Excess Spin and the Dynamics of Antiferromagnetic Ferritin

Temperature-dependent magnetization measurements on a series of synthetic ferritin proteins containing from 100 to 3000 Fe(III) ions are used to determine the uncompensated moment of these antiferromagnetic particles. The results are compared with recent theories of macroscopic quantum coherence which explicitly include the effect of this excess moment. The scaling of the excess moment with protein size is consistent with a simple model of finite size effects and sublattice noncompensation.Comment: 4 pages, 3 Postsript figures, 1 table. Submitted to PR

Relaxation and Landau-Zener experiments down to 100 mK in ferritin

Temperature-independent magnetic viscosity in ferritin has been observed from 2 K down to 100 mK, proving that quantum tunneling plays the main role in these particles at low temperature. Magnetic relaxation has also been studied using the Landau-Zener method making the system crossing zero resonant field at different rates, alpha=dH/dt, ranging from 10^{-5} to 10^{-3} T/s, and at different temperatures, from 150 mK up to the blocking temperature. We propose a new Tln(Delta H_{eff}/tau_0 alpha) scaling law for the Landau-Zener probability in a system distributed in volumes, where Delta H_{eff} is the effective width of the zero field resonance.Comment: 13 pages, 4 postscript figure

Electrical Properties of Cobalt Oxide/Silica Nanocomposites Obtained by Sol-Gel Technique

This work is an extension of our previous studies on cobalt oxide nanoparticles impeded in a silica matrix. Here we study the preparation and characterization of high cobalt content materials (60-90 wt%). In addition, the DC electrical conductivity of the prepared materials in a wide temperature range (350-673 K) was measured and discussed. The activation energy has been obtained according to Mott’s Small-Polaron Hopping (SPH) and Mott’s and Greaves Variable Range Hopping (VRH) models

Structural and Electrochemical Characteristics of Graphene Nanosheets as Supercapacitor Electrodes

In this paper, graphene oxide (GO) was prepared by the Hummers' method and reduced using hydrazine to produce graphene nanosheets (GNS). Physicochemical characterizations of the prepared materials were performed using XRD, FTIR, TGA, DTA, BET, UV-vis, Raman, and FESEM techniques. The results elucidate the structure, morphology, mesoporousity and thermal stability of the prepared samples. Detailed electrochemical studies have been conducted on GNS by CV, galvanostatic and complex impedance measurements indicating some interesting features. GNS shows a specific capacitance of 140 F g-1 at 0.05 A g-1. GNS shows high cyclic stability of about 86% over 1100 cycles at a current density of 1 A g-1. The large electrochemical active surface area suggests that most of the nanosheets are accessible to ions adsorption in the electrolyte system. Impedance spectra show low resistance of GNS, supporting its suitability for supercapacitor electrode applications

Enhancement of Adsorption Efficiency of Methylene Blue on Co3O4/SiO2 Nanocomposite

Single and well-crystalline Co3O4 phase imbedded in an amorphous SiO2 matrix has been obtained by novel aqueous solution method. The structural and morphological properties are investigated using X-ray diffraction, Fourier transform infrared spectrometer, and N2 adsorption–desorption techniques. The apparent crystallite size for Co3O4 was found to be about 13.5 nm, which elucidates the rule of poly ethylene glycol in preventing particle’s agglomeration; moreover, the pours structure of the composite enhances its adsorption ability. Co3O4/SiO2 has a high ability to absorb methylene blue from an aqueous solution. The removal percent of Methelene blue (MB) by Co3O4/SiO2 has reached 95.7%. The effect of various experimental parameters, such as initial dye concentration, contact time, and dose were investigated. Co3O4/SiO2 nanocomposite shows high adsorption capacity of 53.87 mg g−1, which is larger than the adsorption capacity of MB on other materials. Both of Langmuir and Freundlich models were used to analyze the equilibrium adsorption data. The pseudo-second-order model was found to be the most appropriate model to represent the present data. Co3O4/SiO2 nanocomposite material is proposed as a potential adsorbent for water treatment

Co3O4/SiO2 Nanocomposites for Supercapacitor Application

In this study, Co3O4/SiO2 nanocomposites have been successfully synthesized by citrate–gel method by utilizing SiO2 matrix for Co3O4 embedment. Spectroscopy analyses confirm the formation of high crystalline Co3O4 nanoparticles; meanwhile, microscopy findings reveal that the Co3O4 nanoparticles are embedded in SiO2 matrix. Electrochemical properties of the Co3O4/SiO2 nanocomposites were carried out using cyclic voltammetry (CV), galvanostatic charge–discharge, and electrochemical impedance spectroscopy(EIS) in 5 M KOH electrolyte. The findings show that the charge storage of Co3O4/SiO2 nanocomposites is mainly due to the reversible redox reaction (pseudocapacitance). The highest specific capacitance of 1,143 F g−1 could be achieved at a scan rate of 2.5 mV s−1 in the potential region between 0 and 0.6 V. Furthermore, high-capacitance retention (>92 %) after 900 continuous charge–discharge tests reveals the excellent stability of the nanocomposites. It is worth noting from the EIS measurements that the nanocomposites have low ESR value of 0.33 Ω. The results manifest that Co3O4/SiO2 nanocomposites are the promising electrode material for supercapacitor application

Structural, Optical and Electrical Properties of Sol–Gel Prepared Mesoporous Co3O4/SiO2 Nanocomposites

Structures, optical and electrical properties of Co3O4/SiO2 nanocomposites are reported. Well crystalline Co3O4 nanoparticles embedded in an amorphous SiO2 matrix is formed, and confirmed by XRD and FTIR measurements upon calcination of gel precursors up to 800 °C. The obtained nanocomposites have high surface area ∼126–312 m2 g−1, and the Co3O4 particle size was ∼7–15 nm. The optical properties of the Co3O4/SiO2 nanocomposites indicate the presence of two energy gaps; both of them are smaller than those reported for the Co3O4 bulk phase. The first is varied from 1.32 to 1.44 eV and the second one is varied from 1.76 to 1.87 eV depending on the particles size. DC conductivity was measured in the temperatures range 300–673 K. The activation energy for DC conduction varies with particle size. The conduction mechanism was suggested to be through small polarons and variable range hopping mechanisms, at high and low temperatures respectivel