| Résumé | Cu/TiO₂ is a well-known photocatalyst for the photocatalytic transformation of CO₂ into methane. The formation of C₂₊ products such as ethane and ethanol rather than methane is more interesting due to their higher energy density and economic value, but the formation of C–C bonds is currently a major challenge in CO₂ photoreduction. In this context, we report the dominant formation of a C₂ product, namely, ethane, from the gas-phase photoreduction of CO₂ using TiO₂ nanotube arrays (TNTAs) decorated with large-sized (80–200 nm) Ag and Cu nanoparticles without the use of a sacrificial agent or hole scavenger. Isotope-labeled mass spectrometry was used to verify the origin and identity of the reaction products. Under 2 h AM1.5G 1-sun illumination, the total rate of hydrocarbon production (methane + ethane) was highest for AgCu-TNTA with a total CₓH₂ₓ₊₂ rate of 23.88 μmol g⁻¹ h⁻¹. Under identical conditions, the CₓH₂ₓ₊₂ production rates for Ag-TNTA and Cu-TNTA were 6.54 and 1.39 μmol g⁻¹ h⁻¹, respectively. The ethane selectivity was the highest for AgCu-TNTA with 60.7%, while the ethane selectivity was found to be 15.9 and 10% for the Ag-TNTA and Cu-TNTA, respectively. Adjacent adsorption sites in our photocatalyst develop an asymmetric charge distribution due to quadrupole resonances in large metal nanoparticles and multipole resonances in Ag–Cu heterodimers. Such an asymmetric charge distribution decreases adsorbate–adsorbate repulsion and facilitates C–C coupling of reaction intermediates, which otherwise occurs poorly in TNTAs decorated with small metal nanoparticles. |
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