Large-scale photonic crystal films prepared via coating-assisted leveling and gravity-induced assembly

The applications of photonic crystal (PC) films are limited by the challenge in large-scale preparations within short time. Here, we introduce a two-steps method in which large-scale leveling is achieved by blade coating before the assembly of SiO₂ nanospheres was induced by gravity. PC films with the area of 10 cm × 10 cm were created within around 10 min, which were used to enhance the photocatalytic performance of C₃N₄ for organic dyes. The key parameters related to assembly, including nanospheres diameters and mass concentration of SiO₂ nanospheres as well as solvent systems, were studied. The effect of coating speed and blade height during blade coatings were also investigated. The optimal dispersion systems as well as coating conditions were achieved and the forces existing during the two steps were discussed. When SiO₂ nanospheres (198–236 nm) of 15 wt% were dispersed in ethanol, the optimal PC films were prepared at the coating speed of 3 mm s⁻¹ and the blade height of 150 μm. Within 6 h, complete or 80% degradation of RhB solution was achieved in the presence or absence of PC films, respectively. We think that this work provides a method for the preparation of large-scale PC films within short time, exploring their further applications.