Haihui Jiang

Low temperature hydrothermal synthesis of octahedral Fe3O4 microcrystals

Octahedral Fe3O4 crystals in the size range of 200–300 nm have been prepared with a high yield at a low temperature of 90 °C using a simple polyethylene glycol (PEG)-mediated hydrothermal approach. It is found that both PEG molecules and NaOH content are crucial for the formation of Fe3O4 octahedrons because of the selective adsorption of PEG molecules on the (1 1 1) planes of Fe3O4 at higher NaOH concentrations, delaying the crystal growth along the [1 1 1] axis. The formation mechanisms related to Fe3O4 nuclei, octahedral crystals, and their linear self-assembly structures are discussed. Magnetization measurements show that the Fe3O4 octahedrons have a relatively high magnetic saturation value of 85.5 emu g−1 and a coercive field of 118 Oe, which is ascribed to the high crystalline perfection and chain-like structures of the sample.

Preparation of core–shell Fe3O4/SiO2 microspheres as adsorbents for purification of DNA

Nearly monodisperse core–shell Fe3O4/SiO2 microspheres have been prepared via a glycol reduction method followed by a modified Stober process. The thickness of the silica shells can be tuned in the range 33–53u2009nm by varying the amount of tetraethyl silicate (TEOS) during syntheses. The magnetic composite microspheres were characterized with XRD, XPS, FTIR, TEM, ICP–OES and VSM, and further tested as adsorbents for purification of plasmid DNA from Escherichia coli DH5α cells. The magnetic purification of plasmid DNA leads to satisfying integrity, yield and purity in comparison with those isolated by the traditional phenol–chloroform extraction.

Thiol-functionalized Fe3O4/SiO2 microspheres with superparamagnetism and their adsorption properties for Au(III) ion separation

Thiol-functionalized Fe3O4/SiO2 microspheres (Fe3O4/SiO2-SH) with high saturation magnetization (69.3 emu g–1), superparamagnetism, and good dispersibility have been prepared by an ethylene glycol reduction method in combination with a modified Stöber method. The as-prepared composite magnetic spheres are characterized with fourier transform infrared spectroscopy (FT-IR), zeta potential, X-ray powder diffraction (XRD), transmission electron microscopy (TEM), and superconducting quantum interference magnetometer, and tested in separation of Au(III) ions from aqueous solutions. The data for Au(III) adsorption on Fe3O4/SiO2-SH are analyzed with the Langmuir, Freundlich, Temkin, and Dubinin–Radushkevich isotherm models, and the pseudo-first-order, pseudo-second-order, and intraparticle diffusion kinetics models. The adsorption behaviors of Au(III) on Fe3O4/SiO2-SH follow the Langmuir isotherm model, and the adsorption process conforms to the pseudo-second-order kinetic model. The maximum adsorption capacity of Au(III) on Fe3O4/SiO2-SH is 43.7 mg g–1. Acetate anions play an important role yet Cu(II) ions have little interference in the adsorption of Au(III) on the adsorbent. A satisfactory recovery percentage of 89.5% is acquired by using an eluent with 1 M thiourea and 5% HCl, although thiols have a high affinity to Au(III) ions based on the hard-soft acid-base (HSAB) theory by Pearson.