H2C2O4 Solution Research Articles

One-step hydrothermal synthesis and characterization of V–Cr–O nanospheres and their excellent performance in the ammoxidation of 3,4- and 2,6-DCT

Sphere-like V–Cr–O catalyst was successfully synthesized using V2O5, CrO3 and H2C2O4 solution as the starting materials by a facile one pot hydrothermal approach for the first time. The as-obtained samples were characterized by X-ray powder diffraction, X-ray photoelectron spectroscopy, energy dispersive X-ray spectrometer, hydrogen temperature programmed reduction, scanning electron microscopy and Brunauer–Emmett–Teller. The results indicated that V–Cr–O spheres with the diameter about 4μm, consisted of lots of nanoparticles, were formed. The as-obtained V–Cr–O catalyst had large specific surface area: 117m2g−1. Furthermore, V–Cr–O complex was explored as the unsupported catalyst for the synthesis of 3,4- and 2,6-dichlorobenzonitrile by the ammoxidation of 3,4- and 2,6-dichlorotoluene. It was found that it had excellent performance in the ammoxidation reactions, specially, the catalytic temperature was decreased to about 320°C, which was much lower than the previous reports (380–420°C).

The investigation of dissolution behavior of gangue materials during the dissolution of scheelite concentrate in oxalic acid solution

Scheelite mineral which includes CaWO4 as a main compound is one of the most important raw materials used for the industrial production of W. Scheelite concentrate used in this study included CaMoO4 and the oxides of Fe, Ca, Si, P, Al, Mn, S, Zn, Mg, Ba, K, Ti and Sr as gangue materials. CaWO4 reacts with oxalic acid (H2C2O4) to form water-soluble hydrogen aqua oxalato tungstate (H2[WO3(C2O4)H2O]) and insoluble calcium oxalate monohydrate (CaC2O4H2O). Additionally, the dissolution behavior of gangue materials during the leaching of the scheelite concentrate in H2C2O4 solution must be known for the designing of the purification process applied in the industrial production of pure W. The aim of this study was to investigate the effects of temperature and H2C2O4 concentration on the dissolution of gangue materials in the scheelite concentrate. It was found that while the oxides of Si, P, Al, S, Zn, Ba, K, Ti and Sr were not dissolved in H2C2O4 solution, the oxides of Ca, Mo, Fe and Mn were dissolved forming complex oxalate ions. MgC2O4 which was formed from MgO in the scheelite concentrate was also dissolved due to its high solubility.

Effects of a pre-existed anodic alumina on successive anodization behavior of aluminum and structure of its oxide film

The effects of pre-existed anodic alumina on successive anodization behavior of aluminum and the structure characteristic of the successive AAO (anodic aluminum oxide) film were studied by sequential anodization of aluminum substrate in H2SO4 solution and H2C2O4 solution respectively. The pre-existed SAAO (anodic aluminum oxide formed in sulfuric acid) film not only affects the film growth rate in oxalic acid, but also widens anodization potential range. The new prepared film undergoes a continuous change in the morphology from SAAO-like, to transient state, then to OAAO (anodic aluminum oxide formed in oxalic acid)-like, accompanying a process from disorder to order. In the series of changing processes, approximately two thirds of channels of SAAO film successively stop growing.

Fabrication of AAO films with controllable nanopore size by changing electrolytes and electrolytic parameters

In this paper, we fabricate two kinds of anodic aluminum oxide (AAO) films with controllable nanopore size by changing electrolytes and electrolytic parameters. The first AAO film with a four-layer structure was fabricated by sequential anodization of aluminum in aqueous solution of H2SO4, H2C2O4, malonic acid, and tartaric acid at different anodic oxidation voltages. The average pore diameter of the as-prepared AAO film is 25 nm in the first layer, 54 nm in the second layer, 68 nm in the third layer, and 88 nm in the fourth layer, respectively. The pore densities of each layer decrease downwards to Al substrate, which are 300 × 108, 100 × 108, 21 × 108, and 6.9 × 108 cm−2, respectively. Furthermore, another AAO film with periodically changed pore diameter was fabricated by alternating anodization of aluminum in aqueous solution of H3PO4 and tartaric acid under galvanostatic mode. The anodization processes present approximately identical best ordering voltage (195 V) in H3PO4 and tartaric acid under galvanostatic mode. The pore diameter with periodic change can be enlarged through a pore-widening treatment. Both AAO films with special nanopore structures can be used not only as templates for preparing nano-array materials whose pore diameter presents periodic change or gradual increase, but also as nanofilters to separate materials in some special media.

The Use of Oxalic Acid as a Chelating Agent in the Dissolution Reaction of Calcium Molybdate

In this study, the dissolution behavior of calcium molybdate (CaMoO4) was investigated in oxalic acid (H2C2O4) solution. The effects of stirring speed, temperature, H2C2O4 concentration, and particle size on the dissolution reaction of CaMoO4 were determined. The dissolved quantities of molybdenum and calcium were analyzed quantitatively by ICP-OES. Fractional conversion of CaMoO4 vs time and concentration of calcium vs time diagrams were plotted. It was observed that at constant temperatures and lower H2C2O4 concentrations, the dissolution increased by increasing H2C2O4 concentration, but at higher H2C2O4 concentrations, the effect of H2C2O4 concentrations was negligible. The dissolution reaction of CaMoO4 in H2C2O4 solution was performed in two steps as series–parallel type reaction. In the first step, CaMoO4 reacted with H2C2O4 to form the water-soluble calcium aqua oxalato molybdate (Ca[MoO3(C2O4)(H2O)]) intermediate chelate product. In the second step, the intermediate chelate, Ca[MoO3(C2O4)(H2O)], reacted with the reactant, H2C2O4, to yield water-soluble hydrogen oxalato dimolybdate chelate (H2[(MoO3)2(C2O4)]) and insoluble CaC2O4H2O as final products. It was found that 500 rpm was enough to eliminate the resistance of liquid film layer that surrounds the solid particles. It was concluded that the optimum temperature was 313 K (40 °C) and the optimum concentration of H2C2O4 was 1 kmol m−3 to obtain high conversion during the dissolution of CaMoO4.

A novel nanostructure fabricated by an improved two-step anodizing technology

A novel two-tier nanostructure with narrow mouth and wide abdomen in porous anodic alumina (PAA) has been successfully fabricated by an improved two-step anodization in oxalic acid (H2C2O4) and phosphoric acid (H3PO4) solutions. The two-tier nanostructure is clarified by oxide flow model and oxygen bubble mold. The small pores result from oxygen evolution at low critical voltage of ~97V in 2wt.% H2C2O4 solution, the big pores result from oxygen evolution at high critical voltage of ~162V in 2wt.% H3PO4 solution. Electronic current across the barrier layer formed in H2C2O4 is greater than that in H3PO4. This is the primary reason why the porosity of PAA formed in H2C2O4 is greater than that in H3PO4.

Comparative Balancing of Non-Redox and Redox Electrolytic Systems and Its Consequences

In this paper, it is proved that linear combination 2·f(O) － f(H) of elemental balances: f(O) for O and f(H) for H is linearly independent on charge and elemental/core balances for all redox systems of any degree of complexity; it is the primary form of the Generalized Electron Balance (GEB), , considered as the Approach II to GEB. The Approach II is equivalent to the Approach I based on the principle of common pool of electrons. Both Approaches are illustrated on an example of titration of acidified (H2SO4) solution of H2C2O4 with KMnO4. It is also stated, on an example of titration of the same solution with NaOH, that 2·f(O) － f(H) is a linear combination of charge and elemental/core balances, i.e. it is not an independent balance when related to the non-redox system. These properties of 2·f(O) － f(H) can be extended on redox and non-redox systems, of any degree of complexity, i.e. the linear independency/dependency of 2·f(O) － f(H) on other balances related to a system in question is a criterion distinguishing redox and non-redox systems. The GEB completes the set of (charge and concentration) balances and a set of expressions for independent equilibrium constants needed for modeling the related redox system.

The use of Langmuir–Hinshelwood mechanism to explain the kinetics of calcium molybdate leaching in oxalic acid solution

The effects of H2C2O4 concentration, temperature, stirring speed and particle size on the dissolution rate of synthetically prepared CaMoO4 were investigated. Dissolution of CaMoO4 in H2C2O4 solution took place as a series–parallel type reaction. In the first reaction step, which proceeded according to the “Langmuir–Hinshelwood mechanism”, calcium aqua oxalato molybdate (Ca[MoO3(C2O4)(H2O)]) was formed as a complex chelate intermediate product. In the second reaction step, together with insoluble CaC2O4H2O, soluble H2MoO4 was formed during the slow hydrolysis of Ca[MoO3(C2O4)(H2O)], and H2MoO4 reacted rapidly with H2C2O4 to form the water soluble hydrogen oxalato dimolybdate chelate (H2[(MoO3)2(C2O4)]). In the first step, the reaction rate was found to be first order with respect to H2C2O4 concentration at low concentrations while zero order at high concentrations. Activation energies were calculated for first and zero order reactions as 41.4 and 49.9 kJmol−1, respectively. A kinetic equation was derived that explains the relationship between fractional conversion of CaMoO4 and time. In the second step, the reaction rate was found to be first order with respect to H2C2O4 concentration and activation energy was calculated as 43.6 kJmol−1. Kinetic equations were derived that explain the relationship between the concentration of Ca[MoO3(C2O4)(H2O)] and time and the concentration of H2[(MoO3)2(C2O4)] and time. The diagrams plotted according to the model equations were in good agreement with the diagrams obtained experimentally where the protective behavior of CaC2O4H2O was not effective.

Preparation and Characterization of Anodic Alumina Membrane with Nanopore Arrays

Anodic alumina membranes (AAM) with nanopore arrays were prepared by one-step anodization of highly pure aluminum foil. Morphology, structure and composition of AAM were characterized by scanning electron microscopy (SEM), energy dispersion spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). Results showed that AAM owned honeycomb structure which was characterized by close-packed arrays of columnar hexagonal cells, each containing a central pore normal to the substrate. The diameter of pores and the size of cells changed under different anodic conditions, such as temperature, concentration of H2C2O4 solution, voltage and time of anodization. The walls of AAM were composed of two strains of nanoparticles of alumina. Furthermore, the chemical composition of AAM was found to be amorphous alumina. The prepared AAM with nanopore arrays is a kind of ideal template for preparation of many one-dimensional nanomaterials.

ChemInform Abstract: Porous ZnCo2O4 Nanowires Synthesis via Sacrificial Templates: High‐Performance Anode Materials of Li‐Ion Batteries.

AbstractZnCo2(C2O4)3 nanowires are prepared by a microemulsion‐based method by stirring a mixture of cetyltrimethylammonium bromide dissolved in cyclohexane and n‐pentanol, and an aqueous solution of H2C2O4, Zn(NO3)2, and Co(NO3)2 for 2 h at room temperature.

Surface Modification of an Alumina‐Based Bioceramic for Cement Application

AbstractBiograde zirconia toughened alumina (ZTA) has found wide application in load bearing endoprosthetic implants due to high strength, fracture toughness, and wear resistance. In order to enhance bonding to acrylic bone cement (BC) for implants, fixation modification of ZTA with a thin layer of porous anodic alumina (PAA) was investigated. An Al‐layer of approximately 500 nm was sputtered on the ZTA substrate which subsequently was electrochemically oxidized by anodic polarization in H2C2O4 or H3PO4 solution. PAA layers with a total porosity ranging from 11 to 30%, mean pore spacing of 90–200 nm and pore diameters of 30–110 nm were prepared. Compared to unmodified ZTA/BC interface (≈ 30 MPa), the PAA modified specimens (ZTA/PAA/BC) achieved a significantly higher interface bonding strength (≈ 60 MPa) measured by four point bending on composite beam specimens. While crack propagation in the unmodified ZTA/BC specimen was found to proceed along the interface, fracture analysis on the ZTA/PAA/BC specimens showed a mixed mode fracture with part of the fracture propagation localized along the PAA/BC interface and part through BC. Thus, pore structure controlled mechanical interlocking is expected to offer a high potential for applying PAA surface modification to improve biomaterial to BC bonding.

A novel sol–gel method based on FePO4·2H2O to synthesize submicrometer structured LiFePO4/C cathode material

Carbon coated LiFePO4/C cathode material is synthesized with a novel sol–gel method, using cheap FePO4·2H2O as both iron and phosphorus sources and oxalic acid (H2C2O4·2H2O) as both complexant and reductant. In H2C2O4 solution, FePO4·2H2O is very simple to form transparent sols without controlling the pH value. Pure submicrometer structured LiFePO4 crystal is obtained with a particle size ranging from 100 to 500nm, which is also uniformly coated with a carbon layer, about 2.6nm in thickness. The as-synthesized LiFePO4/C sample exhibits high initial discharge capacity 160.5mAhg−1 at 0.1C rate, with a capacity retention of 98.7% after 50th cycle. The material also shows good high-rate discharge performances, about 106mAhg−1 at 10C rate. The improved electrochemical properties of as-synthesized LiFePO4/C are ascribed to its submicrometer scale particles and low electrochemical impedance. The sol–gel method may be of great interest in the practical application of LiFePO4/C cathode material.

Surface modification of carbon microspheres by KMnO4

Carbon microspheres (CMSs) were synthesized by chemical vapor deposition in an Ar atmosphere using deoiled asphalt as carbon source. KMnO4 aqueous solutions with different concentrations were used to oxidize the CMSs to form MnO2-coated CMSs (MnO2/CMS composites) and H2C2O4 solution was used to wash the MnO2/CMS composites to remove MnO2 to obtain oxidized CMSs. The morphology and structure of the CMSs before and after MnO2 deposition,as well as the oxidized CMSs,were characterized by field-emission scanning electron microscopy and X-ray diffraction. The dispersion of the oxidized CMSs in water and ethanol was also investigated. A uniform MnO2 nano-coating was formed on surface of the CMSs when a 0.1 mol/L KMnO4 aqueous solution was used. When an excess amount of H2C2O4 solution was used to wash away the MnO2 nanocoating,the resulting CMSs have oxygen-containing groups,such as hydroxyl,carbonyl and carboxylic,and can be well dispersed in water and partly dispersed in ethanol.

Fabrication of ZnO nanowires at room temperature by cathodically induced sol–gel method

In this study, vertically oriented ZnO nanowires have been fabricated using an Anodized Aluminum Oxide (AAO) template by a cathodically induced sol–gel electrodeposition method at room temperature. For fabrication of the AAO template anodization of Al was carried out in 0.3 M H2C2O4 solution under a constant voltage of 40 V. Electrodeposition of ZnO nanowires in the AAO template was carried out in aqueous Zn(NO3)2 solution. AAO template and ZnO nanowires were characterized by Scanning Electron Microscopy (SEM) and X-ray Diffraction (XRD). It was observed that the ZnO nanowires were approximately 70 nm in diameter and 10 μm in length with high aspect ratio. ZnO nanowires were fabricated in a relatively large area of about 5 cm2.

Immobilization of Cs and Sr to HZr2(PO4)3 using an autoclave

The proton-type crystalline zirconium phosphate, HZr2(PO4)3, was prepared by a thermal decomposition of NH4Zr2(PO4)3 at about 450°C, where NH4Zr2(PO4)3 was obtained in advance by a hydrothermal synthesis using a mixed solution of ZrOCl2, H3PO4 and H2C2O4. Cs or Sr ion was immobilized to HZr2(PO4)3 by mixing HZr2(PO4)3 with an aqueous solution of CsNO3 or Sr(NO3)2 under the molar ratio CsNO3/HZr2(PO4)3=1.0 or Sr(NO3)2/HZr2(PO4)3=0.5. The mixtures were treated thermally in an autoclave at different temperatures from 200 to 275°C and Arrhenius equation was applied to the Cs and Sr immobilization process to HZr2(PO4)3. The activation energy for the immobilization process of Cs or Sr was estimated as 179kJmol−1 and 186kJmol−1, respectively.

One-step anodization fabrication and morphology characterization of porous AAO with ideal nanopore arrays

A fabrication method for one-step anodization of an anodic aluminum oxide (AAO) template with nanopore arrays using pretreated high purity aluminum foil is reported in this article. Morphology of the AAO was characterized by scanning electron microscopy (SEM) and atomic force microscopy (AFM). Results showed that porous AAO with ideal nanopore arrays can be fabricated by one-step anodization fabrication technology on high purity aluminum foil which had been anodized at 45 V direct current (DC), in 0°C, 0.5 M H2C2O4 solution for 48 hours. The average pore diameter and the interpore distance were 80 nm and 120 nm, respectively. Nanopores in porous AAO had very narrow size distribution and were arranged into hexagonal array. The formation mechanism of nanopore arrays in porous AAO is discussed. Porous AAO with ideal nanopore arrays provide an ideal template for preparation of many one-dimensional nanomaterials. One-step anodization of AAO is a simpler procedure and more applicable in industrial application than the previous two-step anodization technology.

Aluminium anodising in oxalate and sulphate solutions. Comparison of chronopotentiometric and overall kinetic response of growth mechanism of porous anodic films

Aluminium anodising was performed in saturated and unsaturated H2C2O4 solutions and in H2SO4 and saturated H2SO4 + Al2(SO4)3 solutions at similar temperatures, concentrations and current density to reveal the effect of anions and condensed electrolyte nanoparticle micelles formed on pore base and wall surfaces on the mechanism of growth of porous anodic alumina films. Chronopotentiometry and overall kinetics showed that the kinetics and mechanism of growth and nanostructure of films are similar in oxalate and sulphate solutions. But differences also appear, like higher field strength across the barrier layer and much lower pore wall dissolution rate in oxalate solutions. These are attributed to dissimilar kind of anions, smaller amount of incorporated ones and depth of penetration in barrier layer and pore walls during the film growth in oxalate solutions and to their participation in a step of oxide dissolution mechanism that becomes the rate controlling in this case. In saturated solutions the condensed H2C2O4 and Al2(SO4)3 micelles affect the kinetics and mechanism of film growth, more H2C2O4, allowing a better design of structure. Results promote the knowledge on growth mechanism and kinetics of anodic films enabling methods to optimise the structure for their many scientific or technological applications.

Enhanced performance of natural graphite in Li-ion battery by oxalatoborate coating

Abstract We report an effect of surface modification on the performance of natural graphite in Li-ion battery. A graphite electrode was treated with a mixed solution of H3BO3 and H2C2O4 (2:3 molar ratio) in methanol, followed by condensation at 100–110 °C under vacuum. The above treatments result in formation of oxalatoborate coating on the graphite surface. It is shown that the resulting coating can effectively increase reversibility of the initial forming cycle of Li/graphite half-cell. More interestingly, such a coating significantly suppresses self-delithiation of the lithiated graphite, which hence increases the storage performance of Li-ion battery, especially at elevated temperatures. With progressive cycling, the coated graphite shows excellent capacity retention while the control one starts fast capacity fading from around 70th cycle.

Immobilization of cesium by crystalline zirconium phosphate

HZr2(PO4)3 was prepared by the thermal decomposition of NH4Zr2(PO4)3 which was synthesized in advance by a hydrothermal reaction from a mixed solution of ZrOCl2, H3PO4 and H2C2O4. Mixtures of HZr2(PO4)3 with various amounts of CsNO3 were treated at 700–1200°C, in order to investigate the immobilization of Cs ion. When a mixture of CsNO3/HZr2(PO4)3 in a molar ratio of 0.36 was treated at 700°C, the main product was suggested to be CsZr2(PO4)3 from XRD measurements. The leaching rate of Cs ion from this product was less than 10−10 g · cm−2 · day−1 in 0.1 mol · 1−1 HCl solution at 100°C, indicating that HZr2(PO4)3 reacts with CsNO3 to give a stable Cs-immobilized product.

Preparation of Various NASICON-Type Crystalline Zirconium Phosphates.

The proton-type crystalline zirconium phosphate, HZr2(PO4)3, was prepared by a thermal decomposition of NH4Zr2(PO4)3 at about 680°C, where NH4Zr2(PO4)3 was obtained in advance by a hydrothermal synthesis using a mixed solution of ZrOCl2, H3PO4 and H2C2O4. This zirconium phosphate was, then, mixed with other metal nitrate, M(NO3)n (M=Li, Na, K, Rb, Sr, Bi, Y, Mg, Ca, Sc, Mn, Fe, Co, Ni, Cu, Zn, Ag, Cd, Cs, Ba, La, Ce, Tl or Pb; n=1, 2 or 3), at room temperature. The TG-DTA curves of these mixtures showed an endothermic weight loss around melting or decomposition temperature of each metal nitrate as a component. From these results, calcination temperature, which is in the range of 500-800°C and 100-200°C higher than the endothermic peak temperature, was determined for each mixture, in order to eliminate the unreacted components. All products thus calcined gave the XRD patterns attributable to M{Zr2(PO4)3}n (n=1 for M(I), n=2 for M(II) and n=3 for M(III)) with a NASICON-type structure.