Preparation and application of magnetic hollow mesoporous SiO₂-Fe_xO_y microspheres from different Fe sources

Magnetic hollow mesoporous SiO₂-Fe_xO_y microspheres (Fe_xO_y/HMS) were prepared by changing Fe sources via one-pot sol-gel approach, with phenolic resin as soft template, cetyltrimethylammonium bromide (CTAB) as a pore-forming agent and tetraethylorthosilicate (TEOS) as the silicon source. The effect of Fe sources on the microspheres formation was investigated. The crystal structure, the morphology and the magnetic performance of Fe_xO_y/HMS was analyzed by XRD, SEM and TEM as well as vibrating sample magnetometer (VSM), respectively. The results indicate that the as prepared Fe_xO_y/HMS obtained from iron acetylacetonate (Fe(acac)₃) has more perfect morphology than those from other Fe sources. Fe(acac)₃ contributes to the formation of shells and improves the structural stability of the composite microspheres. The Fe_xO_y/HMS was magnetized followed by grafting polyacrylonitrile (PAN), which was transformed to polyamidoxime (PAO). The resulting magnetic composite Fe_xO_y/HMS-g-PAO, with a saturated magnetization value of 8.6 emu/g, was used in absorbing Cr(Ⅵ) ions in water. Therefore, the Fe_xO_y/HMS-g-PAO with the absorbed Cr(Ⅵ) could be separated rapidly by magnetic irons. As K₂Cr₂O₇ solution with the concentration of 100 mg/L used as the target solution, the equilibrium adsorption capacity reaches 123.75 mg/g at pH value of 2.