Article (Special Issue on Photocatalysis)Octahedral Cu2O-modified TiO2 nanotube arrays for efficient photocatalytic reduction of CO2

A photocatalyst composed of TiO2 nanotube arrays (TNTs) and octahedral Cu2O nanoparticles was fabricated, and its performance in the photocatalytic reduction of CO2 under visible and simulated solar irradiation was studied. The average nanotube diameter and length was 100 nm and ∼5 μm, respectively. The different amount of octahedral Cu2O modified TNTs were obtained by varying electrochemical deposition time. TNTs modified with an optimized amount of Cu2O nanoparticles exhibited high efficiency in the photocatalysis, and the predominant hydrocarbon product was methane. The methane yield increased with increasing Cu2O content of the catalyst up to a certain deposition time, and decreased with further increase in Cu2O deposition time. Insufficient deposition time (5 min) resulted in a small amount of Cu2O nanoparticles on the TNTs, leading to the disadvantage of harvesting light. However, excess deposition time (45 min) gave rise to entire TNT surface being most covered with Cu2O nanoparticles with large sizes, inconvenient for the transport of photo-generated carriers. The highest methane yield under simulated solar and visible light irradiation was observed for the catalysts prepared at a Cu2O deposition time of 15 and 30 min respectively. The morphology, crystallization, photoresponse and electrochemical properties of the catalyst were characterized to understand the mechanism of its high photocatalytic activity. The TNT structure provided abundant active sites for the adsorption of reactants, and promoted the transport of photogenerated carriers that improved charge separation. Modifying the TNTs with octahedral Cu2O nanoparticles promoted light absorption, and prevented the hydrocarbon product from oxidation. These factors provided the Cu2O-modified TNT photocatalyst with high efficiency in the reduction of CO2, without requiring co-catalysts or sacrificial agents.