Mechanisms for Tungsten Oxide Nanoparticle Formation in Solvothermal Synthesis: From Polyoxometalates to Crystalline Materials

TY - JOUR

T1 - Mechanisms for Tungsten Oxide Nanoparticle Formation in Solvothermal Synthesis: From Polyoxometalates to Crystalline Materials

AU - Juelsholt, Mikkel

AU - Christiansen, Troels Lindahl

AU - Jensen, Kirsten M. O.

PY - 2019/2/28

Y1 - 2019/2/28

N2 - Understanding nucleation mechanisms of the solid state on an atomic scale is crucial in order to develop new synthesis methods for tailored materials. Here, we use in situ X-ray total scattering to follow the structural rearrangements that take place in the formation of tungsten oxide, all the way from the ionic precursor clusters in solution to the final crystalline nanoparticles. The reaction was performed in water and oleylamine to study the influence of solvent, and in both cases, the clusters present in the precursor solution adopted the well-known α-Keggin polyoxometalate structure. However, despite the similarity between precursor cluster and the final crystallographic phase, the reaction route is highly dependent on the solvent, shedding new light on nucleation mechanisms and their influence of defects in the final oxide structure. In water, the precursor cluster partly rearranges to the tungstate Y cluster before crystallization of tungsten bronze nanoparticles with a large degree of [WO 6 ] disorder along the c direction of the unit cell. In oleylamine, the reaction goes through several steps, including an amorphous phase and an intermediate crystalline pyrochlore phase before forming small, ordered tungsten bronze nanoparticles. The solvent thus affects not only the crystallite size but also the atomic structure of the nanoparticles, which we link to the observed reaction mechanism.

AB - Understanding nucleation mechanisms of the solid state on an atomic scale is crucial in order to develop new synthesis methods for tailored materials. Here, we use in situ X-ray total scattering to follow the structural rearrangements that take place in the formation of tungsten oxide, all the way from the ionic precursor clusters in solution to the final crystalline nanoparticles. The reaction was performed in water and oleylamine to study the influence of solvent, and in both cases, the clusters present in the precursor solution adopted the well-known α-Keggin polyoxometalate structure. However, despite the similarity between precursor cluster and the final crystallographic phase, the reaction route is highly dependent on the solvent, shedding new light on nucleation mechanisms and their influence of defects in the final oxide structure. In water, the precursor cluster partly rearranges to the tungstate Y cluster before crystallization of tungsten bronze nanoparticles with a large degree of [WO 6 ] disorder along the c direction of the unit cell. In oleylamine, the reaction goes through several steps, including an amorphous phase and an intermediate crystalline pyrochlore phase before forming small, ordered tungsten bronze nanoparticles. The solvent thus affects not only the crystallite size but also the atomic structure of the nanoparticles, which we link to the observed reaction mechanism.

U2 - 10.1021/acs.jpcc.8b12395

DO - 10.1021/acs.jpcc.8b12395

M3 - Journal article

SN - 1932-7447

VL - 123

SP - 5110

EP - 5119

JO - Journal of Physical Chemistry C

JF - Journal of Physical Chemistry C

IS - 8

ER -