Microemulsion Technique Research Articles

Quantum dots/silica/polymer nanocomposite films with high visible light transmission and UV shielding properties

The dispersion of light-absorbing inorganic nanomaterials in transparent plastics such as poly(ethylene-co-vinyl acetate) (PEVA) is of enormous current interest in emerging solar materials, including photovoltaic (PV) modules and commercial greenhouse films. Nanocrystalline semiconductor or quantum dots (QDs) have the potential to absorb UV light and selectively emit visible light, which can control plant growth in greenhouses or enhance PV panel efficiencies. This work provides a new and simple approach for loading mesoporous silica–encapsulated QDs into PEVA. Highly luminescent CdS and CdS-ZnS core–shell QDs with 5 nm size were synthesized using a modified facile approach based on pyrolysis of the single-molecule precursors and capping the CdS QDs with a thin layer of ZnS. To make both the bare and core–shell structure QDs more resistant against photochemical reactions, a mesoporous silica layer was grown on the QDs through a reverse microemulsion technique based on hydrophobic interactions. By careful experimental tuning, this encapsulation technique enhanced the quantum yield (∼65%) and photostability compared to the bare QDs. Both the encapsulated bare and core–shell QDs were then melt-mixed with EVA pellets using a mini twin-screw extruder and pressed into thin films with controlled thickness. The results demonstrated for the first time that mesoporous silica not only enhanced the quantum yield and photostability of the QDs but also improved the compatibility and dispersibility of QDs throughout the PEVA films. The novel light selective films show high visible light transmission (∼90%) and decreased UV transmission (∼75%).

Electrochemical Properties of Tin Nanoparticles Encapsulated in Different Origin Carbon Buffer Matrix

Tin seems to be a promising anode material due to its lithium uptake at low potential and high theoretical capacity (994 mAh/g for Li4.4Sn alloy phase). However, the major problem during formation of LixSny alloys are cyclic changes of elementary cell volume, reaching up to 300%, which lead to loss of electrical contact between active material and current collector as well as physical damage of the cell caused by high strains. Over the last decade most of the studies related to anode materials based on tin were focused on designing composites containing Sn and a stress-accommodating phase [1-4]. Nevertheless, the multi-step processes used to synthesis of such composites are complex and expensive [5]. The goal of the present work was development two types of carbon-tin nanocomposite anode materials and comparison of their electrochemical properties. In both cases the nanocomposites were obtained in a simple and inexpensive process, consisted of tin-based nanograins encapsulated in a flexible carbon buffer matrix derived from plant polysaccharides in the first series and from water soluble polymer in the latter. The precursor of active material was obtained using a modified reverse microemulsion technique (w/o) and then coated by a source of carbon (potato starch or poly(N-vinylformamide) mixed with pyromellitic acid) [6,7]. The carbon-tin precursors were pyrolyzed, affording formation of tin-based nanograins encapsulated in conductive carbon buffer matrix. Optimal conditions of the thermal treatment were determined by thermal analysis methods (EGA-TGA). The resulting materials with different carbon loading (20-60 wt.%) were investigated by X-ray diffraction (XRD) and by transmission electron microscopy (TEM) as well. Comprehensive electrochemical characterization of obtained nanocomposites including the electrical conductivity (EC), cyclic voltammetry (CV) and impedance spectroscopy (IS) was carried out. Discharge - charge tests were performed in R2032-type coin cells within 0.01–1.5 V potential range. TEM images indicate that the type of carbon precursor has strong impact on morphology of obtained carbon buffer matrix. The study also showed that columbic efficiency and capacity retention in discharge-charge tests strongly depend on carbon loading and sort of a carbon precursor. The authors acknowledge a financial support from the National Science Center of Poland under research grant No. 2012/07/N/ST8/03725 and from the European Institute of Innovation and Technology under the KIC InnoEnergy NewMat project. [1] J. W. Zheng, S. M. L. Nai, M. F. Ng, P. Wu, J. Wei, M. Gupta, J. Phys. Chem. 113 (2009) 14015-14019.[2] L. Zhao, S. Hu, W. Li, L. Li, X. Hou, Rare Metals 27 (2008) 507-512.[3] D. Deng, J.Y. Lee, Angew. Chem. Int. Edit. 48 (2009) 1660-1663.[4] H. Kim, M. G. Kim, T.J. Shin, H. J. Shin, J. Cho, Electrochem. Commun. 10 (2008) 1669-1672.[5] A. Kamali, D.J. Fray, Rev. Adv. Mater. Sci. 27 (2011) 14–24.[6] M. Molenda, A. Chojnacka, M. Bakierska, R. Dziembaj, Mater. Technol. 29 (2014) A88-A92.[7] A. Chojnacka, M. Molenda, M. Bakierska, R. Dziembaj, Procedia Eng. 98 (2014) 2-7.

Synthesis and Characterization of Polyamide-66/Calcium Carbonate Composites

Polyamide-66(PA66)/CaCO3 micro- and nano-composites were prepared using a polymer solution method at filler loading of 0, 1, 2 and 3 weight percent. Nano-size of CaCO3 was synthesized by micro-emulsion technique. The material was characterized by XRD, SEM, FTIR and UV-VIS techniques. XRD results of composites suggested that CaCO3 particles are found in the amorphous phase of the semi-crystalline thermoplastic and α-crystalline form of thermoplastic is thermodynamically more stable than the γ-crystalline forms at room temperature. The uniform dispersion of 1, 2, and 3 wt. % surface modified micro- and nano-CaCO3within PA66 were evidenced from SEM images. FT-IR analysis confirmed the chemical structure of the PA66. Absorption peaks for all required chemical groups were showed in the FTIR spectra: N-H stretch at 3305.52 cm-1, C-H stretch at 2865.02-2936.45 cm-1, Amide-I at 1638.76 cm-1, and Amide-II at 1539.55 cm-1. UV-VIS data showed that the presence of CaCO3 particles in PA66 results in the decrease of energy-band gaps of the composites. In addition, the results showed that incorporation of CaCO3 particles increased the modulus and tensile strength of neat PA66 however decreased its yield and elongation at break.

Effect of textural properties of alumina support on the catalytic performance of Ni/Al2O3 catalysts for hydrogen production via methane decomposition

Catalytic performance of 60 wt.% Ni supported on different morphological structure of alumina was studied for COx-free hydrogen production by methane decomposition. The Al2O3 supports were prepared by reverse microemulsion and precipitation techniques to obtain alumina hollow sphere (HS) and alumina nanoparticles (NP) structures, respectively. These materials were compared with the commercial alumina (bulk) to investigate the effect of the support structure on the catalytic activity and stability of Ni particles. The fresh and used catalysts were characterized by XRD, BET, TGA, H2-TPR, TEM and Raman spectroscopy. The results revealed that the texture properties of Al2O3 support play a crucial role on the catalyst performance. The Ni/Al2O3 nanoparticles (NP) catalyst exhibited the highest catalytic decomposition activity due to its better metal site distribution. The TPR results showed that almost all NiO particles in this catalyst were located extensively on the external surface of Al2O3 nanoparticles. On the other hand, the Ni/Al2O3 hollow sphere (HS) catalyst showed a lower activity due to the formation of large quantities of NiAl2O4 species. TEM and Raman spectroscopy data proved that longer and smaller size of multi-walled carbon nanotubes (MWCNT) with a relatively uniform diameters were obtained on the Ni/Al2O3 nanoparticles, compared to the other catalysts.

Partial hydrogenation of benzene to cyclohexene over Ru/γ-Al2O3 nanocatalyst via w/o microemulsion using boric acid and ethanolamine additives

Ru/γ-Al2O3 nanocatalyst was synthesized by water-in-oil reverse microemulsion technique and characterized by TEM, SEM–EDX, XRD, N2 adsorption–desorption, and H2 chemisorption. The surface area and active sites (S M) of 3 wt% Ru/γ-Al2O3 was obtained around 217.6 m2/g and 45.70 m2/gcat, respectively. The catalyst performance of Ru/γ-Al2O3 was assessed in the selective hydrogenation benzene to cyclohexene in the presence of boric acid (BA) and ethanolamine (EA) additives. The effect of such specific additives alone and in combination on the activity and selectivity of benzene hydrogenation was systematically investigated. Ru catalyst displayed pre-eminent performance at 0.5 mmol ratio of BA to EA exhibiting the highest selectivity (40 %) and yield (16 %) of the intermediate product, cyclohexene at 40 % of benzene conversion.

Multifunctional mesoporous silica nanoparticles in poly(ethylene-co-vinyl acetate) for transparent heat retention films

Transparent inorganic-polymer nanocomposite films are of tremendous current interest inemerging solar coverings including photovoltaic encapsulants and commercial greenhouse plastics, but suffer from significant radiative heat loss. This work provides a new and simple approach for controlling this heat loss by using mesoporous silica/quantum dot nanoparticles in poly(ethylene-co-vinyl acetate) (EVA) films. Mesoporous silica shells were grown on CdS-ZnS quantum dot (QDs) cores using a reverse microemulsion technique, controlling the shell thickness. These mesoporous silica nanoparticles (MSNs) were then melt-mixed with EVA pellets using a mini twin-screw extruder and pressed into thin films of concentration variable controlled thickness. The results demonstrate that the experimental MSNs showed improved infrared and thermal wavebands retention in the EVA transparent films compared to commercial silica additives, even at lower concentrations. It was also found MSNs enhanced the quantum yield and photostability of the QDs, providing high visible light transmission and blocking of UV transmission of interest for next generation solar coatings. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015, 53, 851–859

Structural and electromagnetic behavior evaluation of Nd-doped lithium–cobalt nanocrystals for recording media applications

Nano-crystalline Li0.5Co0.5NdxFe2−xO4 (x=0.0, 0.035, 0.070, 0.105, 0.140, 0.175) ferrites have been synthesized via micro-emulsion technique. Thermal analysis, fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), magnetometer analysis and a.c. electrical studies are employed to observe the impact of Nd3+ doping in Li0.5Co0.5Fe2O4 on crystallite size, spectral bands, dielectric and magnetic parameters. Thermal analysis depicts the weight loss with various temperatures and it illustrates that there is no further weight loss above 950°C. XRD analysis establishes the formation of single phase cubic spinel structure. Although for x=0.0 and thereafter for x⩾0.035 a peak of second phase (NdFeO3) occurs. The XRD data analysis revealed that the Nd substituted Li0.5Co0.5Fe2O4 ferrites revealed crystallite size 52.02–106nm ranges. The lattice parameter and crystallite size show a nonlinear behavior. The FTIR data between 400 and 1000cm−1 defined the intrinsic cation vibrations of the characteristic spinel structure. The dielectric parameters are investigated in the range of 1MHz–3GHz frequency. A damping effect in the dielectric parameters is observed by Nd3+ incorporation and also by increasing the frequency. Magnetic measurements at room temperature exhibit an appreciable increase in the saturation magnetization and coercivity with the substitution of Nd3+ cations. Coercivity is in range of soft ferrite. The dominating effects of doping on dielectric properties propose that these nano-ferrites are useful in the fabrication of high frequency devices, whereas increase in magnetization and coercivity propose the use for high density recoding media.

The superspin glass transition in zinc ferrite nanoparticles

Nanoparticles of the ZnxFe3−xO4 (x = 0.3–0.4) spinel phase having 5 and 15 nm size were synthesized by thermal decomposition of the respective acetylacetonates in a high boiling-point solvent employing surfactants. The collective behaviour of the nanoparticles was probed by dc and ac magnetic measurements of tightly compressed pellets of the particles and silica coated products which were prepared by reverse microemulsion technique. The assembly of bare 5 nm particles remains in the superparamagnetic state with Curie-Weiss characteristics down to 35 K when a rather sharp freezing of superspins is detected. The larger particles show a similar but more diffusive transition at 250 K. The cores encapsulated into the diamagnetic silica do not exhibit glassy freezing.

The Surface Modification and Antimicrobial Activity of Basic Magnesium Hypochlorite Nanoparticles.

The basic magnesium hypochlorite (BMH) nanoparticles were prepared by two micro-emulsion techniques and modified with sodium stearate. The influences of the main technical parameters such as the addition amount of sodium stearate, reaction temperature and reaction time on the Lipophilic degree (LD) of the modified BMH nanoparticles were investigated. The characteristics of the BMH nanoparticles were analysed by means of Malvern Instruments, transmission electron microscopy (TEM), water contact angle measurements, Fourier transform infrared spectroscopy (FTIR) and thermogravimetry analysis (TGA). The antimicrobial activity of the modified BMH nanoparticles was investigated with the antibacterial circle test. The results showed that the average size of the BMH nanoparticles was 305 nm. The BMH nanoparticles had been successfully modified by sodium stearate and the LD of.the modified BMH nanoparticles was 8.4% when the addition amount of sodium stearate was 0.15 g, the reaction temperature was 10 °C and the reaction time was 5 h. The dispersibility and hydrophobicity of the modified BMH nanoparticles were improved and the contact angle was up to 103 °, the modified BMH nanoparticles still had excellent antimicrobial activity after modification.

Electrical Behavior of Tb-Mn Substituted Y-Type Hexa-ferrites for High-Frequency Applications

Single phase nanostructured Tb-Mn substituted Y-type hexaferrites with composition Sr2Co2−x Mn x Tb y Fe12−y O22 (x = 0.0–1, y = 0.0–0.1) have been synthesized by the normal microemulsion technique. X-ray diffraction patterns reveal the formation of Y-type hexagonal single phase. The crystallite size, calculated by Scherer’s formula, is found in the range of 30–48 nm, which is well suitable for obtaining good signal-to-noise ratio in high density recording media. The enhancement in direct current resistivity has been attributed to the reduction in Fe3+ ions at octahedral sites. The Arrhenius plots show that there are two conduction mechanisms operating in the synthesized materials: in the ferri-region, the conduction is due to electrons, whereas in the para-region, it is due to polaron hopping phenomena. The calculated values of activation energy in the para-region are greater than 0.40 eV, which clearly suggests that the conduction phenomenon is due to hopping of polarons. Variation of dielectric constant with frequency depicts that the dielectric constant initially decreases with increase in frequency, while at higher frequency it decreases slowly. The dielectric results are in agreement with the Maxwell–Wagner model. Both the resonance and relaxation peaks at high frequency have been observed in dielectric loss and tan δ data. It has been noted that such types of peaks appear when hopping frequency becomes equal to that of the external applied field. The high values of resistivity and low dielectric loss make these materials best candidates for high frequency applications.

Preparation and investigation of sodium alginate nanocapsules by different microemulsification devices

ABSTRACTNumerous techniques of preparation have been reported for the encapsulation of the core material, but the microemulsion technique is the most effective and commonly used for encapsulation. In this article, three microemulsification devices including ultrasonic stirrer, labo ratory reactor, and mechanical stirrer were used to produce the alginate nanocapsules containing peppermint oil. The effect of different parameters on surface morphology, mean particle size, and size distributions were investigated. The results indicated that the ultrasonic stirrer is the best device to make the nanocapsules containing essential oils prepared by microemulsion method, so that the size of nanocapsules prepared by ultrasonic stirrer was about 56 nm. Also, the results of GC‐MS, FTIR, and TGA show that quantities of the remaining compounds in nanocapsules prepared by ultrasonic stirrer are higher than other devices. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 41904.

Nanocrystalline Co0.5Zn0.5Fe2O4 ferrite: Synthesis, characterization and study of their magnetic behavior at different temperatures

Co0.5Zn0.5Fe2O4 ferrite nanocrystals with average diameter in the range of 5–6nm have been synthesized by reverse microemulsion technique. X-ray diffraction (XRD), transmission electron microscopy (TEM) and vibrating sample magnetometer (VSM) are used to characterize the structural, morphological, and magnetic properties. X-ray analysis showed that the nanocrystals possess cubic spinel structure. The absence of hysteresis, negligible remanence, and coercivity at 300K indicate the superparamagnetic character and single domain in the nanocrystalline Co0.5Zn0.5Fe2O4 ferrite materials. The nanocrystalline Co0.5Zn0.5Fe2O4 ferrite was annealed at 600°C. As a result of heat treatment, the average particle size increases from 5nm to 7nm and the corresponding magnetization value increases to 15.94emu/g at 300K. However, at a low temperature of 100K, the annealed samples show hysteresis loop which is the characteristic of a superparamagnetic to ferromagnetic transition. A comparative study of the magnetic properties of Co0.5Zn0.5Fe2O4 ferrite nanocrystals obtained from (1) reverse microemulsion and (2) chemical co-precipitation route has also been carried out.

Synthesis of nano-bowls with a Janus template.

Colloidal particles with two or more different surface properties (Janus particles) are of interest in catalysis, biological imaging, and drug delivery. Eccentric nanoparticles are a type of Janus particle consisting of a shell that envelops the majority of a core particle, leaving a portion of the core surface exposed. Previous work to synthesize eccentric nanoparticles from silica and polystyrene have only used microemulsion techniques. In contrast we report the sol-gel synthesis of eccentric Janus nanoparticles composed of a silica shell around a carboxylate-modified polystyrene core (Janus templates). In addition, we have synthesized nano-bowl-like structures after the removal of the polystyrene core by organic solvent. These Janus templates and nanobowls can be used as a versatile platform for site-specific functionalization or controlled theranostic delivery.

Guaiacol hydrodeoxygenation reaction catalyzed by highly dispersed, single layered MoS2/C

Single layered MoS2 supported on activated carbon prepared by a microemulsion technique with good catalyst stability even after 4 uses.

Effect of the moist-heat sterilization on fabricated nanoscale solid lipid particles containing rasagiline mesylate.

Background:Nanoscale solid lipid particles of rasagiline mesylate (RM) were fabricated by microemulsion technique. The nanoscale particle must be sterile for intravenous administration, and several approaches are available for sterilization. However, the selection of sterilization technique for the fabricated RM loaded nanoscale solid lipid particles mainly depends on the nature of the drug that needs to be encapsulated and release pattern of the polymer.Materials and Methods:We have preferred moist heat sterilization, as it is the most convenient and the composition of the carrier and incorporated drug should remain unchanged and the incorporated drug should not leak out of the drug carrier. The physical and chemical stability of RM loaded nanoscale solid lipid particles investigated during sterilization and to determine the average mean particle size, polydispersity index, zeta potential (ZP), transmission electron microscopy (TEM), entrapment efficiency (EE), and drug content after autoclaving.Result:There were no significant changes in the average mean particle size, polydispersity index, ZP, TEM, EE, and drug content of RM loaded nanoscale solid lipid particles after autoclaving (121°C for 20 min [15 lbs]).Conclusion:These observations suggest that the moist heat sterilization by autoclaving is the most suitable method for nanoscale solid lipid formulations.

Direct growth of FePO4/reduced graphene oxide nanosheet composites for the sodium-ion battery

The direct growth of FePO4/reduced graphene oxide nanosheet composite cathode material for sodium-ion batteries via a micro-emulsion technique, which exhibits excellent electrochemical performance.

Synthesis of Pt/Al2O3 Catalysts by Microemulsion Technique and Hydrogenation of p-Chloronitrobenzene

Synthesis of Pt/Al2O3 Catalysts by Microemulsion Technique and Hydrogenation of p-Chloronitrobenzene

Synthesis of Zinc Carbonate Hydroxide Nanoparticles Using Microemulsion Process

In order to control the particle size and morphology, zinc carbonate hydroxide Zn5(CO3)2(OH)6 nanoparticles have been synthesized using a reverse microemulsion technique. The pseudo-ternary phase diagrams of the two microemulsion systems, prepared using CTAB/1-butanol/n-octane/aqueous phase system with the aqueous phase comprised of either zinc nitrate (Zn(NO3)2) or sodium carbonate (Na2CO3), were experimentally constructed. The nanoparticles synthesized by mixing of the two emulsion systems were further characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and thermogravimetric analysis (TGA). The nanoparticles were further characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and thermogravimetric analysis (TGA). Several important experimental parameters have been investigated for the ability to control particle size and morphology as the function of water/surfactant molar ratio (ω), water/oil molar ratio (S) and the initial concentration of reactants in the aqueous phase. Results indicate that ω values have the ability to affect the particle size and levels of aggregation, while S values had no apparent effect. In addition, the initial concentration of reactants in the aqueous phase was considered to be an important parameter as raising its values from 0.1M to 0.5M produced an unknown phase of zinc carbonate, exhibiting larger particle size with a unique flake like morphology.

Silica-modified monodisperse hexagonal lanthanide nanocrystals: synthesis and biological properties

Oleic acid-stabilized hexagonal NaYF4:Yb(3+)/Er(3+) nanocrystals, emitting green and red luminescence, were prepared by the high-temperature co-precipitation of lanthanide chlorides. By varying the reaction time and the Ln(3+)/Na(+) ratio, the nanocrystal size can be controlled within the range 16-270 nm. The maximum upconversion quantum yield is achieved under 970 nm excitation. The reverse microemulsion technique using hydrolysis and condensation of tetraethoxysilane is a suitable method to coat the nanocrystal surface with a silica shell to make the particles dispersible and colloidally stable in aqueous media. During the subsequent functionalization, (3-aminopropyl)trimethoxysilane introduced amino groups onto the silica to enable future bioconjugation with the target molecules. All specimens were characterized by TEM microscopy, electron and X-ray diffraction, ATR FT-IR spectroscopy, and upconversion luminescence. Finally, in vitro cytotoxicity and intracellular nanoparticle uptake (using confocal microscopy) were determined with human cervical carcinoma HeLa and mRoGFP HeLa cells, respectively. From the investigated particles, amino-functionalized NaYF4:Yb(3+)/Er(3+) nanocrystals internalized into the cells most efficiently. The nanoparticles proved to be nontoxic at moderate concentrations, which is important when considering their prospective application in biolabeling and luminescence imaging of various cell types.

Effect of ligand substitution in [Fe(H-trz)2(trz)]BF4 spin crossover nanoparticles

Spin crossover iron(II) 1,2,4-triazole-based coordination compounds in the form of nanoparticles were prepared using a reverse microemulsion technique. Ligand substitution approach was applied to decrease the spin crossover temperature towards room temperature in the well-known [Fe(Htrz)2(trz)]BF4 complex. The compositions of the particles were determined by elemental analysis and thermogravimetry. The morphology was monitored by transition electron microscopy (TEM). The effect associated with the ligand substitution was investigated by optical and magnetic measurements. Transition temperature has been reduced by 33 K comparing the unsubstituted sample to that with 5 % substitution.