Sorption of Organic Compounds, Oxyanions, and Heavy Metal Ions on Surfactant Modified Titanate Nanotubes

The adsorption capacities and mechanisms of organic compounds with water solubilities (S-w) ranging from 55 to 75 000 mg/L, oxyanions, and heavy metal ions onto surfactant (hexadecyltrimethylammonium, HDTMA) modified titanate nanotubes (TNT) were investigated. Effects of the HDTMA-modified process on the revolution of microstructures and surface chemical characteristics of TNT were characterized with scanning electron microscopy (SEM), transmission electron microscopy (TEM), nitrogen adsorption-desorption isotherms, Fourier transform infrared spectroscopy (FTIR), and zeta potential. The adsorption isotherms of selected adsorbates on the HDTMA-modified TNT (HMTNT) were measured to understand the effects of the surfactant-modified process on the adsorption properties of TNT. It was found that HMTNT possessed both hydrophilic and hydrophobic surfaces to uptake organic compounds with various S-w values. On the other hand, since the hydrophobic bonding by conglomeration of large C-16 alkyl groups associated with HDTMA could render a positive charge development on the surface of TNT, HMTNT could simultaneously adsorb the oxyanions (on the surface covered by HDTMA) and heavy metal ions (on the surface not covered by HDTMA) through the anion and cation exchange mechanisms, respectively. It was experimentally concluded that HMTNT might be regarded as an amphiphilic and dual-electronic adsorbent, which could effectively remove many different kinds of contaminants. The regeneration of HMTNT was also briefly discussed.