Three-dimensional ZnO Research Articles

Morphology transition of ZnO and Cu2O nanoparticles to 1D, 2D, and 3D nanostructures: hypothesis for engineering of micro and nanostructures (HEMNS)

A novel approach for fabricating one, two, and three-dimensional hybrid ZnO and Cu2O nanostructures has been developed. We have controlled the thickness of hybrid ZnO nanosheets to reach nanoscale at room temperature. The ability of engineering hybrid ZnO nanowires in few minutes is demonstrated. Moreover, supposed mechanism has been suggested and supported by the in situ SEM analysis for a series of picked samples during the reaction. The morphology transition of Cu2O nanoparticles to hierarchical nanowires and nano-flowers is highlighted as experimental evidences for Abdelmohsen theory for morphology transition engineering (ATMTE). In addition, the ability of multi-walled carbon nanotubes (MWCNTs) to act as a structural directing material for engineering nanowires is introduced. A hypothesis for engineering of micro and nanostructures (HEMNS) that may be applied for nearly all solid materials is demonstrated. Finally, the possibility of engineering Zn-oxidene and thin films are introduced.

Controllable three-dimensional ZnO hybrid nanostructures

Novel types of three-dimensional (3D) ZnO hybrid nanostructures (HNSs) were successfully prepared via a simple route using a patterned silicon substrate (PSS). In particular, we fabricated floating layers on top of a PSS, suspended structures slung among the protruding patterns, and contacted networks on the surface of the PSS. The character of the one fabricated depended on the drying temperature of the as-prepared structures, which affects the formation of intermediate phases. Bimodal distribution of pore sizes was detected in the porous networks as well. We controlled the size of the pores by adjusting the number of times they were spin coated and the final annealing temperature and time. The 3D ZnO HNS showed enhanced UV sensitivity compared to flat ZnO film prepared by the same process on flat substrate. This result offers a promising pathway to novel porous structures and an effective approach to low-cost sensor devices.

Biomimetic fabrication and photoelectric properties of superhydrophobic ZnO nanostructures on flexible PDMS substrates replicated from rose petal

Three-dimensional hierarchical ZnO nanostructures have been fabricated on flexible hierarchical PDMS substrates via a combination of facile PDMS casting process and solution growth routine. Fresh rose petal was used as template for the preparation of positive and negative hierarchical PDMS substrates. Morphologies, dimensions and orientation of ZnO nanostructures grown on rose-petal-like flexible PDMS surface can be controlled by adjusting the hydrothermal reaction parameters. ZnO nanostructures grown on the hierarchical PDMS substrate were found to highly influence the surface wetting behavior. Furthermore, the photoelectrical characterizations demonstrate that the flexible device based on superhydrophobic ZnO/PDMS films showed a high sensitivity of UV light and presented potential applications in optoelectronic applications.

Three-dimensional electroactive ZnO nanomesh directly derived from hierarchically self-assembled block copolymer thin films.

Three-dimensional (3D) nanoarchitectures can offer enhanced material properties, such as large surface areas that amplify the structures' interaction with environments making them useful for various sensing applications. Self-assembled block copolymers (BCPs) can readily generate various 3D nanomorphologies, but their conversion to useful inorganic materials remains one of the critical challenges against the practical application of self-assembled BCPs. This work reports the vapor-phase infiltration synthesis of optoelectrically active, 3D ZnO nanomesh architectures by combining hierarchical successive stacking of self-assembled, lamellar-phase polystyrene-block-poly(2-vinylpyridine) (PS-b-P2VP) BCP thin films and a modified block-selective vapor-phase material infiltration protocol. The 3D ZnO nanomesh exhibits optoelectrical functionality, featuring stack-layer-number-dependent electrical conductance resembling the percolative transport originating from the intrinsic morphological network connectivity of the lamellar BCP pattern with symmetric block ratio. The results not only illustrate the first demonstration of electrical functionality based on the ZnO nanoarchitecture directly generated by the infiltration synthesis in self-assembled BCP thin films but also present a new, large-area scalable, metal oxide thin film nanoarchitecture fabrication method utilizing industry-compatible polymer solution coating and atomic layer deposition. Given the large surface area, three-dimensional porosity, and readily scalable fabrication procedures, the generated ZnO nanomesh promises potential applications as an efficient active medium in chemical and optical sensors.

Facile synthesis of three-dimensional ZnO hierarchical microspheres composed of well-ordered nanorods by hydrothermal method

Abstract Three-dimensional (3D) ZnO hierarchical microspheres composed of well-ordered nanorods were synthesized by a facile one-step hydrothermal method without any surfactants. The effects of reaction conditions including reaction temperature, reaction time on the microstructure of hierarchical microspheres were investigated. The results demonstrated that the reaction conditions played an important role in the morphology of 3D ZnO hierarchical microspheres. A three-stage reaction mechanism of 3D ZnO hierarchical microspheres was proposed. Firstly, Zn2+ reacts with OH− and NH4+ to produce nanoparticles. Then the nanoparticles are self-assembled into nucleis. Finally is the formation and growth of the hierarchical structure on the nuclear surface. When the as-synthesized ZnO were used as the anode of the dye sensitization solar cells (DSSCs), the 3D ZnO hierarchical microspheres composed of well-ordered nanorods exhibits the best photoelectric properties, which was attributed to the increased surface area and advantageous electronic transmission path.

Thermal and electrical transport properties in multi-walled carbon nanotube-coated ZnO tetrapods and self-entangled multi-walled carbon nanotube tubes

We present the electrical and thermal properties of highly porous (∼94% porous) three-dimensional (3D) ZnO network structures coated with a thin layer of self-entangled multi-walled carbon nanotubes (MWCNTs), resulting in the formation of MWCNT microtubes (MWCNTTs) around the ceramic backbone. Additionally, we compare the properties of the composite (MWCNT/ZnO) structures to free-standing MWCNTTs, a hierarchical network consisting solely of randomly interconnected MWCNTs. The random 3D architecture of the ZnO network results in isotropic properties, in contrast to the typical one-dimensional (1D) properties of other CNT assemblies. The electrical conductivity of the MWCNT/ZnO composite increases with MWCNT content suggesting that MWCNTs are dominant over the entire temperature range. On the other hand, the thermal conductivity is mainly determined by the ceramic ZnO backbone at low temperature while the thermal conductivity of the MWCNTs is mainly dominant above 300 K. The electrical conductivity of the MWCNT/ZnO composites could reach values of up to 49 ± 2 S m−1 at room temperature whereas the room-temperature thermal conductivity of the MWCNTTs is 0.08 ± 0.02 W m−1 K−1. Direct comparison between both the composite and the pure MWCNTTs allows for a better understanding concerning which material in the composite dominates the transport properties.

The effect of morphology and functionalization on UV detection properties of ZnO networked tetrapods and single nanowires

Rapid detection and fast response of nanoelectronic devices based on semiconducting oxides is nowadays a modern and stringent subject of research. Device performances depend mainly on the morphologies of the metal oxide nanostructures. In the scope of this work, the influence of the structural morphology of three-dimensional (3-D) ZnO nano- and microstructured networks on the room temperature UV detection properties is studied in detail. We show that the formation of multiple potential barriers between the nanostructures, as well as the diameter of the nanostructures, which is in the same order of magnitude as the Debye length, strongly influence the UV sensing properties. Consequently, 3-D ZnO networks consisting of interconnected ultra-long wire-like tips (up to 10 μm) and with small wire diameters of 50–150 nm, demonstrated the highest UV sensing performances (UV response ratio of ∼3100 at 5 V applied bias voltage). Furthermore, we demonstrate the possibility of substantially increasing the UV sensing performances of individual ZnO nanowire (NW) (diameter of ∼50 nm) by surface functionalization with carbon nanotubes (CNTs), showing high response ratio (∼60–50 mW/cm2), as well as fast response (∼1 s) and recovery (∼1 s) times. The obtained results thus provide a platform with respect to the next generation of portable UV radiation detectors based on semiconducting oxide networks.

Fabrication of three-dimensional zinc oxide nanoflowers for high-sensitivity fiber-optic ammonia gas sensors

ZnO is identified as one of the promising coating materials in optical fiber for ammonia gas sensors. In this work, three-dimensional ZnO nanoflowers are fabricated via a facile hydrothermal method and used as sensitive coating materials for optical fiber ammonia gas sensors. Results show that the sensor with ZnO nanoflowers exhibits a high sensitivity of 5.75 pm/(μg·L-1) for ammonia concentration ranging from 0 to 5460 μg·L-1, which is more than 2.6 times higher than that of the sensor with a coating of ZnO microspheres [2.2 pm/(μg·L-1)].

Facile synthesis of core-shell ZnO/Cu2O heterojunction with enhanced visible light-driven photocatalytic performance

As p–n heterojunction photocatalysts usually possess dramatically improved photocatalytic activity than single photocatalysts, a novel ZnO/Cu2O heterojunction was designed by a facile self-templating method in this study. The crystal structure, chemical composition, surface morphology, and optical property of ZnO/Cu2O heterojunction were investigated to clarify the structure-property correlation. Scanning electron microscope and transmission electron microscope images proved the uniform core-shell submicrospheres of ZnO/Cu2O, in which a three-dimensional flower-like ZnO core was coated by a shell comprised of Cu2O nanoparticles. The photoresponse result showed that the band gap of the ZnO/Cu2O core-shell submicrospheres became narrow, and the absorption edge shifted from the ultraviolet region (380 nm) to the visible region (500 nm) compared with the pure ZnO microflowers. For the degradation of Rhodamine B under visible light, the photocatalytic efficiency of ZnO/Cu2O submicrospheres reached 96% within 40 min of reaction time, which was 3.8 times higher than that of pure ZnO microflowers and up to 4.5 times than that for pure Cu2O nanoparticles. The remarkable visible light-driven photocatalytic performance is mainly attributed to the extended photoresponse range and effective separation of the photo-generated electron-hole pairs in the unique heterojunction.

Microwave-assisted solution synthesis and photocatalytic activity of Ag nanoparticles supported on ZnO nanostructure flowers

Ag nanoparticles supported on the surface of three-dimensional (3D) flower-like ZnO nanostructure were synthesized by a microwave-assisted solution method. The obtained products were characterized by X-ray diffraction analysis, field-emission scanning electron microscopy, Fourier-transform infrared spectroscopy, Raman spectrophotometry, X-ray photoelectron spectroscopy, and photoluminescence spectroscopy. The analytical results confirmed homogeneously distributed Ag nanoparticles supported on the surface of flower-like ZnO nanostructure. The photocatalytic effect of the heterostructure Ag/ZnO nanocomposites was investigated using photodegradation under ultraviolet (UV) light of methylene blue as model dye. The heterostructure Ag/ZnO nanocomposites exhibited much higher photocatalytic activity than pure ZnO flowers. The improved photocatalytic properties are attributed to formation of a Schottky barrier at the metal–semiconductor interface of the Ag/ZnO nanocomposites.

Significantly enhanced UV luminescence by plasmonic metal on ZnO nanorods patterned by screen-printing

A smart synthetic method is conceived to construct large batches of ZnO nanostructures to meet market demand for light-emitting diodes. Utilizing the localized surface plasmon resonance of metal nanoparticles (NPs) facilitates the recombination of electron–hole pairs and the release of photons. Compared to raw ZnO nanorods (NRs), ZnO NRs@HfO2@Al NPs show a ∼120× enhancement in ultraviolet (UV) photoluminescence (PL), while ZnO NRs@HfO2@Ag NPs show a six-fold enhancement. Because the surface plasmon energy of Al is nearer the ZnO band gap, the PL enhancement of ZnO NRs covered with Al is stronger than that of those covered with Ag. Based on this analysis, three-dimensional graphical ZnO NR arrays were manufactured by screen-printing, a mass production technique. After covering the arrays with layers of HfO2 and Al NPs, the UV PL intensities of the corresponding substrates were increased by approximately 16×. This indicates the potential to mass-produce highly efficient optoelectronic devices.

Synthesis of composite of ZnO spheres with polyaniline and their microwave absorption properties

Three-dimensional (3D) ZnO microspheres with the composite of polyaniline (PANI) have been successfully synthesized by one-pot solvothermal and in-suit polymerization method. The obtained microspheres were uniform having the diameter of 4 μm–7 μm. These microspheres, inside cushion of PANI polymer, exhibit excellent microwave absorption properties. Composite of ZnO microspheres with PANI increased the complex permeability and enhanced the dielectric loss. Thus, the microwave absorption properties of the composite have been intensified. Despite the fact that the composite of ZnO with PANI herein dissipate the microwaves by dielectric loss, their performance is admirable compared to most of PANI-based composites reported. The morphological, structural and spectral properties have been investigated using scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and the Fourier transform infrared (FT-IR). It is found that the maximum reflection loss value of ZnO@PANI reaches −41 dB at 14 GHz with a thickness of 3.5 mm that is superior to the previously reported composite of PANI with other materials.

Enhanced performance of ZnO-based dye-sensitized solar cells by glucose treatment

Hierarchical ZnO nanosheet-clusters as three-dimensional ZnO photoanodes with surface modification have been achieved via a facile and simple immersion method in glucose solution at room temperature for dye-sensitized solar cells. The surface properties of glucose-modified ZnO nanosheets are analyzed by X-ray photoelectron spectra and transmission electron microscopy. The current-voltage curve measurements show that the dye-sensitized solar cell with an immersion time of 2 min illustrates the best photoelectrochemical performance of 5.31%, which can be attributed to the prevention of the dye aggregation and the large recombination resistance resulting from the self-assembled glucose molecules on ZnO surfaces. From the modulated photo-voltage spectroscopy and intensity modulated photocurrent spectroscopy measurements further illustrate that the glucose-modified ZnO photoanodes possess large electron lifetime and long electron diffusion length. The glucose-modified ZnO nanosheet surfaces not only provide a three-dimensional structure but also avoid extensive Zn2+/dye complexes formation. The findings from our work are important for the design of efficient photoanode materials with superior performance for dye-sensitized solar cells.

Three-Dimensional ZnO Nanostructure Based Gas and Humidity Sensors.

The ZnO nanostructure environmental sensors were prepared via the three-dimensional through silicon via (3D-TSV) technique. For 3D-TSV, the diameter and length of the Si via were about 200 and 400 μm, respectively. For nitrogen oxide (NO), the measured responses were around ~12, ~16, and ~20% when the concentrations of the injected NO gas were 20, 40 and 60 ppm, respectively. For humidity and temperature sensing, the measured nanowire current increased logarithmically with increasing chamber temperature. The response to relative humidity increased with increasing temperature.

Three-Dimensional Hierarchical Structure ZnO@C@NiO on Carbon Cloth for Asymmetric Supercapacitor with Enhanced Cycle Stability.

In this work, we synthesized the hierarchical ZnO@C@NiO core-shell nanorods arrays (CSNAs) grown on a carbon cloth (CC) conductive substrate by a three-step method involving hydrothermal and chemical bath methods. The morphology and chemical structure of the hybrid nanoarrays were characterized in detail. The combination and formation mechanism was proposed. The conducting carbon layer between ZnO and NiO layers can efficiently enhance the electric conductivity of the integrated electrodes, and also protect the corrosion of ZnO in an alkaline solution. Compared with ZnO@NiO nanorods arrays (NAs), the NiO in CC/ZnO@C@NiO electrodes, which possess a unique multilevel core-shell nanostructure exhibits a higher specific capacity (677 C/g at 1.43 A/g) and an enhanced cycling stability (capacity remain 71% after 5000 cycles), on account of the protection of carbon layer derived from glucose. Additionally, a flexible all-solid-state supercapacitor is readily constructed by coating the PVA/KOH gel electrolyte between the ZnO@C@NiO CSNAs and commercial graphene. The energy density of this all-solid-state device decreases from 35.7 to 16.0 Wh/kg as the power density increases from 380.9 to 2704.2 W/kg with an excellent cycling stability (87.5% of the initial capacitance after 10000 cycles). Thereby, the CC/ ZnO@C@NiO CSNAs of three-dimensional hierarchical structure is promising electrode materials for flexible all-solid-state supercapacitors.

A novel multifunctional electrochemical platform for simultaneous detection, elimination, and inactivation of pathogenic bacteria based on the Vancomycin-functionalised AgNPs/3D-ZnO nanorod arrays

A novel fast, sensitive, and specific multifunctional electrochemical platform has been proposed for simultaneous detection, elimination, and inactivation of pathogenic bacteria for the first time. The platform is constituted with three-dimensional ZnO nanorod arrays (3D-ZnO) decorated with sliver nanoparticles (AgNPs) and functionalized with vancomycin (Van). Based on the specific recognition of Van for Gram-positive bacteria, the fabricated electrochemical platform has presented high detection sensitivity to Staphylococcus aureus with a low detection limit of 330cfu/mL and adaptable bacterial-elimination efficiency (50%) at low concentrations (1000–2000cfu/mL). Moreover, the platform has shown high antibacterial activity (99.99%) arising from the synergistic germicidal effect of the composited antibacterial AgNPs and Van units. The current work could provide new strategies to construct advanced platforms for simultaneous detection, elimination, and inactivation of various pathogenic bacteria.

Carbon-coated ZnO mat passivation by atomic-layer-deposited HfO2 as an anode material for lithium-ion batteries

ZnO has had little consideration as an anode material in lithium-ion batteries compared with other transition-metal oxides due to its inherent poor electrical conductivity and large volume expansion upon cycling and pulverization of ZnO-based electrodes. A logical design and facile synthesis of ZnO with well-controlled particle sizes and a specific morphology is essential to improving the performance of ZnO in lithium-ion batteries. In this paper, a simple approach is reported that uses a cation surfactant and a chelating agent to synthesize three-dimensional hierarchical nanostructured carbon-coated ZnO mats, in which the ZnO mats are composed of stacked individual ZnO nanowires and form well-defined nanoporous structures with high surface areas. In order to improve the performance of lithium-ion batteries, HfO2 is deposited on the carbon-coated ZnO mat electrode via atomic layer deposition. Lithium-ion battery devices based on the carbon-coated ZnO mat passivation by atomic layer deposited HfO2 exhibit an excellent initial discharge and charge capacities of 2684.01 and 963.21mAhg−1, respectively, at a current density of 100mAg−1 in the voltage range of 0.01–3V. They also exhibit cycle stability after 125 cycles with a capacity of 740mAhg−1 and a remarkable rate capability.

Hierarchical flower-like ZnO microstructures: preparation, formation mechanism and application in gas sensor

Three-dimensional (3D) flower-like ZnO hierarchical microstructures with high uniformity were fabricated from the decomposition of Zn(OH)4 2− precursor, which were synthesized by a facile hydrothermal reaction. XRD, FESEM and TEM were employed to characterize the morphology and structure of the products. The as-prepared flower-like ZnO microstructures with an average diameter of about 2 μm are assembled by large amounts of nanosheets, which have a thickness of ~43 nm. The morphology of the ZnO architectures can be tailored by changing hydrothermal conditions, e.g., hydrothermal temperature, reaction time, and concentration of Zn2+. On the basis of experimental results, the possible formation mechanism of the flower-like ZnO microstructures was also proposed, and the Zn2+ concentration was found to be a vital role in the growth and crystallzation of the flower-like microstructures. The Brunauer–Emmett–Teller measurement shows that the 3D flower-like ZnO hierarchical microstructures possess a specific surface area of about 34.86 m2/g. Most significantly, the gas sensing test reveals that the sensor made from 3D flower-like ZnO hierarchical microstructures exhibits outstanding gas sensing performance.

3D micro-structured arrays of Zn\u039f nanorods

The fabrication of nanostructures with controlled assembly and architecture is very important for the development of novel nanomaterial-based devices. We demonstrate that laser techniques coupled with low-temperature hydrothermal growth enable complex three-dimensional ZnO nanorod patterning on various types of substrates and geometries. This methodology is based on a procedure involving the 3D scaffold fabrication using Multi-Photon Lithography of a photosensitive material, followed by Zn seeded Aqueous Chemical Growth of ZnO nanorods. 3D, uniformly aligned ZnO nanorods are produced. The increase in active surface area, up to 4.4 times in the cases presented here, provides a dramatic increase in photocatalytic performance, while other applications are also proposed.

Three-dimensional carbon cloth-supported ZnO nanorod arrays as a binder-free anode for lithium-ion batteries

Three-dimensional ZnO nanorod arrays on flexible high surface area carbon cloth were successfully synthesized and directly used as negative electrodes for lithium-ion batteries without using any binder additive. The structure and morphology of the as-prepared hybrid ZnO electrode were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and high-resolution transmission electron microscopy (HRTEM). When tested as anodes in a lithium cell, the hybrid electrode demonstrated a high discharge capacity along with excellent rate capability and good cycling stability, delivering a reversible capacity of 891 mAh g−1 at the second cycle and retaining a capacity of 469 mAh g−1 after 100 cycles.