Exploration of anion effects in solvothermal synthesis using in situ X-ray diffraction.

Solvothermal synthesis presents a facile and highly flexible approach to chemical processing and it is widely used for preparation of micro- and nanosized inorganic materials. The large number of synthesis parameters in combination with the richness of inorganic chemistry means that it is difficult to predict or design synthesis outcomes, and it is demanding to uncover the effect of different parameters due to the sealed and complex nature of solvothermal reactors along with the time demands related to reactor cleaning, sample purification, and characterization. This study explores the effect on formation of crystalline products of six common anions in solvothermal treatment of aqueous and ethanolic precursors. Three different cations are included in the study (Mn2+, Co2+, Cu2+) representing chemical affinities towards different regions of the periodic table with respect to the hard soft acid base (HSAB) classification and the Goldschmidt classification. They additionally belong to the commonly used 3d transition metals and display a suitable variety in solvothermal chemistry to highlight anion effects. The results of the solvothermal in situ experiments demonstrate a clear effect of the precursor anions, with respect to whether crystallization occurs or not and the characteristics of the formed phases. Additionally, some of the anions are shown to be redox active and to influence the formation temperature of certain phases which in turn relates to the observed average crystallite sizes.

Unveiling the formation mechanism of PbxPdy intermetallic phases in solvothermal synthesis using in situ X-ray total scattering.

Pd possesses attractive catalytic properties and nano-structuring is an obvious way to enhance catalytic activity. Alloying Pd with Pb has been shown to enhance the catalytic effect of alcohol oxidation. Further optimization of the catalytic effect can be accomplished by controlling the particle size and key to this is understanding the formation mechanism. By monitoring solvothermal syntheses using in situ X-ray total scattering, this study unveils the formation mechanism of PbxPdy intermetallic nanoparticles. The formation occurs through a multi-step mechanism. Initially, Pd nanoparticles are formed, followed by incorporation of Pb into the Pd-structure, thus forming PbxPdy intermetallic nanoparticles. By varying the reaction time and temperature, the incorporation of Pb can be controlled, thereby tailoring the phase outcome. Based on the in situ solvothermal syntheses, ex situ autoclave syntheses were performed, resulting in the synthesis of Pb3Pd5 and Pb9Pd13 with a purity above 93%. The catalytic effect of these intermetallic phases towards the hydrogen evolution reaction (HER) is assessed. It is found that Pd, Pb3Pd5, and Pb9Pd13 have comparable stabilities, however, the overpotential increases with increasing amounts of Pb.

Pair Distribution Function from Liquid Jet Nanoparticle Suspension using Femtosecond X-ray Pulses.

X-ray scattering data measured on femtosecond timescales at the SACLA X-ray Free Electron Laser (XFEL) facility on a suspension of HfO2 nanoparticles in a liquid jet were used for pair distribution function (PDF) analysis. Despite a non-optimal experimental setup resulting in a modest Qmax of ~8 Å-1 , a promising PDF was obtained. The main features were reproduced when comparing the XFEL PDF to a PDF obtained from data measured at the PETRA III synchrotron light source. Refining structural parameters such as unit cell dimension and particle size from the XFEL PDF provided reliable values. Although the reachable Qmax limited the obtainable information, the present results indicate that good quality PDFs can be obtained on femtosecond timescales if the experimental conditions are further optimized. The study therefore encourages a new direction in ultrafast structural science where structural features of amorphous and disordered systems can be studied.

Synthesis of Ge1-xSnx nanoparticles under non-inert conditions.

Ge1-xSnx nanoparticles are interesting for a variety of different optoelectronic devices, however, the synthesis normally involves highly inert conditions, making it less available and promising for future industry implementation. Here, a new non-inert synthesis route is presented which involves preparation of the synthesis under ambient conditions followed by a reaction in autoclaves at temperatures between 400 °C and 500 °C and pressures between 52 bar and 290 bar. The product formation is also investigated with in situ powder X-ray diffraction (PXRD) to study the effect of the reaction parameters in more detail, e.g. showing that the Sn-precursor catalyzes the reaction. The synthesized phase pure Ge1-xSnx nanoparticles have Sn concentrations ranging from 0 to ∼4% and crystallite sizes ranging from approximately 11 nm to 25 nm. If the Sn-precursor concentration is increased further, ß-Sn is formed as an impurity phase accompanied by an increase in the size of the Ge1-xSnx particles, making sizes of up to about 55 nm available.

Composition space of PtIrPdRhRu high entropy alloy nanoparticles synthesized by solvothermal reactions.

High entropy alloy (HEA) nanoparticles hold promise in heterogeneous catalysis, and recently, simple and benign solvothermal synthesis was achieved for the equimolar PtIrPdRhRu. Here we experimentally explore the available composition space in this system, and we find that single-phase products can be obtained at significant deviations from the equimolar case.