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Engendering Unprecedented Activation of Oxygen Evolution via Rational Pinning of Ni Oxidation State in Prototypical Perovskite: Close Juxtaposition of Synthetic Approach and Theoretical Conception

Rebecca Pittkowski, Spyridon Divanis, Mariana Klementová, Roman Nebel, Shahin Nikman, Harry Hoster, Sanjeev Mukerjee, Jan Rossmeisl, Petr Krtil

Abstract

Rational optimization of the OER activity of catalysts based on LaNiO3 oxide is achieved by maximizing the presence of trivalent Ni in the surface structure. DFT investigations of the LaNiO3 catalyst and surface structures related to it predict an improvement in the OER activity for these materials to levels comparable with the top of the OER volcano if the La content is minimized while the oxidation state of Ni is maintained. These theoretically predicted structures of high intrinsic OER activity can be prepared by a templated spray-freeze freeze-drying synthesis followed by a simple postsynthesis exfoliation-like treatment in acidic media. These nanocrystalline LaNiO3-related materials confirm the theoretical predictions, showing a dramatic improvement in OER activity. The exfoliated surfaces remain stable in OER catalysis, as shown by an in-operando ICP-OES study. The unprecedented OER activation of the synthesized LaNiO3-based materials is related to a close juxtaposition of the theoretical conception of ideal structural motifs and the ability to engender such motifs using a unique synthetic procedure, both principally related to stabilization and pinning of the Ni oxidation state within the local coordination environment of the perovskite structure.

Keywords

electrocatalysis, oxygen evolution, rational catalyst design, DFT

Particle Size Reduction Techniques of Pharmaceutical Compounds for the Enhancement of Their Dissolution Rate and Bioavailability

Rahul Kumar, Amit K. Thakur, Pranava Chaudhari, Nilanjana Banerjee

Abstract

In pharmaceutical research and development, various new chemical entities (NCE) are found to be poorly water-soluble. Therefore, solubility enhancement, a key factor for higher bioavailability, is a major challenge in pharmaceutical industries. Particle size reduction is one such method that increases the surface area of the pharmaceutical compounds and subsequently leads to a higher dissolution rate and bioavailability. Conventional processes such as milling, high-pressure homogenization, and spray drying are well established and widely used for particle size reduction. However, a few disadvantages such as a broader particle size distribution (PSD) and thermal and chemical degradation of the product are major concerns for the product quality. Non-conventional processes such as liquid anti-solvent crystallization, supercritical anti-solvent process, rapid expansion of supercritical solutions, particles from gas saturated solutions, and pulsed laser ablation are emerging as potential alternatives to overcome the disadvantages of conventional processes. This review critically summarizes the milling, spray drying, high-pressure homogenization, liquid anti-solvent crystallization, spray freeze-drying, supercritical carbon dioxide (SCCO2)–based micronization processes, pulsed laser ablation and combinative techniques. The success of these processes in enhancing the dissolution rate and bioavailability of many active pharmaceutical ingredients (APIs) has been critically examined. The advantages and limitations of these processes are also discussed. Finally, opportunities for future research are also proposed.

Keywords

Anti-solvent, Milling, Particle size reduction, Powder, Spray drying, Supercritical carbon dioxide

Effects of drying method and excipient on the structure and physical stability of protein solids: Freeze drying vs. spray freeze drying

Tarun Tejasvi Mutukuri, Nathan E. Wilson, Lynne S. Taylor, Elizabeth M. Topp, Qi Tony Zhou

Abstract

This study aims to determine the impacts of drying method and excipient on changes in protein structure and physical stability of model protein solids. Protein solids containing one of two model proteins (lysozyme or myoglobin) were produced with or without excipients (sucrose or mannitol) using freeze drying or spray freeze drying (SFD). The protein powders were then characterized using solid-state Fourier transform infrared spectroscopy (ssFTIR), differential scanning calorimetry (DSC), circular dichroism spectrometry (CD), size exclusion chromatography (SEC), BET surface area measurements and solid-state hydrogen deuterium exchange with mass spectrometry (ssHDX-MS). ssFTIR and CD could identify little to no difference in structure of the proteins in the formulation. ssHDX-MS was able to identify the population heterogeneity, which was undetectable by conventional characterization techniques of ssFTIR and CD. ssHDX-MS metrics such as Dmax and peak area showed a good correlation with the protein physical instability (loss of the monomeric peak area by size exclusion chromatography) in 90-day stability studies conducted at 40 °C for lysozyme. Higher specific surface area was associated with greater loss in monomer content for myoglobin-mannitol formulations as compared to myoglobin-only formulations. Spray freeze drying seems a viable manufacturing technique for protein solids with appropriate optimization of formulations. The differences observed within the formulations and between the processes using ssHDX-MS, BET surface area measurements and SEC in this study provide an insight into the influence of drying methods and excipients on protein physical stability.

Keywords

Freeze drying, Spray freeze drying, Protein structure, Biopharmaceutical processing, Solid formulation, Solid-state hydrogen/deuterium exchange with mass spectrometric analysis (ssHDX-MS)

A Kinetic Model for Spray-Freezing of Pharmaceuticals

Abstract

Spray freeze-drying (SFD), which includes spray-freezing into droplets and dynamic vacuum drying, presents a promising alternative approach to manufacture dried pharmaceuticals more efficiently than conventional vial freeze-drying. Without reliable predictive models for the SFD conditions of interest, any respective process development still relies on empirical approaches. In this work, we propose an improved modeling framework to describe the fast freezing (<1 s) that sub-millimeter droplets undergo in the present SFD process. The modeled freezing rate accounts for both the kinetics of ice growth and droplet heat transfer mechanisms. Computational fluid dynamics (CFD) simulations and experiments on bulk spray-freezing are combined to refine and validate the proposed reduced-order model. While this study is limited to water-sucrose solutions, the present modeling approach can be extended to other pharmaceutical excipients. For the cooling rates of interest, model results indicate that droplets with initial sucrose concentration higher than 20% w/w will transit to a glassy state before completion of crystallization and, consequently, devitrification is expected during post spray-freezing manipulation of the bulk material. In practice, such compact model does not only allow quantification of process parameters that cannot be measured in real time but also enable the choice of optimal spraying conditions for production of free-flowing, high-quality frozen droplets that meet the target product profile.

Keywords

Crystallization, Freeze-drying, In silico modeling, Lyophilization, Mechanistic modeling, Microsphere(s), Powder technology(s), Spray freeze-drying, Sucrose

Transparent cobalt‐doped yttrium aluminum garnet (Co2+:YAG) ceramics—An innovatory fast saturable absorber

Agnieszka Szysiak, Kamila Leśniewska‐Matys, Helena Węglarz, Przemysław Gołębiewski, Dariusz Podniesiński, Anna Kozłowska

Abstract

Highly transparent Y3Al5O12 (YAG) ceramics doped with 0.025 and 0.05 at.% Co ions were prepared for the first time by the freeze granulation process and reaction sintering. Scanning electron microscopy (SEM) and X‐ray diffraction (XRD) were performed to analyze the microstructure and crystal structure of the samples. The absorption spectra of the Co2+:YAG ceramics were measured at room temperature, and significant absorption bands at 600 nm, as well as at 1535 nm, were observed. The nonlinear behavior of the received material was experimentally demonstrated. Due to the short relaxation time of investigated ceramics, we considered them as fast saturable absorbers. The influence of the postsintering annealing process was examined. The values of saturation intensities of YAG ceramics with different concentrations of cobalt were estimated by fitting experimental data to the theoretical model for fast saturable absorbers.

Keywords

Co:YAG ceramics, Fast saturable absorber, Freeze granulation, Transparent ceramics

Spray freeze granulation of submicrometre α-alumina using ultrasonication

Shaghayegh Ghanizadeh, Prabhu Ramanujam, Bala Vaidhyanathan, Jon Binner

Abstract

Granulation is a key factor towards improvement of the flowability of fine ceramic powders to make them suitable for industrial dry pressing. Controlled granulation of fine alumina particles with a primary particle size of ∼150 nm was carried out using spray-freeze drying, which led to the production of flowable granules with high crushability. The fracture surface of uniaxially die-pressed green bodies made from granules with density values of ≥50 % of theoretical showed a uniform microstructure. Sintering experiments were performed using conventional single- and two-stage radiant heating methods followed by density and grain size measurement and characterisation of the final dense compacts to study the efficiency of two-stage sintering in grain growth elimination. The results have been compared with those of alumina bodies prepared using similar suspension by the slip-casting route.

Photocatalytic Oxidation of HMF under Solar Irradiation: Coupling of Microemulsion and Lyophilization to Obtain Innovative TiO2-Based Materials

Alessandro Allegri, Valeriia Maslova, Magda Blosi, Anna Luisa Costa, Simona Ortelli, Francesco Basile, Stefania Albonetti

Abstract

The photocatalytic oxidation of biomass-derived building blocks such as 5-hydroxymethylfurfural (HMF) is a promising reaction for obtaining valuable chemicals and the efficient long-term storage of solar radiation. In this work, we developed innovative TiO2-based materials capable of base-free HMF photo-oxidation in water using simulated solar irradiation. The materials were prepared by combining microemulsion and spray-freeze drying (SFD), resulting in highly porous systems with a large surface area. The effect of titania/silica composition and the presence of gold-copper alloy nanoparticles on the properties of materials as well as photocatalytic performance were evaluated. Among the lab-synthesized photocatalysts, Ti15Si85 SFD and Au3Cu1/Ti15Si85 SFD achieved the higher conversions, while the best selectivity was observed for Au3Cu1/Ti15Si85 SFD. The tests with radical scavengers for both TiO2-m and Au3Cu1/Ti15Si85 SFD suggested that primary species responsible for the selective photo-oxidation of HMF are photo-generated electrons and/or superoxide radicals.

Keywords

5-hydroxymethyl furfural, spray-freeze drying, photocatalysis, TiO2, microemulsion

Synergistic effects in oxygen evolution activity of mixed iridium-ruthenium pyrochlores

Rebecca K. Pittkowski, Daniel F. Abbott, Roman Nebel, Spyridon Divanis, Emiliana Fabbri, Ivano E. Castelli, Thomas J. Schmidt, Jan Rossmeisl, Petr Krtil

Abstract

Pyrochlore oxides (A₂B₂O₇) simultaneously containing iridium and ruthenium in the B-site are promising catalysts for oxygen evolution reaction (OER) in acid media. The catalytic activity of the pyrochlore based catalysts is increased by the coexistence of Ir and Ru in the B-site of the pyrochlore structure. Lanthanide (Yb, Gd, or Nd) stabilized mixed pyrochlores with a fraction of Ru in the B-site of x_Ru =0.2, 0.4, 0.6, 0.8 were synthesized by the spray-freeze freeze-dry approach. All prepared mixed pyrochlore catalysts are surpassing the OER activity of the corresponding iridium and ruthenium analogues featuring no cation mixing as well as that of the benchmark IrO₂ catalyst. The synergy of Ir and Ru in the B-site of the pyrochlore structure suppresses the effect of the A-site cation radius on the OER activity. The observed OER activity scales with the Ir-Ru bond distance which represents the local structure of the prepared materials. The most active ytterbium catalyst also shows a significant stability improvement under OER operando conditions over the benchmark IrO₂

Keywords

Electrocatalysis, Oxygen evolution, Pyrochlores, Local structure optimization, Synergy

Production of bromelain aerosols using spray-freeze-drying technique for pulmonary supplementation

M. N. Lavanya, R. Preethi, J. A. Moses, C. Anandharamakrishnan

Abstract

Spray-freeze-drying (SFD) is a promising technique to produce inhalable dry powder formulations that able to retain the integrity of bioactive compounds. Therefore, in this study bromelain aerosols were developed using SFD by varying core-to-wall ratios (1:10, 1:25 and 1:50). The maltodextrin was used to protect the bromelain during freezing and drying stages had a significant effect on the developed aerosols; as the concentration increased, the emitted dosage level increased to around 97.2%. The particles were found to be spherical and highly porous, with geometric diameter ranging between 4.71 to 7.46 µm. All formulations were low in density, had excellent flowability and the theoretical mass median aerodynamic diameter (MMADt) ranged between 2.97 to 3.33 µm. The total bromelain concentration ranged between 413.73 to 462 mg/g and the activity was found to be between 333.22 to 404.64 casein digestion units−1 (CDU)−1 for all three formulations. The XRD patterns explained the crystalline nature of these formulations. The in-vitro release profile showed that the release of bromelain was slow and sustained for 12 h and 46 to 55% of release was estimated. In-vitro aerosol performance of particles showed 84.28% fine particle fraction (FPF) and MMAD of 3.2 µm for the 1:25 formulation. Thus, this study confirmed that SFD can produce aerosols with desired properties and the approach can be used for pulmonary supplementation of food bioactives with good retention and activity.

Keywords

Pulmonary supplementation, aerosol delivery system, mass median aerodynamic diameter, spray-freeze-drying, in-vitro release