Abstract

The present research focuses on the comparative investigation of the acid–base surface properties (the isoelectric point, pH_iep and point of zero charge, pH_pzc) of one-dimensional TiO₂ nanomaterials. Different one-dimensional TiO₂ nanomaterials, nanotubes (NTs) and nanowires (NWs) were prepared by an alkaline hydrothermal synthesis procedure. The structural properties of the synthesized TiO₂ nanomaterials were investigated with high-resolution scanning electron microscopy (HR-SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HR-TEM), atomic force microscopy (AFM), powder X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS).

The NWs and NTs were characterized using Raman and Fourier transform infrared (FT-IR) spectroscopy as well as Brunauer–Emmett–Teller (BET) measurements. Surface properties, i.e. pH_iep and pH_pzc of NWs and NTs were determined from electrokinetic measurements, potentiometric mass and electrolyte titrations. The relative acidity for the NWs is found to be in the interval 3 < pH_iep < 4 in comparison with the NTs, with 4 < pH_iep < 6.

The observed differences in the relative acidity are correlated with differences in crystal structure of the studied nanomaterials and their resulting morphology. In addition, our results reveal a strong electrolyte effect on the characteristic points, pH_iep and pH_pzc, especially the higher cation affinity for both TiO₂ nanomaterials surfaces that has a significant effect on the pH of the system. Application of the multisite complexation (MUSIC) model yields a satisfactory description of the electrokinetic data and can explain observed salt effect.

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