Metal ion-intercalated layered hydrogen tri-titanate nanotubes: synthesis, characterization and their use in ultrafast and enhanced removal of hazardous contaminant fluoride from water

Abstract

Titanate nanotubes are a versatile class of materials with a myriad of potential applications. In the present work, hydrogen titanate nanotubes (HTNTs) were functionalized with metal ions, Ce(III), Ca(II), Cu(II), Mg(II), Ni(II) and Ag(I) to enhance the surface properties. The layered crystallographic structure of the HTNTs aided in the efficient intercalation of the metal ions. The developed metal ion-incorporated titanate nanotubes (MTNTs) were thoroughly characterized and studied to understand their physicochemical properties. The phase and structure of the materials were studied through X-ray diffraction, Raman and FTIR spectroscopy. The hollow nanotubular morphology and the incorporation of metal ions into the MTNTs were confirmed by the TEM images and EDS analysis, respectively. The highly porous nature and high surface area of the materials were elucidated by the analysis of BET-based nitrogen adsorption and desorption isotherms. The surface area values were in the range of 165–247 m² g⁻¹. The optical properties were analysed using UV-VIS spectroscopy and the band gaps were found to be in the range of 2.57–3.21 eV. The materials were further applied towards adsorption of fluoride ions from water. The effects of various parameters on the adsorption were studied in batch mode. The Langmuir adsorption capacities of the MTNTs were in the range of 98.35–183.34 mg g⁻¹, in the order CaTNTs > AgTNTs > CuTNTs > CeTNTs > NiTNTs > MgTNTs > HTNTs. In addition to their high efficiencies, the MTNTs also showed ultrafast removal of fluoride from water within just 1 min of contact time. The metal ion incorporation into the HTNT structure therefore made them superior fluoride adsorbents compared to the parent material.