Hexagonal-shaped ZnO Research Articles

Fabrication of zinc oxide nanorods for photocatalytic degradation of docosane, a petroleum pollutant, under solar light simulator.

The use of advanced oxidation processes (AOP) in photocatalysis is critical for treating hazardous chemical compounds in oil-produced water (OPW). ZnO NRs are one of the most important modern and safe photocatalysts and have been easily prepared by a microwave-assisted hydrothermal method and grown on glass substrates. Hexagonal-shaped ZnO NRs and a bandgap energy (Eg) of up to 3.2 eV were characterized using SEM, XRD, UV-Vis, and PL devices, respectively. The effectiveness of photocatalytic degradation on the organic docosane solution was evaluated using a solar light simulator. On the surface area of the ZnO NRs, high photon absorption causes e-/h+ pairs to be excited between the VB and CB, producing free radicals that immediately react with organic contaminants and transform them into harmless chemicals. The photocatalytic degradation efficiency of the compound docosane analysed using GC-MS/MS reached 68.5% at 5 hours of irradiation. A mechanism for the photocatalytic degradation of docosane was proposed at pH ∼ 6.5, and a reduction of 60.5% of the total organic carbon (TOC) was achieved. Thus, the photocatalytic treatment of organic compounds contained in OPW has great potential and serves an important environmental purpose.

ZnO Nanocrystals with Hexagonal Disk Shape Grown by Thermal Evaporation Method in Air at Atmospheric Pressure

Hexagonal-shaped ZnO nanodisks were synthesized at temperatures above 1000oC via thermal evaporation of a mixture of ZnO, SnO, and graphite powders as the source materials. Notably, the ZnO nanodisks were easily formed in ambient air at atmospheric pressure. The ZnO nanodisks could not be obtained without SnO in the source material, which indicated that the SnO powder played a crucial role in the growth of the hexagonal disk shaped ZnO nanocrystals. The ZnO powder in the source material was reduced to Zn vapor due to the graphite and SnO powders. In particular, the SnO is considered to play a role in promoting the reduction of ZnO. As a result, the concentration of Zn vapor increased quickly, leading to the fast nucleation of Zn crystals with a hexagonal close packed crystal structure. In the growth habit of the Zn crystal, the growth rate of <1010> is much faster than that of [0001] because (0001) has the lowest surface energy, resulting in the hexagonal disk shape. Then the hexagonal-shaped ZnO nanodisks were obtained by oxidation of the Zn nanodisks under air atmosphere. The XRD and EDS results showed that the ZnO nanodisks had a hexagonal wurtzite crystal structure and high purity. The ZnO nanodisks formed at 1000oC exhibited a strong ultraviolet emission centered at 380 nm, which was indicative of high crystalline quality.

High performing hexagonal-shaped ZnO nanopowder for Pseudo-supercapacitors applications

Significant research efforts have been dedicated toward developing environmentally friendly energy conversion and storage technologies as a result of the growing demand for ecologically sustainable energy and the rapid depletion of existing fossil fuels. Pseudo-capacitance behavior of hexaogonal shaped ZnO nanopowders were prepared by a simple hydrothermal route. The XRD analysis revealed the formation of the hexaoganal phase of ZnO nanopowders for prepared samples. The pseudo-capacitance behavior of electrodes coated with crystalline ZnO nanopowders was investigated using electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV) and galvanostatic charge-discharge (GCD) systems. Hexaogonal shaped ZnO nanopowders modified electrode was achieved the highest specific capacitance value of 448 F/g in 0.25 A/g at 2 M KOH. The ZnO modified electrode was shown to be highly stable for 5000 cycles at 0.5 A/g, which is significantly more stable than stability of other prepared electrodes. Over 5000 cycles, the assembly of ZnO@NF//AC@NF as an asymmetric supercapacitor has excellent capacitance retention of 99.5% at 0.5 A/g. This is a low-cost and highly efficient device. It is a promising canditate and alternate supercapacitor for energy storage devices.

An Operando X-ray Absorption Spectroscopy Study on Sensing Characteristics of Vertically Aligned ZnO Thin Film for Methane Gas Sensors

In this work, a simple, facile growth approach for a vertically aligned ZnO thin film is fabricated and its application towards methane gas sensors is demonstrated. ZnO thin film was prepared by a combination of hydrothermal and sputtering methods. First, a ZnO seed layer was prepared on the substrate through a sputtering technique, then a ZnO nanorod was fabricated using a hydrothermal method. The surface morphology of the ZnO film was observed by scanning electron microscopy (SEM). A ZnO nanorod coated on the dense seed layer is clearly visible in the SEM image. The average size of the hexagonal-shaped ZnO rod was around 50 nm in diameter, with a thickness of about 1 mm. X-ray absorption near-edge structures (XANES) were recorded to characterize the structural properties of the prepared film. The obtained normalized Zn K-edge XANES of the film showed the characteristic features of ZnO, which agreed well with the standard ZnO sample. The measurement of Zn K-edge XANES was performed simultaneously with the sensing response. The results showed a good correlation between sensor response and ZnO structure under optimal conditions.

PHOTOCATALYTIC PROPERTIES OF BIOLOGICALLY SYNTHESIZED UNCOATED AND CALCIUM COATED ZnO NANOPARTICLES USING CUCUMBER JUICE

Uncoated ZnO and calcium-coated ZnO nanoparticles (Ca-ZnO) were biologically synthesized using cucumber juice as a reducing and capping agent. Cucumber belongs to Cucurbitaceae family, is rich in water content and possesses antioxidant activity. The chemical composition and morphology of the synthesized NPs were determined by scanning electron microscopy (SEM), energy dispersive X-ray spectrophotometer (EDS), high-resolution transmission electron microscopy (HR-TEM), X-ray diffraction (XRD)and FT-IR. The spherical as well as hexagonal-shaped ZnO nanoparticles were obtained in the size range of 4-70 nm. Coated and uncoated ZnO nanoparticles were evaluated for their photo degradability of methylene blue (MB) and rhodamine B (RB) dyes. They showed nearly 100% photodegradation of methylene blue in lesser time, however, showed minimum degradation of rhodamine B dye. Calcium coating over ZnO NPs enhanced their photocatalytic properties.

Ultrafast, trace-level detection of NH3 gas at room temperature using hexagonal-shaped ZnO nanoparticles grown by novel green synthesis technique

Herein, an ultrafast, sensor has been developed for trace-level detection of Ammonia (NH3) gas using hexagonal-shaped ZnO nanoparticles (NPs). The ZnO NPs were grown by low-cost eco-friendly green synthesis process and characterized by various techniques. The electron microscopic images reveal the synthesis of uniform, highly dense and hexagonal-shaped ZnO NPs. The UV–Vis spectra illustrate a band gap of 3.89eV. XRD, XPS and Raman studies explain the high-quality hexagonal wurtzite-structure of ZnO NPs showing presence of electronic/chemical states of ions. The NH3 gas sensing properties of ZnO NPs were evaluated at different concentrations. The sensor exhibited an excellent response value of 2.5 at 5 ppm NH3 wherein quick response time was 5 s and fastest recovery time was 8 s. The sensing results could be attributed to the optimum number of oxygen species and active sites which are responsible for enhanced performance of the developed ZnO NPs based sensor.

Influence of growth temperature and duration on different properties of ultra-long ZnO nanorods grown by modified chemical bath deposition method

In this work, ultra-long ZnO nanorods (NRs) were grown on ZnO buffered Si substrates by using direct heat substrate-modified chemical bath deposition (DHS-MCBD) method. Initially, the growth temperature was varied in the range 140 °C to 250 °C while keeping the time fixed at 4h. In the second stage, the growth temperature was kept fixed at 220 °C and the time was changed from 4h to 8 h. The morphological, structural and optical properties of ZnO NRs at different growth temperatures were investigated by using field emission scanning electron microscope (FESEM), x-ray diffraction (XRD) and photoluminescence (PL) spectroscopy techniques. The surface morphology results revealed the formation of hexagonal-shaped, ultra-long and vertically-aligned ZnO NRs. The average length of the NRs was increased from 5.7 μm to 24.5 μm by increasing the growth temperature from 140 °C to 250 °C. The XRD results specified the formation of c-axis oriented diffraction peak corresponding to hexagonal ZnO NRs in all the samples. The intensity of this peak was increased by increasing the growth temperature up to 220 °C, however, on further increasing the temperature to 250 °C, the c-axis peak intensity was decreased. The PL analysis indicated higher UV to deep level emission intensity ratio (IUV/IDLE) of the NRs grown at 220 °C as compared to the others. Similarly, by changing the growth time from 4h to 8h, the length of ZnO NRs was also increased. The results obtained were correlated and the chemical reactions for ZnO NRs growth were discussed in this paper.

Preparation and photocatalytic properties of hexagonal-shaped ZnO:Sm3+ by microwave-assisted hydrothermal method

Novel 3D rods ZnO:Sm monophasic microcrystals have been synthesized by the microwave-assisted hydrothermal (MAH) method at 140 °C for 10 min. The experimental results revealed that concentration of samarium have a significant influence on the band gap and photocatalysis. On the other hand, the samarium in the ZnO semiconductor structure increases photodegradation activity. ZnO sample doped with 8% Sm3+ exhibited the best activity in the photodegradation of methylene blue dye when compared to that doped with 0–4 mol%. Enhanced photocatalytic activity was attributed to samarium, which inhibits the recombination of electron–hole pairs.

FACILE HYDROTHERMAL SYNTHESIS OF FLOWER-LIKE ZNONANORODS WITHOUT CATALYSTS

A very simple hydrothermal method (one step) was used at low temperature to synthesis flower-like ZnOnanorods on glass substrate without any template, catalyst or buffer layer before the reaction. Flower-like ZnOnanorods were synthesized by hydrothermally heating 0.1 M precursor solution of hexahedral zinc nitrate Zn(NO3)2.6H2O, hexamethylenetetramine (HMT) and NaOH were the starting materials for the chemical reaction under stirring. The field emission scanning electron microscopy (FE-SEM) images showed that the flower-like structures were formed in 3.5 h hydrothermally-heated for sample, whereas the experimental pattern of the films by X-ray diffraction show that diffraction peaks can be assigned to the wurtzite hexagonal-shaped ZnO as shown in the (FE-SEM) images, also the morphology of the films studied by atomic force microscope (AFM) shows that the films have high roughness. The energy gap was estimated and optical behavior was investigated.

Distinct spatial profiles and antibacterial effects of 20-nm Ag nanoparticles dripped on ZnO nanorods grown on a polished Ti substrate

Abstract Ag nanoparticles (NPs) were spread by dropping them on hexagonal-shaped ZnO nanorods (NRs) to obtain nanocomposites. ZnO NRs were grown on a polished Ti substrate. The Ag-ZnO nanocomposites were characterized using field-emission scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction, Fourier-transform infrared spectroscopy and optical imaging. The experimental results indicated that Ag NPs tend to aggregate at the tip of ZnO NR surfaces. Furthermore, antibacterial tests confirmed that adding Ag NPs enhances antibacterial effects. The findings regarding the distinct behaviors of Ag NPs may facilitate the development of future biomedical devices.

Hydrothermal growth of ZnO nano rods without catalysts in a single step

Abstract A very simple one step hydrothermal method was used to prepare ZnO nano rods without any catalyst or buffer layer before the reaction. The process took place inside stainless steel autoclave. ZnO nano rods and flower like were successfully synthesized using. Hexahedral zinc nitrate Zn(NO3)2.6H2O, DE fructose and NaOH were the starting materials for the chemical reaction under stirring with heat treatment. Then the obtained powder screen printed. In order to study the influence of the synthesis process on the morphology and the optical properties crystalinity and structural properties are studied by X-ray diffraction and field emission scanning electron microscope (FE-SEM), the experimental pattern of the films show that diffraction peaks can be assigned to the wurtzite hexagonal-shaped ZnO as shown in the FE-SEM pictures, also the morphology of the films studied by atomic force microscope shows that the prepared thick films have high roughness. The energy gap was estimated and optical behavior was studied.

Synthesis of ZnO nanoplates decorated rhombus-shaped ZnO nanorods and their application in solar cells

Novel nanostructures of ZnF(OH) nanoplates decorated rhombus-shaped ZnF(OH) nanorods were fabricated. The obtained precursors were transformed by calcination to porous hierarchical ZnO nanostructures with the original morphologies retained. Field emission scanning electron microscope images exhibit that the nanoplates are grown in the interstices between the nanorods and on the top of the nanorods. The structure and composition of the obtained products have been confirmed by transmission electron microscope and X-ray diffraction measurements. The obtained ZnO nanostructures have been successfully used in solar cells. The light-to-electricity conversion results show that the complex nanostructures exhibit a power conversion efficiency of 1.36% with a photoelectrode thickness of 4.2µm, which is comparable to those based on 40µm vertically aligned hexagonal-shaped ZnO nanowire array photoelectrodes. These results indicate that the synthesized ZnO nanoplate decorated rhombus-shaped ZnO nanorod nanostructures are more suitable for application as a photoelectrode in solar cells.

Determination of the structure, morphology and complex refractive index in ZnO-nanopencils/P3HT hybrid structures

Well crystallized flower-shaped ZnO-structures composed of a perfectly hexagonal-shaped ZnO structure were successfully synthesized using a simple microwave assisted hydrothermal method. The NPs with a hexagonal stem and a tapering tip grows out of the base of the flower-shapes. ZnO-NPs were incorporated into the nanomorphology of P3HT and two variations of P3HT:C60 and P3HT:PCBM blended films in order to facilitate charge separation and transport. Thermo-gravimetric analysis revealed that ZnO-NPs are more stable and are of high purity. A complete PL quenching was demonstrated upon incorporating ZnO-NPs on the surface of P3HT and blended films indicating a charge transfer along the ZnO/P3HT and ZnO/P3HT:fullerenes induced by the aligned nanorods which are working as effective electron collectors by shortening the average electron diffusion distance in the P3HT and fullerenes network. Spectroscopic ellipsometry demonstrated that infiltrating of ZnO-NPs, results in the improved refractive index, extinction coefficient and shifts to lower photon energies. Such shifts can be inferred to the improved light absorption through the waveguide effect from the NPs and an increased interfacial area between the ZnO-NPs and P3HT. An improvement in the mobility and conductivity of P3HT films was observed with an incorporation of ZnO.

Ultra-high sensitive ammonia chemical sensor based on ZnO nanopencils

This paper reports a very simple, reliable and facile methodology to fabricate ultra-high sensitive liquid ammonia chemical sensor using well-crystalline hexagonal-shaped ZnO nanopencils as an efficient electron mediator. A low-temperature facile hydrothermal technique was used to synthesize ZnO nanopencils. The synthesized nanopencils were characterized in detail in terms of their morphological, structural and optical properties which confirmed that the synthesized nanomaterial is well-crystalline, possessing wurtzite hexagonal phase and possess very good optical properties. A very high sensitivity of ∼26.58μAcm−2mM−1 and detection limit of ∼5nM with a correlation coefficient (R) of 0.9965 and a response time of less than 10s were observed for the fabricated liquid ammonia by I–V technique. To the best of our knowledge, by comparing the literature, it is confirmed that the fabricated sensor based on ZnO nanopencils exhibits highest sensitivity and lowest detection limit for liquid ammonia. This research opens a way that simply synthesized nanomaterials could be used as efficient electron mediators for the fabrication of efficient liquid ammonia chemical sensors.

Lasing: Room Temperature Excitonic Whispering Gallery Mode Lasing from High‐Quality Hexagonal ZnO Microdisks (Adv. Mater. 19/2011)

Ultraviolet excitonic whispering gallery mode (WGM) lasing from individual hexagonal-shaped ZnO microdisks is reported on p. 2199 by Han Dong Sun and co-workers. The inside cover illustrates the five growth processes for the ZnO microdisks and WGM lasing emitted from the edges of such disks. The work provides detailed WGM lasing characteristics for the microdisks, which may lead to promising applications for low-threshold UV lasers and high-sensitivity sensors.

Synthesis and characterization of zinc oxide nanorods on silicon for the fabrication of p-Si/ n-ZnO heterojunction diode

Hexagonal-shaped ZnO nanorods were successfully grown on p-silicon substrate via thermal evaporation of metallic zinc powder in the presence of oxygen. The grown nanorods were characterized in terms of their structural and optical properties by using X-ray diffraction, FESEM, HRTEM and room-temperature photoluminescence (PL) spectroscopy. It is confirmed from the observed structural and optical properties, that the grown nanorods are well-crystalline with the wurtzite hexagonal phase and are preferentially grown along the [0 0 0 1] direction and exhibiting good optical properties. The as-grown n-ZnO nanorods on p-silicon ( n-ZnO/ p-Si) substrate were used to fabricate p– n heterojunction diode which attains a turn-on voltage of ∼0.5 V. Temperature-dependant (298, 323, 343, 363, 383, and 423 K) I– V characteristics for the fabricated diode were also examined and demonstrated in this paper. It was found that the fabricated heterojunction diode was reasonably stable at higher temperatures and the series resistance slightly increases with increasing the temperature.

Sol−Gel Growth of Hexagonal Faceted ZnO Prism Quantum Dots with Polar Surfaces for Enhanced Photocatalytic Activity

The hexagonal faceted ZnO quantum dots (QDs) about 3-4 nm have been prepared via a sol-gel route by using oleic acid (OA) as the capping agent. It is revealed by electron diffraction patterns and high resolution transmission electron microscopy lattice images that the profile surfaces of the highly crystalline ZnO QDs are mainly composed of {100} planes, with the Zn-terminated (001) faces and the opposite (001) faces presented as polar planes. Compared with spherical ZnO QDs, the hexagonal faceted ZnO QDs show enhanced photocatalytic activity for photocatalytic decomposition of methylene blue. A mechanism for the enhanced photocatalytic activity of the hexagonal faceted ZnO QDs for degradation of methylene blue is proposed. In addition to the large specific surface areas due to small size and high crystalline, the enhanced photocatalytic activity can mainly be ascribed to the special hexagonal morphology. The Zn-terminated (001) and O-terminated (001) polar faces are facile to adsorb oxygen molecules and OH(-) ions, resulting in a greater production rate of H(2)O(2) and OH(*) radicals, hence promoting the photocatalysis reaction. The synthesized hexagonal-shaped ZnO QDs with high photocatalytic efficiency will find widespread potential applications in environmental and biological fields.

From Preannealing of Bilayer Catalysts To Explore the Growth Micromechanisms of ZnO Nanorods

The growth of ZnO nanorods was investigated by having the catalysts in bilayer configurations of Au (top)/Al (bottom), Au/Ni, and Au/In. These catalyst layers were preannealed at 700 or 850 °C in an argon atmosphere. The different growth behaviors were investigated for the complex bilayer catalyst systems in order to indirectly explore the growth micromechanism from an atomistic viewpoint. Experimental results demonstrated that the higher preannealing temperature led to smaller rods. The 850 °C preannealed Au/Al catalyst system performed the growth of hexagonal-shaped ZnO nanorods with a size of 100 nm in cross section. Preannealing is thought to modify the surface energy of catalyst templates through the alloying treatments, which is followed by the growth of ZnO nanorods via a vapor−solid growth mechanism. Growth modes are rationalized by considering the state of catalyst in quasi-liquid or crystal and the type of absorbed species in Zn metal or ZnO molecule.

ZnO Nanorods Based Hydrazine Sensors

Electrochemical sensor for the detection of hydrazine has been fabricated at the surface of gold electrode modified with ZnO nanorods. The ZnO nanorods were grown by non-catalytic simple thermal evaporation process by using metallic zinc powder in the presence of oxygen at low-temperature. The detailed structural studies revealed that the as-grown ZnO nanorods are well-crystalline with the wurtzite hexagonal phase and grown along the [0001] direction in preference. A good and reproducible sensitivity of 4.76 microA cm(-2) microM(-1) has been obtained from the fabricated hexagonal-shaped ZnO nanorods based electrochemical sensor. The response time of the fabricated sensor was less than 10 s with a linear range from 0.2 to 2.0 microM and correlation coefficient of R = 0.9914. The limit of detection (LOD), based on S/N ratio was estimated to be 2.2 microM.

Rapid synthesis and dye-sensitized solar cell applications of hexagonal-shaped ZnO nanorods

This paper reports, for the first time, a very rapid and large-scale synthesis and dye-sensitized solar cells (DSSCs) application of well-crystallized hexagonal-shaped ZnO nanorods at very low temperature of about 70 °C in 20 min. The thin films of as-grown nanorods were used as photo-anode materials to fabricate the DSSCs which exhibited an overall light to electricity conversion efficiency (ECE) of 1.86% with a fill factor of 74.4%, short-circuit current of 3.41 mA/cm 2 and open-circuit voltage of 0.73 V.