Thiol-functionalised mesoporous silica-coated magnetite nanoparticles for high efficiency removal and recovery of Hg from water

The preparation and testing of thiol-functionalised silica-coated magnetite nanoparticles (TF-SCMNPs) is described. The characteristics of these particles are assessed at different stages in the production process using X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier Transform Infrared Spectroscopy (FTIR), and a magnetometer. The particles were found to be almost spherical with a uniform mesoporous structure with a pore size of 2.1 nm. The particles were strongly responsive to an external magnetic field making separation from solution possible in less than 1 min. The adsorption characteristics of the particles were quantified in a series of isotherm experiments using Hg(II) solution concentrations between 40 and 1000 mu g l(-1) at adsorbent concentrations of 4 and 8 mg l(-1). The adsorption capacity was higher than for other commonly used adsorbents with 90% of Hg(II) removed during the first 5 min and equilibrium in less than 15 min. Both the Langmuir and Freundlich isotherm models were applied to the isotherm data and the maximum adsorption capacity was achieved when the ratio of adsorbent to adsorbate was low. Both temperature and pH had an effect on adsorption but when the TF-SCMNPs were used for removal of Hg(II) from tap water and bottled water, which contained other ions, there appeared to be no interference. Hg(II) could be successfully desorbed using thiourea in a 3 M HCl solution; this did not result in the destruction of the nanoparticles and they could subsequently be reused without loss of their activity in repetitive adsorption tests. (C) 2012 Elsevier Ltd. All rights reserved.