A Critical Study of Cu2O: Synthesis and Its Application in CO2 Reduction by Photochemical and Electrochemical Approaches

Copper oxide (Cu2O) is a potential material as a catalyst for CO2 reduction. Cu2O nanostructures have many advantages, including interfacial charge separation and transportation, enhanced surface area, quantum efficiency, and feasibility of modification via composite development or integration of the favorable surface functional groups. We cover the current advancements in the synthesis of Cu2O nanomaterials in various morphological dimensions and their photochemical and electrochemical applications, which complies with the physical enrichment of their enhanced activity in every application they are employed in. The scope of fresh designs, namely composites or the hierarchy of copper oxide nanostructures, and various ways to improve CO2 reduction performance are also discussed in this review. Photochemical and electrochemical CO2 transformations have received tremendous attention in the last few years, thanks to the growing interest in renewable sources of energy and green facile chemistry. The current review provides an idea of current photochemical and electrochemical carbon dioxide fixing techniques by using Cu2O-based materials. Carboxylation and carboxylative cyclization, yield valuable chemicals such as carboxylic acids and heterocyclic compounds. Radical ions, which are induced by photo- and electrochemical reactions, as well as other high-energy organic molecules, are regarded as essential mid-products in photochemical and electrochemical reactions with CO2. It has also been claimed that CO2 can be activated to form radical anions.

Rapid fabrication of silver–cuprous oxide core–shell nanowires for visible light photocatalysts

This work reports a novel method that enables facile fabrication of Ag–Cu₂O core–shell nanowires (Ag@Cu₂O NWs) for visible light photocatalysts.

Nitrogen dioxide sensing based on multiple-morphology cuprous oxide mixed structures anchored on reduced graphene oxide nanosheets at room temperature

Sensitive detection of trace nitrogen dioxide (NO₂) gas at room temperature is of urgent necessity in the fields of healthcare and environment monitoring. To achieve this goal, we report on a porous composite film featuring reduced graphene oxide (rGO) nanosheets as the template platform of nanostructured cuprous oxide (Cu₂O) nanowires and nanoparticles via a hydrothermal method. The sensor performance was investigated in terms of sensing response, optimal operation temperature, repeatability, long-term stability, selectivity and humidity effect on NO₂ sensing. The sensor response achieved 0.66 towards 50 ppb NO₂ gas with a full recovery at room temperature (25 °C ± 2 °C), which was among the best cases of Cu₂O-related NO₂ detection concerning sensor response and operation temperature. Moreover, a modest repeatability, stability, selectivity as well as a negligible humidity effect on NO₂ sensing were exhibited. A mass of interspaces existing within nanostructured composites as well as the synergistic effect between rGO and Cu₂O materials endowed the sensing layer with favorable gas accessibility and sufficient gas-solid interaction. Simultaneously, highly conductive rGO nanosheets facilitated an effective electron transfer and collection. In brief, the as-prepared rGO/Cu₂O sensors showed a competitive room temperature detection capability for ppb-level NO₂ gas, providing a vast potential in the future applications such as the real-time monitoring of ultralow emission.

Highly Sensitive p + n Metal Oxide Sensor Array for Low-Concentration Gas Detection

Nowadays, despite the easy fabrication and low cost of metal oxide gas sensors, it is still challenging for them to detect gases at low concentrations. In this study, resistance-matched p-type Cu₂O and n-type Ga-doped ZnO, as well as p-type CdO/LaFeO₃ and n-type CdO/Sn-doped ZnO sensors were prepared and integrated into p + n sensor arrays to enhance their gas-sensing performance. The materials were characterized by scanning electron microscopy, transmittance electron microscopy, and X-ray diffractometry, and gas-sensing properties were measured using ethanol and acetone as probes. The results showed that compared with individual gas sensors, the response of the sensor array was greatly enhanced and similar to the gas response product of the p- and n-type gas sensors. Specifically, the highly sensitive CdO/LaFeO₃ and CdO/Sn-ZnO sensor array had a high response of 21 to 1 ppm ethanol and 14 to 1 ppm acetone, with detection limits of <0.1 ppm. The results show the effect of sensor array integration by matching the two sensor resistances, facilitating the detection of gas at a low concentration.

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-step synthesis of novel Cu@polymer nanocomposites through a self-activated route and their application as nonenzymatic glucose sensors

Novel core–shell Cu@polymer nanocomposites were synthesized through a one-step self-activated route and developed as nonenzymatic glucose sensor.

The exceptional adsorption ability and gas-detection sensitivity of Cu2O with tunable morphologies

The systematic and delicate geometry control of Cu₂O nanostructures with different size can be achieved by simply tuning the dropping speed of NH₂OH HCl, the volume of solvent and the concentration of NaOH.

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.

Facile synthesis of Cr-decorated hexagonal Co₃O₄ nanosheets for ultrasensitive ethanol detection

Cr-decorated hexagonal Co3O4 nanosheets were synthesized by a facile hydrothermal method on a SiO2/Si substrate, followed by a simple physical deposition of Cr film and a thermal annealing treatment. The Co3O4 nanosheets possess a porous and polycrystalline structure consisting of Co3O4 nanoparticles; Cr2O3 nanoparticles are uniformly formed on the surface of the Co3O4 nanosheets after the annealing treatment. The ethanol-sensing properties of the Cr-decorated hexagonal Co3O4 nanosheets were investigated in detail, and compared to pure hexagonal Co3O4 nanosheets, they show unique sensing properties toward ethanol, including high response (5.4) even when the ethanol concentration is as low as 10 ppm, ultrafast response (1 s) and recovery (7 s) rates, and good selectivity at a 300 °C operating temperature. These properties make the Cr-decorated hexagonal Co3O4 nanosheets good candidates for ethanol detection.

Recent advances in hybrid Cu2O-based heterogeneous nanostructures

Hybrid Cu2O-based heterogeneous nanostructures possess novel synergistic properties that arise from the integrated interaction between the disparate components, thereby showing promising potential for various important applications including solar cells, carbon monoxide oxidation, photocatalysts, field emission, sensors, templates and so on. With the rapid progress in nanomaterials science and nanotechnology, hybrid Cu2O-based heterogeneous nanostructures with well-controlled compositions, shapes and sizes have been rationally designed and synthesized. This review attempts to summarize the important advances in the development of different types of hybrid Cu2O-based heterogeneous nanostructures, such as hybrid Cu2O-metal nanostructures, hybrid Cu2O-metal oxide nanostructures and hybrid Cu2O-carbon nanostructures. The correlations between the improved performances and interfacial structures of the hybrid Cu2O-based heterogeneous nanostructures are discussed based on some important and representative examples. Several key scientific issues and perspective research directions in this field are also given.

Synthesis and size-dependent electrochemical nonenzymatic H2O2 sensing of cuprous oxide nanocubes

The smaller size Cu₂O nanocubes can effectively increase the electrocatalytic active areas and subsequently promote electron transfer in the reduction of H₂O₂.

Atmospheric-pressure microplasma as anode for rapid and simple electrochemical deposition of copper and cuprous oxide nanostructures

Atmospheric-pressure microplasma could be applied as gaseous anode for transferring positive charges and controllably electrodepositing Cu and Cu₂O nanocrystals.

Template-free synthesis of Cu2O–Co3O4 core–shell composites and their application in gas sensing

Cu₂O–Co₃O₄ core–shell composites were prepared via a hydrothermal method.

EG-Assisted hand-in-hand growth of prism-like Cu2O nanorods with high aspect ratios and their thermal conductive performance

EG acts as a “bridge” that controls the “hand-in-hand” growth and transforms the Cu₂O wires into prism-like nanorods.

The surface condition effect of Cu2O flower/grass-like nanoarchitectures grown on Cu foil and Cu film

Cu2O flower/grass-like nanoarchitectures (FGLNAs) were fabricated directly on two category specimens of Cu foils and Cu film using thermal oxidation method. The FGLNAs are approximately 3.5 to 12 μm in size, and their petals are approximately 50 to 950 nm in width. The high compressive stress caused by a large oxide volume in the Cu2O layer on the specimen surface played an important role in the growth of FGLNAs. The effects of surface conditions, such as the surface stresses, grain size, and surface roughness of Cu foil and Cu film specimens, on the FGLNA growth were discussed in detail. PACS: 81. Materials science; 81.07.-b Nanoscale materials and structures: fabrication and characterization; 81.16.Hc Catalytic methods.

Solution Combustion Synthesis: Role of Oxidant to Fuel Ratio on Powder Properties

Solution combustion synthesis technique is one of the novel techniques used to prepare nanoparticles, multi-component ceramic oxides and nanocomposites with properties better than conventionally prepared one and these materials have been used for various applications such as sensors, catalysts, and materials for solid oxide fuel cell (SOFCs). In the present work, the method has been used to prepare nanoparticles of 10 mol% Gd doped ceria (GDC) and Cu and its oxides. The oxidant to fuel (O/F) ratio is found to affect the powder properties and even compositional homogeneity. In glycine-nitrate combustion synthesis of GDC, as revealed by XRD studies, phase pure nanoparticles with crystallite size in the range 9-12nm were obtained for all the O/F ratios. TEM measurements of calcined powder showed hexagonal shaped particles of roughly 20nm size. The exothermicity was increased with the oxidant to fuel ratio resulting in high surface area and soft agglomerates. A slightly lean O/F ratio gives surface area of 73 m2/g and soft agglomerates (D50= 5.34 mm), which eventually results into high sintering density at low temperature. Raman Spectra of GDC showed a sharp and intense peak at 467 cm−1which corresponds to CeO2due to F2gsymmetry of the cubic phase. In combustion synthesis of copper nitrate and citirc acid, the compositional homogenity and phase purity was affected by the oxidant to fuel ratio. The combustion at stoichiometric O/F ratio gives Cu nano particles, lean O/F ratio gives nanoparticles of Cu, CuO and Cu2O and rich ratio gives pure CuO nanoparticles. These nanoparticles have been studied with different characterization techniques like XRD, TG-DTA, SEM, TEM, FT-IR and Raman.

Three-dimensional hierarchical flowerlike α-Fe2O3 nanostructures: synthesis and ethanol-sensing properties

The α-Fe(2)O(3) hierarchical nanostructures have been successfully synthesized via a simple solvothermal method. The as-prepared samples are loose and porous with flowerlike structure, and the subunits are irregularly shaped nanosheets. The morphology of the α-Fe(2)O(3) structures was observed to be tunable as a function of reaction time. To demonstrate the potential applications, we have fabricated a gas sensor from the as-synthesized hierarchical α-Fe(2)O(3) and investigated it for ethanol detection. Results show that the hierarchical α-Fe(2)O(3) sensor exhibits significantly improved sensor performances in comparison with the compact α-Fe(2)O(3) structures. The enhancement of sensing properties is attributed to the unique porous and well-aligned nanostructure.

Photodegradation of methyl orange under visible light by micro-nano hierarchical Cu2O structure fabricated by hybrid laser processing and chemical dealloying

Micro-nano hierarchical structure on the substrate was fabricated by a hybrid approach including laser deposition, laser ablation and chemical dealloying. The structure consists of micro bumps with a width of 50 μm and a height of 100 μm, and nanoporous structures with a size of 70-150 nm on the micro bumps. XRD and XPS results confirm that these hierarchical structures were made of Cu(2)O. For use in comparison, three additional structures with feature size in milliscale, microscale, and nanoscale were also prepared respectively by the proposed methods. Under visible light, the micro-nano structure exhibited the best performance of photodegradation. It is the result of the large specific surface and the catalytic reaction driven by the cuprous oxides.