Investigation of the particle growth of fenofibrate following antisolvent precipitation and freeze-drying

peer-reviewedSubmicron to small-micron-sized particles of the hydrophobic drug, fenofibrate, were prepared by controlled crystallization in order to influence its dissolution behavior. An antisolvent precipitation process successfully generated particles (200-300 nm) which matched the size and dissolution behavior of a commercial wet-milled formulation of the drug. Although the preparation of submicron-sized particles was straightforward, retaining their size in suspension and during isolation was a challenge. Additives were employed to temporarily stabilize the suspension, and extend the time window for isolation of the submicron particles. Precipitated particles were isolated primarily by immediate freeze-drying, but drying stresses were found to destabilize the fragile submicron system. The growth pathway of particles in suspension and during oven and freeze-drying were compared. Although the growth pathways appeared considerably different from a visual morphological perspective, an investigation of the electron diffraction patterns and the inner-particle surfaces showed that the growth pathways were the same: molecular addition by Ostwald ripening. The observed differences in the time-resolved particle morphologies were found to be a result of the freeze-drying process.ACCEPTEDpeer-reviewe

TOF-SIMS analysis of curcuminoids and curcumin crystals crystallized from their pure and impure solutions

TOF-SIMS can provide quantitative information on the composition of structurally similar impurities and their locations on the surface of crystals grown in impure solutions

Boosting Hydrogen Production from Formic Acid over Pd Catalysts by Deposition of N-Containing Precursors on the Carbon Support

Formic acid is a promising liquid organic hydrogen carrier (LOHC) since it has relatively high hydrogen content (4.4 wt%), low inflammability, low toxicity and can be obtained from biomass or from CO2. The aim of the present research was the creation of efficient 1 wt% Pd catalysts supported on mesoporous graphitic carbon (Sibunit) for the hydrogen production from gas-phase formic acid. For this purpose, the carbon support was modified by pyrolysis of deposited precursors containing pyridinic nitrogen such as melamine (Mel), 2,2′-bipyridine (Bpy) or 1,10-phenanthroline (Phen) at 673 K. The following activity trend of the catalysts Pd/Mel/C > Pd/C ~ Pd/Bpy/C > Pd/Phen/C was obtained. The activity of the Pd/Mel/C catalyst was by a factor of 4 higher than the activity of the Pd/C catalyst at about 373 K and the apparent activation energy was significantly lower than those for the other catalysts (32 vs. 42–46 kJ/mol). The high activity of the melamine-based samples was explained by a high dispersion of Pd nanoparticles (~2 nm, HRTEM) and their strong electron-deficient character (XPS) provided by interaction of Pd with pyridinic nitrogen species of the support. The presented results can be used for the development of supported Pd catalysts for hydrogen production from different liquid organic hydrogen carriers

Hydrogen production from formic acid vapour over a Pd/C catalyst promoted by potassium salts: evidence for participation of buffer-like solution in the pores of the catalyst

Doping a 1 wt.% Pd/C catalyst with alkali metal carbonates has a very significant promotional effect on its activity in hydrogen production from the decomposition of formic acid vapour (2 vol.%, 1 bar), potassium and caesium carbonates giving the largest effects. The K carbonate species present on the fresh catalysts react with formic acid to form formate ions, these being dissolved in a formic acid/water solution condensed in the pores of the support. The steady-state activities of the samples containing formate ions were 1-2 orders of magnitude greater than those of the unpromoted Pd/C and CO content was lower than 30 ppm. The activation energies for the reaction increased with doping from 66 to 88-99 kJ mo1-1, relatively independent of the cation of the dopant. Similar but lesser effects were found with unsupported Pd nanocrystals doped with K carbonate. The rate-determining step for the promoted samples appears to be the decomposition of formate ions on the Pd surface. (C) 2014 Elsevier B.V. All rights reserved

Investigation of the particle growth of fenofibrate following antisolvent precipitation and freeze-drying

Submicron to small-micron-sized particles of the hydrophobic drug, fenofibrate, were prepared by controlled crystallization in order to influence its dissolution behavior. An antisolvent precipitation process successfully generated particles (200-300 nm) which matched the size and dissolution behavior of a commercial wet-milled formulation of the drug. Although the preparation of submicron-sized particles was straightforward, retaining their size in suspension and during isolation was a challenge. Additives were employed to temporarily stabilize the suspension, and extend the time window for isolation of the submicron particles. Precipitated particles were isolated primarily by immediate freeze-drying, but drying stresses were found to destabilize the fragile submicron system. The growth pathway of particles in suspension and during oven and freeze-drying were compared. Although the growth pathways appeared considerably different from a visual morphological perspective, an investigation of the electron diffraction patterns and the inner-particle surfaces showed that the growth pathways were the same: molecular addition by Ostwald ripening. The observed differences in the time-resolved particle morphologies were found to be a result of the freeze-drying process

Catalytic properties of PdZn/ZnO in formic acid decomposition for hydrogen production

This is one of the first reports, which is related to hydrogen production through formic acid decomposition over Pd/ZnO catalysts widely used for methanol steam-reforming. These catalysts have been investigated in comparison with Pt/ZnO and Pd/Al2O3 catalysts as well as ZnO support. HAADF/STEM, XRD, XPS and DRIFTS in situ studies of the systems were performed. The measured catalyst activity corresponds to the following order: Pd/Al2O3≥Pd/ZnO>Pt/ZnO>ZnO. Among the studied catalysts, Pd/ZnO showed the highest selectivity to hydrogen (up to 99.3%). This was assigned to the formation of a PdZn alloy during the reductive pre-treatment of the catalyst. An increase of the pre-treatment temperature from 573 to 773 K led to a significant increase of the mean PdZn (PtZn) nanoparticle size. However, the catalyst activity did not change, but the selectivity to hydrogen increased. These features closely remind the behavior of Pd/ZnO catalysts in methanol steam reforming implying that the mechanism of formic acid decomposition involves the same key steps and active sites

Tantalum coating inhibits Ni-migration from titanium out-diffusion in NiTi shape memory biomedical alloy

Despite the presence of over 56% Ni by weight, equiatomic NiTi is generally considered biocompatible as it naturally oxidises to form a surface oxide mainly composed of biocompatible oxides of titanium (TiOx). This layer is formed by an oxidation mechanism that promotes out-diffusion of Ti leaving a Ti-depleted, Ni rich subsurface.The long-term in vivo stability of the naturally grown Ti Oxlayer has been a concern as Ni can leach out through this thin, defective layer. The leaching of nickel (Ni) is thus a continuing threat to the alloy’s other wise outstanding bio compatibility. We have found that a layer of reactively sputtered tantalum(Ta)oxide on the bulk NiTi restricts Ti-out-migration through a biocompatible Ti/Tainter-diffusion layer that provides a larger barrier against Ni leaching. We have investigated this inter-diffusion as a function of sputtering process parameters and post processing treatments. Surface and interface analytical techniques such as X-ray photoelectron spectroscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy, cross sectional transmission electron microscopy and non-destructive ion beam analysis techniques such as Rutherford backscattering spectrometry and particle induced X-ray emission were used to evaluate the nature of this interdiffusion layer which can improve long-term biocompatibility of NiT

Boosting hydrogen production from formic acid over Pd catalysts by deposition of N-Containing precursors on the carbon support

Formic acid is a promising liquid organic hydrogen carrier (LOHC) since it has relatively high hydrogen content (4.4 wt%), low inflammability, low toxicity and can be obtained from biomass or from CO2. The aim of the present research was the creation of efficient 1 wt% Pd catalysts supported on mesoporous graphitic carbon (Sibunit) for the hydrogen production from gas-phase formic acid. For this purpose, the carbon support was modified by pyrolysis of deposited precursors containing pyridinic nitrogen such as melamine (Mel), 2,20-bipyridine (Bpy) or 1,10-phenanthroline (Phen) at 673 K. The following activity trend of the catalysts Pd/Mel/C > Pd/C ~ Pd/Bpy/C > Pd/Phen/C was obtained. The activity of the Pd/Mel/C catalyst was by a factor of 4 higher than the activity of the Pd/C catalyst at about 373 K and the apparent activation energy was significantly lower than those for the other catalysts (32 vs. 42-46 kJ/mol). The high activity of the melamine-based samples was explained by a high dispersion of Pd nanoparticles (~2 nm, HRTEM) and their strong electron-deficient character (XPS) provided by interaction of Pd with pyridinic nitrogen species of the support. The presented results can be used for the development of supported Pd catalysts for hydrogen production from different liquid organic hydrogen carriers

Ultrathin oxide controlled photocurrent generation through a metal–insulator– semiconductor heterojunction

Recent advances in nanoscale lasers, amplifiers, and nonlinear optical converters have demonstrated the unprecedented potential of metal–insulator–semiconductor (MIS) structures as a versatile platform to realize integrated photonics at the nanoscale. While the electric field enhancement and confinement have been discussed intensively in MIS based plasmonic structures, little is known about the carrier redistribution across the heterojunction and photocurrent transport through the oxide. Herein, we investigate the photo-generated charge transport through a single CdSe microbelt-Al2O3-Ag heterojunction with oxide thickness varying from 3 nm to 5 nm. Combining photocurrent measurements with finite element simulations on electron (hole) redistribution across the heterojunction, we are able to explain the loss compensation observed in hybrid plasmonic waveguides at substantially reduced pump intensity based on MIS geometry compared to its photonic counterpart. We also demonstrate that the MIS configuration offers a low-dark-current photodetection scheme, which can be further exploited for photodetection applications.</p

Pd Clusters Supported on Amorphous, Low-Porosity Carbon Spheres for Hydrogen Production from Formic Acid

Amorphous, low-porosity carbon spheres on the order of a few micrometers in size were prepared by carbonization of squalane (C₃₀H₆₂) in supercritical CO₂ at 823 K. The spheres were characterized and used as catalysts’ supports for Pd. Near-edge X-ray absorption fine structure studies of the spheres revealed sp² and sp³ hybridized carbon. To activate carbons for interaction with a metal precursor, often oxidative treatment of a support is needed. We showed that boiling of the obtained spheres in 28 wt % HNO₃ did not affect the shape and bulk structure of the spheres, but led to creation of a considerable amount of surface oxygen-containing functional groups and increase of the content of sp² hybridized carbon on the surface. This carbon was seen by scanning transmission electron microscopy in the form of waving graphene flakes. The H/C atomic ratio in the spheres was relatively high (0.4) and did not change with the HNO₃ treatment. Palladium was deposited by impregnation with Pd acetate followed by reduction in H₂. This gave uniform Pd clusters with a size of 2–4 nm. The Pd supported on the original C spheres showed 2–3 times higher catalytic activity in vapor phase formic acid decomposition and higher selectivity for H₂ formation (98–99%) than those for the catalyst based on the HNO₃ treated spheres. Using of such low-porosity spheres as a catalyst support should prevent mass transfer limitations for fast catalytic reactions