Abstract:

A simple solvothermal method was used to control the size and morphology of Fe₃O₄ nanoparticles by changing the dosage of polyethylene glycol （PEG）, the molecular weight of PEG, and the volume fraction of diethylene glycol （DEG） in the reaction system. The prepared Fe₃O₄ nanoparticles were characterized by SEM, TEM, XRD and VSM. The results show that the walnut shaped Fe₃O₄ nanospheres are composed of small grains, as the dosage of PEG-4000 increasing from 0.1 g to 1.5 g, the size of the Fe₃O₄ grain tends to decrease. Appropriately increasing the chain length of PEG, with the molecular weight ranging from 200 to 4 000, is beneficial for promoting the growth of Fe₃O₄ nanocrystals. However, further increasing the length of the chain, at a molecular weight of 20 000, results in smaller Fe₃O₄ nanocrystals and microspheres. Changing the volume fraction of DEG can achieve the shapes transformation of Fe₃O₄ nanoparticles, from rough walnut like large microspheres to smooth small microspheres, and then to regular rectangular crystals. Based on the adsorption, grafting, and steric hindrance effects of PEG and DEG, possible mechanisms for the formation of different morphology and size of nanostructures have been proposed, providing a useful reference for the controllable preparation of Fe₃O₄ nanoparticles. The saturation magnetization of the prepared Fe₃O₄ nanoparticles is about 80 emu/g, showing superparamagnetism.

Key words: Fe₃O₄ nanoparticles, polyethylene glycol （PEG）, diethylene glycol （DEG）