Preparation and characterization of organofunctionalized bentonite clay bearing aminophosphonic groups in heavy metal uptake

Bentonite (Bnt) with covalently immobilized N-propylaminodi(methylenephosphonic) groups (Bnt-ADPA) was obtained through a two-step synthesis including aminosilanization and phosphorylation of resulting aminobentonite through Moedritzer-Irani reaction. The grafting of an aminosilane layer in the interplanar space of the bentonite was investigated by XRD, and the presence of N and P-containing groups was confirmed by FTIR,P- 31 and Si-29 MAS NMR. The immobilization of the organic functional groups increased the interplanar distance in bentonite matrix at 52% that essentially improved filtration properties compared to raw bentonite. The number of surface acid groups was evaluated to 0.8 mmol g(-1). The obtained adsorbent showed high affinity for heavy metal ions according to pH(1/2) sequence Fe (III) (2.3) < Pb (II) (4.6) < Zn (II) (5.3) Cu (II) (5.8) < Cd (II) (6.7). The adsorption/desorption process on Bnt-ADPA is completely reversible and allows multiple uses of the adsorbent for water purification. The Bnt-ADPA was tested for the purification of water samples from the Lybid River (Kyiv, Ukraine). It was demonstrated that filtration of water samples through Bnt-ADPA filter resulted in a complete ( > 97%) elimination of Pb (II) and a significant (59-65%) decrease of the amount of Cu(II) and Zn(II). According to the X-ray fluorescence analysis of the filter, Bnt-ADPA also retained Ca (II), Mn (II) and Sr (II) ions.