Successful self-assembly of monodisperse TiO2 colloidal nanospheres into photonic crystals with bright structural colors via a surface organosilane modification strategy

Monodisperse titanium dioxide (TiO 2 ) colloidal nanospheres, which possess a high refractive index (RI), are ideal building blocks for fabricating colloidal photonic crystals (CPCs) with structural colors. However, the intrinsic surface property, especially the low surface charge density, hinders them from assembling into CPCs with long-range ordered structures. Herein, we develop a surface modification strategy aimed at improving the surface potential of monodisperse TiO 2 nanospheres by utilizing vinyltriethoxysilane (VTES) as the modifier. XPS analysis reveals that the VTES molecules attach to the TiO 2 surface via Ti-O-Si chemical bonds and the presence of additional Si-OH groups, which can increase the surface potential. The as-synthesized VTES-modified TiO 2 nanospheres are subjected to calcination to increase their RI by crystallizing into the anatase phase. CPCs with bright and tunable structural colors throughout the visible range are successfully fabricated by utilizing the monodisperse VTES-modified TiO 2 or anatase-TiO 2 nanospheres as building blocks by self-assembly through a dip coating method.