ABSTRACT
The possibility of controlling materials properties by tailoring their substructure at the nanometer scale is a current topic of great interest. To do so, a fundamental understanding of the growth mechanism is of key importance and an analytical challenge as nanostructured materials are often produced by precipitation methods at high supersaturations where formation kinetics are fast. The current study focuses on the precipitation of copper oxalate, which has been previously shown to produce self-assembled ordered nanostructured particles with the promise of being able to tailor this nanometer substructure. In the current study we investigate in detail the growth mechanism and kinetics of precipitation by using in-situ particle size measurement or by stopping the reaction at various stages and using ex-situ methods. Combining the ex-situ methods of high-resolution scanning electron microscopy, transmission electron microscopy, and X-ray powder diffraction along with the in-situ methods, we were able to follow the growth process from 2 min to 2 weeks. The results in the 2-30 min period lead to the proposal of a core-shell growth model with a poorly ordered core and a well-structured shell of nanosized crystallites (50-70 nm), adding support to the brick-by-brick model previously proposed for this phase of particle growth. Particle evolution over long periods up to 2 weeks show a ripening which produces lens-shaped particles that eliminate the "high" surface energy faces observed in the earlier stages of growth. A more complete growth mechanism for copper oxalate precipitation at moderate supersaturations is proposed similar to recent findings for other self-assembled nanostructured particles.
Subject(s)
Copper/chemistry , Nanostructures/chemistry , Oxalates/chemistry , Chemical Precipitation , Crystallization , Kinetics , Molecular Structure , Particle SizeABSTRACT
CuO powders with a high specific surface area are shown to be able to produce H(2)O(2) in aqueous solution under simulated light irradiation. The highest rate of peroxide production was observed under mild experimental conditions using O(2) and a large surface area photocatalyst CuO irradiated with a solar simulator having light intensities between 60 and 90 mW/cm(2). The CuO employed had a specific surface area (SSA) of 64.8-70.1 m(2)/g and was prepared in a tubular furnace by controlled thermal decomposition of precipitated copper oxalate. The CuO particles produced were 1 mum cubes with primary particles around 15 nm. No peroxide was produced under the same conditions with commercial CuO, with SSA 200 times lower. The CuO synthesized during this work was characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), specific surface area [Brunauer-Emmett-Teller (BET)], porosity, and X-ray photoelectron spectroscopy (XPS). From XPS, it was observed that only Cu(II) was present in the unused and used CuO. This indicates that the redox transient species involving other Cu oxidation states disappear very fast during the reaction, regenerating Cu(II) during H(2)O(2) production. Diverse experiments provided some evidence for the possible interfacial reaction mechanism leading to H(2)O(2), following the initial step of O(2)(-)(.) formation on the CuO surface under irradiation with photons, with energies exceeding the band gap of CuO. A photocatalyzed degradation of a concentrated 4-chlorophenol (4-CP) solution was observed under solar-simulated light in the presence of CuO.
Subject(s)
Copper/chemistry , Hydrogen Peroxide/chemistry , Oxygen/chemistry , Adsorption , Catalysis , Hot Temperature , Hydrogen-Ion Concentration , Microscopy, Electron, Scanning , Nitrogen/chemistry , Oxidation-Reduction , Photochemistry , Spectrum Analysis , Surface PropertiesSubject(s)
Nasal Cavity/abnormalities , Nasopharynx/abnormalities , Adolescent , Female , Humans , MaleABSTRACT
After testing 18 experimental variants against 40 reference strains belonging to different Enterovacteriaceae groups, the authors chose a multitest medium that permits concomitant testing of mobility, indol, lysinedecarboxylase and phenylalanine deaminase (MILP). In this medium, the reactions of 3734 strains belonging to the genera Escherichia, Shigella. Salmonella, Citrobacter, Klebsiella, Enterobacter, Serratia. Proteus and Providencia were concordant with the reactions in individual test media, taking as reference, in a proportion of 99.7 and 100%. The authors, associating the MILP medium to TSI agar, propose a simple scheme consisting of eight test which permits, within only 24 hours, the correct identification of the genus and sometimes of the species of cultures or isolated colonies from selective media.
