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Staniuk M.,ETH Zurich | Zindel D.,ETH Zurich | Van Beek W.,Swiss Norwegian Beamlines at European Synchrotron Research Facility | Hirsch O.,ETH Zurich | And 3 more authors.
CrystEngComm | Year: 2015

Although syntheses in organic solvents provide access to a wide range of copper-based nanoparticles, the correlation between organic reactions in solution and nucleation and growth of nanoparticles with defined properties is not well understood. Here, we utilize the Multivariate Curve Resolution-Alternative Least Squares (MCR-ALS) methodology to examine spectroscopic data recorded in situ during the synthesis of copper-based nanoparticles. While earlier studies showed that depending on the temperature copper(ii) acetylacetonate reacts with benzyl alcohol and forms either copper oxides or copper nanoparticles, we link the inorganic reaction with their organic counterparts. From X-ray Absorption Near Edge Spectroscopy (XANES) and Ultraviolet-visible spectroscopy (UV-vis) data we learn that copper(i) oxide forms directly from the solution and is the final product at low temperature of 140 °C. We observe in Fourier Transformed Infrared (FTIR) spectra an increasing concentration of benzyl acetate that co-occurs with the formation of a copper enolate and evolution of benzaldehyde, which accompanies the reduction of copper ions. We also record the interaction of organic species at the Cu2O surface, which inhibits a further reduction to metallic copper. When we raise the synthesis temperature to 170 °C it turns out that the Cu2O is just an intermediate species. It subsequently transforms by solid-state reduction to metallic copper accompanied by oxidation of benzyl alcohol to benzaldehyde. This journal is © The Royal Society of Chemistry.

Staniuk M.,ETH Zurich | Hirsch O.,ETH Zurich | Kranzlin N.,ETH Zurich | Bohlen R.,ETH Zurich | And 3 more authors.
Chemistry of Materials | Year: 2014

Here, we show a simple approach to synthesize cobalt and cobalt oxide nanoparticles in an organic solvent. We find that the cubic Co3O 4 nanoparticles can be easily obtained, even at temperatures as low as 80 °C. Moreover, exactly the same reaction at 180 °C leads to metallic Co nanoparticles. Thus, in addition to the synthetic efforts, we study the mechanism of occurrence of oxidation and reduction of a Co2+ precursor in benzyl alcohol. Remarkably, the in situ X-ray absorption and diffraction measurements of the synthesis at 140 °C reveal that oxidation of Co2+ to Co3+/2+ and reduction of Co2+ to Co0 reactions take place simultaneously. It is followed by a rapid formation of Co3O4 nanoparticles and its consecutive solid-state reduction to CoO. In parallel, metallic Co nanoparticles begin to grow. In addition, Multicomponent Curve Resolution-Alternating Least Squares (MCR-ALS) analysis of X-ray absorption spectroscopy (XAS) data efficiently reveals the nontrivial interdependence between four different reactions. Our strategy to control reduction and oxidation of Co-based nanoparticles as they grow opens up an elegant pathway for the one-pot-synthesis of the hybrid materials for energy-related applications. © 2014 American Chemical Society.

Kranzlin N.,ETH Zurich | Staniuk M.,ETH Zurich | Heiligtag F.J.,ETH Zurich | Luo L.,ETH Zurich | And 4 more authors.
Nanoscale | Year: 2014

We use in situ X-ray absorption and diffraction studies to directly monitor the crystallization of different titania polymorphs in one and the same solution. We find that, despite the commonly accepted polymorphic-crossover from anatase to rutile triggered by the critical size of nanoparticles, in the solution their respective nucleation and growth are independent processes. Moreover, we find that 5.9 nm rutile nanoparticles are formed prior to the formation of 8.4 nm anatase nanoparticles. Our results suggest that the origins of this crystallization mechanism lie in the formation of an intermediate non-crystalline phase and in time-dependent changes in the chemical environment. This journal is © The Royal Society of Chemistry.

Hirsch O.,ETH Zurich | Zeng G.,ETH Zurich | Luo L.,ETH Zurich | Staniuk M.,ETH Zurich | And 6 more authors.
Chemistry of Materials | Year: 2014

Here, we present a synthesis of MoO2 nanoparticles doped with 2 at% of Ni in a mixture of acetophenone and benzyl alcohol at 200 °C. Based on in situ X-ray absorption near-edge structure (XANES) and ex situ extended X-ray absorption fine structure (EXAFS) measurements at Ni K-edge and Mo K-edge, we discuss scenarios on how the "doping" reaction, that is, the incorporation of Ni in the MoO2, proceeds. We can clearly exclude the formation of NiO or Ni nanoparticles. Moreover, within the resolution of our in situ XANES experiments, we observe that the ternary compound Ni:MoO2 nucleates directly in the final composition. Although the local structure around the Ni ion adopts the MoO2 crystal structure pointing at the substitution of tetravalent Mo by Ni, we find that Ni remains divalent. This aliovalent substitution results in the relaxation of the local structure, which is additionally reflected in the slight shrinking of the total volume of the unit cell of Ni:MoO2. Interestingly, such a small amount of divalent Ni has a tremendous effect on the performance of the material as anode in Li-ion batteries. The initial discharge capacity of Ni:MoO2 based anodes almost doubles from 370 mAh/g for MoO2 to 754 mAh/g for Ni:MoO 2 at 0.1 C (1 C = 300 mA/g). Additionally, we observed an atypical increase of capacity for both MoO2 and Ni:MoO2 anodes upon cycling with increasing cycling rate. © 2014 American Chemical Society.

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