Calixarene Assisted Rapid Synthesis of Silver-Graphene Nanocomposites with Enhanced Antibacterial Activity

Demonstrated herein is a single rapid approach employed for synthesis of Ag–graphene nanocomposites, with excellent antibacterial properties and low cytotoxicity, by utilizing a continuous hydrothermal flow synthesis (CHFS) process in combination with p-hexasulfonic acid calix[6]arene (SCX6) as an effective particle stabilizer. The nanocomposites showed high activity against E. coli (Gram-negative) and S. aureus (Gram-positive) bacteria. The materials were characterized using a range of techniques including transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, UV–vis spectrophotometry, FT-IR, and X-ray powder diffraction (XRD). This rapid, single step synthetic approach not only provides a facile means of enabling and controlling graphene reduction (under alkaline conditions) but also offers an optimal route for homogeneously producing and depositing highly crystalline Ag nanostructures into reduced graphene oxide substrate

Discovery of a maximum damage structure for Xe-irradiated borosilicate glass ceramics containing powellite

In order to increase the waste loading efficiency in nuclear waste glasses, alternate glass ceramic (GC) materials are sought that trap problematic molybdenum in a water-durable CaMoO4 phase within a borosilicate glass matrix. In order to test the radiation resistance of these candidate wasteforms, accelerated external radiation can be employed to replicate long-term damage. In this study, several glasses and GCs were synthesized with up to 10 mol% MoO3 and subjected to 92 MeV Xe ions with fluences ranging between 5 × 10^12 to 1.8 × 10^14 ions/cm2. The main mechanisms of modification following irradiation involve: (i) thermal and defect-assisted diffusion, (ii) relaxation from the ion's added energy, (iii) localized damage recovery from overlapping ion tracks, and (iv) the accumulation of point defects or the formation of voids that created significant strain and led to longer-range modifications. Most significantly, a saturation in alteration could be detected for fluences greater than 4 × 10^13 ions/cm2, which represents an average structure that is representative of the maximum damage state from these competing mechanisms. The results from this study can therefore be used for long-term structural projections in the development of more complex GCs for nuclear waste applications.EPSRC (Grant No. EP/K007882/1

An experimental comparison of three towed underwater video systems using species metrics, benthic impact and performance

Managing ecological systems, which operate over large spatial scales, is inherently difficult and often requires sourcing data from different countries and organizations. The assumption might be made that data collected using similar methodologies are comparable, but this is rarely tested. Here, benthic video data recorded using different towed underwater video systems (TUVSs) were experimentally compared. Three technically different TUVSs were compared on different seabed types (rocky, mixed ground and sandy) in Kingmere Marine Conservation Zone, off the south coast of England. For each TUVS, species metrics (forward facing camera), seabed impact (backward facing camera) and operational performance (strengths and limitations of equipment and video footage) were compared with the aim of providing recommendations on their future use and comparability of data between different systems. Statistically significant differences between species richness, density, cover and assemblage composition were detected amongst devices and were believed to be mostly due to their optical specifications. As a result of their high image definition and large field of vision both the benthic contacting heavy and benthic tending TUVS provided good quality footage and ecological measurements. However, the heaviest TUVS proved difficult to operate on irregular ground and was found to cause the most impact to the seabed. The lightest TUVS (benthic contacting light) struggled to maintain contact with the seabed. The benthic tending TUVS was able to fly over variable seabed relief and was comparably the least destructive. Results from this study highlight that particular care should be given to sled and optic specifications when developing a medium- or long-term marine protected area monitoring programme. Furthermore, when using data gathered from multiple sources to test ecological questions, different equipment specifications may confound observed ecological differences. A benthic tending TUVS is recommended for benthic surveys over variable habitat types, particularly in sensitive areas, such as marine protected areas

Impacts of composition and beta irradiation on phase separation in multiphase amorphous calcium borosilicates

Borosilicate glasses for nuclear waste applications are limited in waste loading by the precipitation of water-soluble molybdates. In order to increase storage efficiency, new compositions are sought out that trap molybdenum in a water-durable CaMoO₄ crystalline phase. Factors affecting CaMoO₄ combination and glass-in-glass phase separation in calcium borosilicate systems as a function of changing [MoO₃] and [B₂O₃] are examined in this study in order to understand how competition for charge balancers affects phase separation. It further examines the influence of radiation damage on structural modifications using 0.77 to 1.34 GGy of 2.5 MeV electron radiation that replicates inelastic collisions predicted to occur over long-term storage. The resulting microstructure of separated phases and the defect structure were analyzed using electron microscopy, XRD, Raman and EPR spectroscopy prior to and post irradiation. Synthesized calcium borosilicates are observed to form an unusual heterogeneous microstructure composed of three embedded amorphous phases with a solubility limit ~ 2.5 mol% MoO₃. Increasing [B₂O₃] increased the areas of immiscibility and order of (MoO₄)²‾anions, while increasing [MoO₃] increased both the phase separation and crystallization temperature resulting in phases closer to metastable equilibrium, and initiated clustered crystallization for [MoO₃] > 2.5 mol%. β-irradiation was found to have favorable properties in amorphous systems by creating structural disorder and defect assisted ion migration that thus prevented crystallization. It also increased reticulation in the borosilicate network through 6-membered boroxyl ring and Si ring cleavage to form smaller rings and isolated units. This occurred alongside an increased reduction of Mo⁶+ with dose that can be correlated to molybdenum solubility. In compositions with existing CaMoO₄ crystallites, radiation caused a scattering effect, though the crystal content remained unchanged. Therefore β-irradiation can preferentially prevent crystallization in calcium borosilicates for [MoO₃] < 2.5mol%, but has a smaller impact on systems with existing CaMoO₄ crystallites.University of Cambridge, Department of Earth Sciences and EPSRC (Grant No. EP/K007882/1) for an IDS. Cambridge Philosophical Society for a supplementary research grant

β-Irradiation Effects on the Formation and Stability of CaMoO4_{4} in a Soda Lime Borosilicate Glass Ceramic for Nuclear Waste Storage

Molybdenum solubility is a limiting factor to actinide loading in nuclear waste glasses, as it initiates the formation of water-soluble crystalline phases such as alkali molybdates. To increase waste loading efficiency, alternative glass ceramic structures are sought that prove resistant to internal radiation resulting from radioisotope decay. In this study, selective formation of water-durable CaMoO$_{4}$ in a soda lime borosilicate is achieved by introducing up to 10 mol % MoO$_{3}$ in a 1:1 ratio to CaO using a sintering process. The resulting homogeneously dispersed spherical CaMoO$_{4}$ nanocrystallites were analyzed using electron microscopy, X-ray diffraction (XRD), Raman and electron paramagnetic resonance (EPR) spectroscopies prior to and post irradiation, which replicated internal β-irradiation damage on an accelerated scale. Following 0.77 to 1.34 GGy of 2.5 MeV electron radiation CaMoO$_{4}$ does not exhibit amorphization or significant transformation. Nor does irradiation induce glass-in-glass phase separation in the surrounding amorphous matrix, or the precipitation of other molybdates, thus proving that excess molybdenum can be successfully incorporated into a structure that it is resistant to β-irradiation proportional to 1000 years of storage without water-soluble byproducts. The CaMoO$_{4}$ crystallites do however exhibit a nonlinear Scherrer crystallite size pattern with dose, as determined by a Rietveld refinement of XRD patterns and an alteration in crystal quality as deduced by anisotropic peak changes in both XRD and Raman spectroscopy. Radiation-induced modifications in the CaMoO$_{4}$ tetragonal unit cell occurred primarily along the c-axis indicating relaxation of stacked calcium polyhedra. Concurrently, a strong reduction of Mo$^{6+}$ to Mo$^{5+}$ during irradiation is observed by EPR, which is believed to enhance Ca mobility. These combined results are used to hypothesize a crystallite size alteration model based on a combination of relaxation and diffusion-based processes initiated by added energy from β-impingement and second-order structural modifications induced by defect accumulation.Univ. of Cambridge, Dept. of Earth Sciences, and EPSRC (Grant No. EP/K007882/1) for an IDS

First round of MaRINET 2 Tidal Energy Round Robin Tests : combined wave and current tests

This second Round Robin Test program aims to establish the influence of the combined wave and current effect on the power capture and performance of a generic tidal turbine prototype. In this paper, we present the results obtained in the first two selected facilities: the IFREMER wave and current circulating tank and the CNR-INM wave towing tank. These facilities were selected on the basis that their dimensions along with the rotor diameter of the turbine translate into low blockage ratio conditions and that both facilities can provide the same range of experimental conditions. The experimental campaigns uses the same setup, except from additional equipment to measure flow characteristics. The performance of the turbine is comparable between the tanks, but because some intrinsic differences in creating wave and current, it may be slightly different for the corresponding conditions. The blockage effect and, in some cases, the velocity disc-integrated averaging need to be accounted for a better agreement. The slight remaining differences observed on the power coefficient curves may be related to turbulence and wave-current interactions. A deeper analysis is required to process the other parameters in order to better understand this phenomena

Shallow forearc mantle dynamics and geochemistry: New insights from IODP Expedition 366

The Mariana forearc is a unique setting on Earth where serpentinite mud volcanoes exhume clasts originating from depths of 15 km and more from the forearc mantle. These peridotite clasts are variably serpentinized by interaction with slab derived fluid, and provide a record of forearc mantle dynamics and changes in geochemistry with depth. During International Oceanic Discovery Program (IODP) Expedition 366, we recovered serpentinized ultramafic clasts contained within serpentinite muds of three different mud volcanoes located at increasing distance from the Mariana trench and at increasing depth to the slab/mantle interface: Yinazao (distance to the trench: 55 km / depth to the slab/mantle interface: 13 km), Fantangisña (62 km / 14 km) and Asùt Tesoru (72 km / 18 km). Four different types of ultramafic clasts were recovered: blue serpentinites, lizardite-serpentinites, antigorite/lizardite- and antigorite-serpentinites. Lizardite-serpentinites are primarily composed of orange serpentine, forming mesh and bastite textures. Raman and microprobe analyses revealed that these textures contain a mixture of Fe-rich brucite (XMg ~ 0.84) and lizardite/chrysotile. Antigorite/lizardite- and antigorite-serpentinites record the progressive recrystallization of mesh and bastite textures to antigorite, magnetite and pure Fe-poor brucite (XMg ~ 0.92). Oxygen isotope compositions of clasts and pore fluids showed that the transition from lizardite to antigorite is due to the increase in temperature from 200 °C to about 400 °C within the forearc area above the slab/mantle interface. Lizardite-, antigorite/lizardite- and antigorite-serpentinites displayed U-shaped chondrite normalized Rare Earth Element (REE) patterns and are characterized by high fluid mobile element concentrations (Cs, Li, Sr, As, Sb, B, Li) relative to abyssal peridotites and/or primitive mantle. The recrystallization of lizardite to antigorite is accompanied by a decrease in Cs, Li and Sr, and an increase in As and Sb concentrations in the bulk clasts, whereas B concentrations are relatively constant. Some clasts are overprinted by blue serpentine, often in association with sulfides. Most of these blue serpentinites were recovered at Yinazao and the uppermost units of Fantangisña and Asùt Tesoru suggesting alteration in the shallower portions of the forearc, possibly during exhumation of the clasts. This episode of alteration resulted in a flattening of REE spectra and an increase of Zn concentrations in serpentinites. Otherwise, no systematic changes of ultramafic clasts chemistry or mineralogy were observed with increasing depth to the slab. The samples document previously undescribed prograde metamorphic events in the shallow portions of the Mariana subduction zone, consistent with a continuous burial of the serpentinized forearc mantle during subduction. Similar processes, induced by the interaction with fluids released from the downgoing slab, likely occur in subduction zones worldwide. At greater depth, breakdown of brucite and antigorite will result in the massive transfer of fluids and fluid mobile elements, such as As, Sb and B, to the source of arc magmas

Chemistry and morphology of dried-up pollen suspension residues

Pollen grains are covered with lots of different biochemical compounds, like proteins, saccharides and lipids, which are only loosely attached to the pollen. Therefore, they can be separated from the pollen by suspending them in water. Since these compounds play a key role in many atmospheric processes (e.g. cloud condensation nucleation, ice nucleation, aerial allergen exposure), their separation and analyzing are of interest. The chemical composition of whole pollen grains is compared by both Raman and infrared spectroscopy with material that could be extracted from pollen with water. The dominant signals in the pollen grain Raman spectra are those from sporopollenin and carotenoids. These bands decrease in the washing water spectra, since sporopollenin is high molecular and thus is not extractable. The released material shows in turn a chemical composition that differs significantly between species, what is quite expected, since they differ even in the optical properties of their aqueous suspensions. The FTIR spectra show some additional bands to appear in comparison to the Raman spectra. Furthermore, we investigated the pollen rupturing and material release in the aqueous suspensions by drying them up and picturing the residues with a scanning electron microscope. We saw that corn pollen ejected loads of micrometer-sized organelles, which are most likely starch granules. The more the pollen disrupted, the more the measured samples were covered with an amorphous film, which consists of the extracted pollen material, like lipids, sugars, and proteins - the same substances we detected by spectroscopy. Copyright (c) 2013 John Wiley & Sons, Ltd