Real-time monitoring of photocatalytic methanol decomposition over Cu₂O-loaded TiO₂nanotube arrays in high vacuum

We report a real-time investigation on the photocatalytic decomposition of methanol over Cu2O-loaded TiO2 nanotube arrays (TNAs) in high vacuum. Cu2O-loaded TNAs were fabricated using all-electrochemical processes. TNAs were prepared by anodizing Ti foils, and Cu2O nanoparticles (CNPs) were pulse-electrodeposited onto anodized TNA surfaces. The photocatalytic decomposition of methanol was monitored using a quadrupole mass analyzer in high vacuum, where the partial pressures of intermediate and final reaction products were measured. Switching phenomena in the partial pressures of hydrogen (H2), formaldehyde (CH2O), water (H2O), and carbon monoxide (CO) were observed simultaneously according to the ON/OFF sequence of ultraviolet irradiations over TNA/CNP composites, thereby revealing that Cu2O can facilitate proton reduction like noble-metal-based cocatalysts such as platinum, even in a high vacuum environment. The intermediate reaction products suggest that the photocatalytic oxidation of gaseous methanol over TNA/CNP proceeds under the coexistence of direct and indirect hole transfer mechanisms.