Optimization of hydrothermal synthesis of Fe-TiO2 nanotube arrays for enhancement in visible light using an experimental design methodology.

We designed an experiment to optimize the hydrothermal modification of iron on anodized TiO2 nanotubes. A central composite design that included five design points was used to determine the condition parameters for hydrothermal reaction time (1-5 h) and hydrothermal temperature (120-180 °C). A statistical method was used to observe the effects of hydrothermal conditions on the material properties and photocatalytic activity of a Fe-TiO2 nanotube catalyst. Scanning electron microscopic (SEM) analysis shows the iron is doped on the TNTs, which is further confirmed by energy-dispersive X-ray spectroscopy. X-ray diffraction indicate the existing states of iron in the form of iron oxide on the TNT. The maximum degradation efficiency (92.3%) was achieved at a hydrothermal temperature of 150 °C and time of 3 h. It is found that the optimal medication of the Fe-TNT catalyst occurred at a particular combination of temperature (150 °C) and reaction time (3 h), that provide the more active sites for iron to enter the crystal lattice of TNT, and that the maximum CR degradation could be achieved.