Stoichiometric Ratio Of Reactants Research Articles

Gas-Solid Phase Reaction Derived Silver Bismuth Iodide Rudorffite: Structural Insight and Exploring Photocatalytic Potential of CO2 Reduction.

Photocatalytic reduction of CO2 is a promising strategy to mitigate the effects of global warming by converting CO2 into valuable energy-dense products. Silver bismuth iodide (SBI) is an attractive material owing to its tunable bandgap and favorable band-edge positions for efficient CO2 photoreduction. In this study, SBI materials, including AgBi2I7, AgBiI4, Ag2BiI5, and Ag3BiI6 are first synthesized, through gas-solid reaction by controlling the stoichiometric ratio of reactants. The X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) results revealed that the distance between Ag-I is proportional to the degree of Ag ions delocalization, which occupies the vacant sites. That greatly retards the charge recombination at vacant sites. In addition, the surface potential via photo-assisted Kelvin probe force measurements of various SBI catalysts shows that Ag3BiI6 exhibits the highest surface potential change due to the rich delocalized Ag ions. This results in effective charge carrier transport and prevention of charge recombination at vacant sites. Taking the above advantages, the averaged CO and CH4 production rates for Ag3BiI6 achieved 0.23 and 0.10µmolg-1h-1, respectively. The findings suggest that Ag3BiI6 has a high potential as a novel photocatalyst for CO2 reduction and sheds light on the possibility of solving environmental contamination and sustainable energy crises.

One-dimensionally oriented self-assembly of ordered mesoporous nanofibers featuring tailorable mesophases via kinetic control

One-dimensional (1D) nanomaterials have sparked widespread research interest owing to their fascinating physicochemical properties, however, the direct self-assembly of 1D porous nanomaterials and control over their porosity still presents a grand challenge. Herein, we report a monomicelle oriented self-assembly approach to fabricate 1D mesoporous nanostructures with uniform diameter, high aspect ratio and ordered mesostructure. This strategy features the introduction of hexamethylenetetramine as a curing agent, which can subtly control the monomicelle self-assembly kinetics, thus enabling formation of high-quality 1D ordered mesostructures. Meanwhile, the micellar structure can be precisely manipulated by changing the reactant stoichiometric ratio, resulting in tailorable mesophases from 3D cubic (Im-3m) to 2D hexagonal (p6mm) symmetries. More interestingly, the resultant mesoporous nanofibers can be assembled into 3D hierarchical cryogels on a large scale. The 1D nanoscale of the mesoporous nanofibers, in combination with small diameter (~65 nm), high aspect ratio (~154), large surface area (~452 m2 g−1), and 3D open mesopores (~6 nm), endows them with excellent performances for sodium ion storage and water purification. Our methodology opens up an exciting way to develop next-generation ordered mesoporous materials for various applications.

Air Tolerant Cadiot-Chodkiewicz and Sonogashira Cross-Couplings.

Cadiot-Chodkiewicz cross-couplings generate an unsymmetric buta-1,3-diyne by way of a Cu(I)-catalyzed coupling between a terminal alkyne and a 1-haloalkyne. Despite their widespread use, Cadiot-Chodkiewicz reactions are plagued by the generation of symmetric buta-1,3-diyne side products, formed through competing: (a) formal reductive homo-coupling of the 1-haloalkyne and (b) oxidative (Glaser-Hay/Eglinton) homo-coupling of the terminal alkyne. To overcome this issue, a large excess of one of the two reacting alkynes is commonly deployed, and difficult separations of cross- and homo-coupled products are often encountered. Here, we demonstrate that the use of ascorbate as a reductant leads to a suppression of these unwanted side reactions, hence permitting excellent yields with a roughly stoichiometric ratio of reactants. The procedure also avoids an inert gas atmosphere and uses a sustainable solvent. A similar approach is effective for cross-couplings involving a Pd(0)/Pd(II) catalytic cycle, with air tolerant Sonogashira couplings also established.

Drug complexes: Perspective from Academic Research and Pharmaceutical Market.

Despite numerous research efforts, drug delivery through the oral route remains a major challenge to formulation scientists. The oral delivery of drugs poses a significant challenge because more than 40% of new chemical entities are practically insoluble in water. Low aqueous solubility is the main problem encountered during the formulation development of new actives and for generic development. A complexation approach has been widely investigated to address this issue, which subsequently improves the bioavailability of these drugs. This review discusses the various types of complexes such as metal complex (drug-metal ion), organic molecules (drug-caffeine or drug-hydrophilic polymer), inclusion complex (drug-cyclodextrin), and pharmacosomes (drug-phospholipids) that improves the aqueous solubility, dissolution, and permeability of the drug along with the numerous case studies reported in the literature. Besides improving solubility, drug-complexation provides versatile functions like improving stability, reducing the toxicity of drugs, increasing or decreasing the dissolution rate, and enhancing bioavailability and biodistribution. Apart, various methods to predict the stoichiometric ratio of reactants and the stability of the developed complex are discussed.

Efficiency of magnesium ions removal from water in processes of its mitigation

Significant concentrations of calcium and magnesium ions in natural waters force the majority of domestic drinking and energy waters to undergo preliminary softening. Therefore, mitigation technologies are becoming particularly acute today, and research in this field is increasing every year. Since water hardness is determined by the total content of calcium and magnesium ions, these elements are the focus of such research. 
 Traditionally, it is believed that calcium ions are the first to be removed, and magnesium ions are less likely to form a solid phase. However, the effectiveness of softening technology depends equally on both cations. Therefore, sufficient attention should also be paid to magnesium ions. Sodium phosphate is considered a promising reagent in this direction. Its use in the processes of removing calcium ions allows to ensure the residual hardness of water at the level of 0.1 - 0.2 mg-eq/dm3 in a wide range of temperatures and hydrogen index. Detailed studies of the use of sodium phosphate in the processes of removing magnesium ions showed its insufficient efficiency. 
 The effectiveness of soda-sodium softening allows to ensure at pH 11.0 - 11.5 the residual hardness of water at the level of 0.4 - 0.6 mg-eq/dm3. But the need to adjust the hydrogen index and the high consumption of reagents make this technology unsuitable for widespread use. The determining factor in water softening processes using phosphate ions is the ratio between the concentrations of phosphate ions and magnesium ions K = [PO43-, mg-eq] / [Mg2+, mg-eq]. Taking into account the strict requirements of current regulatory documents for the content of phosphates in treated waters, it is desirable to carry out the treatment with stoichiometric ratios of reagents for a more complete reaction between the components. The advantage of sodium phosphate as a reagent for removing magnesium ions can be considered the fact that in the pH range of 3.16 - 10.07 at K = 1, the residual hardness ranges from 1.8 to 3.4 mg-eq/dm3. At the same time, the minimum value of the residual stiffness was recorded at the level of 0.75 mg-eq/dm3 at pH 10.07 and K = 2. As the pH decreases, a stable decrease in efficiency is observed, although it is not very significant. Thus, during the transition from an alkaline to an acidic medium, the residual concentration of magnesium ions increases by a factor of 2, regardless of the value of the coefficient K. Similar trends persist in the case of a change in the initial hardness of water. The biggest difference is observed at values ​​of K ≤ 1, which is explained by the deficiency of phosphate anions and the impossibility of forming a solid phase of stoichiometric composition. However, even with a stoichiometric ratio of reactants (K = 1), the residual hardness of treated water is quite significant and ranges from 2.5 to 3 mg-eq/dm3. A further increase in the dose of sodium phosphate allows to slightly reduce the residual hardness of the treated water. Thus, the minimum residual hardness of treated water at K = 2.0 is fixed at the level of 0.7 mg-eq/dm3 with an initial hardness of 22.9 mg-eq/dm3. An increase in the residual hardness of the treated water with a decrease in its initial hardness was also noted. This situation is caused, in our opinion, by a significant increase in the mass of the solid phase and an increase in pH with an increase in the dose of sodium phosphate. 
 A significant advantage of sodium phosphate as a precipitator of calcium ions is the fact that the temperature of the water practically does not affect the efficiency of the process in a wide range of temperatures. This trend is also characteristic of magnesium ions. In the temperature range of 5 - 70 °C, the softening efficiency remains stable. Moreover, the solid phase is formed immediately after draining the solutions. If we take into account the high efficiency of phosphates in removing calcium ions, then in general, the use of phosphates for softening water can be permissible, provided that the formed solid phase is completely separated from the water. Detailed studies of the efficiency of separation of magnesium phosphate particles by settling or filtering are as important as the processes of solid phase formation.

Experimental Investigation of a Continuous Reactor for CO2 Capture and CaCO3 Precipitation

In a climate neutral world, the life cycle greenhouse gas (GHG) emissions of precipitated calcium carbonate (PCC) have to be reduced towards net-zero. Mineral carbonation processes allow to do so by replacing the carbon rich calcium source limestone by carbon free industrial mineral wastes. Various processes have been investigated in literature. They exhibit the benefit of little to no feedstock related emissions and high energy savings due to the avoidance of the CaCO3 calcination step. However, the nature of the process changes significantly, which requires a fundamental understanding of the new mechanisms controlling the process of CO2 absorption and CaCO3 precipitation. Within this work, a CO2 rich gas is contacted with a calcium rich aqueous feed in a continuous reactive crystallizor. The CO2 selectively absorbs and precipitates as either vaterite or calcite. The effect of the liquid and gas feed flow rates, of the feed stoichiometric ratio and of the residence time on key performance indicators, such as the CO2 capture efficiency the CaCO3 precipitation efficiency and the features of the final product, is studied experimentally. As expected, these feed characteristics determine the effective stoichiometric ratio of reactants in the liquid phase, ψ. The particle size increases strongly with ψ; vaterite represents the predominant solid phase at ψ < 1 while otherwise a mix of vaterite and calcite was formed, whereas the latter one accounted for 13%–90% in mass of crystals collected. Moreover, ψ of about one exhibits the highest CO2 capture efficiency exceeding 80%.

Understanding of supramolecular emulsion interfacial polymerization in silico.

The composition and structure of a membrane determine its functionality and practical application. We study the supramolecular polymeric membrane prepared by supramolecular emulsion interfacial polymerization (SEIP) on the oil-in-water droplet via the computer simulation method. The factors that may influence its structure and properties are investigated, such as the degree of polymerization and molecular weight distribution (MWD) of products in the polymeric membranes. We find that the SEIP can lead to a higher total degree of polymerization as compared to the supramolecular interfacial polymerization (SIP). However, the average chain length of products in the SEIP is lower than that of the SIP due to its obvious interface curvature. The stoichiometric ratio of reactants in two phases will affect the MWD of the products, which further affects the performance of the membranes in practical applications, such as drug release rate and permeability. Besides, the MWD of the product by SEIP obviously deviates from the Flory distribution as a consequence of the curvature of reaction interface. In addition, we obtain the MWD for the emulsions whose size distribution conforms to the Gaussian distribution so that the MWD may be predicted according to the corresponding emulsion size distribution. This study helps us to better understand the controlling factors that may affect the structure and properties of supramolecular polymeric membranes by SEIP.

Three-Component Reaction of 3,3-Difluorocyclopropenes, s-Tetrazines, and (benzo) Pyridines.

A new three-component reaction leading to 1-α-(pyridyl-2-[1,2,4]triazolyl)-2-alkyl-ethanones has been discovered while studying the reactivity of monosubstituted 3,3-difluorocyclopropenes in an inverse electronic demand Diels-Alder (IEDDA) cycloaddition-cycloreversion sequence with s-tetrazines. The reaction involving the above-mentioned reactants and (benzo)pyridine as a third component results in a complex transformation proceeding in mild conditions in a stoichiometric ratio of reactants and has high functional group tolerance (phenols, amides, ethers, carboxylic acids, ketones, and acrylic esters). As a result, simple pyridines are selectively functionalized at the α-position in good isolated yields. The reaction mechanism includes a rare azaphilic [4 + 2]-cycloaddition step between s-tetrazine and intermediate 1-hydroxyindolizine, suggested after byproduct identification and tracked with a deuterium label. To date, it is only the third known example of skewed azaphilic cycloaddition of tetrazine. The reaction is truly three-component and cannot be effectively performed stepwise.

PH-mediated synthesis of monodisperse gold nanorods with quantitative yield and molecular level insight

Although gold nanorods (GNRs) have been produced with different dimensions and aspect ratios, the current synthesis methods through seed-mediated growth are far from ideal, for instance, the quality (rod yield) and the quantity (gold conversion) cannot be simultaneously satisfied. More critically, there is no molecular level understanding of the growth mechanism. Here, we solved the problem by employing the stoichiometric ratio of reactants and tuning the reactivity of the reductant through adjusting the initial pH value of the growth solution to achieve both good quality and high quantity simultaneously. We also extended our strategy to other enols besides ascorbic acid, such as phenolic compounds, and found that the optimal pH for GNRs synthesis depends on the structure of the individual compound. The mechanistic insight greatly enriches the toolbox of reductants for GNRs growth and makes it possible to synthesize GNRs at both acidic and basic conditions. An interesting phenomenon is that for most of the phenolic compounds we tested, the morphology of the final products follows the same sphere-rod-sphere trend as the initial pH value of the reaction increases, whether it is under acidic or basic conditions, which cannot be explained by any previously proposed mechanism. The effect of pH is mainly attributed to the regulation of the reduction potential of the reductants, and thus the reaction rate. A model has been proposed to explain the dependence of anisotropic growth of GNRs on the concentration gradient of reactants around the seeds, which is decided by both the reaction rate and diffusion rate.

Performance enhancement of interdigitated flow channel of PEMFC by scaling up study

ABSTRACTThe performance of Proton Exchange Membrane Fuel Cell (PEMFC) with various ribs-to-channel-width ratios on the interdigitated flow field has been investigated by scaling-up from 25 cm2 to 36 cm2 and from 25 cm2 to 49 cm2 using Computational Fluid Dynamics (CFD) fluent-14.0 software. The peak power density is reduced by 18% and 25.5% when scaling up from 25 cm2 to 36 cm2 and from 25 cm2 to 49 cm2 active area of PEMFC, respectively. The validation has been done on the 25 cm2 active area with interdigitated flow channel of PEMFC. The combined effect of design and operating parameters of various combinations on an interdigitated flow channel for the performance enhancement of 25 cm2 PEMFC has been studied using optimization technique. For the reliability of the numerical results, experimental validation of 36 cm2 PEMFC with interdigitated flow field is carried out for the rib-to-channel-width ratio of 1:2, pressure of 2.5 bar, temperature of 343 K, and stoichiometric ratio of reactants of 3.5.

Theoretical Insight into the Au(I)-Catalyzed Intermolecular Condensation of Homopropargyl Alcohols with Terminal Alkynes: Reactant Stoichiometric Ratio-Controlled Chemodivergence.

The mechanisms and chemoselectivities on the Au(I)-catalyzed intermolecular condensation between homopropargyl alcohols and terminal alkynes were investigated by performing DFT calculations. The reaction was indicated to involve three stages: transformation of the homopropargyl alcohol (R1) via intramolecular cyclization to the cyclic vinyl ether (R1'), formation of the C-2-arylalkynyl cyclic ether (P1) via hydroalkynylation of R1' with phenylacetylene (R2), and conversion from P1 to 2,3-dihydro-oxepine (P2). The results revealed the origin of the reaction divergence and rationalized the experimental observations that a 1:3 reactant stoichiometric ratio affords P1 as the major product, whereas the 1:1.1 ratio results in P2 in high yield. The reactant stoichiometric ratio-controlled divergent reactivity is attributed to different catalytic activities of the gold catalyst toward different reaction stages. In the 1:3 situation, the excess R2 induces the Au catalyst toward its dimerization and/or hydration, inhibiting the conversion of P1 to P2 and resulting in product P1. Without excess R2, the Au catalysis follows a general cascade reaction, leading to product P2. Theoretical results described a general strategy controlling the reaction divergence by a different reactant stoichiometric ratio. This strategy may be enlightening for chemists who are exploring various synthesis methods with high chemo-, regio-, and enantioselectivities.

Low temperature synthesis of Titanium diboride by carbothermal method

Titanium diboride powders have been synthesized by means of carbothermal reduction method utilizing Titanium oxide, Boric acid and Graphite. The effect of mechanical activation of mixed raw materials and the use of additional Boric acid on the final phases have been studied. The resultant powders were characterized by X-ray diffraction (XRD) analyzer and Field Emission Scanning Electron Microscope (FESEM). XRD patterns showed that TiB2, TiC and C phases after heat treatment at stoichiometric ratio of reactants. By increasing the milling time, the unwanted phases such as C and TiC will be reduced. Pure TiB2 could be synthesized with mechanical activation of raw materials for 24 h at non-stoichiometric ratio (using additional Boric acid) and heat treatment at low temperature of 1380 °C. In this condition, Titanium diboride could be achieved with residual carbon of 0.92 0.09wt% and mean average particle size of 3.28µm. Thermal analysis (TGA-DTA) was used to determine the reaction progress and mechanism. Results revealed that the intermediate phase, TiBO3, played an important role in getting to lower temperature synthesis. This phase was identified after mechanical milling of raw materials and heat treatment at temperature of 1250 °C.

Design and Analysis of Bipolar Plate for 500w Pem Fuel Cell Stack

The PEM Fuel Cell (PEMFC) performance depends on the operating parameters like temperature, pressure, stoichiometric ratio of reactants, relative humidity, back pressure on anode and cathode flow channels, and the design parameters like rib width to channel width (L:C), channel depth, shape of the flow channel and number of pass on the flow channel. The voltage and power produced by single cell was not enough for practical applications, hence number of cells are connected in series or parallel to generate required current and voltage to form a fuel cell stack. The effective performance of fuel cell stack depends upon the satisfactory operation of individual cells. For effective thermal management, water management and distribution of reactants (H2 and o2) is challengeable task in fuel cell stack. The design of bipolar plate is contributing more in PEM fuel cell stack to meet the above said critical parameters. In this paper numerical investigation of 500w PEM fuel cell stack with each cell of 100 cm2 active area with rib to channel width (L:C-2:2) of single pass, three pass and six pass parallel serpentine flow channel with square channel inlet and outlet were carried out. The three dimensional PEMFC stack with various passes (1,3,6) for serpentine flow channel were modeled by pro-e, meshed by ICEM 14.0 software packages and simulated using CFD Fluent 14.0 under various operating pressure range from 1 bar to 2 bar and flow rate of hydrogen and oxygen as 500ml/min and 250ml/min respectively. The numerical modeling results on performance of PEMFC stack has been studied and compared and the better flow channel design was identified.

Development of a phosphorylated Momordica charantia protein system for inhibiting susceptible dose-dependent C. albicans to available antimycotics: An allosteric regulation of protein

A regulatory Momordica charantia protein system was constructed allosterically by in vitro protein phosphorylation, in an attempt to evaluate antimycological pluripotency against dose-dependent susceptibilities in C. albicans. Fungal strain lineages susceptible to ketoconazole, econazole, miconazole, 5-flucytosine, nystatin and amphotericin B were prepared in laboratory, followed by identification via antifungal susceptibility testing. Protein phosphorylation was carried out in reactions with 5′-adenylic, guanidylic, cytidylic and uridylic acids and cyclic adenosine triphosphate, through catalysis of cyclin-dependent kinase 1, protein kinase A and protein kinase C respectively. Biochemical analysis of enzymatic reactions indicated the apparent Michaelis-Menten constants and maximal velocity values of 16.57–91.97mM and 55.56–208.33μM·min−1, together with an approximate 1:1 reactant stoichiometric ratio. Three major protein phosphorylation sites were theoretically predicted at Thr255, Thr102 and Thr24 by a KinasePhos tool. Additionally, circular dichroism spectroscopy demonstrated that upon phosphorylation, protein folding structures were decreased in random coil, β6-sheet and α1-helix partial regions. McFarland equivalence standard testing yielded the concentration-dependent inhibition patterns, while fungus was grown in Sabouraud's dextrose agar. The minimal inhibitory concentrations of 0.16–0.51μM (at 50% response) were obtained for free protein and phosphorylated counterparts. With respect to the 3-cycling susceptibility testing regimen, individuals of total protein forms were administrated in-turn at 0.14μM/cycle. Relative inhibition ratios were retained to 66.13–81.04% of initial ones regarding the ketoconazole-susceptible C. albicans growth. An inhibitory protein system, with an advantage of decreasing antifungal susceptibilities to diverse antimycotics, was proposed because of regulatory pluripotency whereas little contribution to susceptibility in itself.

Extraction and Esterification of Low-Titer Short-Chain Volatile Fatty Acids from Anaerobic Fermentation with Ionic Liquids.

Ionic liquids can both act as a solvent and mediate esterification to valorize low-titer volatile fatty acids and generate organic solvents from renewable carbon sources including biowaste and CO2 . In this study, four phosphonium ionic liquids were tested for single-stage extraction of acetic acid from a dilute stream and esterification to ethyl acetate with added ethanol and heat. The esterification proceeded with a maximum conversion of 85.9±1.3 % after 30 min at 75 °C at a 1:1 stoichiometric ratio of reactants. Extraction and esterification can be tailored using mixed-anion ionic liquids; this is demonstrated herein using a common trihexyl(tetradecyl)phosphonium cation and a mixed chloride and bis(trifluoromethylsulfonyl)imide anion ionic liquid. As a further proof-of-concept, ethyl acetate was generated from an ionic liquid-driven esterification of an acetic acid extractant generated using CO2 as the only carbon source by microbial electrosynthesis.

Optimization of Flow Channel Design and Operating Parameters on Proton Exchange Membrane Fuel Cell Using MATLAB

Operating parameters like pressure, temperature, the stoichiometric ratio of reactants, relative humidity and design parameters like rib width to channel width (L:C), the shape of the flow channel and the number of passes on the flow channel are influencing the performance of the Proton Exchange Membrane Fuel Cell (PEMFC). In this paper, optimization of operating and design parameters such as pressure, temperature, inlet reactant mass flow rate and various rib width to channel width (L:C) 1:1, 1:2, 2:1 and 2:2 on serpentine and interdigitated flow channel of 25cm2 active area of the PEMFC was considered. Creo Parametric 1.0 and CFD Fluent 14.0 software packages were used to create the 3 Dimensional (3- D) model and simulation of PEMFC. The optimization was carried out on the various parameters with MINITAB 17 software and MATLAB software. From the first stage, the Landing to channel width (L: C) - 1:1 of serpentine and the interdigitated flow channel has the maximum influence on fuel cell performance and square of response factor (R2) was achieved from the Taguchi method by MINITAB 17 software as 99.48 and 99.71 % respectively. In the second stage, the regression equation or mathematical model obtained from MINITAB 17 software were fed into the MATLAB software to get optimized parameters. Further the power densities were obtained corresponding to the optimized parameters using the CFD Fluent 14.0 software.

Numerical Investigation of Performance Studies on Single Pass PEM Fuel Cell with Various Flow Channel Design

The Proton Exchange Membrane (PEM) Fuel Cell performance not only depends on the operating parameters like temperature, pressure, the stoichiometric ratio of reactants, relative humidity and back pressure on anode and cathode flow channels, but it also depends on design parameters like channel width to rib width, channel depth and number of passes on the flow channel. In this paper numerical analysis were carried out with six different cross-sections of the channel, namely square, triangle, parallelogram 14o, parallelogram 26o, trapezium and inverted trapezium of 1.25 cm2 active area with a constant cross sectional area of 0.01 cm2 of single pass PEM fuel cell. The model was created and simulated under various pressures and temperature with a constant mass flow rate by using fluent CFD and the influence of the single pass flow channel on the performance of PEM fuel cell has been investigated.

Structure and mechanical properties of the hybrid films of well dispersed SiO2 nanoparticle in polyimide (PI/SiO2) prepared by sol–gel process

The hybrid films of well dispersed SiO2 nanoparticle in polyimide (PI/SiO2) were prepared through the sol–gel processing. The pure PI was synthesized from 4, 4′,-oxydianaline (ODA) and pyromellitic dianhydride (PMDA). The residual amino groups which were controlled by the reactant stoichiometric ratio reacted with the coupling agent isocyanatopropyltriethoxysilane (ICTOS) to provide an organic–inorganic bonding. A series amount of tetraethoxysilane (TEOS) was then added, thus producing chemically bonded composite films. The films with different silica contents (0 wt %, 5 wt %, 8 wt %, 10 wt %, 13 wt %, and 15 wt %) were characterized by a variety of techniques including FT-IR, SEM, TGA, and tensile analysis. The results indicated that the chemical interaction between the two phases resulted in the formation of well-dispersed nanoparticles (20–30 nm) in the PI matrix, and superior thermal stability of hybrid films. The tensile measurement showed that the mechanical properties were markedly improved with incorporating various amount of silica, and the maximum of tensile strength was 105.4 MPa with10 wt % of silica concentration.

Growth and characterization of ZnO nanoflakes by hydrothermal method: effect of hexamine concentration

Flake-like ZnO nanostructures, which have potential applications in fields of photo catalysts, biosensors, solar cells, et al., were fabricated on indium doped tin oxide substrates through hydrothermal method at 90 °C. Zinc chloride hydrate and hexamine (HMT) were used as zinc source and the alkali source, respectively, no other surfactants were involved. The morphology evolution of ZnO from nanoflakes to the occurrence of nanorods can be attributed to the competition between the absorption effect of chloride ions and HMT. With the adsorption of chloride ions onto the polar faces instead of growth units, ZnO nanoflakes were formed by restraining the crystal growth along direction. Controllable growth of different ZnO nanostructures was achieved by tuning the corresponding stoichiometric ratios of reactants. ZnO nanoflakes were formed with equivalent concentrations of zinc chloride hydrate and HMT. Increase in the concentration of HMT resulted in the fabrication of the rod-on-flake structure, or even multilevel ZnO nanoflakes. Scanning electron microscopy results revealed that all these ZnO nanoflakes are with typical wurtzite hexagonal phase. The crystal and optical properties of the as-synthesized samples were characterized by X-ray diffraction spectrum and room temperature photoluminescence spectrometer, which showed close relationship with structure variations.

Solvent-induced structural diversities from discrete cup-shaped Co8clusters to Co8cluster-based chains accompanied by in situ ligand conversion

Solvent induced structural diversities from a cup-shaped Co8 cluster (1) in methanol to a Co8 cluster-based co-crystal chain (2) in ethanol/n-propanol and a Co8 cluster-based chain (3) in n-butanol under the same stoichiometric ratio of reactants have been reported. In situ ligand conversion has taken place and the new ligand is captured within the metallic core. Magnetic analyses indicate that theses complexes exhibit distinct magnetic behaviours at low temperature.