Adsorption performance of APTMS-DTPA/PVDF chelating membrane toward Ni(II) with the presence of Ca(II), NH4+, lactic acid, and citric acid

Abstract

The 3-aminopropyltrimethoxysilane-diethylenetriaminepentaacetic acid/polyvinylidene fluoride (APTMS-DTPA/PVDF) chelating membrane was prepared to remove Ni(II) from the solutions. The adsorption performance of the membrane toward Ni(II) was investigated by the adsorption experiments and density functional theory (DFT) calculations, considering the existence of Ca(II), NH4+, lactic acid, and citric acid. Ca(II) tended to form more stable complex with the APTMS-DTPA ligand of the chelating membrane than NH4+. Citric acid showed a larger interference on Ni(II) uptake than lactic acid. Lagergren second-order equation and Langmuir model were competent for descriptions of the adsorption kinetics and the isotherms, respectively. The negative ΔG° and ΔH° indicated the spontaneous and exothermic nature of Ni(II) adsorption. The results of DFT calculations were consistent with the experimental data. The complexing sequences of the metal ions with the APTMS-DTPA ligand were in the order of NH4+ < Ca(II) < Ni(II). The stabilities of the Ni(II)–organic complexes followed the order of Ni(II)–lactic acid < Ni(II)–citric acid < Ni(II)–(APTMS-DTPA). Therefore, the complexation between Ni(II) and APTMS-DTPA ligand of the membrane was prominent.