Slow photon photocatalytic enhancement of H2 production in TaON inverse opal photonic crystals

• Published in: Journal of solid state chemistry 2024-01, Vol.329, p.124404, Article 124404
• Main Authors: Maekawa, Taiki, Huang, Yi-Syun, Tateishi, Naoki, Nakanishi, Akihiro, Onoe, Tomoya, Dong, Yusong, Waterhouse, Geoffrey I.N., Murai, Kei-ichiro, Moriga, Toshihiro
• Format: Article
• Language: English
• Subjects: Inverse opal; Oxynitrides; Photocatalytic hydrogen production; Photonic band gap; Slow photons
• ISSN: 0022-4596; 1095-726X
• DOI: 10.1016/j.jssc.2023.124404

In this study, tantalum oxynitride inverse opal (TaON IO) photonic crystals with different macropore diameters (D) were synthesized in a two-step process involving colloidal crystal templating and thermal nitridation, then applied as visible light-driven photocatalysts for hydrogen production. The TaON inverse opals showed photonic band gaps (PBGs) at visible wavelengths, with the PBG position redshifting as the diameter of the macropores increased in accordance with a modified Bragg's law expression. By aligning the electronic absorption edge of TaON (Eg ∼ 2.4 eV) with the blue edge (short-wavelength side) or red edge (long-wavelength side) of the PBGs, slow photon enhancement of photocatalytic H2 generation was realized. H2 production tests conducted in 10 vol% methanol containing H₂PtCl6 under Xe lamp irradiation (150 W) showed that the hydrogen production rate was enhanced by ∼1.3–1.4 times when the TaON absorption edge (∼510 nm) aligned with blue edge of the PBG (0.3421 mmol g−1 h−1) or the red edge of the PBG (0.3254 mmol g−1 h−1) in the inverse opals. The red edge enhancement was due to increased light absorption and charge carrier generation in TaON, whereas the blue edge effect was likely due to suppression of electron-hole pair recombination. Results demonstrate that photonic crystal engineering to exploit slow photon effects is a viable approach for boosting photocatalytic hydrogen production rates. [Display omitted] •Oxynitride TaON photonic crystals with different pore sizes were synthesized.•The templated PMMA particle size and nitridation conditions were controlled.•Samples whose absorption edges coincided with the photonic band gap were observed.•Photocatalytic H2 production under white-light irradiation was compared.•The highest photocatalytic activity was observed for TaON (B: 297 nm) in which the PBG blue edge matched with the absorption edge.