Synthesis And Application Of Magnetite Nanoparticles And Composites

Magnetic nanoparticles are different from the bulk material with unique chemical and physical properties. Fe3O4 magnetic nanoparticles are the very promising and popular candidates because they are known to be biocompatible, displaying no hemolytic activity or genotoxicity with superparamagnetic properties, which have been widely used in biomedicine, catalysis, environment and so on. For many applications, the Fe3O4 nanoparticles are necessary to be chemically stable, well dispersed in liquid environment, biocompatible and uniform in size. This problem can be solved by modifing magnetic nanoparticles with the functional materials. We focus on the synthesis of Fe3O4 magnetic nanoparticles and their composite nanoparticles and their application in catalytic analysis, enzyme immobilization, biological imaging and environment protection. The major contents are summarized as follows:(1) Fe3O4 magnetic nanoparticles were prepared by the co-precipitation method and used as a mimetic peroxidase for the determination of hydrogen peroxide (H2O2) based on their catalytic effect on the oxidation of N, N-diethyl-p-phenylenediamine sulfate (DPD). Because of the peroxidase-like activating effect, Fe3O4 nanoparticles decreased the activation energy of the oxidation of DPD by H2O2 from 62.5 kJ mol-1 to 21.8 kJ mol-1 at room temperature, promoting greatly the oxidation of DPD by H2O2. Fe3O4 nanoparticles were found to be able to activate H2O2 and oxidize DPD to a colored product with a strong absorption maximum at 550 nm, which yielded a satisfactory linear correlation between the absorbance (A) and H2O2 concentration. The parameters for the determination of H2O2 were optimized by the investigations of the effects of reaction conditions on the absorbance of DPD+ produced by the catalytic oxidation of DPD. Under optimized conditions, the absorbance of the product responded linearly to H2O2 concentration in the range from 0.5 to 150×10-6 mol L-1 H2O2 with a detection limit as low as 2.5×10-7 mol L-1.The method was successfully applied to the determination of H2O2 in rainwater, honey and milk samples.(2) Sensitive fluorescent probes for the determination of hydrogen peroxide and glucose were developed by immobilizing enzyme horseradish peroxidase (HRP) on Fe3O4/SiO2 magnetic core-shell nanoparticles in the presence of glutaraldehyde. Compared with Fe3O4 magnetic nanoparticles and HRP, the immobilized enzyme catalyst has high activity and stability. The HRP immobilized nanoparticles were able to activate H2O2 to produce·OH radicals, which oxidized non-fluorescent 3-(4-hydroxyphenyl)propionic acid to a fluorescent dimmer with an emission maximum at 409 nm. Under optimized conditions, a linear calibration curve was obtained over the H2O2 concentrations ranging from 5.0×10-9 to 1.0×10-5 mol L-1, with a detection limit of 2.1×10-9 mol L-1. By simultaneously using glucose oxidase and HRP-immobilized Fe3O4/SiO2 nanoparticles, a sensitive and selective analytical method for the glucose detection was established. The fluorescence intensity of the product responded well linearly to glucose concentration in the range from 5.0×10-8 to 5.0×10-5 mol L-1 with a detection limit of 1.8×10-8 mol L-1. Besides its excellent catalytic activity, the immobilized enzyme could be easily and completely recovered by a magnetic separation, and the recovered HRP immobilized Fe3O4/SiO2 nanoparticles were able to be used repeatedly as catalysts without deactivation.(3) Magnetic Fe3O4/GO nanoparticles were synthesized by in situ precipitation method and used as a substrate for the immobilization of glucose oxidase. The Fe3O4/GO nanoparticles were used as an enzyme-like catalyst to activate H2O2 to produce·OH radicals by homolytic cleavage, which could be produced by the glucose oxidation with glucose oxidase-immobilized nanoparticles.·OH radicals will catalytically oxidize the substrate DPD to the radical cation DPD+ with a strong absorption maximum at 550 nm. We have developed a one-step method for determination of trace concentrations of glucose or H2O2 based on a bienzyme system. Under the optimized conditions, this method could give linear responses to glucose in a range of 5.0×10-7 to 6.0×10-4 mol L-1 with adetection limit of 2.0×10-7 mol L-1. And a linear calibration curve was obtained over the H2O2 concentrations ranging from 1.0×10-7 to 1.0×10-4 mol L-1 with a detection limit of 4.0×10-8 mol L-1.(4) Based on the Stober method, we have developed a simple and reproducible method to synthesize a novel class of Fe3O4/SiO2/dye/SiO2 composite nanoparticles. The inner silica layer is introduced to enhance the adherence of the dye-doped silica layer to the surface of magnetic Fe3O4 particles, and the outer dye-doped silica layer enables the nanoparticles with excellent fluorescent properties. The thickness of the outer shell of silica could be tuned by changing the concentration of the silicon precursor tetraethyl orthosilicate during the synthesis. These multifunctional nanoparticles were found to be highly luminescent, photostable and superparamagnetic. The luminescence intensity of the nanoparticles was increased as the dye concentration was increased in the preparation process. The color of the luminescence was successfully tuned by incorporating different dyes into the nanoparticles. The measurements of the emission spectra indicated that relative to the dye molecules dissolved in ethanol, the emission of the dye-doped nanoparticles exhibited either a red shift or a blue shift owing to the aggregation of dye molecules in the silica matrix or destroyed the coplanar.(5) A simple ultrasound-assisted co-precipitation method in combination with a calcination treatment was developed to prepare magnetic Mg-Al layered double hydroxides composite with layered structure as an adsorbent material to remove fluoride ions from aqueous solutions. The application of ultrasound in the preparation process promoted the formation of the hydrotalcite-like phase and drastically shortened the time being required for preparation of the crystalline composite. It was found that the ultrasound irradiation assistance decreased the size of the composite particles and increased the specific surface area, being favorable to the improvement of the adsorption capacity. The composite prepared under the ultrasound irradiation exhibited fairly high maximum adsorption capacity of fluoride (47.7 mg g-1). Equilibrium adsorption and kinetic data were fitted well with the Langmuir isotherm model and the pseudo-first-order kinetic model. In addition, the magnetic composite can be effectively and simply separated by using an external magnetic field, and then regenerated by desorption and calcination.