CoFe 2 O 4 nanocrystallites have been synthesized by alkalide reduction of Co 2+ and Fe 3+ to form nanoscale CoFe 2 , followed by oxidation with aerated water at room-temperature resulting in the nanocrystalline ferrite. As produced, the material consists of 2-4 nm nanocrystals that are superparamagnetic with an average blocking temperature of ∼350 K. Annealing at 100 °C in air results in a decrease in the blocking temperature to ∼250 K, with no detectable nanocrystallite growth. The dramatic change in the magnetic properties upon annealing is probably due to removal of crystal defects, namely oxygen vacancies. Further annealing to temperatures as high as 400 °C results in little change in the nanocrystallite size or the magnetic properties. Annealing at 500 °C results in the onset of significant growth in the nanocrystallite size, reaching 30 nm for material annealed at 1000 °C. The saturation magnetization, remanence, and squareness ratio, measured at 300 K, increase smoothly with increasing annealing temperature above 500 °C reaching 30 nm, 75 emu/g (94% of bulk value), 28 emu/g, and 0.37 respectively, for material that had been annealed at 1000 °C. The unannealed material has the largest coercivity observed in this study, 5.13 kOe at 5 K falling to 116 Oe at 300 K. The coercivity at 300 K declines dramatically to 0.9 Oe upon annealing at 100 °C, rising sharply to 67 Oe for material annealed at 500 °C, falling to 44 Oe for material annealed at 600 °C, and then steadily growing with increasing annealing temperature to 59 Oe for material annealed at 1000 °C. The anomalous increase in coercivity observed for samples annealed at 500 °C appears to be due to an increase in the average crystallite aspect ratio, which declines upon annealing at higher temperature.
Tb 0.05 ) 2 O 2 CO 3 nanoparticles have been synthesized by subambient homogeneous reduction using alkalide solutions and subsequent oxidation. As synthesized, the material consists of free flowing agglomerates of ill-defined, amorphous, or subnanocrystalline nanoparticles. Thermal analysis shows that 2.83 CO 2 molecules are adsorbed per Y 2 O 3 formula unit in the washed product. The samples annealed at 200 °C or greater are crystalline, consisting of agglomerated nanocrystals. The nanocrystals grow from an average of 15.3-17.6 nm, the agglomerates decrease in size, and the surface area decreases from 88 to 78 m 2 /g as the annealing temperature is raised from 400 to 700 °C. Annealing at 800 °C results in a phase change from the carbonate to (Y 0.95 Tb 0.05 ) 2 O 2 . The crystallite size of the oxide phase increases from 21.4 to 22.6 nm, and the surface area increases from 82 to 86 m 2 /g as the annealing temperature is increased from 800 to 1000 °C. Transmission electron microscopy observations show that the increase in the surface area, even as the average crystallite size increases, is consistent with the breaking up of agglomerates and the creation of a highly textured material, probably due to the release of CO 2 during the phase transition. The washed unannealed product displays luminescence typical of the Tb 3+ ion. The photoluminescence intensity of the green 5 D 4 -7 F 4 transition increases with increasing annealing temperature, from 5% for the unannealed product to 16% for the nanophosphor annealed at 1000 °C.
Banknote evidence is often submitted after a suspect has attempted to disguise or remove red dye stain that has been released because of an anti-theft device that activates after banknotes have been unlawfully removed from bank premises. Three chlorinated compounds have been synthesized as forensic chemical standards to indicate bank security dye bleaching as a suspect's intentional method for masking a robbery involving dye pack release on banknotes. A novel, facile synthetic method to provide three chlorinated derivatives of 1-(methylamino)anthraquinone (MAAQ) is presented. The synthetic route involved Ultra Clorox bleach as the chlorine source, iron chloride as the catalyst, and MAAQ as the starting material and resulted in a three-component product mixture. Two mono-chlorinated isomers (2-chloro-1-(methylamino)anthraquinone and 4-chloro-1-(methylamino)anthraquinone) and one di-chlorinated compound (2,4-dichloro-1-(methylamino)anthraquinone) of the MAAQ parent molecule were detected by gas chromatography mass spectrometry (GC-MS), and subsequently isolated by liquid chromatography (LC) with postcolumn fraction collection. Although GC-MS is sensitive enough to detect all of the chlorinated products, it is not definitive enough to identify the structural isomers. Liquid-state nuclear magnetic resonance (NMR) spectroscopy was utilized to elucidate structurally the ortho- and para-mono-chlorinated isomers once enough material was properly isolated. A reaction mechanism involving iron is proposed to explain the presence of chlorinated MAAQ species on stolen banknotes after attempted bleaching.
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