Shape evolution of Cu2O nanostructures via kinetic and thermodynamic controlled growth

Ligand-Mediated Control of the Surface Oxidation States of Copper Nanoparticles Produced by Laser Ablation

We report on studies that demonstrate how the chemical composition of the surface of copper nanoparticles (CuNPs) - in terms of percentage copper(I/II) oxides - can be varied by the presence of N-donor ligands during their formation via laser ablation. Changing the chemical composition thus allows systematic tuning of the surface plasmon resonance (SPR) transition. The trialed ligands include pyridines, tetrazoles, and alkylated tetrazoles. CuNPs formed in the presence of pyridines, and alkylated tetrazoles exhibit a SPR transition only slightly blue shifted with respect to CuNPs formed in the absence of any ligand. On the other hand, the presence of tetrazoles results in CuNPs characterized by a significant blue shift of the order of 50-70 nm. By comparing these data also with the SPR of CuNPs formed in the presence of carboxylic acids and hydrazine, this work demonstrates that the blue shift in the SPR is due to tetrazolate anions providing a reducing environment to the nascent CuNPs, thus preventing the formation of copper(II) oxides. This conclusion is further supported by the fact that both AFM and TEM data indicate only small variations in the size of the nanoparticles, which is not enough to justify a 50-70 nm blue-shift of the SPR transition. High-resolution transmission electron microscopy (HRTEM) and selected area electron diffraction (SAED) studies further confirm the absence of Cu(II)-containing CuNPs when prepared in the presence of tetrazolate anions.

Protocol to modify the surface of nano-Cu2O using facet controlling and MOF shell coating

The morphology of nano-Cu₂O profoundly determines its catalytic performance. Here, we provide two universal and reliable techniques to modify the surface of nano-Cu₂O. First, we detail steps for the systematic tuning of the exposed facets of nano-Cu₂O ranging from low index to high index using reductant-controlled technique in the presence of sodium dodecyl sulfate. Second, we describe steps for facet-directed precipitation in which the morphology-dependent ZIF-8 (a type of zeolitic imidazolate frameworks) shells on different nano-Cu₂O are well introduced. For complete details on the use and execution of this protocol, please refer to Luo et al. (2022).

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. Various shapes of Cu2O microcrystals were obtained by adjusting the reaction temperature, NaOH concentration,...

A Sensitive Visible Light Photodetector Using Cobalt-Doped Zinc Ferrite Oxide Thin Films

In this study, a highly sensitive trilayer photodetector using Co-doped ZnFe₂O₄ thin films annealed at 400 °C was synthesized successfully. Trilayer-photodetector devices with a film stack of 5 at % Co-doped-zinc-ferrite-thin-film/indium-tin-oxide on p⁺-Si substrates were fabricated by radio-frequency sputtering. The absorbance spectra, photoluminescence spectra, transmission electron microscopy images, and I-V characteristics under various conditions were comprehensively investigated. The outstanding performance of trilayer-photodector devices was measured, including a high photosensitivity of 181 and a fast photoresponse time with a rise time of 10.6 ms and fall time of 9.9 ms under 630 nm illumination. Therefore, the Co-doped ZnFe₂O₄ thin film is favorable for potential photodetector applications in visible light regions.

Controllable CO adsorption determines ethylene and methane productions from CO2 electroreduction

Among all CO₂ electroreduction products, methane (CH₄) and ethylene (C₂H₄) are two typical and valuable hydrocarbon products which are formed in two different pathways: hydrogenation and dimerization reactions of the same CO intermediate. Theoretical studies show that the adsorption configurations of CO intermediate determine the reaction pathways towards CH₄/C₂H₄. However, it is challenging to experimentally control the CO adsorption configurations at the catalyst surface, and thus the hydrocarbon selectivity is still limited. Herein, we seek to synthesize two well-defined copper nanocatalysts with controllable surface structures. The two model catalysts exhibit a high hydrocarbon selectivity toward either CH₄ (83%) or C₂H₄ (93%) under identical reduction conditions. Scanning transmission electron microscopy and X-ray absorption spectroscopy characterizations reveal the low-coordination Cu⁰ sites and local Cu⁰/Cu⁺ sites of the two catalysts, respectively. CO-temperature programed desorption, in-situ attenuated total reflection Fourier transform infrared spectroscopy and density functional theory studies unveil that the bridge-adsorbed CO (CO_B) on the low-coordination Cu⁰ sites is apt to be hydrogenated to CH₄, whereas the bridge-adsorbed CO plus linear-adsorbed CO (CO_B + CO_L) on the local Cu⁰/Cu⁺ sites are apt to be coupled to C₂H₄. Our findings pave a new way to design catalysts with controllable CO adsorption configurations for high hydrocarbon product selectivity.

Effect of Ag Co-catalyst on TiO2-Cu2O nanocomposites structure and apparent visible photocatalytic activity

Although Cu₂O is a commonly used narrow band gap semiconductor to fabricate visible response photocatalysts, up to date there are only a few reports on Ag co-catalysed TiO₂-Cu₂O nanocomposites. Herein we report a facile wet chemical synthesis approach to prepare TiO₂-Ag-Cu₂O ternary hybrid nanomaterials. Uniquely, both the effect of Ag content and the synthesis sequence of Ag deposition step was investigated on the visible decoloration rate. The crystal structure, morphology, optical and dark adsorption properties of the nanostructures were characterized by XRD, SEM, TEM and diffuse reflectance, respectively. Due to the mixed indirect and direct nature of the nanocomposites, the band gap estimation was performed by using both Tauc plot and differential reflectance model. The dark adsorption properties of catalysts could be typically well-approximated by pseudo-second order kinetics, while TiO₂-Ag(5%)-Cu₂O catalyst cannot be described by standard models due to a delayed adsorption behaviour observed in the first 50 min. The apparent visible activities followed pseudo-zero order kinetics. It was found that TiO₂-Ag(3%)-Cu₂O catalyst exhibited the highest rate constant which was ca. two times as high as that of the binary TiO₂-Cu₂O catalyst. The synthesis sequence of the Ag deposition step significantly altered the material properties which resulted in different dark adsorption and apparent visible activities.

Interplay between halides in the electrolyte and the chemical states of Cu in Cu-based electrodes determines the selectivity of the C2product

The interaction between selectivity/activity (CH₄and C₂H₄) and electrode structure (Cu⁰, Cu⁺and Cu²⁺)/electrolyte properties (Cl⁻, Br⁻and I⁻) was investigated.

Preparation of Cu-Al/SiO2 Porous Material and Its Effect on NO Decomposition in a Cement Kiln

Nitrogen oxide (NOx) emissions have attracted much attention for increasing concern on the quality of the atmospheric environment. In view of NO decomposition in the cement production process, the preparation of Cu-Al/SiO₂ porous material and its effect on NO decomposition were studied, and the denitrification mechanism was proposed in this paper. The NO decomposition performance of the Cu-Al/SiO₂ porous material was tested via the experimental setup and infrared spectrometer and micro gas chromatography (GC). The result shows that the Cu-Al/SiO₂ porous material with the template of cetyltrimethylammonium bromide (CTAB) had a better NO decomposition rate than materials with other templates when the temperature was above 500 °C, and NO decomposition rate could approach 100% at high temperatures above 750 °C. Structure analysis indicates that the prepared Cu-Al/SiO₂ material structure was a mesoporous structure. The X-Ray Diffraction (XRD) and Ultraviolet–visible spectrophotometry (UV–Vis) results of the denitrification product show that the Cu-Al/SiO₂ material mainly decomposed to Cu₂O and Si₂O, and the CuO decomposed to Cu₂O and O₂ at high temperature. The Cu(I)O was considered as the active phase. The redox process between Cu(II)O and Cu(I)O was thought to be the denitrification mechanism of the Cu-Al/SiO₂ porous material.

Dynamic growth of rhombic dodecahedral Cu2O crystals controlled by reaction temperature and their size-dependent photocatalytic performance

Compared with low-index {100} or {111} planes of Cu₂O crystals, rhombic dodecahedra (RD) Cu₂O crystals exposing 12 {110} facets exhibit the most superior photodegradation of organic pollutants. Herein, a series of RD Cu₂O crystals with different sizes were successfully synthesized by precisely adjusting the reaction temperature ranging from 40 °C to 100 °C. The results revealed that truncated rhombic dodecahedra (TRD) Cu₂O crystals were fabricated when the temperatures was 40 °C. More importantly, on raising the temperature to above 40 °C, Cu₂O architectures dynamically evolved from TRD to RD. Meanwhile, the sizes gradually decreased with elevation of the temperature, while the RD morphology of Cu₂O crystals remained, demonstrating the importance of temperature for determining the morphology and size of Cu₂O crystals. In addition, we also carefully investigated the visible-light photodegradation performance of Cu₂O crystals for methyl orange (MO). RD Cu₂O crystals exhibited superior photocatalytic activity compared with TRD, and showed size-dependent photocatalytic activity for MO. The photocatalytic activity of RD Cu₂O crystals can be greatly improved by decreasing the size. In particular, RD-60 with the minimum size achieved the best photocatalytic properties compared to the other RD and TRD Cu₂O crystals, and still displayed high photocatalytic efficiency even after three cycles. Such results advance the understanding that temperature modulation serves as an effective means to fabricate RD Cu₂O crystals.

Compared with low-index {100} or {111} planes of Cu₂O crystals, rhombic dodecahedra (RD) Cu₂O crystals exposing 12 {110} facets exhibit the most superior photodegradation of organic pollutants.

Reductive and Coordinative Effects of Hydrazine in Structural Transformations of Copper Hydroxide Nanoparticles

Shape-specific copper oxide nanostructures have attracted increasing attention due to their widespread applications in energy conversion, sensing, and catalysis. Advancing our understanding of structure, composition, and surface chemistry transformations in shaped copper oxide nanomaterials during changes in copper oxidation state is instrumental from both applications and preparative nanochemistry standpoints. Here, we report the study of structural and compositional evolution of amorphous copper (II) hydroxide nanoparticles under hydrazine reduction conditions that resulted in the formation of crystalline Cu₂O and composite Cu₂O-N₂H₄ branched particles. The structure of the latter was influenced by the solvent medium. We showed that hydrazine, while being a common reducing agent in nanochemistry, can not only reduce the metal ions but also coordinate to them as a bidentate ligand and thereby integrate within the lattice of a particle. In addition to shape and composition transformation of individual particles, concurrent interparticle attachment and ensemble shape evolution were induced by depleting surface stabilization of individual nanoparticles. Not only does this study provide a facile synthetic method for several copper (I) oxide structures, it also demonstrates the complex behavior of a reducing agent with multidentate coordinating ability in nanoparticle synthesis.

Noble metal-modified faceted anatase titania photocatalysts: Octahedron versus decahedron

Octahedral anatase particles (OAP, with eight equivalent {101} facets) and decahedral anatase particles (DAP, with two additional {001} facets) were modified with nanoparticles of noble metals (Au, Ag, Cu). The titania morphology, expressed by the presence of different arrangements of exposed crystal facets, played a key role in the photocatalytic properties of metal-modified faceted titania. In the UV/vis systems, two-faceted configuration of DAP was more favorable for the reaction efficiency than single-faceted OAP because of an efficient charge separation described by the transfer of electrons to {101} facets and holes to {001} facets. Time-resolved microwave conductivity (TRMC) and reversed double-beam photoacoustic spectroscopy (RDB-PAS) confirmed that distribution of electron traps (ET) and mobility of electrons were key-factors of photocatalytic activity. In contrast, metal-modified OAP samples had higher photocatalytic activity than metal-modified DAP and metal-modified commercial titania samples under visible light irradiation. This indicates that the presence of single type of facets ({101}) is favorable for efficient electron transfer via shallow ET, whereas intrinsic properties of DAP result in fast charge carriers' recombination when gold is deposited on {101} facets (migration of "hot" electrons: Au→{101}→Au).

pH-Control as a way to fine-tune the Cu/Cu2O ratio in radiation induced synthesis of Cu2O particles

In this work we have optimized the γ-radiation induced synthesis of Cu-Cu2O particles from aqueous CuSO4 solution by investigating the effect of pH. The obtained precipitate was analyzed by XRD and SEM techniques. The results indicated that at solution pH lower than 3.75, quasi-spherical Cu agglomerates can be formed while at pH higher than 4.40 only octahedron-shaped Cu2O particles are produced. At solution pH in the range from 3.75 to 4.40, a Cu-Cu2O mixture is produced. It was found that the relative amount of Cu2O in the Cu-Cu2O precipitate increases with pH in the studied range. The influence of solution pH on the Cu/Cu2O ratios in the product can be explained on the basis of pH-dependent competition kinetics between the reactions leading to either Cu or Cu2O formation. As a consequence, the composition and morphology of the Cu-Cu2O precipitate can be tuned by controlling pH of the aqueous CuSO4 solution during the γ-radiation induced synthesis.

Preparation and characterization of Cu2O nano-particles and their photocatalytic degradation of fluroxypyr

Cu₂O nano-particles were prepared by the liquid-phase reduction method and the effect of the dispersant was studied. The microstructure, surface morphology and optical properties of Cu₂O nano-particles were characterized by X-ray diffractometer, X-ray photoelectron spectroscopy, nitrogen static adsorption, scanning electron microscope, particle size analysis, ultraviolet visible light spectrophotometer and photoluminescence spectrometer. The photocatalytic degradation of fluroxypyr using Cu₂O was studied by the response surface methodology, and the quadratic multinomial mathematical model was established. The results indicated that the Cu₂O crystal particles prepared using the dispersant of polyvinylpyrrolidone were of high purity with the preferential orientation of (111). The average particle size was 605.4 ± 124.8 nm, the specific surface area was 22.641 m²/g, the band gap was approximately 2.04 eV and the absorption edge was about 650 nm. R² of the established quadratic model was 0.9973 and had good fitness, indicating that the established model was reliable. The optimal degradation conditions were obtained as follows: the initial concentration of fluroxypyr was 11.17 mg/L, the pH of the solution was 12.0 and the H₂O₂ concentration was 15 mg/L. The degradation rate of fluroxypyr could reach 83.2% and the relative error was 1.20%. After nine times of recycling, more than 75% of fluroxypyr could be degraded.

Growth of Cuprous Oxide Particles in Liquid-Phase Synthesis Investigated by X-ray Laser Diffraction

Cuprous oxide (Cu₂O) particles obtained by surfactant-assisted liquid-phase synthesis have cuboid shapes but the internal structures are difficult to be visualized by electron microscopy. Herein, we investigated the internal structures of numerous individual Cu₂O particles with submicrometer dimensions by X-ray diffraction imaging (XDI) using X-ray free-electron laser (XFEL) pulses. The reconstructed two-dimensional electron density maps, which displayed inhomogeneous internal structures, were divided into five classes characterized by the positions and shapes of high and low electron density areas. Further analysis of the maps in each class by a manifold learning algorithm revealed that the internal structures of Cu₂O particles varied in correlation with total electron density while retaining the characteristics within each class. On the basis of the analyses, we proposed a growth mechanism to yield the inhomogeneity in the internal structures of Cu₂O particles in surfactant-mediated liquid-phase synthesis.

Facet- and structure-dependent catalytic activity of cuprous oxide/polypyrrole particles towards the efficient reduction of carbon dioxide to methanol

The preparation of cost-effective, stable catalysts for the selective reduction of carbon dioxide (CO2) to C1 products such as methanol is extremely important because methanol can be used directly as a fuel or it can be converted into other value-added products. However, the catalysts currently used for the reduction of CO2 to methanol exhibit poor selectivity, poor stability and very low faradaic efficiency. Herein, we used low-cost, stable cuprous oxide/polypyrrole (Cu2O/Ppy) particles having structures of octahedra and icosahedra (microflowers) that were prepared on linen texture (LT) papers for the selective reduction of CO2 to form a value-added single C1 product, methanol. The Cu2O/Ppy particles possessing both octahedral and microflower shapes with exposed low-index (111) facets and high-index (311) and (211) facets are denoted as Cu2O(OL-MH)/Ppy particles. The as-prepared Cu2O(OL-MH)/Ppy particles exhibited high catalytic activity and selectivity towards the electrochemical reduction of CO2 at -0.85 V vs. RHE to form methanol, with a faradaic efficiency of 93 ± 1.2% and an average methanol formation rate of 1.61 ± 0.02 μmol m-2 s-1. The X-ray photoelectron spectroscopy (XPS) analysis revealed that the pyrrolic nitrogen atoms present in the Ppy shell played a dominant role as active sites for CO2 molecules. The Raman bands of Ppy and Cu2O did not shift even after being subjected to electrolysis for several hours, suggesting superior stability of the Cu2O(OL-MH)/Ppy particles. The high resolution microscopic, spectroscopic, diffraction and electrochemical analysis results clearly revealed that the Ppy shell protected the Cu2O particles and avoided corrosion, dissolution, and structural and crystal facet changes, leading to greater stability. The low-cost, durable, flexible, and catalytically active Cu2O(OL-MH)/Ppy LT paper holds great potential for catalytic, photocatalytic and energy storage applications.

Controlled Synthesis of Cu and Cu₂O NPs and Incorporation of Octahedral Cu₂O NPs in Cellulose II Films

In this study, Cu and Cu₂O nanoparticles (NPs) were synthesized through chemical reduction of soluble copper-chelating ligand complexes using formaldehyde as a reducing agent. The influence of various chelating ligands, such as ethylenediaminetetraacetic acid (EDTA), diethylenetriaminepentaacetic acid (DTPA), and a surface-active derivative of DTPA (C₁₂-DTPA), as well as surfactants (i.e., hexadecyltrimethylammonium bromide (CTAB), dodecyltrimethylammonium chloride (DoTAC), sodium dodecyl sulfate (SDS), and dimethyldodecylamine-N-oxide (DDAO)), on morphology and the composition of produced NPs was investigated. In the absence of surfactants, spherical copper particles with polycrystalline structure could be obtained. X-ray diffraction (XRD) analysis revealed that, in the presence of EDTA, the synthesized NPs are mainly composed of Cu with a crystallite size on the order of 35 nm, while with DTPA and C₁₂-DTPA, Cu₂O is also present in the NPs as a minority phase. The addition of ionic surfactants to the copper–EDTA complex solution before reduction resulted in smaller spherical particles, mainly composed of Cu. However, when DDAO was added, pure Cu₂O nano-octahedrons were formed, as verified by high-resolution scanning electron microscopy (HR-SEM) and XRD. Furthermore, a hybrid material could be successfully prepared by mixing the octahedral Cu₂O NPs with cellulose dissolved in a LiOH/urea solvent system, followed by spin-coating on silica wafers. It is expected that this simple and scalable route to prepare hybrid materials could be applied to a variety of possible applications.

Electrochemical Synthesis of Cu2O Concave Octahedrons with High-Index Facets and Enhanced Photoelectrochemical Activity

High-index-faceted nano-/microcrystals exhibit enhanced catalytic activity and can thus serve as new-generation catalysts owing to their high density of low-coordinated atoms, leading to significantly enhanced catalytic activity. In this study, an effective electrochemical approach termed cyclic scanning electrodeposition (CSE) was developed to convert a thin Cu film into Cu₂O concave octahedrons enclosed by 24 {344} high-index facets at room temperature with high yield and high throughput. The formation mechanism and the role of each ion in the electrolyte were systematically studied, which facilitated the design of a high-index-faceted metal/metal oxide through CSE. We also presented a general formula to identify the structure of an individual crystal enclosed by {khh} high-index facets based on the crystals oriented along three low-index zone axes and imaged by transmission electron microscopy. Experimental results demonstrated the Cu₂O concave octahedrons to be highly efficient, cost-effective catalysts for photoelectrochemical hydrogen production. This new technology is a promising route for the synthesis of metal or metal oxide crystals with high activity and has a great potential for several advanced applications, such as clean energy conversion.

Solution-phase synthesis of transition metal oxide nanocrystals: Morphologies, formulae, and mechanisms

In this review, we provide a broad overview of solution-phase synthesis of transition metal oxide nanocrystals (NCs), including a substantial catalog of published methods, and a unifying classification and discussion. Prevalent subcategories of solution-phase synthesis are delineated and general features are summarized. The diverse morphologies achievable by solution-phase synthesis are defined and exemplified. This is followed by sequential consideration of the solution-phase synthesis of first-row transition metal oxides. The common oxides of Ti, V, Mn, Fe, Co, Ni, Cu, and Zn are introduced; major crystal lattices are presented and illustrated; representative examples are explained; and numerous synthesis formulae are tabulated. Following this presentation of experimental studies, we present an introduction to theories of NC nucleation and growth. Various models of NC nucleation and growth are addressed, and important concepts determining the growth and structure of colloidal NCs are explained. Overall, this review provides an entry into systematic understanding of solution-phase synthesis of nanocrystals, with a reasonably comprehensive survey of results for the important category of transition metal oxide NCs.

One-pot photoassisted synthesis, in situ photocatalytic testing for hydrogen generation and the mechanism of binary nitrogen and copper promoted titanium dioxide

One-pot photosynthesis and in situ testing of binary codoped Cu(0)–N-TiO₂ yields hydrogen rate 675 μmol g⁻¹ h⁻¹; photoluminescence shows mechanism by excitation of N substitutional site.

Hollow CuxO (x = 2, 1) micro/nanostructures: synthesis, fundamental properties and applications

In this review, we comprehensively summarize the important advances in hollow Cu_xO micro/nanostructures, including the universal synthesis strategies, the interfacial Cu–O atomic structures as well as the intrinsic properties, and potential applications. Remarks on emerging issues and promising research directions are also discussed.

Post-illumination activity of SnO2 nanoparticle-decorated Cu2O nanocubes by H2O2 production in dark from photocatalytic "memory"

Most photocatalysts only function under illumination, while many potential applications require continuous activities in dark. Thus, novel photocatalysts should be developed, which could store part of their photoactivity in “memory” under illumination and then be active from this “memory” after the illumination is turned off for an extended period of time. Here a novel composite photocatalyst of SnO₂ nanoparticle-decorated Cu₂O nanocubes is developed. Their large conduction band potential difference and the inner electrostatic field formed in the p-n heterojunction provide a strong driving force for photogenerated electrons to move from Cu₂O to SnO₂ under visible light illumination, which could then be released to react with O₂ in dark to produce H₂O₂ for its post-illumination activity. This work demonstrates that the selection of decoration components for photocatalysts with the post-illumination photocatalytic “memory” could be largely expanded to semiconductors with conduction band potentials less positive than the two-electron reduction potential of O₂.

Facet-Controlled Synthetic Strategy of Cu2O-Based Crystals for Catalysis and Sensing

Shape-dependent catalysis and sensing behaviours are primarily focused on nanocrystals enclosed by low-index facets, especially the three basic facets ({100}, {111}, and {110}). Several novel strategies have recently exploded by tailoring the original nanocrystals to greatly improve the catalysis and sensing performances. In this Review, we firstly introduce the synthesis of a variety of Cu₂O nanocrystals, including the three basic Cu₂O nanocrystals (cubes, octahedra and rhombic dodecahedra, enclosed by the {100}, {111}, and {110} facets, respectively), and Cu₂O nanocrystals enclosed by high-index planes. We then discuss in detail the three main facet-controlled synthetic strategies (deposition, etching and templating) to fabricate Cu₂O-based nanocrystals with heterogeneous, etched, or hollow structures, including a number of important concepts involved in those facet-controlled routes, such as the selective adsorption of capping agents for protecting special facets, and the impacts of surface energy and active sites on reaction activity trends. Finally, we highlight the facet-dependent properties of the Cu₂O and Cu₂O-based nanocrystals for applications in photocatalysis, gas catalysis, organocatalysis and sensing, as well as the relationship between their structures and properties. We also summarize and comment upon future facet-related directions.

Arc-melting to narrow the bandgap of oxide semiconductors

The bandgap of a series of oxide semiconductors is narrowed by a quick and facile arc-melting method. A defective structure is formed in the fast melting and cooling process without changing its phase structure. Enhanced optical and electrical properties are found in the arc-melted oxide, such as enhanced photocatalytic properties of the arc-melted ZnO under visible light.