Facile strategies for synthesis of functionalized mesoporous silicas for the removal of rare-earth elements and heavy metals from aqueous systems

A series of adsorbents of SBA-15-type with ethylenediaminetriacetic (EDTA), phosphonic, and ammonium groups as ligands were synthesized using the template method based on sodium metasilicate as the major starting reagent. The detailed characterizations using SEM, TEM, XRD, and N-2 sorption/desorption measurements of synthesized sorbents confirmed an ordered mesopomus structures with uniform pore diameter and large surface area. Regardless of the functional groups concentration, the synthesized sorbents showed significantly higher adsorption capacities for target ions than neat SBA-15. The observed adsorption mechanisms were predominantly based on complexation and electrostatic interactions between metal ions and various functional groups present on the adsorbent surfaces. The synthesized SBA-15 derivatives were used for removal of different metal ions such as Fe(III), Ni(II), Cu(II), Pb(II), Nd(III), and Dy(III) from water (pH >= 1). The highest adsorption capacity was obtained for the bifunctional (-EDTA/phosphonic groups) modified adsorbent, reaching up to 119.05 mg g(-1) for Fe(III), 246.95 mg g(-1) for Pb(II), 246.95 mg g(-1) for Cu(II), 238.10 mg g(-1) for Nd(III) and 243.90 mg g(-1) for Dy(III). The adsorption data were successfully fitted to the Langmuir and Freundlich models, revealing a monolayer chemisorption of REEs on the mesopomus samples. Metal desorption and adsorbent recycling were also found to be efficient under acidic condition (0.5-1.0 M). These properties highlight the perspective uses of functionalized mesoporous silicas for the rapid and potentially selective removal of REEs and heavy metal ions from the complex water samples and technological mixtures.