氧化亚铜微/纳米结构的形貌可控制备及光催化和防污性能

利用简便易行的液相法,采用葡萄糖为还原剂,通过调整加料方式、反应温度、NaOH用量等条件,实现具有{110}截面八面体、八面体和短足形等形貌的Cu2O微/纳米结构的可控制备,运用透射电子显微镜、扫描电子显微镜、紫外可见分光光度计等对产物进行组成、结构、形貌和光响应的表征,对Cu2O的形貌结构和生长机理进行研究。对比和优化了具有不同形貌的Cu2O微/纳米结构对甲基橙染料的光催化性能。将不同形貌的微/纳米Cu2O作为防污剂复配的自抛光防污涂料,涂层磨蚀率、接触角与实海挂板实验证明该涂料具有良好的防污性能。     

氧化亚铜微/纳米结构的形貌可控制备及光催化和防污性能

利用简便易行的液相法,采用葡萄糖为还原剂,通过调整加料方式、反应温度、NaOH用量等条件,实现具有{110}截面八面体、八面体和短足形等形貌的Cu₂O微/纳米结构的可控制备,运用透射电子显微镜、扫描电子显微镜、紫外可见分光光度计等对产物进行组成、结构、形貌和光响应的表征,对Cu₂O的形貌结构和生长机理进行研究。对比和优化了具有不同形貌的Cu₂O微/纳米结构对甲基橙染料的光催化性能。将不同形貌的微/纳米Cu₂O作为防污剂复配的自抛光防污涂料,涂层磨蚀率、接触角与实海挂板实验证明该涂料具有良好的防污性能。     

Catalysts for low-temperature methanol synthesis. I. A study of the reduction process

A study of the reduction of CuO in a ternary oxide system (Cu:Zn:Al, atomic ratio 62:14:24) demonstrated that at lower temperatures it occurred in two stages, whereas at higher temperatures it was no longer possible to display the formation of Cu₂O. The rate of reduction of CuO was strongly reduced on decreasing the partial pressure of hydrogen, while the presence of CO₂ stabilized the Cu₂O, delaying the reduction to copper. On the basis of simpler systems it was possible to demonstrate the activating effect of Al₂O₃ and the delaying effect of ZnO on the reduction of CuO.     

Cu/Cu2O Electrodes and CO2 Reduction to Formic Acid: Effects of Organic Additives on Surface Morphology and Activity

Copper/copper oxide (Cu/Cu₂O) electrodes are known to display interesting electrocatalytic performances for the reduction of CO₂, and thus, deserve further investigation for optimization. Here, we show that the addition of nitrogen‐based organic additives greatly improves the activity of these electrodes (higher current densities, greater selectivity, and higher faradaic yields). The best effector is found to be tetramethyl cyclam. For example, electrolysis at ?2.0 V versus Fc⁺/Fc in CO₂‐saturated DMF/H₂O (99:1, v/v) in the presence of this effector results in formic acid with almost 90 % faradaic yield. SEM and XPS analysis of the electrode surface reveals that the organic additive promotes the formation of active Cu⁰ nanoparticles from Cu₂O during electrolysis. This simple approach provides a straightforward strategy toward the optimization of Cu/Cu₂O electrodes.     

制备条件对Cu2O结构及甲醛乙炔化性能的影响

以Cu（NO₃）₂·3H₂O为铜源,在液相还原过程中,调变沉淀剂NaOH、还原剂L-抗坏血酸钠的加入顺序制备了Cu₂O,借助X射线粉末衍射（XRD）、傅里叶变换红外光谱（FT-IR）、拉曼光谱（Raman）、俄歇电子能谱（XAES）和H₂程序升温还原（H₂-TPR）等手段研究了制备条件对Cu₂O结构及催化甲醛乙炔化性能的影响.结果表明,调变NaOH及L-抗坏血酸钠的添加方式改变了Cu₂O的结晶度与粒径尺寸,从而使Cu₂O表现出不同的炔化性能.先加入NaOH,后加入抗坏血酸钠,Cu₂O结晶度高,粒径大,难以转化为活性物种炔化亚铜;先加入抗坏血酸钠,后加入NaOH,Cu₂O被过度还原为非活性的金属Cu,两者均造成催化剂活性较低.而NaOH和抗坏血酸钠混合后添加的方式制备出表面Cu₂O结晶完整而体相Cu₂O分散度高的样品,这使得Cu₂O高效转化为炔化亚铜活性物种,表现出最优的炔化性能,在适宜的反应条件下,1,4-丁炔二醇收率达到71.7%,经6次循环后,仍保持在56.5%.     

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。     

Cu‐Based Nanocomposites as Multifunctional Catalysts

Herein, we report the synthesis of Cu/Cu₂O nanocomposites by a one‐step hydrothermal process at 180 °C, for which the resulting morphology is dependent on the hydrothermal reaction time (24, 72, and 120 h). With a longer reaction time of 120 h, a rod‐shape morphology is obtained, whereas at 72 and 24 h assemblies of nanoparticles are obtained. The rod‐shaped (120 h) particles of the Cu/Cu₂O nanocomposites show a much higher efficiency (6.3 times) than the agglomerates and 2.5 times more than the assemblies of nanoparticles for the hydrogen‐evolution reaction. During the oxygen‐evolution reaction, the nanorods produce a current that is 5.2 and 3.7 times higher than that produced by the agglomerated and assembled nanoparticles, respectively. The electrocatalysts are shown to be highly stable for over 50 cycles. As catalysts for organic synthesis, a 100 % yield is achieved in the Sonogashira cross‐coupling reaction with the nanorods, which is higher than with the other nanocomposite particles. This result demonstrates the significant enhancement of yield obtained with the nanorods for cross‐coupling reactions.     

The Functionality of Surface Hydroxy Groups on the Selectivity and Activity of Carbon Dioxide Reduction over Cuprous Oxide in Aqueous Solutions

Carbon dioxide (CO₂) reduction in aqueous solutions is an attractive strategy for carbon capture and utilization. Cuprous oxide (Cu₂O) is a promising catalyst for CO₂ reduction as it can convert CO₂ into valuable hydrocarbons and suppress the side hydrogen evolution reaction (HER). However, the nature of the active sites in Cu₂O remains under debate because of the complex surface structure of Cu₂O under reducing conditions, leading to limited guidance in designing improved Cu₂O catalysts. This paper describes the functionality of surface‐bonded hydroxy groups on partially reduced Cu₂O(111) for the CO₂ reduction reaction (CO₂RR) by combined density functional theory (DFT) calculations and experimental studies. We find that the surface hydroxy groups play a crucial role in the CO₂RR and HER, and a moderate coverage of hydroxy groups is optimal for promotion of the CO₂RR and suppression of the HER simultaneously. Electronic structure analysis indicates that the charge transfer from hydroxy groups to coordination‐unsaturated Cu (Cu_CUS) sites stabilizes surface‐adsorbed COOH*, which is a key intermediate during the CO₂RR. Moreover, the CO₂RR was evaluated over Cu₂O octahedral catalysts with {111} facets and different surface coverages of hydroxy groups, which demonstrates that Cu₂O octahedra with moderate coverage of hydroxy groups can indeed enhance the CO₂RR and suppress the HER.     

CO2 Reduction Mechanism on the Cu2O(110) Surface: A First-Principles Study

Cu₂O is an attractive catalyst for the selective reduction of CO₂ to methanol. However, the mechanism of the reaction and the role of the Cu species in different oxidation states are not well understood yet. In this work, by first-principles calculations, we investigate the mechanism of the reaction on the Cu₂O(110) surface, which is the most selective for methanol, in different degrees of reduction: ideal surface, slightly reduced surface (SRS), and partially reduced surface (PRS). The most favorable reaction pathways on the three surfaces were identified. We found that Cu(I) on the ideal surface is not capable of chemisorbing CO₂, but surface oxygen serves as the active site which selectively converts CO₂ to CH₃OH with a limiting potential of −0.77 V. The Cu(0) on the SRS and PRS promotes the adsorption and reduction of CO₂, while the removal of the residue O* becomes potential/rate limiting with a more negative limiting potential than the ideal surface. The SRS is selective to methanol while the PRS becomes selective to methane. The result suggests that the key to high methanol selectivity is to avoid the reduction of Cu(I), which provides a new strategy for the design of more efficient catalysts for selective CO₂ reduction to methanol.     

Plasma-assisted oxidation of Cu(100) and Cu(111)

Oxidized copper surfaces have attracted significant attention in recent years due to their unique catalytic properties, including their enhanced hydrocarbon selectivity during the electrochemical reduction of CO₂. Although oxygen plasma has been used to create highly active copper oxide electrodes for CO₂RR, how such treatment alters the copper surface is still poorly understood. Here, we study the oxidation of Cu(100) and Cu(111) surfaces by sequential exposure to a low-pressure oxygen plasma at room temperature. We used scanning tunnelling microscopy (STM), low energy electron microscopy (LEEM), X-ray photoelectron spectroscopy (XPS), near edge X-ray absorption fine structure spectroscopy (NEXAFS) and low energy electron diffraction (LEED) for the comprehensive characterization of the resulting oxide films. O₂-plasma exposure initially induces the growth of 3-dimensional oxide islands surrounded by an O-covered Cu surface. With ongoing plasma exposure, the islands coalesce and form a closed oxide film. Utilizing spectroscopy, we traced the evolution of metallic Cu, Cu₂O and CuO species upon oxygen plasma exposure and found a dependence of the surface structure and chemical state on the substrate''s orientation. On Cu(100) the oxide islands grow with a lower rate than on the (111) surface. Furthermore, while on Cu(100) only Cu₂O is formed during the initial growth phase, both Cu₂O and CuO species are simultaneously generated on Cu(111). Finally, prolonged oxygen plasma exposure results in a sandwiched film structure with CuO at the surface and Cu₂O at the interface to the metallic support. A stable CuO(111) surface orientation is identified in both cases, aligned to the Cu(111) support, but with two coexisting rotational domains on Cu(100). These findings illustrate the possibility of tailoring the oxidation state, structure and morphology of metallic surfaces for a wide range of applications through oxygen plasma treatments.

A low-pressure oxygen plasma oxidized Cu(100) and Cu(111) surfaces at room temperature. The time-dependent evolution of surface structure and chemical composition is reported in detail for a range of exposure times up to 30 min.     

Copper immobilized on biomimetic assembled calcium carbonate/carboxymethylcellulose hybrid: a highly active recoverable catalyst for CuAAC reactions

A novel copper immobilized on biomimetic assembled carboxymethylcellulose/calcium carbonate hybrid (Cu^II@CMC/CaCO₃) as an efficient heterogeneous catalyst for the synthesis of 1,2,3-triazoles has been described herein. The fabrication of Cu^II@CMC/CaCO₃ is accomplished through a bioinspired mineralization process using sodium carboxymethylcellulose (CMC-Na) as the template and ion exchange agent, while the metathesis, nucleation, assemble, hybridization, and immobilization of Cu(II) occurred by successful treatment with CaCl₂, Na₂CO₃, and CuSO₄ in water at room temperature. The resultant Cu^II@CMC/CaCO₃ hybrid was well characterized by various analyses such as FT-IR, XRD, SEM, EDX, EDX-mapping, TEM, and TGA techniques. In the presence of low copper loading of Cu^II@CMC/CaCO₃ hybrid, benzylic halides, azide, and alkynes proceeded smoothly to afford 1,4-disubstituted 1,2,3-triazoles in high yields. The catalyst can be conveniently recovered from the reaction mixture by filter and reused for at least 5 consecutive runs with a slight drop in its catalytic activity. The remarkable activity and stability of the catalyst may be attributed to the coordination of both carboxyl and hydroxyl groups of the hybrid of CMC/CaCO₃.

     

Unexpected high selectivity for acetate formation from CO2 reduction with copper based 2D hybrid catalysts at ultralow potentials

Copper-based catalysts are efficient for CO₂ reduction affording commodity chemicals. However, Cu(i) active species are easily reduced to Cu(0) during the CO₂RR, leading to a rapid decay of catalytic performance. Herein, we report a hybrid-catalyst that firmly anchors 2D-Cu metallic dots on F-doped Cu_xO nanoplates (Cu_xOF), synthesized by electrochemical-transformation under the same conditions as the targeted CO₂RR. The as-prepared Cu/Cu_xOF hybrid showed unusual catalytic activity towards the CO₂RR for CH₃COO⁻ generation, with a high FE of 27% at extremely low potentials. The combined experimental and theoretical results show that nanoscale hybridization engenders an effective s,p-d coupling in Cu/Cu_xOF, raising the d-band center of Cu and thus enhancing electroactivity and selectivity for the acetate formation. This work highlights the use of electronic interactions to bias a hybrid catalyst towards a particular pathway, which is critical for tuning the activity and selectivity of copper-based catalysts for the CO₂RR.

A two-dimensional (2D) copper hybrid catalyst (Cu/Cu_xOF) composed of metallic Cu well dispersed on 2D F-doped Cu_xO nanoplates (Cu_xOF) is reported, which shows high catalytic activity toward the CO₂RR for acetate generation.     

New copper-containing catalysts based on modified amorphous silica and their use in flow azide—alkyne cycloaddition

Сopper-containing catalysts supported on amorphous silica modified by amines were prepared using the chemical reduction method. The morphology of copper particles and their chemi calstate depend on the type of the reducing agent used. The use of ascorbic acid results in the formation of monodisperse submicron Cu⁰ particles 200—300 nm in size, whereas Cu⁰ particles with a size ranging from 50 to 150 nm are formed when hydrazine hydrate was used. The morphology and chemical state of the copper particles reduced with sodium borohydride depend substantially on the amount of the reducing agent: Cu⁰ nanoparticles 10—15 nm in size are formed if the reducing agent is an excess, layered Cu₂O plates are formed at the equimolar amount of sodium borohydride, and a decrease in the amount of sodium borohydride results in spherical Cu₂O particles. All the catalysts synthesized in the flow regime showed higher activity in the catalytic cycloaddition of azides to alkynes than the commercially available copper catalysts.     

On the Oxidation State of Cu2O upon Electrochemical CO2 Reduction: An XPS Study

The encouraging selectivity of copper oxides for the electroreduction of CO₂ into ethylene and alcohols has led to a vivid debate on the possible relation between their operando (sub-)surface oxidation state (i. e. fully reduced or partially oxidized) and this distinct reactivity. The high roughness of the Cu oxides used in previous studies on this matter adds complexity to this controversy and motivated us to prepare quasi-planar Cu₂O thin films that displayed a CO₂ reduction selectivity similar to that of oxide-derived copper catalysts reported in previous studies. Most importantly, when the post-mortem thin films were transferred for characterization in an air-free environment, X-ray photoelectron spectroscopy measurements confirmed their complete reduction in the course of the CO₂ reduction reaction. Thus, our results indicate that the selectivity of the Cu oxides featured in previous studies stems from their enhanced roughness, highlighting the importance of controlled sample transfer upon post-mortem characterization with ex situ techniques.     

Manipulating the Oxidation State of CuxO Catalysts to Optimize the Selectivity of Gaseous Products in Electrochemical CO2 Reduction

Copper-based (Cu-based) catalysts can efficiently convert carbon dioxide to multicarbon products by electrochemical reduction. In this paper, the electrocatalyst with the coexistence of three valence states of Cu(0)-Cu(I)-Cu(II) was successfully prepared by adjusting the experimental conditions. The catalyst was derived from Cu/Cu₂O prepared on carbon cloth and exhibited excellent CO₂ reduction performance. For carbon-gaseous products, the Faradaic efficiencies for the Cu-2 catalyst consisting of Cu(0)-Cu(I)-Cu(II) were 35.45±3.40 % at −1.66 V vs. RHE, of which 23.85±1.18 % for C₂H₄. And the synergistic effect of Cu(0)-Cu(I)-Cu(II) significantly improved the selectivity of the catalyst to C₂H₄. This paper provided an efficient method to rationally tune the valence state of Cu-based catalysts to improve CO₂ reduction performance.     

Sulfur Changes the Electrochemical CO2 Reduction Pathway over Cu Electrocatalysts

Electrochemical CO₂ reduction to value-added chemicals or fuels offers a promising approach to reduce carbon emissions and alleviate energy shortage. Cu-based electrocatalysts have been widely reported as capable of reducing CO₂ to produce a variety of multicarbon products (e.g., ethylene and ethanol). In this work, we develop sulfur-doped Cu₂O electrocatalysts, which instead can electrochemically reduce CO₂ to almost exclusively formate. We show that a dynamic equilibrium of S exists at the Cu₂O-electrolyte interface, and S-doped Cu₂O undergoes in situ surface reconstruction to generate active S-adsorbed metallic Cu sites during the CO₂ reduction reaction (CO₂RR). Density functional theory (DFT) calculations together with in situ infrared absorption spectroscopy measurements show that the S-adsorbed metallic Cu surface can not only promote the formation of the *OCHO intermediate but also greatly suppress *H and *COOH adsorption, thus facilitating CO₂-to-formate conversion during the electrochemical CO₂RR.     

Thermal oxidative degradation of isotactic polypropylene catalyzed by copper and copper oxide interfaces

The oxidative degradation of isotactic polypropylene films coated on well-defined Cu(Cu₂O), CuO_0.67, and CuO films in a temperature range of 90–120°C in a quartz-spoon-gauge-reaction vessel was studied. This catalytic reaction has been compared with the oxidation of polypropylene without copper or oxide films. The reaction vessel contained, if needed, P₂O₅ and/or KOH as “getters” for H₂O and CO₂, these substances could be menitored continuously. Cu(Cu₂O) films were transformed during oxidation of the polymer to yellow CuO_0.67 below 100°C and above this temperature to black CuO in the presence of H₂O and CO₂, whereas in the absence of these compounds CuO was formed below 100°C and CuO_0.67 at 120°C. Characteristic autoxidation curves obtained in the absence of H₂O and CO₂ showed induction periods that were shorter for copper oxide-polymer interfaces than for glass-polymer interfaces (i.e., for uncatalyzed oxidation). Abnormalities were observed for Cu(Cu₂O)-polymer interfaces because of further oxidation of Cu during the reaction. The rates of oxygen consumption were faster for CuO_0.67-polymer and CuO-polymer than for the uncatalyzed reaction; the catalytic action of CuO_0.67 was somewhat larger than that of CuO. The important observation was made that the mechanism of oxidation is not the same in the absence and presence of reaction products; that is, H₂O and CO₂. This was confirmed by ion beam scattering experiments, which also revealed that an oxidation-reduction process takes place at Cu and their oxide interfaces. A mechanism for the catalytic oxidation process, based on the ease by which copper ions are released from the metal oxides at the interface, was formulated. These ions diffuse subsequently as actions of carboxylate anions into the bulk of the polymer. Arrhenius equations of oxygen consumption are given for all cases; the energy of activation calculated for the initiation of the uncatalyzed oxidation agrees with its literature value. The energy of activation for the initiation of the catalyzed reaction was a few kilocalories lower than that for the uncatalyzed reaction. Catalytic action is mainly operative for the initiation reaction at the interface and for the decomposition of hydroperoxides by copper ions. Preventing the delivery of copper ions to the polymer would be the most efficient way of inhibiting the catalysis.     

Two-dimensional layer architecture assembled by Keggin polyoxotungstate, Cu(II)-EDTA complex and sodium linker: Synthesis, crystal structures, and magnetic properties

Reaction of Keggin polyoxotungstate with copper(II)-EDTA (EDTA=ethylenediamine tetraacetate) complex under mild conditions led to the formation of hybrid inorganic-organic compounds Na₄(OH)[(Cu₂EDTA)PW₁₂O₄₀]·17H₂O (1) and Na₄[(Cu₂EDTA)SiW₁₂O₄₀]·19H₂O (2). The single-crystal X-ray diffraction analyses reveal their two structural features: (1) one-dimensional chain structure consisting of Keggin polyoxotungstate and copper(II)-EDTA complex; (2) Two-dimensional layer architecture assembled by the one-dimensional chain structure and sodium linker. The results of magnetic measurements in the temperature range 300-2 K indicated the existence of ferromagnetic exchange interactions between the Cu^II ions for both compounds. In addition, TGA analysis, IR spectra, and electrochemical properties were also investigated to well characterize these two compounds.     

Synthesis,magnetochemical studies and X-ray molecular structures of some mononuclear copper(II)–1H-pyrazole adducts and mono(μ-pyrazolate) bridged dicopper(II) complexes derived from N-salicylidenearoylhydrazines

1H-Pyrazole complexes, [Cu(HL)HPz Cl] nH₂O and [Cu(L)HPz] nH₂O were prepared and characterized, where HL and L, respectively, refer to the mononegative and dinegative N-salicylidenearoylhydrazine anions. The X-ray crystal and molecular structure of [monochloro(N-salicylidenebenzoylhydrazinato)ONO(−1)monopyrazole] copper(II) monohydrate, [Cu(HSBzh)HPz Cl] H₂O, and [(N-salicylidenebenzoylhydrazinato)ONO(−2)monopyrazole] copper(II) hemihydrate, [Cu(SBzh)HPz] 1/2H₂O, were determined. The Cu(II) in [Cu(HSBzh)HPz Cl] H₂O is in a distorted square pyramidal environment and is bound in the equatorial plane with the mononegative tridentate aroylhydrazone anion and pyrazole nitrogen, the axial fifth coordination site is occupied by a chloride ion. On the other hand, the complex [Cu(SBzh)HPz] 1/2H₂O consists of two monomeric crystallographically independent but chemically similar molecules. In each molecule, the Cu(II) is in a distorted square planar geometry and is coordinated to the dinegative tridentate aroylhydrazone via the phenoxy oxygen, azomethine nitrogen and enolimide oxygen, and the fourth coordination site is occupied by the pyrazole nitrogen. The mono(μ-pyrazolate) dicopper(II) complexes, K[Cu₂(L)₂Pz] nH₂O, were also prepared and the X-ray molecular structure of K₂[Cu₄(SBzh)₄(Pz)₂] 2H₂O 1/2CH₃OH was determined. In this complex, two copper(II) atoms are bridged by only one pyrazolate anion forming a dicopper mono(μ-pyrazolate) unit. Each two units are connected together by a five coordinate K⁺ cation forming a tetranuclear assembly. These tetranuclear assemblies are connected together by another K⁺ cation forming a supramolecular structure. Variable temperature magnetic studies on these pyrazolate complexes indicated antiferromagnetic behaviour with −2J values varying from 25 to 36 cm⁻¹.     

Copper-Sulfur-Nitrogen Cluster Providing a Local Proton for Efficient Carbon Dioxide Photoreduction

Atomically precise Cu clusters are highly desirable as catalysts for CO₂ reduction reaction (CO₂RR), and they provide an appropriate model platform for elaborating their structure–activity relationship. However, an efficient overall photocatalytic CO₂RR with H₂O using assembled Cu-cluster aggregates as single component photocatalyst has not been reported. Herein, we report a stable crystalline Cu−S−N cluster photocatalyst with local protonated N−H groups (denoted as Cu₆−NH ). The catalyst exhibits suitable photocatalytic redox potentials, high structural stability, active catalytic species, and a narrow band gap, which account for its outstanding photocatalytic CO₂RR performance under visible light, with ≈100 % selectivity for CO evolution. Remarkably, systematic isostructural Cu-cluster control experiments, in situ infrared spectroscopy, and density functional theory calculations revealed that the protonated pyrimidine N atoms in the Cu₆−NH cluster act as a proton relay station, providing a local proton during the photocatalytic CO₂RR. This efficiently lowers the energy barrier for the formation of the *COOH intermediate, which is the rate-limiting step, efficiently enhancing the photocatalytic performance. This work lays the foundation for the development of atomically precise metal-cluster-based photocatalysts.