Synergistic effects of CuO and Au nanodomains on Cu2O cubes for improving photocatalytic activity and stability

Cu₂O is a promising photocatalyst, but it suffers from poor photocatalytic activity and stability, especially for Cu₂O cubes. Herein, we report the deposition of CuO and Au nanodomains on Cu₂O cubes to form dual surface heterostructures (HCs) to improve photocatalytic activity and stability. The apparent quantum efficiency of Au/CuO/Cu₂O HCs was ca. 123 times that of pristine Cu₂O. In addition, the Au/CuO/Cu₂O HCs maintained nearly 80% of its original activity after eight cycles in contrast to five cycles for the Au/Cu₂O material. Therefore, CuO and Au domains greatly improved the photocatalytic activity and stability of the Cu₂O cubes due to the synergistic effect of the HCs.     

Thermal Studies in Cuo−Cu2O−SnO2 System At Two Oxygen Pressures, As Observed by DTA/TG Experiments

This study reports experimental investigations by DTA/TG analysis of (1−x)SnO₂−xCuO compositions, up to 1773 K and at two oxygen partial pressures (i.e. air and argon). In air, DTA/TG results showed thermal effects due exclusively to CuO presence in the initial mixture. No binary compounds were formed. The reduction process of CuO to Cu₂O over 1273 K as well as the formation over 1373 K of the liquid phase, have been evidenced. In argon atmosphere, CuO to Cu₂O reduction reaction is shifted toward 1205 K, while the liquid phase appears in the studied mixtures over 1473 K. The formation of an eutectic composition between SnO₂−Cu₂O, melting at 1491 K, coordinates:0.932Cu₂O+0.068SnO₂, has been experimentally established in argon. This revised version was published online in August 2006 with corrections to the Cover Date.     

Production of hydrogen by oxidative steam reforming of methanol over Cu/SiO2 catalysts

Selective production of hydrogen by oxidative steam reforming of methanol (OSRM) was studied over Cu/SiO₂ catalyst using fixed bed flow reactor. Textural and structural properties of the catalyst were analyzed by various instrumental methods. TPR analysis illustrates that the reduction temperature peak was observed between 510?K and 532?K at various copper loadings and calcination temperatures and the peaks shifted to higher temperature with increasing copper loading and calcination temperature. The XRD and XPS analysis demonstrates that the copper existed in different oxidation states at different conditions: Cu₂O, Cu⁰, CuO and Cu(OH)₂ in uncalcined sample; CuO in calcined sample: Cu₂O and metallic Cu after reduction at 600?K and Cu⁰ and CuO after catalytic test. TEM analysis reveals that at various copper loadings, the copper particle size is in the range between 3.0?nm and 3.8?nm. The Cu particle size after catalytic test increased from 3.6 to 4.8?nm, which is due to the formation of oxides of copper as evidenced from XRD and XPS analysis. The catalytic performance at various Cu loadings shows that with increasing Cu loading from 4.7 to 17.3?wt%, the activity increases and thereafter it decreases. Effect of calcination shows that the sample calcined at 673?K exhibited high activity. The O₂/CH₃OH and H₂O/CH₃OH molar ratios play important role in reaction rate and product distribution. The optimum molar ratios of O₂/CH₃OH and H₂O/CH₃OH are 0.25 and 0.1, respectively. When the reaction temperature varied from 473 to 548?K, the methanol conversion and H₂ production rate are in the range of 21.9–97.5% and 1.2–300.9?mmol?kg^?1?s^?1, respectively. The CO selectivity is negligible at these temperatures. Under the optimum conditions (17.3?wt%, Cu/SiO₂; calcination temperature 673?K; 0.25 O₂/CH₃OH molar ratio, 0.5 H₂O/CH₃OH molar ratio and reaction temperature 548?K), the maximum hydrogen yield obtained was 2.45?mol of hydrogen per mole of methanol. The time on stream stability test showed that the Cu/SiO₂ catalyst is quite stable for 48?h.     

Conversion of CuO Nanoplates into Porous Hybrid Cu2O/Polypyrrole Nanoflakes through a Pyrrole‐Induced Reductive Transformation Reaction

Porous hybrid Cu₂O/polypyrrole nanoflakes have been synthesized from solid CuO nanoplate templates through the pyrrole‐induced reductive transformation reaction at elevated temperature. The conversion mechanism involves the reductive transformation of CuO to Cu₂O and the in situ oxidative polymerization of pyrrole to polypyrrole. In addition, the morphology of the as‐converted nanohybrids depends on the shape of the CuO precursors. The strategy enables us to transform single‐crystalline CuO nanosheets into hollow hybrid Cu₂O/polypyrrole nanoframes. The ability to transform CuO and an organic monomer into porous hybrid materials of conducting polymer and Cu₂O with macrosized morphological retention opens up interesting possibilities to create novel nanostructures. Electrochemical examinations show that these porous hybrid Cu₂O/polypyrrole nanostructures exhibit efficient catalytic activity towards oxygen reduction reaction (ORR), excellent methanol tolerance ability, and catalytic stability in alkaline solution, thus making them promising nonprecious‐metal‐based catalysts for ORR in alkaline fuel cells and metal–air batteries.     

Cu2O/CuO Electrocatalyst for Electrochemical Reduction of Carbon Dioxide to Methanol

Herein, we report the controlled and direct fabrication of Cu₂O/CuO thin film on the conductive nickel foam using electrodeposition route for the electrochemical reduction of carbon dioxide (CO₂) to methanol. The electrocatalytic reduction was performed in CO₂ saturated aqueous solution consisting of KHCO₃, pyridine and HCl at room temperature. CO₂ reduction was carried out at a constant potential of −1.3 V for 120 min to study the electrochemical performance of the prepared electrocatalysts. Cu₂O/CuO shows better electrocatalytic activity with highest current density of 46 mA/cm². The prepared catalyst can be an efficient and selective electrode for the production of methanol.     

Influence of surface morphology on the oxidation of metal electrodes studied by in-situ grazing incidence x-ray diffractometry

The successful application of in-situ grazing incidence x-ray diffractometry (GIXD) for the investigation of oxidation processes at copper electrodes in pH 12 electrolytes is demonstrated. A penetration/escape depth of about 1 μm could be detected for a smooth polycrystalline copper foil and an x-ray incidence angle of 1.7°. Oxide layers generated at overpotentials less than about 0.5 V in respect to the equilibrium formation potentials of Cu₂O or CuO, respectively, showed a dependence of the crystalline oxide formation on the defect density of the copper substrate. Highly disordered ground or polished specimens exhibited an order of magnitude higher GIXD reflexes from crystalline Cu₂O than electrodeposited copper. Beyond overpotentials of 0.5 V, this epitaxial information for the Cu₂O crystal growth became irrelevant. Further, GIXD turned out to be an appropriate tool to monitor atmospheric corrosion processes under thin humidity films with oxygen access. When oxygen diffusion through the polymer window membrane is allowed, oxygen reduction led to the concurrent formation of a crystalline CuO phase coexisting with amorphous Cu(OH)₂ and Cu₂O, though the potential was kept in the region of Cu₂O. Received: 30 July 1997 / Revised: 28 May 1998 / Accepted: 13 July 1998     

Über Kupfer(I)-sulfat Cu2SO4. Darstellung und thermische Eigenschaften

Preparation and Thermal Properties of Copper(I) Sulfate Cu₂SO₄ Copper(I) sulfate Cu₂SO₄ can be prepared in high purity by reaction of Cu₂O with dimethyl sulfate (CH₃)₂SO₄ at 160°C in an argon atmosphere. Using an extremely fine grained Cu₂O, as obtained by reduction of cupric acetate with hydrazine, and a reaction time of 10 minutes a Cu₂SO₄ is obtained that contains less than 1% Cu₂O. Longer reaction times lead to partial decomposition of the Cu₂SO₄ to Cu(met.) and CuSO₄. In a closed system Cu₂SO₄ melts at about 400°C, however, the melt rapidly decomposes to Cu and CuSO₄, solidifying simultaneously. When heated in a thermoanalyzer in flowing argon or in a vacuum, Cu and CuSO₄ react under liberation of SO₂. Increasing the temperature leads to CuO in three steps, which converts to Cu₂O when heated to 1000°C. The question of formation of Cu₂SO₄, occasionally mentioned in the literature, being responsible for the liquid phases observed in the system Cu? S? O at temperatures below 500°C, is discussed.     

Unveiling the Activity Origin of a Copper‐based Electrocatalyst for Selective Nitrate Reduction to Ammonia

Unveiling the active phase of catalytic materials under reaction conditions is important for the construction of efficient electrocatalysts for selective nitrate reduction to ammonia. The origin of the prominent activity enhancement for CuO (Faradaic efficiency: 95.8 %, Selectivity: 81.2 %) toward selective nitrate electroreduction to ammonia was probed. ¹⁵N isotope labeling experiments showed that ammonia originated from nitrate reduction. ¹H NMR spectroscopy and colorimetric methods were performed to quantify ammonia. In situ Raman and ex situ experiments revealed that CuO was electrochemically converted into Cu/Cu₂O, which serves as an active phase. The combined results of online differential electrochemical mass spectrometry (DEMS) and DFT calculations demonstrated that the electron transfer from Cu₂O to Cu at the interface could facilitate the formation of *NOH intermediate and suppress the hydrogen evolution reaction, leading to high selectivity and Faradaic efficiency.     

Unveiling the Activity Origin of a Copper-based Electrocatalyst for Selective Nitrate Reduction to Ammonia

Unveiling the active phase of catalytic materials under reaction conditions is important for the construction of efficient electrocatalysts for selective nitrate reduction to ammonia. The origin of the prominent activity enhancement for CuO (Faradaic efficiency: 95.8 %, Selectivity: 81.2 %) toward selective nitrate electroreduction to ammonia was probed. ¹⁵N isotope labeling experiments showed that ammonia originated from nitrate reduction. ¹H NMR spectroscopy and colorimetric methods were performed to quantify ammonia. In situ Raman and ex situ experiments revealed that CuO was electrochemically converted into Cu/Cu₂O, which serves as an active phase. The combined results of online differential electrochemical mass spectrometry (DEMS) and DFT calculations demonstrated that the electron transfer from Cu₂O to Cu at the interface could facilitate the formation of *NOH intermediate and suppress the hydrogen evolution reaction, leading to high selectivity and Faradaic efficiency.     

Beiträge zum thermischen Verhalten von Sulfaten. VI. Zum chemischen Transport von CuSO4, Cu2OSO4 und CuO

Contributions on the Thermal Behaviour of Sulfates. VI. On the Chemical Transport of CuSO₄, Cu₂OSO₄, and CuO A powder of anhydrous CuSO₄ can be prepared by heating CuSO₄ · 5 H₂O in air or in an argon atmosphere. In the same way it is possible to get a powder of Cu₂OSO₄. But up to now, it was difficult to get crystals of CuSO₄ and there was no method known to synthesize crystals of Cu₂OSO₄. Investigations concerning chemical transport reactions of anhydrous heavy metal sulfates showed, that it is possible to get well formed crystals of CuSO₄ and Cu₂OSO₄ by deposition from a vapour phase. As transport agents for CuSO₄, Cl₂ and HgCl₂ are especially suitable. Less appropriate are HCl, NH₄Cl, and I₂. The chemical vapor deposition of Cu₂OSO₄ proceeds well with HgCl₂. In course of these investigations we recognized, that for CuO in addition to the well approved transport agents also Cl₂, HgCl₂ or I₂ (NH₄Cl less suitable) can successfully be used.     

Contribution of CuxO distribution,shape and ratio on TiO2 nanotubes to improve methanol production from CO2 photoelectroreduction

Many studies are focused on the development of materials for converting carbon dioxide into multicarbon oxygenates such as methanol and ethanol, because of their higher energy density and wider applicability. In this work, TiO₂ nanotubes (NT/TiO₂) were modified with Cu_xO nanoparticles in order to investigate the contribution of different ratio of Cu₂O/CuO and its distribution over NT/TiO₂ for CO₂ photoelectro-conversion to methanol. The photoelectrodes were built by anodization process to obtain NT/TiO₂ layer, and the decoration with Cu_xO hybrid system was carried out by electrodeposition process, using Na₂SO₄ or acid lactic as electrolyte, followed by annealing at different temperatures. X-ray photoelectron spectroscopy analysis revealed the predominance of Cu⁺¹ and Cu⁺² at 150 °C and 300 °C, respectively. X-ray diffraction and scanning electron microscopy indicated that under lactic acid solution, the oxide nanoparticles exhibited small size, cubic shape, and uniform distribution on the nanotube wall. While under Na₂SO₄ electrolyte, large nanoparticles with two different morphologies, octahedral and cubic shapes, were deposited on the top of the nanotubes. All modified electrodes converted CO₂ in methanol in different quantities, identified by gas chromatograph. However, the NT/TiO₂ modified with CuO/Cu₂O (80:20) nanoparticles using lactic acid as electrolyte showed better performance in the CO₂ reduction to methanol (0.11 mmol L⁻¹) in relation to the other electrodes. In all cases, a blend among the structures and nanoparticle morphologies were achieved and essential to create new site of reactions what improved the use of light irradiation, minimization of charge recombination rate and promoted high selectivity of products.

     

Cu/活性炭催化剂：水合肼还原制备及催化甲醇氧化羰基化

以活性炭为载体,水合肼为还原剂制备了负载型Cu/活性炭催化剂,考察了水合肼/硝酸铜物质的量的比对催化甲醇气相氧化羰基化性能的影响,并采用XRD、XPS、H2-TPR和SEM等手段对催化剂进行了表征。结果表明,不加入还原剂水合肼时,催化剂中仅有CuO;随着水合肼/硝酸铜物质的量的比的增加,二价铜逐步被还原为Cu2O和/或单质Cu0,未被还原的Cu(OH)2在催化剂干燥过程中分解形成分散态CuO存在于催化剂表面。当水合肼/硝酸铜物质的量的比为0.75时,催化剂的催化性能最好,碳酸二甲酯的时空收率为120.62 mg.(g.h)-1,选择性为74.51%,甲醇转化率达到3.88%。在93 h反应时间内,催化剂都保持了较高的反应活性和选择性。此时铜物种以Cu2O和分散态CuO为主,Cu2O是主要的活性物种。     

Photodegradation of Chlorinated Organic Wastes with n-TiO2 Promoted by P-CuO

A variety of chlorinated organic wastes were photodecomposed with p-CuO-modified TiO₂ particles (denoted CuO/TiO₂). Based on the photoactivity measured in oxygenated solutions containing sodium 2,2′-dichloropropionate, the photoactivity of TiO₂ is significantly enhanced with p-CuO loading; in the case with 0.4 wt% of CuO, the activity is increased by a facor of 4. Photochemical-TiO₂-slurry cell techniques and voltammetric characterizations suggest this CuO-promoted enhancement is likely to result from the acceleration of oxygen reduction at TiO₂ via Cu_IIO/Cu_I0. Long-term tests showed that these CuO/TiO₂ particles are photochemically robust; within 100-hours' continuous photolysis, insignificant loss in photoactivity was detected. However, increasing loading of p-CuO may jeopardize the photoactivity, due to the deterioration in the TiO₂ absorbability of UV irradiation.     

Neues zum chemischen Transport von CuO und Cu2O

New Results on the Chemical Transport of CuO and Cu₂O The preparation of CuO crystals by chemical transport reactions with HCl is already well known, a comparison with other transport agents based on the principal of thermodynamic equilibrium and also the rate of transport was missing up to now. We report about experiments with the transport agents HgCl₂, Cl₂, I₂, Nh₄Cl, or CuCl; the quantitative evaluation was made by means of the cooperative transport model on the basis of the free energy function. By this way it is possible to find favourable experimental conditions for the suitable transport agents at the outset. It turned out that HgCl₂ is an appropriate transport agent which can easily be weighed. Also I₂ is useful, whereas the effect fo transport with Cl₂ (1 atm/298 K), CuCl, or NH₄Cl is very small. We investigated the chemical transport of Cu₂o and the conditions for the change of its direction of transport.     

A study of copper oxide catalysts used in the methylchorosilane reaction and determination of the fate of oxygen

The relative effectiveness of CuO and Cu₂O were compared as catalysts for the methylchlorosilane (MCS) reaction. MCS reactions catalyzed by CuO had higher rates (0.15 g/g Si-h) than MCS reactions catalyzed by Cu₂O (0.08) AND higher selectivities (4–5 points in % Di higherfor CuO). A synthetic method was found for making ¹⁷O-labeledCu₂O based on reaction of CuCl with excess NaCl and >2equivalents of Na¹⁷OH. The Na¹⁷OH was made from¹⁷O-enriched water and Na. The % enrichment of theCu₂O was determined by reduction of the Cu₂O with H₂ to form Cu and water and then subsequent reaction of the water product with Me₂SiCl₂ to make cyclo-octamethyltetrasiloxane (D₄). The ¹⁷O enrichment of the D₄ wasthen determined by mass spectroscopy. Thus Cu₂O was made with27% ¹⁷O ±5%. The labeled Cu₂Owas used as the catalyst in the MCS lab reactor. A 14% enrichmentin ¹⁷O in D₄ and dichlorotetramethyldisiloxane(M^ClM^Cl) was found vs. the controlexperiment with natural abundance oxygen Cu₂O. Thus all of the oxygen from the copper oxide catalyst ends up as siloxane; 50% of the oxygen in the product siloxane comes from other sources. Copper oxide catalyst was used in the presence of the phosphorus promoters Cu₃P and PEt₃. In both phosphorus promoter experiments, the resultant MCS lab beds were subjected toacetonitrile extraction and then NMR analysis of the extracts. Theseextracts showed that phosphorus-containing species were present and thatwhen Cu₃P was the promoter, phosphorus products containing¹⁷O were present. Thus for Cu₃P, some of thephosphorus reacts with the ¹⁷O from the Cu₂O catalyst.     

Ambient Pressure X-ray Photoelectron Spectroscopy Study of Oxidation Phase Transitions on Cu(111) and Cu(110)

The surface structure effect on the oxidation of Cu has been investigated by performing ambient-pressure X-ray photoelectron spectroscopy (APXPS) on Cu(111) and Cu(110) surfaces under oxygen pressures ranging from 10⁻⁸ to 1 mbar and temperatures from 300 to 750 K. The APXPS results show a subsequential phase transition from chemisorbed O/Cu overlayer to Cu₂O and then to CuO on both surfaces. For a given temperature, the oxygen pressure needed to induce initial formation of Cu₂O on Cu(110) is about two orders of magnitude greater than that on Cu(111), which is in contrast with the facile formation of O/Cu overlayer on clean Cu(110). The depth profile measurements during the initial stage of Cu₂O formation indicate the distinct growth modes of Cu₂O on the two surface orientations. We attribute these prominent effects of surface structure to the disparities in the kinetic processes, such as the dissociation and surface/bulk diffusion over O/Cu overlayers. Our findings provide new insights into the kinetics-controlled process of Cu oxidation by oxygen.     

A second harmonic generation study of the oxidation of copper electrodes

The oxidation of copper in basic media has been studied by in situ second harmonic generation (SHG), where the SHG signal was recorded alongside the cyclic voltammogram. The SHG signal changes markedly as the copper surface is oxidised to first Cu₂O and then CuO in a duplex structure. The development of Cu₂O gives rise to a resonant SHG signal because of the band-gap of the material then the upper CuO layer produces an electric-field induced second harmonic (EFISH) response. A correlation of charge with the SHG signal is informative with regard to the mechanism of reduction of CuO and SHG is shown to be a useful method for the examination of oxidation of electrode surfaces.     

Decomposition of nitrogen and dinitrogen oxides on copper and copper(I) oxide in elemental analysis by reaction gas chromatography

The decomposition of NO and N₂O on Cu and Cu₂O packings was studied in view of the simultaneous determination of N and S in organic compounds by the Pregl-Dumas method in a system of reaction gas chromatography, and the mass balance of the reactions taking place was carried out. The amounts of NO and N₂O that are decomposed on the reduction packing at temperatures within 883 and 1263 °K are quoted. The reduction activity of both packings toward NO decreases with increasing temperature, while both the reduction and sorption activity of Cu₂O is markedly lower than that of the Cu one. No significant sorption of NO was observed at temperatures within 883 and 923 °K and no sorption of gaseous N₂ and N₂O occurred on either packing.     

固相浸渍法和湿浸渍法制备CuO/CeO2催化剂及其CO氧化性能的对比研究

采用固相浸渍法和常规湿浸渍法制备了一系列CuO/CeO₂催化剂,并结合X射线衍射（XRD）、氢气-程序升温还原（H₂-TPR）、激光拉曼光谱（LRS）、原位漫反射红外光谱（in situ DRIFTS）、X射线光电子能谱（XPS）等手段考察了制备方法对催化剂结构性质及其在CO氧化反应中性能的影响. XPS和H₂-TPR结果表明,固相浸渍法更有利于得到高分散的铜物种,并促进CuO物种的还原. LRS结果表明,相比于湿浸渍法,固相浸渍法能产生更多氧空位,而这些氧空位可以活化参与反应的O₂. CO氧化活性测试结果表明,当铜负载量相同时,固相浸渍法制备的催化剂相比于湿浸渍法表现出更好的催化性能. 结合多种表征结果发现,催化剂CO氧化性能与其表面氧空位和Cu⁺-CO浓度紧密相关,提出了CuO/CeO₂催化剂在CO氧化反应中可能的协同作用机制.     

Quantitative determination of phases present in oxidised chalcocite

A sample of chalcocite (Cu₂S) of particle size 45–75 m was heated in air at 10°C min^–1 in a simultaneous TG-DTA apparatus. The phase compositions of the products at various temperatures were quantitatively determined by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, and wet chemical analyses. Copper(II) sulfate, of amount 1.7% by mass, was observed at 435°C and increased rapidly in concentration to 56% at 570°C. From 570–670°C, there was a rapid decrease in CuSO₄ content to 9.8% as the phase converted to CuSO₄·CuO, with the CuSO₄ not being detected at 775°C. From 435–570°C, Cu₂O formed, but at a rather slower rate, reaching 47% at 570°C. The Cu₂O level then decreased to 38% over the range 570–670°C. CuSO₄·CuO was first detected at 570°C by FTIR, although it was not detected by XRD at this temperature. The content of this species reached 41% at 670°C, decreased to 24% at 775°C, and was not detected at 840°C. CuO first appeared at 670°C and rose steadily in concentration until at 840°C it was the only compound present.Dedicated to Prof. Menachem Steinberg on the occasion of his 65th birthday