Optical and Photocatalytic Properties of Three-Dimensionally Ordered Macroporous Ta₂O₅ and Ta₃N₅ Inverse Opals

High Resolution Image Download MS PowerPoint Slide Colloidal crystal templating is a simple yet remarkably versatile synthetic strategy toward inverse opal (IO) photonic crystals for optical sensing and catalytic applications. Herein, we report the successful fabrication of tantalum (V) oxide, Ta 2 O 5, inverse opal thin films and powders using the colloidal crystal templating method, utilizing poly(methyl methacrylate) (PMMA) colloidal crystals as sacrificial templates and TaCl 5 as the tantalum source. The Ta 2 O 5 IO thin films and powders showed structural color at ultraviolet (UV) and visible wavelengths, with the photonic band gap (PBG) position along the [111] direction increasing linearly with the diameter of macropores ( D ) in the inverse opals and also the refractive index of the medium filling the macropores, in excellent accord with a modified Bragg’s law expression. Thermal ammonolysis of the Ta 2 O 5 inverse opals at 700 °C yielded well-ordered Ta 3 N 5 IO films and powders possessing high specific surface areas (37 m 2 g –1 ) and a semiconductor band gap of 2.0–2.1 eV. A Pt/Ta 3 N 5 IO photocatalyst delivered a H 2 production rate of ∼300 μmol g –1 h –1 in aqueous methanol (10 vol % MeOH) under visible-light irradiation (300 W Xe lamp, λ ≥ 420 nm), approximately twice that achieved using conventional Pt/Ta 3 N 5 powder photocatalysts (161 μmol g –1 h –1, 8.4 m 2 g –1 ). Results demonstrate that inverse opal engineering is an effective approach for realizing Ta 2 O 5 IO thin films for sensing applications and Ta 3 N 5 IOs with enhanced photocatalyst performance.