Tuning CH4 Productivity from Visible Light‐Driven Gas‐Phase CO2 Photocatalytic Reduction on Doped g‐C3N4/TiO2 Heterojunctions

Abstract

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.