| Monodisperse ferrite magnetic materials with spinel structure and smalldimensions (MFe2O4, M=Fe, Co, Ni, Zn, Mn, Mg, Cd) have attracted aconsiderable attention because of their outstanding magnetic and electricproperties. As a non-metallic magnetic materials which have typicalspinel structure and ferrimagnetic, Nickel-zinc ferrites Ni1-xZnxFe2O4(0<x <1) possess properties such as high saturation magnetization, highresistivity, chemical stability and low dielectric loss and have extensiveapplications in fields of magnetic fluids, high-frequency devices andmicrowave absorber. The multi-walled carbon nanotubes (MWCNTs)with large specific surface area and a unique one-dimensional tubularstructure exhibit high absorptivity and well stability and a series ofsuperior performance, and thus widely functioned as carrier materials ofthe preparation of nanocomposites. As we know, magnetic spinel ferriteparticles have a strong tendency to agglomerate during their formation.Magnetic ferrite nanoparticles coated MWCNTs could have avoidedagglomeration and improved their superior performances of optical,electrical, magnetic, microwave absorption and gas-sensing. Among thesefunctional nanocomposite, carbon-based magnetic nanocomposites havebecome an interesting area of researches. Considering the excellentproperties of MWCNTs and ferrite nanoparticles, their nanocompositeshave promising applications in the field of magnetic separationtechnology, target-drug delivery, magnetic resonance imaging, stealthmaterial, as well as other biology, military and medical areas.In this work, Ni1-xZnxFe2O4/MWCNT nanocomposites (x=0,0.2,0.4,0.5,0.6,0.8and1) with controllable composition and monodispersion were synthesized via microwave-assisted polyol process without addingsurfactant, which were characterized by XRD, SEM, TEM, HRTEM,SAED and EDS. The composition of ferrite nanoparticles and therelationship between the different composition and the magneticproperties of Ni1-xZnxFe2O4/MWCNTs nanocomposites have beendiscussed.The full text reads as follows:1. Controllable composition Ni1-xZnxFe2O4/MWCNT nanocomposites (x=0,0.2,0.4,0.5,0.6,0.8and1) had been prepared by microwave-assistedpolyol process without adding surfactant. The influence of experimentalconditions on loading had also been investigated. The experimentalresults show that: when the microwave time was8min, the microwavepower was changed from280W,365W to445W. The loading amountincreased with the increase of the microwave power, but nanoparticleswould local agglomeration when the power was445W. When themicrowave power was365W, the microwave time was changed from6min,8min to10min. When the reaction time was6min, thenanoparticles on the surface of carbontubes were distributed unevenly, theloading becomes dense and uniform with increasing the the microwavetime. Nanoparticles were monodisperse dispersion when microwave timewas8min. However, nanoparticles dispersed uniformly when thereaction time was10min. Optimum conditions for the preparation ofnanocomposite materials obtained by analyzing the impact factors duringthe reaction: the mixed nitrate and the acid-treatment MWCNTs withmolar ratio of3%was disperse in triethylene glycol by sonication. Themicrowave power was set to365W and microwave for10min.2. The samples synthesized under conditions of microwave8min andmicrowave power365W were characterized by XRD, SEM, TEM,HRTEM, SAED and EDS. The results showed that the nickel-zinc ferritenanoparticles with face-centered cubic (fcc) structure and average particlesize of about6nm were monodisperse coated on the surface of CNTs. The EDS results showed that the composition of ferrite nanoparticles canbe controlled through adjusting the atomic ratios of the nickel and zincsalts in the mixed nitrate solution.3. The magnetic properties of nanocomposites with different Zn contentswere measured by vibrating sample magnetometer (VSM). The resultsshowed: The magnetic properties of nanoparticles were closely relatedwith the composition of NiZn ferrite nanoparticles. The saturationmagnetization (Ms) of Ni1-xZnxFe2O4/MWCNT nanocomposites graduallyincreases when the x is less than0.5while decreases when the x is largerthan0.5. Ms reached maximum value when the x is0.5. The coercivity(Hc) of nanocomposites is low at room temperature, which exhibitscharacteristic of superparamagnetic. |
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