Magnetic mesoporous silica hybrid nanoparticles for highly selective boron adsorption

Abstract

Novel core–shell magnetic mesoporous silica hybrid nanoparticles were synthesized and functionalized further with a glycidol reagent to produce boron-specific cis-diol, chelating functional derivatives. The resulting core–shell hybrid nanoparticles were found to be a better alternative to the existing boron adsorbents that had been modified with large molecular weight saccharide moieties and polymer functionalities. The magnetic mesoporous silica hybrid nanoparticles had a surface area, diameter, pore size, and saturation magnetization of 629 m² g⁻¹, 200–300 nm, 2.5 nm, and 33.25 emu g⁻¹, respectively. The glycidol-modified nanoparticles with cis-diol functional groups showed high adsorption affinity and excellent selectivity towards boron in an aqueous solution, even in the presence of competitive metal ions (Ni²⁺, Cu²⁺, Cr²⁺ and Fe²⁺) and sulphates and chlorides of Na⁺, K⁺, Ca²⁺ and Mg²⁺ ions. Adsorption equilibrium could be established within 15–20 min, and the level of boron adsorption was 2.37 mmol g⁻¹, which is much higher than the values previously reported for other boron adsorbent materials. The synthesized magnetic mesoporous silica hybrid nanoparticles showed approximately 97% boron removal capacity from a H₃BO₃ solution (100 mg L⁻¹), and the used adsorbent particles could be separated easily from the aqueous suspensions by an external magnetic field. The adsorbent could be used repeatedly after a simple acid treatment (0.1 M HCl) and regenerated by an aqueous ammonia solution (3% NH₃·H₂O).