Uniform metal nanoparticles produced at high yield in dense microemulsions

Microscopic properties and stabilization mechanism of a supercritical carbon dioxide microemulsion with extremely high water content

HYPOTHESIS

Developing the supercritical carbon dioxide microemulsion with a broad water content (W₀) window can provide more possibility for designing highly efficient chemical processes, which is challenging due to the lack of comprehension about its formation mechanism. Molecular dynamics simulation method is expected to reveal the microscopic stabilization mechanism of high-W₀ microemulsions.

SIMULATIONS

All-atom molecular dynamics simulations of the ternary systems with varied W₀ stabilized by 4FG(EO)₂ surfactant were designed according to phase behavior experiments. A systematic investigation was performed concerning the self-assembling, equilibrium morphology and detailed microstructure of the microemulsion droplet. An in-depth comparative study about the distribution of both H₂O and CO₂, the interfacial behaviors of 4FG(EO)₂, as well as the microscopic interactions was conducted.

FINDINGS

For the first time, direct evidence was provided for the formation of water-in-carbon dioxide microemulsion with extremely high W₀ (80) under the effect of 4FG(EO)₂. Furthermore, a unique interfacial phenomenon, i. e. CO₂ accumulating at the interface, was revealed to be responsible for the formation and enhanced stability of the nanosized droplet with high W₀. This should set a new guiding star for synthesizing and selecting effective interfacial modifiers to create high-W₀ microemulsions.

Green synthesis of silver nanoparticles: Advantages of the yeast Saccharomyces cerevisiae model

Background and Purpose:

Microorganism-based synthesis of nanostructures has recently been noted as a green method for the sustainable development of nanotechnology. Nowadays, there have been numerous studies on the emerging resistant pathogenic bacteria and fungal isolates, the probable inability of bacteria and fungi to develop resistance against silver nanoparticles’ (SNPs) antibacterial, antifungal, antiviral and, particularly antibacterial activities. In this study, we aim to use the yeast Saccharomycescerevisiae model for synthesis of SNPs and to investigate its antifungal activity against some isolates of Candidaalbicans.

Materials and Methods:

A standard strain of S.cerevisiae was grown in liquid medium containing mineral salt; then, it was exposed to 2 mM AgNO₃. The reduction of Ag⁺ ions to metal nanoparticles was virtually investigated by tracing the color of the solution, which turned into reddish-brown after 72 hours. Further characterization of synthesized SNPs was performed afterwards. In addition, antifungal activity of synthesized SNPs was evaluated against fluconazole-susceptible and fluconazole-resistant isolates of Candidaalbicans.

Results:

The UV-vis spectra demonstrated a broad peak centering at 410 nm, which is associated with the particle sizes much less than 70 nm. The results of TEM demonstrated fairly uniform, spherical and small in size particles with almost 83.6% ranging between 5 and 20 nm. The zeta potential of SNPs was negative and equal to -25.0 (minus 25) mv suggesting that there was not much aggregation. Silver nanoparticles synthesized by S.cerevisiae, showed antifungal activity against fluconazole-susceptible and fluconazole-resistant Candida albicans isolates, and exhibited MIC₉₀ values of 2 and 4 μg/ml, respectively.

Conclusion:

The yeast S. cerevisiae model demonstrated the potential for extracellular synthesis of fairly monodisperse silver nanoparticles.

Pt Nanoparticles via Oil-in-Water Microemulsions Stabilized by a Technical Grade Surfactant: An Economical and Ecological Approach

This study deals with the synthesis of Pt nanoparticles via oil-in-water microemulsions formulated with the technical grade surfactant BIODAC® 510. For this purpose we studied the influence of the Platinum precursor dimethyl(cyclooctadiene)platinum (Pt(COD)Me2) on the phase behavior of the base microemulsion. It was found that the addition of Pt(COD)Me2 has nearly no effect on the phase boundaries even at relatively high concentrations. Small angle X-ray scattering data confirmed that the addition of the metal organyl also does not influence the size of the microemulsion droplets. According to transmission electron microscopy (TEM) the size of the resulting platinum nanoparticles is independent on the amount of Pt(COD)Me2 in the templating microemulsion. This result was rather surprising since it indicates that a greater amount of precursor in the o/w-microemulsion leads to more rather than to larger nanoparticles.

Bicontinuous microemulsions for high yield, wet synthesis of ultrafine nanoparticles: a general approach

The design of a synthesis strategy for metal nanoparticles by templating dense microemulsions is proposed. Particle size is controlled by surfactant size rather than by microemulsion composition. The strategy was demonstrated with various systems with different surfactant: cationic, anionic and non-ionic and of different sizes. Formulations were determined using the microemulsion phase diagrams. Synthesis was demonstrated for platinum nanoparticles with some examples for gold. The nanoparticles were subsequently extracted from the microemulsion by absorption onto a carbon support, after which the surfactant was recycled.

Sonoelectrochemical synthesis of a new nano lead(II) complex with quinoline-2-carboxylic acid ligand: a precursor to produce pure phase nano-sized lead(II) oxide

A new lead complex, [Pb(Q)2] (1) (Q=quinoline-2-carboxylic acid), was prepared via conventional electrochemical method in a fast and facile process and fully characterized by (1)H and (13)C NMR, IR, UV spectroscopies and elemental analysis. The nano-structures of same compound were successfully prepared at 25, 48 and 60°C by a facile and environment-friendly sonoelectrochemical route. The new nano-structure particles were characterized by scanning electron microscopy, X-ray powder diffraction, IR spectroscopy and elemental analysis. Thermal stability of single-crystal and nano-size samples of the prepared compound was studied by thermogravimetric and differential thermal analysis. The effect of sonoelectrochemical temperature on particle size has been investigated, and possible explanations offered. The photoluminescence properties of the nano-structured and crystalline bulk of the prepared complex at room temperature in the solid state have been investigated in detail. The results indicate that the size of the complex particles has an important effect on the optical properties of it. The prepared complexes, as bulk and as nano-particles, were utilized as a precursor for preparation of PbO nanoparticles by direct thermal decomposition at 600°C in air. The nano-structures of PbO were characterized by scanning electron microscopy, X-ray powder diffraction and IR spectroscopy.

Experimental and molecular dynamics characterization of dense microemulsion systems: morphology, conductivity and SAXS

Microemulsions are exciting systems that are promising as tuneable self-assembling templating reaction vessels at the nanoscale. Determination of the nano-structure of microemulsions is, however, not trivial, and there are fundamental questions regarding their design. We were able to reproduce experimental data for an important microemulsion system, sodium-AOT-n-heptane-water, using coarse-grained simulations involving relatively limited computational costs. The simulation allows visualization and deeper investigation of controversial phenomena such as bicontinuity and ion mobility. Simulations were performed using the Martini coarse-grained force field. AOT bonded parameters were fine-tuned by matching the geometry obtained from atomistic simulations. We investigated several compositions with a constant ratio of surfactant to oil while the water content was varied from 10 to 60% in weight. From mean square displacement calculation of all species, it was possible to quantify caging effects and ion mobility. Average diffusion coefficients were calculated for all charged species and trends in the diffusion coefficients were used to rationalize experimental conductivity data. Especially, the diffusion coefficient of charged species qualitatively matched the variation in conductivity as a function of water content. The scattering function was calculated for the hydrophilic species and up to 40% water content quantitatively matched the experimental data obtained from small angle X-ray scattering measurements. For higher water contents, discrepancies were observed and attributed to a nearby phase separation. In particular, bicontinuity of water and oil was computationally visualized by plotting the coordinates of hydrophilic beads. Equilibrated coarse-grained simulations were reversed to atomistic models in order both to compare ion mobility and to catch finer simulation details. Especially, it was possible to capture the intimate ion pair interaction between the sodium ion and the surfactant head group.

Bicontinuous microemulsions for high yield wet synthesis of ultrafine platinum nanoparticles: effect of precursors and kinetics

We demonstrate that for high yield wet synthesis of monodispersed nanoparticles high surfactant content bicontinuous microemulsions offer an advantageous template as particle size is limited by the embedding matrix whereas particle aggregation is largely prohibited by its structure. We synthesized platinum nanoparticles varying the reaction rate, metal precursor and reducing agent type and concentration, and the composition of the microemulsion in water content and oil type. High yields of up to 0.4% of metal produced per weight of template were achieved without affecting the particle size, ca. 2 nm. We showed that our method is robust in the sense that particle size is hardly dependent on synthesis conditions. This is attributed to the fact that the packing of surfactant on nanoparticle surfaces is the only parameter determining the particle size. It can only be slightly varied with ionic strength, headgroup hydration, and tail solvency through oil variation. Water content mainly affects the microemulsion stability and through that the colloidal stability of the nanoparticles. Hydrazine as a reducing agent poses a special case as it causes dimerization of the surfactant and hence modifies the surfactant parameter as well as the stability. Finally, we highlighted the differences in comparison to nanoparticle synthesis in standard water-in-oil microemulsions, and we propose a mechanism of particle formation.

High yield, controlled synthesis of graphitic networks from dense micro emulsions

We propose a new synthesis method to produce hyper-branched carbon nano structures that we call carbon nano networks. These porous, graphitic materials directly grow into a networked structure, do not require the use of an inorganic support, and can be tailored by experimental conditions to better suit their application.

Green and rapid synthesis of anticancerous silver nanoparticles by Saccharomyces boulardii and insight into mechanism of nanoparticle synthesis

Rapidly developing field of nanobiotechnology dealing with metallic nanoparticle (MNP) synthesis is primarily lacking control over size, shape, dispersity, yield, and reaction time. Present work describes an ecofriendly method for the synthesis of silver nanoparticles (AgNPs) by cell free extract (CFE) of Saccharomyces boulardii. Parameters such as culture age (stationary phase growth), cell mass concentration (400 mg/mL), temperature (35°C), and reaction time (4 h), have been optimized to exercise a control over the yield of nanoparticles and their properties. Nanoparticle (NP) formation was confirmed by UV-Vis spectroscopy, elemental composition by EDX (energy dispersive X-rays) analysis, and size and shape by transmission electron microscopy. Synthesized nanoparticles had the size range of 3–10 nm with high negative zeta potential (−31 mV) indicating excellent stability. Role of proteins/peptides in NP formation and their stability were also elucidated. Finally, anticancer activity of silver nanoparticles as compared to silver ions was determined on breast cancer cell lines.