Synthesis and characterization of carbon modified TiO2 nanotube and photocatalytic activity on methylene blue under sunlight

Tentative photo-degradation mechanism diagram of the MB on the surface of carbon modified TNT. When the TiO2 was under ultraviolet light irradiation, the electrons were excited and transferred from the valence band (VB) to the conduction band (CB), leaving the holes on VB. The electrons were trapped by O2 and formed superoxide anion (O2−). H2O around the TiO2 was oxidized by the holes leaved on VB to hydroxyl radicals (OH). When the TiO2 was modified by carbon, the same is that the electrons of C4+ would be excited from ground state to 2P orbital under visible light irradiation. The electrons and holes can also lead to the generation of the O2− and OH. The oxidability of O2− and OH created around the carbon modified TNT is strong, and could oxidize the MB to CO2 and H2O.