Structure of a new dense amorphous ice

The detailed structure of a new dense amorphous ice, VHDA, is determined by isotope substitution neutron diffraction. Its structure is characterized by a doubled occupancy of the stabilizing interstitial location that was found in high density amorphous ice, HDA. As would be expected for a thermally activated unlocking of the stabilizing "interstitial," the transition from VHDA to LDA (low-density amorphous ice) is very sharp. Although its higher density makes VHDA a better candidate than HDA for a physical manifestation of the second putative liquid phase of water, as for the HDA case, the VHDA to LDA transition also appears to be kinetically controlled

Structure of naturally hydrated ferrihydrite revealed through neutron diffraction and first-principles modeling

Ferrihydrite, with a ‘‘two-line’’ x-ray diffraction pattern (2L-Fh), is the most amorphous of the iron oxides and is ubiquitous in both terrestrial and aquatic environments. It also plays a central role in the regulation and metabolism of iron in bacteria, algae, higher plants, and animals, including humans. In this study, we present a single-phase model for ferrihydrite that unifies existing analytical data while adhering to fundamental chemical principles. The primary particle is small (20–50 Å) and has a dynamic and variably hydrated surface, which negates long-range order; collectively, these features have hampered complete characterization and frustrated our understanding of the mineral's reactivity and chemical/biochemical function. Near and intermediate range neutron diffraction (NIMROD) and first-principles density functional theory (DFT) were employed in this study to generate and interpret high-resolution data of naturally hydrated, synthetic 2L-Fh at standard temperature. The structural optimization overcomes transgressions of coordination chemistry inherent within previously proposed structures, to produce a robust and unambiguous single-phase model

Deep eutectic-solvothermal synthesis of nanostructured ceria.

Ceria is a technologically important material with applications in catalysis, emissions control and solid-oxide fuel cells. Nanostructured ceria becomes profoundly more active due to its enhanced surface area to volume ratio, reactive surface oxygen vacancy concentration and superior oxygen storage capacity. Here we report the synthesis of nanostructured ceria using the green Deep Eutectic Solvent reline, which allows morphology and porosity control in one of the less energy-intensive routes reported to date. Using wide Q-range liquid-phase neutron diffraction, we elucidate the mechanism of reaction at a molecular scale at considerably milder conditions than the conventional hydrothermal synthetic routes. The reline solvent plays the role of a latent supramolecular catalyst where the increase in reaction rate from solvent-driven pre-organization of the reactants is most significant. This fundamental understanding of deep eutectic-solvothermal methodology will enable future developments in low-temperature synthesis of nanostructured ceria, facilitating its large-scale manufacturing using green, economic, non-toxic solvents.We thank the UK ISIS Pulsed Neutron and Muon source at the Rutherford Appleton Laboratory and the UK Engineering and Physical Sciences Research Council (EPSRC) for co-funding a PhD studentship for O.S.H. in the Centre for Doctoral Training in Sustainable Chemical Technologies at the University of Bath (EP/L016354/1; STFC Studentship Agreement 3578) and LTM EPSRC’s Fellowship EP/L020432/2. We thank the ISIS Pulsed Neutron and Muon Source for beam time on the SANDALS instrument under allocation RB1510465. We thank Ursula Potter (Bath) for help with scanning electron microscopic and transmission electron microscopic imaging

Bulk and Confined Benzene-Cyclohexane Mixtures Studied by an Integrated Total Neutron Scattering and NMR Method

AbstractHerein mixtures of cyclohexane and benzene have been investigated in both the bulk liquid phase and when confined in MCM-41 mesopores. The bulk mixtures have been studied using total neutron scattering (TNS), and the confined mixtures have been studied by a new flow-utilising, integrated TNS and NMR system (Flow NeuNMR), all systems have been analysed using empirical potential structure refinement (EPSR). The Flow NeuNMR setup provided precise time-resolved chemical sample composition through NMR, overcoming the difficulties of ensuring compositional consistency for computational simulation of data ordinarily found in TNS experiments of changing chemical composition—such as chemical reactions. Unique to the liquid mixtures, perpendicularly oriented benzene molecules have been found at short distances from the cyclohexane rings in the regions perpendicular to the carbon–carbon bonds. Upon confinement of the hydrocarbon mixtures, a stronger parallel orientational preference of unlike molecular dimers, at short distances, has been found. At longer first coordination shell distances, the like benzene molecular spatial organisation within the mixture has also found to be altered upon confinement.</jats:p

Building Monte Carlo Models of Glasses Using Neutron and/or X-ray Diffraction Data

AbstractNeutron and X-ray diffraction are key techniques that are used to investigate the atomic and nanometric mesoscale structure of glasses and amorphous materials. These experimental methods probe the nuclear (neutron) or atomic (X-ray) pair correlation func- tions between atoms. For a glass containing N atom types, the information content of the data is low, considering that the data are a weighted sum of N(N+1)/2 partial pair correlation terms. This complexity can often make direct interpretation of results difficult or impossible. Modern computational methods can now rapidly refine atomistic models of disordered materials that satisfy the constraints imposed by diffraction data. These models can then be used to investigate how the partial pair correlation functions contribute to the total scattering data, given a chosen set of underlying physico-chemical constraints, and allow us to extract many structural functions of interest such as bond angle distributions and coordination number histograms. To illustrate these capabilities the technique of Empirical Potential Structure Refinement (EPSR), has been applied to a range of results from a selection of oxide-glass systems and the results provide a set of reference parameters that can be used in future studies on similar glass systems where EPSR is the goal