“…Since monodisperse SiO2 spheres with controllable particle size are more convenient to prepare [18][19][20][21][22][23], coating TiO2 nanoclusters on the surface of micron-sized SiO2 spheres can effectively overcome the disadvantage that micron-sized TiO2 particles are difficult to prepare [24][25][26]. TiO2 nanoclusters are usually coated on SiO2 spheres by a sol-gel method, and tetrabutyl titanate (TBOT) is used as the titanium source.…”