Direct photocatalytic conversion of aldehydes to esters using supported gold nanoparticles under visible light irradiation at room temperature

Visible light can drive esteri fi cation from aldehydes and alcohols using supported gold nanoparticles (Au/Al 2 O 3 ) as photo- catalysts at ambient temperatures. The gold nanoparticles (AuNPs) absorb visible light due to the localized surface plasmon resonance (LSPR) e ff ect, and the conduction electrons of the AuNPs gain the energy of the incident light. The energetic electrons, which concentrate at the NP surface, facilitate the activation of a range of aldehyde and alcohol substrates. The photocatalytic e ffi ciencies strongly depend on the Au loading, particle sizes of the AuNPs, irradiance, and wavelength of the light irradiation. Finally, a plausible reaction mechanism was proposed, and the Au/Al 2 O 3 catalysts can be reused several times without signi fi cantly losing activity. The knowledge acquired in this study may inspire further studies in new e ffi cient recyclable photocatalysts and a wide range of organic synthesis driven by sunlight.

Alloying gold with copper makes for a highly selective visible-light photocatalyst for the reduction of nitroaromatics to anilines

Finely control of product selectivity is an essential issue in organic chemical production. In the synthesis of functionalized anilines via reduction of the corresponding nitroarenes, the challenge is to selectively reduce only the nitro group in the presence of other reducible functional groups in nitroarene molecules at a high reaction rate. Normally, the nitroarene is reduced stepwise through a series of intermediates that remain as byproducts, increasing the aniline synthesis cost. Here we report that alloying small amounts of copper into gold nanoparticles can alter the reaction pathway of the catalytic reduction under visible-light irradiation at ambient temperature, allowing nitroaromatics to be transformed directly to anilines in a highly selective manner. The reasons for the high efficiency of the photocatalytic reduction under these comparatively benign conditions as well as the light-excited reaction mechanisms are discussed. This photocatalytic process avoids byproducts, exhibits a high reaction rate and excellent substituent tolerance, and can be used for the synthesis of many useful functionalized anilines under environmentally benign conditions. Switching of the reaction pathway simply by tailoring the bimetallic alloy NPs of the photocatalysts is effective for engineering of product chemoselectivity.

Enhanced resonance light scattering based on biocatalytic growth of gold nanoparticles for biosensors design

The biocatalytic growth of gold nanoparticles (Au-NPs) has been employed in the design of new optical biosensors based on the enhanced resonance light scattering (RLS) signals. Both absorption spectroscopy and transmission electron microscopy (TEM) analysis revealed Au-NP seeds could be effectively enlarged upon the reaction with H2O2, an important metabolite that could be generated by many biocatalytic reactions.

A sensitive NADH and glucose biosensor tuned by visible light based on thionine bridged carbon nanotubes and gold nanoparticles multilayer

A NADH and glucose biosensor based on thionine cross-linked multiwalled carbon nanotubes (MWNTs) and Au nanoparticles (Au NPs) multilayer functionalized indium-doped tin oxide (ITO) electrode were presented in this paper. The effect of light irradiation on the enhancement of bioelectrocatalytic processes of the biocatalytic systems by the photovoltaic effect was investigated.

Detection of neurotransmitters by a light scattering technique based on seed-mediated growth of gold nanoparticles

A simple light scattering detection method for neurotransmitters has been developed, based on the growth of gold nanoparticles. Neurotransmitters (dopamine, L-dopa, noradrenaline and adrenaline) can effectively function as active reducing agents for generating gold nanoparticles, which result in enhanced light scattering signals. The strong light scattering of gold nanoparticles then allows the quantitative detection of the neurotransmitters simply by using a common spectrofluorometer.

A NOVEL DESIGN OF LIGHT-TRANSPARENT GOLD-MINIGRID THIN-LAYER FTIR SPECTROELECTROCHEMICAL CELL WITH VERTICAL CONFIGURATION

A Teflon bridge/edge-eliminator is designed to connect a glass container and a light-transparent gold-minigrid NaCl thin-layer cell to form a vertically configured in-situ FTIR spectroelectrochemical cell. The bridge/edge-eliminator sets an internal reference point for accurate potential control. The size of the thin-layer chamber is 5 X 5 X 0.11mm. A 1900-omega formal resistance of the thin-layer cell was measured in CH2Cl2/0.1 M TBAP solution. Well defined thin-layer cyclic voltammograms and IR spectral changes for ferrocene oxidation were obtained.

Safe fabrication of sharp gold tips for light emission in scanning tunnelling microscopy

Gold is the optimal tip metal for light emission in scanning tunnelling microscopy (LESTM) under ambient conditions. Sharp Au-tips of similar to 10nm radius were produced reliably using a safe, two-step etching method in 20% (w/w) CaCl2 solution. Previous CaCl2-based methods have tended to produce blunter tips, while other etching techniques that do produce sharp Au-tips, do so with the use of toxic or hazardous electrolytes. The tips are characterised using scanning electron microscopy and their efficacy in LESTM is evidenced by high-resolution, simultaneous topographic and photon mapping of Au(1 1 1)- and polycrystalline Au-surfaces. Spectra of the optical emission exhibit only one or two peaks with etched tips in contrast to the more complex spectra typical of cut tips; this feature, together with the highly symmetric geometry of the tips, facilitates a definitive analysis of the light emission process. (c) 2007 Elsevier B. V.. All rights reserved.

Light emission from gold and silver thin films in a scanning tunneling microscope: role of contamination and interpretation of grain structure in photon maps

Scanning tunnelling microscope (STM) tip-induced light emission from Au and Ag has been studied. Thin film samples similar to100nm thick were prepared by thermal evaporation at 0.5nm/s onto a room-temperature glass substrate to produce grains of 20-50nm in lateral dimension at the surface. Light emission from the samples in the STM was quasi-simultaneously recorded with the topography, at 1.8V tip bias and 3-40nA current, alternating pixel by pixel at the same bias. Typically, a surface scan range of 150 nm x 150 nm was surveyed. Au, W and PtIr tips were used.

Plasmon-enhanced dynamic light scattering of gold nanorods in bulk and near a wall

Transportprozesse von anisotropen metallischen Nanopartikeln wie zum Beispiel Gold-Nanostäbchen in komplexen Flüssigkeiten und/oder begrenzten Geometrien spielen eine bedeutende Rolle in einer Vielzahl von biomedizinischen und industriellen Anwendungen. Ein Weg zu einem tiefen, grundlegenden Verständnis von Transportmechanismen ist die Verwendung zweier leistungsstarker Methoden - dynamischer Lichtstreuung (DLS) und resonanzverstärkter Lichtstreuung (REDLS) in der Nähe einer Grenzfläche. In dieser Arbeit wurden nanomolare Suspensionen von Gold-Nanostäbchen, stabilisiert mit Cetyltrimethylammoniumbromid (CTAB), mit DLS sowie in der Nähe einer Grenzfläche mit REDLS untersucht. Mit DLS wurde eine wellenlängenabhängige Verstärkung der anisotropen Streuung beobachtet, welche sich durch die Anregung von longitudinaler Oberflächenplasmonenresonanz ergibt. Die hohe Streuintensität nahe der longitudinalen Oberflächenplasmonenresonanzfrequenz für Stäbchen, welche parallel zum anregenden optischen Feld liegen, erlaubte die Auflösung der translationalen Anisotropie in einem isotropen Medium. Diese wellenlängenabhängige anisotrope Lichtstreuung ermöglicht neue Anwendungen wie etwa die Untersuchung der Dynamik einzelner Partikel in komplexen Umgebungen mittels depolarisierter dynamischer Lichtstreuung. In der Nähe einer Grenzfläche wurde eine starke Verlangsamung der translationalen Diffusion beobachtet. Hingegen zeigte sich für die Rotation zwar eine ausgeprägte aber weniger starke Verlangsamung. Um den möglichen Einfluss von Ladung auf der festen Grenzfläche zu untersuchen, wurde das Metall mit elektrisch neutralem Polymethylmethacrylat (PMMA) beschichtet. In einem weiteren Ansatz wurde das CTAB in der Gold-Nanostäbchen Lösung durch das kovalent gebundene 16-Mercaptohexadecyltrimethylammoniumbromid (MTAB) ersetzt. Daraus ergab sich eine deutlich geringere Verlangsamung.

Interactions of phenyldithioesters with gold nanoparticles (AuNPs): Implications for AuNP functionalization and molecular barcoding of AuNP assemblies

The interactions of phenyldithioesters with gold nanoparticles (AuNPs) have been studied by monitoring changes in the surface plasmon resonance (SPR), depolarised light scattering, and surface enhanced Raman spectroscopy (SERS). Changes in the SPR indicated that an AuNP-phenyldithioester charge transfer complex forms in equilibrium with free AuNPs and phenyldithioester. Analysis of the Langmuir binding isotherms indicated that the equilibrium adsorption constant, Kads, was 2.3 ± 0.1 × 106 M−1, which corresponded to a free energy of adsorption of 36 ± 1 kJ mol−1. These values are comparable to those reported for interactions of aryl thiols with gold and are of a similar order of magnitude to moderate hydrogen bonding interactions. This has significant implications in the application of phenyldithioesters for the functionalization of AuNPs. The SERS results indicated that the phenyldithioesters interact with AuNPs through the C═S bond, and the molecules do not disassociate upon adsorption to the AuNPs. The SERS spectra are dominated by the portions of the molecule that dominate the charge transfer complex with the AuNPs. The significance of this in relation to the use of phenyldithioesters for molecular barcoding of nanoparticle assemblies is discussed.

The encapsulation of gold nanoparticles using RAFT, ATRP and miniemulsion polymerisation techniques

The investigation into the encapsulation of gold nanoparticles (AuNPs) by poly(methyl methacrylate) (PMMA) was undertaken. This was performed by three polymerisation techniques including: grafting PMMA synthesised by reversible addition-fragmentation chain transfer (RAFT) polymerisation to AuNPs, grafting PMMA synthesised by atom transfer radical polymerisation (ATRP) from the surface of functionalised AuNPs and by encapsulation of AuNPs within PMMA latexes produced through photo-initiated oil-in-water (o/w) miniemulsion polymerisation. The grafting of RAFT PMMA to AuNPs was performed by the addition of the RAFT functionalised PMMA to citrate stabilised AuNPs. This was conducted with a range of PMMA of varying molecular weight distribution (MWD) as either the dithioester or thiol end-group functionalities. The RAFT PMMA polymers were characterised by gel permeation chromatography (GPC), ultraviolet-visible (UV-vis), Fourier transform infrared-attenuated total reflectance (FTIR-ATR), Fourier transform Raman (FT-Raman) and proton nuclear magnetic resonance (1H NMR) spectroscopies. The attachment of PMMA to AuNPs showed a tendency for AuNPs to associate with the PMMA structures formed, though significant aggregation occurred. Interestingly, thiol functionalised end-group PMMA showed very little aggregation of AuNPs. The spherical polymer-AuNP structures did not vary in size with variations in PMMA MWD. The PMMA-AuNP structures were characterised using scanning electron microscopy (SEM), transition electron microscopy (TEM), energy dispersive X-ray analysis (EDAX) and UV-vis spectroscopy. The surface confined ATRP grafting of PMMA from initiator functionalised AuNPs was polymerised in both homogeneous and heterogeneous media. 11,11’- dithiobis[1-(2-bromo-2-methylpropionyloxy)undecane] (DSBr) was used as the surface-confined initiator and was synthesised in a three step procedure from mercaptoundecanol (MUD). All compounds were characterised by 1H NMR, FTIR-ATR and Raman spectroscopies. The grafting in homogeneous media resulted in amorphous PMMA with significant AuNP aggregation. Individually grafted AuNPs were difficult to separate and characterise, though SEM, TEM, EDAX and UV-vis spectroscopy was used. The heterogeneous polymerisation did not produce grafted AuNPs as characterised by SEM and EDAX. The encapsulation of AuNPs within PMMA latexes through the process of photoinitiated miniemulsion polymerisation was successfully achieved. Initially, photoinitiated miniemulsion polymerisation was conducted as a viable low temperature method of miniemulsion initiation. This proved successful producing a stable PMMA with good conversion efficiency and narrow particle size distribution (PSD). This is the first report of such a system. The photo-initiated technique was further optimised and AuNPs were included into the miniemulsion. AuNP encapsulation was very effective, producing reproducible AuNP encapsulated PMMA latexes. Again, this is the first reported case of this. The latexes were characterised by TEM, SEM, GPC, gravimetric analysis and dynamic light scattering (DLS).

Noble metal photocatalysts under visible light and UV light irradiation

One of the greatest challenges for the study of photocatalysts is to devise new catalysts that possess high activity under visible light illumination. This would allow the use of an abundant and green energy source, sunlight, to drive chemical reactions. Gold nanoparticles strongly absorb both visible light and UV light. It is therefore possible to drive chemical reactions utilising a significant fraction of full sunlight spectrum. Here we prepared gold nanoparticles supported on various oxide powders, and reported a new finding that gold nanoparticles on oxide supports exhibit significant activity for the oxidation of formaldehyde and methanol in the air at ambient temperature, when illuminated with visible light. We suggested that visible light can greatly enhance local electromagnetic fields and heat gold nanoparticles due to surface plasmon resonance effect which provides activation energy for the oxidation of organic molecules. Moreover, the nature of the oxide support has an important influence on the activity of the gold nanoparticles. The finding reveals the possibility to drive chemical reactions with sunlight on gold nanoparticles at ambient temperature, highlighting a new direction for research on visible light photocatalysts. Gold nanoparticles supported on oxides also exhibit significant dye oxidation activity under visible light irradiation in aqueous solution at ambient temperature. Turnover frequencies of the supported gold nanoparticles for the dye degradation are much higher than titania based photocatalysts under both visible and UV light. These gold photocatalysts can also catalyse phenol degradation as well as selective oxidation of benzyl alcohol under UV light. The reaction mechanism for these photocatalytic oxidations was studied. Gold nanoparticles exhibit photocatalytic activity due to visible light heating gold electrons in 6sp band, while the UV absorption results in electron holes in gold 5d band to oxidise organic molecules. Silver nanoparticles also exhibit considerable visible light and UV light absorption due to surface plasmon resonance effect and the interband transition of 4d electrons to the 5sp band, respectively. Therefore, silver nanoparticles are potentially photocatalysts that utilise the solar spectrum effectively. Here we reported that silver nanoparticles at room temperature can be used to drive chemical reactions when illuminated with light throughout the solar spectrum. The significant activities for dye degradation by silver nanoparticles on oxide supports are even better than those by semiconductor photocatalysts. Moreover, silver photocatalysts also can degrade phenol and drive the oxidation of benzyl alcohol to benzaldehyde under UV light. We suggested that surface plasmon resonance effect and interband transition of silver nanoparticles can activate organic molecule oxidations under light illumination.

School libraries, teacher-librarians and literacy at Gold Coast schools : research findings

This paper reports research about school libraries, teacher-librarians and their contribution to literacy development. It presents an evidenced based snapshot, from the principals’ perspective, of 27 school libraries in the Gold Coast area of Australia. These new Australian findings show: • an evidenced based snapshot of school libraries and teacher-librarians, from the principals’ perspective • indications that school NAPLAN scores for reading and writing were generally higher when (a) student to library staff ratios were lower (i.e. better) and (b) the school had a teacher-librarian. The research responds to the Australian Government inquiry into school libraries and teacher-librarians (2010-11) which identified an urgent need for current data about provision and staffing of school libraries and their influence on student literacy and learning. In light of the National plan for school improvement (Australian Government, 2013), the findings are of potential interest to education authorities, school leadership teams, teacher-librarians, teachers and researchers. They offer evidence to inform policy development, strategic planning and advocacy about school libraries and teacher-librarians in supporting the reading, literacy and learning needs of 21st century learners.

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.

New catalysts for organic synthesis driven by light and efficient sorbents for removal of radioactive ions from water

The body of the thesis contained two separate elements which made an original contribution to fundamental understanding in the areas of photocatalysis, chemical synthesis and water treatment. Research on chemical reactions catalyzed by noble metal nanoparticles (such as gold) or surface complex grafted metal oxides which can be driven by sunlight at ambient temperature and the second element on radioactive cesium (137Cs+) cations and iodine (125I-) anions recovery by the unique structural features of titanate nanostructures for firmly capture and safe storage; the works has been all published in journals that are rated at the top of their respective fields.