Neutron Scattering Spectroscopy Research Articles

A Vision for the Future of Neutron Scattering and Muon Spectroscopy in the 2050s

A Vision for the Future of Neutron Scattering and Muon Spectroscopy in the 2050s

A Vision for the Future of Neutron Scattering and Muon Spectroscopy in the 2050s

A Vision for the Future of Neutron Scattering and Muon Spectroscopy in the 2050s

Supported Metal Nanoparticles‐Based Catalysts and their Interactions with H2: Insights from Inelastic Neutron Scattering Spectroscopy

AbstractThe investigation of supported metal nanoparticle in the presence of H2 is fundamental to better understand their behavior as hydrogenation catalysts. In this respect, this review will focus on the main recent results obtained by Inelastic Neutron Scattering (INS) spectroscopy, which is of particular interest thanks to its ability to provide very detailed vibrational spectra of the H‐containing species in the sample. The review will cover the main results concerning the characterization of the H‐species already present in the pristine catalyst, with a particular focus on carbon‐based materials and their modification upon the interaction with metal nanoparticles. Successively, the forms in which H2 interacts with the catalysts will be examined, starting from H2 physisorption, to then pass to the metal hydride species formed through the splitting of dihydrogen upon the active metallic phase, and finally to the migration of atomic hydrogen from the metal nanoparticles onto the support as a result of hydrogen spillover. The aim of the review is to present an overview of all the hydrogenous species identifiable by INS spectroscopy in hydrogenation catalysts, focusing on the specific case of supported metal nanoparticles systems.

Inelastic neutron scattering study of the H2 interaction with carbon-supported Pt and Pd catalysts

Carbon-supported Pt and Pd catalysts are largely employed as heterogeneous catalysts for hydrogenation reactions. Albeit their routine use in industry, many details about their interaction with H2 are still not completely understood. In this article, we propose a detailed investigation of the behavior in the presence of H2 of an activated carbon and of two catalysts obtained by depositing on it Pt and Pd nanoparticles by means of Inelastic Neutron Scattering (INS) spectroscopy. The high-quality INS spectra of the three samples were measured in absence and in presence of different amounts of H2, providing very detailed information about H2 physisorption on each system and about the nature of the metal hydrides formed upon hydrogenation of the catalysts. In addition, we were also able to obtain a direct observation of the occurrence of hydrogen spillover from the metal nanoparticles onto the activated carbon, as revealed by the increase of the number of C-H species at the borders of the graphenic domains. Overall, this work provides important insights for better understanding the complex nature of the interaction between H2 and Pt and Pd-loaded activated carbon catalysts.

Looking for Minor Phenolic Compounds in Extra Virgin Olive Oils Using Neutron and Raman Spectroscopies.

Extra virgin olive oil (EVOO) is defined as a functional food as it contains numerous phenolic components with well-recognized health-beneficial properties, such as high antioxidant and anti-inflammatory capacity. These characteristics depend on their structural/conformational behavior, which is largely determined by intra- and intermolecular H-bond interactions. While the vibrational dynamics of isolated compounds have been studied in a number of recent investigations, their signal in a real-life sample of EVOO is overwhelmed by the major constituent acids. Here, we provide a full characterization of the vibrational spectroscopic signal from commercially available EVOO samples using Inelastic Neutron Scattering (INS) and Raman spectroscopies. The spectra are dominated by CH2 vibrations, especially at about 750 cm−1 and 1300 cm−1. By comparison with the spectra from hydroxytyrosol and other minor phenolic compounds, we show that the best regions in which to look for the structure–activity information related to the minor polar compounds is at 675 and 1200 cm−1 for hydroxytyrosol, and around 450 cm−1 for all minor polar compounds used as reference, especially if a selectively deuterated sample is available. The regional origin of the EVOO samples investigated appears to be related to the different amount of phenolic esters versus acids as reflected by the relative intensities of the peaks at 1655 and 1747 cm−1.

Inter- vs. Intramolecular Hydrogen Bond Patterns and Proton Dynamics in Nitrophthalic Acid Associates.

Noncovalent interactions are among the main tools of molecular engineering. Rational molecular design requires knowledge about a result of interplay between given structural moieties within a given phase state. We herein report a study of intra- and intermolecular interactions of 3-nitrophthalic and 4-nitrophthalic acids in the gas, liquid, and solid phases. A combination of the Infrared, Raman, Nuclear Magnetic Resonance, and Incoherent Inelastic Neutron Scattering spectroscopies and the Car–Parrinello Molecular Dynamics and Density Functional Theory calculations was used. This integrated approach made it possible to assess the balance of repulsive and attractive intramolecular interactions between adjacent carboxyl groups as well as to study the dependence of this balance on steric confinement and the effect of this balance on intermolecular interactions of the carboxyl groups.

How do the graphenic domains terminate in activated carbons and carbon-supported metal catalysts?

This work is focused on the determination of the most likely border morphologies in the H-terminated graphenic domains that constitute activated carbons, focusing on four different carbons and six supported-metal catalysts. Among the available characterization techniques, Inelastic Neutron Scattering spectroscopy provides detailed vibrational spectra containing the fingerprint of the terminal C-H groups of carbon materials. From the experimental spectra, we observed clear differences among carbons having different origin, and a systematic decrease in the integrated area upon metal deposition that linearly scales with the nanoparticles dispersion. Density Functional Theory simulations are fundamental to assign the experimental bands to specific species. Thus, an extended simulation work on both regular and defective aromatic models was carried out, providing the inelastic neutron scattering fingerprint of a large number of different C-H terminations. By fitting the experimental spectra with a linear combination of the simulated spectra, it was possible to quantify the concentration of each terminal C-H geometry in the samples, and to identify the species most affected by the metal nanoparticles deposition. Specific benzene rings exposing a single C-H group appear to have a decisive role in the interaction with the metal nanoparticles and their deposition procedure.

Onset of Propene Oligomerization Reactivity in ZSM-5 Studied by Inelastic Neutron Scattering Spectroscopy.

The techniques of quasi-elastic and inelastic neutron scattering (QENS and INS) are applied to investigate the oligomerization of propene over a ZSM-5 zeolite. Investigations are performed at low temperatures, allowing identification of the onset of the oligomerization reaction and observation of the low-energy spectral changes due to intermediate formation that are difficult to observe by optical methods. Oligomerization proceeds via formation of a hydrogen-bonded precursor by an interaction of the propene with an internal acid site followed by protonation and chain growth with protonation being the rate-limiting step. The use of quasi-elastic neutron scattering to observe changes in system mobility with temperature via the elastic window scan technique allows identification of the active temperature range where catalyst activity commences and permits targeting of the more time-consuming INS investigations to conditions of interest. From examination of the product’s spectrum, the structure of the resulting oligomer is deduced to be primarily linear.

Morphology of Thin Film Composite Membranes Explored by Small-Angle Neutron Scattering and Positron-Annihilation Lifetime Spectroscopy.

The morphology of thin film composite (TFC) membranes used in reverse osmosis (RO) and nanofiltration (NF) water treatment was explored with small-angle neutron scattering (SANS) and positron-annihilation lifetime spectroscopy (PALS). The combination of both methods allowed the characterization of the bulk porous structure from a few Å to µm in radius. PALS shows pores of ~4.5 Å average radius in a surface layer of about 4 μm thickness, which become ~40% smaller at the free surface of the membranes. This observation may correlate with the glass state of the involved polymer. Pores of similar size appear in SANS as closely packed pores of ~6 Å radius distributed with an average distance of ~30 Å. The main effort of SANS was the characterization of the morphology of the porous polysulfone support layer as well as the fibers of the nonwoven fabric layer. Contrast variation using the media H2O/D2O and supercritical CO2 and CD4 identified the polymers of the support layers as well as internal heterogeneities.

New Insights about CuO Nanoparticles from Inelastic Neutron Scattering.

Inelastic Neutron Scattering (INS) spectroscopy has provided a unique insight into the magnetodymanics of nanoscale copper (II) oxide (CuO). We present evidence for the propagation of magnons in the directions of the ordering vectors of both the commensurate and helically modulated incommensurate antiferromagnetic phases of CuO. The temperature dependency of the magnon spin-wave intensity (in the accessible energy-range of the experiment) conforms to the Bose population of states at low temperatures (T ≤ 100 K), as expected for bosons, then intensity significantly increases, with maximum at about 225 K (close to TN), and decreases at higher temperatures. The obtained results can be related to gradual softening of the dispersion curves of magnon spin-waves and decreasing the spin gap with temperature approaching TN on heating, and slow dissipation of the short-range dynamic spin correlations at higher temperatures. However, the intensity of the magnon signal was found to be particle size dependent, and increases with decreasing particle size. This “reverse size effect” is believed to be related to either creation of single-domain particles at the nanoscale, or “superferromagnetism effect” and the formation of collective particle states.

Synthesis, Computational Studies, Inelastic Neutron Scattering, Infrared and Raman Spectroscopy of Ruthenocene

In this work we report a new and simplified synthesis of ruthenocene that prevents the formation of unwanted by‐products. We have also revisited the vibrational spectroscopy of this iconic molecule and in addition to infrared and variable temperature Raman spectra, we present the first inelastic neutron scattering (INS) spectrum, a technique that is little used in inorganic chemistry. The Raman spectra in the low energy range (< 200 cm–1) clearly show that the mode assigned as the ring–Ru–ring torsion is a librational mode. By generating the INS spectra predicted by previous assignment schemes we are able to show that they are all, at least partially, wrong because they fail to correctly predict the experimental INS spectrum. In the case of ruthenocene, the addition of INS data, in combination with periodic‐DFT calculations, has enabled the first correct assignment of the internal modes of ruthenocene. This straightforward means to test proposed assignments is one of the great strengths of vibrational spectroscopy with neutrons.

Ion Dynamics in Ionic-Liquid-Based Li-Ion Electrolytes Investigated by Neutron Scattering and Dielectric Spectroscopy.

A detailed understanding of the diffusion mechanisms of ions in pure and doped ionic liquids remains an important aspect in the design of new ionic-liquid electrolytes for energy storage. To gain more insight into the widely used imidazolium-based ionic liquids, the relationship between viscosity, ionic conductivity, diffusion coefficients, and reorientational dynamics in the ionic liquid 3-methyl-1-methylimidazolium bis(trifluoromethanesulfonyl)imide (DMIM-TFSI) with and without lithium bis(trifluoromethanesulfonyl)imide (Li-TFSI) was examined. The diffusion coefficients for the DMIM+ cation and the role of ion aggregates were investigated by using the quasielastic neutron scattering (QENS) and neutron spin echo techniques. Two diffusion mechanisms are observed for the DMIM+ cation with and without Li-TFSI, that is, translational and local. The data additionally suggest that Li+ ion transport along with ion aggregates, known as the vehicle mechanism, may play a significant role in the ion diffusion process. These dielectric-spectroscopy investigations in a broad temperature and frequency range reveal a typical α-β-relaxation scenario. The α relaxation mirrors the glassy freezing of the dipolar ions, and the β relaxation exhibits the signatures of a Johari-Goldstein relaxation. In contrast to the translational mode detected by neutron scattering, arising from the decoupled faster motion of the DMIM+ ions, the α relaxation is well coupled to the dc charge transport, that is, the average translational motion of all three ion species in the material. The local diffusion process detected by QENS is only weakly dependent on temperature and viscosity and can be ascribed to the typical fast dynamics of glass-forming liquids.

Hydrogen Bond Dynamics of Cellulose through Inelastic Neutron Scattering Spectroscopy.

This work explores the dynamics of hydrogen bond networks in cellulose through inelastic neutron scattering (INS) and periodic CASTEP calculations. Estimated spectra were based on the crystal structure of cellulose Iα and Iβ and replicate the INS spectrum of cellulose samples with remarkable similarity, allowing a reliable assignment of INS bands to vibrational modes of cellulose. Comparison of cellulose samples from varied sources, from bacterial to kraft pulp, allows the identification of characteristic INS bands, arising from C2-OH torsional motions, which easily identify which allomorph-Iα or Iβ-is prevalent. A high crystallinity index is revealed by the presence of well-defined INS bands associated with highly cooperative CH bending modes along the chain. Hydrating kraft cellulose samples clearly affects those INS bands related with the hydroxymethyl group, identified as the preferred binding site for water molecules. At high humidity content level, a significant proportion of the water molecules is aggregated in clusters within the amorphous cellulose domains. The formation of ice microcrystals leads to a partial disruption of the hydrogen-bond network, as can be concluded from the observed red-shift of the torsional OH vibrational modes. The full assignment and interpretation of cellulose's INS spectra herein provided is a sound basis for future use of INS spectroscopy in the characterization of functionalized cellulose fibers and composite materials.

Quantum twin spectra in nanocrystalline silicon

Using inelastic neutron-scattering spectroscopy, we have identified twin-split scattering spectra in hydrogen-terminated nanocrystalline silicon. We show that this duality originates from the cooperative motion of hydrogen and silicon. Our formalism for the inelastic neutron-scattering spectrum, which is derived from the Hermite orthogonal wave functions in terms of the normal coordinates, elucidates the physical origin of the observed quantum twin spectra and predicts the possible occurrence of this behavior in other materials such as metal hydrides.

Structure and dynamics of cetyltrimethylammonium chloride-sodium dodecylsulfate (CTAC-SDS) catanionic vesicles: High-value nano-vehicles from low-cost surfactants

HypothesisCatanionic vesicles based on large-scale produced surfactants represent a promising platform for the design of innovative, effective and relatively inexpensive nano-vehicles for a variety of actives. Structural, dynamic and functional behavior of these aggregates is finely tuned by the molecular features of their components and can be opportunely tailored for their applications as drug carriers. ExperimentsHere we investigate the aggregates formed by CTAC and SDS, two of the most diffused surfactants, by means of Dynamic Light Scattering, Small Angle Neutron Scattering and Electron Paramagnetic Resonance spectroscopy (EPR). The exploitation of these aggregates as nano-vehicles is explored using the poorly water-soluble antioxidant trans-resveratrol (t-RESV), testing t-RESV solubility and antioxidant activity by means of UV, fluorescence spectroscopy and EPR. FindingsThe presence of a large stability region of catanionic vesicles on the CTAC-rich side of the phase diagram is highlighted and interpreted in terms of the mismatch between the lengths of the surfactant tails and of first reported effects of the chloride counterions. CTAC-SDS vesicles massively solubilize t-RESV, which in catanionic vesicles exerts a potent antioxidant and radical-scavenging activity. This behavior arises from the positioning of the active at the surface of the vesicular aggregates thus being sufficiently exposed to the external medium.

Competitive and Synergistic Interactions between Polymer Micelles, Drugs, and Cyclodextrins: The Importance of Drug Solubilization Locus.

Polymeric micelles, in particular PEO-PPO-based Pluronic, have emerged as promising drug carriers, while cyclodextrins (CD), cyclic oligosaccharides with an apolar cavity, have long been used for their capacity to form inclusion complexes with drugs. Dimethylated β-cyclodextrin (DIMEB) has the capacity to fully breakup F127 Pluronic micelles, while this effect is substantially hindered if drugs are loaded within the micellar aggregates. Four drugs were studied at physiological temperature: lidocaine (LD), pentobarbital sodium salt (PB), sodium naproxen (NP), and sodium salicylate (SAL); higher temperatures shift the equilibrium toward higher drug partitioning and lower drug/CD binding compared to 25 °C ( Valero, M.; Dreiss, C. A. Growth, Shrinking, and Breaking of Pluronic Micelles in the Presence of Drugs and/or β-Cyclodextrin, a Study by Small-Angle Neutron Scattering and Fluorescence Spectroscopy . Langmuir 2010 , 26 , 10561 - 10571 ). The impact of drugs on micellar structure was characterized by small-angle neutron scattering (SANS), while their solubilization locus was revealed by 2D NOESY NMR. UV and fluorescence spectroscopy, Dynamic and Static Light Scattering were employed to measure a range of micellar properties and drug:CD interactions: binding constant, drug partitioning within the micelles, critical micellar concentration of the loaded micelles, aggregation number (Nagg). Critically, time-resolved SANS (TR-SANS) reveal that micellar breakup in the presence of drugs is substantially slower (100s of seconds) than for the free micelles (<100 ms) ( Valero, M.; Grillo, I.; Dreiss, C. A. Rupture of Pluronic Micelles by Di-Methylated β-Cyclodextrin Is Not Due to Polypseudorotaxane Formation . J. Phys. Chem. B 2012 , 116 , 1273 - 1281 ). These results combined together give new insights into the mechanisms of protection of the drugs against CD-induced micellar breakup. The outcomes are practical guidelines to improve the design of drug delivery systems as well as a better understanding of competitive assembly mechanisms leading to shape and function modulation.

Elastic Scattering Spectroscopy (ESS): an Instrument-Concept for Dynamics of Complex (Bio-) Systems From Elastic Neutron Scattering.

A new type of neutron-scattering spectroscopy is presented that is designed specifically to measure dynamics in bio-systems that are difficult to obtain in any other way. The temporal information is largely model-free and is analogous to relaxation processes measured with dielectric spectroscopy, but provides additional spacial and geometric aspects of the underlying dynamics. Numerical simulations of the basic instrument design show the neutron beam can be highly focussed, giving efficiency gains that enable the use of small samples. Although we concentrate on continuous neutron sources, the extension to pulsed neutron sources is proposed, both requiring minimal data-treatment and being broadly analogous with dielectric spectroscopy, they will open the study of dynamics to new areas of biophysics.

PEGylated nanocapsules of perfluorooctyl bromide: Mechanism of formation, influence of polymer concentration on morphology and mechanical properties

PEGylated nanocapsules containing a liquid core of perfluorooctyl bromide (PFOB) were formulated by an emulsion-evaporation process to be further used as ultrasound contrast agents (UCAs). In an attempt to modulate their acoustic response, related to their shell thickness-to-radius ratio, the initial concentration of polymer was varied in the formulation. Indeed, thinner shells may lead to higher echogenicity. PEGylated nanocapsules morphology was studied by electron microscopy, Small Angle Neutron Scattering and 19F NMR spectroscopy and related to their mechanical properties to allow a better understanding of their mechanism of formation. We show that the variation of polymer concentration in the formulation impacts the formation mechanism of nanocapsules, and consequently their morphology and mechanical properties. Using low concentration of Poly(ethylene glycol)-b-poly(dl-lactide-co-glycolide) (PLGA-b-PEG), it is impossible to reduce the shell thickness of the UCA, most probably due to dewetting of the polymer layer at the PFOB/water interface. This leads to the coexistence of thick shells along with free PFOB droplets. On the other hand, for high polymer concentration, PEGylated nanocapsules with thick shells were produced with high encapsulation efficiency.

General Selection Rule in the Inelastic Neutron Scattering Spectroscopy of a Diatomic Molecule Confined Inside a Near-Spherical Nanocavity.

Knowledge of the relevant selection rules is crucial for the accurate interpretation of experimental spectra in general. There has been a consensus for a long time that the incoherent inelastic neutron scattering (INS) spectroscopy of the vibrations of discrete molecular compunds is free from any selection rules. We contradict this widely held view by presenting an analytical derivation of the general selection rule for the INS spectroscopy of a hydrogen molecule inside a near-spherical nanocavity. It defines all forbidden transitions, originating in a range of initial translation-rotation (TR) states, ground and excited, of the caged para- and ortho-H2, as well as HD, that are unobservable in the INS spectra. These predictions are amenable to experimental verification. In addition, we demonstrate that the general selection rule applies to the INS spectroscopy of any diatomic molecule in a nanocavity with near-spherical symmetry, which exhibits strong TR coupling. Its existence strongly suggests that similar selection rules apply to the INS spectra of other molecular and supramolecular systems, and need to be identified.

Assignment of the Internal Vibrational Modes of C70 by Inelastic Neutron Scattering Spectroscopy and Periodic-DFT.

The fullerene C70 may be considered as the shortest possible nanotube capped by a hemisphere of C60 at each end. Vibrational spectroscopy is a key tool in characterising fullerenes, and C70 has been studied several times and spectral assignments proposed. Unfortunately, many of the modes are either forbidden or have very low infrared or Raman intensity, even if allowed. Inelastic neutron scattering (INS) spectroscopy is not subject to selection rules, and all the modes are allowed. We have obtained a new INS spectrum from a large sample recorded at the highest resolution available. An advantage of INS spectroscopy is that it is straightforward to calculate the spectral intensity from a model. We demonstrate that all previous assignments are incorrect in at least some respects and propose a new assignment based on periodic density functional theory (DFT) that successfully reproduces the INS, infrared, and Raman spectra.