Dual functional SiO2@TiO2 photonic crystals for dazzling structural colors and enhanced photocatalytic activity

Abstract

Dazzling colors applied for communication and camouflage in nature can be achieved through the controlled synthesis of photonic crystals; however, to achieve bright photonic pigments, materials with high refractive index are required; herein, we report SiO₂@TiO₂ core–shell nanospheres with adjustable particle size as the structural unit of photonic crystals to achieve multiple structural colors. Ti³⁺ self-doped SiO₂@TiO₂ photonic crystals were obtained by the vertical self-assembly of amorphous nanospheres with uniform particle size, prepared by a mix-solvent method after 4 h insulation at 550 °C. Using transient surface photovoltage, diffuse reflection and ultraviolet visible techniques, we testified that a change in the shell thickness of TiO₂ in the structural unit could change the location of the photon band gap and realize the red shift of the reflection peaks. The introduction of TiO₂ with high refractive index improved the color saturation of photonic colorants and increased the quantum utilization efficiency of the photonic crystals assembled by the core–shell nanospheres through internal multiple reflection and scattering of light. Due to its intermediate energy level, Ti³⁺ reduces the energy required for electron transition to 2.92 eV and improves the degradation efficiency of the photonic pigments under visible light.