Adsorption of Hg2+ by thiol functionalized hollow mesoporous silica microspheres with magnetic cores

Abstract

Novel hollow mesoporous silica spheres with magnetic cores (HMSMCs) were successfully synthesized by using hybrid magnetic carbon (Fe₃O₄/C) spheres as templates. The microspheres were further functionalized with (3-mercaptopropyl)trimethoxysilane (MPTS) to produce thiol functionalized HMSMCs (SH-HMSMCs), and their ability to absorb traces of toxic Hg²⁺ was evaluated. The characterization results revealed that the hollow microspheres were 250–300 nm in diameter. The thickness of the shell was about 50 nm, in which contained an inner core of Fe₃O₄ crystallites with a size of about 10 nm. It was also found that the saturation magnetization of the sample was 62.5 emu g⁻¹ and the BET surface area was 421 m² g⁻¹. These magnetic hybrid silica microspheres with thiol functional groups were found to have a high affinity to Hg²⁺, and were able to reduce even a low concentration of Hg²⁺ (<1 mg L⁻¹) down to about 0.53 μg L⁻¹, which was less than the Hg²⁺ content in the drinking water standard. The super strong affinity towards Hg²⁺ was attributed to the synergistic effect of the thiol groups and the unique structure of the microspheres. Moreover, the microspheres as adsorbents could be easily separated by an external magnetic field, and the adsorbed Hg²⁺ on the adsorbents could be removed by using hydrochloric acid, thus the adsorbents are readily reusable.