Surface Modification of TiO2 Nanotubes Prepared by Porous Titanium Anodization via Hydrothermal Reaction: A Method for Synthesis High-Efficiency Adsorbents of Recovering Sr Ions

The recycling of strontium ions (Sr2+) from sea water has been well known for its good cost-effectiveness and environment friendliness. Herein, we modified the surface of TiO2 nanotubes (TNTs) prepared by porous titanium anodization via hydrothermal (HT) reaction and synthesized a highly efficient adsorbent for the repeated recycling of Sr2+. TNTs with a high specific surface area were manufactured on porous titanium by internal anodic oxidation. The as-prepared TNTs were treated by HT method to synthesize adsorption materials with a tubular bottom and grass-type top structure loaded with Na+. The surface cracks were eliminated by annealing pretreatment, and the investigation found that the 6 h HT reaction most effectively increased the Na+ content in the adsorbent. The as-synthesized adsorbents (HT-6TNTs) were used to recover Sr2+, and the maximum adsorption efficiency (approximately 100%) and adsorption equilibrium were observed within 10 h. Meanwhile, three consecutive cycles of adsorption experiments proved the uniform behavior of the HT-6TNTs in the reproducible recycling of Sr2+. In addition, by increasing the anodization time of TNTs from 0.5 to 3 h, the maximum adsorption capacity can be increased from 4.68 to 36.15 mg·unit–1, approximately 7.7 times higher.