Stiochiometric Ratio Research Articles

Multipurpose Solar Photoelectrochemical Hybrid Multilayer Films Based on Porphyrin and Preyssler Type Polyoxometalates for Solar Cell and Ag Nanomaterial Synthesis

Multilayer films with electrostatic interaction between Preyssler,s Polyanions (NH4)14[NaP5W30O110]14- .31H2O and tetracationic free base porphyrin [H2TN+(Me)3PyP]4+ have been alternately deposited on quartz and ITO substrates. and characterized by UV-visible absorption spectroscopy to follow the successive deposition of multilayer film. Solution phase interaction of both components revealed the stiochiometric ratio of the electrostatic complex formed . The morphology and composition of films were studied by atomic force microscopy and X-ray photoelectron spectroscopy (XPS ) .While permeability to cations in aqueous media and redox behavior were studied by cyclic voltametry . The solar photoctalytic activity of hybrid films is identified by TEM images obtained after heterogeneous aqueous photoreduction of Ag2SO4(aq) and KAuCl4 (aq) to yield diversified nanostructures . The study is first and initial report on preyssler type polyanions and porphyrin based heterogenous photocatalysis that provide a green, solar and multiple applications for precious metal recovery as nanoparticle ,sustainable wastewater purification and solar photocurrent generation.Polyoxometalates (POMs) are metal−oxygen framework of early metal elements in their highest oxidation state , able to undergo reversible, stepwise, multielectron-transfer reactions, which are the basis for many catalytic processes[1].These polyanions clusters exhibit applications in catalysis, medicine, materials science [2]. They offer effective photocatalytic properties in oxidation and reduction processes. On photolysis, the high oxidizing ability of excited POMs can lead to the degradation of a variety of organic compounds such as pollutants, leading to a process for water purification [3]. In the presence of a sacrificial electron donor , their photolysis lead to the formation of reduced POMs which can in turn reduce metallic ions. It could be a good alternative for precious metals recovery or synthesis of metal nanoparticles. [4,5]. However, polyoxometalates absorb in the uv part of spectrum, thus they require UV excitation, which cease its large-scale environmental application. One of obvious strategy is to couple it with some chromophore group which can be sensitized by visible light. Metal porphyrins are attractive components in materials because of their appealing chemical and photochemical properties: high stability, intense visible absorption bands, long-lived excited states, and tunability by chemical derivatization [2]. Figure 1.1 R.H.S. Representation of the porphyrin used 5, 10, 15, 20-Tetrakis (4-trimethylammoniophenyl) porphyrin tetra(p-toluenesulfonate), namely [H2TN+(Me)3PyP]4+) used with the Preyssler type (NH4)14[NaP5W30O110]14- .31H2O . L.H.S. UV-visible record on quartz and ITO shows layer by layer absorbance. Formation of Multilayer Films :H2TN+(Me)3PyP4+] / [(NH4)14[NaP5W30O110]14- .31H2O ] The alternate deposition of positively charged porphyrin, H2TN+(Me)3PyP4+, and negatively charged [NaP5W30O110]14-on slides of quartz and Indium tin Oxide (ITO) lectrodes by layer-by-layer were performed.

Adsorption of Heavy Metal on Active Carbon Derived from Coconut Leaves Agro-Waste

In this paper activated carbon is prepared from coconut leaves by chemical activation during slow pyrolysis at 673 K in an inert atmosphere. Activated carbon is prepared in the stiochiometric ratio of 1:1 (CL1), 2:1 (CL2) and 3:1 (CL3). Optimized 3:1 ratio is preferable for further study. BET surface area of CL3 activated carbon was found 1060.57 m2/g. It is greater than those of CL1 and CL2. The batch sorption study experiments were conducted with respect to solute concentration of 2.5–122.8 mg/l and solution temperature of 313–343 K. The Langmuir, Freundlich and Temkin isotherm studies were conducted. The experimental data fitted very well for the pseudo-first order and pseudo-second-order. The results have established good potentiality for the CL3 activated carbon to be used as a sorbent for the removal of lead from wastewater.

Effective hydrogen production from partial oxidation of propane over composite Ni/Al2O3[sbnd]SiC catalyst

In this work, hydrogen production from partial oxidation (POX) of propane over composite Ni/Al2O3SiC catalyst was investigated. In order to utilize the high thermal conductivity and chemical stability of SiC, the composite Al2O3SiC support of the catalyst was synthesized by precipitation technique, then Ni component was loaded using impregnation method. The as-prepared samples were characterized by X-ray diffraction, BET, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) measurements. As observed, stacking porous structures were appeared after calcination process by doping SiC with certain ratios. According to the stiochiometric ratio, a C3H8O2 (1:1.5) gas mixture was used to study the catalytic activity for hydrogen production from POX of propane. From the results, local overheat of the catalyst bed generated by the exothermic reactions was relieved by doping SiC and Ni/Al2O3SiC (30 wt%) catalyst performed a higher hydrogen production. Aggregation and carbon deposition of Ni/Al2O3SiC (30 wt%) catalyst were reduced compared to Ni/Al2O3 from the observation of SEM and TEM with H2 production up to around 236 μmol/gcat·s and kept stable for 26 h at 600 °C. By means of TGA, non-isothermal oxidative decarburizations of the spent catalysts were studied. It was found that less carbon deposit and lower activation energy for oxidative decarburization were found by doping SiC to Ni/Al2O3.

Performance improvement of the open-cathode proton exchange membrane fuel cell by optimizing membrane electrode assemblies

The oxidant supply coupled with the cooling task in open-cathode proton exchange membrane fuel cells (PEMFCs) creates a simple system configuration. Based on a simulated condition which was previously established for evaluating cell performance of different membrane electrode assemblies, this work has conducted performance optimization by altering electrocatalysts, thickness of micro-porous layer (MPL) and membranes. The thickness of the catalyst layers was around ∼35 μm with 20 wt% Pt/C, and reduced to only 12 μm with 60 wt% Pt/C. Although a thick catalyst layer resulted in a stable performance at various air stiochiometric ratios, especially under high temperatures where cell performance decreased due to a low Pt utilization and poor mass transport of proton and reactants in the cathode. The cathode with 2 mg cm−2 carbon loading in the MPL gave the best performance and the cell voltage varied between 0.71 and 0.62 V at 800 mA cm−2 in the temperature range from 50 °C to 60 °C. Finally, different membranes were investigated, and a thin composite Nafion/PTFE membrane around 17 μm showed better performance comparing to Nafion 211, which can be attributed to a good water retention capacity owing to easy crossover of hydrogen and water through the membrane.

Kinetic Studies on the Curing Reactions of Fluoroepoxy Oligomer and Cycloaliphatic Amine

The curing kinetic analysis is an important technique for the characterization of the curing behavior of reactive polymeric systems. In this study, fluoroepoxy oligomer was synthesized from trifluoromethyl aniline and epichlorohydrin. The epoxide equivalent weight (EEW) and the number average molecular weight (Mn) of the systhesized fluroepoxy oligomer determined from acid titration and gel permeation chromatography were found to be 312.16 g/eq and 534 g/mol, respectively. The mixtures of the fluoroepoxy oligomer were mixed with the cycloaliphatic amine in various stiochiometric ratios (1:1, 1: 1.5 and 1:2). The effects of the stiochiometric ratio on the curing behaviors were studied using both isothermal and non-isothermal DSC methods. Ozawas, Kissingers and Friedmans methods were employed to investigate the kinetic parameters. The results showed that the peak temperature (Tp) increased with the increasing heating rate. The activation energy (Ea) calculated from Ozawas and Kissingers methods were much larger than that from Friedmans method.

Triorganotin(IV) Complexes of Schiff Base Derived from Glycine: Synthesis, CharacteristicSpectral Studies and Antifungal Activity

A series of triorganotin(IV) complexes of N-(2-hydroxy-1-naphthylidene) glycine (1), having general formula [Ph3Sn(Hhngl)] (2), [Bu3Sn(Hhngl)] (3), [Me3Sn(Hhngl)] (4), [where H2hngl= N-(2-hydroxy-1-naphthylidene) glycine] were synthesized by reacting of triorganotin(IV) chloride with the ligand, with the aid of sodium iso-propoxide in appropriate stiochiometric ratios (1:1, 1:2). All the complexes exhibit good antifungal activity against four pathogenic fungi namely, Aspergillus niger, Aspergillus flavus, Penicillium sp. and Fusarium sp.

Non-symmetrically substituted N-heterocyclic carbene–Ag(I) complexes of benzimidazol-2-ylidenes: Synthesis, crystal structures, anticancer activity and transmetallation studies

Non-symmetrically substituted benzimidazolium salts (1 and 2) having bromide counterion undergo metallation with Ag2O at stiochiometric ratio, giving mononuclear bis-carbene Ag(I) complexes (3 and 4), active as anticancer agents against Human Colorectal (HCT 116) cell lines. Both the complexes provide good activity (IC50=13.9μM for 3 and 14.6μM for 4) in the anticancer studies and so distinctly better than the ligand precursors (IC50=119.3μM for 1, and 70.0μM for 2). The molecular structure of Ag complexes 3 and 4 is elucidated by X-ray diffraction studies. The Pd(II)– and Au(I)–NHC complexes (5 and 6) were synthesized from 4 via the technique of transmetallation. However, attempts to produce transmetallated complexes using 3 were unsuccessful.

A new class of solvatochromic material: Geometrically unsaturated Ni (II) complexes

Abstract A series of Ni(II) double stranded binuclear complexes were synthesized upon treating the Ni(II) salts with series of diamino-bis-pyridine ligands, L1H2–L4H2 in 1:1 stiochiometric ratio. The Ni(II) centers existing in octahedral geometry, four of the coordination sites are occupied by two ligand strands, while the remaining two sites are occupied by solvent molecules in each metal centers. The Ni(II) complexes 1a–4a and 1b–4b are binuclear in nature with ClO4 and PF6 counter ions. The crystal structure obtained for complex 1b ascertains the solvent coordination. Solvatochromism though a well established phenomena, such observation is reported first time in the present manuscript in the area of helicate chemistry. Thus the manuscript elicits the solvatochromic property of geometrically unsaturated helicates, by appropriately tuning the d-d transition, adapting suitable solvents.

Effects of mercaptopropionic acid as a stabilizing agent and Cd:Te ion ratio on CdTe and CdHgTe quantum dots properties

In the present work, mercaptopropionic acid (MPA) capped CdTe and CdHgTe quantum dots (QDs) are synthesized using a method based on the bottom up approach in aqueous medium. The CdTe QDs were prepared with a two different ratios of Cd:Te (3:1 and 4:1). It was noticed that there was a minimum concentration of MPA for each Cd:Te ratio. The resulting QDs were characterized using optical absorption spectroscopy, energy dispersion X-ray (EDX) and high resolution transmission electron microscopy (HRTEM). It was found that the EDXs of CdTe and CdHgTe QDs showed that the stiochiometric ratios of CdTe obtained with Cd:Te ratio of 3:1 is 50:50 and for CdHgTe is 40:26:34 for 100 % of Hg. The band gap of CdHgTe QDs varies slightly with composition from 2.21 eV for a pure CdTe to 1.4 eV for a CdHgTe with 100 % of Hg. The HRTEM image showed a good dispersed nano-crystalline structure for the CdTe QDs with average size of 3–4 nm. The existence of the lattice planes on the HRTEM images of the QD indicated that the CdTe QDs are highly crystalline. In addition, the CdHgTe QDs size is 12 nm for 100 % of Hg.

Vacuum Deposition of Stoichiometric Thin Films of II-VI Sulphide Semiconductors

Abstract Compound semiconductors provide a large range of materials with varying band gaps for application in devices. Usually these devices are made in the form of thin films, whose crystalline quality and stoichiometry play a pivotal role in the stability and the performing characteristics of the device. Vacuum deposition of thin films is the most popular and dependable method of preparing thin films. However, it is a general problem that the compound semiconductors thermally dissociate into their constituent components during evaporation. To overcome this difficulty, we optimize a method, wherein good quality films of sulphide semiconductors were grown by using a low ambient H2S atmosphere inside the vacuum chamber while thermally evaporating the sulphide semiconductor materials. The substrate was kept at an elevated temperature, which was high enough for the dissociated sulphur ions to be ejected from the substrate while the dissociated metallic cations quickly combined with the highly reactive H2S molecules to get deposited as sulphide molecules. Such films naturally had better stiochiometric ratio, better crystallinity, and had less structural defects. Such films were remarkably pin hole free and had better adhistivity with the substrates. Such films would be inherently more suitable for any electro-optical devices.

Electrochemical synthesis and characterization of BaB6 from molten melt

Barium hexaboride (BaB6) crystals were electrochemically synthesized using molten salt technique. Barium carbonate (BaCO3) and boron trioxide (B2O3) was used as reactants. Lithium fluoride (LiF) was used as the supporting electrolyte. The molten electrolyte consisted of 50 wt % BaCO3 and B2O3 with different stiochiometric ratios of Ba and B and 50 wt % lithium fluoride. DTA/TGA studies were made to determine the eutectic point of the melt and it was found to be around 821oC. The electrolytic cell had a high purity graphite crucible, which served as the electrolyte holding vessel and also as the anode for the electrolysis. An electro-polished molybdenum rod was employed as the cathode. The electrolysis was performed at 870?C under argon atmosphere, at current densities ranging from 0.2-0.5 A/cm2. The electrodeposited crystals were examined for the phase identification using X-ray diffraction technique. The AAS and the chemical analysis were made for the determination of chemical composition of the synthesized crystals. The purity of the crystals was also assessed using ICP-MS, XRF and EDX, which reveal that the crystals were associated with trace amount of impurities like oxygen, carbon and iron. The compound is found to be more than 99 % pure. The morphology of the crystals was examined using Scanning Electron Microscopy (SEM). From the above studies, it is concluded that the molten salt process is a simple preparative procedure for the synthesis of sub-micron size barium hexaboride crystals.

Biodegradable poly(polyol sebacate) polymers

We have developed a family of synthetic biodegradable polymers that are composed of structural units endogenous to the human metabolism, designated poly(polyol sebacate) (PPS) polymers. Material properties of PPS polymers can be tuned by altering the polyol monomer and reacting stiochiometric ratio of sebacic acid. These thermoset networks exhibited tensile Young's moduli ranging from 0.37 ± 0.08 to 378 ± 33 MPa with maximum elongations at break from 10.90 ± 1.37% to 205.16 ± 55.76%, and glass transition temperatures ranging from ∼7–46 °C. In vitro degradation under physiological conditions was slower than in vivo degradation rates observed for some PPS polymers. PPS polymers demonstrated similar in vitro and in vivo biocompatibility compared to poly( l-lactic-co-glycolic acid) (PLGA).

Stoichiometric Ratio Dependent Photoluminescence Quantum Yields of the Thiol Capping CdTe Nanocrystals

Thioglycolic acid capping CdTe nanocrystals were synthesized under different stoichiometric ratios of Cd to Te precursors in aqueous solution. It was found that the photoluminescence quantum yield (QY) of the nanocrystals increased from 10.3 to 34.0% as the stiochiometric ratio of Cd to Te precursors used increased from 1.5:1 to 5.0:1. It is identified that the stoichiometric ratio of S to Te on the nanocrystal surface increased with increased initial stoichiometric ratio of Cd to Te precursors used in the syntheses, allowing the construction of more perfect surface under higher S/Te ratio. Time-resolved luminescence decay curves indicate there are two different decay lifetimes, corresponding to the intrinsic recombination of populated core states and the surface-related luminescence respectively. The surface-related luminescence is mainly responsible for the increased QY of the nanocrystals.

Constructing a small strain potential for multi-scale modeling

Simulation of bulk materials with some components locally far from equilibrium usually requires a computationally intensive quantum mechanical description to capture the relevant mechanisms (e.g. effects of chemistry). Multi-scale modeling entails a compromise whereby, the most accurate quantum description is used only where needed and the remaining bulk of the material is replaced by a simpler classical system of point particles. The problem of constructing an appropriate potential energy function for this classical system is addressed here. For problems relating to fracture, a consistent embedding of a quantum (QM) domain in its classical (CM) environment requires that the classical system should yield the same structure and elastic properties as the QM domain for states near equilibrium. It is proposed that an appropriate classical potential can be constructed using ab initio data on the equilibrium structure and weakly strained configurations calculated from the quantum description, rather than the more usual approach of fitting to a wide range of empirical data. This scheme is illustrated in detail for a model system, a silica nanorod that has the proper stiochiometric ratio of Si:O as observed in real silica. The potential energy is chosen to be pair wise additive, with the same pair potential functional form as familiar phenomenological TTAM potential. Here, the parameters are determined using a genetic algorithm with force data obtained directly from a quantum calculation. The resulting potential gives excellent agreement with properties of the reference quantum calculations both for structure (bond lengths, bond angles) and elasticity (Young's modulus). The proposed method for constructing the classical potential is carried out for two different choices for the quantum mechanical description: A transfer Hamiltonian method (NDDO with coupled-cluster parameterization) and density functional theory (with plane wave basis set and PBE exchange correlation functional). The quality of the potentials obtained in both cases is quite good, although the two quantum rods have significant differences.

MECHANISM OF SALT TOLERANCE OF TWO OLIVE OLEA EUROPAEA L. CULTIVARS AS RELATED TO ELECTROLYTE CONCENTRATION AND TOXICITY

ISHS XXVI International Horticultural Congress: Environmental Stress and Horticulture Crops MECHANISM OF SALT TOLERANCE OF TWO OLIVE OLEA EUROPAEA L. CULTIVARS AS RELATED TO ELECTROLYTE CONCENTRATION AND TOXICITY

Synthesis and characterization of methylbismuth(III) complexes containing dithio ligands: crystal and molecular structure of [MeBi{S 2COMe} 2] and transformation of [MeBi{S 2CO iPr} 2] to Bi 2S 3

Reactions of sodium/potassium salts of xanthates, dithiocarbamates and dialkyldithiophosphates with methylbismuth dichloride have been carried out in 1:2 stiochiometric ratio in anhydrous benzene and products of the type [MeBi(S 2COR) 2] (R=Me, Et, Pr i), [MeBi(S 2CNR 2) 2] (R=Me, Et, 1/2C 4H 8N) and [MeBi{S 2P(OR) 2} 2] (R=Me, Et, Pr i) have been isolated. All of these complexes were characterized by elemental analyses and by IR and NMR ( 1H, 13C and 31P) spectra. The X-ray structure of [MeBi(S 2COMe) 2] indicates that the immediate environment around the central bismuth atom is distorted square pyramidal. However, inclusion of a significant Bi⋯S intermolecular bond results in pentagonal pyramidal geometry. Thermolysis of [MeBi(S 2CO i Pr) 2] in xylene indicates that it is a good precursor for preparation of Bi 2S 3 at low temperature.

Spectrophotometric Studies of the Coordination Polymers Based on Poly(8-Hydroxyquinoline) Matrix

Incorporation of various metal ions into a poly(8-hydroxyquinoline) (PHQ) matrix via a complexation mechanism to form the corresponding coordination polymers was investigated experimentally and computationally. TGA, DTG, MS, and elemental analysis measurements show that the polymeric chelates of copper(II) ion with the PHQ matrix have a hydrophilic nature about two-times stronger than the salt (i.e., copper acetate monohydrate). The results of DSC, TGA, and DTG suggest that the PHQ-Cu(II) matrix is more thermally stable than the copper acetate complex. A first-order derivative treatment of the UV-visible absorption spectra of the matrixes under investigation is sensitive to at least 1.5-times that of the normal (zero-order derivative) spectra. Analysis of the absorbance vs. mole fraction data for metal ions such as Cu(II), Ni(II), Co(II), and Fe(III), which are coordinated to the PHQ matrix, afforded information about the equilibria that prevailed in solution. The largest stability constant (log β) corresponds to a stiochiometric ratio of 2PHQ:1Mn+. The results are supported by elemental analysis, TGA, DTG, and mass spectroscopic measurements, and are consistent with molecular mechanics (MM+) calculations. A simple, rapid and sensitive method for the spectrophotometric determination of trace amounts of Cu(II) ion in solution by coordination with the PHQ matrix is proposed. The method has been applied successfully to the determination of Cu(II) ion in Heamoton capsule samples (mg/g). The proposed method is in excellent agreement with the determination of Cu(II) ion by atomic absorption spectrometry.

Structural and electrical properties of excess PbO doped Pb(Zr0.48Ti0.52)O3 thin films prepared by a MOD process

Pb(Zr0.52Ti0.48)O3 thin films with 30 mol % excess Pb were deposited on Pt/Ti/SiO2/Si(100) substrates at 600 °C by a metal-organic decomposition process. The Pb/Zr ratio measured by Rutherford backscattering spectroscopy is higher than the stiochiometric ratio. X-ray diffraction measurements show that the PZT film has a perovskite structure but it also contains a PbO2 phase High resolution transmission electron microscope studies reveal that the nano sized PbO2 crystals are dispersed quite uniformly in the film. The film exhibits an abnormally slim polarization loop at low applied electric field probably as a result of domain pinning by the PbO2 crystals. The pinning effect can be overcome by applying a sufficiently high field. The film had good fatigue properties even with the presence of the PbO2 crystals.

Photoelectrochemical properties of dye sensitized Zr-doped SrTiO 3 electrodes

Zr-doped SrTiO 3 was used as a photoanode in a three-electrode electrochemical cell. The three organic dyes Safranin, Fluorescein and Eriochrome black T were used as sensitizers in the cell. The results showed that applying the dyes in photoelectrochemical solar (PECS) cells increased the solar efficiency to 2–3 times its value without dyes. The efficiency reaches its maximum value when the dye concentration is sufficient to cover the surface of the semiconductor electrode with a continuous monolayer. Dye concentration higher than this value resulted in a decrease of the efficiency. Mott-Schottky plots gave a doping density of 1.34 × 10 16cm −3 for the sample and a space charge width of 1.5–2.0 × 10 −6cm (pH dependent). H 2 was produced at zero bias in the presence of Safranin dye at a light intensity of 25mW/cm 2 with an efficiency of about 39%. Both H 2 and O 2 were produced in the stiochiometric ratio. Cyclic voltammetry (c.v.) measurements showed two cathodic current peaks revealing two reduction processes at the semiconductor electrode.