Showing papers on "Oxalic acid published in 2004"

Nitrate Reduction by Zerovalent Iron: Effects of Formate, Oxalate, Citrate, Chloride, Sulfate, Borate, and Phosphate

Abstract: Recent studies have shown that zerovalent iron (Fe0) may potentially be used as a chemical medium in permeable reactive barriers (PRBs) for groundwater nitrate remediation; however, the effects of commonly found organic and inorganic ligands in soil and sediments on nitrate reduction by Fe0 have not been well understood. A 25.0 mL nitrate solution of 20.0 mg of N L-1 (1.43 mM nitrate) was reacted with 1.00 g of Peerless Fe0 at 200 rpm on a rotational shaker at 23 °C for up to 120 h in the presence of each of the organic acids (3.0 mM formic, 1.5 mM oxalic, and 1.0 mM citric acids) and inorganic acids (3.0 mM HCl, 1.5 mM H2SO4, 3.0 mM H3BO3, and 1.5 mM H3PO4). These acids provided an initial dissociable H+ concentration of 3.0 mM available for nitrate reduction reactions under conditions of final pH < 9.3. Nitrate reduction rates (pseudo-first-order) increased in the order: H3PO4 < citric acid < H3BO3 < oxalic acid < H2SO4 < formic acid < HCl, ranging from 0.00278 to 0.0913 h-1, corresponding to surface a...

Enhanced phytoextraction: in search of EDTA alternatives.

Abstract: Enhanced phytoextraction proposes the use of soil amendments to increase the heavy-metal content of above-ground harvestable plant tissues. This study compares the effect of synthetic aminopolycarboxylic acids [ethylenediamine tetraacetatic acid (EDTA), nitriloacetic acid (NTA), and diethylenetriamine pentaacetic acid (DTPA)] with a number of biodegradable, low-molecular weight, organic acids (citric acid, ascorbic acid, oxalic acid, salicylic acid, and NH4 acetate) as potential soil amendments for enhancing phytoextraction of heavy metals (Cu, Zn, Cd, Pb, and Ni) by Zea mays. The treatments in this study were applied at a dose of 2 mmol/kg(-1) 1 d before sowing. To compare possible effects between presow and postgermination treatments, a second smaller experiment was conducted in which EDTA, citric acid, and NH4 acetate were added 10 d after germination as opposed to 1 d before sowing. The soil used in this screening was a moderately contaminated topsoil derived from a dredged sediment disposal site. This site has been in an oxidized state for more than 8 years before being used in this research. The high carbonate, high organic matter, and high clay content characteristic to this type of sediment are thought to suppress heavy-metal phytoavailability. Both EDTA and DTPA resulted in increased levels of heavy metals in the above-ground biomass. However, the observed increases in uptake were not as large as reported in the literature. Neither the NTA nor organic acid treatments had any significant effect on uptake when applied prior to sowing. This was attributed to the rapid mineralization of these substances and the relatively low doses applied. The generally low extraction observed in this experiment restricts the use of phytoextraction as an effective remediation alternative under the current conditions, with regard to amendments used, applied dose (2 mmol/kg(-1) soil), application time (presow), plant species (Zea mays), and sediment (calcareous clayey soil) under study.

Structure and Characterization of Flavolipids, a Novel Class of Biosurfactants Produced by Flavobacterium sp. Strain MTN11

Abstract: Herein we report the structure and selected properties of a new class of biosurfactants that we have named the flavolipids. The flavolipids exhibit a unique polar moiety that features citric acid and two cadaverine molecules. Flavolipids were produced by a soil isolate, Flavobacterium sp. strain MTN11 (accession number AY162137), during growth in mineral salts medium, with 2% glucose as the sole carbon and energy source. MTN11 produced a mixture of at least 37 flavolipids ranging from 584 to 686 in molecular weight (MW). The structure of the major component (23%; MW = 668) was determined to be 4-[[5-(7-methyl-(E)-2-octenoylhydroxyamino)pentyl]amino]-2-[2-[[5-(7-methyl-(E)-2-octenoylhydroxyamino)pentyl]amino]-2-oxoethyl]-2-hydroxy-4-oxobutanoic acid. The partially purified flavolipid mixture isolated from strain MTN11 exhibited a critical micelle concentration of 300 mg/liter and reduced surface tension to 26.0 mN/m, indicating strong surfactant activity. The flavolipid mixture was a strong and stable emulsifier even at concentrations as low as 19 mg/liter. It was also an effective solubilizing agent, and in a biodegradation study, it enhanced hexadecane mineralization by two isolates, MTN11 (100-fold) and Pseudomonas aeruginosa ATCC 9027 (2.5-fold), over an 8-day period. The flavolipid-cadmium stability constant was measured to be 3.61, which is comparable to that for organic ligands such as oxalic acid and acetic acid. In summary, the flavolipids represent a new class of biosurfactants that have potential for use in a variety of biotechnological and industrial applications.

A TiO2/Al2O3 catalyst to improve the ozonation of oxalic acid in water

Abstract: Removal of oxalic acid from water has been accomplished through TiO 2 /Al 2 O 3 catalytic ozonation The combined use of ozone and the titanium catalyst leads to a conspicuous 80% of oxalic acid conversion in 3 h which compares favorably to the hardly 2% reached in the absence of the catalyst at pH 25 At the experimental conditions applied, the catalytic process develops under complete carbon mineralization and does not proceed through hydroxyl radical oxidation The process rate can be described by considering an Eley–Rideal mechanism Thus, it is proposed that adsorbed oxalic acid reacts directly with ozone in solution, the oxalic acid adsorption stage being the rate-limiting step This mechanism justifies the experimental kinetic orders found in the range 1 and 0–1 for oxalic acid and ozone, respectively The apparent activation energy of the catalytic ozonation was also found to be 14 kcal mol −1

Intrinsic kinetics of photocatalytic oxidation of formic and oxalic acid on immobilised TiO2 films

Abstract: Titanium dioxide (TiO2) photocatalysis is a possible alternative/complementary technology to conventional water treatment methods. The TiO2 catalyst may be used as slurry or it may be immobilised onto a supporting substrate. With immobilised TiO2 films mass transfer problems occur in most photocatalytic reactors, which results in a reduction of reactor efficiency and in the accuracy of measured catalyst efficiency and kinetics. In order to determine the real intrinsic kinetics of photocatalytic reactions on immobilised TiO2 films a stirred tank reactor (STR) was used. The reactor incorporated a propeller and a baffle, thus providing good mixing and efficient mass transfer to the TiO2 film. Degussa P25 was immobilised onto borosilicate glass by a dip coating method and the kinetics of the photocatalytic degradation of the model pollutants, formic acid and oxalic acid were investigated as a function of catalyst loading, initial pollutant concentration and propeller rotation speed. The rate of degradation. of either acid. was not mass transfer limited at propeller speeds greater than 1000 rpm. The rate of formic acid degradation was dependent upon catalyst loading up to a maximum loading above which a decrease in the degradation rate was observed. The apparent quantum yield for the photocatalytic degradation was 5% for oxalic acid and 10% for formic acid. This compares very well with usual reported apparent quantum efficiencies for photocatalysis which are similar to1%. The photocatalytic oxidation of both acids could be described using a Langmuir-Hinshelwood kinetic model. (C) 2003 Elsevier B.V. All rights reserved.

Synthesis and characterization of polyaniline doped with organic acids

Abstract: Spectroscopic [UV–visible and Fourier transform IR (FTIR)] and thermal properties of chemically synthesized polyanilines are found to be affected by varying the protonation media (acetic, citric, oxalic, and tartaric acid). The optical spectra show the presence of a greater fraction of fully oxidized insulating pernigraniline phase in polyaniline doped with acetic acid. In contrast, the selectivity in the formation of the conducting phase is higher in oxalic acid as a protonic acid media. The FTIR spectra of these polymers reveal a higher ratio of the relative intensities of the quinoid to benzenoid ring modes in acetic acid doped polyaniline. Scanning electron micrographs revealed a sponge-like structure derived from the aggregation of the small granules in acetic acid and oxalic acid doped polyaniline. A three-step decomposition pattern is observed in all the polymers, regardless of the protonic acid used for the doping. The second step loss related to the loss of dopant is found to be higher in the oxalic acid doped polymer. In accordance with these results the conductivity is also found to be higher in oxalic acid doped material. The temperature dependent conductivity measurements show the thermal activated behavior in all the polymers. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2043–2049, 2004

Simplified method for estimation of composition of alginates by FTIR

Abstract: A modified method of preparing highly purified polymannuronic acid and polyguluronic acid was developed wherein acid hydrolysis was carried out using oxalic acid and separation was made using the difference of solubility with pH value. The simplified method using FTIR measurement to estimate the M/G ratio of alginate was investigated using Ca or Mn salts of alginate. The developed method appears to offer enhanced accuracy compared to that of previous techniques. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 1372–1377, 2004

Biologically induced mineralization in the tree Milicia excelsa (Moraceae) : its causes and consequences to the environment

Abstract: Iroko trees ( Milicia excelsa ) in Ivory Coast and Cameroon are unusual because of their highly biomineralized tissues, which can virtually transform the trunk into stone Oxalic acid (C 2 O 4 H 2 ) and metal-oxalate play important roles in their ecosystems In this study, the various forms of oxalate and carbonate mineralization reactions are investigated by using scanning electron microscopy and X-ray diffraction Calcium oxalate monohydrate is associated with stem, bark and root tissues, whereas calcium oxalate dihydrate is found with wood rot fungi in soils, as well as in decaying wood Laboratory cultures show that many soil bacteria are able to oxidize calcium oxalate rapidly, resulting in an increase in solution pH In terms of M excelsa , these transformations lead to the precipitation of calcium carbonate, not only within the wood tissue, but also within the litter and soil We calculate that c 500 kg of inorganic carbon is accumulated inside an 80-year-old tree, and c 1000 kg is associated with its surrounding soil Crucially, the fixation of atmospheric CO 2 during tree photosynthesis, and its ultimate transformation into calcite, potentially represents a long-term carbon sink, because inorganic carbon has a longer residence time than organic carbon Considering that calcium oxalate biosynthesis is widespread in the plant and fungal kingdoms, the biomineralization displayed by M excelsa may be an extremely common phenomena

Self-organization of a porous alumina nanohole array using a sulfuric/oxalic acid mixture as electrolyte

Abstract: The possibility of fabricating a highly regular nanohole array using different acid mixtures for the anodic oxidation of aluminum was investigated. The regularity of a nanohole array formed using a 1:1 sulfuric/oxalic acid mixture was quantified. Excellent regularity was obtained at around an anode voltage of 32 to 36 V. Cell pitch of the nanohole array at 36 V was 73 nm, which falls between those obtained using sulfuric acid (65 nm at 28 V) and oxalic acid (95 nm at 40 V). The present results strongly suggest that the pitch of the regular nanohole array can be varied by changing the ratio of the different acids.

Synthesis of solid, spherical CeO2 particles prepared by the spray hydrolysis reaction method

Abstract: To avoid the formation of hollow particles during spray pyrolysis, a spray hydrolysis reaction method (SHRM) was studied. Unlike the conventional spray pyrolysis that uses metal salt as a precursor and dry air as a carrier gas, the SHRM introduces a mixture of metal salt and dimethyl oxalate (DMO) as precursors and a gas mixture of water vapor and air as the carrier gas. Spherical, solid CeO2 particles characterized by SEM, BET, and density analysis were produced by the SHRM using Ce(NO3)3 and DMO as the precursors. DMO, as an internal precipitant, hydrolyzed and produced oxalic acid, which precipitated with cerium ions to form volume precipitation in the whole droplet at enough temperature and relative humidity. The volume precipitation induced by the in situ formation of oxalic acid in the whole droplet prevented Ce(NO3)3 nucleation at the droplet surfaces, thus avoiding the formation of hollow particles which usually occur in the conventional spray pyrolysis process. XRD and IR analysis showed that cerium oxalate was an intermediate product in the SHRM process.

Dissolution kinetics of colemanite in oxalic acid solutions

Abstract: Colemanite is one of the most important underground riches of Turkey, having approximately 60% of the world boron deposits, and it has a large portion in the deposits. When colemanite having a 2CaO·3B 2 O 3 ·5H 2 O formula is mined naturally, it contains various clay minerals. In this study, the dissolution of colemanite in aqueous oxalic acid solutions was investigated in a batch reactor employing the parameters of stirring speed, particle size, temperature and acid concentration. It was found that the dissolution rate increases with increasing temperature and decreasing particle size. The conversion rate increased until 250 mol m −3 with increasing acid concentration and then decreased with increasing acid concentration. No important effect of stirring speed was observed. The dissolution kinetics of colemanite was examined according to heterogeneous and homogeneous reaction models, and it was found that the dissolution rate was controlled by product layer (or ash layer) diffusion process. The activation energy of the process was determined to be 9.50 kcal mol −1 . The experimental data were tested by graphical and statistical methods and it was found that the following model best fit the experimental data t = t *[1−3(1− X ) 2/3 +2(1− X )].

Oxidations by the system hydrogen peroxide-dinuclear manganese(IV) complex-carboxylic acid. Part 5. Epoxidation of olefins including natural terpenes

Abstract: Dinuclear manganese(IV) complex [LMn(O)3MnL](PF6)2 (1, L = 1,4,7-trimethyl-1,4,7-triazacyclononane) efficiently catalyzes epoxidation of sterically accessible olefins, including natural compounds by hydrogen peroxide in acetonitrile at room temperature if a small amount of a carboxylic acid is present in the solution. The kinetics of dec-1-ene epoxidation and accompanying dioxygen evolution (catalase activity) under the action of this system in the presence of acetic acid has been studied. The initial rates of both epoxidation and O 2 evolution are proportional to the catalyst initial concentration. First order has been found for catalyst 1 for both processes, whereas the rate dependences of the dec-1-ene epoxidation is first order and the O 2 evolution is second order for H2O2. The epoxidation rate increases and the O2 evolution rate decreases with growing of acetic acid concentration. Zero order has been found for dec-1-ene in its epoxidation. The reaction proceeds with an induction period for a few minutes during which changes in the electronic spectra of the reaction solution are observed. It has been proposed that the processes of the alkane oxidation and dioxygen evolution on the one hand and of the olefin epoxidation on the other hand are induced by different intermediate species. An assumption has been made that the epoxidation occurs with participation of oxo-hydroxy Mn(V) derivative [LMn V ( O)(O)2(HO)Mn IV L] 2+ , whereas di(hydroperoxy) complex [LMn III (OOH)(O)2(HOO)Mn IV L] + is responsible for the alkane oxidation with simultaneous dioxygen evolution. The following equations for the initial rates were proposed for [CH 3CO2H] = 0.25 mol dm −3 : d[epoxide]/dt = keff (epoxide)[1][H2O2] with keff (epoxide) = 2.8–3.7 mol −1 dm 3 s −1 ; d[CyOOH]/dt = keff (CyOOH)[1][H2O2] 2 [CyH] with keff (CyOOH) = 4.1–6.2 mol −3 dm 9 s −1 ; d[O2]/dt = keff (O2)[1][H2O2] 2 with keff (O2) = 2.8–7.0 mol −2 dm 6 s −1 . Many different carboxylic acids were checked as cocatalysts and it has been found that oxalic acid acts with the highest efficiency in the epoxidation whereas the accompanying catalase activity of the system is very low in this case. It has been also demonstrated that complex 1 is unique catalyst because similar compounds containing only one Mn(IV) center (2) or dinuclear complex with bridging phenylboronic acid (3) are very poor catalysts in the olefin epoxidation. No epoxidation has been found when hydrogen peroxide was replaced by tert-butyl hydroperoxide. The system based on 1 ,H 2O2 and acetic and/or oxalic acid was employed for the efficient epoxidation of terpenes limonene, citral, carvone and linalool, while other terpenes containing sterically hindered double bonds (citronellal, - and -isomers of pinene) were epoxidized only with <15% yield. Using limonene as example, it has been demonstrated that regioselectivity of the epoxidation (predominant formation of product with addition of the O atom either to internal ring or external double bond) can be controlled by replacing acetic acid by oxalic acid. © 2004 Elsevier B.V. All rights reserved.

Pyrolysis study of sol—gel derived TiO2 powders: Part III. TiO2-anatase prepared by reacting titanium(IV) isopropoxide with acetic acid

Abstract: Homogeneous TiO2 powders were obtained, via sol-gel method, hydrolysing titanium(IV) isopropoxide, previously reacted with oxalic acid in order to better control the gelling process. The characterization of the amorphous TiO2 powders was carried out by using different techniques such as FT-IR, XRD and N2 adsorption analysis. Coupled thermogravimetric (TG) gas chromatographic (GC) and mass spectrometric (MS) analyses were performed to quantify the organic content present in the titania gel and its release during pyrolysis. A detailed semiquantitative analysis of the evolved chemical species from TG-MS data allowed to describe the chemical composition of the TiO2 gel and the chemical rearrangements occurring in matrix during pyrolysis up to its crystallization to anatase form at 530°C.

Preparation of Sr2CeO4 Blue Phosphor Particles and Rare Earth (Eu, Ho, Tm, or Er)-Doped Sr2CeO4 Phosphor Particles, Using an Emulsion Liquid Membrane System

Abstract: Sr2CeO4 blue phosphor particles were prepared with an emulsion liquid membrane (ELM, water-in-oil-in-water (W/O/W) emulsion) system, which could be utilized as a microreactor for the preparation of size- and morphology-controlled fine particles. In the ELM system, Sr2+ and Ce3+ ions were extracted from the external water phase by extractant (cation carrier, bis(2-ethylhexyl)phosphoric acid) and were stripped into the internal water phase, containing oxalic acid solution, to form the submicrometer-sized composite Sr−Ce oxalate particles, which were much smaller than those obtained in a homogeneous aqueous solution. Calcination of the precursor oxalate particles obtained in the ELM system produced submicrometer-sized Sr2CeO4 particles, which showed a charge-transfer (CT) emission at 467 nm (λex = 254 nm). The photoluminescence properties of rare earth-doped Sr2CeO4 (Sr2CeO4:Ln3+; Ln = Eu, Ho, Tm, or Er) were also investigated, and the characteristic emissions corresponding to doped rare earth ions, effected...

Condensation reactions and formation of amides, esters, and nitriles under hydrothermal conditions.

Abstract: Hydrothermal pyrolysis experiments were performed to assess condensation (dehydration) reactions to amide, ester, and nitrile functionalities from lipid precursors. Beside product formation, organic compound alteration and stability were also evaluated. Mixtures of nonadecanoic acid, hexadecanedioic acid, or hexadecanamide with water, ammonium bicarbonate, and oxalic acid were heated at 300°C for 72 h. In addition, mixtures of ammonium bicarbonate and oxalic acid solutions were used to test the abiotic formation of organic nitrogen compounds at the same temperature. The resulting products were condensation compounds such as amides, nitriles, and minor quantities of N-methylalkyl amides, alkanols, and esters. Mixtures of alkyl amide in water or oxalic acid yielded mainly hydrolysis and dehydration products, and with ammonium bicarbonate and oxalic acid the yield of condensation products was enhanced. The synthesis experiments with oxalic acid and ammonium bicarbonate solutions yielded homologous series of ...

Composition and synthesis of raphide crystals and druse crystals in berries of Vitis vinifera L. cv. Cabernet Sauvignon: Ascorbic acid as precursor for both oxalic and tartaric acids as revealed by radiolabelling studies

Abstract: Biomineralisation in the fleshy pericarp of berries of Vitis vinifera L. gives rise to crystals of two distinct forms, viz. raphides and druses, which are found in exocarp and endocarp cells respectively. Druses have generally been considered as crystalline aggregates of calcium oxalate. However, the organic moiety of raphide crystals has been commonly accepted as tartrate, although we have found no analytical data to support that assumption. We now present TEM and X-ray powder diffraction analysis data showing that raphide crystals of V. vinifera berries are composed of calcium oxalate monohydrate. This work also established ascorbic acid as the biosynthetic precursor of both oxalic and tartaric acids. When ascorbic acid labelled with 14C at position 1 was introduced into berries via the rachis, 21% and 52% of the added radiolabel was recovered as oxalic and tartaric acids respectively. Purified crystals from the radiolabelled grape berries contained approximately 20% of the original radioactivity, further confirming the role of ascorbic acid in oxalic acid biosynthesis. To our knowledge, this is the first evidence to be published on the formation of oxalic and tartaric acids from ascorbic acid via two distinct pathways operating within the same physiological entity (organ).

A mechanistic study of the epoxidation of cinnamic acid by hydrogen peroxide catalysed by manganese l,4,7-trimethyl-l,4,7-triazacyclononane complexes

Abstract: l,4,7-Trimethyl-l,4,7-triazacyclononane (TMTACN), MnSO4 and H2O2, in basic aqueous acetonitrile, is an effective system for the epoxidation of cinnamic acid. The influence of a selection of organic additives, potential co-ligands for the manganese species, on the reactions has been studied by UV–vis spectroscopy and ESI-MS. The mechanism of the most efficient system, with added oxalic acid, has been investigated in more detail using cinnamic acid and seven of its 3- or 4-substituted derivatives. A Hammett correlation of rate data shows that the active oxidant is electrophilic (ρ value −0.63). Oxygen ( 18 O ) labelling experiments reveal that H2O2 and not H2O is the source of the oxygen in the epoxide. Possible mechanisms for the reactions are discussed.

Evidence for immobilized photo-Fenton degradation of organic compounds on structured silica surfaces involving Fe recycling

Abstract: The present study reports on the use of novel structured inorganic silica fabrics loaded with Fe ions by exchange-impregnation as a heterogeneous photocatalyst. These Fe–silica fabrics are denoted EGF/Fe(0.4%). Experimental evidence shows that Fe ions are released from the silica fabrics and react with H2O2 to form oxidative radicals in solution; the Fe ions are reduced to Fe(II) during oxalic acid and oxalate oxidation. The Fe3+ is extracted from the support to the aqueous medium where it is re-oxidized by being re-adsorbed onto the silica fabric. The contributions of the homogeneous and heterogeneous photocatalysis processes during the degradation of oxalic acid and oxalates were quantified as a function of the solution pH and the results presented agree with the modeling of the iron oxide surface in the presence of oxalates at different pH values. By attenuated total reflection infrared spectroscopy (ATRIR), the asymmetric stretching vibration doublet band at 1740 cm−1 and the satellite peaks corresponding to surface carboxylates were followed during the photocatalytic destruction of the oxalates. The results obtained indicate that the oxalate decomposition channel involves a fast light-activated decarboxylation of the Fe complex: [RCO2Fe]2+ → [R˙] + CO2 + Fe2+. The structural features of the EGF/Fe(0.4%) surfaces were investigated before and after the oxalate photocatalysis by high resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS) and gas adsorption studies (BET).