Studying the possibility of adsorption of heavy metal ions on nanoparticles

Abstract

We found both an increase and a decrease in the toxicity of some contaminants (Pb and Cd) when combined with the NP as a result of in vivo experiments conducted in Federal Research Centre of Nutrition and Biotechnology. One possible explanation for the differences in Pb and Cd accumulation levels when combined with NPs can be the difference in the adsorption capacity of NPs with respect to Pb²+ and Cd²+ ions. To verify this hypothesis, an in vitro experiment was carried out, which characterizes the possibility of adsorption of Pb²⁺ and Cd²+ ions on the NPs in a model system. We calculated Amax (maximum limiting adsorption corresponding to the saturation of the adsorption layer, pmol/mg), b (binding constant for instability (concentration of 50 % binding), pmol/mg) based on the results obtained during the work and constructed the equations of the adsorption isotherms in double inverse coordinates. As a result of studies, we determined that in the case of Pb²⁺ adsorption on TiO₂ NPs, SiO2 NPs and Al2O3 NPs, the equation of a single-layer equilibrium adsorption isotherm according to Langmuir is performed. The maximum adsorption of Pb²⁺ on the three types of NPs differs slightly. The Langmuir adsorption isotherm equation is not satisfied in the case of the adsorption of Cd²+ on the three NP types. Therefore, with respect to Cd, the constants b and Amax cannot be correctly defined. The reason for this, apparently, is that the process of binding of Cd²+ ions on the studied types of NPs does not obey the model of single-layer, completely reversible adsorption.