Borohydride Synthesis for Development of Porous Zirconium Oxide Nanopowders for Novel Applications

Abstract

The concept of this Ph.D. research work is to find out a suitable in-situ gas-bubbles evolving aqueous precipitating agent to develop loose or agglomeration free powders of amorphous zirconium hydroxide in the as-synthesized condition and further to develop a moderate temperature stable amorphous or crystalline zirconium oxide nanopowders with porous structure for use in different novel applications.
This research work discloses the importance of aqueous sodium borohydride (NaBH4) as a precipitating agent towards the development of moderate temperature stable amorphous and crystalline nature of zirconium oxide with porous structure. The role of boron species as well as in-situ hydrogen (H2) gas-bubbles present in aqueous NaBH4 are presented in this research work for the development of porous zirconium oxide nanopowders. Also, we are reporting, a new concept of reaction mechanism between aqueous ZrOCl2•8H2O and NaBH4 with the help of Fourier Transformation Infra-Red (FTIR) spectroscopy for producing zirconium hydroxide loose powders in the as-synthesized condition. In addition, we are emphasis on advantages of aqueous NaBH4 for the development of porous zirconium oxide nanopowders for removal of toxic ion such Pb (II) for environmental applications. The removal efficiency of Pb (II) as a function of time as well as adsorption kinetic mechanism and regeneration of Pb (II) loaded zirconium oxide sample was studied in detail. Quick adsorption of almost hundred percentages of toxic lead ions from water solution within 15 minutes as well as regeneration study suggests that the porous zirconium oxide can be a potential adsorbent for removal of toxic ions for environmental applications.
Further, a novel information on the temperature-mediated phase transformation, pore geometry as well as pore hysteresis transformation of in-born porous zirconium hydroxide nanopowders with the help of X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET) isotherm and Transmission Electron Microscopy (TEM) images was also discussed in this research work.The novel hydrogen (H2) gas-bubbles assisted borohydride synthesis route led to develop thermally stable porous zirconium hydroxide/oxide nanopowders with an adequate pore size, pore volume, and surface area and thus these porous materials are further suggested for promising use in different areas of applications.
Moreover, using borohydride synthesis route, the rare earth ions [Eu3+ (5 mol%), Tb3+(5 mol%), and mixture of Eu3+(2 mol%) and Tb3+(5 mol%)] are incorporated in porous zirconium oxide to stabilize t- or c-phase of porous zirconia as well as to develop multi-colour phosphor nanomaterials using various excitation wavelengths ranging from 205 nm to 350 nm. Structure, powder morphology, rare-earth ion distribution, luminescence and sample colour under UV light were studied for these phosphor nanomaterials for suitability in lighting applications.
In summary, the borohydride synthesis route using sodium borohydride is found to be a potential precipitating reagent for the development of moderate temperature stable amorphous as well as crystalline t-zirconia with a porous structure for possible applications in the field of adsorption of heavy metal ions as well as rare earth based porous zirconia powders for lighting applications.