Cleaning the future

Dr Robert Palgrave has been working on a variety of new photocatalysts, with the goal of reducing water and air pollution and finding new sources of clean energ

Chemical vapour deposition of nanoparticulate and nanocomposite thin films.

Gold nanoparticle and gold / semiconductor nanocomposite thin films have been deposited using aerosol assisted chemical vapour deposition. Two gold precursors have been investigated which would be unsuitable for use with conventional atmospheric pressure chemical vapour deposition. HAuCU was used in methanol solution to deposit films at substrate temperatures of 350 - 500 °C. Powder X-ray diffraction and X-ray photoelectron spectroscopy revealed that these films consisted of metallic gold. The optical properties of these films corresponded to nanoscale gold particles, specifically displaying surface plasmon resonance (SPR) absorption. The wavelength of the SPR absorption maximum varied with precursor concentration and substrate temperature from 1000 - 600 nm. Scanning electron microscopy revealed particles a wide variety of sizes and shapes, as well as regions of island growth morphology. Depositions carried out from solutions of HAuCU and a range of quaternary ammonium ion surfactants led to films of particles with narrow size distributions. The use of tetraoctylammonium bromide (TOAB) led to films of spherical particles, the mean diameter of which could be altered by changing HAuCU : TOAB ratio, deposition temperature and solvent volume. Films with mean particle diameters ranging from 65 nm to 120 nm and arithmetic standard deviations of less than 20% of the mean could be deposited in this way. Toluene solutions of pre-formed gold particles were used to deposit films. These films showed similar optical properties to the original precursor solution. Nanocomposite films were deposited by combining HAuCU or pre-formed gold particles with a conventional CVD precursor in a single precursor solution. W(CO)6 , Mo(CO)6 , W(OPh)6 , TiPrU were combined with a gold precursor to deposit metal oxide films with incorporated gold particles. The concentration of gold within the films could be varied by changing the precursor ratios. These films showed SPR peaks that were redshifted compared to gold particles alone

The Price of Consols

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When is a Lattice Not a Lattice? The changing meaning of the term lattice in crystallography and physics

The concept of the lattice is central to the understanding of crystalline solids. However, usage of this word can very often differ between crystallographers, for whom a lattice is a mathematical object that describes the symmetry of a crystal, and physicists and chemists, for whom lattice is commonly used as a word for a regular array of particles. The similarity between the two definitions means they can easily be confused by students or inexperienced practitioners, but the fundamental differences can make the consequences of such confusion significant, an issue rarely tackled directly in popular textbooks. Here we examine the historical roots of this problem of context, and the changing understanding of the word ‘lattice’ over time. While the origins of the term lattice lie with the 19th century mathematical crystallographers, their usage, both in terms of the words used and their meanings, was fluid, and no strong distinction between the lattice and the physical components of a crystal was made. Leading crystallographers in the early 20th century regularly used the word lattice in a way that is unacceptable to some of their modern counterparts. We identify the decade after 1910 as the start of divergence between the physical and crystallographic meaning, catalysed by the discovery of X-ray diffraction and the development of lattice dynamics, although the current definitions did not become entrenched until the 1940s. While history has shown us that this classificatory issue is not just a matter of scientific disagreement and perhaps at its root is a disagreement in our understanding of classification itself. Lastly, we discuss possible resolutions to the matter

Local Government. On the Distribution of the Licenses Proposed to be Transferred in Aid of Local Expenditure

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Structure and lattice dynamics of the wide band gap semiconductors MgSiN2_{2} and MgGeN2_{2}

We have determined the structural and lattice dynamical properties of the orthorhombic, wide band gap semiconductors MgSiN$_{2}$ and MgGeN$_{2}$ using density functional theory. In addition, we present structural properties and Raman spectra of a MgSiN$_{2}$ powder. The structural properties and lattice dynamics of the orthorhombic systems are compared to wurtzite AlN. We find clear differences in the lattice dynamics between MgSiN$_{2}$, MgGeN$_{2}$ and AlN, for example we find that the highest phonon frequency in MgSiN$_{2}$ is about 100~cm$^{-1}$ higher than the highest frequency in AlN and that MgGeN$_{2}$ is much softer. We also provide the Born effective charge tensors and dielectric tensors of MgSiN$_{2}$, MgGeN$_{2}$ and AlN. Phonon related thermodynamic properties, such as the heat capacity and entropy, are in very good agreement with available experimental results.Comment: 9 pages, 11 figures, 6 table

Electro-Oxidation of Titanium Carbide Nanoparticles in Aqueous Acid Creates TiC@TiO2 Core-Shell Structures

Titanium carbide (TiC) is an attractive support material used in electro-catalysis and sensing. We report the electrochemistry of TiC nanoparticles (NPs, 35–50 nm in diameter) in different electrolytes in the pH range of 0 to 8. The TiC NPs undergo irreversible oxidation in acidic, basic, and neutral media, attributed to the partial conversion into titanium dioxide (TiO2) with the amount of oxidation highly dependent on the pH of the solution. In H2SO4 (pH 0), multiple voltammetric scans revealed the conversion to be partial but repeated scans allowed a conversion approaching 100% to be obtained with 20 scans generating a ca 60% level of oxidation. The process is inferred to lead to the formation of TiC@TiO2 core-shell nanoparticles (~12.5 nm core radius and ~5 nm shell width for a 60% conversion) and this value sharply decreases with an increase of pH. Independent measurements were conducted at a single NP level (via nano-impact experiments) to confirm the oxidation of the NPs, showing consistent agreement with the bulk measurements

Patterning of metal oxide thin films using a H₂/He atmospheric pressure plasma jet

A hydrogen-doped helium atmospheric pressure plasma jet (APPJ) is shown to be effective for the chemical reduction of metal oxides. Copper and tin oxide films (CuO and SnO2) show rapid (<2 seconds) and complete reduction to zero valence metal after exposure to the plasma jet, as revealed by X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy, and Raman spectroscopy. After a total residence time of the plasma jet of 100 seconds, titanium oxide (TiO2) produced a surface decorated with Ti2+, Ti3+ and Ti4+ with proportions of 16, 38 and 46 atom%, respectively, as determined by XPS peak integration. Similarly, with tungsten oxide (WO3), after exposure for a few seconds, W5+ was produced, yielding a deep blue electrically conductive coating. The treatment of these oxide films by this dielectric radio frequency (RF) barrier discharge plasma jet provides a level of redox conversion not seen in any other technique, particularly for TiO2, especially with a comparable power input. The precise nature of the reduction is unclear; however, the involvement of free electrons may have an important role in the reduction process

XPS surface analysis of ceria-based materials: Experimental methods and considerations

X-ray photoelectron spectroscopy (XPS) analysis of cerium is ubiquitous amongst the catalytic and materials literature however errors in experimental procedure and data analysis are often easily proliferated. In this work we focus on the best practice for experimental construction when approaching the task of understanding chemical environments in cerium-based materials by XPS

Mixed valence Sn doped (CH3NH3)3Bi2Br9 produced by mechanochemical synthesis

Bismuth halides with formula A3Bi2X9, where A is an inorganic or organic cation, show desirable properties as solar absorbers and luminescent materials. Control of structural and electronic dimensionality of these compounds is important to yield materials with good light absorption and charge transport. Here we report mechanochemical reaction of (CH3NH3)3Bi2Br9 with SnBr2 at room temperature in air, yielding a material with strong absorption across the visible region. We attribute this to mixed valence doping of Sn(II) and Sn(IV) on the Bi site. X-ray diffraction shows no secondary phases, even after heating at 200oC to improve crystallinity. X-ray photoelectron spectroscopy suggests the presence of Sn(II) and Sn(IV) states. A similar approach to dope Sn into the iodide analogue (CH3NH3)3Bi2I9 was unsuccessful