Abstract
In this study, we report the influences of distilled water and ammonium fluoride (NH4F) on morphology of pores in honeycomb-like titanium dioxide (TiO2) nanotube arrays. We observed the structure and arrangement of pores in the TiO2 nanotube arrays based on scanning electron microscopy images and analyzed the spatial distribution of the pores using fast Fourier transform and Voronoi diagram. We studied the individual pore properties including pore diameter, wall thickness, and interpore distance and found that locally connected ordering defects decreased with increasing distilled water concentration. Furthermore, we found that the optimum conditions of well-ordered hexagonal pore arrangement were 2 and 10 vol% distilled water with 0.2 and 0.4 wt% NH4F, respectively. Throughout this study, we provide a better understanding about the roles of distilled water and NH4F in forming well-ordered nanoscale pore structure with less ordering defects in the honeycomb-like TiO2 nanotube arrays.
Highlights
TiO2 nanotube arrays have gained a lot of interest because their high surface area and effective separation[1,2,3,4,5] for both photo-electrons and photo-holes are attractive for a variety of applications like photocatalysts[6,7], solar cells[8,9], gas sensors, supercapacitors[10,11], and filtering systems[12]
We investigated the effects of the concentrations of NH4F and distilled water on microstructure of the pores, configuration of defects, hexagonal pore arrangement, and pore size distribution, wall thickness as well as interpore distance
We can see that the pores of all samples are hexagonally arranged to form honeycomb-like structure. This is because the TiO2 nanotube arrays are connected to each other in a close packed manner by the two-step anodization[29]
Summary
TiO2 nanotube arrays have gained a lot of interest because their high surface area and effective separation[1,2,3,4,5] for both photo-electrons and photo-holes are attractive for a variety of applications like photocatalysts[6,7], solar cells[8,9], gas sensors, supercapacitors[10,11], and filtering systems[12]. If the TiO2 nanotube arrays have a specific functional layer on the surface of the nanotubes, the close packed hexagonally arranged pores, which form the most efficient channel structure, can be used in photocatalysis and self-cleaning systems[12]. To elucidate this effect, we analyzed the influences of the concentrations of NH4F and distilled water on the pore distribution of the TiO2 nanotube arrays. We present the optimal concentrations of the ethylene glycol electrolyte for uniform distribution of the pores
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