Mixed Valence Copper Oxides Research Articles

(Invited) Next Generation Electrified Membrane Technology for Simultaneous Wastewater Treatment and Production of Nitrogen Fertilizer

Recovery and repurposing of wastewater nitrogen such as nitrate (NO3 −) and nitrite (NO2 −) receive increasing attention as the current approaches of biological nitrogen removal or conversion into nitrogen gas (N2) renders high energy footprints. This study reported the first electrified membrane upcycling of NO3 − into NH3 that further converted into ammonia sulfate (NH4SO4), a liquid fertilizer readily for use. Paired electrolysis was used to couple simultaneous cathodic and anodic electrochemical half-reactions to enable nitrate reduction and eliminate the external acid/base consumption. Under a partial current density of 63.8±4.4 mA·cm−2 on a cathodic membrane made of a mixed-valence copper oxide and a polytetrafluoroethylene (PTFE) hydrophobic substrate, a recovery rate and energy consumption of 3100±91 g-(NH4)2SO4·m−2·d−1 and 21.8±3.8 kWh·kg−1-(NH4)2SO4 were achieved with the synthetic feed solution (150 mM NO3 −) flowing into the cathode chamber and the produced NH3 migrating across the cathodic membrane into a trap and anode chambers filled with the flowing 0.5 M Na2SO4 solution. 99.9% NO3 − was removed in the feed after 5 h operation with a NH3 recovery rate of 99.5%. This electrified membrane process was demonstrated to achieve comparable performances of synergistic nitrate decontamination and nutrient recovery using real nitrate wastewater with durable catalytic activity and stability. Specifically, the required electricity cost for converting 10 to 100 mM NO3 − to (NH4)2SO4 was $675 to $408 ton−1, respectively. The obtained (NH4)2SO4 may be sold as fertilizer at a price of 533 $·ton−1 (according to USDA) and further offset the cost of the NO3 − removal.According to the International Fertilizer Association, in 2018 the U.S. ranked second in nitrogen production, representing 11.6% of global production. However, it still requires the importation of nitrogen fertilizer, to fully meet the national demand. The US Environmental Protection Agency reports that in 2013, ~38 kg of nitrogen per acre per year was used for fertilization, and in 2016, 94 million acres of corn were planted in the US, representing ~40% of US fertilizer demand. Roughly, this equates to ~8.9 billion kg of nitrogen per year needed to meet total US fertilization demand. The nitrogen available in drinking water sources is roughly 65 million kg per year, and the nitrogen available in wastewater sources is roughly 2.4 billion kg per year. Thus, by fully recovering the nitrogen from wastewater 34.3% of the US nitrogen fertilizer requirement could be met. This could also further mitigate the increase in nitrogen fertilizer prices due to blocked nitrogen fertilizer imports and even free the US from nitrogen fertilizer imports. According to U.S. Department of Agriculture, the average U.S. farm price of sulfate of ammonium fertilizers is $533 per ton. Even leaving aside the revenue generated by the treatment of nitrogen-containing sewage, the market size of nitrogen fertilizer produced through sewage is as high as $12.8 billion.

Encapsulation of mixed-valence copper oxide nanoparticles in aluminum carboxymethylcellulose composite microspheres: an efficient synergistic catalyst for boosting aldehyde–alkyne–amine coupling reactions

Encapsulation of mixed-valence copper oxide nanoparticles in aluminum carboxymethylcellulose composite microspheres: an efficient synergistic catalyst for boosting aldehyde–alkyne–amine coupling reactions

Mixed valence copper oxide composites derived from metal–organic frameworks for efficient visible light fuel denitrification

CuxO-300 has the best photocatalytic performance, and its denitrification rate reaches 81% after 4 hours of visible light (≥420 nm) irradiation.

Glycine–Nitrate Combustion Synthesis of Cu-Based Nanoparticles for NP9EO Degradation Applications

Copper-based nanoparticles were synthesized using the glycine–nitrate process (GNP) by using copper nitrate trihydrate [Cu(NO3)2·3H2O] as the main starting material, and glycine [C2H5NO2] as the complexing and incendiary agent. The as-prepared powders were characterized through X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy analysis. Using Cu(NO3)2·3H2O as the oxidizer (N) and glycine as fuel (G), we obtained CuO, mixed-valence copper oxides (CuO + Cu2O, G/N = 0.3–0.5), and metallic Cu (G/N = 0.7). The XRD and BET results indicated that increasing the glycine concentration (G/N = 0.7) and reducing the particle surface area increased the yield of metallic Cu. The effects of varying reaction parameters, such as catalyst activity, catalyst dosage, and H2O2 concentration on nonylphenol-9-polyethoxylate (NP9EO) degradation, were assessed. With a copper-based catalyst in a heterogeneous system, the NP9EO and total organic carbon removal efficiencies were 83.1% and 70.6%, respectively, under optimum operating conditions (pH, 6.0; catalyst dosage, 0.3 g/L; H2O2 concentration, 0.05 mM). The results suggest that the removal efficiency increased with an increase in H2O2 concentration but decreased when the H2O2 concentration exceeded 0.05 mM. Furthermore, the trend of photocatalytic activity was as follows: G/N = 0.5 > G/N = 0.7 > G/N = 0.3. The G/N = 0.5 catalysts showed the highest photocatalytic activity and resulted in 94.6% NP9EO degradation in 600 min.

Potential dependent growth of Cu(OH)2 nanostructures on Cu and their thermal conversion to mixed-valent copper oxides p-type photoelectrode

Herein, we report the anodic growth of nanostructured Cu(OH)2 thin films on the copper surface by potentiostatic and potentiodynamic methods. The phase formation, crystalline feature, morphology and the progressive growth of Cu(OH)2 thin films were controlled by the applied potential and concentrations of alkali utilized in anodization process. Electrochemical investigations suggest the rapid growth of Cu(OH)2 and passivation at higher anodization potentials. In contrast, the lower anodization potentials favours the progressive growth of Cu(OH)2 nanorod like features. The thermal treatment of Cu/Cu(OH)2 reveals the formation of crystalline mixed copper oxide film with predominantly Cu2O phase at 673 K and 773 K. Photoelectrochemical investigations of these copper oxide thin films exhibit the p-type behavior with repeatable photovoltage (55 mV) and stable photocurrent responses (20–60 μA cm−2). The hydrogen evolution studies show better activity with nanostructured Cu(OH)2 and copper oxides than with aggregated thin films and bare substrate.

A computational exploration of CO2 reduction via CO dimerization on mixed-valence copper oxide surface.

The catalytic role of Cu ions in CO2 reduction on oxide-derived Cu has been elusive. In the presence of oxygen vacancy, COCO dimerization is predicted to be thermodynamically favorable with an accessible barrier on Cu4O3(202). The material's mixed valency is responsible for stabilizing the charge-separated (OC)δ+(CO)δ- intermediate.

Thermally and Chemically Stable Mixed Valence Copper Oxide Cluster Ions Revealed by Post Heating

Copper oxide clusters, Cu(n)O(m)(+) (n = 5-12), were prepared in the gas phase by laser ablation of a copper metal rod in the presence of oxygen diluted in He as the carrier gas. The stoichiometry of the cluster ions was investigated using mass spectrometry. The number ratio of copper atoms and oxygen atoms in Cu(n)O(m)(+) was distributed from n:m = 1:1-3:2, which was not affected significantly by the concentration of oxygen in the carrier gas as long as it exceeded 2%. When the cluster ions were heated up to 573 K downstream of the cluster source (post heating), Cu(n)O(m)(+) (n:m ≈ 3:2) clusters were selectively and dominantly formed as a result of thermal dissociation. No further changes in the ratio were observed when the clusters were heated up to 623 K. From the stoichiometry, Cu(n)O(m)(+) is considered to comprise both Cu(I) and Cu(II). Hence, the mixed valence states are found to be thermally stable for the small clusters in the gas phase, but they are not stable in the bulk phase. In addition to the thermal stability, we observed reactivity of Cu(n)O(m)(+) with CO molecules. It was found that Cu12O8(+) hardly binds to CO and that Cu9O6(+) and Cu6O4(+) along with other clusters with n:m ≈ 3:2 bind to CO very weakly, whereas CO attaches strongly to oxygen-rich clusters with release of an oxygen molecule.

Synthesis of CuO, Cu and CuNi alloy particles by solution combustion using carbohydrazide and N-tertiarybutoxy-carbonylpiperazine fuels

Solution combustion synthesis has been used for the preparation of finely dispersed copper oxide, copper and copper–nickel bimetallic particles. The structure and morphology of the materials are studied by XRD and SEM techniques. The fuel content in the combustion mixture is found to be a crucial factor in controlling the formation of oxide and metal particles. Starting with copper nitrate trihydrate as oxidizer (O) and carbohydrazide as fuel (F), we obtained CuO (F/O=0.75–1), mixed valence copper oxides, CuO+Cu 2O, (F/O=1.0–1.5) and metallic Cu (F/O=2). At very low fuel content (F/O=0.5), a polymeric phase of copper hydroxide nitrate is isolated from the combustion residue. We also report the use of a new organic fuel N-tertiarybutoxy-carbonylpiperazine for the preparation of Cu, Ni and CuNi bimetallic particles.

Hole-doping routes for understanding the relationship between atomic arrangements and superconductivity properties in multi-layered copper oxides

Since the ‘snow’ thawed in the period of 1984–86, the ‘village’ of layered mixed-valent copper oxides has been packed with ‘children’ playing vigorously ‘games’ related to high-Tc superconductivity. In this contribution, we utilize materials chemistry ‘rules’ for the game, and present a systematic view for controlling the charge inhomogeneity over the crystals of layered copper oxides and tailoring their superconductivity properties. We start with a generalized scheme of ‘homologous series’ for categorizing the high-Tc superconductive and related materials. Applying the bond–valence–sum scheme to the crystals of homologous series converges to the concept of ‘hole-doping routes’. Functioning of the different routes for doping the CuO2 planes with holes is demonstrated for representative high-Tc superconductive materials. Subsequently, the hole distribution over the crystal is shown to be controlled by the choice of the hole-doping routes. It follows further that the control of the hole distribution is essential for tailoring the high-Tc superconductivity properties. A ‘road map’ for refining the concepts of hole-doping routes and hole distribution is presented so that they may be utilized for not only tailoring the high-Tc superconductors but also understanding the nature of high-Tc superconductivity.

Spectroscopic analysis of plasma during rf magnetron sputtering of a YBCO target: Evidence for oxidation on the surface of the cathode

In this article, we present spectroscopic analysis of plasma during reactive rf magnetron sputtering of a YBa2Cu3O7 target. Particular attention is paid to the influence of oxygen pressure on the emission lines of cationic species. From the optical response of barium and copper resonance lines, we have deduced that the oxidation of barium into barium oxide BaO (or BaO2) is complete for an oxygen content up to 10% whereas the oxidation of copper into copper oxide CuO needs an oxygen content of up to 30% which corresponds to the value of the gas composition generally used by different groups. We have shown that these oxidation reactions are represented by a mass law in the vapor phase. These results are confirmed by x-ray photon spectroscopy analysis and give the experimental process for mixed valence copper oxide sputtering deposition.

Influence of angular distribution on the deposition rate of species sputtered from a multicomponent target in different configurations: Applications to mixed valence copper oxides

This work deals with calculation of the thickness distribution of films deposited by sputtering in different configurations: ‘‘on axis’’ and ‘‘off axis’’ diodes, facing target and hollow cathode, and for different polar distributions of ejected species. We demonstrate that a difference in the polar distribution may induce deviations from stoichiometry especially in the diode configuration. In the facing target and hollow cathode configurations, the deviations are strongly reduced. The theoretical calculations fit well with the experimental results that were obtained with mixed valence copper oxide sputtered films.

Atomic oxygen radio-frequency source and its application to the treatment of mixed valence copper oxide thin films

An atomic oxygen source is presented, consisting of a radio-frequency wave- sustained low-pressure discharge in a small diameter tube. The flowing afterglow is used to oxidize with good efficiency YBaCuO thin films which initially present oxygen deficiency.

Mixed-valence copper oxides: A large family of high Tc superconductors related to the perovskites

Mixed-valence copper oxides: A large family of high Tc superconductors related to the perovskites

Crystal Chemistry and Properties of Mixed Valence Copper Oxides

The role played by the mixed valence of oxides of transition elements in the metal-like properties is well known since the discovery of the sodium tungsten bronzes Na{sub x}WO{sub 3} by Hagg and Magneli. The synthesis of mixed valence copper oxides with metal-like properties has opened the route to the discovery of superconductivity at high temperature in the La{sub 2}CuO{sub 4}-type family. The chemistry of copper oxides offers great possibilities for nonstoichiometry on the oxygen sublattice because of the Jahn-Teller effect of cooper than can induce several coordinations in the same framework: octahedral (CuO{sub 6}), pyramidal (CuO{sub 5}), and square planar (CuO{sub 4}). Thus, one can easily imagine that starting from a perfect octahedral framework it could be possible to create tunnels or cage structures, or lamellar oxides by removing oxygen atoms. Similarly, it can be expected that such oxygen- deficient copper oxides will be able to intercalate oxygen and return to the stoichiometric phase. The perovskite structure, with its great flexibility, is a potential candidate for such a realization. However, the Cu(II)-Cu(III) mixed valence in oxides is not so easily obtained. Before 1980 trivalent copper could only be stabilized in some oxides under oxygen pressures of several kbars. Moremore » recently basic cations like the alkaline earths were introduced as guest elements in the copper oxygen host lattice in order to stabilize the upper oxidation state Cu(III) under normal oxygen pressure. Several series of oxides were produced that can be classified mainly as having either a tunnel structure or a layered structure.« less

Oxygen nonstoichiometry and superconductivity in mixed valence copper oxides

The structures of the new superconductors involving bismuth and thallium are described. For all these oxides and the La 2CuO 4-type compounds, the structures result in intergrowth of oxygen deficient perovskite layers and rock salt-type layers leading to the general formulation (AO) n (A'Ca m−1 Cu m O 2 m+1 ) where n and m are the multiplicity of the rock salt and perovskite layers respectively. The oxygen nonstoichiometry in the “123” superconductors is explained by the existence of a partial disproportiona of Cu(II) into Cu(I) and Cu(III). Some extended defects, observed by high resolution microscopy in the bismuth and thallium superconductors, are presented. The role of the mixed valence of copper in superconductivity is discussed. A model is presented, involving a dynamic redox reaction, in the case of the thallium compounds.

Crystal chemistry of perovskite superconductors

The relationships between structure and superconductivity of the mixed-valence copper oxides related to the perovskite are presented. The following points are discussed: oxygen non-stoichiometry, symmetry and extended defects. A particular attention is paid for the influence of Cu(III) (or Cu I I −O −) content upon T c : a model involving disporportionation of Cu(II) into Cu(III) and Cu(I) is presented for YBa 2Cu 3O 7− δ.

Concentration induced phase transition in the T C magnetic superconductors

We investigate theoretically the influence of copper ions valence fluctuations on magnetic interactions in superconducting mixed-valent copper-oxides. The magnetic properties of these materials are explained in terms of mutual competition of double-exchange and superexchange interactions. By mean field arguments we show that the high T c superconductors should exhibit ferro- + antiferromagnetism coexistent state.

What chemistry is there in high-temperature superconductivity? II. Why these mixed-valent copper oxides, and where else?

A local-pair mechanism for high-temperature superconductivity in the quaternary copper oxide families based on (La/Sr)2CuO4 and YBa2Cu3O7 is developed. The available experimental data (as of 29 June 1987) are assessed particularly from a materials point of view, to make clear what the combination of features is in these systems that is so unusual as effectively to restrict high-temperature superconductivity to the mixed-valent copper oxides-and then only to certain of these. All the principal enabling factors ensue from the position of copper in the periodic table, and the potential core-like stability of the d10 configuration. The latter permits monovalence to be added to di- and trivalence for this element, as for silver and gold, though it is in copper that all three valencies are most readily stabilised. The proposed mechanism does not involve disproportionation, but fluctuations on pre-existing 3+d8 sites to 1+d10, using electrons drawn from the d9 sites over which the superconductivity is dominantly mediated. The late position of copper in the transition-metal series secures heavy p/d hybridisation which leads to the absence of pair-breaking local moments being established both at the di- and trivalent sites. Support for the present negative-U model is extracted from the author's earlier work on the metal-insulator transition. A more magnetically oriented model like the resonant valence bond model which has recently associated with observations in d1 TiOCl, etc., does not really seem suited to the geometry and electronic conditions in the present copper oxides. However it is suggested that TiB2, La3S4 and the Chevrel phases might be open to treatment by such a model. Comment is also made about how the superconductivity of PdHx and Ba(Pb/Bi)O3 might be seen in the light of the present model, and attention is directed once again to what might be happening in pressure-quenched CuCl and CdS.

Oxygen non-stoichiometry and superconductivity in mixed valence copper oxides

Oxygen non-stoichiometry and superconductivity in mixed valence copper oxides

High-temperature superconductivity in mixed-valent copper oxides: Relation between Tc and the nominal ratio

Abstract The superconducting T c in the various copper oxides shows a broad maximum at a certain value of the nominal Cu 3+ Cu 2+ ratio. The significance of this important feature is discussed and a model based on strong correlations is suggested to explain the results.