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.