Tunable slow photon effect and local surface plasmon in Ag-immobilized TiO2 inverse opal films for enhancing pollutant photodegradation

Abstract

Plasmonic silver-decorated TiO₂ inverse opal has shown an interesting potential for photocatalysis owing to its physically tunable optical absorbance, highly active area, and flexible fabrication. In this study, electrophoretic deposition was used as a key technique to overcome the disadvantages of traditional inverse opal (IO)-fabricating methods, resulting in high reproducibility, chemical stability, and periodic area. The use of IO structural engineering, beneficially delocalizing and enhancing absorbed visible light, accounted for 46% of the total solar light, leading to the enhancement of the localized surface plasmonic resonance (LSPR) hot electrons of Ag NPs and an enhanced local electromagnetic (EM) field for the formation of photogenerated electrons on TiO₂. These enhancements in Ag-deposited TiO₂ IO promoted the excellent photocatalytic kinetic constant of methylene blue degradation around 17 × 10⁻³ min⁻¹, responding to tunable optical absorption at the stopband edge of TiO₂ IO containing 288-nm sized pores and low absorbance of Ag in the overlapped band. The explanation for the enhanced photocatalytic mechanism was studied based on high Ag deposition density, decrease in photocurrent, increase in electron lifetime in electrolytes, and the contribution of a slow photon effect to these characteristics. The proposed photocatalysis mechanism concerned the enhancement of EM-generated electrons on TiO₂ that immigrate to the Ag surface for photoreduction while photooxidation occurred at the TiO₂ surface by the holes. This study provides an interesting strategy to improve the photocatalysis of semiconductor–metal composite systems.