Synthesis and characterization of bifunctional mesoporous silica adsorbent for simultaneous removal of lead and nitrate ions

A novel acid-base bifunctional adsorbent was synthesized using a three-stage process involving (i) synthesis of MCM-41 mesoporous silica (MS) carrier, (ii) acidic modification of the carrier by aluminum isopropoxide dosing (Al-MS), and (iii) basic modification by amino groups post-grafting (Al-MS2). Large spatial hindrance amino groups were selected for the basic modification step to avoid spontaneous recombination and neutralization reactions between the two antagonist functional groups. X-ray diffraction, transmission electron microscopy, NH3-based temperature-programmed desorption, Fourier transform infrared spectroscopy, and N-2 adsorption-desorption techniques were used to characterize the samples obtained at each step. Then, the simultaneous adsorption capacities of lead (Pb(II)) and nitrate (NO3-) ions were investigated and compared. The results revealed that Al-MS2 had good adsorption efficiency for Pb(II) and NO3-, achieving maximum adsorption capacities of 712 mu mol/g for Pb(II) and 1120 mu mol/g for NO at pH 5.0. The proposed mechanism for the simultaneous removal of Pb(II) and NO3- by the adsorbents were also discussed. The results showed that Al-MS2 was successfully modified with two antagonist adsorption groups, thus providing a new strategy for designing multifunctional adsorbents for the simultaneous removal of toxic metal cations and anions from wastewater. (C) 2015 Elsevier B.V. All rights reserved.