Noble-Metal-Free Modified TiO₂ Nanotube Arrays (TNTAs) for Efficient Photocatalytic Reduction of CO₂ to CO Under Visible Light

In the past decades, TiO₂ nanotube arrays (TNTAs) have gained a great attention as a durable photocatalyst for CO₂ reduction due to their unique properties. TNTAs have been widely modified with noble metals for increasing their absorption of visible light and limiting their associated rapid electron-hole recombination rate. However, these metals are extremely expensive, which limits their practical applications in the fields of energy and environment. In this study, three noble-metal-free materials of graphitic carbon nitrides, metal–organic framework, and reduced graphene oxide were used for modifying pure TNTAs through a simple drying-deposition method. The modified TNTAs samples were characterized by X-ray diffraction, Fourier transform infrared, field emission scanning electron microscopy and energy-dispersive X-ray spectroscopy analyses for approving successful synthesis of these nanocomposites. Finally, the modified TNTAs nanocomposites were investigated for their ability in converting the CO₂ gas to CO under visible light. However, the TNTAs modified with graphitic carbon nitrides displayed the highest CO productions of 27551 µmol m⁻² which represents 16% enhancement compared to that of pure TNTAs (23871 µmol m⁻²). The enhanced CO₂ photoreduction performance of modified TNTAs is attributed to promoted light absorption, increased surface area, and improved electrical conductivity.