Synthesis of magnetic core-shell Fe3O4@SiO2@Mg(OH)2 composite using waste bischofite and its catalytic performance for ozonation of antibiotics

This study investigated the possibility of recycling bischofite which was discarded with a great quantity from salt industry as catalyst for ozonation of sulfathiazole. Bischofite was used to successfully synthesize nano-scaled magnetic core-shell Fe3O4@SiO2@Mg(OH)(2) which could be easily separated for reuse by an external magnetic field. Element mapping showed that this composite microsphere was composed of a Fe3O4 core, a SiO2 shell and a Mg(OH)(2) outer shell. Reaction rate, operation conditions, mineralization, and antibacterial activity of catalytic ozonation of sulfathiazole using Fe3O4@SiO2@Mg(OH)(2) were investigated. The reaction rate constant of Fe3O4@SiO2@Mg(OH)(2) treatment was almost twice that of single ozonation. Operation conditions including catalyst dosage of 0.15 g/L, pH of 7.0, and temperature of 25 degrees C were optimal for removal of sulfathiazole by catalytic ozonation. Over 99.0% of sulfathiazole could be removed within 10 min by catalytic ozonation with Fe3O4@SiO2@Mg(OH)(2). About 99.0% of sulfathiazole could be removed by catalytic ozonation with Fe3O4@SiO2@Mg(OH)(2) that was reused 4 times. About 40.1% of total organic carbon was removed within 60 min by catalytic ozonation with Fe3O4@SiO2@Mg(OH)(2) to exhibit good mineralization feature for sulfathiazole. Catalytic ozonation played important role in affecting antibacterial activity of sulfathiazole. Initial concentration of sulfathiazole and inorganic ions had negative effect on removal efficiency. Sulfathiazole was degraded through cleavage and oxidation processes during catalytic ozonation by Fe3O4@SiO2@Mg(OH)(2). This study provides a new core-shell magnetic material for antibiotic pollution control and a promising new application pathway for using waste bischofite.