Natalia Nedelko

Structural and magnetic properties of iron nanowires and iron nanoparticles fabricated through a reduction reaction

Summary The main goal of this work is to study the structural and magnetic properties of iron nanowires and iron nanoparticles, which have been fabricated in almost the same processes. The only difference in the synthesis is an application of an external magnetic field in order to form the iron nanowires. Both nanomaterials have been examined by means of transmission electron microscopy, energy dispersive X-ray spectrometry, X-ray diffractometry and Mössbauer spectrometry to determine their structures. Structural investigations confirm that obtained iron nanowires as well as nanoparticles reveal core–shell structures and they are composed of crystalline iron cores that are covered by amorphous or highly defected phases of iron and iron oxides. Magnetic properties have been measured using a vibrating sample magnetometer. The obtained values of coercivity, remanent magnetization, saturation magnetization as well as Curie temperature differ for both studied nanostructures. Higher values of magnetizations are observed for iron nanowires. At the same time, coercivity and Curie temperature are higher for iron nanoparticles.

Electron paramagnetic resonance studies of human liver tissues

Lyophilized samples of human liver have been investigated by means of electron paramagnetic resonance spectroscopy and conventional magnetic methods over the temperature range of 4–300 K. The experimental results exhibit two main magnetic contributions. One of them can be attributed to Fe2+ ions of hemoglobin and the second one, originating from the Fe3+ ions of ferritin grains, shows a transition into the superparamagnetic state atT>20 K.

Adsorption of reactive red dye (RR-120) on nanoadsorbent O-carboxymethylchitosan/γ-Fe2O3: kinetic, equilibrium and factorial design studies

In this study, a novel magnetically separable nanoadsorbent, consisting of a γ-Fe2O3 and O-carboxymethylchitosan (O-CM), was synthesized in a three-step procedure. The structure of O-CM was characterized by Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TG), vibrating-sample magnetometer (VSM), and transmission electron microscope (SEM). Adsorption features of the magnetic nanoadsorbent were evaluated using the dye reactive red 120 (RR120). The isotherms, kinetics, and thermodynamics of the dye adsorption were studied in various experimental conditions, i.e., initial dye concentration, contact time, solution pH and temperature. The effects of pH, initial dye concentration and temperature were investigated by the 33 Box–Behnken factorial experimental design method, and the statistical approach analysis of variance was used to optimize the operating conditions. The results obtained fitted well to the Langmuir–Freundlich model, and the kinetics of the adsorption process were found to follow the pseudo-second-order kinetics. The thermodynamic study was conducted by calculating a number of thermodynamic parameters, such as the standard changes in ΔG°, ΔH° and ΔS°. The high sensitivity of the magnetic nanoadsorbent to the external magnetic field culminates in its efficient and easy separation and good adsorption ability, demonstrating great potential in the application of water treatment.

Synthesis of Ag@Fe2O3 nanocomposite based on O-carboxymethylchitosan with antimicrobial activity

In this paper, nano-hybrid particles of Ag@Fe2O3 based on O-carboxymethylchitosan were successfully synthesized using different reducing agents (NaBH4, sucrose) and without reducing agent. The smallest silver nanoparticles were those prepared without reducing agent (∼5±3nm). The average size of silver particles prepared with NaBH4 is around 5-15nm, and for samples prepared with sucrose, the average particle size is 10-25nm. The magnetization curves are roughly reversible, indicating that γ-Fe2O3 nanoparticles transit to a superparamagnetic state. Nanocomposites subjected to antimicrobial tests showed great antimicrobial activity against gram-positive (Staphylococcus aureus) and gram-negative (Escherichia coli) bacteria, and good activity against the yeast Candida albicans and resistant strains of Staphylococcus aureus. The antibacterial behavior as a function of time was investigated in microbial growth kinetics, and the best nanocomposite was the one without reducing agent, which completely inhibited microbial growth for 48h.