Synthesis of core–shell structured magnetic mesoporous silica microspheres with accessible carboxyl functionalized surfaces and radially oriented large mesopores as adsorbents for the removal of heavy metal ions

Abstract

In this work, we report the fabrication of novel multifunctional microspheres which are composed of ordered mesoporous silica shells with accessible carboxyl functionalized surfaces and radially oriented large mesopores, and nonporous silica-coated magnetite cores (Fe₃O₄), aiming to remove heavy metal ions from aqueous media. The well-designed multifunctional microspheres were thoroughly characterized with transmission electron microscopy, scanning electron microscopy, infrared spectroscopy, N₂ adsorption–desorption, X-ray diffraction as well as magnetization measurements. The as-prepared microspheres possess unique properties including stably grafted and accessible carboxyl groups, highly open mesopores (11.03 nm), high magnetization (34.5 emu g⁻¹), and large BET surface areas (165 m² g⁻¹), and as a result, the as-prepared microspheres exhibit an enhanced performance for the removal of Cd(II), Cu(II), and Pb(II) from wastewater, with a high adsorption capacity, a rapid adsorption rate, and an easy magnetically separable process.