Molybdic Acid Research Articles

Pressurized Hot Water Procedures for Use on Small Farms in Developing Countries

Soil analysis for small farms in developing countries is often inconvenient and prohibitively expensive, yet the information gained from these soil tests could result in significant benefits. Based on tests done on a limited range of soils, the pressurized hot water (PHW) extraction coupled with colorimetric or turbidimetric analysis is a promising alternative. Before this extraction and analysis can be used in developing countries, testing is needed across the range of soils found in these countries. At Brigham Young University (BYU), 228 soils from Guatemala and Morocco were analyzed for NO3‐N, phosphorus (P), and potassium (K) using standard methods (water–CTA, Olsen–molybdic acid and ammonium acetate–atomic absorption, respectively). Results were correlated to values obtained from the PHW extraction coupled with colorimetric or turbidimetric analytical procedures. The relationships between these tests were good (r2 values of 0.96, 0.71, and 0.52 for NO3‐N, P, and K, respectively). In an additional study comparing several P extraction methods for Guatemala soils, relationships between PHW‐extractable P and Olsen‐, Bray I–, and Mehlich I–extractable P (r2 values of 0.75, 0.67, and 0.46, respectively) suggest that PHW is a promising P‐extraction procedure for use in Guatemala. Overall, PHW extraction and accompanying analyses are a less expensive alternative to current soil nutrient extraction and analysis procedures for the soils of Morocco and Guatemala.

A Fast Sequential Injection Analysis System for the Simultaneous Determination of Ammonia and Phosphate

A flow system is described that is based on sequential injection analysis (SIA) and is suitable for the fast determination of ammonia and phosphate in river and marine waters. It is applicable to nutrient mapping in inhomogeneous coastal areas like the Wadden Sea, and was optimised on several cruises on the North Sea. The high sample throughput of 120 samples per analyte per hour and the low reagent consumption (ammonia: 62.5 µL; phosphate: 60 µL) were achieved using a home made programme written in the python programming language. The determination of free reactive phosphate is based on the reaction of phosphate with acidic molybdate to phosphomolybdate which forms nonfluorescent ion pairs with rhodamine 6G. The remaining rhodamine fluorescence is detected at 550 nm with an excitation at 470 nm. Ammonia is determined with the help of o-phthaldialdehyde and sodium sulfite. At 85 °C and a reaction time of at least one minute a fluorescent species (exc. 365 nm, em. 425 nm) is formed. The detection limits are (3σ) 0.3 µmol L−1 for phosphate and 1 µmol L−1 for ammonia.

From Layered Molybdic Acid to Lower-Dimensional Nanostructures by Intercalation of Amines under Ambient Conditions

Nanostructures of varied dimensionality such as rods, scrolls, and disks of molybdenum oxide have been synthesized in gram quantities under ambient conditions using exfoliation of the layers as a synthetic tool. Intercalation of alkylamines (CnH2n+2NH2, where n = 3, 4, 8, 12, and 16) into yellow molybdic acid (MoO3·2H2O) and subsequent treatment with nitric acid resulted in molybdenum oxide nanorods, nanodisks, or oxide−amine composite nanorods. The sizes of the nanoparticles range from a few nanometers to micrometers in length and 10 to 200 nm in diameter. Detailed X-ray, scanning electron microscopy, and transmission electron microscopy analyses reveal an inverse relation between the size of the nanoparticles and the chain length of the guest molecules. Infrared and thermogravimetric studies throw light on the driving force for the amine intercalation and the orientation of the intercalated amine molecules.

Molybdate doping of networks in epoxy–silica hybrids: Domain structuring and corrosion inhibition

Epoxy–silica hybrids were prepared from a silane-functionalized resin mixture of two diglycidyl ether bis-phenol A oligomers with different molecular weights, using molybdate anions as dopants for the siloxane domains. The functionalization of the epoxy resin was carried out using suitable trimethoxysilane compounds, respectively, containing amine and mercaptan reactive groups. The molybdate anions were added as “bound” species in the form of salts produced from pre-reactions with a fractional amount of the cycloaliphatic amine hardener, and as “free” molybdic acid. The co-continuous silica domains within the epoxy networks were produced by the incorporation of pre-hydrolysed mixtures of tetraethoxy silane and γ-glycidoxyl trimethoxysilane into the precursor solution used for the production of epoxy–silica hybrids. The addition of a source of molybdate anions to the hybrid precursor solution gave rise to the formation of a denser siloxane network and to a substantial increase in the T g of the organic phase. This resulted also in a large increase in the rubbery-plateau modulus, and in a substantial reduction in both the rate of solvent uptake and the equilibrium amount of solvent absorption. It was shown that the presence of organic–inorganic hybrid networks allows the “entrapped” molybdate anions to be released at a slow and controlled rate. Furthermore, when the precursor solution mixtures for the formation of such doped networks are used as coatings for ferrous metal substrates, the molybdate anions slowly migrate to the interface and provide an enhanced mechanism for the passivation of the metal substrate. The enhancement of the corrosion protection capability of the coatings was found to be greater when the molybdate anions were added in “bound” form, as amine molybdate, than as “free” molybdic acid.

Using sequential injection analysis for fast determination of phosphate in coastal waters

A sequential injection analysis system (SIA) is described which is suited for the fast determination of filterable molybdate reactive phosphate (FRP, 0.2 μm) in coastal waters. It processes up to 270 samples per hour with a detection limit (3σ) of 0.05 μM and is used for surface mapping of phosphate in areas with steep concentration gradients like the Wadden Sea. The determination is based on the reaction of phosphate with acidic molybdate to phosphomolybdate, which builds non-fluorescent ion pairs with rhodamine 6G. The remaining rhodamine fluorescence is detected at 550 nm with an excitation at 470 nm. Syringe pump, valve and detector were controlled by a self made python programme, which was optimised for high speed SIA measurements in monitoring applications.

Electrosynthesis of molybdenum oxide thin films onto stainless substrates

The electrodeposition of uniform, nanocrystalline and highly oriented molybdenum oxide thin films was investigated at room temperature onto stainless steel substrates using citric acid as a complexing agent. The electrodeposition process of molybdenum oxide thin films from molybdic acid of various concentrations onto stainless steel substrate were studied by utilizing the electrochemical techniques. The prepared films were characterized for their structural, surface morphological and compositional properties by means of X-ray diffraction, scanning electron microscopy, transmission electron microscopy and energy dispersive X-ray analysis. X-ray diffraction and transmission electron microscopy experiment reveals that the films are of crystallized size. XRD experiment showed that the crystallized product is composed of molybdenum oxide with dominant orientations of MoO 3.

Design of active molybdenum oxides: β-MoO 3 and/or silicomolybdic acid supported on mesoporous MCM-41 catalysts

A silicomolybdic acid (SMA) supported on mesoporous MCM-41 catalyst was successfully prepared by an impregnation with a molybdic acid solution via ion exchange of a Na 2MoO 4 · 2H 2O solution. On the other hand, β-MoO 3, the metastable phase of molybdenum oxide, was predominantly generated on MCM-41 by use of the molybdic acid solution adjusted by nitric acid and was anchored by the formation of SMA on the support. The molybdic acid is an attractive precursor to design either SMA or β-MoO 3 as well as to stabilize them on MCM-41 by the formation of SMA. Those catalysts showed interesting performances in partial oxidation of methane to formaldehyde by molecular oxygen.

Polyoxometalate-Supported Transition Metal Complexes and Their Charge Complementarity: Synthesis and Characterization of [M(OH)6Mo6O18{Cu(Phen)(H2O)2}2][M(OH)6Mo6O18{Cu(Phen)(H2O) Cl}2]·5H2O (M = Al3+, Cr3+)

Two Anderson-type heteropolyanion-supported copper phenanthroline complexes, [Al(OH)6Mo6O18[Cu(phen)(H2O)2]2]1+ (1c) and [Al(OH)6Mo6O18[Cu(phen)(H2O)Cl]2]1- (1a) complement their charges in one of the title compounds [Al(OH)6Mo6O18[Cu(phen)(H2O)2]2][Al(OH)6Mo6O18[Cu(phen)(H2O)Cl]2].5H2O [1c][1a].5 H2O 1. Similar charge complementarity exists in the chromium analogue, [Cr(OH)6Mo6O18[Cu(phen)(H2O)2]2][Cr(OH)6Mo6O18[Cu(phen)(H2O)Cl]2].5 H2O [2c][2a].5 H2O 2. The chloride coordination to copper centers of 1a and 2a makes the charge difference. In both compounds, the geometries around copper centers are distorted square pyramidal and those around aluminum/chromium centers are distorted octahedral. Three lattice waters, from the formation of intermolecular O-H.....O hydrogen bonds, have been shown to self-assemble into an "acyclic water trimer" in the crystals of both 1 and 2. The title compounds have been synthesized in a simple one pot aqueous wet-synthesis consisting of aluminum/chromium chloride, sodium molybdate, copper nitrate, phenanthroline, and hydrochloric acid, and characterized by elemental analyses, EDAX, IR, diffuse reflectance, EPR, TGA, and single-crystal X-ray diffraction. Both compounds crystallize in the triclinic space group P. Crystal data for 1: a = 10.7618(6), b = 15.0238(8), c = 15.6648(8) angstroms, alpha = 65.4570(10), beta = 83.4420(10), gamma = 71.3230(10), V = 2182.1(2) angstroms3. Crystal data for 2: a = 10.8867(5), b = 15.2504(7), c = 15.7022(7) angstroms, alpha = 64.9850(10), beta = 83.0430(10), gamma = 71.1570(10), V = 2235.47(18) angstroms3. In the electronic reflectance spectra, compounds 1 and 2 exhibit a broad d-d band at approximately 700 nm, which is a considerable shift with respect to the value of 650-660 nm for a square-pyramidal [Cu(phen)2L] complex, indicating the coordination of [M(OH)6Mo6O18]3- POM anions (as a ligand) to the monophenanthroline copper complexes to form POM-supported copper complexes 1c, 1a, 2c, and 2a. The ESR spectrum of compound 1 shows a typical axial signal for a Cu2+ (d9) system, and that of compound 2, containing both chromium(III) and copper(II) ions, may reveal a zero-field-splitting of the central Cr3+ ion of the Anderson anion, [Cr(OH)6Mo6O18]3-, with an intense peak for the Cu2+ ion.

Synthesis of β‐MoO3 by Simple Evaporation of Molybdic Acid Solution Containing Nitric Acid.

AbstractFor Abstract see ChemInform Abstract in Full Text.

CML24, regulated in expression by diverse stimuli, encodes a potential Ca2+ sensor that functions in responses to abscisic acid, daylength, and ion stress.

Changes in intracellular calcium (Ca(2+)) levels serve to signal responses to diverse stimuli. Ca(2+) signals are likely perceived through proteins that bind Ca(2+), undergo conformation changes following Ca(2+) binding, and interact with target proteins. The 50-member calmodulin-like (CML) Arabidopsis (Arabidopsis thaliana) family encodes proteins containing the predicted Ca(2+)-binding EF-hand motif. The functions of virtually all these proteins are unknown. CML24, also known as TCH2, shares over 40% amino acid sequence identity with calmodulin, has four EF hands, and undergoes Ca(2+)-dependent changes in hydrophobic interaction chromatography and migration rate through denaturing gel electrophoresis, indicating that CML24 binds Ca(2+) and, as a consequence, undergoes conformational changes. CML24 expression occurs in all major organs, and transcript levels are increased from 2- to 15-fold in plants subjected to touch, darkness, heat, cold, hydrogen peroxide, abscisic acid (ABA), and indole-3-acetic acid. However, CML24 protein accumulation changes were not detectable. The putative CML24 regulatory region confers reporter expression at sites of predicted mechanical stress; in regions undergoing growth; in vascular tissues and various floral organs; and in stomata, trichomes, and hydathodes. CML24-underexpressing transgenics are resistant to ABA inhibition of germination and seedling growth, are defective in long-day induction of flowering, and have enhanced tolerance to CoCl(2), molybdic acid, ZnSO(4), and MgCl(2). MgCl(2) tolerance is not due to reduced uptake or to elevated Ca(2+) accumulation. Together, these data present evidence that CML24, a gene expressed in diverse organs and responsive to diverse stimuli, encodes a potential Ca(2+) sensor that may function to enable responses to ABA, daylength, and presence of various salts.

Preparation of MoO3/g-Al2O3 catalyst by the reaction of a-boehmite with MoO3/H2O slurry - dual role of MoO3 as active phase and texture stabilizer during calcination

Catalyst MoO3/g-Al2O3 was prepared by the reaction of a-boehmite with molybdic acid in slurry MoO3/H2O followed by calcination. The deposited MoO3 functioned as thermal stabilizer and inhibited sintering of Al2O3 phase during calcination. After calcination at 550 and 650oC the surface area of Al2O3 obtained from a-boehmite was 207 and 172 m2 g-1, respectively, and of MoO3/Al2O3 obtained from MoO3/a-boehmite was 323 and 285 m2 g-1, respectively. On the other hand, molybdic acid did not work as peptization agent and the mechanical strength of MoO3/Al2O3 was not higher than of Al2O3. The catalyst was sulfided and its activity in thiophene hydrodesulfurization was tested; it exhibited about the same activity as reference industrial MoO3/Al2O3 catalyst.

Synthesis of β-MoO3 by Simple Evaporation of Molybdic Acid Solution Containing Nitric Acid

Abstract β-MoO3 was successfully synthesized through a simple evaporation of a molybdic acid solution prepared by a cation exchange of an aqueous solution of Na2MoO4·2H2O. The key was an addition of a small amount of nitric acid before the evaporation. Heating the dried molybdic acid at 573 K in oxygen resulted in a formation of a bright yellow powder, which was confirmed to be β-MoO3 free from α-MoO3 by XRD and Raman spectroscopy.

CeHMT-1, a Putative Phytochelatin Transporter, Is Required for Cadmium Tolerance in Caenorhabditis elegans

Phytochelatins (PCs), (gamma-Glu-Cys)n Gly polymers that were formerly considered to be restricted to plants and some fungal systems, are now known to play a critical role in heavy metal (notably Cd2+) detoxification in Caenorhabditis elegans. In view of the functional equivalence of the gene encoding C. elegans PC synthase 1, ce-pcs-1, to its homologs from plant and fungal sources, we have gone on to explore processes downstream of PC fabrication in this organism. Here we describe the identification of a half-molecule ATP-binding cassette transporter, CeHMT-1, from C. elegans with an equivalent topology to that of the putative PC transporter SpHMT-1 from Schizosaccharomyces pombe. At one level, CeHMT-1 satisfies the requirements of a Cd2+ tolerance factor involved in the sequestration and/or elimination of Cd x PC complexes. Heterologous expression of cehmt-1 in S. pombe alleviates the Cd2+-hypersensitivity of hmt- mutants concomitant with the localization of CeHMT-1 to the vacuolar membrane. Suppression of the expression of ce-hmt-1 in intact worms by RNA interference (RNAi) confers a Cd2+-hypersensitive phenotype similar to but more pronounced than that exhibited by ce-pcs-1 RNAi worms. At another level, it is evident from comparisons of the cell morphology of ce-hmt-1 and cepcs-1 single and double RNAi mutants that CeHMT-1 also contributes to Cd2+ tolerance in other ways. Whereas the intestinal epithelial cells of ce-pcs-1 RNAi worms undergo necrosis upon exposure to toxic levels of Cd2+, the corresponding cells of ce-hmt-1 RNAi worms instead elaborate punctate refractive inclusions within the vicinity of the nucleus. Moreover, a deficiency in CeHMT-1 does not interfere with the phenotype associated with CePCS-1 deficiency and vice versa. Double ce-hmt-1; ce-pcs-1 RNAi mutants exhibit both cell morphologies when exposed to Cd2+. These results and those from our previous investigations of the requirement for PC synthase for heavy metal tolerance in C. elegans demonstrate PC-dependent, HMT-1-mediated heavy metal detoxification not only in S. pombe but also in some invertebrates while at the same time indicating that the action of CeHMT-1 does not depend exclusively on PC synthesis.

Chemical solution deposition preparation of double perovskite Sr2FeMoO6 film on LaAlO3 (001) substrate

Sr2FeMoO6 film was successfully deposited on LaAlO3 (00l) substrate via chemical solution deposition using low cost precursor materials of Sr nitrate, Fe nitrate, and ammonia-complexed molybdic acid. The X-ray diffraction, field-emission scan electron microscopy and atomic force microscopy results showed that the Sr2FeMoO6 film was highly (00l)-oriented and relatively smooth and dense with few undesired SrMoO4 phase. The transport and magnetic measurements showed that the Sr2FeMoO6 film had a Curie temperature at 368 K and behaved like semiconductors, which could be attributed to the large Fe/Mo disorders. Further works about improving the Fe/Mo order as well as the low-field magnetoresistance are being carried out and will be reported elsewhere.

Evaluation of on-line preconcentration and flow-injection amperometry for phosphate determination in fresh and marine waters

Dissolved reactive phosphorus (DRP) was determined as orthophosphate (PO 4-P) in fresh and saline water samples by flow-injection (FI) amperometry, without and with in-valve column preconcentration. Detection is based on reduction of the product formed from the reaction of DRP with acidic molybdate at a glassy carbon working electrode (GCE) at 220 mV versus the Ag/AgCl reference electrode. A 0.1 M potassium chloride solution was used as both supporting electrolyte and eluent in the preconcentration system. For the FI configuration without preconcentration, a detection limit of 3.4 μg P l −1 and sample throughput of 70 samples h −1 were achieved. The relative standard deviations for 50 and 500 μg P l −1 orthophosphate standards were 5.2 and 5.9%, respectively. By incorporating an ion exchange preconcentration column, a detection limit of 0.18 μg P l −1 was obtained for a 2-min preconcentration time (R.S.D.s for 0.1 and 1 μg P l −1 standards were 22 and 1.0%, respectively). Potential interference from silicate, sulfide, organic phosphates and sodium chloride were investigated. Both the systems were applied to the analysis of certified reference materials and water samples.

Solvothermal Morphology Studies: Alkali and Alkaline Earth Molybdates.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Dissolution Kinetics of Synthetic Amorphous Silica in Biological-Like Media and Its Theoretical Description

Different types of synthetic amorphous silica have been dissolved under biological-like conditions in a buffer system. The buffer solution named TRIS buffer provides a system with comparable pH value, buffer capacity, and osmotic pressure as it can be found in extracellular fluid. Additionally, the phospholipid l-α-dipalmitoylphosphatidylcholine (DPPC) has been used in several dissolution experiments to simulate conditions which are found in extracellular lung fluid. The molybdic acid method (used as standard procedure) and partly ICP−OES have been applied to determine the total amount of silica dissolved. The dissolution of nanodisperse silica shows a strong size effect, which leads to a significant higher silica concentration when compared with the bulk phase. At longer dissolution time a slight decrease of solubility can be observed. The Gibbs free energy of cluster formation is calculated numerically for the dissolution process to predict the temporal development of silica concentration. Theoretical curves are adapted by nonlinear regression of a free parameter. This parameter can be understood as the rate constant of the dissolution process.

Solvothermal Morphology Studies: Alkali and Alkaline Earth Molybdates

AbstractA convenient and systematic solvothermal pathway towards alkali and alkaline‐earth molybdates has been established. The solvothermal treatment of a molybdenum‐based precursor material (yellow molybdic acid, MoO3⋅2 H2O) with ionic additives (alkali or alkaline‐earth halides) provides access to a spectrum of molybdates. Their particle morphology can further be addressed by optimizing the reaction conditions. The resulting products cover a wide scope of sizes and morphologies, ranging from molybdenum oxide fibres with high aspect ratios and nanoscale diameters to millimeter‐sized crystals of novel alkali molybdates. Both anionic and cationic additives exhibit certain synthetic profiles that offer the perspective of turning this approach into a ‘toolbox’ for the tailoring of molybdate‐based materials.

One-Step Synthesis of Submicrometer Fibers of MoO3

Nanorods of MoO3 are accessible in gram quantities from MoO3·2H2O via a flexible one-step solvothermal reaction. Several hours of treatment in water at 180 °C are sufficient to convert the starting material quantitatively into rods with diameters around 100 nm and microscale lengths. The formation of MoO3 rods proceeds in both neutral ionic and acidic media within a wide parameter window encompassing reaction temperatures between 90 and 180 °C and time scales ranging from several hours to 7 d. The rod morphology can be tuned by selecting a proper additive, and the nanorods withstand heating to 400 °C. Furthermore, the reaction pathways in various solvothermal media were investigated and both intermediate molybdic acids and the bulk nanorod products were characterized by means of EXAFS spectroscopy.

Determination of trace amounts of phosphate by flow-injection photometry.

This paper describes a simple and rapid procedure for determination of traces of phosphate by means of molybdenum blue chemistry. The use of a cost-effective home-made flow cell with a long path length in combination with a light emitting diode (LED) and a photodiode (PD) is demonstrated as a simple absorbance detector for flow-injection analysis. In this method, a sample is injected into the carrier stream through an injection valve and mixed online with mixed reagent (a mixture of molybdate, bismuth, and ascorbic acid in sulfuric acid). The color intensity of the resulting association complex, molybdenum blue, is measured photometrically ( lambda(max) 875 nm). The proposed method can be used to detect phosphate in the range 0.02-4.0 mg x L(-1) and the precision of the proposed procedure is less than 5% at 0.1 mg x L(-1) phosphorus as phosphate. The method has been successfully applied to a variety of natural water samples.