Lead (II) complexation with 3-mercaptopropyl-groups in the surface layer of silica nanoparticles: Sorption, kinetics and EXAFS/XANES study

In this work, mono-dispersed mercapto-functionalized silica (SiO2@SH) particles with a narrow particle size distribution of around (420 +/- 10) nm were prepared by the sol-gel method for the adsorption of aqueous dissolved lead (Pb-2+) ions from modeled wastewater. Transmission Electron Microscopy (TEM), in combination with Energy-Dispersive X-ray Spectroscopy (EDXS), was used to obtain information about the particle size and morphology of the prepared samples. Dispersive X-ray Spectroscopy (EDXS) indicated strong signals of Si and S, implying successful completion after the mercapto ( SH) functionalization of the silica (SiO2) surfaces. Fourier Transform Infrared Spectroscopy (FTIR) was used to determine the occurrences of Si-O-Si and SH vibrations within the samples and, thus, come to a conclusion about the formations of the mercapto-functionalized samples. Analysis was performed of Pb2+ adsorption with mercapto-groups ( SH) on the surface of the SiO2@SH particles. The results for Pb2+ adsorptions from the modeled wastewater showed affinity of around 55% and the obtained value of the maximum amount of adsorbed Pb2+ ions with the SiO2@SH samples was 10.82 mg/g under the conditions used during this study. The results of the adsorptions were fitted with the Langmuir and Freundlich isotherm models and the pseudo-first and pseudo -second kinetic models were evaluated. We employed Pb-L-3 edge Xray absorption spectroscopy techniques XANES (X-ray Absorption Near Edge Structure) and EXAFS (Extended X-ray Absorption Fine Structure) for probing the local environments of Pb within the tentative Pb-S complex after adsorptions of Pb2+ by the mercapto groups. The EXAFS/XANES analysis indicated complete Pb2+ complexation with two SH groups of the prepared SiO2@SH samples. (C)2016 Elsevier B.V. All rights reserved.