Synthesis of early transition metal oxide nanomaterials and their conversion to nitrides
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RESEARCH PAPER
Synthesis of early transition metal oxide nanomaterials and their conversion to nitrides Anastasia M. Kastl & Andrew P. Purdy J. Butcher
&
Raymond
Received: 23 December 2019 / Accepted: 2 October 2020 # This is a U.S. Government work and not under copyright protection in the US; foreign copyright protection may apply 2020
Abstract The synthesis of nanorods and nanowires of early transition metal oxides by hydrothermal methods and the conversion of some bulk oxides to nitrides in NH3 flow are both well established. However, the conversion of such oxide nanostructures to nitrides is not as well explored but could be a valuable method of producing nanowires, nanorods, and other asymmetric or high aspect ratio nanoparticles of the highly conductive metal nitrides. In this work, nanostructures of TiO2, V2O5, MoO3, and WO3 and mixtures thereof were synthesized by hydrothermal reactions, and conversion into nitride was attempted by heating the oxide material under NH3 flow with or without N2 flow. It was found that slow heating produces the best shape retention, but the nitridized products are porous in even the most favorable cases. The products were characterized by X-ray powder diffraction and scanning electron Electronic supplementary material The online version of this article (https://doi.org/10.1007/s11051-020-05038-8) contains supplementary material, which is available to authorized users. A. M. Kastl NREIP Intern, Chemistry Division, Naval Research Laboratory, Washington 20375 DC, USA A. P. Purdy (*) Chemistry Division Code 6100, Naval Research Laboratory, Washington, DC 20375, USA e-mail: [email protected] R. J. Butcher College of Arts & Sciences, Professor of Inorganic & Structural Chemistry, Howard University, Washington, DC 20059, USA
microscopy. Two-point conductivity measurements were done on the nitride materials, and optical measurements to characterize the plasmon absorption were done in favorable cases. Keywords Nanowires . Nanorods . Titanium dioxide . Vanadium oxide . Molybdenum oxide . Tungsten oxide . Titanium nitride . Vanadium nitride . Molybdenum nitride . Nitridation . Hydrothermal reactions . Crystal structures
Introduction Most of the nitrides of the early transition metals are refractory materials with metallic electrical conductivity and in the case of TiN is actually more conductive than elemental Ti (Lengauer et al. 1995). Conductive nanowires are useful for a number of purposes such as the preparation of conductive transparent composites (Zhang and Engholm 2018; Lang et al. 2020), and inexpensive methods of bulk preparation of conductive nitride nanowires are desirable. Few methods exist for the direct synthesis of metal nitride nanowires (for some, see Joshi et al. 2005; Ding et al. 2013), but most of the early transition metal oxides, with the exception of ZrO2 and HfO2, can be converted to the nitrides by heating at 1200 °C or less under flowing NH3 (Gou et al. 2017; Mangamma et al. 2007; Howell et al. 2018; Tan et al. 1994; Sharma et al. 2001; Lerch 1996;
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