Study of Pd(II) adsorption over titanate nanotubes of different diameters

Hydrogenotitanates (HNTs) nanotubes with different diameters were prepared by hydrothermal treatment of TiO2 (P25) followed by washing with HCl aqueous solution. The prepared samples were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, thermal analysis and N2 adsorption/desorption. In order to determine the palladium uptake ability of different HNT samples, the interaction between HNTs and Pd(II) was subsequently studied in aqueous solution at pH 9 (NH+4/NH3 buffer). Transmission electron microscopy showed that the diameter of the nanotubes depends on the preparation conditions. Chemical analysis of residual sodium and thermal studies showed that the chemical formula of the two prepared HNT was HxNa2 − xTi2O5⋅H2O with x=1.61x=1.61 or 1.65. The HNTs are mesoporous materials with a multi-walled nanotubular structure and high specific surface area. In order to determine the capacity of palladium retention of different HNTs samples, the interaction between HNTs and Pd(II) was subsequently studied in aqueous solution at pH 9 (NH+4/NH3 buffer). The adsorption kinetics of Pd(II) on the HNTs was very fast. The isotherms of Pd(II) on the HNTs showed that the adsorption occurred (1) initially through cationic exchange and (2) when the concentration of Pd(II) is high by precipitation of different Pd salts. The adsorption capacity of Pd(II) is strongly altered by the morphology of the HNTs samples.

The HNTs-1 sample (a) is formed of nanotubes with uniform inner and outer diameters (outer diameter ≈ 20 nm). Careful analysis of the HNTs-1 nanotubes showed that they present a multi-layered structure (2 to 5 layers) (inset a). The interlamellar space ranges between 0.25 and 0.37 nm. On the contrary, the HNTs-2 nanotubes (b) have an outside diameter 10 times more important than for the HNTs-1 nanotubes (outer diameter ≈ 100–300 nm). Moreover, the multi-layered structure was not clearly apparent.Figure optionsDownload as PowerPoint slide