Hollow ZnO Research Articles

Photo-electrochemical Behaviors of Hollow ZnO Spheres Prepared by Zinc in Aqueous Solution

Abstract ZnO with abundant morphologies has been widely applied in photo-electrochemical water splitting. A novel Pt-induced faint electrochemical route is developed to synthesize hollow ZnO spheres from zinc dust in aqueous solution at room temperature. Here, the Zn|ZnO serves as an anode and Pt|H2O|H2 serves as a cathode. The hollow ZnO spheres exhibit enhanced photocurrent intensity due to a multiple light reflection.

Enhanced photovoltaic performance utilizing effective charge transfers and light scattering effects by the combination of mesoporous, hollow 3D-ZnO along with 1D-ZnO in CdS quantum dot sensitized solar cells

A combination of 3-dimensional (3D) hollow mesoporous ZnO microspheres (ZnO HMSP) and vertically grown one-dimensional ZnO nanowires (1D ZnO NWs) on a fluorine doped tin oxide (FTO) coated glass substrate has been investigated as a photoanode for a CdS quantum dot-sensitized solar cell (QSSC). A comparative study of the photovoltaic performance of the solar cell with devices fabricated with pristine ZnO HMSPs and ZnO NWs was carried out. The proposed photovoltaic device exhibits an enhancement in power conversion efficiency (PCE) upto ∼74% and ∼35%, as compared to the 1D ZnO NW and ZnO HMSP based solar cells. The maximum incident photon-to-current conversion efficiency (IPCE) for the solar cell was observed to be ∼40%, whereas for the devices fabricated with bare ZnO HMSP and ZnO NW the IPCE were only ∼32% and ∼19%, respectively. The enhanced photovoltaic performance of the solar cell is attributed to the high Brunauer-Emmett-Teller (BET) surface area, efficient light-scattering effects and facilitated diffusion of the electrolyte for better functioning of the redox couple (S(2-)/Sn(2-)) in the hybrid photoanode. Moreover, a faster electron transport through 1D ZnO NWs provides better charge collection from the photoactive layer, which leads to an increase in the short circuit current density of the device. The present study highlights the design and development of a new hybrid photoanode for solar harvesting.

Facile synthesis of novel hierarchical hollow ZnO microspheres

Novel hierarchical hollow ZnO microspheres, composed of large ZnO crystals on the outer surfaces and small ZnO crystals on the inner surfaces, were synthesized by a chemically induced self-transformation process, employing the ester elimination between zinc formate dihydrate and ethanol.

Sonochemical Fabrication of Twinned ZnO Hollow Ellipses for Electrochemical Biosensing

Twinned ZnO hollow ellipses (ZnO HEs) have been successfully fabricated by a one-step template-free sonochemical route. The products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results showed that the ZnO HEs had a hexagonal wurtzite structure, the wall of which was composed of ZnO nanorods. A possible growth mechanism for the formation of ZnO HEs was proposed, in which sonication played a crucial role. The highly efficient H2O2 electrochemical biosensor was fabricated using the film immobilized with hemoglobin, ZnO HEs and chitosan on glassy carbon electrode. The biosensor showed high stability and excellent electrocatalytic activity toward H2O2 with a linear range from 0.5 to 250 microM and a detection limit of 0.15 microM.

Fabrication of hollow ZnO hexahedral nanocrystals grown on Si(100) substrate by a facile route

Using a facile two-step of wet chemical procedure to synthesize hollow hexahedral zinc oxide on a Si(100) substrate is described. The X-ray powder diffraction (XRD), scanning electron microscope (SEM) and transmission electron microscope (TEM) were employed to investigate the structure and morphology of products, also the photocatalytic and ferromagnetic properties were examined. The results showed that the diameter of ZnO with hollow structure is 200nm and a hole with diameter of 100nm, which is expected to be utilized as a catalyst support material in environmental remediation. The formation mechanism of hollow hexahedral ZnO is based on a dehydration reaction of Zinc 4-coordinated complexes and a preferential defect-etching process. Further investigation on the photocatalytic activity of the products showed the degradation of tetracycline is high to 98% in 120min, also the hollow ZnO nanocrystals were proved having ferromagnetic property.

From the ZnO Hollow Cage Clusters to ZnO Nanoporous Phases: A First-Principles Bottom-Up Prediction

A family of ZnkOk (k = 12, 16) cluster-assembled solid phases with novel structures and properties has been characterized utilizing a bottom-up approach with density functional calculations. Geometries, stabilities, equation of states, phase transitions, and electronic properties of these ZnO polymorphs have been systematically investigated. First-principles molecular dynamics (FPMD) study of the two selected building blocks, Zn12O12 and Zn16O16, with hollow cage structure and large HOMO–LUMO gap shows that both of them are thermodynamically stable enough to survive up to at least 500 K. Via the coalescence of building blocks, we find that the Zn12O12 cages are able to form eight stable phases by four types of Zn12O12–Zn12O12 interactions, and the Zn16O16 cages can bind into three phases by the Zn16O16–Zn16O16 links of H′, C′, and S′. Among these phases, six ones are reported for the first time. This has greatly extended the family of ZnO nanoporous phases. Notably, some of these phases are even more stable than the synthesized metastable rocksalt ZnO polymorph. The hollow cage structure of the corresponding building block ZnkOk is well preserved in all of them, which leads to their low-density nanoporous and high flexibility features. In addition the electronic integrity (wide-energy gap) of the individual ZnkOk is also retained. Our calculation reveals that they are all semiconductor with a large direct or indirect band gap. The insights obtained in this work are likely to be general in II–VI semiconductor compounds and will be helpful for extending the range of properties and applications of ZnO materials.

Preparation and Characterization of ZnO Hollow Micro-spheres with Excellent Property of Blue Emission

Preparation and Characterization of ZnO Hollow Micro-spheres with Excellent Property of Blue Emission

Nanostructures: Synthesis of Small Hollow ZnO Nanospheres from the Gas Phase (Part. Part. Syst. Charact. 5/2013)

The hollow nanospheres were obtained by chemical vapor synthesis from diethylzinc as described by Markus Winterer and co-workers on page 434. The color coded TEM image displays hollow nanospheres of about 50 nm in diameter consisting of shells of polycrystalline ZnO with a thickness of 20 nm consistent with the column length obtained from Rietveld analysis of X-ray diffraction data. Experiments are consistent with a Kirkendall formation mechanism and metallic zinc nanoparticles as intermediate.

Controllable and enhanced HCHO sensing performances of different-shelled ZnO hollow microspheres

Hollow ZnO microspheres with tunable interior architecture are successfully synthesized by a simple green chemistry routes at low temperature. This process is environmentally friendly processing, which based on without using solvents, employing carbon microspheres as template and reaction at low temperature. The layer-control of hollow ZnO microspheres can be easily adjusted by varying the concentration of the zinc precursor added. To demonstrate the usage of such hollow ZnO microspheres, gas sensors have been fabricated from the as-synthesized hollow ZnO microspheres with different shelled and investigated for formaldehyde (HCHO) detection. Interestingly, the response of hollow ZnO microspheres increased with increasing the number of shell structures. These results indicate that three-shelled ZnO sensor displays about 1.5 and 3–4 fold enhancement in response compared to double and single-shelled one, respectively. The mechanism of enhanced sensor performances is also proposed.

Synthesis of Small Hollow ZnO Nanospheres from the Gas Phase

Synthesis of small hollow ZnO nanospheres is performed using a template-free, gas-phase driven process. The experiments demonstrate the influence of the synthesis parameters on the structure of the hollow spheres and the formation mechanism of the ZnO hollow spheres.

Fabrication of Hollow ZnO Particles and Its Photocatalytic Property by Modifying of Nano ZnS

Large scale hollow ZnO spheres were prepared by a solvothermal method with the help of the solvent. And ZnS nanoparticles were successfully fabricated on the surface of ZnO via a hydrothermal process. These heterostructured ZnO/ZnS core/shell particles are around 1-2 microm in diameter, the ZnS shell formed on the surface of hollow ZnO sphere is comprise of the primary crystals about 30 nm in diameter. The products prepared were characterized by field emission scanning electron microscope (FE-SEM), X-ray powder diffraction (XRD), transmission electron microscope (TEM), and photo-luminescence spectroscope (PL). Theoretical calculation and experimental results have demonstrated that the combination of ZnO and ZnS (two wide band gap semiconductors) could yield a novel material with the photoexcitation threshold energy lower than the individual components. The electron transfers between ZnO core and ZnS shell, which strongly affect the photoluminescence and photocatalytic performances. The photocatalytic activities of the products were evaluated by methyl orange degradation as a probe reaction. The relationship of ZnO/ZnS core/shell particles as excellent photocatalyst could be anticipated.

ZnO hollow microspheres with exposed porous nanosheets surface: Structurally enhanced adsorption towards heavy metal ions

The micro/nanostructured materials can be used for the high efficient adsorbents owing to their high specific surface area, high surface activity and high stability against aggregation. In this paper, standing porous nanosheet-built ZnO hollow microspheres are produced through a modified hydrothermal route. Such ZnO hollow microspheres with exposed porous nanosheets surface exhibit significantly structurally enhanced adsorption performance for heavy metal cations [Cu(II), Pb(II), Cd(II), and Ni(II), etc.], compared with the commercial ZnO nanopowders, and show much higher adsorption capacities than the surface functionalized activated carbon reported previously. The adsorption isotherms can be described by Langmuir model or Freundlich model, depending on the electronegativity of the heavy metals. This ZnO hollow microspheres with exposed porous nanosheets surface can be used as adsorbent for efficient removal of heavy metal ions from the contaminated water with weak acidity or alkalescence, and easily separated from solution. This study also deepens understanding adsorption behavior of micro/nanostructured ZnO to heavy metal cations.

A feasible route to prepare hollow ZnO microtube via modulating reagent’s vapor pressure and growth temperature

Abstract

Synthesizing tubular and trapezoidal shaped ZnO nanowires by an aqueous solution method

In this paper we present a novel bottom-up method suitable for developing vertically aligned hollow ZnO nanowires, ZnO nanotubes as well as longitudinally half ZnO nanowires. The procedures used for synthesizing such crystals combine chemical and electrochemical growth processes in aqueous solution at low temperatures (<90 °C), with a growth block process. A thin layer of gold, deposited when the nanowire growth process is at half way, has the crucial role of blocking the growth along the intended directions. The possibility of fabricating highly aligned crystals on a wide range of polymeric substrates, including flexible or transparent ones, is also illustrated. Our proposed methods hold potential for new developments in piezotronics and piezophotonics by allowing fabrication of nanodevices in the inner region of the hollow nanowires and nanotubes.

Ultrasensitive electrochemiluminescence detection of lengthy DNA molecules based on dual signal amplification

Aimed at the facile detection of lengthy DNA molecules, an easily operated sandwich-type electrochemiluminescence (ECL) DNA biosensor was constructed on a glassy carbon electrode (GCE) based on CdTe quantum dots coated hollow ZnO nanoparticles (CdTe-ZnO NPs)-S(2)O(8)(2-) ECL system in this work. To fabricate a high-performance protocol, the GCE surface was successively modified by graphene nanosheet (GS), carbon nanotube (CNT) and gold nanoparticles (AuNPs) to form AuNPs dotted CNT-GS composites (Au@CNT-GS) platform, which improved the electronic transmission rate as well as increased the amount of immobilized capture probe CMV-F (S(1)). For further ultrasensitive, stable and low-potential ECL detection, CdTe-ZnO NPs were synthesized, and employed to label signal probe T7 promoter (S(3)). Based on the hybridization effect, the immobilized capture probe S(1), target DNA and labeled signal probe S(3) formed a sandwich-type DNA complex, which produced the ECL emission in the presence with S(2)O(8)(2-) coreactant. Under optimal conditions, the DNA ECL biosensor showed a good linear range over 10(-14) M to 10(-19) M with a low detection limit of 0.61 × 10(-19) M. The proposed strategy demonstrates a reproducible, stable, and potent method that can be expanded to detect the genome which exists in living cells.

Template-free synthesis and gas sensing properties of hierarchical hollow ZnO microspheres

Hierarchical hollow ZnO microspheres were prepared via a one-pot template-free hydrothermal synthesis. It's worth mentioning that the hollowness of these microspheres could be controlled by adjusting the zinc source concentration. Furthermore, these microspheres were integrated into a sensorial structure which exhibited fast response and recovery times and good selectivity to ethanol.

Band edge emission enhancement by quadrupole surface plasmon–exciton coupling using direct-contact Ag/ZnO nanospheres

Periodic Ag nanoball (NB) arrays on ZnO hollow nanosphere (HNS) supporting structures were fabricated in a large area by a laser irradiation method. The optimized laser power and spherical supporting structure of ZnO with a certain size and separation were employed to aggregate a sputtering-deposited Ag nano-film into an ordered, large-area, and two dimensional Ag NB array. A significant band edge (BE) emission enhancement of ZnO HNSs was achieved on this Ag NB/ZnO HNS hybrid structure and the mechanism was revealed by further experimental and theoretical analyses. With successfully fabricating the direct-contact structure of a Ag NB on the top of each ZnO HNS, the highly localized quadrupole mode surface plasmon resonance (SPR), realized on the metal NBs in the ultraviolet region, can effectively improve the BE emission of ZnO through strong coupling with the excitons of ZnO. Compared with the dipole mode SPR, the quadrupole mode SPR is insensitive to the metal nanoparticle's size and has a resonance frequency in the BE region of the wide band gap materials, hence, it can be potentially applied in related optoelectronic devices.

Multi-hot spot configuration on urchin-like Ag nanoparticle/ZnO hollow nanosphere arrays for highly sensitive SERS

Urchin-like Ag nanoparticle (NP)/ZnO hollow nanosphere (HNS) arrays were fabricated employing a simple, low cost and wafer scale method consisting of nanosphere lithography (NSL) and solution processes. This three-dimensional (3D) multi-hot spot decorated nanocomposite presents an as high as 108 Raman enhancement using Rhodamine 6G (R6G) as the probe with the concentration down to 10−10 M. The high density hot spots in a unit area and strong field intensity around each individual hot spot in 3D layout are believed to be the major reasons for this high sensitivity Raman phenomenon, which is further proved by the theoretical simulation results. Given its high Raman sensitivity and good reproducibility in a large area, this urchin-like Ag NP/ZnO HNS hybrid nanoarray can be reasonably proposed to be used as a SERS substrate in practical applications, including bio-sensing, materials characterization, environmental science and so on.

Stress induction, UV emission variation and efficiency variation in dye-sensitized solar cells of hollow ZnS/ZnO/ZnS nanostructures

We synthesized a hollow ZnS/ZnO/ZnS nanostructure via a two-step chemical colloidal process. The structural and optical properties, and application of the samples were examined in detail. We found that a E2(high) mode with a red-shift of 6 cm−1 compared with original ZnO hollow nanostructure was induced in the Raman spectra. The red-shift of the E2(high) mode is attributed to stress induction in the hollow ZnS/ZnO/ZnS nanostructure. When the thickness of the ZnS nanoshell increases, a blue-shift UV emission band of approximately 6 nm is displayed in the room temperature photoluminescence spectra. The blue-shift of the UV emission band of the as-synthesized sample deteriorates when the thickness of the ZnS nanoshell becomes thicker. Although, the hollow ZnS/ZnO/ZnS nanostructure can help in increasing the optical path length within the electrode of dye-sensitized solar cells (DSSC) due to the multiple scattering of the ZnS–ZnO–ZnS interface. In this study, a low performance N719 DSSC was obtained. A possible reason for the lower performance of DSSC with a hollow ZnS/ZnO/ZnS nanostructure electrode is discussed.

Hollow, porous, and yttrium functionalized ZnO nanospheres with enhanced gas-sensing performances

We report the synthesis of a hierarchical nanostructure of hollow and porous ZnO nanospheres with a high specific surface area as a novel sensing material to toxic formaldehyde by a simple template-free hydrothermal technique in organic solution. We demonstrate that the liquid mixture ratio and hydrothermal time play a pivotal role in forming such unique morphology and propose a growth mechanism of Ostwald ripening coupled with grain rotation induced grain coalescence. Comparison investigations reveal that yttrium allows resistance reduction of sensors and enhances significantly gas-sensing performances of ZnO nanospheres toward the formaldehyde over the commonly used undecorated ZnO nanoparticles. Such hollow, porous, and yttrium functionalized ZnO nanospheres could therefore serve as hybrid functional materials for chemical gas sensors. The results represent an advance of hierarchical nanostructures in enhancing further the functionality of gas sensors, and the facile method presented could be applicable to many other sensing materials.