Visible light responsive photocatalytic hydrogen production over composites of anodized TiO2 nanotube array and graphitic carbon nitride measured with a gas circulating reactor

Gas phase photocatalysis over composites of electrochemically anodized titania nanotube (TNT) arrays and graphitic carbon nitride (g-C3N4) nanoparticles were examined with a home-made, gas-circulating reactor system. g-C3N4 nanoparticles were deposited onto anodized TNT surfaces by facile thermal polymerization using melamine and urea as precursors. The existence of g-C3N4 on TNT arrays clearly improved hydrogen production from gas phase photocatalytic decomposition of water/methanol mixture under visible light (VIS) irradiation (370-800 nm). The enhanced production of hydroxyl radicals via water photooxidation for TNT/g-C3N4 composites was also ascertained by photoluminescence measurement using terephthalic acid as a radical trap. These results deriving from synergetic effects of TNT and g-C3N4 can be attributed to the photogenerated hole-electron separation enhanced at TNT/g-C3N4 interface, suggesting that g-C3N4 is a metal-free sensitizer for enabling VIS responsive photocatalysis in anodized TNTs even for gas phase reactions.