Measuring and modeling metal ions adsorption on αAl2O3, SiO2 and TiO2 nanoparticles in the presence of organic ligands

Abstract

Nanoparticles (NPs) can be used to remove metal ions from aqueous solutions. However, removal efficiency of metal ions using NPs is influenced by organic ligands. The aims of this study were to investigate cadmium (Cd), nickel (Ni) and zinc (Zn) removal using αAl2O3, SiO2 and TiO2 NPs, to study the effect of organic ligands on metal adsorption and to simulate metal removal in mixed metal–organic systems using PHREEQC program. The experiments were performed in the pH range 2.0–8.0, solid–solution ratio 0.5–10 g L−1, contact time 10 min to 24 h and the citric and malic concentration from 0.2 to 2 mM. Adsorption of metal ions increased with increasing initial pH, adsorbent dosage and contact time. In the presence of citric acid adsorption of Cd on SiO2 NPs decreased noticeably with increasing concentration of citric acid from 0 to 2 mM while an increase in adsorption was observed when 0.2 mM malic acid added to SiO2 NPs. The adsorption of Ni in the presence of citric acid was inhibited, and low malic acid concentration (0.2 mM) promoted Ni adsorption on SiO2 and αAl2O3 NPs. These findings reveal that metal adsorption in the presence of organic ligands was not constant. A double-layer model and the NICA-DONNAN model were used to simulate the adsorption behavior. The results showed that monodentate complexes provide the best fit to the data and that the model could be used as a tool to assess adsorption of metal ions on NPs in the presence of organic ligands.