Presence Of Small Nanoparticles Research Articles

A model for nanoparticle transport and distribution with particle-interface interaction during binary alloy solidification

The interaction between nanoparticles and the solid-liquid interface during the solidification of binary alloys containing nanoparticles affects the nanoparticle transport and subsequently the final nanoparticle distribution and solid growth. Thus, a model to capture the engulfment or pushing of nanoparticles by the interface and the resulting change in nanoparticle transport and distribution is important. In this work, a numerical model to capture the nanoparticle transport and solute transport during the micro-scale solidification of binary alloy containing nanoparticles is presented. To develop the model, a sharp interface enthalpy method-based solidification model is used. The nanoparticle transport is governed by nanoparticle diffusion due to Brownian motion and by nanoparticle engulfment/pushing at the interface. The nanoparticle engulfment or pushing is modeled as a function of critical engulfment velocity and interface velocity. Thus, the effect of nanoparticle size and local interface movement velocity on nanoparticle engulfment can be predicted by the model. Simulation results show poor engulfment of smaller nanoparticles and relatively higher engulfment of larger nanoparticles. This results in slower dendrite growth rate in presence of smaller nanoparticles. It is also observed that as the dendrites grow, there is a transition from engulfment of nanoparticles to pushing of nanoparticles. This transition depends on the nanoparticle size and is delayed for larger nanoparticles. Thus, more uniform distribution of larger nanoparticles is observed in the solidified binary alloy nanocomposites.

Measuring the concentration of protein nanoparticles synthesized by desolvation method: Comparison of Bradford assay, BCA assay, hydrolysis/UV spectroscopy and gravimetric analysis

The desolvation technique is one of the most popular methods for preparing protein nanoparticles for medicine, biotechnology, and food applications. We fabricated 11 batches of BSA nanoparticles and 2 batches of gelatin nanoparticles by desolvation method. BSA nanoparticles from 2 batches were cross-linked by heating at +70 °C for 2 h; other nanoparticles were stabilized by glutaraldehyde. We compared several analytical approaches to measuring their concentration: gravimetric analysis, bicinchoninic acid assay, Bradford assay, and alkaline hydrolysis combined with UV spectroscopy. We revealed that the cross-linking degree and method of cross-linking affect both Bradford and BCA assay. Direct measurement of protein concentration in the suspension of purified nanoparticles by dye-binding assays can lead to significant (up to 50–60%) underestimation of nanoparticle concentration. Quantification of non-desolvated protein (indirect method) is affected by the presence of small nanoparticles in supernatants and can be inaccurate when the yield of desolvation is low. The reaction of cross-linker with protein changes UV absorbance of the latter. Therefore pure protein solution is an inappropriate calibrator when applying UV spectroscopy for the determination of nanoparticle concentration. Our recommendation is to determine the concentration of protein nanoparticles by at least two different methods, including gravimetric analysis.

Comparative Study of the Characteristics and Activities of Pd/γ-Al2O3 Catalysts Prepared by Vortex and Incipient Wetness Methods

5 wt% Pd/γ-Al2O3 catalysts were prepared by a modified Vortex Method (5-Pd-VM) and Incipient Wetness Method (5-Pd-IWM), and characterized by various techniques (Inductively coupled plasma atomic emission spectroscopy (ICP-AES), N2-physisorption, pulse CO chemisorption, temperature programmed reduction (TPR), X-ray photoelectron spectroscopy (XPS), scanning transmission electron microscopy (STEM), and X-ray diffraction (XRD)) under identical conditions. Both catalysts had similar particle sizes and dispersions; the 5-Pd-VM catalyst had 0.5 wt% more Pd loading (4.6 wt%). The surfaces of both catalysts contained PdO and PdOx with about 7% more PdOx in 5-Pd-VM. High-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) and scanning electron microscope (SEM) images indicated presence of PdO/PdOx nanocrystals (8–10 nm) on the surface of the support. Size distribution by STEM showed presence of smaller nanoparticles (2–5 nm) in 5-Pd-VM. This catalyst was more active in the lower temperature range of 275–325 °C and converted 90% methane at 325 °C. The 5-Pd-VM catalyst was also very stable after 72-hour stability test at 350 °C showing 100% methane conversion, and was relatively resistant to steam deactivation. Hydrogen TPR of 5-Pd-VM gave a reduction peak at 325 °C indicating weaker interactions of the oxidized Pd species with the support. It is hypothesized that smaller particle sizes, uniform particle distribution, and weaker PdO/PdOx interactions with the support may contribute to the higher activity in 5-Pd-VM.

Antimicrobial Photodynamic Activity of Cationic Nanoparticles Decorated with Glycosylated Photosensitizers for Water Disinfection

AbstractThe antimicrobial photodynamic approach has been demonstrated as an efficient and sustainable process for the eradication of microbial pathogens. In this work, silica‐coated magnetite nanoparticles (NPs) were used as carriers of glycosylated porphyrins and phthalocyanines. Their subsequent cationization resulted in the production of stable antimicrobial photosensitizing materials, effective against E. coli. Suspensions of the photocatalysts in water present bimodal size distributions formed by big clusters and small NPs with hydrodynamic diameters between 8 and 38 nm. The presence of small NPs in the suspensions is related to an effective photodynamic inactivation (PDI) of E. coli cells. Glycosylation of the PS showed a positive effect on the PDI performance, which could be related to a higher accumulation of the photocatalyst over the bacterial cell membrane. In addition, these biocidal agents proved to be photostable and their photoactive performance decreased only between 23 % and 28 % upon 5 PDI cycles, mostly because of the loss of material between cycles, which makes them promising materials for water disinfection purposes.

Voltammetric, dynamic light scattering (DLS) and electrophoretic mobility characterization of FeS nanoparticles (NPs) in different electrolyte solutions

Voltammetric response of FeS nanoparticles (NPs) dispersion based on the oxidation exchange voltammetric peak between Hg electrode and FeS NPs at around−0.45 V was studied in different electrolytes (chloride, acetate, perchlorate). Several experiments were designed to monitor in parallel to voltammetric measurements, physicochemical and surface characteristics of the formed FeS NPs (ζ- potential and size) under same experimental conditions. It was shown that recorded voltammetric peak produced by FeS NPs from bulk solution is changing with electrolyte concentration and composition, as well as observed size and ζ-potential of the studied FeS NPs. Our measurements indicate relationship between measured ζ-potential of FeS NPs dispersions and recorded voltametric peak charge and potential, pointing to a promising potential of voltammetry in characterization of physicochemical and surface chemistry features of metal sulphide NPs in water environment. The best voltammetric response is obtained in presence of small NPs, <100 nm.

Solution combustion synthesis and physicochemical characterization of ZrO 2–MoO 3 nanocomposite oxides prepared using different fuels

A series of MoO 3–ZrO 2 nanocomposite oxides with MoO 3 content in the range of 2–20 mol% were prepared by solution combustion method. Three different fuels namely urea, glycine and hexamethylenetetramine (HMTA) were used for the preparation of MoO 3–ZrO 2 oxides. For the sake of comparison, the MoO 3–ZrO 2 composite oxides were also prepared by impregnation of zirconia with molybdenum salt precursor and subsequent heat treatment. The synthesized nanomaterials were characterized by XRD, SEM, TEM and UV–vis spectroscopic technique. XRD study indicated selective stabilization of the tetragonal phase of zirconia in the presence of MoO 3. The method of preparation was found to be crucial for the phase composition of zirconia in the composite oxide. The crystallite size and rms stain were calculated from the Fourier line shape analysis of the broadened X-ray diffraction profiles. With increase in the MoO 3 content, the crystallite size of the tetragonal zirconia phase was found to be decreased. TEM study indicated the presence of small nanoparticles with size in the 5–10 nm range. UV–vis study of the composite oxide materials revealed well dispersion of the molybdenum oxide component in the form of monomer, dimers and nanoclusters in the zirconia matrix. The nature of fuel was found to be crucial in determining the morphology and shape of the particles.