Solar spectrum photocatalytic conversion of CO2 to CH4 utilizing TiO2 nanotube arrays embedded with graphene quantum dots

TiO2 nanotube arrays (TNT) offer an exciting prospect as a photocatalytic material architecture due to the combined properties of high surface area, 1-D vectorial charge transfer, and reduced photogenerated charge recombination. However the TiO2 band gap (approximate to 3.2 eV) limits light absorption to the UV region, which comprises but a small fraction of the solar spectrum energy. Graphene is known to effectively absorb visible light, and due to its high conductivity promote efficient charge transfer. Herein, we present a novel photocatalyst composed of TNTs sensitized with electrodeposited graphene quantum dots (GQDs). GQDs electrodeposition-duration is varied to optimize photocatalytic performance of the resulting nanostructured graphene-TNT (G-TNT) films. Under solar spectrum illumination we find optimal G-TNT samples promote a CO2 to CH4 photocatalytic conversion rate of 1.98 ppm cm(-2) h(-1), with carbon origin confirmed by (CO2)-C-13 isotopic test.