Direct synthesis of efficient silica-based adsorbents carrying EDTA groups for the separation of Cu(II) and Ni(II) ions

Cations of copper and nickel belong to the category of heavy metals that coexist in wastewater from the mining and chemical industries and have similar structures. Selective extraction of their soluble forms is an urgent task in ecoanalytical chemistry. In this study, spherical organosilica particles with ethylenediaminetriacetic acid (EDTA) chelating groups were prepared via a one-pot approach for the purpose of Cu(II) and Ni(II) cation extraction from aqueous solutions. The isoelectric point for such samples is observed at pH = 2–3. It was found that the order of introduction of different components (Si(OEt)₄, EDTA–silane) into the reaction solution significantly affects the morphology, particle size (672–915 nm) and porosity (260–447 m² g^–1), without affecting the number of chelating groups (0.56–0.59 mmol g^–1) and the sorption capacity. The polysilsesquioxane samples acquired from bis-silane with ethylene bridge and EDTA–silane showed a similar number of EDTA groups (0.93–1.11 mmol g^–1) regardless of the silane ratio, with the possibility of controlling the specific surface area values (10–431 m² g^–1) and particle size (300–1200 nm) by varying the proportion of bridged silane. The EDTA-polysilsesquioxanes exhibited sorption capacity up to 1.72 mmol g^–1 for Cu(II) and 1.53 mmol g^–1 for Ni(II). These samples containing EDTA and silanol groups can be effectively used for the selective removal of copper(II) ions from the cationic mixture by varying the initial pH value of the solution.