Microemulsion-mediated Synthesis Research Articles

New Ionic Liquid Microemulsion-Mediated Synthesis of Silver Nanoparticles for Skin Bacterial Infection Treatments.

This work reports a new approach for the synthesis of extremely small monodispersed silver nanoparticles (AgNPs) (2.9-1.5) by reduction of silver nitrate in a new series of benzyl alkyl imidazolium ionic liquids (BAIILs)-based microemulsions (3a-f) as media and stabilizing agents. Interestingly, AgNPs isolated from the IILMEs bearing the bulkiest substituents (tert-butyl and n-butyl) (3f) displayed almost no nanoparticle agglomeration. In an in vitro antibacterial test against ESKAPE pathogens, all AgNPs-BAIILs had potent antibiotic activity, as reflected by antibacterial efficiency indices. Furthermore, when compared to other nanoparticles, these were the most effective in preventing biofilm formation by the tested bacterial strains. Moreover, the MTT assay was used to determine the cytotoxicity of novel AgNPs-BAIILs on healthy human skin fibroblast (HSF) cell lines. The MTT assay revealed that novel AgNPs-BAIILs showed no significant toxic effects on the healthy cells. Thus, the novel AgNPs-BAIILs microemulsions could be used as safe antibiotics for skin bacterial infection treatments. AgNPs isolated from BAIIL (3c) was found to be the most effective antibiotic of the nanoparticles examined.

CO2-Responsive Hydrophobic Deep Eutectic Solvent Based on Surfactant-Free Microemulsion-Mediated Synthesis of BaF2 Nanoparticles.

A new form of surfactant-free microemulsion (SFME) including hydrophobic deep eutectic solvent (HDES)/ethanol/water was constructed based on its CO2 response, and three regions, that is, HDES-in-water (HDES/W), bicontinuous (B.C.), and water-in-HDES (W/HDES) regions, were recognized. It is anticipated that SFMEs with tunable microstructures have outstanding applications as nanoreactors in reaction processes. The feasibility of preparing nanoparticles from HDES/ethanol/water SFME using barium fluoride (BaF2) as a model nanoparticle was investigated. HDES-based microemulsions benefit from HDES's excellent properties (novel, low toxicity, CO2-responsive, easy availability) and have potential in universal reactions, drug delivery, advanced material fabrication, etc. In this research, HDES-based microemulsions were prepared using HDES as the oil phase. Phase equilibria and microstructure were investigated using a ternary phase diagram, UV spectrophotometry, and the conductivity method. The CO2 switchable characteristics of the HDES-based microemulsions were investigated. HDES-based microemulsions were proposed as nanoreactors for the synthesis of barium fluoride nanomaterials. The microemulsion structure can modulate the size, morphology, and physicochemical properties of the nanoparticles through the CO2 switchable properties. It is argued that nanoreactors constructed with versatile HDES will offer a new direction for creation of cutting-edge scientific applications.

Solid and hollow nanoparticles templated using non-ionic surfactant-based reverse micelles and vesicles

Surfactants play a critical role in nanoparticle morphology control in microemulsion-mediated synthesis. Herein tuning the morphology of silica nanoparticles from solid to hollow is investigated by varying the phase structure within reverse microemulsions using a non-ionic surfactant (Triton X-100, TX100). Assisted with dynamic light scattering and rheology, it is found that increasing the concentration of TX100 leads to a transition from small reverse micelles to larger double-layered reverse vesicles. Transmission Electron Microscopy is employed to show this phase change corresponds to the synthesis of solid and hollow silica nanoparticles, respectively. It is also found that adding another co-surfactant, ethanol, is also able to tune the synthesized particles from solid to hollow, as well as the shell thickness of the hollow nanoparticles. This study shows how the microemulsion phase structure can be used to tune the morphology of nanoparticles.

One-pot microemulsion-mediated synthesis of Bi-rich Bi4O5Br2 with controllable morphologies and excellent visible-light photocatalytic removal of pollutants

The novel Bi-rich Bi4O5Br2 with tunable morphologies of two-dimentional (2D) nanosheets (NSs), three-dimentional (3D) monodisperse layered microspheres (LMs) and hollow spheres (HSs) have been successfully synthesized via an ionic liquid-in-water (IL/W) microemulsion method. Surfactant TX-100 served as the stabilizer of the IL/W microemulsion, and its concentration significantly influenced the morphology and size of the resulting Bi4O5Br2 crystal. Possible formation mechanisms have also been discussed. UV–vis diffuse-reflectance spectra and Density function theory (DFT) calculations indicated that Bi4O5Br2 possessed stronger visible light adsorption and more negative conduction band minimum (CBM), which is beneficial to effectively activate molecular oxygen to produce O2−. The photocatalytic activity of Bi-rich Bi4O5Br2 with varied shapes was investigated and compared with BiOBr for the removal of fungicide o-phenylphenol (OPP) and antibacterial agent norfloxacin (NOR) and tetracycline hydrochloride (TC) under visible light irradiation. The as-prepared Bi4O5Br2 HSs and LMs possess higher photocatalytic efficiency than Bi4O5Br2 and BiOBr NSs, which is attributed to the hollow/layered spherical structures and Bi-rich strategies. The O2− and h+ are identified to be the major photoactive species during the photo-degradation process by scavenger experiments and EPR methods. This study is expected to provide a stepping stone to purposively design and explore other novel hollow structures with controllable morphology and enhanced photocatalytic activity.

Microemulsion-mediated synthesis, characterization and optical properties of spherical nickel tungstate nanocrystals

Nickel tungstate (NiWO4) nanocrystals with wolframite structure were prepared in the presence of microemulsion systems including a cationic cetyltrimethylammonium bromide (CTAB) or nonionic polyethyleneglycol (PEG) surfactant. The water pools formed in the microemulsion system acted as nanoscale reactors for the reaction of nickel and tungstate ions to produce nickel tungstate nanocrystals. X-ray diffraction analysis revealed the formation of monoclinic phase after the heat treatment of the as-prepared materials. Elemental compositions and morphological structures were studied by energy dispersive X-ray analysis (EDX) and scanning electron microscopy (SEM). SEM analysis showed the spherical morphology of NiWO4. The average crystallite sizes of NiWO4 were about 38 and 26 nm in the presence of PEG and CTAB surfactants, respectively. The study of UV–Vis absorption spectrum showed the presence of direct band gap in the NiWO4 nanomaterial, found to be 2.7 and 2.6 eV in the presence of PEG and CTAB surfactants, respectively. A reasonable crystal growth mechanism has also been proposed.

Microemulsion-mediated synthesis of sedum rubrotinctum shaped Cu2O architecture with efficient sunlight driven photocatalytic activity

Schematic of photo-activation of sedum rubrotinctum shaped Cu2O photocatalyst and degradation of MB.

Synthesis of Nanostructured Catalytic Materials from Microemulsions

Since the 1980s [1,2], colloidal systems such as microemulsions (ME) have been widely investigated, especially for the synthesis of nanomaterials for various applications.[...]

Reverse Microemulsion-mediated Synthesis of Monometallic and Bimetallic Early Transition Metal Carbide and Nitride Nanoparticles

Reverse Microemulsion-mediated Synthesis of Monometallic and Bimetallic Early Transition Metal Carbide and Nitride Nanoparticles

Reverse Microemulsion-mediated Synthesis of Monometallic and Bimetallic Early Transition Metal Carbide and Nitride Nanoparticles.

A reverse microemulsion is used to encapsulate monometallic or bimetallic early transition metal oxide nanoparticles in microporous silica shells. The silica-encapsulated metal oxide nanoparticles are then carburized in a methane/hydrogen atmosphere at temperatures over 800 °C to form silica-encapsulated early transition metal carbide nanoparticles. During the carburization process, the silica shells prevent the sintering of adjacent carbide nanoparticles while also preventing the deposition of excess surface carbon. Alternatively, the silica-encapsulated metal oxide nanoparticles can be nitridized in an ammonia atmosphere at temperatures over 800 °C to form silica-encapsulated early transition metal nitride nanoparticles. By adjusting the reverse microemulsion parameters, the thickness of the silica shells, and the carburization/nitridation conditions, the transition metal carbide or nitride nanoparticles can be tuned to various sizes, compositions, and crystal phases. After carburization or nitridation, the silica shells are then removed using either a room-temperature aqueous ammonium bifluoride solution or a 0.1 to 0.5 M NaOH solution at 40-60 °C. While the silica shells are dissolving, a high surface area support, such as carbon black, can be added to these solutions to obtain supported early transition metal carbide or nitride nanoparticles. If no high surface area support is added, then the nanoparticles can be stored as a nanodispersion or centrifuged to obtain a nanopowder.

Reverse microemulsion-mediated synthesis of Au@SiO2 hybrid nanoparticles with different morphologies

In this study, we report a simple synthesis of multiple Au nanodots core-silica shell nanoparticles (multi-Au@SiO2 NPs). The Au@SiO2 hybrid nanoparticles were synthesized in a water-in-oil microemulsion with a composition of polyoxyethylene(10) tertoctylphenyl ether (Triton X-100)/1-hexanol/cyclohexane/H2O and have been fully characterized by transmission electron microscopy (TEM), high-resolution TEM (HR-TEM) observations, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FTIR), UV-vis measurements, and thermogravimetric analysis (TGA). The morphologies of the hybrid nanoparticles of Au@SiO2 can be easily tuned by the molar ratio of HAuCl4 to NaBH4 and the volume ratio of HAuCl4 aqueous solution to TEOS. As the morphologies of Au@SiO2 nanoparticles varied, the optical properties also changed as revealed by UV absorption spectrum. These Au@SiO2 hybrid nanoparticles which possess these properties make them fascinating candidates for a variety of applications such as catalysis and life science.

Reverse microemulsion-mediated synthesis of Bi2S3–QD@SiO2–PEG for dual modal CT–fluorescence imaging in vitro and in vivo

Monodispersed Bi2S3-QD@SiO2-PEG nanoparticles are prepared by a one-pot method in a reverse microemulsion system, which exhibited remarkable performances in CT and fluorescence imaging in vitro and in vivo.

Microemulsion-mediated synthesis and characterization of monodispersed nickel molybdate nanocrystals

Abstract The present work reports the preparation of nickel molybdate nanocrystals via a microemulsion method. The microemulsion system included cationic surfactant CTAB, 1-butanol as co-surfactant, isooctane as oil phase, and aqueous solutions of nickel chloride and sodium molybdate. The produced water pools in the microemulsion system act as nanoreactors for reaction of nickel and molybdate ions to produce nickel molybdate nanomaterial. After calcination, the structure and morphology of the product were characterized by Fourier-transform infrared (FT-IR) and UV–vis spectroscopies, X-ray diffraction (XRD), energy-dispersive X-ray analysis (EDX), transmission electron microscopy (TEM), and thermogravimetric analyses (TGA). The synthesized α-NiMoO4 nanocrystals have a monoclinic structure with lengths of 140–150 nm and widths of 60–70 nm.

Fabricating ordered functional nanostructures onto polycrystalline substrates from the bottom-up

Microemulsion-mediated synthesis has emerged as a powerful bottom-up procedure for the preparation of ferroelectric nanostructures onto substrates. However, periodical order has yet to be achieved onto polycrystalline Pt-coated Si substrates. Here, we report a new methodology that involves microemulsion-mediated synthesis and the controlled modification of the surface of the substrate by coating it with a template-layer of water-micelles. This layer modifies the surface tension of the substrate and yields a periodic arrangement of ferroelectric crystalline nanostructures. The size of the nanostructures is decreased to the sub-50 nm range and they show a hexagonal order up to the third neighbors, which corresponds to a density of 275 Gb in−2. The structural analysis of the nanostructures by synchrotron X-ray diffraction confirms that the nanostructures have a PbTiO3 perovskite structure, with lattice parameters of a = b = 3.890(0) A and c = 4.056(7) A. Piezoresponse force microscopy confirmed the ferro-piezoelectric character of the nanostructures. This simple methodology is valid for the self-assembly of other functional oxides onto polycrystalline substrates, enabling their reliable integration into micro/nano devices.

Microemulsion-Mediated Synthesis and Characterization of YBO3:Ce3+ Phosphors

Monophasic YBO3:Ce3+ phosphors were successfully synthesized via microemulsion route with various volumetric ratios of water to oil (Ws). The phosphors had uniform size distribution on the nanometer scale with spherical morphology owing to confinement of the constituent cations by the aqueous micelles. As Ws was decreased from 0.1 to 0.025, the average size of the produced particles decreased from 189 to 90 nm due to reduced sizes of aqueous micelles. Upon 363 nm excitation, the phosphors exhibited strong and broad blue emission ranging from 375 to 520 nm, which arise from the 5d to 2F5/2 and 2F7/2 transitions of Ce3+ ions. The emission intensity declined with the decrease of particle size, and this result can be ascribed to the increment of surface defects in small particles. YBO3:Ce3+ phosphors, that were prepared with Ws = 0.1 at high calcination temperatures, exhibited high luminescent intensity due to less defects. The mechanisms of enhanced crystallinity and luminescence as a function of Ws and calcinations temperature were investigated in detail.

Spark plasma sintering of nanocrystalline BaTiO 3-powders: Consolidation behavior and dielectric characteristics

BaTiO 3 nanopowders prepared by two different wet chemical routes, one based on microemulsion-mediated synthesis (M-BT) and the other one on the alkoxide–hydroxide method (A-BT) were consolidated by spark plasma sintering (SPS). The densification process, the linear shrinkage rates and the relative densities achieved were strongly dependant on the synthetic route. The results show that fully densified BaTiO 3 ceramics with a grain size of about 200 nm can be obtained in both cases by controlling the sintering temperature during the SPS process. The study of dielectric properties revealed that M-BT derived ceramics show higher permittivity values compared to those obtained for A-BT. The influence of the barium/titanium ratio on the sintering behavior and the dielectric properties is discussed.

Reverse Microemulsion-Mediated Synthesis of SiO2-Coated ZnO Composite Nanoparticles: Multiple Cores with Tunable Shell Thickness

Monodispersed SiO(2)-shell/ZnO-core composite nanospheres have been prepared in an oil-in-water microemulsion system. By using cyclohexane as the oil phase and Triton X-100 as the surfactant, composite nanospheres with high core loading levels and tunable shell thickness were obtained. Utilization of PVP capping agent on ZnO allowed the synthesis of composite nanospheres without forming any coreless SiO(2) spheres or shell-less ZnO particles. The photoactivity of ZnO nanoparticles was greatly reduced by SiO(2)-coating, which enables their applications as durable, safe, and nonreactive UV blockers in plastics, coating, and other products.

Microemulsion-mediated synthesis of cobalt (pure fcc and hexagonal phases) and cobalt–nickel alloy nanoparticles

By choosing appropriate microemulsion systems, hexagonal cobalt (Co) and cobalt–nickel (1:1) alloy nanoparticles have been obtained with cetyltrimethylammonium bromide as a cationic surfactant at 500 °C. This method thus stabilizes the hcp cobalt even at sizes (<10 nm) at which normally fcc cobalt is predicted to be stable. On annealing the hcp cobalt nanoparticles in H 2 at 700 °C we could transform them to fcc cobalt nanoparticles. Microscopy studies show the formation of spherical nanoparticles of hexagonal and cubic forms of cobalt and Co–Ni (1:1) alloy nanoparticles with the average size of 4, 8 and 20 nm, respectively. Electrochemical studies show that the catalytic property towards oxygen evolution is dependent on the applied voltage. At low voltage (less than 0.65 V) the Co (hexagonal) nanoparticles are superior to the alloy (Co–Ni) nanoparticles while above this voltage the alloy nanoparticles are more efficient catalysts. The nanoparticles of cobalt (hcp and fcc) and alloy (Co–Ni) nanoparticles show ferromagnetism. The saturation magnetization of Co–Ni nanoparticles is reduced compared to the bulk possibly due to surface oxidation.

Reverse Microemulsion-Mediated Synthesis of Silica-Coated Gold and Silver Nanoparticles

A reverse microemulsion method is reported for preparing monodispersed silica-coated gold (or silver) nanoparticles without the use of a silane coupling agent or polymer as the surface primer. This method enables a fine control of the silica shell thickness with nanometer precision. As compared to the Stöber method reported for direct silica coating, which can only coat large gold particles ( approximately 50 nm in diameter) at low concentrations (<1.5 x 10(10) particles/mL), this new approach is capable of coating gold particles of a wide range of sizes (from 10 to 50 nm) at a much higher concentration ( approximately 1.5 x 10(13) particles/mL). Moreover, it enables straightforward surface functionalization via co-condensation between tetraethyl orthosilicate and another silane with the desired functional groups. The functional groups introduced by this method are readily accessible and thus useful for various applications.

Electronic and structural promotion of barium hexaaluminate as a ruthenium catalyst support for ammonia synthesis

Barium hexaaluminate (BHA) with large surface area (49 m2 g−1) is synthesized by microemulsion-mediated synthesis technique and examined as a support promoting ammonia synthesis by particulate Ru. The Ru/BHA catalyst exhibits higher activity and stability than Ba-promoted Ru/MgO, the previously most active oxide-supported catalyst system for ammonia synthesis. The rate of ammonia synthesis over Ru/BHA is 5426 μmol g−1cat h−1 (653 K, 1.1 MPa), more than twice of that of Ba–Ru/MgO, and no decrease in the rate is observed over reaction for 80 h at 653 K and 0.1 MPa. Characterization of this catalyst system by various techniques reveals that the electronic and structural interactions between BHA and Ru particles are key factors responsible for the elevated activity and stability of this catalyst.

Synthesis and Characterization of Ultrafine Tungsten and Tungsten Oxide Nanoparticles by a Reverse Microemulsion-Mediated Method

Ultrafine tungsten and tungsten oxide powders with controllable particle size and structure have been synthesized by a reverse microemulsion-mediated synthesis method. The nanoparticles were characterized by transmission electron microcopy, X-ray diffraction, and thermal analysis. Synthesis conditions, including water-to-surfactant ratio, annealing temperature, water-to-alkoxide ratio, and drying method, have been shown to be critical in controlling the size and structure of tungsten nanoparticles. Using the same synthesis technique, carbon-supported metallic tungsten and tungsten oxide nanoparticles with controllable size and dispersion can also be prepared. The ultrafine nanoparticles prepared by this synthesis method may find interesting applications in various fields such as catalysis, electronics, illumination, gas sensors, and so forth.