Richard D. Tilley

Oxide-based inorganic/organic and nanoporous spherical particles: synthesis and functional properties.

Abstract This paper reviews the recent progress in the preparation of oxide-based and heteroatom-doped particles. Surfactant-templated oxide particles, e.g. silica and titania, are possible candidates for various potential applications such as adsorbents, photocatalysts, and optoelectronic and biological materials. We highlight nanoporous oxides of one element, such as silicon or titanium, and those containing multiple elements, which exhibit properties that are not achieved with individual components. Although the multicomponent nanoporous oxides possess a number of attractive functions, the origin of their properties is hard to determine due to compositional/structural complexity. Particles with a well-defined size and shape are keys for a quantitative and detailed discussion on the unique complex properties of the particles. From this viewpoint, we review the synthesis techniques of the oxide particles, which are functionalized with organic molecules or doped with heteroatoms, the physicochemical properties of the particles and the possibilities for their photofunctional applications as complex systems.

Chemical reactions on surface molecules attached to silicon quantum dots.

This Article describes research on chemical reactions on molecules attached to the surface of silicon quantum dots that have been performed to produce quantum dots with reactive surface functionalities such as diols and epoxides. Characterization of the surface reactions includes NMR and FT-IR studies, and the quantum dots were characterized by transmission electron microscopy (TEM) and energy dispersive spectroscopy (EDS). Cytotoxicity and cell viability assay conducted on silicon dots capped with polar molecules indicated low toxicity with quantum dots with more reactive functionalities found to be more toxic. The silicon quantum dots photoluminesce and have been used as a blue chromophore for the biological imaging of cells.

Chemical Insight into the Origin of Red and Blue Photoluminescence Arising from Freestanding Silicon Nanocrystals

Silicon nanocrystals (Si NCs) are attractive functional materials. They are compatible with standard electronics and communications platforms and are biocompatible. Numerous methods have been developed to realize size-controlled Si NC synthesis. While these procedures produce Si NCs that appear identical, their optical responses can differ dramatically. Si NCs prepared using high-temperature methods routinely exhibit photoluminescence agreeing with the effective mass approximation (EMA), while those prepared via solution methods exhibit blue emission that is somewhat independent of particle size. Despite many proposals, a definitive explanation for this difference has been elusive for no less than a decade. This apparent dichotomy brings into question our understanding of Si NC properties and potentially limits the scope of their application. The present contribution takes a substantial step forward toward identifying the origin of the blue emission that is not expected based upon EMA predictions. It describes a detailed comparison of Si NCs obtained from three of the most widely cited procedures as well as the conversion of red-emitting Si NCs to blue emitters upon exposure to nitrogen-containing reagents. Analysis of the evidence is consistent with the hypothesis that the presence of trace nitrogen and oxygen even at the parts per million level in Si NCs gives rise to the blue emission.

Ultrafast Growth of Highly Branched Palladium Nanostructures for Catalysis

Palladium is widely used as a catalyst in pharmaceutical and chemical syntheses as well as in the reduction of harmful exhaust emissions. Therefore, the development of high performance palladium catalysts is an area of major concern. In this paper, we present the synthesis of highly branched palladium nanostructures in a simple solution phase reaction at room temperature. By varying the nature of the organic stabilizer system we demonstrate control over the reaction kinetics and hence the shape of the nanostructures. Investigations into the structural evolution of the nanostructures show that they form from multiply twinned face centered cubic (fcc) nanoparticle nuclei. Reaction kinetics then determine the resulting shape where ultrafast growth is shown to lead to the highly branched nanostructures. These results will contribute greatly to the understanding of complex nanoparticle growth from all fcc metals. The nanostructures then show excellent catalytic activity for the hydrogenation of nitrobenzene to aniline.

In Situ and Ex Situ Studies of Platinum Nanocrystals: Growth and Evolution in Solution

In situ studies on the growth and evolution of platinum nanocrystals in solution were carried out using synchrotron-based X-ray diffraction (XRD) techniques. Ex situ low- and high-resolution transmission electron microscopy (TEM) were used to investigate the nanocrystal morphologies through the different growth stages. In a reaction with low precursor concentration, both XRD and TEM results show that growth occurs at a relatively slow rate and yields faceted morphologies, which are characteristic of a thermodynamically controlled regime. In contrast, the platinum nanocrystals in the high-concentration reaction form branched structures and grow at much greater rates under a kinetically controlled regime. Additionally the growth mechanism of the high-concentration reaction involves a morphology transformation from octapod-like shapes to porous nanostructures, which is brought about by a novel mechanism involving selective growth and etching processes that occur simultaneously and at comparable rates.

Synthesis of SnS Quantum Dots

Highly mondispersed SnS nanocrystals have been synthesized using ethanolamine ligands. SnS nanocrystals are small enough to be in the quantum confinement regime.

Solution Synthesis, Optical Properties, and Bioimaging Applications of Silicon Nanocrystals

Understanding and unlocking the potential of semiconductor nanocrystals (NCs) is important for future applications ranging from biomedical imaging contrast agents to the next generation of solar cells and LEDs. Silicon NCs (Si NCs) have key advantages compared with other semiconductor NCs due to silicons high natural abundance, low toxicity and strong biocompatibility, and unique size, and surface dependent optical properties. In this Account, we review and discuss the synthesis, surface modification, purification, optical properties, and applications of Si NCs. The synthetic methods used to make Si NCs have improved considerably in the last 5-10 years; highly monodisperse Si NCs can now be produced on the near gram scale. Scaled-up syntheses have allowed scientists to drive further toward the commercial utilization of Si NCs. The synthesis of doped Si NCs, through addition of a simple elemental precursor to a reaction mixture or by the production of a single source precursor, has shown great promise. Doped Si NCs have demonstrated unique or enhanced properties compared with pure Si NCs, for example, magnetism due to the presence of magnetic metals like Fe and Mn. Surface reactions have reached a new level of sophistication where organic (epoxidation and diol formation) and click (thiol based) chemical reactions can be carried out on attached surface molecules. This has led to a wide range of biocompatible functional groups as well as a degree of emission tuneability. The purification of Si NCs has been improved through the use of size separation columns and size selective precipitation. These purification approaches have yielded highly monodisperse and pure Si NCs previously unachieved. This has allowed scientists to study the size and surface dependent properties and toxicity and enabled the use of Si NCs in biomedical applications. The optical properties of Si NCs are complex. Using a combination of characterization techniques, researchers have explored the relation between the optical properties and the size, surface functionalization, and preparation method. This work has led to a greater fundamental understanding of the unique optical properties of Si NCs. Si NCs are being studied for a wide range of important applications, including LEDS with tunable electroluminescence ranging from NIR to yellow, the encapsulation of Si NCs within micelles terminated with proteins to allow targeted in vivo imaging of cells, Si NC-polymer hybrid solar cells, and the use of Si NCs in battery anodes with high theoretical capacity and good charge retention.

Simple synthesis and functionalization of iron nanoparticles for magnetic resonance imaging.

Magnetic nanoparticles (NPs) are increasingly important in many biomedical applications, such as drug delivery, hyperthermia, and magnetic resonance imaging (MRI) contrast enhancement. For MRI, iron oxide NPs are the only commercial T2 or negative contrast agents, due to their biocompatibility and ease of synthesis and research in the area is highly active. The efficacy of these contrast agents depends mainly on the surface chemistry and magnetic properties of the NPs. Materials with larger magnetization could induce more efficient transverse (T2) relaxation of protons and result in greater contrast enhancement. As iron has the highest saturation magnetization at room temperature among all elements, and is biocompatible, it is an ideal candidate for MRI contrast enhancement. Nevertheless, the development of using iron NPs for magnetic applications has been challenging and limited compared to those of its oxides, due to the difficulty in preparing stable iron NPs with simple synthesis methods and precursors. 6] Under ambient conditions, iron NPs of 8 nm or smaller oxidize completely upon exposure to air. For larger NPs, an oxide shell of 3–4 nm forms instantly on the surface, forming iron/iron oxide core/shell NPs. Groundbreaking studies for the synthesis of iron NPs of larger than 8 nm has largely been achieved by decomposition of iron pentacarbonyl, [Fe(CO)5]. [6,8] Additional reports include the use of other precursors in forming iron nanocubes. However, all of these processes are limited in terms of ease of synthesis and scalability; [Fe(CO)5] is volatile and highly toxic, [5] and other processes involve precursors that are expensive and airsensitive, or require high decomposition temperatures. Here, we chose an easy to handle iron organometallic sandwich compound as the precursor and prepared singlecrystal iron NPs using a simple, low-temperature synthesis method. The iron nanocrystals oxidized naturally to form highly crystalline iron/iron oxide core/shell NPs. The ease of this synthesis facilitates the larger-scale application of stabilized iron NPs. To enable the use of these NPs in biological applications, the NP surface was modified to make the NPs water soluble. The strongly magnetic core/shell NPs are shown to be more effective T2 contrast agents for in vivo MRI and small tumor detection, compared to pure iron oxides. The successful detection of small tumors in vivo demonstrated here holds a great promise for accurate detection of early metastases in human lymph nodes, which has a large impact on the treatment and prognosis of a range of cancers. The iron/iron oxide core/shell NPs were prepared by first synthesizing iron nanocrystals by decomposition of the iron precursor [Fe(C5H5)(C6H7)], in the presence of oleylamine (OLA) stabilizing molecules. The non-carbonyl, sandwich compound was chosen for its simple preparation and ease of decomposition compared to other more stable sandwich compounds such as ferrocene. The synthesis was carried out in a closed reaction vessel under a mild hydrogen atmosphere, at 130 8C. The temperature required was lower than the usual temperature range (150–300 8C) needed for decomposition of other iron precursors in previous studies. Once [*] Dr. K. W. Feindel, Prof. P. T. Callaghan, Prof. R. D. Tilley School of Chemical and Physical Sciences and The MacDiarmid Institute for Advanced Materials and Nanotechnology, Victoria University of Wellington, Wellington 6012 (New Zealand) Fax: (+ 64)4-463-5237 E-mail: richard.tilley@vuw.ac.nz Dr. S. Cheong, Dr. B. Ingham Industrial Research Limited and The MacDiarmid Institute for Advanced Materials and Nanotechnology P. O. Box 31-310, Lower Hutt 5040 (New Zealand) Dr. P. Ferguson, Dr. I. F. Hermans Malaghan Institute of Medical Research P. O. Box 7060, Wellington 6012 (New Zealand)

Synthesis, Alignment, and Magnetic Properties of Monodisperse Nickel Nanocubes

This Communication describes the synthesis of highly monodispersed 12 nm nickel nanocubes. The cubic shape was achieved by using trioctylphosphine and hexadecylamine surfactants under a reducing hydrogen atmosphere to favor thermodynamic growth and the stabilization of {100} facets. Varying the metal precursor to trioctylphosphine ratio was found to alter the nanoparticle size and shape from 5 nm spherical nanoparticles to 12 nm nanocubes. High-resolution transmission electron microscopy showed that the nanocubes are protected from further oxidation by a 1 nm NiO shell. Synchrotron-based X-ray diffraction techniques showed the nickel nanocubes order into [100] aligned arrays. Magnetic studies showed the nickel nanocubes have over 4 times enhancement in magnetic saturation compared to spherical superparamagnetic nickel nanoparticles.

Sized controlled synthesis, purification, and cell studies with silicon quantum dots

This article describes the size control synthesis of silicon quantum dots with simple microemulsion techniques. The silicon nanocrystals are small enough to be in the strong confinement regime and photoluminesce in the blue region of the visible spectrum and the emission can be tuned by changing the nanocrystal size. The silicon quantum dots were capped with allylamine either a platinum catalyst or UV-radiation. An extensive purification protocol is reported and assessed using (1)H NMR to produce ultra pure silicon quantum dots suitable for biological studies. The highly pure quantum dots were used in cellular uptake experiments and monitored using confocal microscopy. The results showed that the amine terminated silicon nanocrystals accumulated in lysosome but not in nuclei and could be used as bio-markers to monitor cancer cells over long timescales.