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

In this study, the templated fabrication of hollow SiO 2 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 SiO 2 microspheres. Hydrophobic PU cores of PU- g -PDMA copolymer emulsifier micelles were in-situ entrapped in the formed SiO 2 layers, while hydrophilic PDMA shells were completely exposed on the surfaces of the SiO 2 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 SiO 2 microspheres. The resulting hollow SiO 2 microspheres with thiol-rich surfaces, described as SiO 2 @SH in the text, demonstrated a promising recyclable adsorption for toxic metal ions. ~88% of adsorption capacity for Pb 2+ has been maintained after four cycles of adsorption-desorption. The structure of hollow SiO 2 @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.