structure of ferrihydrite using synchrotron radiation [Michel et al., Science (2007) doi: 10.1126/science.1142525]. The researchers synthesized a number of ...
RESEARCH NEWS
Emulsions restore frescos SURFACE SCIENCE Natural deposits, pollution, or inappropriate preservation materials constitute a significant threat to our cultural heritage, particularly in Italy where there are many Renaissance fresco masterpieces. Researchers from the University of Florence have developed microemulsions that can remove contamination where direct application of bulk solvents or cleaning agents would be either ineffective or too harsh [Carretti et al., Langmuir (2007) 23, 6396]. In one case, 17th century wall paintings in Florence had been encrusted with gypsum and asphaltenes as a result of flooding of the Arno river in 1966. The team applied p-xylene and ammonium carbonate emulsified using the surfactant Triton X-100 to remove the highly insoluble deposits. In another case, a 15th century painting by Vecchietta in Siena was coated with an acrylic polymer from a previous preservation attempt in the late 1960s. Applying p-xylene emulsified using alkyl polyglycosides allowed a reduction in the amount of applied solvent of up to 95%. Pure organic solvents can remove acrylic polymers, but can also devastate fragile paint layers and lift them from the wall. The microemulsions, however, strip the polymer off but do not penetrate the surface, leaving the painting intact.
Mark E. Greene
Correction In the June issue of Materials Today, we mistakenly referred to Eli A. Sutter of Brookhaven National Laboratory as ‘he’ instead of ‘she’ [Petite pipette reveals drops’ dancing facets. Materials Today (2007) 10 (6), 9]. We sincerely apologize for any offence or confusion caused.
Nanofiber films detect explosives NANOTECHNOLOGY
Researchers from Southern Illinois University, the University of Illinois at Urbana-Champaign, and the Chinese Academy of Sciences have fabricated organic nanofiber films of alkoxycarbonyl-substituted, carbazole-cornered, arylene-ethynylene tetracycles (ACTC) to detect the vapor of explosive compounds such as 2,4,6-trinitrotoluene (TNT) and 2,4dinitrotoluene (DNT) [Naddo et al., J. Am. Chem. Soc. (2007) 129, 6978]. The sensor material works through fluorescence quenching. When the ACTC nanofibers are irradiated with ultraviolet light, the excited state relaxes to the ground state by emitting blue light. “In the presence of the explosives molecules, the excited state of ACTC is quenched by transferring an electron to the explosives molecule,” explains Ling Zang of Southern Illinois University. “As a result, the emission intensity of the nanofiber is decreased.” The decrease in intensity enables efficient detection of the hazardous materials. The high porosity of the nanofiber film allowed free diffusion of gaseous molecules throughout, and the sensing efficiency was found to be independent of film thickness. Thicker films tend to be more robust but organic films for sensing applications need to be thin (10 nm or less) to be highly efficient. These nanofiber films demonstrated both efficiency and reliability. Fluorescence-quenching sensing was shown for both the nitro-aromatic explosives TNT and DNT and the non-aromatic nitro-based compound
Molecular structure of ACTC. (Credit: Ling Zang.)
2,3-dimethyl-2,3-dinitrobutane (DMNB), an explosives taggant. The detection limit for TNT could be as low as 10 ppt, says Zang, which should enable the detection of buried landmines. TNT vapor is ~40 ppt directly above a mine, but the best electronic systems can only detect a level of 100 ppt. Zang expects that the nanofibril film will detect other nitro-based explosives like RDX, a common ingredient in plastic explosives, and PETN, an extremely volatile component of Semtex. Mark E. Greene
Ferrihydrite nanostructure revealed CHARACTERIZATION Ferrihydrite is a common, naturally occurring Fe oxide material found in the Earth’s crust. It is a precursor to minerals such as hematite and goethite and is used in a variety of industrial applications. Despite its mineralogical and commercial importance, its exact structure has remained controversial because of its nanocrystalline nature. Now a research team from Stony Brook University, Temple University, and the Advanced Photon Source at Argonne National Laboratory have determined the structure of ferrihydrite using synchrotron radiation [Michel et al., Science (2007) doi: 10.1126/science.1142525]. The researchers synthesized a number of samples using different methods, then collected diffraction data from a focused high-energy X-ray beam and computed the pair distribution function (PDF). The PDF provides the distribution of all the interatomic distances in the samples, which the researchers compared to calculated PDFs for several potential structures.
They found that ferrihydrite nanoparticles ranging from 2-6 nm can be adequately described by a single phase with the hexagonal space group P63mc with average unit cell dimensions a = 5.95 Å and c = 9.06 Å and a chemical formula Fe10O14(OH)2. Regardless of which route was used to synthesize ferrihydrite, the distribution of interatomic distances was the same at large distances up to 20 Å, explain F. Marc Michel and John B. Parise of Stony Brook University. The PDF method has been used for decades to study poorly crystalline materials such as glasses and liquids, but is becoming more popular in studies of nanocrystalline materials. “Because the largest distance in the PDF would be the one from one side of a particle to the other, the PDF provides a measure of particle size in situ,” say Michel and Parise. “This is a powerful way to study particle growth and is an excellent complement to small angle scattering and transmission electron microscope studies.”
Mark E. Greene
JULY-AUGUST 2007 | VOLUME 10 | NUMBER 7-8
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