between spin and orbital degrees of freedom, are candidates for the realization of such a paradigm. In this work, we study the magnetoelectric coupling in epitaxial $$\hbox {BiMnO}_3$$ thin films which exhibit a large saturation magnetization. By combining X-ray absorption spectroscopy data and theoretical modeling, we demonstrate that $$\hbox {BiMnO}_3$$ thin films have an improper magnetoelectric behavior, characterized by competing antiferromagnetic and ferromagnetic correlations. As a consequence, we show that in these materials the Mn-3d orbital and magnetic orders can be tuned via the ferroelectric polarization, opening perspectives for the realization of novel spintronic devices.

Structural characterization of 3d metal adsorbed AgNPs

Abstract Silver nanoparticles AgNPs having small (6–8 nm) diameter, were synthesized in water in solutions and left interacting with diluted 3d metals (Co2+ or Ni2+ ions) solution (1–5 ppm range). The interactions between AgNPs and the metallic ions modify the optical response of the nanoparticles demonstrating their ability to capture metallic ions from water and making them valuable as metal contamination sensor. Here the coordination chemistry of Co and Ni adsorbed onto AgNPs is probed combining X-ray absorption spectroscopy (XAS) and X-ray photoelectron spectroscopy (XPS).