A Time-Interval\nStrategy to Prepare Porous SiO<sub>2</sub> Spheres with Adjustable\nCore–Shell Ratio for Multiple\nGuest Loading

Porous microspheres with desired pore size and distribution\nare\nin high demand for loading various guest materials, especially various\npollutants that are several nanometers in size or stably suspended\nin liquid. Herein, multilevel porous SiO<sub>2</sub> microspheres\nwith arbitrarily adjustable core–shell ratios are prepared\nby solely regulating the time interval between the start of the hydrolysis\nreaction and the addition of organic solvent. The core–shell\nratio of the SiO<sub>2</sub> microspheres increases gradually with\nprolongation of the addition time interval; meanwhile, the specific\nsurface area can be adjusted from 543.2 m<sup>2</sup> g<sup>–1</sup> to 992.9 m<sup>2</sup> g<sup>–1</sup>, and the average pore\ndiameter varies from 2.3 to 5.7 nm together with a high pore volume\nreaching 0.91 cm<sup>3</sup> g<sup>–1</sup>. Moreover, the\nhierarchical core–shell SiO<sub>2</sub> microspheres with an\nadjustable core–shell ratio, a large specific surface area,\nand a multilevel pore size could be obtained on a large scale. These\nSiO<sub>2</sub> microspheres demonstrate excellent performance in\ncoloading platinum nanoparticles and various dye molecules, suggesting\ntheir great potential in treating various pollutants in printing and\ndyeing wastewater.