Unveiling the Ir single atoms as selective active species for the partial hydrogenation of butadiene by operando XAS.

Single-atom catalysts represent an intense topic of research due to their interesting catalytic properties for a wide range of reactions. Clarifying the nature of the active sites of single-atom catalysts under realistic working conditions is of paramount importance for the design of performant materials. We have prepared an Ir single-atom catalyst supported on a nitrogen-rich carbon substrate that has proven to exhibit substantial activity toward the hydrogenation of butadiene with nearly 100% selectivity to butenes even at full conversion. We evidence here, by quantitative operando X-ray absorption spectroscopy, that the initial Ir single atoms are coordinated with four light atoms i.e., Ir-X4 (X = C/N/O) with an oxidation state of +3.2. During pre-treatment under hydrogen flow at 250 °C, the Ir atom loses one neighbour (possibly oxygen) and partially reduces to an oxidation state of around +2.0. We clearly demonstrate that Ir-X3 (X = C/N/O) is an active species with very good stability under reactive conditions. Moreover, Ir single atoms remain isolated under a reducing atmosphere at a temperature as high as 400 °C.

Imprinting isolated single iron atoms onto mesoporous silica by templating with metallosurfactants.

HYPOTHESIS: One of the main drawbacks of metal-supported materials, traditionally prepared by the impregnation of metal salts onto pre-synthesized porous supports, is the formation of large and unevenly dispersed particles. Generally, the larger are the particles, the lower is the number of catalytic sites. Maximum atom exposure can be reached within single-atom materials, which appear therefore as the next generation of porous catalysts. EXPERIMENTS: Herein, we designed single iron atom-supported silica materials through sol-gel hydrothermal treatment using mixtures of a non-ionic surfactant (Pluronic P123) and a metallosurfactant (cetyltrimethylammoniumtrichloromonobromoferrate, CTAF) as porogens. The ratio between the Pluronic P123 and the CTAF enables to control the silica structural and textural properties. More importantly, CTAF acts as an iron source, which amount could be simply tuned by varying the non-ionic/metallo surfactants molar ratio. FINDINGS: The fine distribution of iron atoms onto the silica mesopores results from the iron distribution within the mixed micelles, which serve as templates for the polymerization of the silica matrix. Several characterization methods were used to determine the structural and textural properties of the silica material (XRD, N2 sorption isotherms and TEM) and the homogeneous distribution and lack of clustering of iron atoms in the resulting materials (elemental analysis, magnetic measurements, pair distribution function (PDF), MAS-NMR and TEM mapping). The oxidation and spin state of single-iron atoms determined from their magnetic properties were confirmed by DFT calculations. This strategy might find straightforward applications in preparing versatile single atom catalysts, with improved efficiency compared to nanosized ones.

First synthesis of silicon nanocrystals in amorphous silicon nitride from a preceramic polymer.

We report the first synthesis of silicon nanocrystals embedded in a silicon nitride matrix through a direct pyrolysis of a preceramic polymer (perhydropolysilazane). Structural analysis carried out by XRD, XPS, Raman and TEM reveals the formation of silicon quantum dots and correlates the microstructures with the annealing temperature. The photoluminescence of the nanocomposites was investigated by both linear and nonlinear measurements. Furthermore we demonstrate an enhanced chemical resistance of the nitride matrix, compared to the typical oxide one, in both strongly acidic and basic environments. The proposed synthesis via polymer pyrolysis is a striking innovation potentially allowing a mass-scale production nitride embedded Si nanocrystals.

In situ insight into the unconventional ruthenium catalyzed growth of carbon nanostructures.

We report on the in situ analysis of the growth process of carbon nanostructures catalyzed by Ru nanoparticles using syngas, a mixture of hydrogen and CO, as the carbon source at a medium temperature (500 °C). The structural modifications of the dual nanotube/nanoparticle system and the general dynamics of the involved processes have been directly followed during the growth, in real time and at the atomic scale, by transmission electron microscopy in an environmental gas cell at atmospheric pressure. After a reduction step under hydrogen and syngas, the particles became very active for the carbon growth. The growth rate is independent of the particle size which mainly influences the nanotube wall thickness. Other subtle information on the general behavior of the system has been obtained, as for instance the fact that the regular changes in the direction of the particle originate generally from the particle shape fluctuation. The main result is the evidence of a new growth mode in relation to the presence and the high instability of the ruthenium carbide phase which acts as a carbon reservoir. For the first time, a relaxation oscillation of the growth rate has been observed and correlated with the metal-carbide structural transition at the particle sub-surface.

Reactivity and structural evolution of urchin-like Co nanostructures under controlled environments.

In situ transmission electron microscopy (TEM) of samples in a controlled gas environment allows for the real time study of the dynamical changes in nanomaterials at high temperatures and pressures up to the ambient pressure (105 Pa) with a spatial resolution close to the atomic scale. In the field of catalysis, the implementation and quantitative use of in situ procedures are fundamental for a better understanding of the behaviour of catalysts in their environments and operating conditions. By using a microelectromechanical systems (MEMS)-based atmospheric gas cell, we have studied the thermal stability and the reactivity of crystalline cobalt nanostructures with initial 'urchin-like' morphologies sustained by native surface ligands that result from their synthesis reaction. We have evidenced various behaviors of the Co nanostructures that depend on the environment used during the observations. At high temperature under vacuum or in an inert atmosphere, the migration of Co atoms towards the core of the particles is activated and leads to the formation of carbon nanostructures using as a template the initial multipods morphology. In the case of reactive environments, for example, pure oxygen, our investigation allowed to directly monitor the voids formation through the Kirkendall effect. Once the nanostructures were oxidised, it was possible to reduce them back to the metallic phase using a dihydrogen flux. Under a pure hydrogen atmosphere, the sintering of the whole structure occurred, which illustrates the high reactivity of such structures as well as the fundamental role of the present ligands as morphology stabilisers. The last type of environmental study under pure CO and syngas (i.e. a mixture of H2 :CO = 2:1) revealed the metal particles carburisation at high temperature.

Robust raspberry-like metallo-dielectric nanoclusters of critical sizes as SERS substrates.

Raspberry-like nano-objects made of large plasmonic satellites (>10 nm) covering a central dielectric particle have many potential applications as photonic materials, superlenses and (bio-) sensors, but their synthesis remains challenging. Herein, we show how to build stable and robust raspberry-like nano-systems with close-packed satellites, by combining monodisperse silica particles (80 or 100 nm diameter) and oppositely charged noble metal nanoparticles (Au or Ag) with well-defined sizes (10-50 nm). The spectral characteristics of their associated plasmonic resonances (wavelength, linewidth, extinction cross-section) and the electromagnetic coupling between satellites were observed using the spatial modulation spectroscopy technique and interpreted through a numerical model. The composite nano-objects exhibit numerous hot spots at satellite junctions, resulting in excellent surface-enhanced Raman scattering (SERS) performance. The SERS efficiency of the raspberry-like clusters is highly dependent on their structure.

Effectiveness of prolotherapy in the treatment of chronic rotator cuff lesions.

BACKGROUND: Rotator cuff lesions are one of the major causes of shoulder pain and dysfunction. Numerous non-surgical treatment modalities have been described for chronic rotator cuff lesions, but the debate continues over the optimal procedure. The aim of this report is to present the results of prolotherapy in the treatment of chronic refractory rotator cuff lesions. HYPOTHESIS: Dextrose prolotherapy will reduce pain and improve shoulder function and patient satisfaction. MATERIAL AND METHODS: We recruited 120 patients with chronic rotator cuff lesions and symptoms that persisted for longer than 6 months. Patients were divided into two groups: one treated with exercise (control group; n=60) and the other treated with prolotherapy injection (prolotherapy group; n=60). In the latter, ultrasound-guided prolotherapy injections were applied under aseptic conditions. In the former, patients received a physiotherapy protocol three sessions weekly for 12 weeks. Both groups were instructed to carry out a home exercise program. Clinical assessment of shoulder function was performed using a visual analog scale (VAS) for pain, Shoulder Pain and Disability Index (SPADI), Western Ontario Rotatory Cuff (WORC) Index, patient satisfaction, and shoulder range of motion. Patients were examined at baseline, weeks 3, 6, and 12, and last follow-up (minimum of one year). RESULTS: A total of 101 patients (44 controls and 57 in the prolotherapy group) completed all study protocols and were included in the study. Using a within-group comparison, both groups achieved significant improvements over baseline, as measured by the VAS, SPADI, WORC index, and shoulder range of motion (P<0.001). Using a between-group comparison, a significant difference was found in the VAS scores at baseline, weeks 3, 6, and 12, and last follow-up. In addition, significant differences were found in the SPADIs and WORC indices at weeks 6 and 12 and the last follow-up. Significant differences were found in shoulder abduction and flexion at week 12 and last follow-up, and in internal rotation at last follow-up. However, no significant was found in external rotation at any follow-up period. In the prolotherapy group, 53 patients (92.9%) reported excellent or good outcomes; in the control group, 25 patients (56.8%) reported excellent or good outcomes. CONCLUSION: Prolotherapy is an easily applicable and satisfying auxiliary method in the treatment of chronic rotatory cuff lesions. STUDY TYPE: Randomized prospective comparative trial. LEVEL OF EVIDENCE: Level of evidence 1.

Synthesis engineering of iron oxide raspberry-shaped nanostructures.

Magnetic porous nanostructures consisting of oriented aggregates of iron oxide nanocrystals display very interesting properties such as a lower oxidation state of magnetite, and enhanced saturation magnetization in comparison with individual nanoparticles of similar sizes and porosity. However, the formation mechanism of these promising nanostructures is not well understood, which hampers the fine tuning of their magnetic properties, for instance by doping them with other elements. Therefore the formation mechanism of porous raspberry shaped nanostructures (RSNs) synthesized by a one-pot polyol solvothermal method has been investigated in detail from the early stages by using a wide panel of characterization techniques, and especially by performing original in situ HR-TEM studies in temperature. A time-resolved study showed the intermediate formation of an amorphous iron alkoxide phase with a plate-like lamellar structure (PLS). Then, the fine investigation of PLS transformation upon heating up to 500 °C confirmed that the synthesis of RSNs involves two iron precursors: the starting one (hydrated iron chlorides) and the in situ formed iron alkoxide precursor which decomposes with time and heating and contributes to the growth step of nanostructures. Such an understanding of the formation mechanism of RSNs is necessary to envision efficient and rational enhancement of their magnetic properties.

Difference between Spinecor brace and Thoracolumbosacral orthosis for deformity correction and quality of life in adolescent idiopathic scoliosis.

Although there are several conservative treatment options, only bracing has been found to be effective in preventing curve progression and a subsequent need for surgery in adolescent idiopathic scoliosis. The objective of this study is to compare the results of SpineCor brace and thoracolumbosacral orthosis (TLSO) for treatment of adolescent idiopathic scoliosis radiologically and clinically. Sixty-four patients with adolescent idiopathic scoliosis treated with brace included in this study. Height, T1-Coccygx distance, and gibbosity were measured. Rib hump deformity was evaluated with a scoliometer. An SRS-22 questionnaire was used to determine the quality of life of patients after the first year of brace treatment. Differences in Cobb angles and gibbosity were insignificant for both groups. SRS-22 questionnaire results showed significant differences in pain, self-image and function/activity subgroups. Patients' mental health and satisfaction scores were insignificant. These braces have a similar effect on deformity correction. The surgery rates and success rates of braces are approximately equal. The major difference between SpineCor and TLSO is health-related quality of life.

Towards nanoprinting with metals on graphene.

Graphene and carbon nanotubes are envisaged as suitable materials for the fabrication of the new generation of nanoelectronics. The controlled patterning of such nanostructures with metal nanoparticles is conditioned by the transfer between a recipient and the surface to pattern. Electromigration under the impact of an applied voltage stands at the base of printing discrete digits at the nanoscale. Here we report the use of carbon nanotubes as nanoreservoirs for iron nanoparticles transfer on few-layer graphene. An initial Joule-induced annealing is required to ensure the control of the mass transfer with the nanotube acting as a 'pen' for the writing process. By applying a voltage, the tube filled with metal nanoparticles can deposit metal on the surface of the graphene sheet at precise locations. The reverse transfer of nanoparticles from the graphene surface to the nanotube when changing the voltage polarity opens the way for error corrections.

A 3D insight on the catalytic nanostructuration of few-layer graphene.

The catalytic cutting of few-layer graphene is nowadays a hot topic in materials research due to its potential applications in the catalysis field and the graphene nanoribbons fabrication. We show here a 3D analysis of the nanostructuration of few-layer graphene by iron-based nanoparticles under hydrogen flow. The nanoparticles located at the edges or attached to the steps on the FLG sheets create trenches and tunnels with orientations, lengths and morphologies defined by the crystallography and the topography of the carbon substrate. The cross-sectional analysis of the 3D volumes highlights the role of the active nanoparticle identity on the trench size and shape, with emphasis on the topographical stability of the basal planes within the resulting trenches and channels, no matter the obstacle encountered. The actual study gives a deep insight on the impact of nanoparticles morphology and support topography on the 3D character of nanostructures built up by catalytic cutting.

Structural transitions at the nanoscale: the example of palladium phosphides synthesized from white phosphorus.

Stoichiometric reactions of Pd(0) nanoparticles with various amounts of white phosphorus (P4) are an efficient route to convert them into the corresponding Pd phosphides Pd(x)P(y). Formation of crystallized palladium phosphide nanoparticles is a two-step process, which allows exploring in detail the phase transitions of the Pd(x)P(y) system, from amorphous Pd-P nanoparticles (formed in a first step at moderate temperature) to crystallization (at higher temperature). The second temperature was found to be strongly dependent on the Pd/P ratio: PdP2, Pd5P2 and Pd3P stoichiometries form the amorphous phases, but only PdP2 and Pd5P2 could be further crystallized from them. Although it exists as a bulk crystalline material, Pd3P could only be crystallized by starting from the more Pd-rich Pd6P composition. Phase-to-phase transformations from P-poor phosphides (Pd3P and Pd5P2) to the P-rich PdP2 were also demonstrated, and a first Pd-P phase diagram at the nanoscale was tentatively produced.

Mapping the 3D distribution of CdSe nanocrystals in highly oriented and nanostructured hybrid P3HT-CdSe films grown by directional epitaxial crystallization.

Highly oriented and nanostructured hybrid thin films made of regioregular poly(3-hexylthiophene) and colloidal CdSe nanocrystals are prepared by a zone melting method using epitaxial growth on 1,3,5-trichlorobenzene oriented crystals. The structure of the films has been analyzed by X-ray diffraction using synchrotron radiation, electron diffraction and 3D electron tomography to afford a multi-scale structural and morphological description of the highly structured hybrid films. A quantitative analysis of the reconstructed volumes based on electron tomography is used to establish a 3D map of the distribution of the CdSe nanocrystals in the bulk of the films. In particular, the influence of the P3HT-CdSe ratio on the 3D structure of the hybrid layers has been analyzed. In all cases, a bi-layer structure was observed. It is made of a first layer of pure oriented semi-crystalline P3HT grown epitaxially on the TCB substrate and a second P3HT layer containing CdSe nanocrystals uniformly distributed in the amorphous interlamellar zones of the polymer. The thickness of the P3HT layer containing CdSe nanoparticles increases gradually with increasing content of NCs in the films. A growth model is proposed to explain this original transversal organization of CdSe NCs in the oriented matrix of P3HT.