纳米SiO2及磁性γ-Fe2O3@SiO2对Hg2+的吸附及去除

Adsorption and Removal of Hg^(2+) by Nano-Silica and Magneticγ-Fe_2O_3@SiO_2

首先用微乳法合成了纳米SiO_2和纳米γ-Fe_2O_3,然后利用传统的St9ber方法合成出核壳结构的γ-Fe_2O_3@SiO_2,并利用X射线衍射仪(XRD)、透射电子显微镜(TEM)、振动样品磁强计(VSM)对其进行了表征。采用双硫腙光度法在551nm处,测定了Hg^(2+)在纳米SiO_2、纳米γ-Fe_2O_3和γ-Fe_2O_3@SiO_2表面的吸附等温线,发现三者的吸附等温线类型依次为Ⅱ、Ⅲ和Ⅰ型,等温线类型与纳米材料的分散性、表面硅羟基、离子空位以及磁性有关。利用双吸附等温线法、准一级和准二级动力学模型对吸附数据进行拟合得出:纳米SiO_2和γ-Fe_2O_3@SiO_2对Hg^(2+)的吸附符合Langmuir等温式,而纳米γ-Fe_2O_3对Hg^(2+)的吸附符合Freundlich等温式。三者对Hg^(2+)的去除率均与pH有关,均属于准二级动力学模型。

The traditional St ber method was employed to prepare core-shell structuredγ-Fe 2O 3@SiO 2 particles by coating silica shell on theγ-Fe 2O 3 nano-particles,which was made by microemulsion method.The obtained magnetic core-shellγ-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-shellγ-Fe 2O 3@SiO 2,is 14.5 emu/g,less than the Ms ofγ-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 andγ-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 andγ-Fe 2O 3 belong to typeⅡand typeⅢ,respectively.However adsorption isotherms of Hg 2+onγ-Fe 2O 3@SiO 2 changes into typeⅠ,because the formed Fe-O-Si bond on the surface ofγ-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 andγ-Fe 2O 3@SiO 2 are found to be well fitted by Langmuir isotherm,while adsorption of Hg 2+onγ-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.