Fe3O4 nanoparticles: protein-mediated crystalline magnetic superstructures.

The synthesis of magnetic, monodisperse nanoparticles has attracted great interest in nanoelectronics and nanomedicine. Here we report the fabrication of pure magnetite nanoparticles, less than ten nanometers in size, using the cage-shaped protein apoferritin (Fe(3)O(4)-ferritin). Crystallizable proteins were obtained through careful successive separation methods, including a magnetic chromatography that enabled the effective separation of proteins, including a Fe(3)O(4) nanoparticle (7.9 ± 0.8 nm), from empty ones. Macroscopic protein crystals allowed the fabrication of three-dimensional arrays of Fe(3)O(4) nanoparticles with interparticle gaps controlled by dehydration, decreasing their magnetic susceptibilities and increasing their blocking temperatures through enhanced dipole-dipole interactions.

A comparison of the cyclic voltammetry of the Sn/Sn(II) couple in the room temperature ionic liquids N-butyl-N-methylpyrrolidinium dicyanamide and N-butyl-N-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide: solvent induced changes of electrode reaction mechanism.

The Sn/Sn(II) couple is studied in the room temperature ionic liquids N-butyl-N-methylpyrrolidinium dicyanamide, [C(4)mpyrr][N(CN)(2)] and N-butyl-N-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide, [C(4)mpyrr][NTf(2)] using cyclic voltammetry. The Sn(II) species is introduced into each of the ionic liquids by dissolving either SnCl(2) or Sn(CF(3)SO(3))(2). The diffusion coefficient of the Sn(II) species produced is found to vary with the ionic liquid, partly reflecting the difference in the viscosity of the two liquids, but also to vary with the Sn(II) salts used, indicating that different Sn(II) species may be present. The mechanism for the stripping of deposited tin is found to change with potential and also vary with the Sn(II) salt/ionic liquid combination used. In [C(4)mpyrr][N(CN)(2)] the mechanism for the tin stripping process is broadly similar for both of the Sn(II) salts used indicating that the morphology of the tin deposit is similar and that the stripping mechanism is largely independent of the Sn(II) salt anion. In [C(4)mpyrr][NTf(2)] a large difference was seen in the voltammetry of the different Sn(II) salts. Tafel analysis is used to show that the mechanism of the oxidation of Sn is sensitive to the solvent, the salt and the potential. The rate determining step was found to vary between the first electron transfer, the second electron transfer and a step likely involving reactions of a Sn(+) intermediate.

Kinetic and thermodynamic parameters of the Li/Li+ couple in the room temperature ionic liquid N-butyl-N-methylpyrrolidinium bis(trifluoromethylsulfonyl) imide in the temperature range 298-318 K: a theoretical and experimental study using Pt and Ni electrodes.

The Li/Li+ couple is investigated in the room temperature ionic liquid N-butyl-N-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide, [C4mpyrr][NTf2], at a range of temperatures varying from 298 to 318 K.Experiments are conducted using both nickel and platinum microelectrodes. On nickel, a single stripping peak is observed for the stripping of bulk lithium that allowed thermodynamic and kinetic parameters to be extracted via computational simulation. At 298 K, the electrochemical rate constant (k0) ) 1.2 X 10-5 cms-1, the diffusion coefficient (D) ) 4.5 X 10-8 cm2 s-1, the formal potential (E(f)0 ) -3.26 V versus the Fc/Fc+ reference couple, and the transfer coefficient (alpha) = 0.63. On platinum, multiple stripping peaks are observed due to the stripping of Li-Pt alloys in addition to the stripping of bulk lithium. The ratio of the different stripping peaks is found to change with temperature, indicating that Li-Pt alloys are more thermodynamically stable than pure bulk lithium and platinum.

General theory of cathodic and anodic stripping voltammetry at solid electrodes: mathematical modeling and numerical simulations.

Theory is presented to describe the voltammetric signals associated with the stripping phase of stripping voltammetry at solid electrodes. Three mathematical models are considered, and the importance of the hemispherical diffusion associated with electrochemical dissolution of particles in the micrometer range is investigated. Model A considers a "monolayer" system where the coverage at a specific point cannot exceed a maximum value. Model B considers a thin layer of metal or metal oxide, but in contrast to model A, the maximum surface coverage is not restricted. Model C represents the stripping of a "thick layer" where the deposition is also unrestricted.