Selective adsorption of Pb2+ and Cu2+ on amino-modified attapulgite: Kinetic, thermal dynamic and DFT studies.

Amino-modified attapulgite (M-ATP) was prepared to remove Pb2+ and Cu2+ from the aqueous solution. Fourier transform infrared spectroscopy (FT-IR) spectrums and X-ray powder diffraction (XRD) patterns revealed that a new Si-O-Si bond formed after modification. The result indicates that the graft reaction of ATP occurred at Si-O (2 0 0) tetrahedron crystal face. No matter whether in a single or binary heavy metal ion system, the adsorption experiments displayed that the equilibrium adsorption capacity of M-ATP towards Pb2+ was much higher than Cu2+, which indicated M-ATP more readily adsorbs the Pb2+. The selective adsorption mechanism of Pb2+ and Cu2+ on modified attapulgite was studied by density functional theory (DFT). The Eads of Pb (- 2.01 eV) adsorbed on M-ATP is lower than Cu (- 1.79 eV) through the DFT calculation of adsorption energy (Eads), which indicate that the Pb2+ adsorbed on M-ATP is more stable than Cu2+. Both adsorption experiments and theoretical calculations revealed that due to the stability of Pb2+ adsorption on M-ATP, Pb2+ is more readily adsorbed by M-ATP, and it is difficult for Cu2+ to exchange Pb2+ from M-ATP.