Metal Oxalates Research Articles

Isostructural crystal hydrates of rare-earth metal oxalates at high pressure: from strain anisotropy to dehydration

Abstract The crystal structures of a series of isostructural rare-earth metal oxalates, (REE)2(C2O4)3·10H2O (REE=Sm, Y) and a 1:1 YSm(C2O4)3·10H2O solid solution, have been studied in situ by single-crystal X-ray diffraction and optical microscopy. The structures were followed from ambient pressure to 6 GPa in a DAC with paraffin as the hydrostatic fluid. Bulk compressibilities, anisotropic lattice strain on hydrostatic compression and the corresponding changes in the atomic coordinates were followed. Discontinuities/sharp changes in the slopes of the pressure dependences of volume and selected cell parameters have been observed for yttrium-containing salts at ~3.5 GPa. This may be related to the re-distribution of water molecules within the crystal structure. Y2(C2O4)3·10H2O undergoes a partial dehydration at 1 GPa, forming monoclinic Y2(C2O4)3·6H2O as single-crystalline inclusions in the original phase.

Direct shaping of oxides by laser insolation of transition metal oxalates

Films of copper and cobalt-iron oxalates were prepared from suspensions of powders in ethane-1,2-diol deposited on glass or polycarbonate substrates. Two-dimensional structures of oxides, resolved on the scale of less than ten micrometers, were formed by laser insolation of these films, using a photolithography machine. The nature of the constitutive phases of the oxides formed tends to show that the laser heating makes it possible to reach locally, temperatures higher than 1000°C. The oxides formed are thus sintered. The residual oxalate can be removed by washing or dissolving, leaving the oxide structure on its substrate. In spite of a perfectible sintering, the formed structures could interest different technological applications (electronic or magnetic devices, gas sensors, photovoltaic systems…) requiring the shaping of simple or mixed oxides on a scale close to the micrometer. The process of selective laser decomposition of oxalates, could subsequently be suitable for additive manufacturing of 3D parts.

Hydrogenation of Carbon Dioxide over K‐Promoted FeCo Bimetallic Catalysts Prepared from Mixed Metal Oxalates

AbstractThe hydrogenation of carbon dioxide over K‐promoted FeCo bimetallic catalysts prepared by sequential oxalate decomposition and carburization of FeCo with CO was studied in a fixed‐bed reactor at 240 °C and 1.2 MPa. The initial CO2 conversion was found to be dependent on K loading, whereas both unpromoted and K‐promoted FeCo catalysts (except 90Fe10Co3.0K) exhibited similar levels of CO2 conversion after a few hours of time on stream. A decarburization study on freshly activated and used FeCo suggests that potassium increases the stability of iron carbides and graphitic carbon under a reducing atmosphere. Also, K addition tends to decrease the hydrogenation function of FeCo bimetallic catalysts and, thus, controls product selectivity. Under similar CO2 conversions, potassium enhanced acetic acid formation while suppressing ethanol production, which indicates that a common intermediate might be responsible for the changes observed with C2 oxygenates.

N,N-Diethyl-diaminopropane-copper(ii) oxalate self-reducible complex for the solution-based synthesis of copper nanocrystals.

Metal oxalates (C2O42-, ox) have been explored as promising precursors for the direct transformation of their oxalate moieties into metallic or metal oxide crystals via thermal decomposition without the formation of any byproducts due to releasing CO2 gas. The copper(ii) oxalate (Cu(ox)) crystal is a coordination polymer composed of an infinite coordination network with a thermal decomposition temperature around 300 °C; however, their insoluble nature in any solvents and relatively high decomposition temperature do not allow the solution-based syntheses of surface-modified metallic Cu nanocrystals (NCs) in the presence of various surfactants such as long-chain alkylamines and alkylcarboxylates which have been used for increasing the dispersibility of NCs in organic solvents. In this study, the insoluble nature of Cu(ox) is overcome by mixing Cu(ox) crystals and N,N-diethyl-1,3-diaminopropane (dedap) to form a discrete complex, [Cu(ox)(dedap)2], whose structure is determined by X-ray crystallographic analysis. The obtained complex is well soluble in polar solvents and miscible with surfactants. Furthermore, it is decomposed at a moderate temperature of <170 °C with the evolution of CO2 gas; as a result, Cu NCs dispersible in organic solvents have been synthesized in suitable surfactants, such as the mixture of oleic acid, dodecylamine, and octylamine utilized as a reaction solvent. In addition, their potential application of the surface-modified Cu NCs as a conductive-ink has been preliminarily tested. The Cu film sintered at 280 °C exhibits a resistivity of 40 μΩ cm.

Template-directed syntheses of two 3D metal oxalates: in situ N-methylation and crystal structures

Two isomorphic organically templated zinc/cobalt oxalates, (dmdabco)[Zn2(C2O4)3]·4H2O (1), and (dmdabco)[Co2(C2O4)3]·4H2O (2) (C2O42− = oxalate; dmdabco = N,N′-dimethyl-1,4-diazabicyclo[2,2,2]octane), have been prepared under solvothermal conditions and characterized by X-ray structural analyses. The dmdabco2+ templating agent was derived from simple in situ N-alkylation between methanol and 1,4-diazabicyclo[2,2,2]octane (dabco). Distinct from conventional Eschweiler-Clarke methylation containing excess formic acid and formaldehyde, such one-step methylation from methanol molecules is convenient. Both 1 and 2 exhibit a uninodal 3-connected 3-D interrupted open-framework, in which oxalate ligands have in-plane and out-of-plane connection modes.

Rare earth elements concentrations and speciation in rainwater from Guiyang, an acid rain impacted zone of Southwest China

Rare earth elements (REEs) and major ions were determined in rainwater samples collected from Guiyang in the acid rain impacted zone of Southwest China. The concentrations of total dissolved and acid-soluble REEs in rainwater are higher than those of most of the world's cities as well as the local surface water. The dissolved REE concentrations are negatively correlated to pH in rainwater. This is consistent with acidification of rainwater resulting in increasing REE concentrations. Speciation calculations using the PHREEQC-Model predict that the free REE metal ion (i.e., Ln3+), sulfate (LnSO4+), oxalate (LnOx+ and LnOx2−) and fluoride (LnF2+) complexes were relatively important forms of dissolved REE. Although the contribution to rainwater acidity of oxalic acid is much lower than that of sulfuric acid, the proportion of REE-oxalate complexes is not lower than that of REE-sulfate complexes in rain waters. The rainwater is enriched in the middle REEs (MREE) compared to both the light REEs (LREE) and heavy REEs (HREE). REE-phosphate complexes, phosphatic minerals and a Fe-Mn-oxyhydroxide coating are more likely controls on the development of MREE enrichment in the rainwater. Complexation of sulfate and REE played little role in the development of MREE enrichment, even though sulfate is the most important anion in acidic rainwater. In the shale-normalized REE pattern plot, La showed a clear positive anomaly. La might have two main anthropogenic sources in rainwater. One of the important sources could be automobile emission; another main source of excess La in rainwater could be the REE fertilizer that has been widely used in the agriculture of China for approximately 30years.

Reduced Graphene Oxide Sheets Attached Tin Oxalate Dihydrate As a High Capacity Anode for Lithium Ion Rechargeable Batteries

Lithium ion batteries have been widely applied as power sources for electronic devices to electric vehicle because of their high energy density, and long cycle life. Commercial graphite is the most commonly used as the anode material for lithium ion batteries. However graphite has its low theoretical capacity (372 mAh g-1). Therefore, to satisfy the growing power requirements, we need to explore alternative materials to replace graphite anode. For these reason, the silicon-based materials, transition metal oxides have been intensively investigated to replace the commercial graphite due to their high capacities, 700 ~ 1000 mAh g-1. Metal oxalate MC2O4 (M : Mn, Fe, Co, Ni, Sn, Cu, Zn) are also interesting because of high capacity. In this study, we synthesize tin oxalate by hydrothermal reaction, of SnCl2ㆍ6H2O (0.001 M), NaC2O4 (0.005 M), distilled water (9 ml), and ethylene glycol (EG, 16 ml) were mixed in a beaker and the mixed solution was stirred at room temperature for 6 h to form transparent solution. This solution was filled in a Teflon-lined autoclave (100ml capacity). This autoclave was sealed and heated at 100 oC - 200 oC for 12 h. After then, the autoclave was cooled to room temperature. The reacted solution were filtered and washed several times with de-ionized water and then dried at 80 oC for 24 h in a convection oven. Also, various contents of rGO were attached by layer by layer method. The obtained powder was analyzed by X-Ray diffraction (XRD, Rigaku, D-max 2000) using CuKα radiation. The XRD data were obtained with 0.03 step size and a 1 s count time. The particle morphologies of the products were analyzed by scanning electron microscopy (SEM, Hitachi, S-4700) and transmission electron microscopy (TEM, Hitachi, H-800). Electrochemical properties were measured in 2032 coin type cell. Electrodes were fabricated from a mixture of the prepared SnC2O4ㆍ2H2O powders (80 wt%), ketjen black (5 wt%), super-P (5 wt%) and polyacrylic acid (10 wt%) in distilled water. The obtained slurry was then applied onto Copper foil and dried in a vacuum oven at 80 oC for 1 h. The electrode was further dried over night at 80 oC under vacuum. The used electrode solution was 1M LiPF6 in a 3 : 7 volume mixture of ethylene carbonate (EC) and dimethyl carbonate (DMC) mixture. The XRD pattern of the products showed single phase SnC2O4ㆍ2H2O and rGO attached both were obtained without impurity. The fabricated cells were charged and discharged in the range of 0 - 3 V applying a constant current of 100 mAg-1 at 25 oC. The bare sample delivered capacity approximately 643 mAh g-1 at initial charge. Also, the delivered capacities increased to 1170, 1220, 1440 mAh g-1 with increasing the amount of rGO (10, 20, 30 wt%). The rate capability demonstrate that the 30 wt% rGO composite SnC2O4ㆍ2H2O / rGO electrode delivered 467 mAh g-1 at 10 C-rate. Figure 1

Minerals with metal-organic framework structures.

Metal-organic frameworks (MOFs) are an increasingly important family of advanced materials based on open, nanometer-scale metal-organic architectures, whose design and synthesis are based on the directed assembly of carefully designed subunits. We now demonstrate an unexpected link between mineralogy and MOF chemistry by discovering that the rare organic minerals stepanovite and zhemchuzhnikovite exhibit structures found in well-established magnetic and proton-conducting metal oxalate MOFs. Structures of stepanovite and zhemchuzhnikovite, exhibiting almost nanometer-wide and guest-filled apertures and channels, respectively, change the perspective of MOFs as exclusively artificial materials and represent, so far, unique examples of open framework architectures in organic minerals.

Supramolecular Templating Approach for the Solvent-Free Synthesis of Open-Framework Metal Oxalates.

A series of open-framework metal oxalates (metal = Zn, Co, Mn, Bi, In) were prepared under solvent-free conditions by a supramolecular templating approach. These compounds have cationic, anionic, and neutral frameworks with pore apertures ranging from small 8-membered rings (8 MRs) to extra-large 16 and 20 MRs. The zinc oxalate exhibits a proton conductivity of 2.6 × 10(-3) S cm(-1) at 60 °C under 98% relative humidity.

Reactive ion exchange processes of nonferrous metal leaching and dispersion material synthesis

Two combining reactive ion exchange processes with the application of cation exchange resins have been considered: the cation resin exchange leaching of metal ions from mineral and technogenic raw materials using cation exchange resin in the form of hydrogen and the anion resin exchange precipitation of metal ions in the insoluble compound form with the application of anion exchange resin in hydroxide and salt forms. The applications of methods are illustrated by examples for selective leaching of metals from its oxides, hydroxides, and silicates, as well as by the synthesis of hydroxides, carbonates, oxalates of nickel, cobalt, and other metals.

Lightweight Polyanion Frameworks for Li- and Mg-Ion Batteries

Mg-ion batteries are a promising “beyond Li-ion” technology as they offer high theoretical capacities, use cheap and abundant materials, and Mg metal can be used as the anode.1 However, the search for high voltage cathodes has been hindered by electrolyte incompatibility and sluggish kinetics which can impede intercalation and charging rates.2 MgMB2O5 (M = Mn, Fe, Co) are shown to be high voltage, high capacity cathode materials for both Li- and Mg-ion batteries. The open structure facilitates ion diffusion while the light weight polyanion framework increases capacity and voltage. The materials are produced from metal oxalate and boric acid starting materials via a solid state synthesis process. The Mg:M ratio can be altered to manipulate capacity and ordering of the cations.Mg can be fully removed from MgMnB2O5 giving a capacity of up to 300 mAhg-1 while maintaining the structure. Removal of Mg is confirmed by refinement of powder neutron diffraction data. In a full Mg-ion cell a reversible discharge capacity of ~100 mAhg-1 has been achieved. However, due to the incompatibility of the cell with available electrolytes this is accompanied by irreversible side reactions on charge. Some promising resolutions to the electrolyte problem are discussed. Mg can also be removed from the structure when M = Co or Fe, with the change in transition metal leading to a change in operating voltage. The results presented show that this class of material is a promising candidate for a high capacity, high voltage Mg-ion cathode material.In a Li-ion battery 1.5 Li can be intercalated into the manganese based material after Mg has been removed, giving a specific capacity of up to 250 mAhg-1 above 1.5 V. The capacity is retained over hundreds of cycles with little drop off observed even at rates of 5C. Ex-situ XRD shows a doubling of the unit cell when the material is cycled, suggesting charge ordering is occurring. Neutron diffraction refinements show a change in volume of ~2%, associated with insertion or removal of Li ions.

Potential signatures of heavy metal complexes in lichen reflectance spectra

ABSTRACTLichens are sensitive to atmospheric pollutants emitted from anthropogenic activities and are thus effective biomonitors. A variety of heavy metals, such as nickel (Ni), iron (Fe), lead (Pb), copper (Cu), and cadmium (Cd), can be emitted by metal smelters. The purpose of this study was twofold: (1) to measure the spectral reflectance properties (350–2500 nm) of expected heavy metal complexes in lichens (oxalates and sulphides); and (2) to determine whether these complexes contribute features to reflectance spectra of lichens from the vicinity of a heavy metal smelter. Some metal oxalate spectra are characterized by crystal field transition absorption bands in the 500–1300 nm region, which are specific to the particular metal cation they contain and its oxidation state. The 1900–2500 nm region exhibits multiple absorption bands attributable to the oxalate molecule. The metal sulphide reflectance spectra are characterized by generally low reflectance and few if any strong or diagnostic spectral features; those that are found can be related to a specific cation and its oxidation state. These spectra were used to determine whether reflectance spectra of a diverse suite of lichens collected downwind of a smelter showed spectral evidence indicative of heavy metal oxalates or sulphides. The lichen spectra, coupled with the oxalate and sulphide spectra and independently determined heavy metal concentration, failed to reveal spectral features that could be unambiguously related to heavy metal complexes. This was likely due to a number of causes: lichen reflectance spectra have absorption bands that overlap those of oxalates; oxalate and sulphide concentrations may have been too low to allow for their unambiguous identification, and lichen spectra are naturally diverse in the region below 1300 nm. There were no strong or significant linear trends between metal concentrations and distance from the smelter (coefficient of determination (R2) values <0.05), or between absorption band depths in the lichen spectra and distance from the smelter (R2 values <0.06). This was likely due to the inclusion of multiple lichen species in the analysis, which may interact with airborne pollutants in different ways, and microenvironmental effects.

Solvent-free synthesis of new open-framework metal oxalates with different 4-connected topologies

Three open-framework metal oxalates, formulated as (Hdbu)[In2(OH)(ox)3] (1), (Hthfa)[Eu2(Hthfa)(H2O)(ox)4]⋅3H2O (2), and (Hepc)[Bi(ox)2] (3), were prepared under solvent-free conditions, where dbu=1,8-diazabicyclo[5.4.0]undec-7-ene, ox=oxalate, thfa=tetrahydrofurfurylamine, and epc=4-ethylpiperazine-1-carbaldehyde. Topological analyses reveal that these compounds have different 4-connected networks with sra (for 1), lon (for 2), and dia (for 3) topologies. Compound 2 displays a bright red luminescence as a result of excitation at 397nm.

Extraction of extracellular polymeric substances from activated sludge using sodium oxalate

In this study, sodium oxalate was employed to extract extracellular polymeric substances (EPS) from activated sludge samples. The optimum dose of sodium oxalate was 1.34 g/g VSS (volatile suspended solids), and the extraction time was 60 min at pH 7. The total EPS contents obtained under the optimized conditions were approximately 191 mg/g VSS, and they predominantly consisted of proteins, polysaccharides and humic substances. The extraction efficiencies of the chosen method for the major biopolymers were 39, 43 and 410 % higher compared with the ethylenediaminetetraacetic acid (EDTA), cation exchange resin and control methods. Cell lysis measured in terms of deoxyribonucleic acid, and unidentified EPS were approximately 50 % lower in the sodium oxalate method than in the NaOH and EDTA methods. The EPS composition and the ratio of proteins/polysaccharides (1.38–2.21) were extremely dependent on the operating conditions maintained during the extraction. The inductively coupled plasma spectroscopic results demonstrated that the release of divalent metals, such as Ca2+ and Mg2+, from the sludge matrix was directly correlated with higher EPS extraction efficiencies in the sodium oxalate protocol. Moreover, the precipitation of Ca2+ and Mg2+ as metallic oxalates disrupted the floc structure and subsequently enhanced the EPS recovery. Fourier transform infrared studies revealed the presence of functional groups due to EPS molecules in all extracted samples.

Surface analysis of transition metal oxalates: Damage aspects

The behavior of transition metal oxalates in vacuum, under X-ray irradiation and low-energy Ar+ ion bombardment was studied. A comparative mass-spectrometric analysis was carried out of gas evolution from the surface of Mn, Co, Ni and Cu oxalate hydrates in vacuum, during exposure to X-rays and after termination of X-ray irradiation. The rates of H2O and CO2 liberation from the oxalates were found to be in an inverse correlation with the temperatures of dehydration and decomposition, respectively. X-ray photoelectron spectroscopy (XPS) was employed to study the X-ray induced damage in NiC2O4 and CuC2O4 by measuring the various XP spectral characteristics and surface composition of the oxalates as a function of time of exposure to X-rays. It was shown that Cu oxalate underwent a significantly faster degradation than Ni oxalate and demonstrated a high degree of X-ray induced reduction from the Cu2+ to the Cu1+ chemical state. 500eV Ar+ sputter cleaning of CoC2O4 for 10min was found to cause a strong transformation of the oxalate structure which manifested itself in an appreciable alteration of the XP core-level and valence band spectra. The analysis of changes in stoichiometry and comparison of XP spectra of bombarded oxalate with respective spectra of a reference carbonate CoCO3 implied that the bombardment-induced decomposition of CoC2O4 gave rise to the formation of CoO-like and disordered CoCO3-like phases.

Facile fabrication of cobalt oxalate nanostructures with superior specific capacitance and super-long cycling stability

Transition metal oxalate materials have shown huge competitive advantages for applications in supercapacitors. Herein, nanostructured cobalt oxalate supported on cobalt foils has been facilely fabricated by anodization, and could directly serve as additive/binder-free electrodes for supercapacitors. The as-prepared cobalt oxalate electrodes present superior specific capacitance of 1269 F g−1 at the current density of 6 A g−1 in the galvanostatic charge/discharge test. Moreover, the retained capacitance is as high as 87.2% as the current density increases from 6 A g−1 to 30 A g−1. More importantly, the specific capacitance of cobalt oxalate retains 91.9% even after super-long cycling of 100,000 cycles. In addition, an asymmetric supercapacitor assembled with cobalt oxalate (positive electrode) and activated carbon (negative electrode) demonstrates excellent capacitive performance with high energy density and power density.

Water as an agent for the morphology modification of metal oxalate materials on the nanoscale: from sheets to rods.

A number of approaches have been used to control the shape of metal oxalates, which often used as precursors for metal oxide nanomaterials. However, attempts to use water as a regulator have not been reported. Here in we report systematic studies on related topics: nanosheets, composed of 1-dimensional [M(C2O4)(EG)] (M = Zn or Co) polymeric structure, could be transformed into nanorods by using water as a shape-shifting agent because water can readily substitute EG ligand, leading alternation of inter-chain hydrogen bonding interactions. In addition, heat-treatment of these nanomaterials with diverse morphologies resulted in porous metal oxides with high degrees of shape retention.

The Sintering Effect on the Phase Formation and Transport Current Properties of SmBa2Cu3O7−δ Ceramic Prepared from Nano-Coprecipitated Precursors

High-temperature superconducting ceramic with the formula SmBa2Cu3O7−δ was prepared from metal oxalate precursors with an average grain size < 35 nm using the coprecipitation method. The metal oxalate powders were heated at 900 °C for 12 h, where they were pelletized and then sintered at different temperatures (920, 930, 940, and 950 °C) for 15 h. All sintered samples exhibited a metallic behavior with zero-resistance transition temperatures, T C(R = 0), of 92.8, 92.5, 89.5, and 84.0 K when the samples sintered from 920–950 °C, respectively. The critical current density (J C) decreased as the sintering temperature increased due to the formation of non-superconducting phases or insulator that enhanced the weak-link effect. X-ray diffraction (XRD) data showed the formation of impurity phases (Sm-211 and Sm210) at 930 and 940 °C, respectively. The crystalline size remains unchanged for all samples, and the best results were obtained for the sample sintered at 920 °C, where the single phase of an orthorhombic structure was detected and the highest T C was recorded. Scanning electron microscope (SEM) micrographs showed large grain sizes that were randomly distributed; the number of gaps between the grains increased as the sintering temperature increased due to the decomposition mechanism that enhanced the weak links between the grains and suppressed the transport current properties. The obtained results proved that high-quality Sm123 superconductor with minimum or no impurities can be produced when the sintering was applied at 920 °C for 12 h. This sintering temperature is sufficient to convert the nano-sized metal oxalates as a starting precursor to pure and high-quality polycrystalline SmBa2Cu3O7−δ . These results are important to simplify the preparation of SmBa2Cu3O7−δ at a lower temperature for HTSC device applications.

Hydrothermal decomposition of actinide(IV) oxalates: a new aqueous route towards reactive actinide oxide nanocrystals

AbstractThe hydrothermal decomposition of actinide(IV) oxalates (An= Th, U, Pu) at temperatures between 95 and 250 °C is shown to lead to the production of highly crystalline, reactive actinide oxide nanocrystals (NCs). This aqueous process proved to be quantitative, reproducible and fast (depending on temperature). The NCs obtained were characterised by X-ray diffraction and TEM showing their size to be smaller than 15 nm. Attempts to extend this general approach towards transition metal or lanthanide oxalates failed in the 95–250 °C temperature range. The hydrothermal decomposition of actinide oxalates is therefore a clean, flexible and powerful approach towards NCs of AnO2 with possible scale-up potential.

Platinum and palladium oxalates: positive-tone extreme ultraviolet resists

Here, we present platinum and palladium mononuclear complexes with EUV photosensitivity and lithographic performance. Many platinum and palladium complexes show little or no EUV sensitivity; however, we have found that metal carbonates and metal oxalates (L2M(CO3) and L2M(C2O4); M=Pt or Pd) are sensitive to EUV. The metal carbonates give negative-tone behavior. The most interesting result is that the metal oxalates give the first positive-tone EUV resists based on mononuclear organometallic compounds. In particular, (dppm)Pd(C2O4) (dppm=1,1-bis(diphenylphosphino)methane) (23) prints 30-nm dense lines with Esize of 50 mJ/cm2. Derivatives of (23) were synthesized to explore the relationship between the core metal and the resist sensitivity. The study showed that palladium-based resists are more sensitive than platinum-based resists. The photoreaction has been investigated for two of our most promising resists, (dppm)Pd(C2O4) (23) and (Ph2EtP)2PdC2O4 (27). Our experiments suggest the loss of CO2 and the formation of a zerovalent L4Pd complex upon exposure to light. We have identified dppm2Pd(δ(P)23.6) as the main photoproduct for (23) and (Ph2EtP)4Pd (δ(P)32.7) as the main photoproduct for (27).