Preparation And Application Of Zn, Mn Ferrite And Carbon Nanotube Composites

Zinc ferrite (ZnFe2O4) is one of important member in the soft magnetic materials. ZnFe2O4 shows the properties of superparamagnetism, gas sensitivity, high conductivity, which can be used as microwave absorbing materials, semiconductor, catalyst, and battery materials. Magnetic nanomaterials especially the ferrites with moderate saturation magnetization and small coercivity have been widely used in environmental purification applications as adsorbents.In this paper, the nanosized ZnFe2O4 with normal spinel structure was prapared by a coprecipitation method. The sample was characterized by using a number of techniques, which demonstrated that the as-prepared ZnFe2O4 is normal spinel structure. The magnetic and thermadynamic properties of the ZnFe2O4 nanomaterials were studied.Magnetic nanomaterials were synthetised by a simple and feasible method, and magnetic composites (multi-walled carbon nanotubes coated by the magnetic materials) were prepared at the same time. These composite were used as adsorbents to adsorb the dye methyl orange and Congo red from water.The main works are listed as the following:1. Normal spinel zinc ferrite (ZnFe2O4) nanoparticles (NPs) with zero net magnetization were synthesized by a facile coprecipitation method in which two kinds of organic alkali, 1-amino-2-propanol (MIPA) and bis(2-hydroxypropyl)-amine (DIPA) were used. The diameters of the ZnFe2O4 NPs were determined to be about 7 and 9 nm for samples prepared with MIPA and DIPA, respectively, and the normal spinel structure was confirmed by the magnetic property measurement at room temperature and the temperature dependence of the DC magnetization. These results are different from those reported in the literature where ZnFe2O4 NPs show a non-zero net magnetization. The heat capacity of the ZnFe2O4 NPs synthesized using DIPA was measured using a Physical Property Measurement System (PPMS) in the temperature range from 2 to 300 K, and the thermodynamic functions were calculated based on the curve fitting of the experimental heat capacity data. The heat capacity of the ZnFe2O4 NPs was compared with that of a nanosized (Zn0.795Fe0.205)[Zn0.205Fe1.795]O4 material studied in the literature, indicating that our Debye temperature is more comparable with that of the bulk sample reported by Westrum et al..2. Multi-walled carbon nanotubes (MWCNTs) coated by magnetic ZnLa0.02Fe1.98O4 clusters were synthesized via one-pot solvothermal method. The MWCNTs were treated by HNO3 solution, which resulted in the formation of carboxyl groups and enhanced the dispersion and suspension in aqueous solution. The content of the MWCNTs contained in the composite was determined to be about 34.1 wt% based on TG analysis. The pore size, surface area, and pore volume for the ZnLa0.02Fe1.98O4/MWCNTs were obtained as about 2.5 nm,59 m2/g, and 0.27cm3/g, respectively. The saturation magnetization (Ms) of the composite reached to 61 emug/g, which is convenient to separate from an aqueous solution by an external magnetic field. The composite can be used as an adsorbent to adsorb methyl orange (MO) from the solution, which the maximum adsorption capacity is about 81 mg/g, and it takes shorter time to the adsorption equilibrium (30-40 min) than those reported. The Langmuir model was suitable to fit the experimental results, which indicated the single layer adsorption. Kinetic analyses were used pseudo-first and second-order models. The results showed that the adsorption kinetics was more accurately described by pseudo-second-order model. The adsorption progress was exothermic and spontaneous based on the thermodynamic functions.3. Manganese ferrite (MnFe2O4) nanoparticles (NPs) were synthesized by a facile coprecipitation method in which organic alkali, 1-amino-2-propanol (MIPA), was used. Different sizes and magnetizations of the MnFe2O4 nanoparticles were synthesized by addition of cetyltrimethylammonium bromide (CTAB). When the concentration of CTAB is 0.5 mM, the MnFe2O4 showed maximum magnetization (Ms=51 emu/g) and the Ms was higher than those reported. The MnFe2O4 coated the different amounts of the MWCNTs were synthesized by the same method. The contents of the MWCNTs contained in the composites were determined to be about 9.40 wt%,19.84 wt%,39.83 wt% and 60.76 wt% based on TG analysis, respectively. The pore size, surface area, and pore volume were increased with increasing content of MWCNTs and these were obtained as about 3.0 nm,116 m2/g, and 0.51cm3/g, respectively, for the composite (60.76 wt% MWCNTs). The composite were used as an adsorbent to adsorb congo red (CR) from the solution, which the maximum adsorption capacity is about 90 mg/g, which it was higher than those reported. The Langmuir model was suitable to fit the experimental results, which indicated the single layer adsorption. The results showed that the adsorption kinetics was more accurately described by pseudo-second-order model. The adsorption progress was exothermic and spontaneous based on the thermodynamic functions.