Effect of formamide in electrolyte on morphology and photocatalytic activity of TiO2 nanotube arrays by anodization

The influence of the fomamide concentration in the electrolytes on the morphology and structure was investigated in the electrolytes of 0.5%HF water solution (A), 0.3 mol/L NH4F+70%H2O+30% formamide (volume fraction) (B), 0.3% mol/L NH4F+30%H2O+70% formamide (volume fraction) (C) and 0.3 mol/L NH4F+3%H2O+97% formamide (volume fraction) (D). The nanotube becomes long and its wall thickness becomes smaller with increasing formamide concentration in electrolyte. The results show that the nanotube becomes longer and its wall thickness becomes smaller with increasing formamide concentration in electrolyte. The tube length, pore diameter and wall thickness of TiO2 nanotube arrays anodized in water-based electrolyte A are about 600 nm, 100 nm and 5 nm, respectively. The tube length, wall thickness and pore diameter for sample anodized in formamide-based electrolyte D are about 10 μm, 5 nm and 60 nm, respectively. After being annealed at 450°C for 2 h in oxygen, the single anatase structure is obtained for sample anodized in electrolyte A. In contrast, the mixed anatase and rutile phase are observed in TiO2 nanotube for the other three samples. The results of photodegradation of methyl orange (MO) show that TiO2 nanotubes with longer tube length and thinner wall thickness have higher photocatalytic activity.