Preparation and Characterization of Alkylcarboxylate-Stabilized-Magnesium Nanoparticles

Abstract

Long chain carboxylate shell stabilized magnesium (Mg) nanoparticles (NPs) were synthesized. In the core-shell type NPs the cores are Mg metal and the shells are long chain carboxylates. Synthesis of magnesium nanoparticles (Mg-NPs) involve: i) preparation of water soluble Na-salts of long chain fatty acids in alcoholic medium followed by ii) temperature controlled reaction with magnesium salts in aqueous medium in presence of suitable surfactant, poly vinyl pyrrolidone (PVP). The synthesis procedure used in this work was originally applied for the fabrication of long chain carboxylate capped magnesium nanoparticles. Structural and geometrical probabilities of prepared NPs were proposed on the basis of evidences from elemental analysis, optical and spectral studies. The compositions of the NPs were determined by elemental analysis. The experimental and calculated data for carbon (C), hydrogen (H), oxygen (0) and metal were compared. The presence and percentages of C, H and 0 revealed the presence of alkyl carboxylates and is proposed that these alkyl carboxylates act as protected shefls to the Mg-N Ps. From the titration of magnesium laurate, magnesium myristate, magnesium palmitate and magnesium stearate 7.83%, 7.02%, 6.54% and 5.93% Mg were found respectively. These values show that all the substances contain relatively higher amount of Mg than those of the molar ratio. These results exposed metallic Mg in the samples. It is proposed that this metallic Mg may be positioned at the core of the NPs. Melting point (MP) data also provide auspicious evidence about the formation of Mg-NPs. The Fourier Transform Infrared Spectroscopy (FTIR) spectra provide information about the presence of moisture or adhering free water and/or crystalline water and alkyl carboxylates in the NPs. Broad peak at —3040 to 3520 cm 1 appears due to 0-H stretching vibrations of hydroxyl (—OH) group. This may be due to the presence of moisture absorbed by the sample or water of crystallization. Two characteristic peaks at —1510 to 1600 cm 1 and at —1400 to 1510 cm1 were found and these may be due to C=O stretching and C-O stretching of carboxylates respectively. V Transmission Electron Microscopy (TEM) photographs showed the particles have the dimensions over a range of 25-90 nm. At higher magnifications, the NPs were recognized as spherical or oval in shape in all cases. The NPs are hygroscopic in nature as they absorbed 8.54-12.22% moisture. The moistures and/or crystallized water are also evidenced by the Differential Thermal Analysis (DTA) and Thermogravimetric Analysis (TGA) of the respective NPs. Both DTA and TGA demonstrated the presence of alkyl carboxylates or organic part in the NPs. The loss of organic parts at higher temperatures also corresponds to the decomposition of the NPs at higher temperature in a normal furnace as investigated by FTIR analysis.