Is There a Negative Thermal Expansion in Supported Metal Nanoparticles? An In-Situ X-ray Absorption Study Coupled with Neural Network Analysis

Interactions with their support, adsorbates and unique structural motifs are responsible for the many intriguing properties and potential applications of supported metal nanoparticles (NPs). At the same time, they complicate the interpretation of experimental data. In fact, the methods and approaches that work well for the ex situ analysis of bulk materials may be inaccurate or introduce artifacts in the in situ analysis of nanomaterials. Here we revisit the controversial topic of negative thermal expansion and anomalies in the Debye temperature reported for oxide-supported metal NPs. In situ X-ray absorption experimental data collected for Pt NPs in ultrahigh vacuum and an advanced data analysis approach based on an artificial neural network demonstrate that Pt NPs do not exhibit intrinsic negative thermal expansion. Similarly as for bulk materials, in the absence of adsorbates the bond lengths in metal NPs increase with temperature. The previously reported anomalies in particle size-dependent Debye temperatures can also be linked to the artifacts in the interpretation of conventional X-ray absorption data of disordered materials such as NPs

Genética bioquímica del calamar argentino, Illex Argentinus

Previously reported results on natural populations of the Argentinean squid, Illex argentinus, urged further studies using electrophoretically detectable loci. The muscles of 202 adult squids caught in the Argentinean Sea were examined. Electrophoretic and staining methods for the 46 enzymes studied are given in detail. Forty-seven loci were detected (20 polymorphic), 45 of which are considered useable in population genetics screening. The expression of the loci coding for these enzymes is described and interpreted, and the presented results will serve as a basis for a more detailed examination of genetic variation in Argentinean squid populations.Estudios biológicos previos realizados en el calamar argentino, Illex argentinus, han sugerido la conveniencia de profundizar en el conocimiento de la estructura poblacional de la especie, utilizando el análisis genético de proteínas detectables electroforéticamente. Con esta finalidad se analizó el músculo esquelético de un total de 202 individuos capturados en el Mar Argentino. Se utilizó la técnica de electroforesis horizontal en gel de almidón al 11%. Se estudiaron 46 sistemas enzimáticos distintos. La expresión de los loci para estos enzimas son descritos e interpretados en detalle. Un total de 47 loci fueron detectados (20 polimórficos), de los cuales 45 se consideran utilizables para el análisis de la estructura poblacional de la especie

Unequal Partnerships in Higher Education: Pedagogic Innovations in an Electronics within Physics Degree Course

This cross-European research partnership reports on supporting pro-active learning and teaching. The two-part project firstly explored student beliefs about electronics within a physics degree and secondly, the use of peer assessment of a Mathematica notebook to develop understandings of standards and quality. Student beliefs were explored because of the negative perceptions tutors thought students brought to the Engineering course within the Physics degree. The results showed that tutors’ fears were unfounded and that the students were highly motivated. Secondly, through peer assessment of a notebook, students developed critical understandings of standards and quality. Generally, students valued the content support and appreciated both the work of their peer and how this helped their own understanding. Esta investigación realizada por un partenariado transeuropeo se centra en el apoyo proactivo de la enseñanza y el aprendizaje en la educación superior. Este proyecto consta de dos partes. Primero se exploraron las creencias de los estudiantes sobre la electrónica en el grado de Física para, después, usar la evaluación por pares del manual Mathematica para desarrollar la comprensión de los estandares y calidad. Las creencias de los estudiantes se exploraron teniendo en cuenta las percepciones negativas que los tutores pensaban que tenían los estudianties del curso de Ingeniería en el grado de Física. Los resultados destacaron que los miedos de los tutores eran infundados y que los estudiantes se mostraban altamente motivados. Segundo, a través de la evaluación a pares del manual, el alumnado desarrolló una comprensión crítica de los estandares y su calidad. Generalmente, el alumnado valoró el apoyo sobre el contenido y apreció tanto el trabajo de sus compañeros y como éste les había ayudado en su comprensión

Piece by Piece-Electrochemical Synthesis of Individual Nanoparticles and their Performance in ORR Electrocatalysis

The impact of individual HAuCl4 nanoreactors is measured electrochemically, which provides operando insights and precise control over the modification of electrodes with functional nanoparticles of well‐defined size. Uniformly sized micelles are loaded with a dissolved metal salt. These solution‐phase precursor entities are then reduced electrochemically—one by one—to form nanoparticles (NPs). The charge transferred during the reduction of each micelle is measured individually and allows operando sizing of each of the formed nanoparticles. Thus, particles of known number and sizes can be deposited homogenously even on nonplanar electrodes. This is demonstrated for the decoration of cylindrical carbon fibre electrodes with 25±7 nm sized Au particles from HAuCl4‐filled micelles. These Au NP‐decorated electrodes show great catalyst performance for ORR (oxygen reduction reaction) already at low catalyst loadings. Hence, collisions of individual precursor‐filled nanocontainers are presented as a new route to nanoparticle‐modified electrodes with high catalyst utilization

Identifying structure-selectivity correlations in the electrochemical reduction of CO₂: a comparison of well-ordered atomically-clean and chemically-etched Cu single crystal surfaces

Despite significant theoretical efforts, the identification of the active sites for the electrochemical reduction of CO2 (CO2RR) to specific chemical products has remained elusive. This is partially due to insufficient experimental data gathered on clean and atomically well-ordered electrode surfaces. Here, ultrahigh vacuum based preparation methods and surface science characterization techniques are used together with gas chromatography to demonstrate that subtle changes in the preparation of well-oriented Cu(100) and Cu(111) single crystal surfaces drastically affect their CO2RR selectivity. Copper single crystals with clean, flat, and atomically ordered surfaces are theoretically predicted to yield hydrocarbons. However, these were found experimentally to favour the production of H2. Only when roughness and defects are introduced, for example through an electrochemical etchingor a plasmatreatment, significant amounts of hydrocarbons are generated. These results clearly indicate that structural and morphological effects are the key factors determining the catalytic selectivity of CO2RR

Identifying structure-selectivity correlations in the electrochemical reduction of CO₂: a comparison of well-ordered atomically-clean and chemically-etched Cu single crystal surfaces

Despite significant theoretical efforts, the identification of the active sites for the electrochemical reduction of CO2(CO2RR) to specific chemical products has remained elusive. This is partially due to insufficient experimental data gathered on clean and atomically well-ordered electrode surfaces. Here, ultrahigh vacuum based preparation methods and surface science characterization techniques are used together with gas chromatography to demonstrate that subtle changes in the preparation of well-oriented Cu(100) and Cu(111) single crystal surfaces drastically affect their CO2RR selectivity. Copper single crystals with clean, flat, and atomically ordered surfaces are theoretically predicted to yield hydrocarbons. However, these were found experimentally to favour the production of H2. Only when roughness and defects are introduced, for example through an electrochemical etching or a plasma treatment, significant amounts of hydrocarbons are generated. These results clearly indicate that structural and morphological effects are the key factors determining the catalytic selectivity of CO2RR

Comparative analysis of rigidity across protein families

We present a comparative study in which 'pebble game' rigidity analysis is applied to multiple protein crystal structures, for each of six different protein families. We find that the main-chain rigidity of a protein structure at a given hydrogen bond energy cutoff is quite sensitive to small structural variations, and conclude that the hydrogen bond constraints in rigidity analysis should be chosen so as to form and test specific hypotheses about the rigidity of a particular protein. Our comparative approach highlights two different characteristic patterns ('sudden' or 'gradual') for protein rigidity loss as constraints are removed, in line with recent results on the rigidity transitions of glassy networks

Shape-Selection of Thermodynamically Stabilized Colloidal Pd and Pt Nanoparticles Controlled via Support Effects

Colloidal chemistry, in combination with nanoparticle (NP)/support epitaxial interactions is used here to synthesize shape-selected and thermodynamically stable metallic NPs over a broad range of NP sizes. The morphology of three-dimensional palladium and platinum NPs supported on TiO₂(110) was investigated using scanning tunneling microscopy. Well-defined Pd and Pt NPs were synthesized via inverse micelle encapsulation. The initially spherical NPs were found to become faceted and form an epitaxial relationship with the support after high-temperature annealing (e.g., 1100 °C). Shape selection was achieved for almost all Pd NPs, namely, a truncated octahedron shape with (111) top and interfacial facets. The Pt NPs were however found to adopt a variety of shapes. The epitaxial relationship of the NPs with the support was evidenced by the alignment of the cluster’s edges with TiO₂(110)-[001] atomic rows and was found to be responsible for the shape control. The ability of synthesizing thermally stable shape-selected metal NPs demonstrated here is expected to be of relevance for applications in the field of catalysis, since the activity and selectivity of NP catalysts has been shown to strongly depend on the NP shape

Promoted Thermal Reduction of Copper Oxide Surfaces by N-Heterocyclic Carbenes

The influence of metallic and oxide phases coexisting on surfaces is of fundamental importance in heterogeneous catalysis. Many reactions lead to the reduction of the oxidized areas, but the elucidation of the mechanisms driving these processes is often challenging. In addition, intermediate species or designed organic ligands increase the complexity of the surface. In the present study, we address the thermal reduction of a copper oxide overlayer grown on Cu(111) in the presence of N-heterocyclic carbene (NHC) ligands by means of scanning tunneling microscopy (STM) and density functional theory (DFT). We show that the NHC ligands actively participate in the copper oxide reduction, promoting its removal at temperatures as low as 470 K. The reduction of the oxide was tracked by employing scanning tunneling spectroscopy (STS), providing a chemical identification of metallic and oxide areas at the nanometric scale

Growth of N-Heterocyclic Carbene Assemblies on Cu(100) and Cu(111): from Single Molecules to Magic-Number Islands

N-Heterocyclic carbenes (NHCs) have superior properties as building blocks of self-assembled monolayers (SAMs). Understanding the influence of the substrate in the molecular arrangement is a fundamental step before employing these ligands in technological applications. Herein, we study the molecular arrangement of a model NHC on Cu(100) and Cu(111). While mostly disordered phases appear on Cu(100), on Cu(111) well-defined structures are formed, evolving from magic-number islands to molecular ribbons with coverage. This work presents the first example of magic-number islands formed by NHC assemblies on flat surfaces. Intermolecular interactions, diffusion and commensurability are key factors explaining the observed arrangements. These results shed light on the molecule-substrate interaction and open the possibility of tuning nanopatterned structures based on NHC assemblies