L-lysine coated iron oxide nanoparticles: Synthesis, structural and conductivity characterization

Abstract

l-lysine coated iron oxide (LCIO) nanoparticles were synthesized by a co-precipitation method in the presence of amino acid. XRD analysis confirmed the presence of cubic magnetite phase with an average crystallite size of 8 ± 4 nm. Particle size estimated from TEM, by log-normal fitting, is ∼114 nm. The difference between the crystallite size from XRD and particle size from TEM indicates polycrystalline nature of synthesized particles. FT-IR show that the binding of l-lysine on the surface of iron oxide through carboxyl groups is via unidentate linkage. The presence of l-lysine on iron oxide is also confirmed by zeta potential measurements on LCIO nanoparticles, revealing a partial coverage of iron oxide with l-lysine. In order to obtain chemically stable, well-dispersed and uniform sized nanoparticles, amino acids are suitable because they play a very important role in the body. Conductivity measurements were performed to investigate the influence of the coating on the conduction characteristics of iron oxide and results show the existence of a hopping conduction mechanism. Magnetic transition is observed at ∼70 °C for uncoated iron oxide and LCIO samples. Frequency (1 Hz to 3 MHz) and temperature (290–420 K) dependant AC conductivity measurements have resulted in AC activation energies between 0.048 and 0.041 eV for uncoated and 0.050–0.044 eV for LCIO nanoparticles. Temperature-dependant DC resistivity measurements of iron oxide and LCIO at high temperatures resulted in the DC activation energies of 0.22 and 0.43 eV respectively. The higher activation energy value for LCIO is the result of coating by insulating l-lysine layer.