Targeted Synthesis of Nanostructured Oxide Materials
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Targeted Synthesis of Nanostructured Oxide Materials Greta Ricarda Patzke, and Ying Zhou Institute of Inorganic Chemistry, University of Zurich, Winterthurerstrasse 190, Zurich, CH8057, Switzerland ABSTRACT Morphology control is a key challenge in the straightforward hydrothermal production of technologically relevant anisotropic oxide materials. The use of readily available ionic additives as growth modifiers is discussed and compared for molybdenum- and tungsten oxide-based systems, and it is extended to the formation of ternary W/Mo-oxides. Generally, the one-step hydrothermal synthesis of ternary and higher oxides is an important goal, because their properties often outperform those of the binary oxides. This holds especially for the Bi2O3MoO3-VOx (BIMOVOx) system as a rich source of new materials. We present a new solutionbased approach to α-Bi2O3 nanobelts starting from commercial Bi2O3 and K2SO4 as a key step on the way to anisotropic BIMOVOx-oxides. This hydrothermal process is an illustrative example of highly selective and efficient morphology control through an inorganic additive. As mechanistic and kinetic studies are crucial for the design of complex oxide nanomaterials, the Bi2O3-K2SO4 system is compared to our previous studies on Mo-, W- and V-oxides with respect to its hydrothermal parameter window and robustness. INTRODUCTION Transition metal oxides (TMOs) are an indispensable part of modern materials chemistry [1-3]. Their manifold structural motifs lead to a wide variety of applications, e.g. as semiconductors, catalysts, sensors, battery and electrochromic materials and superconductors [4, 5]. Therefore, the production of anisotropic nanostructured TMOs and their combination with other oxide materials is important to provide building blocks for a future nanotechnology [6 - 9]. This calls for efficient, straightforward and ecologically friendly synthetic methods. Hydrothermal methods fulfil all these criteria, and they offer exceptional synthetic flexibility as an additional advantage [10]. This renders them especially appropriate for the challenging synthesis of anisotropic TMO nanoparticles on a larger scale [11-12]. Their only drawback is that they often require a very specific adjustment of the reaction parameters within a given experimental window. How can the width of a given parameter window be estimated when setting up a new hydrothermal process? Over the past years, our research has been focused on the hydrothermal preparation of anisotropic molybdenum- [13-14], tungsten- [15] and vanadium oxides [16]. Special emphasis has been placed on the elucidation of the mechanistic pathways leading to oxide rods with a high application potential, especially for the development of catalysts and sensors. Therefore, we have assigned the hydrothermal growth mechanisms of MoO3 rods, nanostructured tungstates and mixed nanostructured W/Mo-oxide materials with new in situ EDXRD/EXAFS approaches [13, 15, 17]. The study of mixed oxide systems is exceptionally important, because they often disp
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