Influence of supporting electrolyte on electrochemical formation of copper nanoparticles and their electrocatalytic properties

Comparative analysis of copper nanoparticles (CuNPs) obtained by electrodeposition on highly oriented pyrolytic graphite (HOPG) substrates from different supporting electrolytes containing sulphate anions, was performed. Voltammetric results indicated that Cu electrodeposition follows a diffusion-controlled nucleation and crystal growth model for three solutions studied (Na2SO4, H2SO4 and Na2SO4+H2SO4). Na2SO4 solution was found to be most effective because the copper reduction occurs at most positive potential value, reaching the highest current density. Analysis of potentiostatic current transients revealed that the process can be described predominantly by a model involving 3D-progressive nucleation mechanism, which was corroborated by scanning electron microscopy (SEM) analysis. SEM images showed high density of hemispherical shaped Cu particles of different sizes (mostly between 80-150 nm), randomly distributed on the HOPG surface for Na2SO4 electrolyte solution. In the presence of H2SO4, the size dispersion decreased, resulting in particles with greater diameters (up to 339 nm). The use of electrolyte solution with Na2SO4+H2SO4 revealed lower particle density with a considerable crystal size dispersion, where very small crystallites are prevailing. Cyclic voltammetry was used to evaluate qualitatively the catalytic activity of CuNPs deposited from three electrolyte solutions towards the nitrate reduction reaction. An enhanced catalytic effect was obtained when copper particles were prepared from either Na2SO4 or H2SO4 supporting electrolytes.

In situ small-angle X-ray scattering investigation of X-ray-induced gold nanoparticle synthesis without stabilizer

The X-ray irradiation of gold salt aqueous solutions in the synthesis of gold nanoparticles (AuNPs) in the absence of any reducing agent or stabilizer is presented. The size, dispersion, number of particles, yield and morphology evolution during the radiolytic formation of AuNPs were followed simultaneously using in situ small-angle X-ray scattering. This study provides an insight into the overall kinetics and formation mechanisms at the initial stage of AuNP synthesis without reductants and stabilizers. The pH-dependent speciation of aqueous HAuCl4 and its influence on the synthesis, structure and properties of AuNPs were observed. The result sheds light on the key parameters required to obtain stable monomodal particles and the influence of the surface charge and reactivity of the chemical solution on the final particle size and shape.

Laser-ablative synthesis of stable size-tunable Bi nanoparticles and their functionalization for radiotherapy applications

Nanoformulations of high-Z elements can improve therapeutic outcome in radiotherapy-based treatment of tumors, but current nanomedicine implementations in radiotherapy still need biocompatible, non-toxic nano-agents exhibiting low polydispersity and high colloidal stability. Here, we elaborate methods of femtosecond (fs) laser ablation in water and organic solvents to fabricate stable aqueous colloidal solutions of ultrapure elemental Bi nanoparticles (NPs) and characterize them. We show that fs laser ablation of Bi target leads to the formation of spherical elemental Bi NPs having 25 nm mean size and wide size-dispersion. NPs prepared in water undergo fast conversion into 400-500 nm flake-like nanosheets, while NPs prepared in acetone demonstrate a high colloidal stability. We then employ methods of fs laser fragmentation to control mean size and size dispersion of Bi NPs. Stable aqueous solution of Bi NPs suitable for biomedical applications can be obtained by coating with Pluronic® F-127. We finally show that surface modification of Bi NPs increases its colloidal stability in phosphate buffer saline (PBS) solution by more than 6 fold. Exempt of any toxic synthetic by-products, laser-ablated Bi NPs present a novel appealing nanoplatform for image-guided combination photo- and radiotherapy.

A Green, Simple and Facile Way to Synthesize Silver Nanoparticles Using Soluble Starch. pH Studies and Antimicrobial Applications

Along with the progress of nanoscience and nanotechnology came the means to synthesize nanometric scale materials. While changing their physical and chemical properties, they implicitly changed their application area. The aim of this paper was the synthesis of colloidal silver nanoparticles (Ag-NPs by ultrasonic disruption), using soluble starch as a reducing agent and further as a stabilizing agent for produced Ag-NPs. In this context, an important parameter for Ag-NPs preparation is the pH, which can determine the particle size and stability. The physical-chemical behavior of the synthesized Ag-NPs (shape, size, dispersion, electric charge) is strongly influenced by the pH value (experiment being conducted for pH values in the range between 8 and 13). The presence of a peak located at 412 nm into the UV-VIS spectra demonstrates the presence of silver nano-spheres into the produced material. In UV/VIS spectra, we observed a specific peak for yellow silver nano-spheres located at 412 nm. Samples characterization was performed by scanning electron microscopy, SEM, energy-dispersive X-ray spectroscopy, EDX, Fourier-transform infrared spectroscopy, and FT-IR. For all Ag-NP samples, we determined the zeta and observed that the Ag-NP particles obtained at higher pH and have better stability. Due to the intrinsic therapeutic properties and broad antimicrobial spectrum, silver nanoparticles have opened new horizons and new approaches for the control of different types of infections and wound healing abilities. In this context, the present study also aims to confirm the antimicrobial effect of prepared Ag-NPs against several bacterial strains (indicator and clinically isolated strains). In this way, it was confirmed that the antimicrobial activity of synthesized Ag-NPs was good against Staphylococcus aureus (ATCC 25923 and S. aureus MSSA) and Escherichia coli (ATTC 25922 and clinically isolated strain). Based on this observation, we conclude that the prepared Ag-NPs can represent an alternative or auxiliary material used for controlling important nosocomial pathogens. The fungal reference strain Candida albicans was more sensitive at Ag-NPs actions (zone of inhibition = 20 mm) compared with the clinically isolated strain (zone of inhibition = 10 mm), which emphasizes the greater resistance of fungal strains at antimicrobial agent’s action.

Design of Silica Nanoparticles-Supported Metal Catalyst by Wet Impregnation with Catalytic Performance for Tuning Carbon Nanotubes Growth

The catalytic activity of cobalt and iron nanoparticles for the growth of carbon nanotubes (CNTs) was studied by a specific reproducible and up-scalable fabrication method. Co and Fe catalysts were deposited over SiO2 nanoparticles by a wet-impregnation method and two different annealing steps were applied for the catalyst formation/activation. The samples were calcined at an optimal temperature of 450 °C resulting in the formation of metal oxide nano-islands without the detection of silicates. Further reduction treatment (700 °C) under H2 successfully converted oxide nanoparticles to Co and Fe metallic species. Furthermore, the catalytic efficiency of both supported-metal nanoparticles at 2 and 5% in weight of silica was evaluated through the growth of CNTs. The CNT structure, morphology and size dispersion were tailored according to the metal catalyst concentration.

Underwater Holographic Sensor for Plankton Studies In Situ Including Accompanying Measurements

The paper presents an underwater holographic sensor to study marine particles—a miniDHC digital holographic camera, which may be used as part of a hydrobiological probe for accompanying (background) measurements. The results of field measurements of plankton are given and interpreted, their verification is performed. Errors of measurements and classification of plankton particles are estimated. MiniDHC allows measurement of the following set of background data, which is confirmed by field tests: plankton concentration, average size and size dispersion of individuals, particle size distribution, including on major taxa, as well as water turbidity and suspension statistics. Version of constructing measuring systems based on modern carriers of operational oceanography for the purpose of ecological diagnostics of the world ocean using autochthonous plankton are discussed. The results of field measurements of plankton using miniDHC as part of a hydrobiological probe are presented and interpreted, and their verification is carried out. The results of comparing the data on the concentration of individual taxa obtained using miniDHC with the data obtained by the traditional method using plankton catching with a net showed a difference of no more than 23%. The article also contains recommendations for expanding the potential of miniDHC, its purpose indicators, and improving metrological characteristics.

Influence of size effects and granule distribution by size on optical and magneto-optical properties of nanocomposites

In this paper, the spectral dependences of the transverse Kerr effect (ТКЕ) are studied experimentally and theoretically. The results are obtained for deposited and annealed samples with a corresponding variation in the size of the granules. It was found that thermomagnetic annealing leads to an increase in the ТКЕ value in magnetic nanostructures, while the most noticeable changes in the effect value were observed in the range of medium and high concentrations of the magnetic component in the visible region of the spectrum. The expediency of using the effective medium approach for calculating magneto-optical effects in granular systems, taking into account the size distribution of granules within the lognormal distribution of granules, is shown. Based on this approach, the main features of the optical and magneto-optical properties of nanocomposites are explained by the example of (Co45Fe45Zr10)X(Al2O3)1–X. All calculations are performed in the Bruggemann approximation, which effectively describes the properties of nanostructures in the region of average concentrations. Size effects are clearly manifested in nanocomposites and have a significant impact on the optical and magneto-optical properties of nanocomposites, especially in the IR region of the spectrum, which is associated with intraband transitions. Taking into account the particle size distribution makes it possible to significantly improve the description of such promising inhomogeneous nanostructures. The solved problem is very important and relevant both from the fundamental point of view – the study of magneto-optical, optical and transport phenomena in nanocomposites – and from the point of view of the great possibilities of their application in modern electronics and nanoelectronics. Taking into account the size effects and the particle size dispersion makes it possible to find new promising functional materials and control their properties in a wide spectral range.

2D boron nitride nanosheets for polymer composite materials

Hexagonal boron nitride nanosheets (BNNSs) are promising two-dimensional materials to boost the mechanical, thermal, electrical, and optical properties of polymer nanocomposites. Yet, BNNS-polymer composites face many challenges to meet the desired properties owing to agglomeration of BNNSs, incompatibility, and weak interactions of BNNSs with the host polymers. This work systematically reviews the fundamental parameters that control the molecular interactions of BNNSs with polymer matrices. The surface modification of BNNSs, as well as size, dispersion, and alignment of these nanosheets have a profound effect on polymer chain dynamics, mass barrier properties, and stress-transfer efficiency of the nanocomposites.

Exciton-Related Raman Scattering, Interband Absorption and Photoluminescence in Colloidal Cdse/Cds Core/Shell Quantum Dots Ensemble

By using the numerical discretization method within the effective-mass approximation, we have theoretically investigated the exciton-related Raman scattering, interband absorption and photoluminescence in colloidal CdSe/CdS core/shell quantum dots ensemble. The interband optical absorption and photoluminescence spectra have been revealed for CdSe/CdS quantum dots, taking into account the size dispersion of the ensemble. Numerical calculation of the differential cross section has been presented for the exciton-related Stokes–Raman scattering in CdSe/CdS quantum dots ensemble with different mean sizes.