Cyclic voltammetry of copper in sodium hydroxide solutions

The cyclic voltammograms of the Cu electrode were, obtained in NaOH solution as a function of the voltage scanning rate, electrolyte concentration and voltage range. A correlation was made between three well-defined anodic peaks and their corresponding cathodic ones. The anodic peaks were found to correspond successively to the formation of a monolayer of Cu₂O, formation of a thick multilayer film of CuO and finally Cu₂O₃ upon which O₂ is evolved. It is suggested that CuO is formed from the oxidation of Cu₂O and/or direct oxidation of metallic copper.Below 0.1 M NaOH the ratio of anodic to cathodic charges was found to be about unity, indicating the quantitative reduction of solid oxidation products, while at higher alkali concentrations higher charge ratios were obtained due to increasing proportions of soluble reaction products.The behaviour of the copper electrode in NaOH was found to be quite complicated. Thus, no simple relations were found between the voltage scanning rate and both the peak current and peak potential or between the peak current and the alkali, concentration. Further work is needed to obtain a definitive explanation of this behaviour.     

Multicycle chronoamperometry at rotating ring-disc electrode as a method of current separation into partial currents of silver ionization,Ag<Subscript>2</Subscript>O formation and its chemical dissolution in alkaline medium

A method of multicycle chronoamperometry at rotating ring-disc electrode is suggested for experimental separation of the disc polarization current into its components that correspond to the substrate metal ionization, an oxide formation, and the oxide chemical dissolution. The method was validated by the example of the Ag|Ag₂O|OH^?(H₂O) system. At moderate anodic potentials of Ag-disc (0.48–0.51 V), silver active dissolution from open areas of its surface and through film’s pores dominates; the phase-forming current, hence, the current efficiency of this process drops down rapidly. At the potentials of the maximum at voltammograms (0.52–0.53 V), when the silver active dissolution current is suppressed, the phase-forming currents dominate; they exceed the oxide chemical dissolution rate significantly. The Ag₂O film thickness increases rapidly, the current efficiency of the oxide formation process approaches 100% during the entire disc polarization period. The Ag(I)-oxide chemical dissolution rate constant practically does not depend on the anodic phase-formation potential; however, it somewhat varies depending on the oxide film thickness, thus reflecting changes in the film structure and, possibly, chemical composition (from AgOH to Ag₂O).     

TiO2纳米管阵列负载不同形貌Cu2O薄膜的制备及光电性能研究

本论文采用阳极氧化法在金属钛基底上制备高度有序的TiO2纳米管阵列薄膜,然后采用脉冲电流法在TiO2纳米管阵列上沉积Cu2O,从而制备出Cu2O-TiO2纳米管阵列异质结复合薄膜。借助X射线衍射仪(XRD),场发射扫描电子显微镜(FESEM)和透射电子显微镜(TEM)等表征手段,详细探讨了Cu2O沉积过程中电解液的不同扰动方式(静止、磁力搅拌和超声搅拌)对复合薄膜物相和形貌的影响。实验结果表明电解液的扰动方式会影响Cu2O沉积过程中的离子扩散和微区化学环境,从而影响Cu2O的形貌。通过漫反射紫外-可见吸收光谱(UV-Vis)和光电流性能测试可知所制备的负载Cu2O型TiO2纳米管阵列薄膜具有显著的可见光响应效应。     

Fabrication of p/n heterojunctions by electrochemical deposition of Cu2O onto TiO2 nanotubes

This work describes the TiO₂ nanotubes formation by anodic oxidation under different experimental conditions and the following attempts to optimize the electrochemical deposition of Cu₂O within the nanotubular structure. The as-formed Cu₂O/TiO₂ interface is a p/n junction that could be used in various light-assisted devices. The effect of the F^– concentration, the polarization duration and the post-thermal treatment on the TiO₂ nanotubes is recalled. Then the electrochemical deposition of cuprous oxide is investigated by cyclic voltammetry and the influence of the pH on the morphology and crystal structure is studied. Finally, potential pulses were applied to optimize the Cu₂O film morphology in order to improve the nanotubes covering.     

One‐Step Hydrothermal Synthesis of a Porous Cu2O Film and Its Photoelectrochemical Properties

A cuprous oxide (Cu₂O) film with a novel porous structure is successfully synthesized on Cu foil by using a simple hydrothermal method. A redox reaction occurs between Cu and Cu²⁺ in aqueous solution to form the Cu₂O film. The porous structures are formed as a result of the Ostwald ripening mechanism. In addition, photoluminescence measurements indicate that the porous Cu₂O film may reduce the recombination of photogenerated electrons and holes. The UV/Vis absorption property of the porous Cu₂O film is better than that of the granular Cu₂O film, and its high photocurrent is expected to make the porous Cu₂O film more suitable for solar energy applications.     

Kinetics of the transformation process of PbSO4 to PbO2 in a lead anodic film

The kinetics of the nucleation and growth of PbO₂ during the potentiostatic oxidation of PbSO₄ in a lead anodic film was studied using linear sweep voltammetry, potential-step and ac impedance tracing methods. The film investigated is the partially reduced anodic PbO₂ film formed by polarizing a lead electrode in 4.5 M H₂SO₄ solution first at 1.3 V vs. Hg|HgSO₄ for 20 min and then at 0.9 V for 5 min. The nucleation and growth process begins some time after the potential step and is completed within 60 s. The pre- and post-nucleation and growth processes correspond to the growth of the anodic film formed by the oxidation of the lead substrate. The mathematical equations representing the current-time and capacitance-time transients are derived taking the background oxidation current into account. The experimental results are well fitted by these equations. The process obeys the laws of two-dimensional instantaneous nucleation and growth.     

Factors influencing the growth behaviour of nanoporous anodic films on iron under galvanostatic anodizing

The growth behaviour of nanoporous anodic films on iron during galvanostatic anodizing in ethylene glycol electrolytes containing NH₄F and H₂O is examined at various current densities, H₂O concentrations in electrolytes and temperatures. The film morphology is mainly controlled by the formation voltage, regardless of anodizing conditions. Relatively regular cylindrical pores are formed at formation voltages less than 50 V, while rather disordered pores are formed above 100 V. The decrease in the H₂O concentration suppresses chemical dissolution of anodic films in addition to the increased growth efficiency, resulting in the formation of anodic films with a steady thickness of ～7 μm. The cell size of the anodic films depends upon the H₂O concentration as well as the formation voltage, but not upon the current density. Findings in this study will be useful for controlled growth of the anodic films on iron.     

TPR investigations on the reducibility of Cu supported on Al2O3, zeolite Y and SAPO-5

Reducibility of Cu supported on Al₂O₃, zeolite Y and silicoaluminophosphate SAPO-5 has been investigated in dependence on the Cu content using a method combining conventional temperature programmed reduction (TPR) by hydrogen with reoxidation in N₂O followed by a second the so-called surface-TPR (s-TPR). The method enables discrimination and a quantitative estimation of the Cu oxidation states +2, +1 and 0. The quantitative results show that the initial oxidation state of Cu after calcination in air at 400 °C, independent on the nature of the support, is predominantly +2. Cu²⁺ supported on Al₂O₃ is quantitatively reduced by hydrogen to metallic Cu⁰. Comparing the TPR of the samples calcined in air and that of samples additionally pre-treated in argon reveals that in zeolite Y and SAPO-5 Cu²⁺ cations are stabilized as weakly and strongly forms. In both systems, strongly stabilized Cu²⁺ ions are not auto-reduced by pre-treatment in argon at 650 °C, but are reduced in hydrogen to form Cu⁺. The weakly stabilized Cu²⁺ ions, in contrast, may be auto-reduced by pre-treatment in argon at 650 °C forming Cu⁺ but are reduced in hydrogen to metallic Cu⁰.     

Copper oxides: kinetics of formation and semiconducting properties. Part I. Polycrystalline copper and copper-gold alloys

The anodic formation of Cu(I) and Cu(II) oxides on polycrystalline copper and copper-gold alloys (4 and 15 at% Au) in deoxygenated 0.1 M KOH was examined by voltammetry, chronoamperometry, and chronopotentiometry with a synchronous registration of photocurrent and photopotential, in situ spectroscopy of photocurrent as well as XPS and SEM measurements. The band gap of p-Cu₂O is 2.2 eV for indirect optical transitions independent of the concentration of gold in Cu-Au alloy. It grows on CuOH or n-Cu₂O underlayer. The increase of anodic potential results in a thickening of oxide film which is a mixture of Cu(I) and Cu(II) oxides. The latter is a p-type semiconductor with a low photosensitivity. The rate of oxide formation on the alloys is lower than on copper. The structure-dependent properties of the oxide phase on the alloys and copper are different. Copper is prone to corrosive oxidation even in deoxygenated alkaline solution by the traces of molecular oxygen. The corrosive growth of Cu(I) oxide film occurs according to the parabolic law. After the cathodic polarization, the surface of copper remains free of corrosive oxide no longer than 15–20 min. The preliminary anodic formation even of a thin Cu₂O film as well as the alloying of copper with gold suppresses the corrosive oxidation of copper.     

A P/N type compounded Cu<Subscript>2</Subscript>O/TiO<Subscript>2</Subscript> photo-catalytic membrane for organic pollutant degradation

A heterojunction thin film consisting of n-type titanium dioxide (TiO₂) and p-type cuprous oxide (Cu₂O) was fabricated on an FTO conducting glass. The TiO₂ films were grown on the FTO glass by sol–gel and spray pyrolysis methods, and Cu₂O was deposited on it via the hydrothermal method. The morphology, crystalline structure, and optical absorption characteristics were studied by scanning electron microscopy, X-ray diffraction, and ultraviolet–visible diffuse reflectance spectrum, respectively. The results show that the surface of the Cu₂O/TiO₂ film was composed of net and large grains, which contributed to a large specific surface area. The crystal phase of the TiO₂ in the Cu₂O/TiO₂ film remained anatase. The crystal phase of the Cu₂O could not be detected as it is found in traces. The Cu₂O/TiO₂ film had a stronger optical absorption ability than the pure TiO₂ film. To investigate catalytic activity, a photocatalytic degradation experiment of the Cu₂O/TiO₂ film was performed in a homemade thin-layer micro-reactor. The photocatalytic degradation of methylene blue increased with increasing amounts of deposited Cu₂O until a maximum limit was reached. The photocatalytic activity might have declined with an increase in Cu₂O content. The metallic oxide has the potential to screen other photocatalysts from the UV source.     

A study by voltammetry and the photocurrent response method of copper electrode behavior in acidic and alkaline solutions containing chloride ions

The electrochemical behavior of Cu electrodes in Cl⁻ solutions was studied in a wide range of pH. The results were compared with those obtained in solutions containing F⁻, Br⁻, I⁻ and So²⁻₄ ions at pH 8.5, and discussed in terms of the competitive formation of Cu₂O and CuCl films on the Cu surface and the influence of CuCl on the properties of Cu₂O. At pH 8.5 or higher, Cu₂O was formed first, whereas at pH 5.7 or lower the Cu₂O film was formed on the Cu surface under the CuCl layer which was formed initially. It is believed that the Cu₂O films doped with Cl⁻ ions exhibited poor protective properties against Cu corrosion.     

Cuprous oxide nanospheres as probes for light scattering imaging analysis of live cells and for conformation identification of proteins

A facile solution-phase synthesis route of highly uniform Cu₂O nanospheres (Cu₂O NPs) with the size of 57.7 ± 4.7 nm was developed, and then the nanoparticles were applied to live cell imaging under a common dark-field microscope. Starting from copper(II) salts, the synthesis of Cu₂O NPs was made in the presence of cetyltrimethylammonium bromide (CTAB) by reducing the copper(II) with sodium borohydride (NaBH₄) in aqueous medium and by aging process in the air. Monitoring of morphology evolution process of Cu₂O NPs with scanning electron microscopy (SEM) and measuring of the UV-visible spectra showed that the synthesis of Cu₂O NPs follows the reduction-oxidation coupled process of Cu²⁺ into Cu⁰ species at first and then the resulted Cu⁰ species into Cu₂O NPs in the air. Light scattering (LS) features have been measured with a common spectrofluorometer and a common dark-field microscope, and it was found that the as-prepared Cu₂O NPs display strong blue scattering light and can be applied for cell imaging. If incubated with human bone marrow neuroblastoma, transferrin-conjugated Cu₂O NPs can get into the cells and show strong pure blue light in cytoplasm. Further investigations showed that the Cu₂O NPs could be applied for probes for conformation of proteins.     

不同形貌的Cu_2O:可控合成及光学性质(英文)

Cuprous oxide(Cu₂O) hexapodal branch structure with high uniformity was prepared by a solution phase route using sodium dodecyl sulfate as a capping agent. The shapes of Cu₂O crystal(flower-like structure, nanocube and nanoplate) were tuned by varying species and concentrations of surfactants to control the growth rate on different crystal planes of Cu₂O. Cu₂O nanostructures were characterized by UV-Vis spectroscopy, XRD, TEM and SEM. XRD result shows that the obtained Cu₂O belongs to cubic phase. TEM and SEM results demonstrate that specie and concentration of surfactants play a key role in the formation of various morphologies of Cu₂O. The formation mechanism is discussed. Moreover, the optical properties of the obtained Cu₂O are shape-dependent.     

Photoluminescence dependence on imposing bias for ZnGa2O4 and ZnGa2O4 activated with Mn or Cr n-type semiconductor electrodes

Photoluminescence (PL) dependence was investigated by imposing cathodic and anodic bias for ZnGa₂O₄, ZnGa₂O₄:Mn and ZnGa₂O₄:Cr n-type semiconductor electrodes. Under the cathodic bias PL intensity was weak at about 1/3 times compared with imposing no bias, while under the anodic bias the intensity was strong at about 2 times maximally by using the ZnGa₂O₄:Mn and ZnGa₂O₄:Cr electrodes although no change about the intensity was observed by using the ZnGa₂O₄ electrode. These results suggest that the emission attributed to recombination between electrons and holes is decreased by flow of cathodic current under the cathodic bias while the emission is increased to decrease at non-radiative transition rates under the anodic bias when the energy relaxation occurs.     

TiO2/Cu2O Core/Ultrathin Shell Nanorods as Efficient and Stable Photocatalysts for Water Reduction

P‐type Cu₂O has been long considered as an attractive photocatalyst for photocatalytic water reduction, but few successful examples has been reported. Here, we report the synthesis of TiO₂ (core)/Cu₂O (ultrathin film shell) nanorods by a redox reaction between Cu²⁺ and in‐situ generated Ti³⁺ when Cu²⁺‐exchanged H‐titanate nanotubes are calcined in air. Owing to the strong TiO₂‐Cu₂O interfacial interaction, TiO₂ (core)/Cu₂O (ultrathin film shell) nanorods are highly active and stable in photocatalytic water reduction. The TiO₂ core and Cu₂O ultrathin film shell respectively act as the photosensitizer and cocatalyst, and both the photoexcited electrons in the conduction band and the holes in the valence band of TiO₂ respectively transfer to the conduction band and valence band of the Cu₂O ultrathin film shell. Our results unambiguously show that Cu₂O itself can act as the highly active and stable cocatalyst for photocatalytic water reduction.     

不同结构Cu_2O多晶的合成及其对高氯酸铵热分解的催化作用

利用均相反应器,在没有添加剂的条件下合成了具有多孔结构的Cu2O微球.考察了合成时间以及反应器旋转速度对Cu2O微球结构的影响.通过增加聚乙烯吡咯烷酮(PVP)的用量,使得Cu2O从多孔微球转变为立方体孪晶,最终形成十四面体孪晶结构.同时,将不同结构的Cu2O多晶应用于催化高氯酸铵(AP)的热分解,结果表明:多孔Cu2O微球较其它结构的Cu2O对AP的热分解具有更高的催化活性,使得AP的低温分解温度降低了37.4°C,而AP在低温阶段的分解量也由8.7%增加至49.0%.     

Cu2O@HKUST-1核壳结构材料的制备及其抗氧化性能

以球状纳米Cu_2O为核心,直接牺牲其表面的部分Cu_2O,与溶液中的均苯三羧酸(H_3BTC)配体反应,原位生成具有核壳结构的Cu_2O@HKUST-1材料。采用O_2程序升温脱附(O_2-TPD)、H_2程序升温还原(H2-TPR)及CO氧化反应对Cu_2O@HKUST-1核壳材料的抗氧化能力进行了研究,证明金属-有机框架材料(MOFs)HKUST-1对反应气体起到富集、缓释作用,保护Cu_2O核不被氧化,显著提高了其抗氧化能力。     

TiO2/Cu2O/Pt复合空心微球的制备及其光催化性能

以锐钛矿相TiO₂溶胶为基底,采用沉淀法和液相沉积法制备了TiO₂/Cu₂O/Pt复合空心微球,通过改变n₍Ti⁴⁺)∶n_Cu2+和H₂Pt Cl₆·6H₂O溶液的加入量对TiO₂的形貌和结构进行调控,采用不同的方法对不同样品的物相及结构、微观形貌和光学性能进行了对比分析。分析结果表明,复合材料中Pt与Cu₂O的引入产生协同效应,不仅在一定程度上阻止了电子-空穴的复合,还降低了禁带宽度,在可见光区域光吸收明显增强。与TiO₂、Cu₂O和TiO₂/Cu₂O光催化剂相比较,TiO₂/Cu₂O/Pt降解有机污染物的能力显著增强,首次光照120 min可降解93%的甲基橙(MO)溶液,4次循环后降解率为71%,具有良好的光催化...     

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%.     

脉冲沉积制备Cu2O/TiO2纳米管异质结的可见光光催化性能

在用阳极氧化法制备有序排列TiO₂纳米管阵列薄膜的基础上,引入脉冲沉积工艺,成功实现了均匀、弥散分布的Cu₂O纳米颗粒修饰改性TiO₂纳米管阵列,形成Cu₂O/TiO₂ 纳米管异质结复合材料. 利用场发射扫描电镜（FESEM）、场发射透射电镜（FETEM）、X射线衍射（XRD）、X射线光电子能谱（XPS）和紫外-可见漫反射光谱（UV-Vis DRS）对样品进行表征,重点研究了Cu₂O/TiO₂ 纳米管异质结的光电化学特性和对甲基橙（MO）的可见光催化降解性能. 结果表明,Cu₂O纳米颗粒均匀附着在TiO₂纳米管阵列的管口和中部位置,所制备的Cu₂O/TiO₂ 纳米管异质结具有高效的可见光光催化性能;在浓度为0.01 mol·L^-1的CuSO₄溶液中制得的Cu₂O/TiO₂纳米管异质结表现出最好的电化学特性和光催化性能;另外,对Cu₂O纳米颗粒影响光催化活性的机理进行了讨论.