Cu2O Microcrystals Research Articles

Efficient electrocatalytic CO2 reduction to ethylene using cuprous oxide derivatives.

Copper-based materials play a vital role in the electrochemical transformation of CO2 into C2/C2+ compounds. In this study, cross-sectional octahedral Cu2O microcrystals were prepared in situ on carbon paper electrodes via electrochemical deposition. The morphology and integrity of the exposed crystal surface (111) were meticulously controlled by adjusting the deposition potential, time, and temperature. These cross-sectional octahedral Cu2O microcrystals exhibited high electrocatalytic activity for ethylene (C2H4) production through CO2 reduction. In a 0.1M KHCO3 electrolyte, the Faradaic efficiency for C2H4 reached 42.0% at a potential of -1.376V vs. RHE. During continuous electrolysis over 10h, the FE (C2H4) remained stable around 40%. During electrolysis, the fully exposed (111) crystal faces of Cu2O microcrystals are reduced to Cu0, which enhances C-C coupling and could serve as the main active sites for catalyzing the conversion of CO2 to C2H4.

Role of Interfacial Water Structure in the Electroreduction of NO over Cu2O.

The electrochemical nitric oxide reduction reaction (NORR), which utilizes water as the sole hydrogen source, has the potential to facilitate ammonia production while concurrently mitigating pollutants. However, limited research has been dedicated to characterizing the structure of interfacial water due to the challenges associated with probing this intricate system, impeding the development of more efficient catalysts for the NORR process. Herein, the Cu2O microcrystals with distinct exposed facets, including {100}, {110}, and {111}, are employed for the model catalysts to investigate interfacial water structure and intermediate species in the NORR process. The results from shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS) indicated that the NORR performance in 0.1 M Na2SO4 (with heavy water as the solvent) was positively correlated to the proportion of hydrated Na+ ion water. In addition, a sequence of intermediates from the NORR, including *NOH, *NH, *NH2, and *NH3, was detected by employing a combination of multiple in situ characterization methods. Furthermore, in conjunction with experimental results and theoretical calculations, we revealed the potential reaction pathway of NORR. This study offers novel insights into the NORR mechanism and valuable guidance for the design of high-performance catalysts for ammonia production.

Planar GaN/Cu2O Microcrystal Composite Junction Photoanode for Efficient Solar Water Splitting.

Cu2O microcrystals are electrodeposited on an epitaxial GaN layer on a Si(111) substrate to improve the solar water splitting efficiency of a GaN photoanode. The performance of the GaN/Cu2O composite junction photoanode is investigated as a function of the Cu2O deposition amount for Cu2O microcrystal formation. For optimum Cu2O deposition amount, the photocurrent density is significantly enhanced compared to that of the bare GaN photoanode. The improved water splitting performance is attributed to the built-in electric field and band offsets of the n-GaN/p-Cu2O heterostructure, promoting the separation of photogenerated electrons and holes and the transport of the hole to the surface.

Differentiating the Impacts of Cu2O Initial Low‐ and High‐Index Facets on Their Reconstruction and Catalytic Performance in Electrochemical CO2 Reduction Reaction

AbstractOxide‐derived Cu catalysts from Cu2O microcrystals are capable of electrochemically converting CO2 into various value‐added chemicals. However, their structural transformation and associated preferred products remain unclear, requiring further investigation. Herein, Cu2O microcrystals with controllable low‐ and high‐index facets exposure are fabricated to differentiate the effects of initial exposed facets on their structural reconstruction and product selectivity in electrochemical CO2 reduction reaction. Combined in situ characterizations and theoretical investigation reveal the direct correlations of Cu2O reconstruction and product selectivity to its initial facet exposure. The Cu2O low‐index facet, being more stable with a high energy barrier on material reduction, tends to partially maintain its original crystalline structure and larger Cu2O particle size throughout the transformation. The derived flatter surface and limited Cu2O/Cu interfaces result in a favorable selectivity toward 2‐electron transfer products. The chemically active Cu2O high‐index facet (311) is energetically favorable to be reduced owing to the feasible protonation process, thus experiencing a drastic reconstruction with rich newly formed Cu nanoparticles and evolved fine Cu2O grains; Such a reconstruction creates uncoordinated Cu species and abundant boundaries, benefiting charge transfer and increasing the local pH by confining OH−, thus leading to a high selectivity toward C2+ products.

Interfacial charge transfer effects of α-Fe2O3/Cu2O heterojunction and enhancement mechanism of its photocatalytic oxidation

In order to construct Cu2O based heterostructures with high efficiency of interfacial charge transfer and clarify the enhancing mechanism of its photocatalytic performance for degrading antibiotics, and reveal the characteristics of band reconstruction and the photocatalytic reaction path, the α-Fe2O3/Cu2O heterojunction was established based on hydrothermal method. The crystal plane structure, morphological state, photoelectric conversion properties and photocatalytic degradation kinetics of α-Fe2O3/Cu2O heterojunction were revealed by XRD, XPS, UV-Vis, BET, SEM, TEM and RSM, and the reconstruction principles of bandgap formations of heterojunction were analyzed by the density function theory. The reaction intermediates of levofloxacin were distinguished with HPLC-MS/Ms, and the reactive sites and photocatalytic oxidation paths of levofloxacin were clarified from the frontier electron density calculation. It turned out that the constructed α-Fe2O3/Cu2O heterojunction emerged high energy (111) preferred crystal plane orientation and significantly enhanced the specific surface area and visible spectral excitation efficiency. The micromorphologies of Cu2O, M1-Cu2O, M2-Cu2O and M3-Cu2O crystals were cube, irregular polyhedron and approximate sphere, respectively. The introduction of Fe 3d hybrid orbital in α-Fe2O3/Cu2O heterojunction widened the band gap of Cu2O microcrystals, resulting in the migration of spectral absorption edging to high energy level and causing blueshift. Photogenerated superoxide radicals and hydroxyl radicals were the dominant active species for photocatalytic oxidation of levofloxacin. The removal rate of levofloxacin by α-Fe2O3/Cu2O heterojunction could still reach more than 70% after eight cycles and show high material durability. The ring opening reaction process and decarboxylic reaction of quinolone group and piperazine side chain were the main pathways for photocatalytic oxidation of levofloxacin. This study systematically revealed the interfacial charge transfer characteristics and photocatalytic reaction mechanism of α-Fe2O3/Cu2O heterojunction.

Directional growth of quasi-2D Cu2O monocrystals on rGO membranes in aqueous environments.

The preparation technology of unconventional low-dimensional Cu2O monocrystals, which exhibit specific crystal planes and present significantly unique interfacial and physicochemical properties, is attracting increasing attention and interest. Herein, by integrating a high-temperature oxidation process under vacuum and a pure-water incubation process under ambient conditions, we propose the self-assembled growth and synthesis of quasi-two-dimensional Cu2O monocrystals on reduced graphene oxide (rGO) membranes. The prepared Cu2O crystals have a single (110) crystal plane, regular rectangular morphology, and potentially well conductivity. Experimental and theoretical results suggest that this assembly is attributed to the pre-nucleation clusters aggregation and directional attachment of Cu and O on the rGO membranes in aqueous environment and cation-π interactions between the (110) crystal plane of Cu2O and rGO surface. Our findings offer a potential avenue for the discovery and design of advanced low-dimensional single-crystal materials with specific interfacial properties in a pure aqueous environment.

Single-particle exciton-initiated photo-catalytic reaction mapping on defective cuprous oxide

Although the exciton-triggered photocatalysis has recently been confirmed, so far it is limited to the low-dimensional semiconductors, and the characterization approaches are impossible to image and characterize the photo-catalytic reaction on single semiconductor photocatalysts. Herein by combining dark-field microscopy with 3, 3′, 5, 5′-tetramethylbenzidine as the chromogenic probe, we visually map the exciton-initiated photo-catalytic reaction on defective Cu2O microcrystals in real time at the single-particle level. Single-particle imaging results reveal the heterogeneity in reactivity among different individuals and at different regions within the same microcrystal. Moreover, the reaction rate constant of this photocatalytic reaction is determined as well. The theoretical simulations suggest that the introduction of Mn2+ can modulate the electronic structure and enhance the oxygen affinity of Cu2O, facilitating the production of 1O2. This high spatio-temporal-resolution imaging approach is general, which is also appropriate for investigating the exciton effects on Fe2+-doped Cu2O microcrystals.

Facet-controlled synthesis and morphological evolution of Cu2O microcrystals

Cu2O microcrystals were prepared through reduction of Cu2+ ions by glucose in an alkaline aqueous solution.

Probing Individual Cuprous Oxide Microcrystals towards Carbon Dioxide Reduction by using In Situ Raman‐coupled Scanning Electrochemical Microscopy

AbstractIn this work, the simultaneous investigation of a single cuprous oxide microcrystal towards CO2 electroreduction (CRR, CO2 reduction reaction) by using Raman microscopy and scanning electrochemical microscopy (SECM) is shown. Cu2O microcrystals were electrochemically crystallized on an indium‐doped tin oxide‐substrate (ITO). Structural changes of the Cu2O microcrystal are observed in situ by Raman microcopy, which indicates their fast conversion into elemental Cu at low overpotentials. Simultaneously, detection of products of the CO2 reduction is carried out electrochemically using the sample‐generation tip‐collection mode (SG/TC) of SECM and formate ions are the main product of CRR, as detected by a 10 μm Pt ultramicroelectrode (UME). Thus, with our approach, the very beginning of the CRR (onset potential), potential‐dependent product formation as well as structural changes in the catalyst can be precisely investigated.

Ultra-fast Cu-based A3-coupling catalysts: faceted Cu2O microcrystals as efficient catalyst-delivery systems in batch and flow conditions

Cu(I) catalysts were studied for the synthesis of a propargylamine via A3-coupling of aldehyde, amine, and alkyne, under solvent-free and low loading conditions, using batch microwave or flow thermal heating. We explored ultra-low loading conditions with Cu(I) salts as fast and active catalysts featuring turnover frequencies (TOFs) above 105 h−1. Well-defined octahedral and cubic Cu2O microcrystals were also successfully applied and compared with this reaction. Both types of microcrystals exhibited excellent catalytic activities within minutes, via in situ generation of low dose of Cu(I) ions within the reaction medium, to achieve TON beyond 2000 and recycling up to 10 times in a flow reactor. The study of the catalytic system demonstrated that the activity was surface-structure dependent and allowed for the design of low Cu contamination A3-coupling systems, affording a product at the decigram scale, with Cu contamination below FDA recommendations for drug synthesis, without the need for a purification procedure.

Hydrothermal synthesis of Cu2O with morphology evolution and its effect on visible-light photocatalysis

Cu2O micro-sized crystals was synthesized through a hydrothermal reaction of CuCl2 and NaOH solution adding ascorbic acid (AH2) as reductant. The morphology changed from truncated octahedral to six-corners-{111} truncated octahedral along with the increasing molar ratio of NaOH/CuCl2. The preferential growth rates of the {111} and {110} faces affected by the concentration of [Cu(OH)4]2−, resulting in the morphological evolution. The sufficient AH2 has an etching effect to form a quasi-spherical Cu2O structure. The highly-truncated octahedral Cu2O with the dominant {110} faces has higher adsorption and also photocatalytic activity with a methyl orange (MO) degradation rate of 90.3% under visible light. It’s proposed that the {110} faces of Cu2O microcrystals possess higher photocatalytic activity than {111} faces, and are even more active than the {100} faces.

Rydberg excitons in Cu2O microcrystals grown on a silicon platform

Cuprous oxide (Cu2O) is a semiconductor with large exciton binding energy and significant technological importance in applications such as photovoltaics and solar water splitting. It is also a superior material system for quantum optics that enabled the observation of intriguing phenomena, such as Rydberg excitons as solid-state analogue to highly-excited atomic states. Previous experiments related to excitonic properties focused on natural bulk crystals due to major difficulties in growing high-quality synthetic samples. Here, the growth of Cu2O microcrystals with excellent optical material quality and very low point defect levels is presented. A scalable thermal oxidation process is used that is ideally suited for integration on silicon, demonstrated by on-chip waveguide-coupled Cu2O microcrystals. Moreover, Rydberg excitons in site-controlled Cu2O microstructures are shown, relevant for applications in quantum photonics. This work paves the way for the wide-spread use of Cu2O in optoelectronics and for the development of novel device technologies.

Morphology selective electrodeposition of Cu2O microcrystals on ZnO nanotube arrays as efficient visible-light-driven photo-electrode

ZnO nanotube arrays were synthesized by the electrodeposition method and Cu2O microcrystals with two kinds of morphologies were deposited on ZnO nanotube arrays successfully. At the deposition potential of −0.5 or −0.7 V, the cubic or spherical Cu2O microcrystals were selectively deposited on ZnO nanotube arrays. By adjusting the deposition time, Cu2O microcrystals with different sizes were obtained. The optical properties and photo-electrochemical performance of ZnO/Cu2O were measured. The results showed that the as-prepared ZnO/Cu2O heterojunction exhibited improved visible light absorption and enhanced photocurrent due to the excellent ability of Cu2O microcrystals for harvesting visible light, and the effective separation and transfer of photo-generated electrons and holes owing to p-n junction between ZnO and Cu2O. The experimental results demonstrate that the photo-electrochemical performance of ZnO/Cu2O heterojunction nanotube arrays can be manipulated by controlling the morphology and the size of Cu2O microcrystals.

Rhombic Dodecahedral Cu2O‐Catalysed Synthesis of Novel Alkenyl Pyrazoles

The design of efficient catalyst is of great importance in pyrazole derivatives synthesis. Herein, rhombic dodecahedra Cu2O microcrystals were successfully synthesized, and employed as catalysts in the direct synthesis of alkenyl pyrazoles. The catalytic activity of the obtained Cu2O catalyst toward the synthesis of alkenyl pyrazoles via the reaction of p‐chlorophenyl hydrazone and 2,4‐pentanedione was studied. The results showed that the high yields of alkenyl pyrazoles was achieved by using a rhombic dodecahedra Cu2O catalyst. Moreover, the rhombic dodecahedra also exhibited excellent catalytic activity for a variety of different hydrazones, which demonstrates their potential as a versatile catalyst. The Cu2O catalyst shows good reusability. Hence, the rhombic dodecahedra Cu2O microcrystals can be viewed as a highly useful catalyst for synthesis of alkenyl pyrazoles.

Porous-CdS/Cu2O/graphitic-C3N4 dual p-n junctions as highly efficient photo/catalysts for degrading ciprofloxacin and generating hydrogen using solar energy

We develop facile hydrothermal and precipitation approaches to fabricate porous CdS (pCdS) nanoparticles on octahedral Cu2O (1 1 1) microcrystals on C3N4 and thus enabling to build novel pCdS/Cu2O/g-C3N4 dual p-n Junctions. This dual p-n Junction structure would enhance charge carrier separation and transfer ability for achieving highly efficient photo/catalysis, which is much better than individual g-C3N4 or pCdS/Cu2O p-n junctions. The degradation of ciprofloxacin (CIP) using pCdS/Cu2O/g-C3N4 composites as a catalyst will make the reaction remarkably faster (over 18 times) than pure g-C3N4. Its photocatalytic effect is well demonstrated through water splitting under simulated sunlight irradiation, where the hydrogen generation rate of 1.84 mmol h−1 g−1, i.e. over 18.40 times higher than pure g-C3N4, is achieved benefiting from its higher charge separation rate. This work provides not only a new insight into the catalyst design but also offer a stable and reusable pCdS/Cu2O/g-C3N4 dual p-n Junctions composite as a highly efficient catalyst for use in environmental rumination and hydrogen generation. The comparison of the photocatalytic hydrogen production performance of the presented photocatalyst with some recent papers published especially in leading journals in this field proves further its significant advancement in this field.

Controlled synthesis of Cu2O microcrystals in membrane dispersion reactor and comparative activity in heterogeneous Fenton application

A surfactant-free approach is proposed to fabricate various-shaped Cu2O particles with good uniformity by ceramic membrane dispersion. Glucose reduced cupric salt and precipitated Cu2O (dimension ca. 1 μm and crystal size 18.5 nm) whose homogeneity was distinctly improved by distributing glucose solution through the ceramic mesoporous membrane. Particle shape including cube, sphere-like, octahedron and eight-pod was controlled kinetically by changing the concentration of sodium carbonate and sodium citrate with constant copper concentration. Morphologic transformation mechanism was studied with diffraction intensity ratio of (111)/(100) crystal planes. Micro-cubes formed at low pH and octahedral ones formed at high pH since crystal facet (111) is more stable than (100) with increased alkalinity. At the same pH, eight-pod grains were formed instead of cubes by adding citrate anions. Cu2O powders in octahedral shape was of the highest catalytic activity to degrade the organic pollutants in a heterogeneous Fenton reaction. CODs in an industrial pulp wastewater was eliminated from initial value 133 mg/L as low as to 26 mg/L. Reduction rate of CODs in water by the octahedral Cu2O was 80% while the commercial Cu2O was only 30%.

Controllable synthesis of cuprite (Cu 2 O) microcrystals and their shape‐dependent photocatalytic performances

Microcrystals of cuprite (Cu2O) samples exhibiting octahedral and spherical morphologies were synthesised via a facile chemical method and were then characterised by X-ray powder diffraction and scanning electron microscopy. It was observed that the potassium sodium tartrate (KNaC4H4O6·4H2O, PST) and gelatin addition had a prominent effect on the morphologies. The possible formation mechanism of Cu2O microcrystals was discussed based on the effects of PST and gelatin. Furthermore, the photocatalytic activities of the prepared Cu2O microcrystals were investigated by UV–vis spectrophotometry, demonstrating that their behavior was influenced by the different morphologies, and the Cu2O microspheres possessed the highest activity.

3D Network and 2D Paper of Reduced Graphene Oxide/Cu2O Composite for Electrochemical Sensing of Hydrogen Peroxide.

In this study, two-dimensional (2D) and three-dimensional (3D) freestanding reduced graphene oxide-supported Cu2O composites (Cu2O-rGO) were synthesized via simple and cost-efficient hydrothermal and filtration strategies. The structural characterizations clearly showed that highly porous 3D graphene aerogel-supported Cu2O microcrystals (3D Cu2O-GA) have been successfully synthesized, and the Cu2O microcrystals are uniformly assembled in the 3D GA. Meanwhile, paper-like 2D reduced graphene oxide-supported Cu2O nanocrystals (2D Cu2O-rGO-P) have also been prepared by a filtration process. It was found that the products prepared from different precursors and methods exhibited different sensing performances for H2O2 detection. The electrochemical measurements demonstrated that the 3D Cu2O-GA has high electrocatalytic activity for the H2O2 reduction and excellent sensing performance for the electrochemical detection of H2O2 with a detection limit of 0.37 μM and a linear detection range from 1.0 μM to 1.47 mM. Meanwhile, the 2D Cu2O-rGO-P structure also showed good electrochemical sensing performance toward H2O2 detection with a much wider linear response over the concentration range from 5.0 μM to 10.56 mM. Compared to the previously reported sensing materials, the as-obtained 2D and 3D Cu2O-rGO materials exhibited higher electrochemical sensing properties toward the detection of H2O2 with high sensitivity and selectivity. The 2D and 3D Cu2O-rGO composites also exhibited high sensing performance for the real-time detection of H2O2 in human serum. The present study indicates that 2D and 3D graphene-Cu2O composites have promising applications in the fabrication of nonenzymatic electrochemical sensing devices.

New electrochemiluminescence catalyst: Cu2O semiconductor crystal and the enhanced activity of octahedra synthesized by iodide ions coordination

Cuprous oxide (Cu2O) crystals are usually used as the photocatalysts of water splittings and carbon monoxide oxidations. Herein, we report the new catalytic properties of Cu2O to the electrochemilumenescence (ECL) reactions of luminol and oxygen. Adjusting the shape of Cu2O microcrystals from cube to octahedra also facilities the improved electrocatalytic acticity, where octahedral Cu2O microcrystals possess higher ECL signal by 25% at −0.6 V (versus Ag/AgCl) at pH 7.4. The octahedral Cu2O microcrystals are synthesized by the coordination of iodide ions to the surface, which alters the crystals shapes from cubes to octahedra. Size-distribution of octahedra is improved with this mehod compared to the previous studies with only hydroxide ions as the coordinates. The catalytic activity of octahedral Cu2O crystals is expected to be compared with the noble metal nanomaterials and constructed the high-efficiency and low-cost ECL biosensors.

Investigation on the shape evolution of Cu2O crystals in the antibacterial process

In this work Cu2O microcrystals with various morphologies including octahedrons, cubes and hollow spheres were employed as the antimicrobial for the devitalization of Escherichia coli (E. coli). It was found that during the devitalization of E. coli, Cu2O microcrystals with various shapes presented similar change trend and finally was converted into flowerlike microstructures constructed by abundant nanosheets. Also, the shape change always started from {100} planes.