Size‐Controlled Synthesis of Sub‐10 nm PtNi3 Alloy Nanoparticles and their Unusual Volcano‐Shaped Size Effect on ORR Electrocatalysis

Dealloyed Pt bimetallic core–shell catalysts derived from low‐Pt bimetallic alloy nanoparticles (e.g, PtNi₃) have recently shown unprecedented activity and stability on the cathodic oxygen reduction reaction (ORR) under realistic fuel cell conditions and become today's catalyst of choice for commercialization of automobile fuel cells. A critical step toward this breakthrough is to control their particle size below a critical value (≈10 nm) to suppress nanoporosity formation and hence reduce significant base metal (e.g., Ni) leaching under the corrosive ORR condition. Fine size control of the sub‐10 nm PtNi₃ nanoparticles and understanding their size dependent ORR electrocatalysis are crucial to further improve their ORR activity and stability yet still remain unexplored. A robust synthetic approach is presented here for size‐controlled PtNi₃ nanoparticles between 3 and 10 nm while keeping a constant particle composition and their size‐selected growth mechanism is studied comprehensively. This enables us to address their size‐dependent ORR activities and stabilities for the first time. Contrary to the previously established monotonic increase of ORR specific activity and stability with increasing particle size on Pt and Pt‐rich bimetallic nanoparticles, the Pt‐poor PtNi₃ nanoparticles exhibit an unusual “volcano‐shaped” size dependence, showing the highest ORR activity and stability at the particle sizes between 6 and 8 nm due to their highest Ni retention during long‐term catalyst aging. The results of this study provide important practical guidelines for the size selection of the low Pt bimetallic ORR electrocatalysts with further improved durably high activity.     

Effects of the variation of mass loading and particle density in gas-solid particle flow in pipes

The method of two dimensional Reynolds Averaged Navier-Stokes (RANS) equations has been employed for the simulation of turbulent particulate flow. This approach was fitted with appropriate closure equations that take into account all the pertinent forces and effects on the solid particles, such as: particle-turbulence interactions; turbulence modulation; particle-particle interactions; particle-wall interactions; gravitation, viscous drag and lift forces. The flow domain in all cases was a cylindrical pipe and the computations were carried for upward pipe flow. The finite volume technique was used for the numerical solution of the governing and closure equations. The results show the effect of loading and particle density on the profiles of the velocity, the turbulence intensity and the solids concentration.     

Optimization of exopolysaccharide yields in sourdoughs fermented by lactobacilli

In this study, the yields of exopolysaccharides (EPS) produced in situ during sourdough fermentations with Lactobacillus reuteri TMW 1.106 synthesizing glucan from sucrose were investigated under variation of the fermentation parameters dough yield (DY), pH, sucrose content and fermentation substrate. The obtained amounts of EPS after 1 day of fermentation were higher in softer (DY 500) than in firmer (DY 220) doughs. With the regulation of the pH to a constant value of 4.7, the optimum for EPS synthesis in liquid medium, the EPS production in dough also increased. The EPS yield could further be improved by additional sucrose fed-batch during fermentation. Fermentations with wheat flours, a rye-wheat mixture and rye bran with 10% sucrose as fermentation substrate showed, that the use of rye bran is a promising tool to get high dextran formation through L. reuteri even in the first 8 h of fermentation. Further, alternative production of oligosaccharides and organic acids from sucrose was investigated. Lactobacillus reuteri synthesized high amounts of acetic acid leading to low fermentation quotient values. In wheat doughs, the formation of maltooligosaccharides was observed. Confirmatory experiments with fructan producing Lactobacillus sanfranciscensis TMW 1.392 revealed the same trends with a few distinct differences, indicating that this approach is transferable to other EPS types and producers.     

YBa2Cu3O7−x dispersion in iodine acetone for electrophoretic deposition: Surface charging mechanism in a halogenated organic media

Electrophoretic deposition (EPD) performance strongly depends on the particles surface chemistry and the ability to manipulate surface-liquid interfaces. In this study an extensive investigation of YBCO suspension in dry acetone, acetone-water mixtures and acetone-iodine is reported. Chemical instability of YBCO particles determines their colloidal behaviour. Charging mechanism of particles has therefore had to be deeply investigated for complete dispersion understanding. In order to determine the conditions of the YBCO suspension stability, measurements of pH, conductivity, zeta-potential, settling tests, modelling of the particle networks and electrophoretic deposition were done. The influence of the water and iodine concentration, and their role as stabilizers was evaluated. Based on experimental results, pair particle potentials were calculated and then different charging mechanisms of YBCO surfaces in acetone were proposed.     

An Endoperoxide‐Based Hybrid Approach to Deliver Falcipain Inhibitors Inside Malaria Parasites

The emergence of artemisinin‐resistant Plasmodium falciparum malaria in Southeast Asia has reinforced the urgent need to discover novel chemotherapeutic strategies to treat and control malaria. To address this problem, we prepared a set of dual‐acting tetraoxane‐based hybrid molecules designed to deliver a falcipain‐2 (FP‐2) inhibitor upon activation by iron(II) in the parasite digestive vacuole. These hybrids are active in the low nanomolar range against chloroquine‐sensitive and chloroquine‐resistant P. falciparum strains. We also demonstrate that in the presence of FeBr₂ or within infected red blood cells, these molecules fragment to release falcipain inhibitors with nanomolar protease inhibitory activity. Molecular docking studies were performed to better understand the molecular interactions established between the tetraoxane‐based hybrids and the cysteine protease binding pocket residues. Our results further indicate that the intrinsic activity of the tetraoxane partner compound can be masked, suggesting that a tetraoxane‐based delivery system offers the potential to attenuate the off‐target effects of known drugs.     

Responses of simple optical standing wave sensors

Optical standing wave sensors have been manufactured by amorphous silicon deposition. The responses of these sensors, when subjected to standing waves, have been calculated and measured. It is shown that the responses are different depending on the way the standing wave is created. The responses also depend on the thickness and material properties of the layers used to create the sensors. Quantitative agreement between measurements and model calculations can be obtained by including alignment errors, incoherent light interaction and scaling factors. The simple construction of the sensors allows for a broad application range.     

Plasmonic Light Trapping in Thin-film Silicon Solar Cells with Improved Self-Assembled Silver Nanoparticles

Plasmonic metal nanoparticles are of great interest for light trapping in thin-film silicon solar cells. In this Letter, we demonstrate experimentally that a back reflector with plasmonic Ag nanoparticles can provide light-trapping performance comparable to state-of-the-art random textures in n-i-p amorphous silicon solar cells. This conclusion is based on the comparison to high performance n-i-p solar cell and state-of-the-art efficiency p-i-n solar cells deposited on the Asahi VU-type glass. With the plasmonic back reflector a gain of 2 mA/cm(2) in short-circuit current density was obtained without any deterioration of open circuit voltage or fill factor compared to the solar cell on a flat back reflector. The excellent light trapping is a result of strong light scattering and low parasitic absorption of self-assembled Ag nanoparticles embedded in the back reflector. The plasmonic back reflector provides a high degree of light trapping with a haze in reflection greater than 80% throughout the wavelength range 520-1100 nm. The high performance of plasmonic back reflector is attributed to improvements in the self-assembly technique, which result in a lower surface coverage and fewer small and irregular nanoparticles.     

Application of particle tracking velocimetry for studying the dispersion of particles in a turbulent gas flow

A method for the determination of the dispersion of solid particles in a turbulent gas flow has been presented. This method is based on recording the particle trajectories with a high-speed video camera on separate regions of a flow, located at various distances from a point source of particles, and the subsequent processing of the frames. This method has been used to study the dispersion of solid particles under the conditions of turbulence in a horizontal channel with a rectangular cross section of 200 × 400 mm for a measuring region length of 2 m. Turbulence of the gas flow was generated by means of a grid with square meshes of the size of 16 mm. The average velocity of the gas flow in the measuring region was 5.1 m/s. The dispersion of 36-, 56- and 128-micron glass particles of spherical shape was studied in a region 450 mm long from the point source of particles. It has been shown that the dispersion of these particles in the direction of the action of the gravity force is larger than their dispersion in the perpendicular direction to the gravity force. The results of this study have shown that an increase in the size of particles leads to a decrease in the dispersion at small flight times of the particles (short-time dispersion).     

Control of the porosity of anatase thin films prepared by EISA: Influence of thickness and heat treatment

Mesoporous anatase thin films were prepared by the evaporation-induced self-assembly process. This paper reports a study of the influence of several physical parameters on the long-range ordering of the mesopores. A preliminary study was done to set the best humidity conditions during dip-coating and ageing of the films. The withdrawal speed, already known to modify the thickness of the deposited film, was shown to exert a strong influence on the percentage of porosity. This was studied by step profilometry combined with Rutherford backscattered spectrometry (RBS). In parallel, small angle X-ray scattering (SAXS), X-ray diffraction (XRD), transmission electron microscopy (TEM) and RBS were used to tune the precise thermal treatment applied to the so-obtained films, in order to preserve the porous mesostructure and promote the nanocrystallization of anatase TiO₂.