Adsorption and desorption of Cd(II) onto titanate nanotubes and efficient regeneration of tubular structures.

Efficient regeneration of desorbed titanate nanotubes (TNTs) was investigated with cycled Cd(II) adsorption and desorption processes. After desorption of Cd (II) from TNTs using 0.1M HNO3, regeneration could be simply achieved with only 0.2M NaOH at ambient temperature, i.e. 2% of the NaOH needed for virgin TNTs preparation at 130°C. The regenerated TNTs displayed similar adsorption capacity of Cd(II) even after six recycles, while significant reduction could be detected for desorbed TNTs without regeneration. The virgin TNTs, absorbed TNTs, desorbed TNTs and regenerated TNTs were systematically characterized. As results, the ion-exchange mechanism with Na(+) in TNTs was convinced with obvious change of -TiO(ONa)2 by FTIR spectroscopy. The easy recovery of the damaged tubular structures proved by TEM and XRD was ascribed to asymmetric distribution of H(+) and Na(+) on the surface side and interlayer region of TNTs. More importantly, the cost-effective regeneration was found possibly related to complex form of TNTs-OCd(+)OH(-) onto the adsorbed TNTs, which was identified with help of X-ray photoelectron spectroscopy, and further indicated due to high relevance to an unexpected mole ratio of 1:1 between exchanged Na(+) and absorbed Cd(II).