Chemical Engineering Journal 171 (2011) 1004–1011 Contents lists available at ScienceDirect Chemical Engineering Journal jo u r n al hom epage: www.elsevier.com/locate/cej Synthesis and characterization of thiol-functionalized silica nano hollow sphere as a novel adsorbent for removal of poisonous heavy metal ions from water: Kinetics, isotherms and error analysis Rahele Rostamian a,b , Mojgan Najafi c , Amir Abbas Rafati a,b,∗ a Department of Physical Chemistry, Faculty of Chemistry, Bu-Ali Sina University, P.O. Box 65174, Hamedan, Iran b Phytochemistry Research Center, Bu-Ali Sina University, Hamedan, Iran c Department of Materials Engineering, Hamedan University of Technology, Hamedan, Iran a r t i c l e i n f o Article history: Received 27 February 2011 Received in revised form 22 April 2011 Accepted 22 April 2011 Keywords: Silica nano hollow sphere Thiol functionalized Heavy metals Novel adsorbent Isotherm models Error analysis a b s t r a c t In this study, a strategy has been provided for the preparation of silica nano hollow spheres and its func- tionalization with the thiol group. Scanning electron microscopy, energy dispersive spectroscopy, X-ray diffraction, N 2 adsorption and Fourier transform infrared spectroscopy have been used to characterize the structure of nanoparticles before and after functionalization. This new synthesized nano hollow sphere was applied to remove heavy toxic metals such as Hg 2+ , Pb 2+ and Cd 2+ from water samples. The effect of initial concentration of heavy metals and interaction time were investigated in batch mode. In order to determine the best fit model for each system, non-linear regressions was carried out. For this, three error functions were applied to predict the optimum model. The goodness of fit of experimental data was observed with Sips and Redlich–Peterson isotherms. The pseudo-second order kinetic model rep- resented our experimental data very well. Adsorption data showed that the adsorption capacity of thiol functionalized silica nano hollow sphere (thiol-SNHS) for Hg 2+ is higher than Pb 2+ and Cd 2+ . © 2011 Elsevier B.V. All rights reserved. 1. Introduction Metals with specific gravity of about 5 g cm -3 or greater are gen- erally defined as heavy. Heavy metals such as lead, mercury and cadmium, often are found in industrial wastewater. The stricter environment regulation on the discharge of heavy metals makes it necessary to develop various technologies for their removal. Waste streams containing low to moderate levels of heavy metals are often encountered in metal plating industries and mining, chemical pharmaceutical, electroplating corrosion of galvanized piping, pig- ments and alloys, battery manufacture, fertilizer, electronic device manufactures and many others. Most of heavy metals are dangerous to health or to the environ- ment and are not biodegradable and tend to accumulate in living organisms, thus causing different disorders; therefore it is neces- sary to remove them from the polluted streams in order to meet increasingly stringent environmental quality standards. A wide range of methods including chemical precipitation, solvent extrac- tion, vacuum evaporation, membrane technologies, adsorption, ion ∗ Corresponding author at: Department of Physical Chemistry, Faculty of Chem- istry, Bu-Ali Sina University, P.O. Box 65174, Hamedan, Iran. Tel.: +98 811 828 2807; fax: +98 811 825 7407. E-mail addresses: rafati aa@yahoo.com, aa rafati@basu.ac.ir (A.A. Rafati). exchange and membrane separation have been used to treat such streams [1–3]. Traditional chemical precipitation is the most eco- nomic but is inefficient for dilute solution. Adsorption is one of the best available environmental control technologies for the heavy metal removal from water resources [2], especially using low-cost natural adsorbents such as agricultural wastes, clay materials, zeo- lite, biomass, and seafood processing wastes [4,5]. Improvement of adsorbent materials into nanoporous structures has shown to significantly enhance their performance in metal removal when compared to conventional adsorbents [6]. For analytical purposes, functionalized silica particles with organic functional groups are commonly used since the material silica provides many advantages such as inert, good adsorption and cation exchange capacity, easy to prepare with chemical compound and particular impregnate medium to create several modified silica surfaces, high mechanic and thermal stability [2,7,8]. For envi- ronmental applications, the development and introducing of new functionalized nanoporous materials is necessary, especially for the preparation of heavy metal adsorbents. Synthesis and characteri- zation of nano hollow structures have been extensively done in recent years. The nano hollow particles often exhibit substantially different properties such as low density, large specific surface area, stability, and surface permeability, from those of common parti- cles [9]. This is making them attractive from both scientific and technological viewpoints. 1385-8947/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.cej.2011.04.051