Preparation of Magnetic Ni0.5Zn0.5Fe2O4/ZnO Nanocomposites and Their Photocatalytic Performances for Methylene Blue in Aqueous Solution.

Magnetic Ni0.5Zn0.5Fe2O4/ZnO-R (NZFO/ZnO-R) nanocomposites are prepared via the rapid combustion-coprecipitation process, and they are characterized by the Fourier Transform Infrared Spectroscopy (FTIR), the X-ray Diffraction (XRD), the Scanning Electron Microscopy (SEM), the Energy Dispersive X-ray Detector (EDX), the Specific Surface Area (BET), the UV-vis Diffuse Reflection Spectroscopy (DRS), and the Vibrating Sample Magnetometer (VSM). The photocatalytic activity of NZFO/ZnO-R nanocomposites is assessed in ultraviolet light (365 nm) by decoloration of methylene blue (MB). The results show that the magnetic NZFO/ZnO-0.2 nanocomposites consist of particles and rods. The size of particles is 18 nm. The width and length of rods are 66 nm and 198 nm, respectively. NZFO/ZnO-0.5 nanocomposites have better photocatalytic performance than that of NZFO, ZnO and NZFO/ZnO-R (R = 0.2, 0.3, 0.4, 0.6, or 0.7) from the results. Through careful investigation of influencing parameters (the amount of catalysts, pH and concentration of MB solution), the degradation efficiency of MB is closely connected with the transparency of solution and surface charge of catalysts. The enhanced photocatalytic activity of NZFO/ZnO-0.5 nanocomposites can be ascribed to the matching band positions between ZnO and NZFO, which results in a low recombination between the photogenerated electron-hole pairs. The possible mechanism is proposed for the improved ultraviolet photocatalytic activity of NZFO/ZnO-0.5 nanocomposites.

Immobilization and Performance of Penicillin G Acylase on Magnetic Ni0.7Co0.3Fe2O4@SiO2-CHO Nanocomposites.

Magnetic Ni0.7Co0.3Fe2O4 nanoparticles that were prepared via the rapid combustion process were functionalized and modified to obtain magnetic Ni0.7Co0.3Fe2O4@SiO2-CHO nanocomposites, on which penicillin G acylase (PGA) was covalently immobilized. Selections of immobilization concentration and time of fixation were explored. Catalytic performance of immobilized PGA was characterized. The free PGA had greatest activity at pH 8.0 and 45oC while immobilized PGA's a ctivities peaked a t pH 7.5 and 45°C. Immobilized PGA had better thermal stability than free PGA at the range of 30-50°C for different time intervals. The activity of free PGA would be 0 and that of immobilized PGA still retained some activities at 60°C after 2 h. Vmax and Km of immobilized PGA were 1.55 mol/min and 0.15 mol/l, respectively. Free PGA's Vmax and Km separately were 0.74 mol/min and 0.028 mol/l. Immobilized PGA displayed more than 50% activity after 10 successive cycles. We concluded that immobilized PGA with magnetic Ni0.7Co0.3Fe2O4@SiO2-CHO nanocomposites could become a novel example for the immobilization of other amidohydrolases.

Covalent immobilization and characterization of penicillin G acylase on amino and GO functionalized magnetic Ni0.5Zn0.5Fe2O4@SiO2 nanocomposite prepared via a novel rapid-combustion process.

Magnetic Ni0.5Zn0.5Fe2O4@SiO2 nanocomposite was prepared via the rapid combustion process, and its surface was modified to obtain amino-functionalized magnetic Ni0.5Zn0.5Fe2O4@SiO2-NH2 nanocomposite. The modified nanocomposite was loaded on graphene oxide (GO), on which penicillin G acylase (PGA) was covalently immobilized. The structure for docking was visualized between PGA and penicillin G using the PyMol program, which revealed the configuration of the active site. Selections of immobilization conditions including immobilization concentration and time of fixation, were explored. The catalytic performance of the immobilized PGA was characterized. The immobilized and free PGA had the highest activity at pH 8.0 and 45 °C. Compared with the activity of the free PGA, the activity of the immobilized PGA was affected less by pH and temperature. The immobilized PGA exhibited the high-effective activity and good stability. Vmax and Km of immobilized PGA were 0.8123 mol·min-1 and 0.0399 mol·L-1, respectively. Free PGA's Vmax and Km were 0.6854 mol·min-1 and 0.0328 mol·L-1. Immobilized PGA remained >70% in relative activity after 9 successive cycles.

Effects of Solution Concentration on Magnetic NiFe2O4 Nanomaterials Prepared via the Rapid Combustion Process.

A rapid combustion process for the preparation of magnetic NiFe2O4 nanomaterials was introduced. The experimental results showed that the solution concentration of ferric nitrate was a key factor to control the structure and the properties of magnetic NiFe2O4 nanomaterials: the magnetic NiFe2O4 nanorods with the diameter of about 15 nm, the length of approximately 100 nm and the saturation magnetization of 18.4-25.3 emu/g could be formed when the solution concentration of ferric nitrate was equal or greater than 1.68 mol/L; the magnetic NiFe2O4 nanoparticles with the average particle sizes of 20-32 nm and the saturation magnetization of 10.0-31.8 emu/g could be formed when the solution concentration of ferric nitrate was lower than 1.12 mol/L.

Removal of Congo Red by Magnetic MnFe2O4 Nanosheets Prepared via a Facile Combustion Process.

Magnetic MnFe2O4 nanosheets were prepared via the facile combustion process, the morphology, chemical composition, microstructure and magnetic properties of them were investigated by SEM, EDX, XRD, TEM, SAED and VSM. The as-prepared magnetic MnFe2O4 nanosheets calcined at 400 °C for 2 h with absolute alcohol of 30 mL were characterized with average diameter of about 55 nm, the thickness of around 20 nm, the specific magnetization of 44.0 Am²/kg and the specific surface area of 49.6 m²/g. The removal behavior of Congo red (CR) from aqueous solutions onto MnFe2O4 nanosheets was investigated by UV spectroscopy at room temperature; the adsorption kinetics data related to the adsorption of CR from aqueous solutions were in good agreement with the pseudo-second-order kinetic model in the initial concentrations of 80-400 mg/L. By comparison of the Langmuir, Freundlich and Temkin models for adsorption isotherms of CR, the Temkin model (correlation coefficient R² = 0.998) could be used to evaluate the adsorption isotherm of CR onto the magnetic MnFe2O4 nanosheets at room temperature, which suggested that the adsorption of CR onto the magnetic MnFe2O4 nanosheets was a hybrid of monolayer and multilayer absorbing mechanism.

Optimization of Citrate-Gel Preparation Process for Magnetic Ni-Zn Ferrite Nanoparticles.

Magnetic Ni-Zn ferrite nanoparticles were prepared via the citrate-gel process, their microstructure and the properties were characterized by XRD, VSM, SEM, and TEM techniques. For smaller grain size and larger specific saturation magnetization, the preparation technology for magnetic Ni-Zn ferrite nanoparticles was optimized, and the optimization conditions followed as: the molar ratio of Ni, Zn and Fe was 1:1:4, citric acid was applied according to the mole ratio of 1:1 for citric acid and metal, the solvent of 100 mL was the mixed liquor of alcohol and water with volume ratio of 1:1, pH value was 1, reaction time was 24 h, the calcination temperature was 400 °C, and the heating rate was 3 °C/min. The average crystallite size of the as-prepared Ni0.5Zn0.5Fe2O4 nanoparticles calcined under the optimization conditions was around 14 nm, and the specific saturation magnetization was about 46 emu/g.