Synthesis of Anodized TiO2 Nanotube Arrays as Ion Sieve for Lithium Extraction

Abstract

AbstractTitanium type lithium ion‐sieve nanotubes synthesized by the hydrothermal method were extensively explored over recent years due to its promising properties. However, on account of nanotubes′ tangled structure impeding the lithium adsorption in the interior nanotube walls, unalterable dimensions of the synthesized nanotubes, and a long period of annealing, the anodizing technique was proposed. It is shown that lithium uptake and adsorption capacity is improved because of easier mass transfer during the ion exchange process. This work focuses on a novel anodizing method for nanotube ion‐sieve synthesis. The optimum anodizing condition was discovered by altering anodizing voltage, time, and fluoride concentration to have a proper nanotube morphology and corresponding high surface area for achieving the most suitable adsorption properties. Nanotubes were grown on Ti foil in Ethylene Glycol (EG) electrolyte with different amounts of NH4F in a range of anodizing voltage (40–70 V) and time (1–4 hours). TiO2 Nanotube array morphology, dimension, and phase characterization were derived from FESEM and XRD analysis. As a result, the optimum condition discovered in this research to obtain acceptable morphology and high aspect ratio nanotubes was at 0.5 wt % NH4F, 40 V, 3 hours. Lithium titanate spinel with nanotube morphology was synthesized by chemical lithiation in the LiOH solution and then acid‐treated to obtain H4Ti5O12 adsorbent. ICP‐OES analysis revealed that the H4Ti5O12 lithium‐ion sieve with nanotube array structure obtain adsorption capacity up to 37.5 mg/g in LiOH and LiCl solutions (112 mg/L Li, pH 12), designating that the Hydrogen titanate (HTO) ion sieve could effectively extract Li+from the enriched solutions.