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Structure and composition of natural ferrihydrite nano-colloids in anoxic groundwater
Fe-rich mobile colloids play vital yet poorly understood roles in the biogeochemical cycling of Fe in groundwater by influencing organic matter (OM) preservation and fluxes of Fe, OM, and other essential (micro-)nutrients. Yet, few studies have provided molecular detail on the structures and compositions of Fe-rich mobile colloids and factors controlling their persistence in natural groundwater. Here, we provide comprehensive new information on the sizes, molecular structures, and compositions of Fe-rich mobile colloids that accounted for up to 72% of aqueous Fe in anoxic groundwater from a redox-active floodplain. The mobile colloids are multi-phase assemblages consisting of Si-coated ferrihydrite nanoparticles and Fe(II)-OM complexes. Ferrihydrite nanoparticles persisted under both oxic and anoxic/sulfidic conditions, which we attribute to passivation by Si and OM. These findings suggest that mobile Fe-rich colloids generated in floodplains can persist during transport through redox-variable soils and could be discharged to surface waters. These results shed new light on their potential to transport Fe, OM, and nutrients across terrestrial-aquatic interfaces.
Stabilization of Plutonium Nano-Colloids by Epitaxial Distortion on Mineral Surfaces
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Optimizing the SERS activity of 1,10 Phenanthroline molecule adsorbed on Au-Ag core-shell nano colloid
No abstract prepared.
Challenges in gravure and ink-jet printing of nano-colloidal inks.
Abstract not provided.
Dispersible Colloid Facilitated Release of Organic Carbon From Two Contrasting Riparian Sediments
In aqueous systems, including groundwater, nano-colloids (1–100 nm diameter) and small colloids (<450 nm diameter) provide a vast store of surfaces to which organic carbon (OC) can sorb, precluding its normal bioavailability. Because nanomaterials are ubiquitous and abundant throughout Earth systems, it is reasonable that they would play a significant role in biogeochemical cycles. As such, mineral nano-colloids (MNC) and small colloids, formed through mineral weathering and precipitation processes, are both an unaccounted-for reservoir and unquantified vector for transport of OC and nutrients and contaminants within watersheds. Water extractions and leaching experiments were conducted under (1) aerobic (ambient) and (2) anaerobic (environmental chamber) conditions for each of two contrasting riparian sediments from (1) Columbia River, Washington and (2) Tims Branch, South Carolina. Water dispersible colloid-adsorbed OC was as high as 48% of OC for Tims Branch anaerobic batch water extraction and as low as 0% for Columbia River aerobic batch water extractions. Anaerobic leaching from column experiments yielded higher colloid and OC release rates. Transmission electron microscopy with electron dispersive spectroscopy mapping revealed organic carbon associated with aggregations of nano-particulate silicate minerals and Mossbauer identified nano-particulate goethite. This exploratory study demonstrates that mineral facilitated release of OC in riparian sediments is both significant and variable between locations.
Sorption and Precipitation of Plutonium in the Presence of Goethite at Elevated Temperatures
We have examined the behavior of aqueous Pu(IV) and intrinsic Pu(IV) nano-colloids and interaction with goethite at 25 and 80°C and over a range of concentrations from undersaturated to oversaturated with respect to PuO 2 (am, hyd). In the presence or absence of goethite, temperature does not appear to greatly affect Pu concentrations in solution. The strong affinity of aqueous Pu(IV) for the goethite surface is explained by the epitaxial growth of bcc Pu 4 O 7 nano-colloids on the goethite substrate. The behavior is affected minimally by temperature. This strong affinity cannot be achieved when intrinsic Pu(IV) nano-colloids are reacted with goethite over 103 days. The results indicate that the fate of Pu is dependent on its initial form and its subsequent stability under changing geochemical conditions. Epitaxial growth of Pu 4 O 7 on the goethite surface will produce a strong association between Pu and goethite, which could also lead to significant colloid-facilitated transport. Both intrinsic colloids and those sorbed to goethite have the potential to be transported with groundwater. The long-term stability and desorption characteristics of these forms of colloidal Pu will be the focus of ongoing research in FY12. A comprehensive characterization of Pu sorbed to other minerals, such as, clays is the subject of ongoing research in FY11 and FY12.
Sorption Behavior and Morphology of Plutonium in the Presence of Goethite at 25 and 80°C
In this study, we examined the sorption behavior of Pu at elevated temperatures in the presence of one relevant mineral, goethite (α-FeOOH), over a range of concentrations that span solubility-controlled to adsorption-controlled concentrations. We focused on the sorptive behavior of two common forms of Pu: aqueous Pu(IV) and intrinsic Pu(IV) nano-colloids at 25 and 80°C in a dilute pH 8 NaCl/NaHCO 3 solution. The morphology of Pu sorbed to goethite was characterized using transmission electron microscopy (TEM). We examined the relative stability of PuO 2 precipitates, PuO 2 nano-colloids, Pu 4 O 7 surface precipitates, and monomeric sorbed Pu as a function of temperature and over a time scale of months.
Colloidal nano-MOFs nucleate and stabilize ultra-small quantum dots of lead bromide perovskites
We demonstrate a simple and effective host–guest strategy for preparing ultra-small lead bromide perovskite QDs through the use of nano-sized MOFs that function as nucleating and host sites.
Transport of Materials and Chemicals by Nano-scale Colloids and Micro to Macro-scale Flocs in Marine, Freshwater, and Engineered Systems
No abstract prepared.
Pair distribution function analysis of nano-object assemblies
The atomic pair distribution function (aPDF) analysis technique, also known as the total scattering method, which considers both Bragg and diffuse scattering, has been used extensively to probe local atomic arrangements in crystalline and disordered materials. In contrast, there have been limited applications of the PDF in self-assembled nanomaterials, which represent a class of materials built from nanoscale objects, such as nano-colloids, micelles and proteins. As distinguished from atoms, nano-objects have polydispersity in size and shape, and such form-factor effects complicate the application of PDF analysis to nano-systems. Here, in this paper, the application of the PDF is extended to spherical nano-object assemblies and the formulae for the nano-PDF (nPDF) are derived, showing some differences from the aPDF. By numerical simulations, the properties of the nPDF (peak broadening and pattern profile) are studied systematically as a function of structural features, such as nano-object parameters (size and size polydispersity) and assembly structural features (size, shape, structure type and lattice disorder), and of data processing parameters ( q cut-off and `missing' data in ultra-small-angle regions). The nPDF analysis method is found to provide an effective route to revealing not only nanoscale but also mesoscale structural properties, for example the morphology of a nano-assembly.
Influence of the goethite (α-FeOOH) surface on the stability of distorted PuO2 and PuO2–x phases
Abstract Experiments by [Powell, B. A., Dai, Z. R., Zavarin, M., Zhao, P. H., Kersting, A. B.: Stabilization of plutonium nano-colloids by epitaxial distortion on mineral surfaces. Environ. Sci. Technol.
Propagation of electro-kinetic waves in magnetized GaN semiconductor with nano-sized ion colloids
Based on hydrodynamic model of multi-component plasma, an analytical study on propagation of longitudinal electro-kinetic (LEK) waves in wurtzite and zincblende structures of GaN is carried out. Nano-sized ion colloids (NICs) are embedded in the sample by the technique of ion-implantation. The implanted NICs are considered massive by an order as compared to the host lattice points and do not participate in Based LEK perturbations. Though, the NICs are continuously bombarded by the electrons as well as the holes yet, the former acquires a net negative charge owing to relatively higher mobility of electrons and consequently results into depletion of electron density in the medium. It i s found that the presence of charged NICs significantly modifies the dispersion and amplification characteristics of LEK waves in magnetized GaN semiconductor plasma and their role becomes increasingly effective as the fraction of charge on them increases.
Spin echo small-angle neutron scattering using superconducting magnetic Wollaston prisms
Here, we show the implementation of superconducting magnetic Wollaston prisms for spin echo small-angle neutron scattering. Two calibration methods for the spin echo length are presented: one utilizing spin echo modulated small-angle neutron scattering and the other based on the neutron refraction by quartz wedge crystals. Our experimental results with polystyrene nano-particle colloids showcase the system’s efficacy in measuring both dilute and concentrated colloidal systems. Additionally, investigations into the pore diameter and pitch of a nano-porous alumina membrane demonstrate its capability in analyzing nano-porous materials. Furthermore, we discuss potential optimizations to further extend the accessible spin echo length.
Electro-Optic Effects in Colloidal Dispersion of Metal Nano-Rods in Dielectric Fluid
In modern transformation optics, one explores metamaterials with properties that vary from point to point in space and time, suitable for application in devices such as an “optical invisibility cloak” and an “optical black hole”. We propose an approach to construct spatially varying and switchable metamaterials that are based on colloidal dispersions of metal nano-rods (NRs) in dielectric fluids, in which dielectrophoretic forces, originating in the electric field gradients, create spatially varying configurations of aligned NRs. The electric field controls orientation and concentration of NRs and thus modulates the optical properties of the medium. Using gold (Au) NRs dispersed in toluene, we demonstrate electrically induced change in refractive index on the order of 0.1.
Soft matter roadmap
Soft materials are usually defined as materials made of mesoscopic entities, often self-organised, sensitive to thermal fluctuations and to weak perturbations. Archetypal examples are colloids, polymers, amphiphiles, liquid crystals, foams. The importance of soft materials in everyday commodity products, as well as in technological applications, is enormous, and controlling or improving their properties is the focus of many efforts. From a fundamental perspective, the possibility of manipulating soft material properties, by tuning interactions between constituents and by applying external perturbations, gives rise to an almost unlimited variety in physical properties. Together with the relative ease to observe and characterise them, this renders soft matter systems powerful model systems to investigate statistical physics phenomena, many of them relevant as well to hard condensed matter systems. Understanding the emerging properties from mesoscale constituents still poses enormous challenges, which have stimulated a wealth of new experimental approaches, including the synthesis of new systems with, e.g. tailored self-assembling properties, or novel experimental techniques in imaging, scattering or rheology. Theoretical and numerical methods, and coarse-grained models, have become central to predict physical properties of soft materials, while computational approaches that also use machine learning tools are playing a progressively major role in many investigations. This Roadmap intends to give a broad overview of recent and possible future activities in the field of soft materials, with experts covering various developments and challenges in material synthesis and characterisation, instrumental, simulation and theoretical methods as well as general concepts.
Early stage structural development of prototypical zeolitic imidazolate framework (ZIF) in solution
Given the wide-ranging potential applications of metal organic frameworks (MOFs), an emerging imperative is to understand their formation with atomic scale precision. This will aid in designing syntheses for next-generation MOFs with enhanced properties and functionalities. Major challenges are to characterize the early-stage seeds, and the pathways to framework growth, which require synthesis coupled with in situ structural characterization sensitive to nanoscale structures in solution. Here we report measurements of an in situ synthesis of a prototypical MOF, ZIF-8, utilizing synchrotron X-ray atomic pair distribution function (PDF) analysis optimized for sensitivity to dilute species, complemented by mass spectrometry, electron microscopy, and density functional theory calculations. We observe that despite rapid formation of the crystalline product, a high concentration of Zn(2-MeIm) 4 (2-MeIm=2-methylimidazolate) initially forms and persists as stable clusters over long times. A secondary, amorphous phase also pervades during the synthesis, which has a structural similarity to the final ZIF-8 and may act as an intermediate to the final product.
Deformation of Nano‐Metallic Glasses Made using Colloidal Synthesis
Final report