Effect of NaBF₄ addition on the anodic synthesis of TiO₂ nanotube arrays photocatalyst for production of hydrogen from glycerol-water solution

Addition of NaBF₄ during anodic synthesis of TiO₂ nanotube arrays (TNTAs) photocatalyst and its application for generating hydrogen from glycerol-water solution has been investigated. The TNTAs were synthesized by anodic oxidation of titanium metal in glycerol electrolyte solution containing NH₄F. During the process, the NaBF₄ with different concentrations were added to the solution. Annealing of the formatted TNTAs were performed at 500 °C for 3 h under 20% H₂ in argon atmosphere, to produce crystalline phase photocatalyst. FESEM analysis showed that self-organized and well ordered TNTAs have range of inner diameters, wall thicknesses and lengths approximately 62-130 nm, 27 nm and 1.53 μm, respectively. FTIR analysis indicated that carbon, nitrogen and boron were incorporated into the TNTAs lattice. Refer to UV-Vis DRS and XRD analysis, the TNTAs photocatalysts prepared have the band gap range of 2.70-3.10 eV, with mostly have anatase phase. The NaBF₄ addition during synthesis, resulted modified TNTAs that can reduce the recombination of photo-induced electrons-holes. Photocatalytic hydrogen production test, from glycerol-water solution, indicated that TNTAs with the addition of NaBF₄ during anodic synthesis process showed higher hydrogen production comparing to the one without NaBF₄ addition. Among them the TNTAs,b (with the addition 5 mM of NaBF₄) showed up to 32% improvement in the hydrogen production and can be considered as the optimum condition.