Abstract:
The traditional St ber method was employed to prepare core-shell structured
γ-Fe
2O
3@SiO
2 particles by coating silica shell on the
γ-Fe
2O
3 nano-particles, which was made by microemulsion method. The obtained magnetic core-shell
γ-Fe
2O
3@SiO
2 microspheres with a thin silica layer about 15 nm in thickness were characterized by wide-angle X-ray diffraction (XRD), transmission electron microscopy (TEM) and vibrating sample magnetometer (VSM). The specific saturation magnetization, Ms of the core-shell
γ-Fe
2O
3@SiO
2, is 14.5 emu/g, less than the Ms of
γ-Fe
2O
3 at 47.2 emu/g. Using dithizone chromometer method at 551 nm, the adsorption isotherms of Hg
2+ on the surface of three kinds of nanometer materials including nano-silica,
γ-Fe
2O
3 and
γ-Fe
2O
3@SiO
2 were determined, the changes of adsorption isotherms of Hg
2+ are found that adsorption isotherms of Hg
2+ on nano-silica and
γ-Fe
2O
3 belong to type Ⅱ and type Ⅲ, respectively. However adsorption isotherms of Hg
2+ on
γ-Fe
2O
3@SiO
2 changes into type Ⅰ, because the formed Fe-O-Si bond on the surface of
γ-Fe
2O
3@SiO
2 may play a leading role in the action with Hg
2+. Adsorption isotherms of Hg
2+ are related to the dispersibility, surface silicon hydroxyl, ion vacancy and magnetic properties of the nanomaterials. After fitting of the experimental results by double adsorption isotherm method, the pseudo-first-order kinetic model and the pseudo-second-order kinetic model, the adsorption of Hg
2+ on nano-silica and
γ-Fe
2O
3@SiO
2 are found to be well fitted by Langmuir isotherm, while adsorption of Hg
2+ on
γ-Fe
2O
3 nano-particles is well fitted by Freundlich isotherm. The removal of Hg
2+ by these three kinds of nanometer materials is pH-dependent, and all well fitted by the pseudo-second-order kinetic model.