Mie theory and the dichroic effect for spherical gold nanoparticles: an experimental approach.

The attractive optical properties of metallic nanoparticles include the optically interesting but surprisingly not well understood dichroic effect, defined in this research as when particle colloids display different colours in transmitted and reflected light. Here we use a systematic experimental approach supplemented by theoretical Mie theory analysis to study the origin of this effect. The CloudSpec spectrophotometer has been utilised to produce quantitative scattering and absorption spectra for monodisperse spherical gold nanoparticles, allowing precise links to be made between the optical spectra and the colours observed. The source of the dichroic effect has been conclusively linked to particle size with no special particle shapes or size distributions required. These results experimentally demonstrate the relationship between particle size and the ratio of scattering to absorption predicted by Mie theory, which has important implications for users of Mie theory calculations.

Ecofriendly Palladium on Wool Nanocatalysts for Cyclohexene Hydrogenation.

Use of natural wool fiber supports in the fabrication of novel composite materials incorporating metal nanoparticles, which offer the possibility of "environmentally friendly" catalytic materials, has been investigated. The catalytic hydrogenation of cyclohexene to cyclohexane by palladium nanoparticles immobilized on wool (Pd/wool) was studied using moderate pressure of pure hydrogen gas. The performance of wool-supported catalysts was explored over a palladium nanoparticle loading ranging from 1.6 to 2.6 wt %. The effect of the catalytic testing conditions, including stirring rate, amount of reactants, gas pressure, and target temperature were explored. A systematic series of catalytic-activity tests carried out at 400 psi H2 for 5 and 24 h reaction times at 40 °C using a stirring rate 750 rpm allowed us to identify differences in performance within the series of Pd/wool nanocatalysts studied. The most catalytically active samples contained Pd nanoparticles with average sizes of ca. 5 nm located predominantly on the surface and within the topmost layer of wool fibers, making them more accessible to the reactants.

Combining Stress and Dopamine Based Models of Addiction: Towards a Psycho-Neuro-Endocrinological Theory of Addiction.

The literature on the two main models of addiction (dopamine-based positive reinforcement and stress-based negative reinforcement models) have made many important contributions to understanding this brain disorder. However, rarely has there been a comprehensive critique of the limitations of both models. This article seeks to resolve theoretical issues inherent to each model, as well as propose a more comprehensive psycho-neuro-endocrinological theory of addiction which reconciles important elements of both. We suggest that there is not only direct interaction of dopaminergic and stress systems throughout the addiction cycle, from initial use, via the abusing stage, to the endpoint of addiction, but that this interaction is present prior to initial use. A combination of genetic factors and/or experiences of adversity may result in a stress-triggered sensitisation of dopaminergic networks which is present before the onset of substance use, which cannot be explained solely in terms of dopaminergic (positive) reinforcement. Rather these processes are best explained by an allostatic model which reconciles aspects of both models of addiction and shows how dopamine/stress interactions become increasingly pathological in the addiction cycle. Our model suggests that chronic stress eventually creates baseline hypodopaminergic activity, but also prompts dopaminergic hyperactivity in cue reactivity. This is the neural marker of allostatic mechanisms observed at endpoint addiction. We propose a multi-circuit explanation of how this cumulative effect of stress increasingly impacts on dopaminergic networks of reward, affect, attention, memory and behavioural control. This revised model provides a useful frame of reference for further research and ultimately clinical practice.

Colored and functional silver nanoparticle-wool fiber composites.

Silver nanoparticles utilizing the surface plasmon resonance effect of silver have been used to color merino wool fibers as well as imparting antimicrobial and antistatic properties to them to produce a novel silver nanoparticle-wool composite material. This is accomplished by the reduction of silver ions in solution by trisodium citrate (TSC) in the presence of merino wool fibers or fabrics. The silver metal nanoparticles simultaneously bind to the amino acids of the keratin protein in the wool fibers using TSC as the linker. The colors of the resulting merino wool-silver nanoparticle composites range from yellow/brown to red/brown and then to brown/black, because of the surface plasmon resonance effect of silver, and are tuned by controlling the reduction of silver ions to silver nanoparticles to give the required particle size on the fiber surface. In addition to the surface plasmon resonance optical effects, the silver nanoparticle-wool composites exhibit effective antimicrobial activity, thus inhibiting the growth of microbes and also an increase in the electrical conductivity, imparting antistatic properties to the fibers. Therefore, silver nanoparticles function as a simultaneous colorant and antimicrobial and antistatic agent for wool. Chemical and physical characterizations of the silver nanoparticle-merino wool composite materials have been carried out using scanning electron microscopy, transmission electron microscopy, energy-dispersive spectroscopy, synchrotron radiation X-ray diffraction, atomic absorption spectroscopy, X-ray photoelectron spectroscopy, direct-current electrical conductivity measurements, wash-fast and rub-fast tests, and antimicrobial tests.

Hybrid materials of kaolinite clay with polypyrrole and polyaniline.

Composites of the alumino silicate mineral kaolinite, with the conducting polymers polypyrrole and polyaniline have been successfully synthesised. In doing so hybrid materials have been produced in which the high surface area of the mineral is retained, whilst also incorporating the desired chemical and physical properties of the polymer. Scanning electron microscopy shows polypyrrole coatings to comprise of individual polymer spheres, approximately 10 to 15 nm in diameter. The average size of the polymer spheres of polyaniline was observed to be approximately 5 nm in diameter. These spheres fuse together in a continuous sheet to coat the kaolinite platelets in their entirety. The reduction of silver ions to metallic silver nanoparticles onto the redox active surface of the polymers has also been successful, and thus imparts anti-microbial properties to the hybrid materials. This gives rise to further applications requiring the inhibition of microbial growth. The chemical and physical characterization of the hybrid materials has been undertaken through scanning electron microscopy, energy dispersive spectroscopy, electrical conductivity, cyclic voltammetry, X-ray diffraction, infra red spectroscopy, X-ray photoelectron spectroscopy, thermogravimetric analysis and the testing of their anti-microbial activity.

Nano-structured calcium silicate hydrate functionalised with iodine.

Nano-structured calcium silicate hydrate can physisorb or chemisorb iodine, making it interesting for medical or materials science applications, where a slow, controlled release of iodine is desired. It was found that iodine can be sorbed and released by applying the elemental halogen in solution, either as a gas or as a solid. At ambient temperatures the sorption and desorption process is quantitative and physical, meaning that the same amount of iodine is taken up and released. At temperatures above 32.5 degrees C (305.7K) iodine reacts with the calcium silicate hydrate forming a complex, which is stable above the sublimation temperature of iodine. The formation energy for the iodine calcium silicate hydrate complex was established to be 41.8+/-0.8kJmol(-1) by calorimetry and the nature of the complex was investigated using X-ray photoelectron spectroscopy.

Novel hybrid materials of magnetic nanoparticles and cellulose fibers.

In this study, magnetic cellulose fibers have been prepared by coating bleached Kraft fibers (Pinus radiata) with magnetite nanoparticles. In doing so, the inherent properties of the fiber (such as tensile strength and flexibility) have been preserved, but imparted to it are the magnetic properties of the coating. The surface coating approach used differs from other methods in the literature in which the lumen loading or in situ approach is taken. After successive washings and sonication, the particles remained bonded to the surface of the fiber, and the fibers could be formed into a paper sheet. The chemical and physical characterization of these materials were carried out using scanning electron microscopy (SEM), electron dispersive spectroscopy (EDS), X-ray fluorescence spectroscopy (XRF), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and SQUID magnetometry. SEM shows the surface of the fibers to be completely encapsulated by the ferrite nanoparticles. This is also confirmed by EDS. XRD line broadening analysis shows the average particle sizes of the nanoparticles range from 12-26 nm. Magnetically responsive cellulose fibers such as those synthesized in this study, will allow the investigation of new concepts in papermaking and packaging, security paper, and information storage. Potential applications are in electromagnetic shielding, magnetographic printing and magnetic filtering.

Functionalised hybrid materials of conducting polymers with individual wool fibers.

Composites of natural protein materials, such as merino wool, with the conducting polymers polypyrrole (PPy) and polyaniline (PAn) have been successfully synthesised. In doing so, hybrid materials have been produced in which the mechanical strength and flexibility of the fibers is retained whilst also incorporating the desired chemical and electrical properties of the polymer. Scanning electron microscopy shows PPy coatings to comprise individual polymer spheres, approximately 100 to 150 nm in diameter. The average size of the polymer spheres of PAn was observed to be approximately 50 to 100 nm in diameter. These spheres fuse together in a continuous sheet to coat the fibers in their entirety. The reduction of silver ions to silver metal nanoparticles onto the redox active polymer surface has also been successful and thus imparts anti-microbial properties to the hybrid materials. This gives rise to further applications requiring the inhibition of microbial growth. The chemical and physical characterisation of such products has been undertaken through scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), electrical conductivity, cyclic voltammetry, X-ray photoelectron spectroscopy (XPS) and the testing of their anti-microbial activity.

Sorption and binding of nanocrystalline gold by Merino wool fibres--an XPS study.

Uniform, monodisperse gold nanocrystals have been adsorbed and chemically bound to Merino wool fibres, providing a permanent colouration through the interaction of visible light with the plasmon resonant modes of the nanocrystals. Surface analysis by X-ray photoelectron spectroscopy confirmed that the nanocrystalline gold was bound through the nitrogen of the amino groups on the surface of the gold to the keratin of the fibres. No shift in the absorptions attributed to the plasmon resonance modes of the nanocrystals were observed.

Immobilisation of fully sulfonated polyaniline on nanostructured calcium silicate.

Up to 7.4% (w/w) of the sulfonated polyaniline, poly(2-methoxyaniline-5-sulfonic acid) (PMAS) can be absorbed onto nanostructured calcium silicates. Spectroscopic and leaching studies on the novel PMAS-silicate nanocomposites obtained indicate that attachment of the PMAS occurs via electrostatic binding of PMAS sulfonate groups to Ca2+ sites on the silicates. The surface area and pore volume of the nanocomposites are comparable to those of pure silicate and increase the surface area of the PMAS polymer by several orders of magnitude. The PMAS emeraldine salt in the nanocomposites retains its chemical reactivity, being readily oxidised and reduced to its pernigraniline and leucoemeraldine forms, respectively. The conductivity of the composite is comparable to that of the pure PMAS, several orders of magnitude higher than that of dried nanostructured calcium silicate.

Hydrothermal oxidation of waste lipids, protein, and starch from New Zealand meat- and vegetable-processing plants.

Disposal of organic waste materials from the meat- and vegetable-processing industries historically has been undertaken by dumping, drying followed by combustion, or biological oxidation. As a result of higher intensity processing rates and increasingly stringent legislation, these are no longer economical. Hydrothermal oxidation, also referred to as "wet" oxidation, has been used to lower the chemical and biological oxygen demand of waste samples from the above two industries. The starch-based wastes were readily oxidized without a catalyst. For the lipid and protein-based wastes, the use of copper calcium silicate and nitrate catalysts provided a significant reduction in oxygen demand at 230 degrees C.