Hollow SiO2 microspheres with thiol-rich surfaces: The scalable templated fabrication and their application for toxic metal ions adsorption

Abstract

In this study, the templated fabrication of hollow SiO2 microspheres with thiol-rich surfaces and their application as adsorbents for toxic metal ions were demonstrated. (Cyclohexane + TEOS)-in-water Pickering emulsion was first prepared employing detachable polyurethane-g-poly (N,N-dimethyl acrylamide) (PU-g-PDMA) copolymer micelles as emulsifiers. The subsequent Pickering emulsion interface directing sol-gel reaction of TEOS led to the formation of SiO2 microspheres. Hydrophobic PU cores of PU-g-PDMA copolymer emulsifier micelles were in-situ entrapped in the formed SiO2 layers, while hydrophilic PDMA shells were completely exposed on the surfaces of the SiO2 shells, forming polymer brush-like structure. The subsequent removal of PDMA shells through the cleavage of the reversible disulfide linkages between PU core and PDMA shells left a large number of thiol groups on the surfaces of hollow SiO2 microspheres. The resulting hollow SiO2 microspheres with thiol-rich surfaces, described as SiO2@SH in the text, demonstrated a promising recyclable adsorption for toxic metal ions. ~88% of adsorption capacity for Pb2+ has been maintained after four cycles of adsorption-desorption. The structure of hollow SiO2@SH microspheres was carefully characterized with scanning electron microscope (SEM), transmission electron microscope (TEM), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FT-IR) and Raman spectroscopy, respectively.