The effect of Reynolds number on TiO₂ nanosponges doped with Li⁺ cations

Abstract

TiO2 nanosponges and nanotubes were doped with Li+, which resulted in higher photocurrent densities, especially in nanosponges.

Original Approach to Synthesize TiO2/ZnO Hybrid Nanosponges Used as Photoanodes for Photoelectrochemical Applications

“…The procedure followed to obtain a nanosponge structure was optimized in previous studies [ 11 , 13 , 14 , 16 ]. Titanium rods (8 mm in diameter and 99.3% purity) were polished with 240–4000 silicon carbide (SiC) papers until a mirror surface was reached.…”

“…Finally, photoelectrodes were annealed at 450 °C for 1 h in air atmosphere with a heating rate of 15 °C/min to transform TiO 2 nanostructures to the anatase phase. Annealing improves conductivity and lifetime of charge carriers [ 13 , 33 ].…”

“…The authors obtained a new type of titanium oxide nanostructure (nanosponge) when anodization was performed under hydrodynamic conditions in glycerol/water/ammonium fluoride (NH 4 F) electrolytes. As an advantage, the nanosponge morphology—which consists of a strongly interconnected network of TiO 2 —offers a considerably higher specific area and provides a directly connected path of electrons [ 11 , 13 , 14 ]. TiO 2 nanosponges have a significantly rougher morphology than other nanostructures such as TiO 2 nanotubes, which provides greater electrical conductivity and number of defects.…”

“…TiO 2 nanosponges have a significantly rougher morphology than other nanostructures such as TiO 2 nanotubes, which provides greater electrical conductivity and number of defects. Furthermore, with a nanosponge morphology, there is a displacement of the Fermi level towards the edge of the conduction band, which facilitates the charge separation, resulting in a lower probability of charge recombination [ 11 , 13 ]. In order to transform amorphous TiO 2 nanosponges prepared by anodization into a crystalline structure, it is necessary to perform an annealing treatment.…”

“…One of the most negative aspects of using TiO 2 as photocatalyst is that it has a wide band gap (3.2 eV for anatase phase, λ = 390 nm), which limits its photocatalytic applications to ultraviolet (UV) irradiation [ 6 ]. There are different options to solve this problem such as doping TiO 2 nanostructures with noble metals [ 10 , 15 ], inserting ions in the TiO 2 lattice [ 13 , 16 ], using microporous materials [ 17 ], and synthesizing hybrid nanostructures [ 18 , 19 ]. Among all these solutions, the most studied option is doping TiO 2 with noble metals.…”