Mikkel Juelsholt1
University of Oxford1
The goal of materials science is to develop new materials with useful properties that can improve the world we live in. At the moment synthesising new materials rely almost solely on educated guesses and trial-and-error methods.<sup>1,2</sup> As materials become more and more complex, this approach becomes unsustainable because the number of possible synthetic parameters grows infinitely large.<sup>1,2</sup> Instead, we need to move to a rational synthesis approach where we design the synthesis of materials based on an in-depth knowledge of the chemistry governing the formation of solids.<sup>1,2</sup> However, we currently have little knowledge of the chemistry controlling the formation of a new phase.<sup>1,2</sup> To understand the chemistry of materials formation, it is necessary to investigate the chemical reaction as they happen using in situ methods.<sup>2,3,4</sup><br/>In this study, we use in situ total scattering with Pair Distribution Function (PDF) analysis to investigate the solvothermal synthesis of tungsten oxide nanoparticles. We show how the structure of the precursor at the moment just prior to nucleation can induce the formation of a metastable phase. We show how both solvent and temperature can also influence the precursor structure and induce the formation of a metastable phase. The tungsten oxide nanoparticles are synthesised from a solution of polyoxometalates, which are large polyanions composed of tungsten and oxygen. The use of <i>in situ</i> total scattering and PDF enables us to follow the entire reaction in one experiment and identify the different polyoxometalates formed as well as all formed solid phases. This enables us to map the hydrothermal chemistry of tungsten oxide as a function of pH, precursor and counterions and how they govern the formation of metastable phases.<br/><br/>1. Soderholm, L.; Mitchell, J. F., Perspective: Toward “synthesis by design”: Exploring atomic correlations during inorganic materials synthesis. <i>APL Materials </i><b>2016,</b> <i>4</i> (5), 053212.<br/>2. Bojesen, E. D.; Iversen, B. B., The chemistry of nucleation. <i>CrystEngComm </i><b>2016,</b> <i>18</i> (43), 8332-8353.<br/>3. Juelsholt, M.; Lindahl Christiansen, T.; Jensen, K. M. Ø., Mechanisms for Tungsten Oxide Nanoparticle Formation in Solvothermal Synthesis: From Polyoxometalates to Crystalline Materials. <i>The Journal of Physical Chemistry C </i><b>2019</b>.<br/>4. Juelsholt, M.; Aalling-Frederiksen, O.; Lindahl Christiansen, T.; Kjær, E. T. S.; Lefeld, N.; Kirsch, A.; Jensen, K. M. Ø. Influence of Precursor Structure on the Formation of Tungsten Oxide Polymorphs. <i>ChemRxiv</i> <b>2023</b>