The influence of sodium alginate in water-based electrolyte on the morphology of TiO₂ nanotube prepared by anodization method

Fabrication of a highly-ordered TiO₂ nanotube array (TNA) with an anodization method in a water-based electrolyte using sodium alginate (NaAlg) as a thickening agent was presented for the first time. The titanium foil was anodized with various concentrations of NH₄F, NaAlg, and the pH variation for the electrolyte solution. The anodization curve profile (current versus time) in various electrolyte compositions and their correlation to resulting morphologies, depletion layer values, and photocurrent of the fabricated samples were discussed. Based on SEM characterization and Fast Fourier Transformation (FFT) image, it is evidenced that the use of NaAlg can control the oxidation and dissolution rate in the anodization process so that a highly-ordered TNA with better uniformity and circularity can be obtained in 1.5 h anodization time. However, the presence of NaAlg was observed to give a wider variety of tube lengths. The increase in NH₄F concentration led to a wider and uncircular nanotube but did not significantly affect wall thickness and tube length. The higher H⁺ concentration leads to wider tube diameter, thinner tube wall, and shorter tube length. The highest Regularity Ratio of the TNA sample was obtained when 0.3% NH₄F and NaAlg at pH 3 was used, while the longest tube length was obtained at pH 4. It was found that the morphology observed follows a certain trend based on the nucleation time and anodization current density. It was also observed that the TNA porosity, wall thickness, tube length, and depletion layer influence photocurrent activity in complex relations. However, it was generally found that the NaAlg addition to the electrolyte resulted in a TNA having better regularity and photocurrent activity compared to the electrolyte without NaAlg.