Silicate nanoparticles(nSiO2) are a kind of widely used engineering material. In order to improve the Cd2+ adsorption ability, the EDTA-modified nSiO2 nanoparticles were prepared by grafting method and characterized by TEM, N2 adsorption-desorption, FTIR, and TGA. The effects of solution pH, contact time, temperature and ionic strength were examined. The adsorption mechanism was further investigated by XPS. The results showed that the EDTA-nSiO2 nanoparticles possessed excellent stability, and were successfully prepared. Cd2+ adsorption was mainly controlled by solution pH. The raw nSiO2 had limited Cd2+ adsorption ability, while the EDTA-modified nSiO2 particles had significantly improved adsorption performance. At high pH, the Cd2+ adsorption rate increased and kept balance above pH 4.0. The Cd2+ adsorption was an endothermic spontaneous process which could be finished within 1 h. Langmuir model could be used to describe the adsorption isotherm. The temperature ranged from 293-313 K during the process, while the maximum adsorption was observed at higher temperature. Higher ionic strength could inhibit the Cd2+ adsorption. The Cd2+ adsorption decreased from 0.433 to 0.294 mmol·g-1, when NaCl concentration varied from 0 to 100 mmol·L-1. The desorption of Cd2+ from the EDTA-nSiO2 nanoparticles was carried out with distilled water, 0.1 mol·L-1 NaCl and 0.1 mol·L-1 HCl. The maximum Cd2+ desorption of 94.36% was obtained at 0.1 mol·L-1 HCl. Based on the results of thermodynamics, pH, ionic strength, and XPS analysis, it could be concluded that Cd2+ adsorption was a multiple process dominated by chemical chelating reaction, physical adsorption and ion exchange. This study indicated that the EDTA-nSiO2 is an effective engineering nanomaterial that could be used in Cd2+ adsorption.
Keywords: Cd2+; EDTA; adsorption; modification; nSiO2 nanoparticle.