Effective heavy metal removal from aqueous systems by thiol functionalized magnetic mesoporous silica

A thiol-functionalized magnetic mesoporous silica material (called SH-mSi@Fe₃O₄), synthesized by a modified Stöber method, has been investigated as a convenient and effective adsorbent for heavy metal ions. Structural characterization by powder X-ray diffraction, N₂ adsorption-desorption isotherm, Fourier transform infrared spectroscopy and elemental analyses confirms the mesoporous structure and the organic moiety content of this adsorbent. The high saturation magnetization (38.4 emu/g) make it easier and faster to be separated from water under a moderate magnetic field. Adsorption kinetics was elucidated by pseudo-second-order kinetic equation and exhibited 3-stage intraparticle diffusion mode. Adsorption isotherms of Hg and Pb fitted well with Langmuir model, exhibiting high adsorption capacity of 260 and 91.5 mg of metal/g of adsorbent, respectively. The distribution coefficients of the tested metal ions between SH-mSi@Fe₃O₄ and different natural water sources (groundwater, lake water, tap water and river water) were above the level of 10⁵ mL/g. The material was very stable in different water matrices, even in strong acid and alkaline solutions. Metal-loaded SH-mSi@Fe₃O₄ was able to regenerate in acid solution under ultrasonication. This novel SH-mSi@Fe₃O₄ is suitable for repeated use in heavy metal removal from different water matrices.