Preparation Of Fe₃O₄-MWCNTs Nanocomposites By Microwave Assisted Polyol Method And Their MRI Enhancement Properties

Magnetic Fe₃O₄ nanoparticles and MWCNTs decorated with Fe₃O₄ nanoparticles ontheir external surface have been intensely studied recently due to their exceptionalperformances and have been applied in many domains, such as MRI contrast agents,magnetic bio-separation, target drug delivery and hyperthermia. At present, manyapproaches have been used to synthesize Fe₃O₄ nanoparticles and Fe₃O₄-MWCNTsnanocomposites, mainly including coprecipitation, hydrothermal and polyol methods. TheFe₃O₄ nanoparticles fabricated by coprecipitation method have wide size distributions, poorcrystallization and small saturated magnetization; The surface of sample synthesized byhydrothermal method is hydrophobic and need complicated surface modification; Polyolmethod developed in these years could prepare particles with narrow size distribution, highcrystallization, hydrophilic surface and well controlled particle size, which could satisfydiversity demand for different applications. However, they almost need consume longreactive time, and their preparation efficiency is very low.On the basis of Yadong Yin's work, we have prepared Fe₃O₄ nanoparticles coated byPAA rapidly and efficiently through polyol method with irradiation of microwave, thesynthesis time was reduced from several hours to only 20min, and we proved thatmicrowave could improve the preparation efficiency. The products fabricated by thismethod are highly crystallized , superparamagnetic and well dispersed in water for a longtime. The influence of solvent property and the amount of alkali to the products wasstudied. It was found that the particle sizes were larger when the reductibility of the polyolsolvent was stronger and the amount of alkali was bigger, so we could complishcontrollable fabrication of Fe₃O₄ nanoparticles through the ways mentioned above.After we testified that microwave irradiation could improve the efficiency offabrication of Fe₃O₄ nanoparticles by polyol method, the efficient and excellentpurification and functionalization of MWCNTs was processed through oxidation with strong acid under irriadation of microwave. The impurity was removed and the productscould be well dispersed in water because of many functional groups on their outside wall.After functionalization, we fabricatied Fe₃O₄-MWCNTs nanocomposites through polyolmethod under the irradiation of microwave fastly. The processing time has been shortenedto 15 min through microwave induced reaction, and the magnetic MWCNTs withdepositon of uniform Fe₃O₄ nanoparticles with diameters of 3-5 nm. The as- synthesizedFe₃O₄-MWCNTs nanocomposites exhibit superparamagnetic property and can be stablydispersed in water for 2 months. The transverse relaxivity of the sample was 146.46 FemM-1S-1, which is bigger than a commercial contrast agent-Feridex(110 Fe mM-1S-1),andthe gray scale of MR imaging varied with the concentrations of the sample. All the resultsmentioned above could testified that the nanocomposites could potentially be applied as T2enhanced MRI contrast agents. Finnaly, the influence of reaction temperature to themorphology and performance of the products was studied, it was found that the size ofFe₃O₄ nanoparticles coated on the surface of MWCNTs was larger and the magnetizationof the sample was stronger when the reaction temperature was higher. As a result, we couldfabricate Fe₃O₄-MWCNTs nanocomposites with different morphologies and performance,which could satisfy diversity demand for applications in different domains.