Removal of lead(II) from aqueous solution using modified palygorskite, contribution of inverse gas chromatography

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 E_ads of Pb (- 2.01 eV) adsorbed on M-ATP is lower than Cu (- 1.79 eV) through the DFT calculation of adsorption energy (E_ads), 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.

Using activated attapulgite as sorbent for solid-phase extraction of melamine in milk formula samples

In this study, a simple solid-phase extraction (SPE) approach by using activated attapulgite as sorbent was successfully developed for the determination of melamine in milk formula samples. Crucial factors impacting the extraction efficiency, including sample solvent, elution solvent, and sample loading volume, were investigated. Under the optimal extraction conditions, the sample loading volume was up to 200 mL and the adsorption capacity of the melamine gave rise to 1154 μg g(-1). Excellent linear calibration curves (r (2)  > 0.999) were achieved, and then the limit of detection (S/N = 3) and the limit of quantification (S/N = 10) were found to be 0.15 and 0.5 ng mL(-1), respectively. The recoveries of the melamine spiked in four milk formula samples at three concentration levels ranged from 83.5 to 111.0 % with relative standard deviations (RSDs) less than 10.2 %. Furthermore, RSDs of batch to batch (n = 4) of the acidified attapulgite used in this developed method were in the range of 2.3∼7.3 %. In comparison to the commercial Oasis MCX, the acidified attapulgite sorbent even outperformed (at least in terms of reproducibility) for melamine analysis in real food samples. Because of its simplicity, the newly developed SPE method based on acidified attapulgite nanoparticles should provide a promising tool for daily monitoring of doped melamine in milk formula or other complex matrices.