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

• A novel bifunctional adsorbent modified with acids and organic amines was prepared.
• Large spatial hindrance groups were selected to avoid spontaneous recombination.
• The adsorbent can simultaneously remove Pb(II) and NO3− ions from Pb(NO3)2 solution.
• The absorbent exhibited high adsorption efficiency for cations and anions at pH 5.0.

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 N2 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 μmol/g for Pb(II) and 1120 μmol/g for NO3− 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.

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