Two-step Preparation Research Articles

Experimental investigation and model development for effective viscosity of Al2O3–glycerol nanofluids by using dimensional analysis and GMDH-NN methods

Nanofluids are new heat transfer fluids which aimed to improve the poor heat removal efficiency of conventional heat transfer fluids. The dispersion of nanoparticles into traditional heat transfer fluids such as ethylene glycol, glycerol, engine oil, gear oil and water has become widely applicable in engineering systems because of their superior heat transfer properties. However, viscosity increase due to nanoparticle dispersion is an issue which needs attention and proper experimental investigation. Therefore, in this study, it is experimentally optimized the two-step preparation procedure for Al2O3–glycerol nanofluids consisting of 19, 139 and 160nm particle sizes, and then studied the effective viscosity between 20 and 70°C for the range of 0 to 5% volume fractions. The nanofluids' viscosity showed a characteristic increase as volume fraction increases; decrease as the working temperature increases; and the smallest nanoparticles showed the highest shear resistance. Based on the available experimental data, an empirical correlation has been offered using dimensional analysis. Thereafter, a hybrid neural network based on the group method of data handling (GMDH-NN) has been employed for modeling the effective viscosity of Al2O3–glycerol nanofluid. The correlations obtained from both modeling procedures showed higher accuracy in the prediction of the present experimental data when compared to most cited models from the open literature.

Research on quantum efficiency for reflection-mode InGaAs photocathodes with thin emission layer.

In order to understand the photoemission mechanism of the reflection-mode InGaAs photocathode with a thin emission layer, the formula describing reflection-mode quantum efficiency is revised by solving the one-dimensional continuity equation, in which the electrons generated in the GaAs buffer layer are considered. Compared with the conventional formula, the revised formula is proved to be more suitable for the reflection-mode InGaAs photocathode with a thin emission layer. In experiment, the InGaAs sample goes through two-step surface preparation including a wet chemical cleaning process and a heat treatment process. Then the sample is activated by Cs/O and the experimental quantum efficiency curves are measured simultaneously every other hour. The measured results show that the shapes of the quantum efficiency curves degrade with time because of the contamination of residual gases in the vacuum system. All the quantum efficiency curves are well fitted by the revised formula.

PEG-Phospholipids Coated Quantum Rods as Amplifiers of the Photosensitization Process by FRET.

Singlet oxygen ((1)O2) generated upon photostimulation of photosensitizer molecules is a highly reactive specie which is utilized in photodynamic therapy. Recent studies have shown that semiconductor nanoparticles can be used as donors in fluorescence resonance energy transfer (FRET) process to excite attached photosensitizer molecules. In these studies, their unique properties, such as low nanoscale size, long-term photostability, wide broad absorbance band, large absorption cross section, and narrow and tunable emission bands were used to provide advantages over the traditional methods to produce singlet oxygen. Previous studies that achieved this goal, however, showed some limitations, such as low FRET efficiency, poor colloidal stability, nonspecific interactions, and/or complex preparation procedure. In this work, we developed and characterized a novel system of semiconductor quantum rods (QRs) and the photosensitizer meso-tetra(hydroxyphenyl) chlorin (mTHPC), as a model system that produces singlet oxygen without these limitations. A simple two-step preparation method is shown; Hydrophobic CdSe/CdS QRs are solubilized in aqueous solutions by encapsulation with lecithin and PEGylated phospholipid (PEG-PL) of two lipid lengths: PEG350 or PEG2000. Then, the hydrophobic photosensitizer mTHPC, was intercalated into the new amphiphilic PEG-PL coating of the QR, providing a strong attachment to the nanoparticle without covalent linkage. These PEGylated QR (eQR)-mTHPC nanocomposites show efficient FRET processes upon light stimulation of the QR component which results in efficient production of singlet oxygen. The results demonstrate the potential for future use of this concept in photodynamic therapy schemes.

Two-step preparation of laser-textured Ni/FTO bilayer composite films with high photoelectric properties

A two-step strategy, i.e. sputtering Ni layers on FTO glass combined with magnetic-field-assisted laser irradiation, was proposed to prepare laser-textured Ni/FTO bilayer composite films. By analyzing surface morphology, crystal structure and photoelectric properties of Ni/FTO films with different Ni layer thicknesses, the Ni/FTO film with a 10-nm-thick Ni layer (Ni10/FTO film), which had the best overall photoelectric property, was chosen to undergo magnetic-field-assisted laser irradiation with different laser fluences. Magnetic-field-free laser irradiation of the Ni10/FTO film was also carried out for comparison purpose. It was found that magnetic-field-assisted laser irradiation using a fluence of 1.0J/cm2 was more effective for simultaneously achieving texturing and annealing, resulting in formation of ideal grating textures and significantly increased grain size. The corresponding film (MLI-NF1.0 film) showed the highest figure of merit of 22.8×10−3Ω−1 compared to 13.1×10−3Ω−1 of the FTO glass and 1.4×10−3Ω−1 of the Ni10/FTO film, suggesting that the two-step strategy is excellent for preparing textured Ni/FTO films with high photoelectric properties.

High performance PEM fuel cell catalyst layers with hydrophobic channels

Polymer electrolyte membrane fuel cell performance has been enhanced with efficient water management by modification of the structure of the catalyst layer. Polytetrafluoroethylene (PTFE) was added to the catalyst layer structure by using two-step catalyst ink preparation method. Physical and electrochemical characterization of catalyst layers with hydrophobic nanoparticles were investigated via TGA-DTA, XRD, nitrogen physisorption, SEM, TEM, EDX analysis, and cyclic voltammetry technique. In addition, performance tests of MEAs were carried out. Catalyst layer structure after performance tests was observed by SEM analysis. Tubular open-ended mesopores have been constructed through the catalysts with hydrophobic nanoparticle addition. PTFE addition to the catalyst layer structure decreased both electrochemical surface area and Pt utilization. Mesoporous hydrophobic channels in the catalyst layer provided decreasing mass transport limitations at higher current densities, by this way, power density of Pt/C-Nafion/PTFE catalyst enhanced. It is concluded that mesoporous hydrophobic channels through the catalyst layer facilitate water removal.

The remarkable effect of the preparation procedure on the catalytic activity of CoBEA zeolites in the Fischer–Tropsch synthesis

This work deals with the investigation of the influence of the preparation procedure and Co content on the activity of CoBEA zeolite in Fischer–Tropsch synthesis. For this purpose the Co-containing zeolites were prepared by a conventional wet impregnation (CoxAlBEA series) and a two-step postsynthesis method (CoxSiBEA series). Calcination at 500 °C, for 3 h in air and then reduction at 500 °C in flow of 95% H2–5% Ar stream of as prepared CoxAlBEA and CoxSiBEA zeolites led to obtain Red-C-CoxAlBEA and Red-C-CoxSiBEA catalysts with different properties in Fischer–Tropsch reaction. The most active catalysts were Red-C-Co10SiBEA and Red-C-Co20SiBEA with high CO conversion of 90–95% and selectivity towards liquid products of 85% containing C7–C18 n-alkanes, isoalkanes and small amount of olefins. In the case of Red-C-CoxAlBEA catalysts the CO conversion was of 68% and selectivity towards liquid products of 57%. The identified liquid products were mainly C7–C16 n-alkanes. Moreover, Red-C-CoxSiBEA catalysts demonstrated better stability and resistance to coke formation than Red-C-CoxAlBEA ones. It is probably related to higher dispersion of cobalt nanoparticles in Red-C-CoxSiBEA than in Red-C-CoxAlBEA catalysts and absence of strong Brønsted acidic sites in the former after removal of aluminum in the first step of two-step postsynthesis preparation procedure.

Asymmetric Synthesis of Two Hydroxylated Pyrrolizidines From a C-Allyl Epoxypyrrolidine

The efficient two-step preparation of a new pivotal C-allyl epoxypyrrolidine intermediate from an enantio-enriched epoxyaldehyde precursor is described. The synthetic potential of this building block is demonstrated with the first enantioselective synthesis of two hydroxylated pyrrolizidine relying on a regio- and stereocontrolled epoxide opening reaction.

Two-step solid-state synthesis of PEPPSI-type compounds.

The two-step mechanochemical preparation of carbene-pyridine complexes of palladium and platinum is reported. The organometallic products, which represent a class of commercially available catalysts, are rapidly formed in excellent yield proving solvent-free synthesis to be a viable synthetic alternative even in the case of NHC-containing compounds.

An improved procedure to prepare 3-methyl-4-nitroalkylenethylisoxazoles and their reaction under catalytic enantioselective Michael addition with nitromethane.

Herein, we describe a short synthesis of 3-methyl-4-nitro-5-alkylethenyl isoxazoles and their reactivity as Michael acceptors. The title compounds reacted with nitromethane under phase-transfer catalysis to provide highly enantioenriched adducts (up to 93% ee) which were then converted to the corresponding γ-nitroacids.

Fine-tuning the nonequilibrium behavior of oppositely charged macromolecule/surfactant mixtures via the addition of nonionic amphiphiles.

The various commercial applications of oppositely charged polyelectrolytes (P) and ionic surfactants (S) with added nonionic amphiphiles initiated intensive research on the polyion/mixed surfactant interaction. A large group of earlier studies revealed that one of the major effects of the nonionic cosurfactants is the suppression of the associative phase separation of P/S systems. In contrast, recent studies indicated that in the dilute surfactant concentration range the added uncharged amphiphile enhances the precipitation concentration range. In order to rationalize these observations, the mixtures of poly(diallyldimethylammonium chloride) (PDADMAC), sodium dodecyl sulfate (SDS), and dodecyl maltoside (C12G2) are investigated using a variety of experimental methods. It is shown that the nonionic cosurfactant has two distinct and competing impacts on the mixed surfactant binding onto the polyions. The composition dependent variation of the chemical potentials of the amphiphiles determines which of these effects is the dominant one, explaining the seemingly diverse earlier observations and their interpretations. We also demonstrate that the nonionic amphiphile affects considerably the nonequilibrium features of polyion/ionic surfactant complexation. Namely, the presence of the uncharged surfactant can destabilize the colloidal dispersion of P/S nanoparticles formed in the two-phase composition range. However, at the same concentration range highly stable dispersions of polyion/mixed surfactant nanoparticles can be produced through the application of a new two-step solution preparation technique. This method is based on the order of addition effect of the two surfactants which can be utilized in future scientific and industrial applications.

Growth of TiO2(B)(001) on Au(111) by chemical vapor deposition

This study presents how a TiO2(B) film exposing the (001) face can be grown on Au(111) by chemical vapor deposition. Identification and characterization of the TiO2(B)(001) layer are carried out with low-energy electron diffraction (LEED), synchrotron radiation photoelectron spectroscopy (PES), scanning tunneling microscopy (STM) and X-ray absorption spectroscopy (XAS). Formation of the TiO2(B) film requires a two-step preparation procedure: deposition at 280 °C followed by annealing to 500 °C. This suggests that the interaction between a substrate and an overlayer stabilizes the TiO2(B) film, preventing the formation of thermodynamically more stable rutile islands. The study thus gives insight into how the morphology and the atomic structure of the titania overlayer can be controlled.

The antimicrobial activity of mono-, bis-, tris-, and tetracationic amphiphiles derived from simple polyamine platforms

A series of 34 amphiphilic compounds varying in both number of quaternary ammonium groups and length of alkyl chains has been assembled. The synthetic preparations for these structures are simple and generally high-yielding, proceeding in 1–2 steps without the need for chromatography. Antibacterial MIC data for these compounds were determined, and over half boast single digit MIC values against a series of gram-positive and gram-negative bacteria. MIC variation mostly hinged on the length of the alkyl chain, where a dodecyl group led to optimal activity; surprisingly, the number of cations and/or basic nitrogens was less important in dictating bioactivity. Additional structural variation was prepared in a trisamine series dubbed 12,3,X,3,12, providing a series of potent amphiphiles functionalized with varied allyl, alkyl, and benzyl groups. Tetraamines were also investigated, culminating in a two-step preparation of a tetracationic structure that showed only modestly improved bioactivity versus amphiphiles with two or three cations.

Control of multilayered core–shell dispersed particles in HPP/EPR/EbP blends and its influences on crystallization and dynamic mechanical behavior

According to a two-step preparation technique consisting of temperature-gradient extraction fractionation (TGEF) and subsequent solution-mixing, a series of polypropylene/ethylene-propylene random copolymer/ethylene-propylene block copolymer (HPP/EPR/EbP) blends containing multilayered core–shell dispersed particle with bridges were prepared to explore the influences of dispersed phase on crystallization and dynamic mechanical behavior. The inner core of the core–shell dispersed particles was mainly composed of EbP with long ethylene chain segment, and the intermediate layer was EPR and outer layer was EbP with long propylene chain segment. The size and layer thickness of the core–shell dispersed particle could be regulated by varying the ratio of EPR/EbP. With the decrease of EbP content, the outer interfacial thickness of core–shell structure decreases and the blends presented elevated melting points, which might be ascribed to enhanced nucleation ability. Meanwhile, the special simultaneous depression of glass-transition temperatures (Tg) of HPP and EPR was observed in all HPP/EPR/EbP blends compared with the Tgs of neat components, which was attributed to the enlarging free volume by imperfect co-crystals and infiltration of long ethylene chain segments of EbP component at interface.

Synthesis and microstructure analysis of aligned carbon nanotube/pyrocarbon composites

A two-step preparation of aligned CNT (ACNT)/pyrolytic carbon composites was carried out with chemical vapor deposition and chemical vapor infiltration by filling the space within the ACNT film with pyrolytic carbon, using methane as carbon precursor. The structure of the composites was investigated by scanning electron microscopy and Raman spectroscopy. Results showed that the CNTs were coated unevenly with densely-packed carbon spheres at 950 °C. At 1050 °C, the CNTs were uniformly coated which increased their diameters from 20-60 nm to 400-500 nm and closed pores were formed as a result of the fast formation and a slow diffusion of carbonaceous nuclei during the latter stages of deposition. At both temperatures, the density of the film increased more than four fold when the pyrolytic carbon was graphitized.

Two-step preparation of AlON transparent ceramics with powder synthesized by aluminothermic reduction and nitridation method

Abstract

Silicate ionic liquid synthesis of zeolite merlinoite: Crystal size control from crystalline nanoaggregates to micron-sized single-crystals

A new procedure for zeolite synthesis based on a silicate ionic liquid is reported. The method consists of a two-step precursor preparation. In the first step, a liquid silicate is prepared by hydrolyzing tetraethylorthosilicate (TEOS) with KOH–H2O mixture, which induces coacervation resolved into full phase demixing and subsequent separation from a water–ethanol phase by simple decantation. In the second step, an appropriate amount of an alkaline aluminate is mixed with the first liquid silicate, avoiding therefore precipitation. To the best of our knowledge, this represents the first example of homogeneous liquid synthesis, and not a clear sol or a gel, of an Al-rich zeolite, free of organic template. The approach is exemplified by the synthesis of merlinoite with potassium hydroxide as mineral base and could be extended to other zeolitic systems by varying the chemical composition and the nature of the alkali cation. The synthesis yield depends on the Al content and the crystalline products showed a very large range of particle sizes varying from nanometer scale to about a hundred microns when increasing the Al concentration. Crystallization proceeds most likely through nucleation from a liquid where nucleation and growth directly affects the ultimate crystal size and morphology.

Hole blocking PbI2 /CH3 NH3 PbI3 interface

Modulated charge separation across (MO)/CH3NH3PbI3 and (MO)/PbI2/CH3NH3PbI3 (MO = TiO2, MoO3) interfaces was investigated by surface photovoltage (SPV) spectroscopy. Perovskite layers were deposited by solution-based one-step preparation and two-step preparation methods. An unreacted PbI2 layer remained at the interface between the metal oxide and CH3NH3PbI3 for two-step preparation. For the two-step preparation on TiO2, the SPV signal related to absorption in CH3NH3PbI3 increased in comparison to the one-step preparation due to electron transfer from CH3NH3PbI3 via PbI2 into TiO2 whereas the SPV signal related to defect transitions decreased. For the one-step preparation on MoO3, holes photogenerated in CH3NH3PbI3 recombined with electrons in MoO3. In contrast, a hole transfer from CH3NH3PbI3 towards MoO3 was blocked by the PbI2 interlayer for the two-step preparation on MoO3. (© 2014 WILEY-VCH Verlag GmbH &Co. KGaA, Weinheim)

Isoxazole Platform for Polyketide Assembly: Cycloaddition of Stable Benzonitrile Oxides to Stable ortho-Quinone Monoacetals and Dehydrogenation

Abstract A two-step preparation of highly functionalized polycyclic isoxazoles is described via regioselective 1,3-dipolar cycloaddition of ortho-disubstituted benzonitrile oxides to ortho-quinone monoacetals and dehydrogenation by NiO2.

Influence of Li2O content on the structural and electrochemical properties of layered-layered-spinel composite cathode materials LixMn4/6Ni1/6Co1/6O(1.75+0.5x)

The layered-layered-spinel composite cathode materials LixMn4/6Ni1/6Co1/6O(1.75+0.5x) with different content of Li2O have been synthesized by the two-step co-precipitation method and evaluated in lithium cells. Powder X-ray diffraction provides the evidence that the structures of LixMn4/6Ni1/6Co1/6O(1.75+0.5x) composite transform from ‘layered-layered’ to ‘layered-layered-spinel’ as the content of Li2O decreasing. Electrochemical charge/discharge profiles suggest that Li1.3Mn4/6Ni1/6Co1/6O2.4 electrode with low content of Li2O delivers a large initial discharge capacity which is about 305.3 mAh·g−1, and that the discharge capacities of Li1.3Mn4/6Ni1/6Co1/6O2.4 electrode change little at the first three cycles, because of that a considerable amount of spinel phase in electrode facilitating Li ions diffusion. Nevertheless, the discharge capacities of Li1.4Mn4/6Ni1/6Co1/6O2.45 and Li1.5Mn4/6Ni1/6Co1/6O2.5 electrode in the first three cycles gradually rise as cycles continuing, which is expected to be that Li ions diffusion paths are not fully opened. The irreversible electrochemical reaction that Li2O component separates from Li2MnO3 to form MnO2 happens at the first charge at 4.7V, and the structure of layered Li2MnO3 component converts into the spinel component during continuously cycles. The LixMn4/6Ni1/6Co1/6O(1.75+0.5x) composites also display good cycling performance and rate performance. The capacity retention of LixMn4/6Ni1/6Co1/6O(1.75+0.5x) composites exceeds 100%, and its coulombic efficiency is greater than 98% after 50 cycles. We conclude that electrochemical performances of LixMn4/6Ni1/6Co1/6O(1.75+0.5x) composites are improved by using the two-step co-precipitation preparation method, especially in terms of large discharge capacity of Li1.3Mn4/6Ni1/6Co1/6O2.4 composite due to the appearance of spinel components.

Disordered ZnO nanoparticles with extremely intense deep-level emission and enhanced photocatalytic activity

Abstract Core–shell nested structure of amorphous carbon coated on crystalline ZnO (carbonized ZnO) was synthesized by sol–gel method as precursor. Disordered ZnO nanoparticles were successfully prepared by annealing the carbonized the ZnO precursor. HRTEM, Raman and XPS analyses showed that the ZnO nanoparticles contain high concentration of oxygen-deficiency defects which enable them exhibiting an abnormal intense deep-level emission centered at green luminescence and spreading over a wide wave length range of 420–660 nm and having a negligible UV emission in its photo luminescence (PL) spectrum. They also show an enhanced photocatalytic activity in degradation of methylene blue (MB). Experiments and theoretical simulation based on density functional theory showed that the intense deep-level emission and improved photocatalytic ability should attributed to their abundant oxygen-deficiency defects in the ZnO nanoparticles introduced by the two-step preparation method.