ZnO Whiskers Research Articles

Synthesis and Mechanism of 1D ZnO Based on Alkaline Dissolution-Conversion Strategy of High Stable and Soluble ɛ-Zn(OH)2.

A high soluble and stable ɛ-Zn(OH)2 precursor is synthesized at below room temperature to efficiently prepare ZnO whiskers. The experimental results indicate that the formation of ZnO whiskers is carried out mainly via two steps: the formation of ZnO seeds from ɛ-Zn(OH)2 via the in situ solid conversion, and the following growth of whiskers via dissolution-precipitation route. The decrease of temperature from 25 to 5 °C promotes the formation of ɛ-Zn(OH)2 with higher solubility and stability, which balances the conversion and dissolution rates of precursor. The Rietveld refinement, DFT calculations and MD simulations reveal that the primary reason for these characteristics is the expansion of ɛ-Zn(OH)2 lattice due to temperature, causing difficulties in the dehydration of adjacent ─OH. Simultaneously, the larger specific surface area favors the dissolution of ɛ-Zn(OH)2. Based on this precursor, well-dispersed ZnO whiskers with 9.82µm in length, 242.38nm in diameter, and an average aspect ratio of 41 are successfully synthesized through a SDSN-assisted hydrothermal process at 80 °C. The process has an extremely high solid content of 2.5% (mass ratio of ZnO to solution) and an overall yield of 92%, which offers a new approach for the scaled synthesis of high aspect ratio ZnO whiskers by liquid-phase method.

High‐performance epoxy vitrimer composites based on double dynamic covalent bonds

AbstractThermoset epoxy resin materials can be endowed with unique dynamic properties by introducing dynamic covalent bonds (DCB) into the cross‐link network of the epoxy resin. However, it remains a challenge to obtain epoxy materials with high mechanical, thermodynamic, and dynamic properties. In this work, a series of epoxy vitrimers with double DCBs were prepared by using a curing agent with imine bonds (PAMD) and an epoxy resin with disulfide bonds (BGPDS). PAMD and BGPDS are cross‐linked and form a uniform aromatic framework that ensures the mechanical and thermal properties of the material. High‐density DCBs ensure the dynamic performance of epoxy vitrimer. In addition, tetra‐needle‐like ZnO whiskers (T‐ZnOw) were added to the epoxy vitrimer for further reinforcement. The results demonstrated that epoxy vitrimer composites with T‐ZnOw content of 10 wt.% exhibit high tensile strength, high Tg, high healing efficiency, shape reconfiguration, reprocessing and rapid degradation. The degradation products can recycle and produce new epoxy vitrimer, leading to a closed‐loop recycling which reduced the environmental pollution and resource waste.

Simultaneously Enhanced In-Plane and Out-of-Plane Thermal Conductivity of a PI Composite Film by Tetraneedle-like ZnO Whiskers and BN Nanosheets

Simultaneously Enhanced In-Plane and Out-of-Plane Thermal Conductivity of a PI Composite Film by Tetraneedle-like ZnO Whiskers and BN Nanosheets

In-Situ Growth of ZnO Whiskers on Ti2ZnC MAX Phases.

ZnO whiskers have many applications, such as in medical and photocatalysis fields. In this study, an unconventional preparation approach is reported, realizing the in-situ growth of ZnO whiskers on Ti2ZnC. The weak bonding between the layer of Ti6C-octahedron and the Zn-atom layers leads to the easy extraction of Zn atoms from Ti2ZnC lattice points, resulting in the formation of ZnO whiskers on the Ti2ZnC surface. This is the first time that ZnO whiskers have been found to grow in-situ on Ti2ZnC substrate. Further, this phenomenon is amplified when the size of the Ti2ZnC grains is mechanically reduced by ball-milling, which bodes a promising route to prepare ZnO in-situ on a large scale. Additionally, this finding can also help us better understand the stability of Ti2ZnC and the whiskering mechanism of MAX phases.

Effect of one-dimensional tetra-needle-like ZnO whiskers on the electrical properties of montmorillonite/silicon carbide/epoxy micro-nanocomposites

Effect of one-dimensional tetra-needle-like ZnO whiskers on the electrical properties of montmorillonite/silicon carbide/epoxy micro-nanocomposites

Building of soft-hard compound brush in porous PVA/NH2@TAtZnO plural gel and the high-efficiency anti-interference removal on Pb(II)

In order to promote the heavy metal ions removal of porous gel adsorbent and protect the adsorbent from other pollutants in wastewater, the tetrapod ZnO whiskers (tZnO) modified by amino-chain brush was introduced into the polyvinyl alcohol (PVA) matrix to prepare the PVA/NH2@TAtZnO composites with brush structure for toxic Pb(II) removal. The adsorption property, adsorption process and adsorption mechanism were studied by adsorption isotherms, adsorption kinetics, adsorption thermodynamics, SEM-EDS analysis and XPS analysis. And the anti-interference ability and anti-interference mechanism were researched by SEM-EDS analysis and XPS analysis. It was found that the PVA/NH2@TAtZnO composites displayed a soft-hard compound pore-brush structure and showed a good selective adsorption on Pb(II). The research of isotherms and kinetics indicated that the adsorption process was fitted well to Langmuir model and pseudo-second-order model, respectively, and the research of thermodynamics revealed the endothermic nature. The adsorption mechanism was inferred as the combination of predominant chemisorption and subsidiary physisorption. Comparing with the neat PVA matrix, the PVA/NH2@TAtZnO composites displayed a good anti-interference property on Pb(II) adsorption and showed an alleviative clogging pore-canal structure in the wastewater with SiO2 NPs or PAC flocculants. The anti-interference intensity ΔQ and anti-interference factor χ were proposed to reflect the anti-interference ability of this adsorbent which was promoted with the increasing amino brush length or density. By the analysis of SEM-EDS and XPS, the anti-interference mechanism was explored as the steric-hinerance effect of tZnO hard brush to suspended SiO2 NPs pollutant and the coordination effect of functional amino soft brush to soluble PAC pollutant. Besides, the prepared PVA/NH2@TAtZnO adsorbent possessed a good reusability under multiple adsorption-desorption processes and also presented a well applicability in real water matrix. The research indicated the huge potential of prepared PVA/NH2@TAtZnO adsorbent in heavy metal ions removal.

Surface treated ZnO whisker optimizing the comprehensive performance of the self-adaptive dielectrics

The application of self-adaptive dielectrics (SADs) is a promising approach to enhancing the insulation performance as well as downsizing of most high voltage apparatus. Beside nonlinear electrical property, good thermal and mechanical performances of SADs are also expected. However, heavy load of functional fillers often leads to poor elasticity of traditional SADs and it is a challenge to decrease filler concentration while ensuring satisfied thermal and nonlinear electrical conductivity. In this paper, tetrapod-shaped ZnO whisker coated with oxides shell and its silicone rubber composites have been manufactured. The core-shell interface equips the ZnO whisker with nonlinear conducting behavior and the composites also exhibit similar self-adaptive electrical property like traditional SADs. Due to the relative large respect ratio, the coated whisker can reduce the filler concentration to about 10 vol% which guarantees good mechanical property of the material. The thermal conductivity of the composites and traditional SADs are compared and an optimized filler concentration range considering comprehensive property of the composite is obtained. This work is helpful to design smart composites to self-adaptively control high electrical field of electrical and electronic devices and increase their stability and durability.

Enhancing direct solar thermochemical performance of modified CaCO3 with thermal transport networks composed of tetrapod-shaped ZnO whiskers

The CaCO 3 /CaO based thermochemical system has great potential in Concentrating Solar Power (CSP) plants. However, the CaCO 3 suffers from high sintering speed, poor thermal conductivity, and weak light absorption, which is not conducive to being directly driven by solar energy. Herein, The Mn and Cr elements were doped into CaCO 3 through the sol-gel method. The synergistic effect between the two elements can maintain the storage density at 1057.3 kJ/kg after 20 cycles at 800 °C. The light absorption under AM 1.5G spectrum was obviously improved to 64.5% and reached 73.3% after 20 cycles. To further improve the thermal conductivity of the composite, the tetrapod-shaped zinc oxide whiskers (TZnO) were directly mixed into the composite. The TZnO acts as the thermal conductance bridge in the composites and can retain its original morphology at high temperatures without reacting with CaCO 3 . When 5% mole ratio of TZnO was added to the Cr/Mn doped CaCO 3 , the thermal conductivity increased by 17.8%. Through the non-isothermal analysis of the reaction kinetics, it is found that the addition of TZnO can effectively accelerate the reaction, especially at a higher heating rate, which is very beneficial to direct solar-driven applications. The optimized composites showed excellent properties in light absorption, sintering resistance, thermal conductivity, and reaction kinetics, which can guide the direct photothermal utilization of CaCO 3 . • Thermophysical properties of solar driven CaCO 3 -based composites are studied. • Tetrapod-shaped ZnO whiskers can serve as the thermal transport networks for CaCO 3. • The thermal conductivity increased by 17.8% after 5% mole ratio of TZnO was added. • The high thermal transfer network formed by TZnO accelerates the reaction kinetics.

The regulation of electro-optical properties of the polymer dispersed liquid crystal films doped ZnO whiskers under applied pre-orientation voltage

ABSTRACT This study demonstrates a simple and effective method for the fabrication of PDLC films with low driving voltage by applying a pre-orientation voltage during the photoinitiated polymerisation process. The results indicated that the electro-optical performances of PDLC films have been regulated successfully with the pre-orientation voltage method, in which the voltage could pre-orient the LC molecules and change the interface between the LC molecules and the polymer matrix. By manipulating the proportion of liquid crystal and polymer monomers and introducing ZnO whiskers as the dopant, the driving voltage was dramatically reduced and the sample could be fully driven by an electric field with a voltage of 32 V below the safe voltage. The results indicated that the polymer meshes were broadened by the addition of ZnO whiskers due to their excellent UV-absorbing properties that result in a slower polymerisation rate, while the contrast ratio could maintain a good value of 31. It has been found that both application of pre-orientation voltage and doped ZnO whiskers can optimise the electro-optical performance of the PDLC and reduce the driving voltage. Therefore, this experiment is expected to provide certain research value to fabricate the low-driven PDLC films for practical applications.

Changes in photocatalytic activity and optical properties of ZnO whiskers induced by UV irradiation

Controlling the surface properties of ZnO micro-nanostructured materials by surface engineering is a current research hotspot. The tetrapod-like ZnO whisker is a multifunctional material, which has applications in many fields. In this research, ZnO whiskers were first prepared by reactive evaporation, and then the surface properties of the ZnO whiskers were changed by ultraviolet (UV) irradiation. The experimental results show that many oxygen vacancies (VO) are generated on the ZnO whiskers surface under UV irradiation. The presence of surface VO is confirmed by Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and photoluminescence spectroscopy. It is found that an appropriate amount of surface VO can enhance the photocatalytic activity of ZnO whiskers. This is chiefly ascribed to two factors: (1) a moderate amount of surface VO is beneficial to the separation of photogenerated electrons and holes; (2) the existence of VO improves the light absorption in the visible light region.

Thermal and mechanical properties of in situ polymerized polyethylene/tetra‐needle likeZnOwhisker composite

AbstractA 3‐aminopropyltriethoxysilane modified tetra‐needle like ZnO whiskers fillers containing Ziegler‐Natta catalyst is synthesized through a coagglomeration method. The surface of filler is fully wrapped with Ziegler‐Natta catalyst and the active sites are well dispersed in the catalyst. It exhibits good activity (28.7 g‐polyethylene/g‐cat) towards ethylene polymerization to give a composite of polyethylene and tetra‐needle like ZnO whiskers filler with enhanced thermal stability and mechanical properties due to the good dispersion and interface adhesion of the filler to polyethylene matrix. Therefore, this study provides a simple method to prepare high‐performance polyethylene with uniform filler distribution, good thermal stability, rigidity, and toughness.

Development of ZrC/T-shaped ZnO whisker coated dual-mode Janus fabric for thermal management

The emergence of thermal management technologies is vital to enhancement of personal thermal comfort and reduction in building energy consumption. Despite of tremendous advancement in thermoregulative textiles, the cooling and heating functions are often achieved separately, failing to meet the practical requirements under a dynamically changing thermal environment. Regarding such a significant scientific and technological challenge, we report on an innovative Janus thermoregulative fabric with cooling and heating modes, based on solar heat shielding and photothermal conversion, respectively. The Zirconium carbide (ZrC) nanoparticles with broad-band absorption and photo-thermal conversion were deposited one side of a polyester fabric substrate using magnetron sputtering, while the T-shaped ZnO (TZ) micro-whiskers minimizing heat gain in the visible and near-infrared (NIR) were coated on the opposite side with polydimethylsiloxane (PDMS) and polyurethane (PU) resin. The home-made chambers covered by the Janus fabric are cooled by 5–7 °C and warmed by 2–3 °C under both indoor and outdoor environments. The photothermal enhancement in the heating mode is significantly improved by over 20% in the solar irradiance absorption, and in the cooling mode, the Janus fabric has a large reflectivity (∼90%) and a high emissivity (>90%) in the mid-infrared simultaneously. The fabrication of the present Janus fabric is highly scalable, showing great potential in improving personal thermal management and energy saving of indoor air conditioning.

Synergistic effects of ZnO whiskers and MWCNTs on the friction-induced vibration of a polymer

Weakening the deformation behaviors on contact interfaces or improving the damping property of polymer matrix composite is conducive to reducing or eliminating friction-induced vibration behaviors. A new high-density polyethylene (HDPE) matrix composite consisting of tetra-needle-like ZnO whiskers (T-ZnOw) and multi-walled carbon nanotubes (MWCNTs) was fabricated. The friction and vibration experiments illustrated that T-ZnOw clearly weakened the deformation behaviors, meanwhile MWCNTs embowed polymer with good damping property. Hence, MWCNTs jointed with T-ZnOw could reduce frictional force and enhance vibration absorbing ability, finally keeping the stability of the contact interface and reducing the friction-induced vibration behaviors. It would help in understanding the synergistic effect of MWCNTs and T-ZnOw on vibration behaviors and developing novel composites with low friction and high damping properties.

Interface design and the strengthening-ductility behavior of tetra-needle-like ZnO whisker reinforced Sn1.0Ag0.5Cu composite solders prepared with ultrasonic agitation

To develop a lead-free solder with high strength and ductility, a novel interface was designed between the tetra-needle-like ZnO whisker (T-ZnOw) and Sn1.0Ag0.5Cu solder matrix. First, surface modification of T-ZnOw was conducted using a pyrolysis method based on self-assembly to deposit NiO nanoparticles densely and evenly on the whisker surface. The interfacial relationship between T-ZnOw (100) and NiO (101) planes was semi-coherent with a misfit of 0.145. In-situ transmission electron microscopy was used to explore the surface modification mechanism. Next, a composite solder of 0.3mass% NiO/T-ZnOw reinforced Sn1.0Ag0.5Cu was prepared with ultrasonic agitation, and the introduced reinforcement was uniformly distributed in the solder matrix. A thin NiO transition layer existed between the reinforcement and matrix, indicating the formation of the Sn1.0Ag0.5Cu/NiO/T-ZnOw sandwich structure interface. No gaps, pores, or new phases were formed at the interface, and atomic interdiffusion occurred at the interface to form effective bonding. The composite solder shows improved wettability compared with plain solder. The ultimate tensile strength (UTS) and elongation of the composite solder were 32.5 MPa and 28.1%, respectively, being 19.0% and 35.1% higher than those of the plain Sn1.0Ag0.5Cu solder. The strengthening-ductility mechanisms primarily included load transfer, grain refinement, and misfit dislocation effects.

Luminescent properties of a ZnO whisker array as a scintillation detector material

We have studied luminescent properties of a ZnO whisker array, a promising crystalline material for scintillation detectors, capable of ensuring a fast and strong response and a short afterglow time. Measurements have been performed under X-ray and UV optical excitation. We present a comparative analysis of spectral features of the near-band-edge emission of the whisker array at low (∼80 K) and room temperatures in relation to the excitation method.

Ultraviolet Luminescence of ZnO Whiskers, Nanowalls, Multipods, and Ceramics as Potential Materials for Fast Scintillators

The presented work is dedicated to the study and comparison of scintillating properties of zinc oxide samples prepared in different morphologies: whiskers, nanowalls, multipods, and ceramics. It was shown that total transmittance, photo- and radioluminescence spectra, and radioluminescence kinetics can vary significantly depending on sample structure and preparation conditions. The highest total transmittance was registered for ZnO ceramics (>50% at 0.5 mm thickness). Differences in the transmittance of whiskers, nanowalls, and multipods can be attributed to their shape and thickness which affects the amount of light refraction and scattering. The study of radioluminescence demonstrated that all samples, except undoped ceramics and air annealed whiskers, have predominantly fast luminescence with a decay time <1 ns. High transmittance of ceramics opens the way for their use in the registration of high energy X-ray and gamma radiation, where a large volume of scintillators is required. In cases, where large scintillator thickness is not a necessity, one may prefer to use other ZnO structures, such as ensembles of whiskers and nanowalls. Studies of near-band-edge luminescence components at low temperatures showed that the structure is quite similar in all samples except Ga doped ceramics.

Dielectric, magnetic, and microwave absorbing properties of Ag-plated terapod-like ZnO whiskers

Thin thickness, lightweight, wideband and high absorption intensity are highly desirable properties for the next-generation electromagnetic wave absorbing materials. This study investigates the dielectric, magnetic, and microwave absorbing properties of terapod-like ZnO whisker (ZnOW) modified by Ag nanocrystals (Ag-ZnOW), synthesized by vacuum evaporation method. The complex permittivity and permeability were measured at a microwave frequency range of 2–18 GHz. Ag nanocrystals plated on the surface of whiskers enhance the magnetic loss of ZnOW. The Ag-ZnOW possesses much broader bandwith of absorbing peak than that of unplated ZnOW. The maximum reflectivity (R) is about −30.27 dB at 11.40 GHz and the corresponding bandwidth below −10 dB is more than 5.25 GHz with a matching thickness of 3.0 mm. The calculated results show that the peak of R shifts to lower frequency region with the increase of thickness, and the Ag-ZnOW is an excellent candidate for designing lightweight and multipurpose microwave absorbers.

Manipulating conductive network formation via 3D T-ZnO: A facile approach for a CNT-reinforced nanocomposite

Abstract To achieve an efficient conductive network while preserving the properties of carbon nanofillers is a challenging and essential issue for the fabrication of highly conductive polymeric nanocomposites. The present paper reports a facile approach to manipulate the network formation in the polymer matrix via introducing the tetrapod ZnO whisker (T-ZnO) in the carbon nanotube (CNT)-reinforced epoxy composite. The influence of T-ZnO on the CNT dispersion was evaluated by UV-Vis spectroscopy, rheological measurement, scanning electron microscopy (SEM), and electrical and mechanical properties of the bulk composite. The results showed that the CNTs tend to disperse more uniformly with an increase in T-ZnO loading. An optimized ratio of 1:2 between CNTs and T-ZnO was found to significantly enhance the electrical conductivity by 8 orders of magnitude. A low percolation threshold of 0.25 wt% CNTs was achieved in this hybrid CNTs/T-ZnO composite, which is only 40% of the threshold value in the pure CNTs/epoxy. The flexural strength and modulus of the hybrid composite were also improved noticeably in comparison to the CNTs/epoxy. The mechanism for increasing the performance of the nanocomposite was analyzed. These results indicated that the T-ZnO can assist to efficiently improve the dispersion and the formation of the conductive network, which is beneficial to the enhancement of the mechanical and electrical performance of the nanocomposite.

Paper machine manufactured photocatalysts - Lateral variations

Abstract Paper machine manufacturing of photocatalysts can enable low cost devices for removal of low concentrated pollutants. Lateral variations originating from the paper making process leads to variations of the catalytic activity over the paper area. Paper machine manufactured papers made from tetrapodal ZnO whiskers and kraft pulp were investigated in this test geometry using simulated solar light. Photocatalytic ZnO papers were laminated between polyethylene sheets and an indicator solution seeped into the laminated photocatalytic paper, to create a test geometry where the indicator ink is confined to a small volume between the polyethylene sheets. The photocatalyst papers exhibited surprisingly similar photocatalytic behavior although having different catalyst loading 15, 30 and 45 wt percent. All papers exhibited lateral variations that peaked during the conversion. The results show that production of effective photocatalytic composite papers can be scaled. Further, the results show that variations must be considered for photocatalytic papers.

Flexural damage and failure behavior of glass fiber epoxy composites repaired by patch embedded with ZnO whiskers

Three-point bending tests are employed to research the damage behavior of glass fiber epoxy composites repaired by patch embedded with ZnO whiskers. In particular, the role of ZnO whiskers is discussed in detail. In the whole process, acoustic emission and digital image correlation are performed to monitor the damage behaviors in real time. The results indicate that matrix cracking and delamination damage are the main failure mode between the patch and the motherboard during the process of fracture failure. Correspondingly, the acoustic emission signals with high relative energy and high amplitude are generated. Besides, the cumulative hits increase dramatically. Therefore, the stress concentration at the interface of composites can be analyzed indirectly by the change of acoustic emission signals. ZnO whiskers and resin matrix have a good bonding property, the failure load and matrix strength of the repaired specimens increase significantly. Moreover, ZnO whiskers collaborate with the resin matrix to resist some external forces, increasing the stiffness and the resistance ability to deformation of the repaired composite specimens.