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Nanosized hollow silica spheres with average diameters from 43 to 70 nm were prepared by removal of Fe3O4 templates with hydrochloric acid from silica-coated Fe3O4 core-shell composites. The shells of the hollow silica spheres had nanopores with average diameters of 0.92-1.25 nm. When the silica-coated Fe3O4 core-shell composites were prepared at a high pH value or with a low mole ratio of Na2SiO3 to Fe3O4, the resulting hollow silica spheres consisted of highly porous shells. When the silica-coated Fe3O4 core-shell composites were prepared with a high mole ratio of Na2SiO3 to Fe3O4, the resulting hollow silica spheres had large diameters and thick shells. The release rate of herbicide, ammonium glyphosate, could be tuned by using hollow silica spheres with different shell thicknesses.
Nanosized hollow silica spheres with average diameters from 43 to 70 nm were prepared by removal of Fe3O4 templates with hydrochloric acid from silica-coated Fe3O4 core-shell composites. The shells of the hollow silica spheres had nanopores with average diameters of 0.92-1.25 nm. When the silica-coated Fe3O4 core-shell composites were prepared at a high pH value or with a low mole ratio of Na2SiO3 to Fe3O4, the resulting hollow silica spheres consisted of highly porous shells. When the silica-coated Fe3O4 core-shell composites were prepared with a high mole ratio of Na2SiO3 to Fe3O4, the resulting hollow silica spheres had large diameters and thick shells. The release rate of herbicide, ammonium glyphosate, could be tuned by using hollow silica spheres with different shell thicknesses.