Chemically stable magnetic nanoparticles for metal adsorption and solid acid catalysis in aqueous media

We have developed a magnetically collectable, reusable adsorbent and a catalyst for concentrating heavy metal ions in acidic aqueous solutions and solid acid catalysis in aqueous media. Chemically stable, magnetic rattle-type core-shell particles, comprising metallic cobalt nanoparticles in hollow silica microspheres, were prepared by the sol-gel reaction of alkylsilyl trichlorides around water droplets in a water-in-oil emulsion. Sulfonic groups were immobilized on the external surface of the core-shell particles through silylation with 3-mercaptopropyl(trimethoxysilane) and subsequent oxidization of the thiol groups by nitric acid. The sulfonic groups acted as adsorption sites for Zn and Pb ions under acidic conditions and as catalytically active sites for the hydrolysis of ethyl acetate in aqueous media. The enclosed Co was not eroded during the regeneration of the adsorbent/catalyst by 1 M HCl. The chemical stability arose from the dense non-porous shell, which prevents the passage of solvents.