Slow Light Effect Enhances the Photocatalytic Effect of Inverse Opal TiO₂-Based Photonic Nanocrystals

The slow light effect at the band gap edge of photonic nanocrystals (PhCs) can improve the light utilization efficiency of photocatalysts by enhancing light collection. This study reported an anatase inverse opal TiO₂ (IO TiO₂) with a 3D closely packed face-centered cubic structure prepared using a PhC template. The simulation of the electric field modulus distribution in the inverse opal structure was performed, and the enhancement of photocatalytic efficiency caused by the slow light effect at the red and blue edges of the photonic band gap was analyzed. The experimental results of rhodamine B degradation agreed with the simulation. IO TiO₂ has a high specific surface area (91 m²/g), which is 4.33 times that of powder TiO₂, and also has high pore volumes (0.13 cm³/g). In addition, it facilitates the separation of photogenerated carriers due to the existence of large pores that are periodically interconnected, thus, significantly improving photocatalytic efficiency. The apparent rate constant of IO TiO₂ is 9.96 × 10^-3 min^-1, which is 1.81 times that of powder TiO₂. The blue edge of 200 nm IO TiO₂ is spectrally closer to the electronic band gap of TiO₂. Also, it presents optimal photodegradation efficiency (70.02%), and its rate constant is 2.13 times higher than porous block TiO₂ without a band gap. Moreover, a detailed path of a possible reaction mechanism is proposed based on the results of the free radical trapping experiment and EPR analysis. This research offered opportunities for a deeper understanding and more efficient utilization of the blue-edge slow light effect. The slow light can be leveraged to enhance the optical nonlinear effect, which has practical significance for solar energy collection and conversion, optical switches, and photocatalysis.