Thermodynamics And Electrochemical Characterization Of Core-shell Type Gold-coated Superparamagnetic Iron Oxide Nanoparticles

¹Institute of Advanced Technology, Universiti Putra, Serdang, 43300 Selangor, Malaysia

²Department of Environmental Toxicology, Southern University and A&M College, Baton Rouge, LA 70813, USA

³Department of Chemistry, Uka Tarsadia University, Maliba Campus, Gopal Vidyanagar, Bardoli 394350, India 

Adv. Mater. Lett., 2014, 5 (6), pp 315-324

DOI: 10.5185/amlett.2014.amwc.1030

Publication Date (Web): Mar 23, 2014

Copyright © IAAM-VBRI Press

E-mail: tanvirarfin@ymail.com

Abstract

In continuation to our previous work, the superparamagnetic Fe₃O₄@Au core-shell type nanoparticles (NPs) were further characterized by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), electrical conductivity, impedance and cyclic voltammetry measurements. From the analysis of DSC and TGA results with our Fe₃O₄@Au NPs of about 6.25 ± 0.6 nm size, we observed a clear endothermic peak at 310°C due to the decomposition of the oleic acid/oleylamine surface ligands and the particles found to contain more than 80% of the metallic content from the mixed compositions of gold and iron oxide were observed. Because of the conduction through the Fe₃O₄@Au grain, the impedance profile of the pellet exhibited a well-resolved semi-circle and an inclined spike in a far low-frequency region. The electrical conductivity of the Fe₃O₄@Au material found to be increased with an increase of temperature. The standard Gibbs free energy (ΔG) of the reaction provided a criterion for spontaneous changes in the equilibrium of the material. From the analysis of the results of ΔG, it appears that at 25°C temperature, ΔS found to be negative. The calculated enthalpy, ΔH = -0.635 kJ/mol, at the corresponding entropy of ΔS = -0.132 kJ/mol. Finally, the activation energy in temperature range of 25-200°C for the Fe₃O₄@Au core-shell material was calculated using Line fitting and the surface characterization by using cyclic voltammetry. The electrochemical redox property of the Fe₃O₄@Au shows quasi-reversible wave corresponding to Au³⁺/Au²⁺.In addition, the electrochemical parameters for Fe₃O₄@Au NPs of E^c_p, E^a_p, E^o_1/2 and were also obtained. Since the Fe₃O₄@Au material has low activation energy at low temperature range which makes it a good candidate as an ion conductor and even has the potential uses in many solid state devices and also in the future prospects of electrochemistry applications.

Keywords

Fe₃O₄@Au, gold nanoshell, Core-shell structure, electrical conductivity, impedance measurements, Gibbs free energy, activation energy