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International audience; Photocatalytic production of fuels, even in small quantities, from the mineralization of hazardous pollutants, is a promising and renewable way of recycling wastewater. In the present work, the potential of methyl functionalized inorganic aluminosilicate nanotubes (methyl imogolite/Imo-CH3) as photocatalytic nanoreactors for this application is demonstrated. Using the phototoxic polycyclic aromatic hydrocarbon dibenzo(a,h)anthracene (DBAN) as a model pollutant, we show that DBAN molecules can be efficiently trapped inside Imo-CH3 nanotubes from an aqueous medium to undergo subsequent oxidative photo-degradation under UV light. The kinetics of this photo-degradation were shown to depend strongly on both the initial DBAN concentration in the nanotubes and the presence/absence of dissolved dioxygen. The photo-degradation process followed a complex mechanistic pathway, consisting of combined photo-oxidation and photo-cycloaddition reactions, where detection of carbon dioxide (CO2) as a photo-oxidation product confirmed the mineralization of encapsulated DBAN. CO and CH4 molecules were also formed, however these could arise from the further photo-reduction of CO2 on the external surface of the nanotubes. Moreover, dihydrogen (H2) was produced upon UV illumination under anaerobic conditions due to water reduction reactions on the external surfaces of Imo-CH3 nanotubes. The possible mechanistic pathways of these processes are proposed, and the dual capability of Imo-CH3 nanotubes for simultaneous pollutant degradation and H2 production is then demonstrated – a rare feat for a single photocatalyst material.

Using the 90–105 keV gamma-rays for determining Pu isotopic composition is studied for dilute Pu solutions (0.0001–0.05 μg/mm3) as well as Pu-U mixed solutions. It is shown that for concentrations higher than 0.001 μg/mm3 Pu, results match well with those of mass spectrometric results. However, in mixed solutions, beyond 0.005 mg/mm3 U concentration, the errors on isotopic compositions of Pu increased as U content increased.

Galvanic replacement between metals has received notable research interest for the synthesis of heterometallic nanostructures. The growth pattern of the nanostructures depends on several factors such as extent of lattice mismatch, adhesive interaction between the metals, cohesive forces of the individual metals, etc. Due to the difficulties in probing ultrafast kinetics of the galvanic replacement reaction and particle growth in solution, real-time mechanistic investigations are often limited. As a result, the growth mechanism of one metal on the surface of another metal at the nanoscale is poorly understood so far. In the present work, we could successfully probe the galvanic replacement of silver ions with nickel nanoparticles, stabilized in a polymer membrane, using two complementary methods, namely, small-angle X-ray scattering (SAXS) and radiolabeling, and the results are supported by density functional theory (DFT) computations. The silver-nickel system has been chosen for the present investigation because of the high degree of bulk immiscibility caused by the large lattice mismatch (15.9%) and the weak adhesive interaction, which makes it a perfect model system for immiscible metal pairs. Membrane, as a host medium, plays a crucial role in retarding the kinetics of atomic and particle rearrangements (nucleation and growth) due to slower mobility of the atoms (monomers) and particles within the polymer network. This allowed us to examine the real-time concentration of silver monomers during galvanic replacement of silver ions with nickel nanoparticles and evolution of Ni/Ag nanoparticles. From combined experiment and DFT computations, it has been demonstrated, for the first time to the best of our knowledge, that the majority of silver atoms, which are produced on the nickel nanoparticle surface by galvanic reactions, do not form traditional core-shell nanostructures with nickel and undergo a self-governing sequential nucleation and growth of silver nanoparticles via formation of intermediate prenucleation silver clusters, leading to the formation of mixed metallic nanoparticles in the membrane. The surface of NiNPs has a heterogeneous effect on the silver nucleation pathway, which is evident from the reduced critical free energy barrier of nucleation (Δ

We report the H I bond activation on free and confined silver tetramer clusters using the first principles approach. The objective of this study is to underscore the effect of confinement on the chemical reactivity of Ag4. All calculations were carried out under the density functional theory formalism using both atomic and plane wave basis sets. We have used armchair carbon nanotube as a model system for confinement. The results show that the interaction energy is increased inside nanotube, leading to enhanced bond stretching. The origin of such effect has been demonstrated using molecular orbital theory and electronic density of state analysis.

This paper presents a standardless non-destructive method for simultaneous assay of uranium and plutonium in mixed samples relevant to nuclear safeguards, forensics and fuel cycle. The method is based on an in-situ absolute efficiency calibration of a γ-ray detector using plutonium γ-rays that can subsequently be used for quantification of uranium in the sample. The method was tested by assaying U–Pu samples with known amounts of U and Pu with varying mass, geometry, composition, reactor type, age and fissile isotope enrichment.

A catalytic nanoreactor with remarkable activity has been prepared by in-situ synthesis of colloidal silver nanoparticles of different sizes in a tailor made pore filled anion exchange membrane (AEM). Time resolved small angle X-ray scattering (SAXS) and field-emission scanning electron microscopy (FE-SEM) probe the evolution of size distribution of the nanoparticles during the course of synthesis. Borohydride reduction of para -nitrophenol to para -aminophenol has been used as a model reaction for catalysis throughout the study. Role of nanoparticle size vis-a-vis the role of nanoscale confinement on catalytic reaction has been investigated. It has been demonstrated that the overall catalytic performance of the silver nanoparticles is improved significantly in the nanoconfined environment as compared to that of the bare nanoparticles. The origin of such improved catalytic activity of spatially confined silver nanoparticles has been attributed to the effect of “nanoconfinement” that seems to accelerate the catalytic reduction. It has been shown that the catalytic rate constant is strongly dependent on the average occupancy of the para -nitrophenol molecule per pore when it is significantly less than one. This extraordinary effect may be attributed to the compartmentalization of the reactant molecules in nanoscale subvolumes, which essentially favours the forward reaction because of reduced molecular mixing of reactant with product.

Size controlled synthesis of nanoparticles in a structured media, such as a membrane, has not yet been achieved successfully in comparison to that in solution due to the lack of mechanistic investigations on the nucleation and growth of nanoparticles in these media. Slower diffusion of precursor and monomer species inside these structured media complicates the nanoparticle formation mechanism. We herein report a novel experimental approach to reveal the mechanism of nucleation and growth during the synthesis of silver nanoparticles in a Nafion-117 membrane using radiolabeling and small angle X-ray scattering (SAXS). The study has been conducted under the conditions of continuous supply of precursor (silver citrate). Repetitive “LaMer type” nucleations have been found to occur in the membrane leading to the formation of polydispersed spherical nanoparticles as evident from time resolved small angle X-ray scattering. These repetitive nucleations have been shown to be responsible for continuous birth of new seeds, which grow to larger particles, mainly by random coagulation introducing non-uniformity in the growth profile of nanoparticles. The additional nucleation events have been successfully ceased by careful tuning of reaction temperature and precursor concentration, thereby eliminating the nanoparticle growth by random coagulation. This has led to the formation of silver nanoparticles with improved morphology and size distributions, which has been manifested in remarkable improvement in the optical quality of the silver nanoparticles. The present study is the first of its kind showing the crucial role of the membrane host in retarding the reaction kinetics which allowed successful probing of temporal variation of monomer concentration during nucleation and growth using a radiotracer. This was hitherto difficult to probe in solution due to its ultrafast kinetics. Additionally, using the experimental monomer concentrations during nucleation, the free energy of activation (ΔGcrit) and the critical radius (rcrit) for nucleation have been estimated and found to be 73 kJ mol−1 and 6.6 A, respectively. The present work validates the well known theoretical model by La Mer for the synthesis of nanoparticles in a membrane under continuous precursor supply.

Segmented gamma-ray scanning (SGS) is a traditional practice, globally, for the non-destructive assay of special nuclear materials (SNMs) in large volume radioactive waste drums. The conventional SGS is a relative two pass method and requires a standard drum of identical geometry. The present work is focused on identifying the limitations of traditional segmented gamma scanning methodology for the assay of waste drums containing plutonium lumps. It has been observed that, for drums containing Pu lumps, the conventional SGS methodology severely underestimates the assay results (~ 2–6 times depending on the gamma-ray energy) due to attenuation under-correction. An alternate single pass absolute efficiency approach following the principle of infinite energy extrapolation of apparent mass has been proposed for the assay of waste drums containing Pu lumps in various random and biased spatial distributions and has been found to agree within 1–10% with the actual value with a maximum uncertainty of 8%. The method has been further validated at higher collimator widths and it has been demonstrated that an increase in collimator width from 5.1 to 10.3 cm increases the throughput of the present system without much of losing the accuracy.

Large volume radioactive waste drums with low/intermediate level of alpha activity, generated in radiochemical laboratories, are in general screened for special nuclear materials (SNM) in a segmented gamma scanner (SGS) before disposal. The assay methodology traditionally requires a standard drum of identical geometry and thereby making the procedure relying on the availability of a true standard, which is often difficult to organize. Here, we report a non-conventional absolute segmented gamma scanning (ASGS) methodology for the assay of 200 L waste drums, avoiding the use of a standard drum. The present analysis employ the full energy peak (FEP) efficiency, ingeniously determined using a standard 152Eu point source. From combined experiment and Monte Carlo simulation, it has been established that, the FEP efficiencies of the detector for a 200 L cylindrical sample can be well reproduced using a point source. While verifying the applicability of the point source FEP efficiencies for the assay of plutonium in 200 L drums, an energy dependent bias has been seen, which confirms the presence of lump attenuation in addition to the general matrix attenuation. An infinite energy extrapolation of apparent mass approach has been adopted for the assay of large volume waste drums which takes care of the gamma-ray attenuation from all sources that is otherwise difficult to correct for in a sample drum of unknown history.

We report the preparation of an optical test strip for quantitative assay of hydrogen peroxide (H2O2) in aqueous solution. Silver nanoparticles(AgNPs) with good optical quality are synthesized by in-situ reduction of silver ions in Nafion-117 membrane previously absorbed with ascorbate ion (HA(-)). The nanocomposite membrane exhibits a narrow Localized Surface Plasmon Resonance (LSPR) band at 413 nm. The extent of decrease in intensity of the LSPR band in presence of H2O2 solution gives quantitative estimate of H2O2 concentration. The detector has been found to show a good analytical response towards H2O2 detection at pH 7 over a wide concentration range. The detection limit has been calculated to be 2.6 x 10(-8) mol L-1, which is lower than the conventional enzyme based biosensors. The present test strip has been succesfully employed for the quantitative assay of H2O2 in milk. The mechanism of change in LSPR in presence of H2O2 (1.0 x 10(-3) mol L-1) has been explored for the first time using time resolved Small-Angle X-ray Scattering and radiotracer techniques. The results show that at this concentration of H2O2, its sharp oxidative sawing action is responsible for cutting off the nanoparticles into smaller fragments resulting in rapid reduction of absorption crossection. (C) 2017 Elsevier B.V. All rights reserved.

Formation of highly stable metal nanostructures in a Nafion® membrane with various aspect ratios has been of considerable research interest in recent years. However, there is a need for a proper understanding of the growth mechanism of such nanostructures in Nafion® (sometimes larger than the size of water–sulfonate ionic clusters of the membrane). In this work, the early growth kinetics of silver nanoparticles (NPs) in Nafion®-117 ion-exchange membrane during in situ L-ascorbic acid reduction of Ag+ ions by time resolved in situ small-angle X-ray scattering (SAXS) using synchrotron radiation with a time resolution of 50 ms are revealed for the first time. The SAXS analyses, corroborated by transmission electron microscopy, showed that the sizes of NPs increase rapidly together with their number density until they attain a certain size that could be accommodated in the ∼5 nm water–sulfonate ionic clusters. Further growth takes place either by self-agglomeration of the particles ejected out from the water–sulfonic acid clusters or by continuous reduction of metal ions on the existing NP surfaces (uniformly or on a specific plane) leading to formation of bigger nanostructures with various aspect ratios. The time resolved information of NP growth provides an opportunity for the controlled synthesis of metal NPs with a definite size, shape and size distribution for a specific application. The catalytic properties of Ag NPs formed in the membrane were examined using borohydride reduction of a model dye methylene blue. It was observed that smaller Ag NPs with a mean diameter ∼3 nm, confined in the hydrophilic clusters of the Nafion® matrix, have reasonably good catalytic activity and a lower lag time for the onset of reduction.

Interference of high amount of americium in the plutonium isotopic composition analysis has been studied by simulating gamma-ray spectra for Am-Pu samples over a wide composition range (5-97% (241)Am) for both power and research reactor grade plutonium. An alternate way for isotopic composition analysis has been proposed by correlating the isotopic ratios available in our old database with the experimentally obtained (241)Pu/(239)Pu isotopic ratio. The proposed method has been validated using simulated spectra of known isotopic compositions.

Isotopic composition of dilute Pu solutions (1–3900 μg/mL) has been determined by analysis of HPGe detector response function in the 90–105 keV region of gamma ray spectra. Results are in excellent agreement with that obtained from mass spectrometric measurements. The present method has been successfully applied for samples of low Pu concentrations, which otherwise is not possible using the conventional 120–415 keV region of plutonium γ ray spectra.

Assembled diglycolamides (DGAs) have a strong affinity toward f-element ions at high nitric acid concentrations. Small angle X-ray scattering studies revealed that nitric acid concentration dependent changes occur in the geometrical arrangement of the DGA units of monomeric methacryloyl-DGA and the corresponding polymeric DGA. Cylindrical aggregates of methacryloyl-DGA were formed in 10:1 n-dodecane:1-decanol (added for solubility reasons) upon equilibration with nitric acid. The lengths and diameters of the cylindrical methacryloyl-DGA aggregates increased on varying the nitric acid concentration from 3 to 4 mol L-1. This resulted in an increase of the distribution coefficient (D) of Eu3+ ions from 72 to 197. The physical structure of cross-linked (10 mol %) poly(methacryloyl-DGA) reorganized distinctly upon equilibration with nitric acid. In this case, also the DEu3+ values increased significantly from 147 mL g-1 at 1 mol L-1 HNO3 to ∼4000 mL g-1 at 4 mol L-1 HNO3. Hydrogen bonds between the outer sphere of Eu3+/Am3+/Pu4+ nitrate and DGA units provide stabilization in the hydrophobic environment. This results in enhancement of their extraction upon increasing nitric acid concentration both in the organic phase as well as in the polymer matrix. Though monomeric and polymeric methacryloyl-DGA are different in their physical assembling, the normalized DI values for a same f-element ion upon varying HNO3 concentrations show remarkably similar patterns in both forms. In addition, the unusual stoichiometry deduced from the slopes of the log D vs log[HNO3] curves at fixed nitrate concentration seems to suggest that the normal extraction mechanism may not be operating in the hydrogen bonded DGA assemblies. (Figure Presented).

We demonstrate for the first time the intrinsic role of nanoconfinement in facilitating the chemical reduction of metal ion precursors with a suitable reductant for the synthesis of metal nanoparticles, when the identical reaction does not occur in bulk solution. Taking the case of citrate reduction of silver ions under the unusual condition of [citrate]/[Ag(+)] ≫ 1, it has been observed that the silver citrate complex, stable in bulk solution, decomposes readily in confined nanodomains of charged and neutral matrices (ion-exchange film and porous polystyrene beads), leading to the formation of silver nanoparticles. The evolution of growth of silver nanoparticles in the ion-exchange films has been studied using a combination of (110m)Ag radiotracer, small-angle X-ray scattering (SAXS) experiments, and transmission electron microscopy (TEM). It has been observed that the nanoconfined redox decomposition of silver citrate complex is responsible for the formation of Ag seeds, which thereafter catalyze oxidation of citrate and act as electron sink for subsequent reduction of silver ions. Because of these parallel processes, the particle sizes are in the bimodal distribution at some stages of the reaction. A continuous seeding with parallel growth mechanism has been revealed. Based on the SAXS data and radiotracer kinetics, the growth mechanism has been elucidated as a combination of continuous autoreduction of silver ions on the nanoparticle surfaces and a sudden coalescence of nanoparticles at a critical number density. However, for a fixed period of reduction, the size, size distribution, and number density of thus-formed Ag nanoparticles have been found to be dependent on physical architecture and chemical composition of the matrix.

Ionomer membranes are promising platforms for the metal nanostructures and provide possibilities for utilizing unique properties of the nanostructures. However, it is not known how local environment prevailing in the membrane matrix plays a role in the process of formation of different dimensional metal nanostructures, and the subsequent fate of the mesoscopic physical architecture of the matrix. Therefore, different dimensional silver nanostructures were formed in the Nafion-117 membrane by manipulating local environment using carefully selected reductants, varying temperature, and controlled loading of Ag+ ions in the matrix by ion-exchange process. Ag nanostructures thus formed had different sizes and shapes, spherical nanoparticles, nanorods, and nanosponge depending upon in situ reduction and growth conditions. These nanocomposites were studied by combination of transmission electron microscopy (TEM) and small-angle X-ray scattering (SAXS) for understanding the formation and subsequent modifications in the shape of the metal nanostructure as well as in the self-assembling morphology of the matrix in different post reduction counterionic environment. Under specific conditions, silver nanorods having similar to 8 nm mean diameter and similar to 40 nm length were formed. The embedded Ag nanostructures of different sizes and shapes were found to affect the self-diffusion mobility of Na+ and Cs+ counterions in the nanocomposite matrixes differently due to variation in reorganizations of the ionomer matrix.

Different dimensional silver nanostructures were synthesized in the cation exchange ionomer matrix Nafion-117 by varying temperature. The nanostructures formed were different sizes spherical nanoparticles depending upon the in situ reduction temperature. Mesoscopic architecture of the nanocomposite thin films containing different dimensional silver nanostructures has been studied by small angle x-ray scattering (SAXS) in different counterionic environment. Investigation of the modifications in nanostructure pattern along with modification in self-assembling morphology of the ionomer in metal-ionomer nanocomposites in different post reduction counterionic environment was found to be unique. The post reduction neutralization by different counterions having different degree of hydration resulted to reorganization of the embedded nanostructures along with the crystalline polymer backbone of the ionomer. This influenced the polydispersity of the nanostructures significantly.