Removal of Pb 2+ , Cr 3+ and Hg 2+ ions from aqueous solutions using SiO 2 and amino-functionalized SiO 2 particles

Herein we present silica (SiO 2 ) and amino-functionalized SiO 2 particles (NH 2 @SiO 2 ) based on the Stöber method involving the reaction of hydrolysis and condensation of alkoxide precursors tetraethoxysilane (TEOS), 3- (trimethoxysilylpropyl) diethylenetriamine (DETA) and (3-aminopropyl) trimethoxysilane (APTMS) for specific and selective removal of heavy metal ions such as Lead (Pb 2+ ), Chromium (Cr 3+ ) and Mercury (Hg 2+ ). The prepared SiO 2 and NH 2 @SiO 2 particles were characterized by Fourier Infrared Spectroscopy (FTIR) spectroscopy, thermogravimetric analysis (TGA), specific surface area (BET), transmission electron microscopy (TEM), zeta potential (ζ) measurements and potential titration measurements. We studied the adsorption efficiency toward heavy metal ions (Pb 2+ , Cr 3+ and Hg 2+ ) in model salt solutions. The adsorption process was evaluated in terms of adsorption efficiency, adsorption capacity, adsorption isotherms, kinetics and thermodynamic parameters and desorption efficiency based on the result of the atomic absorption spectroscopy (AAS) measurements for Pb 2+ and Cr 3+ ions and inductively coupled plasma optical emission spectrometer (ICP-OES) measurements for Hg 2+ . The results showed the highest adsorption efficiency and capacity for heavy metal ions (Pb 2+ , Cr 3+ and Hg 2+ ) by NH 2 @SiO 2 using APTMS. Furthermore, the adsorption efficiency was 99.3 % for Pb 2+ , 98.4 % in the case of Cr 3+ ions and 88% for Hg 2+ . The adsorption process for Pb 2+ , Cr 3+ and Hg 2+ ions using non-functionalized SiO 2 and NH 2 @SiO 2 particles follows pseudo-second-order kinetics and is best described by the Langmuir adsorption model. The desorption results showed potential for reusing NH 2 @SiO 2 particles with more than 91.8 % desorbed Pb 2+ ions using 0.1 M HCl and 100% desorbed Hg 2+ ions using 1.5 M C 6 H 8 O 7 . Three alkoxide precursors (tetraethoxysilane (TEOS), 3-(trimethoxysilylpropyl), diethylenetriamine (DETA) and (3-aminopropyl) trimethoxysilane (APTMS)) were used in the one-pot synthesis of silica (SiO 2 ) and amino-functionalized SiO 2 (NH 2 @SiO 2 ) particles. The prepared adsorbent materials were characterized and used for adsorption tests and desorption toward heavy metals ions (Pb 2+ , Cr 3+ and Hg 2+ ). Adsorption efficiency, adsorption capacity, adsorption isotherms, kinetics and thermodynamic parameters were determined. Desorption efficiency was tested using 0.1 M HCl or 1.5 M C 6 H 8 O 7 .