The Raman spectra of approximately 20 reference samples of cobalt-based green and violet artists' pigments of various provenance (present day manufactory, historical reference pigments and samples from a contemporary artist's studio) were acquired to assist in the identification of unknown cobalt-based pigments in works by Pablo Picasso (1881-1973) and Jasper Johns (b. 1930. Specifically, Raman spectra were obtained for various cobalt titanate greens (Co 2 TiO 4 ), highlighting variability in peak positions because of ionic substitutions in the spinel structures of such pigments. The Raman spectra of the cobalt violet pigments magnesium cobalt arsenate (Mg x Co 3-x (AsO 4 ) 2 ) and hydrated forms, ammonium cobalt phosphate hydrate (NH 4 CoPO 4 *H 2 O), and anhydrous cobalt phosphate, Co 3 (PO 4 ) 2 were also recorded; some of which are presented here for the first time. Fourier Transform Infrared spectroscopy (FTIR), x-ray fluorescence spectrometry (XRF) and x-ray diffraction (XRD) were employed to confirm the composition of the reference materials. An optimal technique to characterize microscopic cross sections from the studied artworks is Raman microscopy, which can also provide valuable information on the hydration states of the examined phases. The multi-analytical methodology allowed the identification of the unknown green pigment used by Jasper Johns as cobalt titanate green (C.I. PG 50); representing the first documented occurrence of this pigment in the palette of a renowned contemporary artist. Both magnesium cobalt arsenate (in anhydrous and hydrated forms) and anhydrous cobalt phosphate were identified in the Picasso painting.This research advances the knowledge of 20th century synthetic inorganic pigments used by artists and documents their usage in actual works of art.
Zinc oxide nanowires have been synthesized without using metal catalyst seed layers on fluorine-doped tin oxide (FTO) substrates by a modified vapor phase transport deposition process using a double-tube reactor. The unique reactor configuration creates a Zn-rich vapor environment that facilitates formation and growth of zinc oxide nanoparticles and wires (20–80 nm in diameter, up to 6 μm in length, density <40 nm apart) at substrate temperatures down to 300°C. Electron microscopy and other characterization techniques show nanowires with distinct morphologies when grown under different conditions. The effect of reaction parameters including reaction time, temperature, and carrier gas flow rate on the size, morphology, crystalline structure, and density of ZnO nanowires has been investigated. The nanowires grown by this method have a diameter, length, and density appropriate for use in fabricating hybrid polymer/metal oxide nanostructure solar cells. For example, it is preferable to have nanowires no more than 40 nm apart to minimize exciton recombination in polymer solar cells.
The anatase to rutile phase transformation via thermal and chemical (HF etching) routes of TiO 2 P25 has been investigated. The treatment parameters and properties of the resulting anatase and rutile nanoparticles are analyzed and discussed. Since the nature of TiO 2 surfaces plays a significant role in determining the physical and chemical properties of the TiO 2 nanoparticles, it is important to investigate the surface properties, including the morphology, the main exposed faces, the defectiveness, to be correlated with their peculiar properties, and then reactivity. Herein, we report an infrared spectroscopy investigation, employing the adsorption of CO probe molecule at low temperature, including 12 CO and 12 CO-13 CO isotopic mixtures, at the surface sites of TiO 2 P25, previously heated from room temperature to 1,023 K under vacuum conditions. The same FTIR experiments were adopted on HF-etched TiO 2 . X-ray diffraction and transmission electron microscopy analyses were adopted to elucidate the role played by the thermal and the HF-etching treatments in modifying not only the distribution of exposed surfaces, but even the phase composition of the pristine TiO 2 P25 samples, which are initially dominated by the most thermodynamically stable (101) facets of the anatase phase. The present study helps in the crystal and exposed facet engineering for the development of highly efficient photocatalysts.
Advancements in dye-sensitized solar cell (DSSC) technology are occurring at an everincreasing rate, as the development of novel carbon-based materials, the increasing research into new 3D surface morphologies and cell design, and the focus on the development of new sensitizers and electrolytes have allowed many new possibilities for DSSCs. Solar cells that are three-dimensionally structured offer significant advantages over traditional crystalline / semicrystalline panels in that they can convert incident photons that strike them at large incident angles, can be flexible / used in applications which require non-rigid materials, and can be substantially cheaper to produce than traditional panels, especially with the replacement of more expensive, traditional electrode materials by carbon materials in the working / counter electrode.The use of carefully selected and engineered sensitizers like quantum dots with these threedimensionally structured solar cells have seen them achieve ever-increasing power conversion efficiencies, and it's likely that they will soon rival traditional crystalline / semi-crystalline panels for both mass power generation and use in more niche applications such as flexible photovoltaic textile fibers. This review covers DSSCs constructed with several different materials, and the advantages and disadvantages of a variety of cell designs.
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