Photoactivity of amorphous and crystalline TiO 2 nanotube arrays (TNA) films in gas phase CO 2 reduction to methane with simultaneous H 2 production.

This study assessed the photoactivity of amorphous and crystalline TiO ₂ nanotube arrays (TNA) films in gas phase CO ₂ reduction. The TNA photocatalysts were fabricated by titanium anodization and submitted to an annealing treatment for crystallization and/or cathodic reduction to introduce Ti ³⁺ and oxygen vacancies into the TiO ₂ structure. The cathodic reduction demonstrated a significant effect on the generated photocurrent. The photoactivity of the four TNA catalysts in CO ₂ reduction with water vapor was evaluated under UV irradiation for 3 h, where CH ₄ and H ₂ were detected as products. The annealed sample exhibited the best performance towards methane with a production rate of 78 μmol g _cat ^-1 h ^-1 , followed by the amorphous film, which also exhibited an impressive formation rate of 64 μmol g _cat ^-1 h ^-1 . The amorphous and reduced-amorphous films exhibited outstanding photoactivity regarding H ₂ production (142 and 144 μmol g _cat ^-1 h ^-1 , respectively). The annealed catalyst also revealed a good performance for H ₂ production (132 μmol g _cat ^-1 h ^-1 ) and high stability up to five reaction cycles. Molecular dynamic simulations demonstrated the changes in the band structure by introducing oxygen vacancies. The topics covered in this study contribute to the Sustainable Development Goals (SDG), involving affordable and clean energy (SDG#7) and industry, innovation, and infrastructure (SDG#9).
Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
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