Tuning CH₄ productivity from visible light driven gas‐phase CO₂ photocatalytic reduction on doped g‐C₃N₄/TiO₂ heterojunctions

Herein, visible light‐driven gas‐phase photocatalytic CO₂ reduction into CH₄ is tuned by designing optimized three‐component Au/doped C₃N₄/TiO₂ composite photocatalysts. The key point strategy consists in the formation of high‐quality C₃N₄/TiO₂ heterojunction by associating low containing doped graphitic carbon nitride to commercially available TiO₂ UV‐100. Those heterojunctions result in both visible light sensitization and increased charge‐carrier separation. Further deposition of small Au nanoparticles (≈3 nm), quite exclusively onto TiO₂ surfaces, mainly acts as electron trapping/cocatalytic functions without excluding surface plasmonic effects. The resulting doped g‐C₃N₄ material exhibits enhanced visible light harvesting properties, especially in the case of C‐doping. In addition, it is assumed that B– and C–C₃N₄ doping, leading to a more or less lower conduction band position, is the impacting factor toward total CH₄ selectivity achievement. The (0.77 wt%)Au/(0.59 wt%)C–C₃N₄/TiO₂ composite photocatalyst, exhibiting the best compromise between the various impacting factors, leads to a continuous productivity rate of CH₄ of 8.5 μmol h⁻¹ g⁻¹ under visible light irradiation over at least 10 h. To the best of knowledge, this level of performance is unprecedented under continuous gas‐phase flowing CO₂ in the presence of water as reducing agent, without addition of any sacrificial agent.