ZnO Rods Research Articles

Sonochemical synthesis and visible light induced photocatalytic property of reduced graphene oxide@ZnO hexagonal hollow rod nanocomposite

Abstract The reduced graphene oxide (RGO) sheets (1–4 wt %) containing ZnO hexagonal hollow rods (GZC) nanocomposites were fabricated via sonochemical method. The synthesized composites were characterized using Fourier transform-infrared spectroscopy (FT-IR), X-ray diffraction (XRD), UV-vis diffuse reflectance spectroscopy (UV-vis-DRS), Raman spectroscopy, thermo gravimetric analysis (TGA), field-emission scanning electron microscopy (FE-SEM), energy dispersive analysis of X-rays (EDX), high resolution transmission electron microscopy (HRTEM) and electrochemical impedance spectroscopy. The formation of hexagonal hollow ZnO rod was discussed with growth mechanism and their morphology was confirmed with FESEM and HRTEM analysis. The visible light driven photocatalytic activity of pure ZnO and an incorporation of varying weight percentages of GO into ZnO catalyst (GZC) were evaluated by using the methyl orange (MO) and methylene blue (MB) aqueous dye solutions as model organic pollutants. Among the developed nanocomposites, 3 wt% GZC nanocomposites possesses the highest degradation efficiency, that is, 90.72, 89.72% at 180, 240 min for MB and MO respectively with enhanced visible light absorption range.

Effect of the Concentration of Citrate on the Growth of Aqueous Chemical Bath Deposited ZnO and Application of the Film to Cu(In,Ga)Se2 Solar Cells

ZnO thin films are of considerable interest because they can be customized by various coating technologies to have high electrical conductivity and high visible light transmittance. Therefore, ZnO thin films can be applied to various optoelectronic device applications such as transparent conducting thin films, solar cells and displays. In this study, ZnO rod and thin films are fabricated using aqueous chemical bath deposition (CBD), which is a low-cost method at low temperatures, and environmentally friendly. To investigate the structural, electrical and optical properties of ZnO for the presence of citrate ion, which can significantly affect crystal form of ZnO, various amounts of the citrate ion are added to the aqueous CBD ZnO reaction bath. As a result, ZnO crystals show a nanorod form without citrate, but a continuous thin film when citrate is above a certain concentration. In addition, as the citrate concentration increases, the electrical conductivity of the ZnO thin films increases, and is almost unchanged above a certain citrate concentration. Cu(In,Ga)Se2 (CIGS) solar cell substrates are used to evaluate whether aqueous CBD ZnO thin films can be applicable to real devices. The performance of aqueous CBD ZnO thin films shows performance similar to that of a sputter-deposited ZnO:Al thin film as top transparent electrodes of CIGS solar cells.

Failure analysis of zinc electrode using hydroponic gel and liquid electrolytes in zinc-air batteries at elevated temperatures

Zinc-air batteries were fabricated separately using hydroponic gel (HPG)-6 M potassium hydroxide (KOH) and 6 M liquid KOH, respectively, as the electrolyte. Both batteries were compared in terms of their self-discharge by measuring their open-circuit voltage (OCV) and discharge characteristics at 25, 40, 60 and 80 °C using a constant current of 50.0 mA. As the temperature increased, the OCV dropped. The highest OCV was approximately 1.5 V at room temperature, and all the OCVs were more than 1.4 V at this temperature. At 40 °C, the capacities of the cells were 662.5 mAh g−1 (liquid electrolyte) and 341.3 mAh g−1 (HPG electrolyte). The failure of the batteries was mainly due to the formation of ZnO rod- and flower-like structures and changes to the shape of the anode.

Effect of surface properties of ZnO rods on the formation of anatase-phase TiO2 tubes prepared by liquid deposition method

The effects of the surface properties of ZnO rods on the formation of anatase-phase TiO2 tubes prepared by liquid deposition method is reported. A template made of ZnO rods was prepared on FTO-coated glass by chemical bath deposition and this was then treated under different experimental conditions in an aqueous solution of ammonium hexafluorotitanate and boric acid to investigate the role of the neutral and polar (zinc/oxygen terminated) surfaces of ZnO rods on the formation of TiO2. A calcination step at 550 °C in air was applied to convert the developed Ti-based complexes on the ZnO rods into anatase-phase TiO2 nanostructures. It was observed that a 10-min deposition process led to the development of a mixture of end-capped, open-ended and perforated TiO2 tubes with dimensions resembling those of the ZnO template. Further chemical modification of the surfaces of ZnO rod templates led to the development of anatase-phase TiO2 tubes with open-ends. The surfaces of ZnO rods act as reaction sites for the synthesis of Ti-based complexes. The production of these complexes on the ZnO surface takes place on the neutral side facets of the ZnO rods, while etching of the ZnO rods occurs preferentially along the c-axis (i.e. on the Zn-(O) terminated faces. Consequently, the deposition of TiO2 is considered to happen in two stages: an early and a late stage. The early stage is characterised by the development of Ti-based complexes (Ti hydroxide monomers) on the ZnO surfaces, while the late stage is characterised by polymerisation of these monomers into Ti hydroxide polymers. At the early stage, the deposition process starts on lateral surfaces constituting a foundation for more Ti hydroxide development. Upon calcination at 550 °C in air, these tubular amorphous structures are converted into end-capped anatase-phase TiO2 tubes.

Porous Mo-C coverage on ZnO rods for enhanced supercapacitive performance.

ZnO is a promising electrode material with advantages such as high environmental benignity, low cost and easy synthesis. Like other non-carbon electrode materials, ZnO has low resistivity and is therefore often combined with carbon materials to obtain favorable electronic conductivity. Herein, ZnO rods were prepared and coated with a carbon layer (Mo-C) as a supercapacitive electrode material for supercapacitors. Particularly, the porosity of the carbon layer is increased by modification with MoO42- which serves as chelating agent during the carbonation of dopamine hydrochloride. Compared to dense carbon coating layers, the porous carbon coverage is more favorable for electrolyte accessibility, thereby simultaneously promoting electronic and ionic transmission to ZnO. With these favorable features, the resultant ZnO@Mo-C composite displayed outstanding capacitances (900 F g-1 at 1 A g-1) and high rate capability (650 F g-1 at 10 A g-1). In addition, an asymmetric supercapacitor device was constructed using ZnO@Mo-C and activated carbon as the positive and negative electrodes, respectively, which realized an enlarged voltage profile of 0-1.5 V, stable cyclability with a capacitance retention of 97% and acceptable power/energy densities. Moreover, the method to produce the ZnO@Mo-C rods is facile and environmentally friendly and can be readily extended to other carbon coated materials.

Photocatalytic performance of ZnO carbon composites for the degradation of methyl orange dye

High yield, low cost, environmentally friendly chemical bath synthesis process is used to produce submicron structures of ZnO and ZnO-carbon composites. Synthesis of ZnO rod structures (submicron sized) were confirmed using SEM images. To synthesis ZnO-carbon composites, well characterized carbon spheres produced using aerosol assisted CVD technique was used. Use of carbon spheres as a seed during synthesis of ZnO is observed to produce multipod structures of ZnO on to the surface of carbon spheres; the growth is explained by proposing suitable model. Room temperature photoluminescence spectra recorded for ZnO and ZnO-carbon composites synthesized show a systematic disappearance of a band-edge emission (sharp peak present at ∼380 nm observed for pure ZnO) with increased number of carbon spheres. Competent photo-catalytic activity of synthesized composite is confirmed by studying photo degradation investigation performed using a model dye molecule i.e. methyl orange. The work reveals possibility to use synthesized composites as a nontoxic and biocompatible catalyst for fragmentation of a methyl orange dye molecule. Photo-degradation mechanism of a methyl orange dye is proposed herewith considering the role of carbon spheres and ZnO in presence of UV photon.

Developing high-sensitivity UV sensors based on ZnO nanorods grown on TiO2 seed layer films using solution immersion method

TiO2:ZnO nanorods thin film has the great properties of packed ZnO nanorods with good crystallinity and improved UV absorption properties which are suitable for optoelectronic device applications. ZnO nanorods array was fabricated by using a seeding method with TiO2 as seed layer. As a result, well aligned of ZnO rods with good distribution can grow. Different samples of TiO2, ZnO and TiO2:ZnO nanorods thin film were used as based material in UV sensor devices. The responsivities of the sensors are 1.70 × 10−1A/W, 7.76 × 10−5 A/W and 2.22 × 10−7 A/W for TiO2:ZnO nanorods, TiO2 seed layer and ZnO rods based UV sensors respectively. Results indicate that the TiO2:ZnO nanorods UV sensor exhibits rapid and high response to UV light compared with TiO2 and ZnO sensor because of its small size of nanorods and seed layer acting as an absorbance assisted and capacitive layer on the glass surface.

Synthesized zinc oxide nano rods and flowers studies for optical, di-electrical and photocatalytic applications

ZnO being most avid semiconductor metal oxide with a wide band gap of 3.37 eV. ZnO nanostructures were synthesized in the shape of nano rods and flowers to finds their proficiency in the field of photocatalysis and photovoltaics. ZnO nanostructures were investigated in the shape of nano rods and flowers by, X Ray Diffractometer (XRD) confirms pure hexagonal wurtzite structure of ZnO, Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) images showed high crystalline morphology and the formation of nano rods and flowers. Ultraviolet and Photoluminescence (PL) study confirms the absorption at 375, 371 nm for ZnO rods and flower which leads to an increase in the band gap and the peak observed at the violet, blue and green emission. The peaks shift is due to increase in defect in flower nanostructures of ZnO, Dynamic Light Scattering (DLS) calculated the average particles size 617 and 823 nm for rods and flower respectively. Conductivity analysis prove that nano flowers are more conductive having more defects and large number of photocatalytic active sites and large number of electron-hole pairs make best suited for photocatalytic specie. Thus, ZnO nano flowers were observed ideal for photocatalysis and photovoltaic applications due its large number of active sites and defects.

Bulk superhydrophobility of wood via in-situ deposition of ZnO rods in wood structure

Bulk superhydrophobic wood can improve the anti-abrasion performance and durability of wood during application. However, the fabrication of bulk superhydrophobic wood remains challenging, especially it is difficult to realize the superhydrophobicity of wood internal surfaces (cross section and longitudinal section). In this study, the robust bulk superhydrophobic wood was prepared by combining hydrothermal method and vacuum impregnation method. First, zinc oxide rods were formed in situ using a hydrothermal method and vacuum impregnation method to construct a micro/nano rough structure in pristine wood. Then, hydroxyls on the wood cell and zinc oxide surface were substituted with long-chain alkyl to endow wood with low surface energy. The characterization results from morphology, composition and elemental analysis illustrates that zinc oxide rods form in the wood microstructure surfaces and ensure bulk superhydrophobic performance after long-chain hydrophobic group treatment. The contact angle of the treated wood can reach 155°. The surface contact angle is maintained at approximately 150° in 180 s after sawing and abrasion, stating that the superhydrophobic properties exist throughout wood entire structure along with excellent wear resistance. After treatment with different reagents, the contact angle of modified wood is maintained around 150°, indicating great chemical durability. These treatment methods can provide an inspiration to improve the stability and durability of superhydrophobic wood during its utilization, with the potential to be applied in wood manufacturing.

Synergetic effect of g-C3N4/ZnO binary nanocomposites heterojunction on improving charge carrier separation through 2D/1D nanostructures for effective photocatalytic activity under the sunlight irradiation

The heterojunction between the two different semiconductors shown to increase the photocatalytic activity due to their ability in improving the photo-generated electron-hole pairs separation. Hence designing and synthesizing such heterojunctions employing different semiconducting materials to improve the photocatalytic efficiency using various methods have gained importance. For this purpose graphitic like carbon nitride (g-C3N4) is a hopeful photocatalytic material for environmental remediation but its photogenerated charge carriers recombination rate limits g-C3N4 for practical applications. Hence, in the present work we synthesized heterojunction of g-C3N4/ZnO binary nanocomposites in 2D/1D by sonication assisted hydrothermal method. X-ray diffraction analysis confirms the formation of g-C3N4/ZnO binary nanocomposites. Transmission electron microscope analysis shows that the binary nanocomposites consists ZnO rods coupled with sheet like structure of g-C3N4. The band gap of g-C3N4 is 2.67 eV; however, the g-C3N4/ZnO binary nanocomposites shifts the band gap to 2.9 eV. Photoluminescence spectral analysis evidently shows the recombination rate of electron-hole pairs in the g-C3N4/ZnO binary nanocomposites is effectively reduced due to the formation of the heterojunction. The photoelectrochemical analysis shows that g-C3N4/ZnO binary nanocomposites enhance the photocurrent to 1.5 μA and effectively separate the electron-hole pairs when compared with that of bare ZnO and g-C3N4. Hence, the g-C3N4/ZnO binary nanocomposites effectively enhanced RhB dye degradation to 99% for 20 min and enhanced the 4-chlorophenol degradation to 90% for 40 min. under the sunlight irradiation.

Tuning electronic energy band in a piezoelectric semiconductor rod via mechanical loading

Based on the k·p model with 8 × 8 band Hamiltonian, we demonstrate that the electronic energy band in a wurtzite piezoelectric semiconductor (PSC) rod can be tuned by a pair of uniaxial mechanical tractions. This tuning is achieved by solving two sub-problems: the electro-mechanical fields induced by a pair of axial tractions applied at the two ends of the rod, and the band energy based on the calculated strains and electric potential via the k·p model. Numerical results indicate that, when the magnitude of the applied load is relatively small, the induced PSC fields predicted by the linear model in the rod generally agree with those based on the present rigorous nonlinear model. Otherwise, the linear model will be invalid and the present nonlinear model has to be used to characterize correctly the intrinsic nonlinear property in the PSC rod. It is the first time that the heavy hole (HH), light hole (LH), spin-orbit split-off (SO) and conduction band (CB) in ZnO and GaN rods are all analyzed in details at different locations of the rod under different magnitudes of the applied traction. It is shown that the mechanical load could significantly affect the energy band edges, particularly near the ends of the rod where the loads are applied. Furthermore, the coupling effect of the valence band (VB) and CB is discussed in an InN rod where the material has a narrow bandgap. This work provides a unique opportunity in nanodevice design where nano energy is a key parameter.

Synthesis and in situ nitrogen doping of ZnO nanomaterials using a microwave plasma system at atmospheric pressure

A microwave plasma system operated at atmospheric pressure was utilized to not only synthesize ZnO nanostructures from a micro-sized Zn powder, but also dope with nitrogen simultaneously by changing the ratio of O2 and N2 gas mixture. When pure N2 gas was used, ZnO was not produced due to oxygen deficiency. When the ratio of O2 to N2 was 10:90, 20:80, and 50:50 (vol.%), tetrapod-shaped ZnO rods with a diameter of 29.8 and a length of 256.5 nm were synthesized. When only oxygen was used, ZnO nanorods with a diameter of 626.5 and a length of 852.6 nm were primarily synthesized. Furthermore, it was confirmed from Raman and X-ray photoelectron spectroscope (XPS) analyses that the doping concentration of nitrogen increased with the increase of N2 gas proportion to 50, 80, and 90 vol.%. The increase of the absorbance and the luminescence in the visible light region were confirmed by the change of the energy level due to the N-doping on ZnO. The most effective gas mixture ratio of O2 to N2 for synthesis of ZnO nanomaterials and in situ N-doping was confirmed to be 20:80 (vol.%). This work demonstrates the effectiveness of a microwave plasma system at atmospheric pressure which is available for synthesis of ZnO nanomaterials and simultaneous functional doping on it.

Formation Mechanism and Properties of Foam-Structured ZnO Films Prepared Using Catalyst-Free Carbothermal Method

Foam-structured ZnO films were formed on c-axis Al2O3 substrates by using a catalyst-free carbothermal method. The morphological properties of the films strongly depended on their substrate position in the reactor, implying that the quantity of Zn vapor transported played a crucial role in determining the film structure. The formation mechanism of the films is proposed to be as follows: with increased transport of Zn vapor, vaporized Zn elements transformed into liquid Zn nanoparticles, and the liquid Zn elements on the rods promoted the new nucleation of ZnO nanorods. The repeated growth of ZnO rods at the nucleation sites led to the foam-like structure. The as-formed foam-structured ZnO films exhibited the wurtzite crystal structure, and the atomic composition ratio of Zn to O was 1 : 0.85. The main photoluminescence emissions were centered at 3.3 and 2.5 eV, and they were attributed to band-to-band and defect-related transitions, respectively.

Enhanced photocatalytic activity of CuS-ZnO rods towards degradation of pollutants under visible-light-driven nanostructured photocatalyst

A facile low temperature synthesis of ZnO rods and decoration of CdS and CuS on ZnO rods were synthesised via sonication assisted one-pot hydrothermal method. The synthesised samples were characterised by XRD, UV–visible DRS, XPS and FE-SEM. The photocatalytic degradation of methylene blue (MB) was studied. When CuS was loaded on ZnO rods, it showed higher degradation of MB of 98.2% and 90% by CdS-ZnO and 48% by ZnO nanorods at a reaction time of 210 min. The pH, photocatalyst dosage and initial dye concentration were kept same for all the three photocatalyst during the degradation.

A highly efficient porous rod-like Ce-doped ZnO photocatalyst for the degradation of dye contaminants in water.

A mild and simple method was developed to synthesize a highly efficient photocatalyst comprised of Ce-doped ZnO rods and optimal synthesis conditions were determined by testing samples with different Ce/ZnO molar ratios calcined at 500 °C for 3 hours via a one-step pyrolysis method. The photocatalytic activity was assessed by the degradation of a common dye pollutant found in wastewater, rhodamine B (RhB), using a sunlight simulator. The results showed that ZnO doped with 3% Ce exhibits the highest RhB degradation rate. To understand the crystal structure, elemental state, surface morphology and chemical composition, the photocatalysts were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM) and inductively coupled plasma emission spectroscopy (ICP), respectively. The newly developed, robust, field-only surface integral method was employed to explore the relationship between the remarkable catalytic effect and the catalyst shape and porous microstructure. The computational results showed that the dipole-like field covers the entire surface of the rod-like Ce-doped ZnO photocatalyst and is present over the entire range of wavelengths considered. The optimum degradation conditions were determined by orthogonal tests and range analysis, including the concentration of RhB and catalyst, pH value and temperature. The results indicate that the pH value is the main influential factor in the photocatalytic degradation process and the optimal experimental conditions to achieve the maximum degradation rate of 97.66% in 2 hours are as follows: concentration (RhB) = 10 mg/L, concentration (catalyst) = 0.7 g/L, pH 9.0 and T = 50 °C. These optimum conditions supply a helpful reference for large-scale wastewater degradation containing the common water contaminant RhB.

Synthesis of silver-loaded ZnO nanorods and their enhanced photocatalytic activity and photoconductivity study.

Herein, we synthesized ZnO nanorods using a solvothermal reaction technique at 200 °C for 24 h, and the prepared ZnO nanorods were decorated with silver (Ag) nanoparticles to enhance their photocatalytic activity. The Ag nanoparticles were photochemically deposited on the ZnO rods with varying molar concentrations (from 0.5 to 10 mol%), and their various physicochemical properties were studied. The prepared material was characterised using different spectroscopic techniques. XRD revealed the formation of a highly crystalline hexagonal phase of ZnO. For a higher silver loading (>5 mol%), separate peaks corresponding to cubic silver were observed in the XRD pattern. The photoluminescence spectra of the Ag/ZnO nanostructures show two distinct peaks at 390 and 500 nm; interestingly, the PL intensity of the ZnO emission peak at 500 nm decreases with an increase in the silver concentration. The diffuse reflectance spectra of Ag/ZnO indicate absorbance at 380 nm due to ZnO and a slight hump at 440 nm that corresponds to silver nanoparticles. The FE-SEM and TEM analysis indicates the formation of a hexagonal rod-like morphology, with the lengths of the rods ranging from around 50 to 200 nm and a diameter of around 30 nm. TEM also confirms the presence of Ag nanoparticles with sizes in the range of 20 to 30 nm on the surface of the ZnO nanorods. The photocatalytic activity of the Ag/ZnO nanostructures was evaluated by following the degradation of methylene blue (MB) dye under a 400 W mercury vapour lamp. ZnO with 10 mol% Ag loading shows the highest photocatalytic activity as compared to the 0.5, 1 & 5 mol% Ag-ZnO catalysts. The observed apparent rate constant for the photocatalytic MB degradation using 10 mol% Ag-ZnO (Kapp = 6.01 × 10-2 min-1) was six times that of pure ZnO (Kapp = 1.09 × 10-2 min-1). A gradual increase in the photocatalytic activity of Ag/ZnO was observed with an increase in the silver concentration. The photocurrent response of the prepared Ag-ZnO nanostructures was examined by a photoconductivity study. Moreover, the photocatalytic performance of the sample was correlated with the photoconductivity of the samples. The photoconductivity of the samples was stable, and the photoconductivity of 10 mol% Ag-ZnO was almost 20 times that of pure ZnO, resulting in a higher photocatalytic activity.

Two-Step Preparation of ZnO/ZnSe Heterostructure with Remarkable Photocatalytic Activity by Ultrasonic and Hydrothermal Approach

In order to improve the light absorption capacity of ZnO and reduce the charge recombination, the heterostructure of ZnO/ZnSe was prepared by a simple synthetic route. The heterostructure was composed of spherical ZnSe growing on ZnO rod, in which the ZnO rods were synthesized by an ultrasonic method. The concentration of ammonia in the reaction solution was the key factor to determine the nucleation and growth rate of ZnO/ZnSe heterostructure. In addition, the relationship between structure and photocatalytic activity was studied. Compared with bare ZnO rods and spherical ZnSe, as-prepared ZnO/ZnSe heterostructure exhibited excellent photocatalytic activity for the degradation of methyl orange dye, which was attributed to the effective charge transport performance generated by the coupling of ZnO and ZnSe.

Oriented Polarization Tuning Broadband Absorption from Flexible Hierarchical ZnO Arrays Vertically Supported on Carbon Cloth.

A novel strategy is used to design large-scale polarized carbon-based dielectric composites with sufficient interaction to electromagnetic waves. Highly uniform polar zinc oxide arrays are vertically grown on a flexible conductive carbon cloth substrate (CC@ZnO) via an in situ orientation growth process. Anion regulation is found to be a key factor to the morphology of hierarchical ZnO arrays including single-rod, cluster and tetrapod-shaped. As a typical dielectric loss hybrid composite, the electromagnetic parameters of the CC@ZnO system and charge density distribution in polarized ZnO rods confirm that the 3D intertwined carbon cloth is used as a conductive network to provide ballistic electron transportation. Moreover, the defect-rich ZnO arrays are well in contact with the CC substrate, favoring interface polarization, multiscattering, as well as impedance matching. Surprisingly, the efficient absorption bandwidth of the CC@ZnO-1 composite can reach 10.6 GHz, covering all X and Ku bands. The oriented ZnO possesses oxygen vacancies and exposure to a large amount of intrinsic polar surfaces, encouraging the polarization behavior under microwave frequency. Optimized CC@ZnO materials exhibit fast electron transportation, strong microwave energy dissipation, and superior wide absorption. The results suggest that the CC@ZnO composites have promising potential as flexible, tuning, and broadband microwave absorbers.

Correction to: Photoelectrochemical performance of dye and semiconductor sensitization on 1-D hollow hexagonal ZnO rods: A comparative study

Unfortunately, in the original publication of the article, the Fig. 7 has an oversight. On Y-axis current density is “uA” rather than “mA”. The correct Figure is given below. The authors regret this error.

Micro structure of hydrothermal ZnO rods on micro cantilever surface

This study reports the microstructure of Hydrothermal ZnO rods on Micro cantilever Surface. Synthesis of ZnO rods consists of two processes e.g. a formation of seed layer using Zinc asetate dihydrate by a dip-coating and a growth of the ZnO rods using Zinc-Nitrate-Tetrahydrate at temperature 95°C for time variations of 1 hours, 2 hours, 3 hours, 4 hours, 5 hours, and 6 hours. Drying condition for both seed layer and growth of ZnO rods was done at a temperature of 120°C for 2 hours. The characterization of ZnO rods morphology was done by Field Emission-Scanning Electron Microscopy (FE-SEM), chemical element composition was performed with Energy Dispersive Spectrometry (EDS), crystal structure was done by X-ray Diffraction (XRD) and functional group analysis was done by Fourier Transform Infrared (FTIR). The characterization results show that the formation of Zinc Oxide with confirmed hexagonal form of FE-SEM and XRD results. The FE-SEM results show that the variation in growth time has an effect on the diameter size formed above the microcantilever. The longer the growth time, the larger the diameter of ZnO rods.