Cu2O Microcrystals Research Articles

Cross‐coupling reactions using porous multipod Cu2O microcrystals as recoverable catalyst in aqueous media

Porous multipod Cu2O microcrystals were found to be an efficient, highly recyclable and eco‐friendly catalyst for the cross‐coupling reactions of aryl halides and terminal alkynes with high yields in aqueous media. Noteworthy, the Cu2O catalyst can be reused for several times without significant decrease in catalytic activity.

A Facile Method Synthesis of {100}-Truncated Rhombic Dodecahedral Cu2O Microcrystals and Its Photocatalytic Activity

In this study, we report a facile solution-based one-step reduction method to synthesis of {100}-truncated rhombic dodecahedral Cu2O crystals. Each {100}-truncated rhombic dodecahedral Cu2O has six square {100} faces in addition to twelve {110} facets. The obtained microstructures were characterized by SEM, TEM, HRTEM, XRD and UV-vis spectrum. The adsorption and photocatalytic activity of as-prepared {100}-truncated rhombic dodecahedral Cu2O polyhedral for decomposition of methylene blue were investigated and compared to that of octahedral. It is found that the {100}-truncated rhombic dodecahedron Cu2O have a much better photocatalytic activity than octahedron. The{100}-truncated rhombic dodecahedra exposing the {110} facets exhibit an exceptionally good photocatalytic activity toward the fast and complete photo degradation of methylene blue due to a high number density of surface copper atoms, demonstrating the importance of their successful preparation.

The effect of different exposed facets on the photoelectrocatalytic degradation of o-chlorophenol using p-type Cu2O crystals

Although it is known that the efficacy of photoelectrocatalysts is enhanced by increasing the amount of high energy surface exposed, the development of a universal synthesis method with both superior activity and simplicity is needed for scalable applications. We herein controllably fabricated cuprous oxide (Cu2O) micro crystals with different morphologies, evolving from cubes, cuboctahedra, truncated octahedra and finally to octahedra on indium tin oxide (ITO) glass substrates, by a facile electrochemical deposition method. The structures of facet-engineered Cu2O samples and the underlying mechanism for the morphology evolution were investigated. The separation of photogenerated hole-electron pairs on Cu2O crystals with different exposed facets was characterized by measuring the photocurrent densities with chopped illumination, which increased with the increased concentrations of PVP: the octahedral Cu2O crystals, with the highest proportion of {111} facets exposed, exhibited the lowest electro-hole recombination in contrast to the cubes, cuboctahedra, and truncated octahedra, respectively. The photoelectrocatalytic degradation efficiency of the o-chlorophenol (2-CP) pollutant under sunlight irradiation with Cu2O-coated photocathode was further investigated to reveal the effect of different exposed facets. Due to the increased number of surface active sites available for degradation reactions, the octahedral Cu2O microcrystals presented higher photoelectrocatalytic activity compared to other shapes. Active oxygen species detected by electron spin-resonance (ESR) spectrometry implied that abundant superoxide radicals (O2●−) were the dominant active radicals in the degradation.

Evolution of the morphology of Cu2O microcrystals: cube to 50-facet polyhedron through beveled cube and rhombicuboctahedron

We present a simple morphology-controlled method for the synthesis of Cu2O microcrystals. The Cu2O microcrystals are prepared via the reduction of copper with glucose in an alkaline aqueous solution. The concentration of NaOH plays an important role in the morphology evolution of the resulting microcrystals. We observed the evolution of the morphology of the Cu2O microcrystals, which changes from a cube to a beveled cube and then to a rhombicuboctahedron and a 50-facet polyhedron upon the increase in the NaOH concentration. A mechanism is proposed to explain the evolution of the morphology of Cu2O.

Tuning the Exposed Facets of Photocatalysts to Improve the Performance

Exposed crystal facets of the photocatalysts are one of the most important factors to determine the photocatalytic activities. We investigated several photocatatlysts, revealing the relationship between the morphology, especially the exposed facets, and the photocatalytic activities. Cu2O microcrystals demonstrate better performance in producing hydrogen by degrading formaldehyde solution under visible light in comparison with other materials. Cu2O microcrystals exposing {110} facets show higher activity than Cu2O exposing {111} facets because of a larger density of surface copper atoms. BiOCl microsized square nanosheets exposing {001}facets, with a large lateral size of 3−5 µm and the side length/thickness ratio of about 100, present good photocatalytic activity toward decoloring Rhodamine B solution under the ultraviolet-visible light irradiation. {020} is the active facet of orthorhombic WO3•0.33H2O. The orthorhombic WO3•0.33H2O exposing most {020} facets shows much higher activity than other samples in decoloring Rhodamine B solution under visible light. LaTi2O7, with the layered perovskites structure, prefers to grow into nanosheets exposing the {010} facets. By exposing small {012} facets with high surface energy, the photocatalytic hydrogen releasing rate has been substantially increased. References Min Li, Junying Zhang, Hong Gao, Feng Li, Sten-Eric Lindquist, Nianqiang Wu, Rongming Wang, ACS Applied Materials & Interface, 2016, 8, 6662−6668Yesheng Li, Zilong Tang, Junying Zhang, Zhongtai Zhang, CrystEngComm, 2015, 17, 9102-9110Hong Gao,Junying Zhang, Rongming Wang, Mei Wang, Applied Catalysis B: Environmental, 2015, 172, 1-6

Morphological evolution of hexapod Cu2O microcrystals by a rapid template-free autoclaving technique

Morphologically tuned Cu2O micro-crystals were synthesized by one-pot autoclaving method at 150°C for a shorter reaction time in the presence of copper nitrate and di-methyl formamide (DMF) without using any external templating agents. Powder X-ray diffraction (PXRD) and X-ray photoelectron spectroscopy (XPS) showed the formation of phase pure Cu2O in the as-prepared samples. Morphological analysis indicated the formation of hexapod Cu2O with twenty four {111} facets at 150°C/2h. The hydrolysis product of DMF, i.e., di-methyl amine (Me2NH) and formic acid (HCOOH) played a significant role as growth controller and reducing agent, respectively for the formation of Cu2O micro-crystals. A proposed formation mechanism was illustrated.

Design of Cu2O-Au composite microstructures for surface-enhanced Raman scattering study

Octahedral Cu2O-Au composite microstructures (CMSs) were synthesized with a facile in situ method and were attempted as surface-enhanced Raman scattering (SERS) substrates. The density of the Au nanoparticles (NPs) on the surface of the octahedral Cu2O microcrystals can be controlled by tuning the concentration of the gold precursor, which can further influence the SERS activity of the Cu2O-Au CMSs system. The CMSs system exhibited a charge transfer from Au to Cu2O. Furthermore, metallic NPs deposited on the semiconductor material formed a local electromagnetic field, which altered the interfacial charge distribution. The SERS signal enhancement from the Cu2O-Au CMSs system is attributed to a combination of electromagnetic and chemical enhancement mechanisms occurring simultaneously at the semiconductor-metal interface. Overall, the proposed CMSs system will provide a new model for SERS study and application.

Hydrothermal syntheses of CuO, CuO/Cu2O, Cu2O, Cu2O/Cu and Cu microcrystals using ionic liquids

In this paper, CuO, CuO/Cu2O, Cu2O, Cu2O/Cu and Cu microcrystals were synthesized via a hydrothermal method by mixing Cu(NO3)2·3H2O and NaOH together in the presence of an ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate([BMIM]BF4) or 1-butyl-3-methylimidazolium chloride([BMIM]Cl). The structures and the morphologies of the obtained products were characterized by means of X-ray diffractometer( XRD), field-emission scanning electron microscopy/energy-dispersive spectroscopy(FESEM/EDS), transmission electron microscopy/selected area electron diffraction(TEM/SAED) and Raman spectroscopy. The result of XRD indicates that Cu2O and Cu microcrystals are cubic phase and the Raman spectra confirm the presence of carbon. The results of FESEM and TEM images show Cu2O microcrystals as rule cubes of 2 μm in length and Cu particles of 5 μm in diameter. According to the difference between crystal structures, bi-component and single component products were synthesized by adjusting the reaction conditions. A possible formation mechanism of Cu2O and Cu was proposed in [BMIM]BF4.

Synthesis of Cu2O@Ag Polyhedral Core–Shell Nanoparticles by a Thermal Decomposition Approach for Catalytic Applications

AbstractCu2O@Ag polyhedral core–shell nanoparticles with different morphologies (rhombicuboctahedral, cuboctahedral, truncated octahedral, and octahedral) have been successfully synthesized by a thermal decomposition approach. The Cu2O@Ag polyhedral core–shell nanoparticles were characterized by X‐ray diffraction, electron microscopy, surface‐area analysis, and diffuse reflectance spectroscopy. The XRD results confirm the presence of Cu2O and silver in the Cu2O@Ag samples. Electron microscopy studies prove the formation of a shell of silver nanoparticles on the polyhedral Cu2O microcrystals. The diffuse reflectance spectra of the Cu2O@Ag polyhedral core–shell nanoparticles show band‐gap absorption owing to Cu2O as well as surface plasmon resonance owing to silver nanoparticles. The catalytic activities of the Cu2O@Ag polyhedral core–shell nanoparticles were explored for the reductions of 4‐nitrophenol and methylene blue in aqueous solutions. The Cu2O@Ag core–shell nanoparticles with octahedral morphology show higher catalytic activity than the other Cu2O@Ag samples. The core–shell nanoparticles show a higher turnover frequency (TOF) and activity parameter (kact) for 4‐nitrophenol reduction and a higher apparent rate constant (kapp) for methylene blue reduction compared to the previously reported values. The reusability of the Cu2O@Ag polyhedral core–shell nanoparticles was also tested, and they show stability for up to five cycles without loss of efficiency.

A surfactant-free solvothermal synthesis of Cu2O microcrystals and their photocatalytic activity.

The Cu2O octahedral microcrystals have been successfully fabricated by a surfactant-free solvothermal approach. The morphology and structure of the as-prepared sample were characterized by scanning electron microscopy, X-ray powder diffraction and UV-Vis spectroscopy. It was found that the structure and morphology of Cu2O microcrystals were strongly affected by synthesis time and temperature. Based on the time-dependent experiment, the possible formation mechanism of Cu2O octahedral microcrystals was proposed. The photocatalytic activities of as-prepared Cu2O samples were also evaluated for degradation of methyl orange under visible-light irradiation. The results showed that the Cu2O synthesized at 180 °C for 4 h had a better photocatalytic performance due to its high percentage of exposed (111) crystal facet and the lowest band gap energy.

Effect of Growth Temperature and Time on Morphology and Gas Sensitivity of Cu2O/Cu Microstructures

A facile hydrothermal synthesis with CuSO4as the copper source was used to prepare micro/nano-Cu2O. The obtained samples have been characterized by X-ray diffraction, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). With increasing the reaction temperature and time, the final products were successively Cu2O octahedron microcrystals, Cu2O/Cu composite particles, and a wide range of Cu spherical particles. The gas sensitivity of products towards ethanol and acetone gases was studied. The results showed that sensors prepared with Cu2O/Cu composites synthesized at 65°C for 15 min exhibited optimal gas sensitivity. The gas sensing mechanism and the effect of Cu in the enhanced gas response were also elaborated. The excellent gas sensitivity indicates that Cu2O/Cu composites have potential application as gas sensors.

Hydrothermal synthesis of morphology controllable Cu2O and their catalysis in thermal decomposition of ammonium perchlorate

Cu2O micro-crystals with different morphologies (including three branching structures) were synthesized through hydrothermal method by using sodium tartrate as chelating reagent. Branching growth patterns of Cu2O microcrystals have a strong dependence on the amount of sodium tartrate. These different Cu2O microcrystals were used as catalysts to promote the thermal decomposition of ammonium perchlorate (AP). The thermal decomposition of AP in the presence or absence of Cu2O micro-crystals was investigated non-isothermally through thermogravimetry and differential scanning calorimetry (DSC). The data obtained from DSC were applied for the calculation and comparison of the kinetic parameters of AP decomposition process through a model-free approach.

Hierarchical Shape Evolution of Cuprous Oxide Micro- and Nanocrystals by Surfactant-Assisted Electrochemical Deposition

Cu2O microcrystals (MCs) and nanocrystals (NCs) of various shapes were potentiostatically deposited on Ti substrates by exploiting the capping effects of differently charged surfactants on certain surfaces. Positively charged hexamethylenetetramine was adsorbed onto the {111} and {100} planes of the Cu2O crystals (copper- and oxygen-terminated surface) while negatively charged poly(vinylpyrrolidone) was adsorbed onto the {111} planes (Cu-terminated surface due to Coulombic interaction). The difference in the adsorption behaviors of the two surfactants resulted in the synthesis of differently shaped Cu2O MCs. We were also able to systematically control the shape evolution of Cu2O NCs synthesized as cubes, truncated cubes, truncated octahedrons, and stepped octahedrons into perfect octahedrons by adding or removing surfactants successively during the electrochemical deposition process. This method is a simple, flexible, and cost-effective one and should aid in the elucidation of the shape-transformation phe...

Facile synthesis and shape evolution of oleic acid decorated Cu2O microcrystals

A facile synthetic method of oleic acid decorated Cu2O microcrystals has been developed by thermal decomposition of copper formate-octylamine complexes in paraffin using oleic acid as dispersing agent. This new method showed many advantages, which include free-reducing agent, enhancing antioxidant properties of Cu2O and good dispersity in paraffin, etc. The phase structure and morphology were investigated by means of XRD, SEM and TEM. It is found that the reaction time and temperature play the important roles in the crystallite morphology. With the increase of the reaction time, the Cu2O rhombic dodecahedron is gradually transformed into the spherical particle by intraparticle ripening. The shape evolution of Cu2O microcrystals can be accelerated with the increase of temperature.

Morphology‐controlled Synthesis of Octahedral‐to‐Rhombic Dodecahedral Cu2O Microcrystals and Shape‐dependent Antibacterial Activities

Morphology‐controlled synthesis of cuprous oxide (Cu2O) microcrystal was achieved using a solvothermal method. The morphologies of the Cu2O microcrystals, namely octahedral, truncated octahedral, truncated rhombic dodecahedral, and rhombic dodecahedral, were fine‐tuned by varying the oleylamine and sodium oleate concentrations. Only the {111} and {110} facets of the Cu2O microcrystals were involved in this morphological transition. Octahedral Cu2O microcrystals were obtained in the absence of oleylamine and at the highest sodium oleate concentration. Rhombic dodecahedral Cu2O microcrystals were obtained at the highest oleylamine concentration or at the lowest sodium oleate concentration. The rhombic dodecahedron, which exposed only the {110} facets, exhibited better antibacterial activities against Escherichia coli compared to the octahedron, which exposed only the {111} facets.

Direct Synthetic Control over the Size, Composition, and Photocatalytic Activity of Octahedral Copper Oxide Materials: Correlation Between Surface Structure and Catalytic Functionality.

We report a synthetic approach to form octahedral Cu2O microcrystals with a tunable edge length and demonstrate their use as catalysts for the photodegradation of aromatic organic compounds. In this particular study, the effects of the Cu(2+) and reductant concentrations and stoichiometric ratios were carefully examined to identify their roles in controlling the final material composition and size under sustainable reaction conditions. Varying the ratio and concentrations of Cu(2+) and reductant added during the synthesis determined the final morphology and composition of the structures. Octahedral particles were prepared at selected Cu(2+):glucose ratios that demonstrated a range of photocatalytic reactivity. The results indicate that material composition, surface area, and substrate charge effects play important roles in controlling the overall reaction rate. In addition, analysis of the post-reacted materials revealed photocorrosion was inhibited and that surface etching had preferentially occurred at the particle edges during the reaction, suggesting that the reaction predominately occurred at these interfaces. Such results advance the understanding of how size and composition affect the surface interface and catalytic functionality of materials.

Crystal-facet-controllable synthesis of Cu2O microcrystals, shape evolution and their comparative photocatalytic activity

Single crystal Cu2O materials with morphologies of cube, truncated cube, truncated octahedron, octahedron etc. have been synthesized by a facile glucose reduction method. Polyvinylpyrrolidone concentration dependent, crystal-facet-controllable growth mechanism of the synthesized Cu2O crystals has been proposed in the article. The photocatalytic test results show that the octahedral Cu2O crystals with dominant {111} planes have super photocatalytic activity than the cubic ones packaged by {100} surfaces, which could be explained by that the polar, highly active {111} facets with unsaturated “Cu” have more excellent activity on the methyl orange dye degradation. This article will contribute to promote the morphology construction and crystal-dependent catalytic properties of metal oxide semiconductor materials.

Cuprous oxide microcrystals via hydrothermal approach: morphology evolution and photocatalytic properties

Cuprous oxide (Cu2O) microcrystals with various morphologies were prepared under mild hydrothermal condition. The samples were characterized by means of XRD, SEM, and UV/DRS. The morphology of the as-prepared Cu2O microcrystals typically had cubic symmetry and the morphology evolution from radial, six hollow branches to truncated octahedra (again cubic) were realized by adding acetic acid. The peak relative intensity of XRD pattern shows that the exposed planes of samples is consistent with their morphology. A possible growth mechanism of Cu2O microcrystals is also proposed. The behavior of adsorption and photocatalysis of Cu2O microcrystals was investigated by degrading methyl orange (MO) in aqueous solution. The results show that the as-prepared Cu2O radial six hollow branches microcrystals with exposed {110} planes have higher degradation efficiency to methyl orange (MO) than cubic ones with exposed {100} planes and truncated octahedral with exposed {111} planes microcrystals.

Synthesis of octahedral and cubic Cu2O microcrystals in sub- and super-critical methanol and their photocatalytic performance

A simple and potentially scalable sub- and super-critical methanol technique was applied to synthesize cuprous oxide. Cu2O microcrystals with two morphologies were obtained in methanol of subcritical domain by adjusting the feeding methods. The effects of the reaction time, temperature, pressure, and feeding method on the formation of Cu2O microcrystals were investigated. XRD, SEM, and XPS were applied to analyze the composition and morphology of products. Results showed that pure cuprous oxide could be obtained in subcritical methanol of 230 °C, 7.8 MPa for 15 min. The two as-obtained products displayed octahedral and cubic morphology with an average edge length of 4 and 2 μm by solution and solid feeding methods, respectively. The formation and crystal growth mechanism of Cu2O in subcritical methanol were also proposed on the basis of above results. Furthermore, the two microcrystals were employed as catalysts in the photodecomposition of negatively charged molecule methyl orange. Results showed that both microcrystals possessed excellent photocatalytic activities. However, the obvious difference between cubic and octahedral in photocatalytic performance was not found in the scale of micrometer (2–4 μm).

Cuprous oxide microcrystals via hydrothermal approach: morphology evolution and photocatalytic properties

Cuprous oxide (Cu2O) microcrystals with various morphologies were prepared under mild hydrothermal condition. The samples were characterized by means of XRD, SEM, and UV/DRS. The morphology of the as‐prepared Cu2O microcrystals typically had cubic symmetry and the morphology evolution from radial, six hollow branches to truncated octahedra (again cubic) were realized by adding acetic acid. The peak relative intensity of XRD pattern shows that the exposed planes of samples is consistent with their morphology. A possible growth mechanism of Cu2O microcrystals is also proposed. The behavior of adsorption and photocatalysis of Cu2O microcrystals was investigated by degrading methyl orange (MO) in aqueous solution. The results show that the as‐prepared Cu2O radial six hollow branches microcrystals with exposed {110} planes have higher degradation efficiency to methyl orange (MO) than cubic ones with exposed {100} planes and truncated octahedral with exposed {111} planes microcrystals.