Supported gold nanoparticles as photocatalysts utilising the full solar spectrum for organic synthesis

This thesis is an innovative study for organic synthesis using supported gold nanoparticles as photocatalysts under visible light irradiation. It especially examines a novel green process for efficient hydroamination of alkynes with amines. The investigation of other traditional reduction and oxidation reactions also adds significantly to the knowledge of gold nanoparticles and titania nanofibres as photocatalysts for organic synthesis.

Production of metal oxide nanoparticles

Particles having at least regions of at least one metal oxide having nano-sized grains are produced by providing particles of a material having an initial, nonequiaxed particle shape, prepg. a mixt. of these particles and at last one metal oxide precursor, and treating the mixt. such that the precursor reacts with the particles. The process can be a co-pptn. process, sol-gel synthesis, micro-emulsion method, surfactant-based process, or a process that uses polymers. Complex metal oxide nanoparticles are produced by (a) prepg. a soln. contg. metal cations, (b) mixing the soln. with a surfactant to form micelles within the soln., and (c) heating the micellar liq. to form metal oxide and to remove the surfactant. The formed metal oxide particles have essentially the same morphol. (particle size and shape) as the initial morphol. of the material particles provided. [on SciFinder(R)]

An investigation of silver electrodeposition from ionic liquids : influence of atmospheric water uptake on the silver electrodeposition mechanism and film morphology

The electrodeposition of silver from two ionic liquids, 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIm][BF4]) and N-butyl-N-methyl-pyrrolidinium bis(trifluoromethanesulfonyl)imide ([C4mPyr][TFSI]), and an aqueous KNO3 solution on a glassy carbon electrode was undertaken. It was found by cyclic voltammetry that the electrodeposition of silver proceeds through nucleation–growth kinetics. Analysis of chronoamperometric data indicated that the nucleation–growth mechanism is instantaneous at all potentials in the case of [BMIm][BF4] and [C4mPyr][TFSI], and instantaneous at low overpotentials tending to progressive at high overpotentials for KNO3. Significantly, under ambient conditions, the silver electrodeposition mechanism changes to progressive nucleation and growth in [C4mPyr][TFSI], which is attributed to the uptake of atmospheric water in the IL. It was found that these differences in the growth mechanism impact significantly on the morphology of the resultant electrodeposit which is characterised ex situ by scanning electron microscopy and X-ray diffraction.

The formation of gold nanoparticles using hydroquinone as a reducing agent through a localized pH change upon addition of NaOH to a solution of HAuCl4

We demonstrate a rapid synthesis of gold nanoparticles using hydroquinone as a reducing agent under acidic conditions without the need for precursor seed particles. The nanoparticle formation process is facilitated by the addition of NaOH to a solution containing HAuCl4 and hydroquinone to locally change the pH; this enhances the reducing capability of hydroquinone to form gold nucleation centres, after which further growth of gold can take place through an autocatalytic mechanism. The stability of the nanoparticles is highly dependent on the initial solution pH, and both the concentration of added NaOH and hydroquinone present in solution. The gold nanoparticles were characterized by UV–visible spectroscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, atomic force microscopy, dynamic light scattering, and zeta potential measurements. It was found that under optimal conditions that stable aqueous suspensions of 20 nm diameter nanoparticles can be achieved where benzoquinone, the oxidized product of hydroquinone, acts as a capping agent preventing nanoparticles aggregation.

The active site behaviour of electrochemically synthesised gold nanomaterials

Even though gold is the noblest of metals, a weak chemisorber and is regarded as being quite inert, it demonstrates significant electrocatalytic activity in its nanostructured form. It is demonstrated here that nanostructured and even evaporated thin films of gold are covered with active sites which are responsible for such activity. The identification of these sites is demonstrated with conventional electrochemical techniques such as cyclic voltammetry as well as a large amplitude Fourier transformed alternating current (FT-ac) method under acidic and alkaline conditions. The latter technique is beneficial in determining if an electrode process is either Faradaic or capacitive in nature. The observed behaviour is analogous to that observed for activated gold electrodes whose surfaces have been severely disrupted by cathodic polarisation in the hydrogen evolution region. It is shown that significant electrochemical oxidation responses occur at discrete potential values well below that for the formation of the compact monolayer oxide of bulk gold and are attributed to the facile oxidation of surface active sites. Several electrocatalytic reactions are explored in which the onset potential is determined by the presence of such sites on the surface. Significantly, the facile oxidation of active sites is used to drive the electroless deposition of metals such as platinum, palladium and silver from their aqueous salts on the surface of gold nanostructures. The resultant surface decoration of gold with secondary metal nanoparticles not only indicates regions on the surface which are rich in active sites but also provides a method to form interesting bimetallic surfaces.

The facile formation of silver dendritic structures in the absence of surfactants and their electrochemical and SERS properties

In this work a simple approach to the creation of highly dispersed electrocatalytically active silver microstructured dendrites on indium tin oxide in the absence of any surface modification or surfactant is presented. It is found that the addition of low concentrations of supporting electrolyte to the AgNO3 solution dramatically influences the morphology of electrodeposited silver which is independent of both the anion and the cation employed. The silver dendrites are characterized by SEM, XRD, XPS as well as by cyclic voltammetry under alkaline conditions. It is found that the surface oxide formation and removal processes are significantly influenced by the microstructured morphology of the silver electrodeposits compared to a smooth macrosized silver electrode. The facile formation of dendritic silver microstructures is also shown to be beneficial for the electrocatalytic oxidation of both formaldehyde and hydrazine and oxygen reduction. The formation of a continuous film of dendritic silver is also investigated for its SERS activity where the connectivity between the individual dendrites is found to be particularly important.

A study of the galvanic replacement reaction at surfaces and the role of lateral charge propagation

The galvanic replacement of isolated nanostructures of copper and silver on conducting supports as well as continuous films of copper with gold is reported. The surface morphology was characterized by scanning electron microscopy and the replacement with gold was confirmed by EDX analysis. It was found that lateral charge propagation during the replacement reaction had a significant effect in all cases. For the isolated nanostructures the deposition of gold was observed not only at the sacrificial template but also at the surrounding unmodified areas of the conducting substrate. In the case of copper films the role of lateral charge propagation was also confirmed by connecting it to an ITO electrode through an external circuit upon which gold deposition was also observed to occur. Interestingly, by inhibiting the rate of charge propagation, through the introduction of a series resistor, the morphology of gold on the copper substrate could be changed from discrete surface decoration with cube like nanoparticles to a more porous rough surface.

Liquid metal marbles

Liquid metal marbles that are droplets of liquid metal encapsulated by micro- or nanoparticles are introduced. Droplets of galinstan liquid metal are coated with insulators (including Teflon and silica) and semiconductors (including WO3, TiO2, MoO3, In2O3 and carbon nanotubes) by rolling over a powder bed and also by submerging in colloidal suspensions. It is shown that these marbles can be split and merged, can be suspended on water, and are even stable when moving under the force of gravity and impacting a flat solid surface. Furthermore, the marble coating can operate as an active electronic junction and the nanomaterial coated liquid metal marble can act as a highly sensitive electrochemical based heavy metal ion sensor. This new element thus represents a significant platform for the advancement of research into soft electronics.

Continuous production of Bi-2212 thick film on silver tape

Bi-2212 thick film on silver tapes are seen as a simple and low cost alternative to high temperature superconducting wires produced by the Powder In Thbe (PIT) technique, particularly in react and wind applications. A rig for the continuous production of Bi-2212 tapes for use in react and wind component manufacture has been developed and commissioned. The rig consists of several sections, each fully automatic, for task specific duties in the production of HTS tape. The major sections are: tape coating, sintering and annealing. High temperature superconducting tapes with engineering critical current densities of 10 kA/cm2 (77 K, self field), and lengths of up to 100 m have been produced using the rig. Properties of the finished tape are discussed and results are presented for current density versus bend radius and applied strain. Depending on tape content and thickness, irreversible strain tirrm varies between 0.04 and 0.1 %. Cyclic bending tests when applied strain does not exceed Eirrm showed negligible reduction in J c along the length of the tape.

Plasmonic effect of gold nanoparticles in organic solar cells

Light trapping, due to the embedding of metallic nanoparticles, has been shown to be beneficial for a better photoabsorption in organic solar cells. Researchers in plasmonics and in the organic photovoltaics fields are working together to improve the absorption of sunlight and the photon–electron coupling to boost the performance of the devices. Recent advances in the field of plasmonics for organic solar cells focus on the incorporation of gold nanoparticles. This article reviews the different methods to produce and embed gold nanoparticles into organic solar cells. In particular, concentration, size and geometry of gold nanoparticles are key factors that directly influence the light absorption in the devices. It is shown that a careful choice of size, concentration and location of gold nanoparticles in the device result in an enhancement of the power conversion efficiencies when compared to standard organic solar cell devices. Our latest results on gold nanoparticles embedded in on organic solar cell devices are included. We demonstrate that embedded gold nanoparticles, created by depositing and annealing a gold film on transparent electrode, generate a plasmonic effect which can be exploited to increase the power conversion efficiency of a bulk heterojunction solar cell up to 10%.

Colloidal drug probe : method development and validation for adhesion force measurement using atomic force microscopy

This study demonstrates a novel technique of preparing drug colloid probes to determine the adhesion force between the drug salbutamol sulphate (SS) and the surfaces of polymer microparticles to be used as carriers for the dispersion of drug particles from a dry powder inhaler (DPI) formulation. Initially model silica probes of approximately 4 μm size, similar to a drug particle used in DPI formulations, were coated with a saturated SS solution with the aid of capillary forces acting between the silica probe and the drug solution. The developed method of ensuring a smooth and uniform layer of SS on the silica probe was validated using X-Ray Photoelectron Spectroscopy (XPS) and Scanning Electron Microscopy (SEM). Using the same technique, silica microspheres preattached on the AFM cantilever were coated with SS. The adhesion forces between the silica probe and drug coated silica (drug probe) and polymer surfaces (hydrophilic and hydrophobic) were determined. Our experimental results showed that the technique for preparing the drug probe was robust and can be used to determine the adhesion force between hydrophilic/hydrophobic drug probe and carrier surfaces to gain a better understanding on drug carrier adhesion forces in DPI formulations.

Silver deposits in cutaneous burn scar tissue is a common phenomenon following application of a silver dressing

BACKGROUND Silver dressings have been widely and successfully used to prevent cutaneous wounds, including burns, chronic ulcers, dermatitis and other cutaneous conditions, from infection. However, in a few cases, skin discolouration or argyria-like appearances have been reported. This study investigated the level of silver in scar tissue post-burn injury following application of Acticoat, a silver dressing. METHODS A porcine deep dermal partial thickness burn model was used. Burn wounds were treated with this silver dressing until completion of re-epithelialization, and silver levels were measured in a total of 160 scars and normal tissues. RESULTS The mean level of silver in scar tissue covered with silver dressings was 136 microg/g, while the silver level in normal skin was less than 0.747 microg/g. A number of wounds had a slate-grey appearance, and dissection of the scars revealed brown-black pigment mostly in the middle and deep dermis within the scar. The level of silver and the severity of the slate-grey discolouration were correlated with the length of time of the silver dressing application. CONCLUSIONS These results show that silver deposition in cutaneous scar tissue is a common phenomenon, and higher levels of silver deposits and severe skin discolouration are correlated with an increase in the duration of this silver dressing application.

Silver absorption on burns after the application of Acticoat : data from pediatric patients and a porcine burn model

Silver dressings have been widely used to successfully prevent burn wound infection and sepsis. However, a few case studies have reported the functional abnormality and failure of vital organs, possibly caused by silver deposits. The aim of this study was to investigate the serum silver level in the pediatric burn population and also in several internal organs in a porcine burn model after the application of Acticoat. A total of 125 blood samples were collected from 46 pediatric burn patients. Thirty-six patients with a mean of 13.4% TBSA burns had a mean peak serum silver level of 114 microg/L, whereas 10 patients with a mean of 1.85% TBSA burns had an undetectable level of silver (<5.4 microg/L). Overall, serum silver levels were closely related to burn sizes. However, the highest serum silver was 735 microg/L in a 15-month-old toddler with 10% TBSA burns and the second highest was 367 microg/L in a 3-year old with 28% TBSA burns. In a porcine model with 2% TBSA burns, the mean peak silver level was 38 microg/L at 2 to 3 weeks after application of Acticoat and was then significantly reduced to an almost undetectable level at 6 weeks. Of a total of four pigs, silver was detected in all four livers (1.413 microg/g) and all four hearts (0.342 microg/g), three of four kidneys (1.113 microg/g), and two of four brains (0.402 microg/g). This result demonstrated that although variable, the level of serum silver was positively associated with the size of burns, and significant amounts of silver were deposited in internal organs in pigs with only 2% TBSA burns, after application of Acticoat.

Plasmonic photocatalysts of supported gold nanoparticles for organic conversions

This thesis is a comprehensive study of plasmonic gold photocatalysts for organic conversions. It presents the advantages of plasmonic gold photocatalysts in the selective oxidation, reduction, and acetalisation. It is discovered that plasmonic gold photocatalysts exhibit better catalytic performance (higher selectivity or activity) in these organic conversions. The study in this thesis highlights the capacity of plasmonic gold photocatalysts in harvesting solar energy for converting organic raw materials to value-added chemicals, and the great potential of gold photocatalysts in chemical production.

A new dasyurid marsupial from Kroombit Tops, south-east Queensland, Australia : the Silver-headed Antechinus, Antechinus argentus sp. nov. (Marsupialia: Dasyuridae)

Antechinus argentus sp. nov. is currently only known from the plateau at the eastern escarpment of Kroombit Tops National Park, about 400km NNW of Brisbane and 60km SSW of Gladstone, south-east Queensland, Australia. Antechinus flavipes (Waterhouse) is also known from Kroombit Tops NP, 4.5km W of the nearest known population of A. argentus; A. mysticus Baker, Mutton and Van Dyck has yet to be found within Kroombit Tops, but is known from museum specimens taken at Bulburin NP, just 40km ESE, as well as extant populations about 400km to both the south-east and north-west of Kroombit NP. A. argentus can be easily distinguished in the field, having an overall silvery/grey appearance with much paler silver feet and drabber deep greyish-olive rump than A. flavipes, which has distinctive yellow-orange toned feet, rump and tail-base; A. argentus fur is also less coarse than that of A. flavipes. A. argentus has a striking silver-grey head, neck and shoulders, with pale, slightly broken eye-rings, which distinguish it from A. mysticus which has a more subtle greyish-brown head, pale buff dabs of eyeliner and more colourful brownish-yellow rump. Features of the dentary can also be used for identification: A. argentus differs from A. flavipes in having smaller molar teeth, as well as a narrower and smaller skull and from A. mysticus in having on average a narrower snout, smaller skull and dentary lengths and smaller posterior palatal vacuities in the skull. A. argentus is strongly divergent genetically (at mtDNA) from both A. flavipes (9.0–11.2%) and A. mysticus (7.2–7.5%), and forms a very strongly supported clade to the exclusion of all other antechinus species, in both mtDNA and combined (mtDNA and nDNA) phylogenies inferred here. We are yet to make detailed surveys in search of A. argentus from forested areas to the immediate east and north of Kroombit Tops. However, A. mysticus has only been found at these sites in low densities in decades past and not at all in several recent trapping expeditions conducted by the authors. With similar habitat types in close geographic proximity, it is plausible that A. argentus may be found outside Kroombit. Nevertheless, it is striking that from a range of surveys conducted at Kroombit Tops in the last 15 years and intensive surveys by the authors in the last 3 years, totalling more than 5 080 trap nights, just 13 A. argentus have been captured from two sites less than 6 km apart. If this is even close to the true geographic extent of the species, it would possess one of the smallest distributions of an Australian mammal species. With several threats identified, we tentatively recommend that A. argentus be listed as Endangered, pending an exhaustive trapping survey of Kroombit and surrounds.