Redispersion Of Nanoparticles Research Articles

Polyolefin nanocomposites with polyelectrolyte coated redispersible nanoparticles produced continuously and massively via reactive flash nanoprecipitation

Redispersibility of nanoparticles to a polymer matrix was crucial for composite performances. In order to massively produce redispersible nanoparticles for industrial applications, this study for the first time realized a continuous process of the reactive flash nanoprecipitation (RFNP) with a confined impinging jets (CIJ) micromixer and the developed desktop device even with low power-output pumps. A nanosuspension of magnesium hydroxide (MH) was successfully produced and simultaneously coated with a polyelectrolyte of sodium alginate (NaAlg) via RFNP. The produced NaAlg/MH nanoparticles had a good compatibility with polypropylene (PP) as well as a good redispersibility during their melt blending. The produced PP/NaAlg/MH nanocomposite showed a significant deduction of the initial decomposition temperature even with a low MH feed for flame retardancy. This study created a genetic way to massively and rapidly produce narrow sized and redispersible nanoparticles for nanocomposites and would also push forward the FNP and analogous methods to a real industrial implementation.

Reaction-Induced Formation of Stable Mononuclear Cu(I)Cl Species on Carbon for Low-Footprint Vinyl Chloride Production.

Copper catalysts are attractive candidates for Hg-free vinyl chloride monomer (VCM) production via acetylene hydrochlorination due to their non-toxic nature and high stability. However, the optimal architecture for Cu-based catalysts at the nanoscale is not yet fully understood. To address this gap, the metal precursor and the annealing temperature are modified to prepare copper nanoparticles or single atoms, either in chlorinated or ligand-free form, on an unmodified carbon support. Evaluation in the reaction reveals a remarkable convergence of the performance of all materials to the stable VCM productivity of the single-atom catalyst. In-depth characterization by advanced microscopy, quasi in situ and operando spectroscopy, and simulations uncover a reaction-induced formation of low-valent, single atom Cu(I)Cl site motif, regardless of the initial nanostructure. Various surface oxygen groups promote nanoparticle redispersion by stabilizing single-atom CuClx species. The anchoring site structure does not strongly influence the acetylene adsorption energy or the crucial role they play in stabilizing key reaction intermediates. A life-cycle assessment demonstrates the potential environmental benefits of copper catalysts over state-of-the-art alternatives. This work contributes to a better understanding of optimal metal speciation and highlights the sustainability of Cu-based catalysts for VCM production.

Particle Attachment Growth of Au@Ag Core–Shell Nanocuboids

In the templated synthesis of colloidal core-shell nanoparticles, the monomer attachment growth mechanism has been widely accepted to describe the growth process of shells. In this work, by using advanced transmission electron microscope techniques, we directly observe two alternative particle attachment growth pathways that dominate the growth of Au@Ag core-shell nanocuboids. One pathway involves the in situ reduction of AgCl nanoparticles attached to Au nanorods and the subsequent epitaxial growth of the Ag shell. The other pathway involves the adherence of Ag-AgCl Janus nanoparticles to Au nanorods with random orientations, followed by nanoparticle redispersion and the resulting formation of epitaxial Ag shells on the Au nanorods. The particle-mediated growth of Ag shells is accompanied by the redispersion of surface atoms, tending to form a uniform structure. The validation of the particle attachment growth processes at the atomic scale provides a new mechanistic understanding of core-shell nanostructure synthesis.

Rhodium Catalyst Structural Changes during, and Their Impacts on the Kinetics of, CO Oxidation.

Catalysts can undergo structural changes during the reaction, affecting the number and/or the shape of active sites. For example, Rh can undergo interconversion between nanoparticles and single atoms when CO is present in the reaction mixture. Therefore, calculating a turnover frequency in such cases can be challenging as the number of active sites can change depending on the reaction conditions. Here, we use CO oxidation kinetics to track Rh structural changes occurring during the reaction. The apparent activation energy, considering the nanoparticles as the active sites, was constant in different temperature regimes. However, in a stoichiometric excess of O2, there were observed changes in the pre-exponential factor, which we link to changes in the number of active Rh sites. An excess of O2 enhanced CO-induced Rh nanoparticle disintegration into single atoms, affecting catalyst activity. The temperature at which these structural changes occur depend on Rh particle size, with small particle sizes disintegrating at higher temperature, relative to the temperature required to break apart bigger particles. Rh structural changes were also observed during in situ infrared spectroscopic studies. Combining CO oxidation kinetics and spectroscopic studies allowed us to calculate the turnover frequency before and after nanoparticle redispersion into single atoms.

Kinetic and Thermodynamic Factors Influencing Palladium Nanoparticle Redispersion into Mononuclear Pd(II) Cations in Zeolite Supports

Palladium cations and nanoparticles supported on oxides and zeolites are used as catalysts and adsorbents for a wide range of chemical reactions of practical importance, with various and distinct active site requirements. Consequently, sintering and redispersion processes that interconvert site-isolated Pd cations and agglomerated nanoparticles underpin catalyst activation and deactivation phenomena, yet the influence of Pd nanoparticle size distribution and gas conditions on the thermodynamic and kinetic factors influencing such interconversion is imprecisely understood. Here, we prepare Pd nanoparticles of different particle size and distribution (normal, log–normal) supported on high-symmetry crystalline zeolites to access well-defined materials whose Pd site distributions can be quantitatively characterized by experiments and modeled accurately by theory. Ab initio thermodynamic modeling and isothermal (593–973 K) wet and dry air treatments of Pd-zeolites reveal that the widely observed deactivation in low-temperature hydrous environments reflects site interconversion thermodynamics that favor the agglomeration of isolated Pd cations into nanoparticles. Under high-temperature anhydrous conditions, experimental kinetic measurements and kinetic Monte Carlo simulations evince the preeminence of kinetic factors on Pd nanoparticle redispersion into cations, which proceeds at rates that are strongly influenced by the initial Pd particle size distribution and via a substrate diffusion-mediated Ostwald ripening process whereby Pd monomers are captured in an atom trapping process at anionic exchange sites (framework Al) in the zeolite support. These findings resolve longstanding questions regarding the roles of H2O and support interactions in Pd redispersion processes and identify strategies to enhance or suppress Pd site interconversion by modifying oxide supports and gas conditions.

MXene-Supported, Atomic-Layered Iridium Catalysts Created by Nanoparticle Re-Dispersion for Efficient Alkaline Hydrogen Evolution.

Tailoring the structure of metal components and interaction with their anchored substrates is essential for improving the catalytic performance of supported metal catalysts; the ideal catalytic configuration, especially down to the range of atomic layers, clusters, and even single atoms, remains a subject under intensive study. Here, an Ir-on-MXene (Mo2 TiC2 Tx ) catalyst with controlled morphology changing from nanoparticles down to flattened atomic layers, and finally ultrathin layers and single atoms dispersed on MXene nanosheets at elevated temperature, is presented. The intermediate structure, consisting of mostly Ir atomic layers, shows the highest activity toward the hydrogen evolution reaction (HER) under industry-compatible alkaline conditions. In addition, the better HER activity of Ir atomic layers than that of single atoms suggests that the former serves as the main active sites. Detailed mechanism analysis reveals that the nanoparticle re-dispersion process and Ir atomic layers with a moderate interaction to the substrate associate with unconventional electron transfer from MXene to Ir, leading to suitable H* adsorption. The results indicate that the structural design is important for the development of highly efficient catalysts.

Enhanced Stability and Oral Bioavailability of Cannabidiol in Zein and Whey Protein Composite Nanoparticles by a Modified Anti-Solvent Approach.

Wide applications of cannabidiol (CBD) in the food and pharmaceutical industries are limited due to its low bioavailability, sensitivity to environmental pressures and low water solubility. Zein nanoparticles were stabilized by whey protein (WP) for the delivery of cannabidiol (CBD) using a modified anti-solvent approach. Particle size, surface charge, encapsulation efficiency, and re-dispersibility of nanoparticles were influenced by the zein to WP ratio. Under optimized conditions at 1:4, zein–WP nanoparticles were fabricated with CBD (200 μg/mL) and further characterized. WP absorbed on zein surface via hydrogen bond, hydrophobic forces, and electrostatic attraction. The zein–WP nanoparticles showed excellent storage stability (4 °C, dark) and effectively protected CBD degradation against heat and UV light. In vivo pharmacokinetic study demonstrated that CBD in zein–WP nanoparticles displayed 2-times and 1.75-fold enhancement in maximum concentration (C max) and the area under curve (AUC) as compared to free-form CBD. The data indicated the feasibility of developing zein–WP based nanoparticles for the encapsulation, protection, and delivery of CBD.

Transformation of nanoparticles into compacts: A study on PLGA and celecoxib nanoparticles

Oral delivery of nanoparticles possesses many advantages for delivery of active pharmaceutical ingredients (APIs) to the gastrointestinal tract. However, the poor physical stability of nanoparticles in liquid state is often a challenge. Removing water from the nanosuspensions and transforming the nanoparticles into solid particulate matter in the form of, e.g., tablets could be a potential approach to increase the stability of nanoparticles. The aim of this study was to transform nanoparticles into compacts and to investigate the redispersion of nanoparticles from compacts as well as the dissolution behavior of these compacts. DL-lactide-co-glycolide copolymer (PLGA) nanoparticles and celecoxib (CLX) nanoparticles were used as two model nanoparticle systems and fabricated into nano-embedded microparticles (NEMs) and subsequently compressed into compacts. The compacts were evaluated with respect to the redispersibility of the nanoparticles, as well as the dissolution characteristics of CLX. The results showed that the NEMs could be readily compressed into compacts with sufficient mechanical strength. The size of the redispersed PLGA nanoparticles from the compacts using 2-hydroxypropyl-β-cyclodextrin (HPβCD) as stabilizer was comparable to the original nanoparticles. In contrast, the redispersibility of CLX nanoparticles from the compacts was not as effective as for the PLGA nanoparticles evidenced by a significant increase in the size and polydispersity index (PDI) of the redispersed nanoparticles. Nonetheless, an obvious enhancement in dissolution rate of CLX was observed from the compacts with CLX nanoparticles. It is concluded that transforming polymeric nanoparticles into compacts via NEMs provides stabilization and allows redispersion into original nanoparticles. Despite the reduced redispersibility, compacts loaded with nanoparticles exhibited improved dissolution rate compared with the crystalline drug. Loading of nanoparticles into compacts is a promising approach to overcome the poor stability of nanoparticle within oral drug delivery of nanoparticles.

Supercritical CO2 assisted preparation of chitosan-based nano-in-microparticles with potential for efficient pulmonary drug delivery

Nano-in-microparticles used for inhalation lung cancer therapy combine the advantages of microparticles with aerodynamic diameters of 1∼5 μm for deep lung deposition and nanoparticles for long residence time in lung, high mucus penetrating and cancer cells uptake efficiency. In this work, nano-in-microparticles composed of chitosan nanoparticles and mannitol were prepared using a modified supercritical CO2 assisted atomization (SAA-HCM) technique. Influences of process parameters of CO2/liquid mass flow ratio, total mass concentration and nanoparticles/mannitol ratio on size and morphologies of nano-in-microparticles were investigated in detail. Well-defined spherical nano-in-microparticles with theoretical mass median aerodynamic diameter of 1∼2 μm were obtained under optimized conditions. Fraction of about 40 % of nanoparticles was redispersed in deionized water at nanoparticles/mannitol ratio of 10:90. Meanwhile, quick disintegration of nano-in-microparticles was observed under conditions simulating high humidity in lung. In summary, dissociation of nano-in-microparticles and redispersibility of nanoparticles were determined by the structure of nano-in-microparticles according to particles formation mechanism. This work will expand the applicability of SAA-HCM to the preparation of nano-in-microparticles from nanosuspension and provide more references for designing of particles with elaborate structures.

Converting nanosuspension into inhalable and redispersible nanoparticles by combined in-situ thermal gelation and spray drying

While nanoparticulate drugs for deep lung delivery hold promise for particular disease treatments, their size-related physical instability and tendency of being exhaled during breathing remain major challenges to their inhaled formulation development. Here we report a viable method for converting drug nanosuspensions into inhalable, stable and redispersible nano-agglomerates through combined in-situ thermal gelation and spray drying. Itraconazole (ITZ) nanosuspensions were prepared by flash nanoprecipitation, and co-spray dried with two different grades of the gel-forming polymer, methylcellulose (MC M20 and MC M450) as protectants. MC M20 was found superior in protecting ITZ nanoparticles against thermal stress (through nanoparticle entrapment within its gel network structure) during spray drying. In terms of redispersibility, an Sf/Si ratio (i.e., ratio of nanoparticle sizes after and before spray drying) of unity (1.02 ± 0.03), reflecting full particle size preservation, was achieved by optimizing the suspending medium content and spray drying parameters. Formulation components, nanosuspension concentration and spray drying parameters all showed a significant impact on the aerosol performance of the resulting agglomerates, but an absence of defined trends or correlations. Overall, the MC-protected nano-agglomerates displayed excellent in-vitro aerosol performance with fine particle fractions higher than 50% and mass median aerodynamic diameters within the 2–3 µm range, which are ideal for deep lung delivery.

Preserved in a Shell: High‐Performance Graphene‐Confined Ruthenium Nanoparticles in Acetylene Hydrochlorination

AbstractThe potential implementation of ruthenium‐based catalysts in polyvinyl chloride production via acetylene hydrochlorination is hindered by their inferior activity and stability compared to gold‐based systems, despite their 4‐fold lower price. Combining in‐depth characterization and kinetic analysis we reveal the superior activity of ruthenium nanoparticles with an optimal size of 1.5 nm hosted on nitrogen‐doped carbon (NC) and identify their deactivation modes: 1) nanoparticle redispersion into inactive single atoms and 2) coke formation at the metal sites. Tuning the density of the NC carrier enables a catalytic encapsulation of the ruthenium nanoparticles into single layer graphene shells at 1073 K that prevent the undesired metal redispersion. Finally, we show that feeding O2 during acetylene hydrochlorination limits coke formation over the nanodesigned ruthenium catalyst, while the graphene layer is preserved, resulting in a stability increase of 20 times, thus rivalling the performance of gold‐based systems.

Isolation of Itraconazole Nanostructured Microparticles via Spray Drying with Rational Selection of Optimum Base for Successful Reconstitution and Compaction.

The addition of matrix formers within a formulation provides a means for enhancing the redispersibility of nanoparticles (NPs) enabling them to retain their advantageous properties imparted onto them by their sub-micron size. In this work, NPs were isolated in the solid state via spray drying with a range of sugars. The processed powders were characterized, establishing that itraconazole (ITR) nanostructured microparticles (NMPs) spray dried in the presence of mannitol and trehalose had favorable redispersibility confirmed by dynamic light scattering and nanoparticle tracking analysis. Solid-state analysis confirmed the crystalline nature of NMPs based on mannitol and the amorphous character of trehalose-based NMPs. The NMPs powders were compacted at a range of pressures, producing tablets with high tensile strength without compromising their disintegration time. A greater amount of ITR was solubilized from trehalose NMPs compared to the mannitol-based compacts in 0.1M HCl, showing a promise for enhanced in vivo activity. Overall, as trehalose exhibited superior carrier properties for ITR NMPs, this type of excipient included in the formulation warrants careful consideration. The structured approach to matrix former selection and tabletting studies can reduce the amount of material and time required for testing in the initial stages of product development.

Effects of starch composition and type of non-solvent on the formation of starch nanoparticles and improvement of curcumin stability in aqueous media

In this study, we evaluated the effects of amylopectin/amylose ratio and non-solvent type on starch nanoparticle formation including the average particle size, polydispersity index, size distribution, and nanoparticle morphology using dynamic light scattering (DLS) and scanning electron microscopy (SEM). The most uniform particles were obtained from normal corn starch with ethanol. The average particle size was 98.8 ± 1.8 nm using DLS while combination of size distribution study and SEM images showed that particle size ranged between 60 and 90 nm. A bimodal distribution was observed with two defined groups of nanoparticles when waxy corn starch (Amioca) was nanoparticulated with ethanol. SEM images of freeze dried samples and DLS size distribution curves of fresh samples showed that high amylose starch including Hylon V and Hylon VII gave uniform, spherical and small nanoparticles in the size range of 20–60 and 15–50 nm, respectively. The smallest nanoparticles were fabricated by precipitation with methanol, followed by ethanol and the largest nanoparticles were formed using acetone. Re-dispersion of nanoparticles was good when nanoparticles were fabricated using ethanol and acetone especially for Amioca, whereas redispersion of samples in aqueous PBS solution, precipitated using methanol was difficult especially in the case of Hylon VII. Stability of curcumin in the presence of 1 mg/ml native starch nanoparticles was much higher (83.7 ± 3.1%) than curcumin in phosphate buffered saline at pH 7.0 (5.5 ± 1.5%) over 10 days at ambient temperature. Interaction between iodine-potassium iodide solution and starch nanoparticles showed that the helical structures of amylose and amylopectin molecules remain in the nanoparticles and curcumin may interact with these helical structures giving it the stability which is not observed in water.

Burstable nanostructured micro-raspberries: Towards redispersible nanoparticles from dry powders

Despite immense progress in nanoscience and technology, one of the yet unsolved challenges is the redispersion of nanoparticles from dry powders back to the individual, primary particles. Herein, an easy to handle powder consisting of nanostructured micron sized raspberry-like particles is presented. These nanostructured micro-raspberries are composed of individual nanoparticles which are equipped with molecules that introduce a separating effect or “spring” functionality. Thereby, a powder system is obtained that allows for an easy and complete redispersibility of the agglomerates down to the level of individual nanoparticles in solvents and polymers. The mechanism of redispersibility involves mechanic stimuli/force as well as solvent like disintegration aspects (“like dissolves like” effect). Furthermore, by tailoring the degree of spacer-equipped particles, the bursting behavior can also be tuned, yielding different redispersion degrees. The redispersibility of the nanostructured micro-raspberries is demonstrated in solvents and silicone-based nanocomposites.

A convenient purification method for metal nanoclusters based on pH-induced aggregation and cyclic regeneration and its applications in fluorescent pH sensors

Herein, we report a convenient approach to purify water-soluble bovine serum albumin (BSA)-capped metal nanoclusters by pH-induced precipitation under acidic conditions. The fluorescence of metal nanoclusters could be completely recovered upon the re-dispersion of nanoparticles into basic media. BSA metal nanoclusters have been prepared to monitor pH at highly acidic medium. When pH decreased, the fluorescence of the nanoclusters under a UV lamp decreased and completely disappeared after pH 4. And a fluorescent pH sensor for pH monitoring has been developed based on the “OFF–ON” signal switch of the gold clusters agarose hydrogel.

Pt Nanoparticle Sintering and Redispersion on a Heterogeneous Nanostructured Support

Understanding how nanostructure and atomic-scale defects of the support affect metal catalyst nanoparticle sintering is of crucial importance to minimize thermal deactivation, as well as to understand the origin of widely observed but still unexplained phenomena, such as transient multimodal particle size distributions and nanoparticle redispersion. To shed light on these issues, we present a generic experimental approach that relies on nanofabrication to introduce controlled structural heterogeneity in a chemically homogeneous model catalyst support. This is achieved by fabricating arrays of nanocone structures separated by flat areas, where both are homogeneously sputter-coated with a thin amorphous alumina layer. Using ex situ aberration-corrected scanning transmission electron microscopy (STEM) to analyze Pt model catalyst nanoparticles on such nanostructured supports prior and after exposure to 4% O2 in Ar carrier gas at 600 °C, we find that the initial particle size distributions and their time evol...

Nanonized itraconazole powders for extemporary oral suspensions: Role of formulation components studied by a mixture design

Itraconazole (ITZ) nanocrystal-containing powders were prepared through the combined use of high pressure homogenization (HPH) and spray drying (SD). These powders were intended as base materials for the preparation of extemporary oral suspensions of the drug. The role and the effect of stabilizers on the size of re-dispersed particles were studied using a mixture design and a Scheffé model relating the dried nanosuspension composition to the mean particle diameters. The homogenization process required a surface active agent (Tween 20) to obtain the efficient comminution of itraconazole micronized powder. SD was carried out on ITZ nanosuspensions after addition of a cellulose derivative (Methocel® E5) that allowed the prompt re-dispersion of nanoparticles under “in use” conditions. The powders obtained by drying of homogenized systems showed in vitro dissolution profile faster than that of the micronized drug, suggesting a potential ameliorated GI absorption of itraconazole released from the nanosuspensions.

Crosslinking to enhance colloidal stability and redispersity of layered double hydroxide nanoparticles

This article introduces a strategy for stabilizing and redispersing layered double hydroxide (LDH) nanoparticles by crosslinking bovine serum albumin (BSA) coated onto the surface. The strategy involves optimization of the amount of the crosslinking agent glutaraldehyde (GTA) to achieve minimal aggregation and ready redispersion. LDH nanoparticles were prepared by co-precipitation and hydrothermal treatment, with subsequent BSA coating at the BSA/LDH mass ratio of 5:2. BSA coated onto LDH nanoparticles was crosslinked with different amounts of GTA. Aggregation studies using dilution assays, dynamic light scattering, and zeta potential analysis indicated that severe aggregation at lower LDH nanoparticle concentrations can be prevented by proper crosslinking of BSA with GTA. The GTA-crosslinked BSA-coated nanoparticles showed excellent redispersity compared to the non-crosslinked nanoparticles. In vitro cytotoxicity and cell uptake were found to be minimally affected by GTA-crosslinking. The new strategy therefore provides a much more effective method for the prevention of LDH nanoparticle aggregation and improved LDH nanoparticle redispersion for use in a wide variety of bio-applications in vitro and in vivo.

Encapsulation of antigen-loaded silica nanoparticles into microparticles for intradermal powder injection

Epidermal powder immunisation (EPI) is being investigated as a promising needle-free delivery methods for vaccination. The objective of this work was to prepare a nanoparticles-in-microparticles (nano-in-micro) system, integrating the advantages of nanoparticles and microparticles into one vaccine delivery system for epidermal powder immunisation. Cationic mesoporous silica nanoparticles (MSNP-NH2) were prepared and loaded with ovalbumin as a model antigen. Loading was driven by electrostatic interactions. Ovalbumin-loaded silica nanoparticles were subsequently formulated into sugar-based microparticles by spray-freeze-drying. The obtained microparticles meet the size requirement for EPI. Confocal microscopy was used to demonstrate that the nanoparticles are homogeneously distributed in the microparticles. Furthermore, the silica nanoparticles in the dry microparticles can be re-dispersed in aqueous solution showing no aggregation. The recovered ovalbumin shows integrity compared to native ovalbumin. The present nano-in-micro system allows (1) nanoparticles to be immobilized and finely distributed in microparticles, (2) microparticle formation and (3) re-dispersion of nanoparticles without subsequent aggregation. The nanoparticles inside microparticles can (1) adsorb proteins to cationic shell/surface voids in spray-dried products without detriment to ovalbumin stability, (2) deliver antigens in nano-sized modes to allow recognition by the immune system.

Role and Evolution of Nanoparticle Structure and Chemical State during the Oxidation of NO over Size- and Shape-Controlled Pt/γ-Al2O3 Catalysts under Operando Conditions

The structure and chemical state of size-selected Pt nanoparticles (NPs) supported on γ-Al2O3 were studied during the oxidation of NO using X-ray absorption near-edge spectroscopy and extended X-ray absorption fine-structure spectroscopy measurements under operando conditions. The data revealed the formation of PtOx species in the course of the reaction that remained present at the maximum temperature studied, 350 °C. The PtOx species were found in all samples, but those with the smallest NPs showed the highest degree of oxidation. Moreover, NO-induced nanoparticle redispersion was observed at temperatures below 150 °C for all catalysts studied. Catalytic tests showed activity toward the oxidation of NO for all samples. Nevertheless, the catalyst with the smallest NPs was found to be the least active, which is explained by a more extensive formation of PtOx species in this catalyst and their detrimental contribution to the oxidation of NO.