CuO nanostructures: Synthesis, characterization, growth mechanisms, fundamental properties, and applications
Introduction
Nanostructured transition metal oxides (MOs), a particular class of nanomaterials, are the indisputable prerequisite for the development of various novel functional and smart materials. These transition MO nanocrystals have been attracting much attention not only for fundamental scientific research, but also for various practical applications because of their unique physical and chemical properties [1], [2], [3], [4], [5], [6], [7], [8], [9], [10], [11], [12], [13], [14], [15], [16], [17], [18], [19], [20], [21], [22], [23], [24], [25], [26], [27], [28]. These physical and chemical properties are strongly dependent on the sizes, shapes, compositions, and structures of the nanocrystals. Interesting phenomena such as remarkable increase in surface-to-volume ratio, significant change in surface energy, and quantum confinement effects occur when transition MOs are reduced to nanoscale dimension [7], [20], [21]. These phenomena result in a variety of new physical and chemical properties that are not feasible for materials with bulk dimensionality. Therefore, the manipulation of well-controlled synthesis and fabrication of nanostructured transition MOs with different sizes, shapes, chemical compositions, and structures is crucial in the advancement in nanoscience and nanotechnology. Consequently, various nanostructured transition MOs have been synthesized by diverse chemical, physicochemical, and physical strategies [1], [2], [3], [4], [5], [6], [7], [9], [14], [15], [16], [17], [20], [21], [25], [28]. Compared with their micro or bulk counterparts, nanostructured transition MOs exhibit unique structural characteristics and size confinement effects as well as novel properties. These properties contribute to the potential of transition MOs as candidates for both theoretical studies and practical applications in micro/nanodevices.
Cupric oxide (CuO) has been a hot topic among the studies on transition MOs because of its interesting properties as a p-type semiconductor with a narrow band gap (1.2 eV in bulk) and as the basis of several high-temperature superconductors and giant magneto resistance materials [25], [29], [30], [31], [32], [33], [34], [35]. CuO nanostructures with large surface areas and potential size effects possess superior physical and chemical properties that remarkably differ from those of their micro or bulk counterparts. These nanostructures have been extensively investigated because of their promising applications in various fields. CuO nanostructures are also considered aselectrode materials for the next-generation rechargeable lithium-ion batteries (LIBs) because of their high theoretical capacity, safety, and environmental friendliness [36]. They are also promising materials for the fabrication of solar cells because of their high solar absorbance, low thermal emittance, relatively good electrical properties, and high carrier concentration [37]. Furthermore, CuO nanostructures are extensively used in various other applications, including gas sensors [38], bio-sensors [39], nanofluid [40], photodetectors [41], energetic materials (EMs) [42], field emissions [43], supercapacitors [44], removal of inorganic pollutants [45], [46], photocatalysis [47], and magnetic storage media [48]. Recent studies have demonstrated that nanoscale CuO can be used to prepare various organic–inorganic nanocomposites with high thermal conductivity, high electrical conductivity, high mechanical strength, high-temperature durability, and so on [32], [33], [49], [50]. Moreover, the nanoscale CuO is an effective catalyst for CO and NO oxidation as well asin the oxidation of volatile organic chemicals such as methanol [51], [52], [53]. In addition, some reports have demonstrated the excellent activities of nanoscale CuO as catalyst in the C–N coupling and C–S cross-coupling of thiols with iodobenzene reactions [51], [54], [55]. The superhydrophobic properties of CuO nanostructures render these materials as promising candidates in Lotus effect self-cleaning coatings (anti-biofouling), surface protection, textiles, water movement, microfluidics, and oil–water separation [56]. Thus, nanoscale CuO with different shapes and dimensions, such as zero-dimensional (0D) nanoparticles, one-dimensional (1D) nanotubes, 1D nanowires/rods, two-dimensional (2D) nanoplates, 2D nanolayers, and several complex three-dimensional (3D) nanoflowers, spherical-like, and urchin-like nanostructures have been synthesized using numerous methodologies. More interesting applications of CuO nanostructures are being explored.
Cuprous oxide (Cu2O), another important copper (Cu)-based oxide, is also one of the first known p-type semiconductor materials [57]. However, Cu2O and CuO have striking contrasting colors, crystal structures, and physical properties [58]. Cu2O is a reddish p-type semiconductor of both ionic and covalent nature with cubic structure (space group, ) that exhibits various excitonic levels. By contrast, CuO has an iron-dark color with a more complex monoclinic tenorite crystallographic structure (space group, C2/c) and displays promising antiferromagnetic ordering [58], [59]. Cu2O is expected to have an essentially full Cu 3d shell with a direct forbidden band gap of 2.17 eV in bulk, which can only absorb light up to the visible region. CuO has an open 3d shell with a direct band gap (1.2 eV in bulk) of charge-transfer type, which can absorb light up to the near infraredregion [59], [60]. Recent reports have demonstrated that CuO has higher conductivity than Cu2O but with lower carrier mobility [61].
Although these two Cu-based oxides have contrasting properties, both oxides are of considerable interest in photovoltaics, gas sensors, CO oxidation catalysts, various heterogeneous catalysts, and LIBs, because of their low band-gap energy, high optical absorption, high catalytic activity, nontoxic nature, and low-cost [30], [31], [62], [63]. In recent years, the size- and morphology-controlled synthesis and application of Cu2O and CuO have been intensively investigated [25], [28], [29], [30], [31]. However, CuO is more stable than Cu2O because Cu(II) ions are much more stable in ambience, which makes it more important in practical applications. Furthermore, the synthesis, properties, and applications of various Cu2O nanostructures have been extensively reviewed [28], [31], [64], [65], [66]. Therefore, the recent advancement in Cu2O will not be covered in this article to avoid overlapping reviews.
Additionally, compared with other MO nanostructures, such as TiO2 [7], [9], ZnO [14], WO3 [21], and SnO2 [17], CuO nanostructures have more interesting magnetic and superhydrophobic properties. Additionally, these nanostructures demonstrate unique applications in heterogeneous catalysis in the complete conversion of hydrocarbons into carbon dioxide, enhancement of thermal conductivity of nanofluid, nanoenergetic materials (nEMs), and superhydrophobic surfaces. CuO nanostructures as anode materials for LIBs have not been paid as much attention as SnO2 [17], [67] and TiO2 [67], [68]. However, the simplicity of preparation, scalability, non-toxicity, abundance, and low-cost of CuO nanostructures is expected to increase the application of these nanomaterials as anode materials for LIBs. MOs, including SnO2, ZnO, TiO2 along with their various sub-stoichiometric forms [38], are widely considered for gas sensor applications. Thus, the study of CuO for gas sensors is expected to increase rapidly because of the easy synthesis of high-quality and single-crystalline CuO nanostructures.
However, only few reports have described the synthesis strategies adopted for CuO nanostructures along with the introduction of their related applications [25], [29], [31]. Furthermore, most of these review papers only focused on the 1D CuO nanostructures [25], [30], [31]. No review for the systematic introduction of the recent progresses of various CuO nanostructures has been published. This article will begin with a systemic discussion on the synthesis of different CuO nanostructures. For each synthetic method, critical comments will be provided based on our knowledge and related research experience. Next, the associated synthesis mechanisms for controlling the size, morphology, and structure of CuO nanostructures will be addressed. The fundamental properties of CuO nanostructures will also be introduced. The promising applications of 0D CuO nanoparticles, 1D CuO nanotubes, 1D nanowires/rods, 2D CuO nanostructures, and several complex 3D CuO nanostructures along with perspectives in terms of future research on CuO nanostructures will be highlighted. This review aims to provide a critical discussion of the synthesis of CuO nanostructures. The potential of CuO nanostructures as functional components for fabrication of micro/nanodevices are also evaluated and highlighted. In particular, we focus on the fundamental properties and various nanostructured forms of CuO that have been reported in the literature to date and summarize the various synthetic strategies. Promising selections and interesting applications are presented, and finally some perspectives on the future research and development of CuO nanostructures are provided.
Section snippets
Synthesis of CuO nanostructures
The development of synthetic methods has been widely accepted as an area of fundamental importance to the understanding and application of nanoscale materials. It allows scientists to modulate different parameters such as morphology, particle size, size distributions, and composition. Numerous methods have been recently developed to synthesize various CuO nanostructures with diverse morphologies, sizes, and dimensions using various chemical and physical strategies. In this review, we present
Growth mechanisms
The development of nanotechnology has resulted in the fabrication of CuO nanostructures with various morphologies and sizes using different synthetic methods. However, the growth mechanisms responsible for the formation of CuO nanostructures with various morphologies during syntheses are still not fully understood, and extensive studies have been conducted to determine the growth mechanisms of different CuO nanostructures. In this section, we briefly review the most important mechanisms that
Fundamental properties
Table 3 lists the key physical properties of bulk CuO. However, the reduction of CuO dimensions to the nanoscale or even smaller scale results insignificant deviation of some of its physical properties from its bulk counterpart because of the “quantum-size effects.” Therefore, a thorough understanding of the fundamental properties of CuO nanostructures is crucial to their synthesis and applications and a key to the rational design of CuO nanostructure-based functional devices. In this section,
Applications
This section we focus on the recent developments in the different CuO nanostructures as building blocks for applications in a wide range of fields. These fields include LIBs, supercapacitors, sensors, solar cells, photodetectors, catalysis, nanofluid, nanoenergetic materials (nEMs), field emissions, superhydrophobic surfaces, and removal of arsenic and organic pollutants from waste water. The toxicity of CuO nanoparticles is also briefly addressed.
Conclusion and outlook
In summary, CuO nanostructures have been widely studied and are receiving increasing interest because of their interesting properties and promising applications in various areas. In this study, we present a comprehensive review of the state-of-the-art research activities of different CuO nanostructures. We focus on the main synthetic strategies along with associated formation mechanisms, their interesting fundamental properties, and promising applications. Investigation of the synthetic
Acknowledgments
This work was supported by Hong Kong Research Grants Council (Project No. CityU 125412) and NSAF (Grant No. U1330132).
References (520)
- et al.
Zero-dimensional, one-dimensional, two-dimensional and three-dimensional nanostructured materials for advanced electrochemical energy devices
Prog Mater Sci
(2012) Gas sensing applications of 1D-nanostructured zinc oxide: insights from density functional theory calculations
Prog Mater Sci
(2012)- et al.
Synthesis and applications of one-dimensional semiconductors
Prog Mater Sci
(2010) - et al.
Role of defects in tailoring structural, electrical and optical properties of ZnO
Prog Mater Sci
(2009) - et al.
Quasi-one dimensional metal oxide semiconductors: preparation, characterization and application as chemical sensors
Prog Mater Sci
(2009) - et al.
Synthesis, properties, and applications of magnetic iron oxide nanoparticles
Prog Cryst Growth Charact Mater
(2009) - et al.
Nanostructured electrodes for lithium-ion and lithium-air batteries: the latest developments, challenges, and perspectives
Mater Sci Eng R Rep
(2011) - et al.
A CuO nanowire infrared photodetector
Sensor Actuat A: Phys
(2011) - et al.
Tailoring CuO nanostructures for enhanced photocatalytic property
J Colloid Interface Sci
(2012) - et al.
Fabrication of cuprous and cupric oxide thin films by heat treatment
Appl Surf Sci
(2009)
Morphologically controlled synthesis of Cu2O nanocrystals and their properties
Nano Today
Branched nanowires: synthesis and energy applications
Nano Today
Continuous hydrothermal synthesis of Fe2O3, NiO, and CuO nanoparticles by superrapid heating using a T-type micro mixer at 673 K and 30 MPa
Chem Eng J
Structural and magnetic properties of CuO nanoneedles synthesized by hydrothermal method
Appl Surf Sci
Gas sensing properties of CuO nanorods synthesized by a microwave-assisted hydrothermal method
Sensor Actuat B: Chem
Morphologically controlled synthesis of copper oxides and their catalytic applications in the synthesis of propargylamine and oxidative degradation of methylene blue
Colloids Surf Physicochem Eng Aspects
Fine tuning of the morphology of copper oxide nanostructures and their application in ambient degradation of methylene blue
J Colloid Interface Sci
Hierarchical CuO hollow microspheres: controlled synthesis for enhanced lithium storage performance
J Alloys Compd
CuO shuttle-like nanocrystals synthesized by oriented attachment
J Cryst Growth
The transformation of Cu(OH)2 into CuO, revisited
Solid State Sci
Synthesis and characterization of CuO flower-nanostructure processing by a domestic hydrothermal microwave
J Alloys Compd
CuO urchin-nanostructures synthesized from a domestic hydrothermal microwave method
Mater Res Bull
Novel route to synthesize CuO nanoplatelets
J Solid State Chem
Fabrication of CuO nanoplatelets for highly sensitive enzyme-free determination of glucose
Electrochim Acta
Large-scale synthesis of single-crystalline CuO nanoplatelets by a hydrothermal process
Mater Res Bull
Recent advances in manganese oxide nanocrystals: fabrication, characterization, and microstructure
Chem Rev
Titanium dioxide nanomaterials: synthesis, properties, modifications, and applications
Chem Rev
Nanostructured oxides in chemistry: characterization and properties
Chem Rev
Magnetic iron oxide nanoparticles: synthesis, stabilization, vectorization, physicochemical characterizations, and biological applications
Chem Rev
Semiconductor nanowires for energy conversion
Chem Rev
Synthesis of metal oxide nanostructures by direct sol–gel chemistry in supercritical fluids
Chem Rev
One-dimensional nanostructures: synthesis, characterization, and applications
Adv Mater
On the design of advanced metal oxide nanomaterials
Int J Nanotechnol
Zinc oxide nanostructures: growth, properties and applications
J Phys: Condens Matter
Recent advances in the use of TiO2 nanotube and nanowire arrays for oxidative
J Phys Chem C
One-dimensional SnO2 nanostructures: synthesis and applications
J Nanotechnol
Shape control of semiconductor and metal oxide nanocrystals through nonhydrolytic colloidal routes
Angew Chem Int Ed (English)
Nanomaterials of high surface energy with exceptional properties in catalysis and energy storage
Chem Soc Rev
Synthesis of monodisperse spherical nanocrystals
Angew Chem Int Ed
Nanostructured tungsten oxide – properties, synthesis, and applications
Adv Funct Mater
One-dimensional metal-oxide nanostructures: recent developments in synthesis, characterization, and applications
Adv Funct Mater
Fabrication and application of inorganic hollow spheres
Chem Soc Rev
Nanoscale advances in catalysis and energy applications
Nano Lett
Synthesis of TiO2 and CuO nanotubes and nanowires
Sci Adv Mater
A general procedure to synthesize highly crystalline metal oxide and mixed oxide nanocrystals in aqueous medium and photocatalytic activity of metal/oxide nanohybrids
Nanoscale
Hollow micro-/nanostructures: synthesis and applications
Adv Mater
Scalable strategies for the synthesis of well-defined copper metal and oxide nanocrystals
Chem Soc Rev
Emergent methods to synthesize and characterize semiconductor CuO nanoparticles with various morphologies—an overview
J Exp Nanosci
One-dimensional metal oxide nanotubes, nanowires, nanoribbons, and nanorods: synthesis, characterizations, properties and applications
Crit Rev Solid State Mater Sci
Copper oxide nanowires: a review of growth
Nanotechnology
Cited by (1134)
Interface engineering by redox reaction on ferrites to prepare efficient electromagnetic wave absorbers
2024, Journal of Materials Science and TechnologyHigh entropy oxide catalysts with SO<inf>2</inf> resistance in RWGS reaction
2024, Applied Catalysis B: EnvironmentalThe generation of noise-like pulses and various solitons with CuO nanorods as a broadband saturable absorber
2024, Journal of Alloys and CompoundsSynthesis and characterization of new nanocomposite PW<inf>11</inf>Mn@CuO@PAN as an efficient nanocatalyst for deep oxidative desulfurization of real/model fuels
2024, Materials Science and Engineering: BProgress in the development of copper oxide-based materials for electrochemical water splitting
2024, International Journal of Hydrogen Energy