Formation of necklace-shaped haematite nanoconstructs through polyethylene glycol sacrificial template technique

Abstract

Haematite nanoparticles have been synthesised on polyethylene glycol (PEG) template, through a two-step method consisting of oriented attachment followed by growth. The process involves the binding of Fe2+ centres to PEG, followed by a high temperature calcination reaction. During the calcination process, the template is sacrificed and Fe2+ is converted to α-Fe2O3. Infrared spectroscopy and thermogravimetric analysis indicate that the template leaves behind a carbonaceous residue over the haematite surface, which prevents further aggregation of the nanoparticles even after the removal of the template. PEG helps in connecting the crystal flocs through a bridging mechanism. The residual magnetic moment, particle size, shape and ionic strength of the synthesised haematite nanoparticles promote the formation of necklace-shaped structures. Directional growth of haematite nanoparticles brought about by PEG results in an increase in coercivity and near-zero remnant magnetisation at zero field strength. The magnetisation curves do not attain saturation even at a field strength of 7 kOe, indicating a superparamagnetic behaviour. Such nanoparticles with a carbonaceous coat, a necklace structure and superparamagnetic behaviour can find extensive use in targeted drug delivery.