Pure ZnO Nanorods Research Articles

Investigation of structural, optical, surface, electrochemical and corrosion properties of ZnO and AZO nanorod arrays for dye absorption applications

In dye-sensitized solar cells (DSSC), photoanodes have special importance in the processes of dye support, photon absorption and electron transport. ZnO nanorod arrays are promising photoanode materials, but their properties need to be improved by innovative fabrication approaches to improve the performance of ZnO-based DSSCs. In this study, pure and Al-doped ZnO (AZO) nanorod arrays were grown by hydrothermal method onto ZnO seed layers produced by sol-gel spin coating. As far as we know, for the first time in the literature, HMTA-HMDA ligand mixture was used instead of HMTA in the preparation of hydrothermal precursor solutions. To investigate the potential use of ZnO and AZO nanostructured films as photoanodes in DSSCs; their surface, structural and optical properties were examined. Additionally, charge transfer kinetics, corrosion resistance and dye loading capacities were determined by advanced analyzes such as electrochemical impedance spectroscopy, potentiodynamic polarization and adsorption-desorption methods. The supporting HMDA ligand and Al impurity used in the preparation of hydrothermal precursor solutions led potential usages as photoanode of ZnO nanorod arrays to increase by improving their structural, optical, surface, and electrochemical properties, corrosion resistance and dye loading capacities.

Study of the ZnO/MoS2 heterostructures-based gas sensor for humidity-independent response

In this study, several strategies including coating with a hydrophobic MoS2 layer, UV light illumination, raising temperature, alternating current (AC), and four-probe measurement have been systematically studied to overcome humidity dependence response behavior for the ZnO sensor. Catalyst-free CVD method was used to prepare pure ZnO nanorods and ZnO/MoS2 heterostructures, and the prototypes were then fabricated on the substrates with Pt interdigital (ID) electrodes, respectively. The gas sensing properties of two sensors were systematically investigated. The ZnO/MoS2 heterostructures-based sensor with four-probe measurement operating at 150 °C shows stable responses during a wide humidity variation range. Furthermore, the ZnO/MoS2 sensor obtains excellent sensing performance to NO2 with a high sensitivity of 12.6 %/ppm and high sensor responses at 150 °C and UV light illumination. Additionally, a low theoretical LoD of 6.5 ppb NO2 is achieved for ZnO/MoS2 heterostructures-based sensor.

Biotemplate-Assisted Growth of ZnO in Gas Sensors for ppb-Level NO2 Detection.

With the growing concern over the adverse effects of environmental pollution on human health, the combination of environmentally friendly and nontoxic biomaterials with metal oxide semiconductor materials for electronic devices has emerged as a prominent trend in current research. In this study, we utilized 150 mg apple biotemplates to assist in the hydrothermal synthesis of ZnO nanospheres. It successfully achieved high sensitivity for detecting 35 and 350 ppb NO2 at room temperature, with responses of 13.74 and 132.44%, respectively. Simultaneously, the 5-cycle repeatability and multiple-gas selectivity exhibited significant improvements. The ZnO nanospheres demonstrated enhanced sensing performance compared to pure ZnO nanorods, which is attributed to the following mechanisms: reason I, the modified surface morphology increasing the surface-to-volume ratio; reason II, an increase in oxygen vacancies, leading to reduced crystallinity and a higher electron concentration; reason III, incorporation of carbon elements on the nanostructure surface to increase active sites. The novel gas sensor assisted by the apple pectin biotemplate offers a promising solution for NO2 gas detection, featuring low operating temperatures, low concentrations, and high response sensitivity.

High performance surface plasmon enhanced ZnO-Pt @ AlN core shell UV photodetector synthesized by magnetron sputtering

ZnO, a potential optoelectronic material, is attracting significant attention in ultraviolet (UV) photodetectors. However, low photoelectric conversion efficiency is a shortcoming because of its surface defect. In this paper, a plasmonic enhanced high speed UV photodetector was fabricated by ZnO-Pt@AlN core shell nanowires arrays using chemical vapor deposition (CVD) and magnetron sputtering methods. As shown in experiment results, the core shell nanowire arrays exhibit 3.7 times enhancement of UV emission and inhibition of visible emission by surface defect. In addition, compared to the pure ZnO nanorod array detector, the introduction of Pt nanoparticles and AlN shell layer resulted in a device with faster rising and falling edges (from 5.67 s to 3.09 s; from 41.18 to 0.32 s) as well as higher bright-to-dark current ratio (from 6.6 to 310.5). As shown in simulation results, the optical field would be localized in the shell of ZnO nanorods, and the ZnO-Pt@AlN core–shell structure can effectively improve the absorption of 365 nm UV light. In one word, this paper employs two general methods to improve the optoelectronic performance of ZnO, and obtains plasmonic enhanced high speed UV photodetector fabricated by ZnO-Pt@AlN core shell nanowires array as well as the mechanism of enhancement is explained.

Ag nanoparticles decorated ZnO nanopagodas for Photoelectrochemical application

Photoelectrochemical water splitting (PEC-WS) utilizing solar energy and photoelectrodes immersed in an electrolyte has sparked an increased interest in hydrogen production. The PEC-WS efficiency is enhanced by controlling the nanostructure of photoelectrodes and sensitizing them with plasmonic metals. This study shows how the transformation from ZnO nanorods to ZnO nanopagodas and the deposition of Ag nanoparticles improve the photocurrent and PEC conversion efficiency under sunlight. The deposition of an optimal amount of Ag nanoparticles over ZnO nanopagodas exhibited the highest photocurrent of 2.15 mA cm−2 at 1.23 V vs RHE, while pure ZnO nanorods and nanopagodas achieved 0.90 and 1.43 mA cm−2, respectively. This extraordinary improvement in photocurrent density was thoroughly analyzed using various PEC and optical measurements as well as electromagnetic simulation. As a result, two main reasons for the improvement were derived. Firstly, ZnO nanopagodas can reduce the charge recombination rate due to the reduced structural defects and improve the light-harvesting ability due to their distinct superstructure characteristics. Secondly, the deposition of plasmonic Ag nanoparticles can improve the interfacial charge transfer and increase the ability to capture visible light due to their localized surface plasmon resonance effects.

ZnO/CuSe composite-mediated bandgap modulation for enhanced photocatalytic performance against methyl blue dye

The removal of toxic dye pigments from the environment is of utmost importance since even trace amounts of these pollutants can lead to harmful impacts on ecosystems. Heterogeneous photocatalysis is a potential technique for eliminating microbiological, inorganic, and organic pollutants from wastewater. Here, we report the band gap alteration of ZnO by making its composites with CuSe to enhance photocatalytic activity. The purpose is to develop metal oxide nanocomposites (ZnO/CuSe) as an effective and efficient material for the photodegradation of methyl blue. The photocatalysts, ZnO nanorods, CuSe, and ZnO/CuSe nanocomposites of different weight ratios were synthesized by the simple and cost-effective technique of precipitation. UV–Vis spectra verified that the ZnO/CuSe photocatalyst improved absorption in the visible region. The optical bandgap of ZnO/CuSe nanocomposites reduced from 3.37 to 2.68 eV when CuSe concentration increased from 10 to 50%. ZnO/CuSe composites demonstrated better photocatalytic activity than ZnO when exposed to UV–visible light. The pure ZnO nanorods could absorb UV light and the nanocomposites could absorb visible light only; this was attributed to the transfer of excited high-energy electrons from ZnO to CuSe.

Enhanced photoelectrochemical performance of ZnO/α-Fe2O3 heterojunction photoelectrode fabricated by facile hydrothermal and spin-coating method

The present study reports the successful fabrication of ZnO/α-Fe2O3 heterojunctions by facile and simple hydrothermal and spin-coating methods. The effect of spin-coating different FeCl3 precursor layers on the photoelectrochemical performance has been investigated. Additionally, the procedure of spin-coating FeCl3 precursors was simulated by fluent software. It is noteworthy that ZnO/α-Fe2O3 heterojunctions increase the absorption of visible light, promote the separation and transfer of photogenerated charge carriers, reduce the interfacial resistance between the photoelectrode and electrolyte, and provide a larger electrochemically active contact area in contrast to pure ZnO nanorods. The highest photocurrent density and the highest IPCE (incident photon-to-current efficiency) reach 1.82 mA cm−2 and 40 % respectively when spin-coating three layers. Moreover, the mechanism of enhanced PEC performance was further discussed via EIS (electrochemical impedance spectroscopy), Mott-Schottky curves, Energy band structure diagram, and the electrochemical active surface area (ECSA) test.

A DFT theoretical and experimental study of the effect of indium doping within electrochemical deposited ZnO

The effect of indium doping within ZnO-NRs nanorods on FTO substrates was studied using integrated theory and experiments. The electrochemical deposited In-ZnO NRs were examined by X-ray diffraction (XRD), Scanning electron microscopy (SEM), UV–vis spectrophotometer, electrochemical cell, and Photocurrent spectroscopy. The obtained electronic and optical characteristics of the developed ZnO and In-ZnO films were validated by density functional theory (DFT) calculations using the TB-mBJ and PBE-GGA approximations. XRD patterns demonstrate that all electrodeposited films were crystalline having a hexagonal wurtzite with a preferred growth orientation (002). Furthermore, the crystallite particle size and (002) diffraction peak intensity of the samples reduces with In doping, suggesting a reduction in crystallinity with increasing indium. SEM images reveal a nicely defined hexagonal shape morphology of pure and In-doped ZnO nanorods, with an approximate mean diameter of ∼100 nm. UV spectrophotometry experiments and DFT calculations showed that the inclusion of In leads to a minor reduction in the optical gap energy. Mott-Schottky analysis displays an improvement in the conductivity attributed to an enhanced electronic injection in In-ZnO the conduction band, thus enhancing the photoelectrochemical properties of the zinc oxide film.

Synthesis, structural, photoluminescence, ultraviolet blocking and antibacterial performances of Ba-doped ZnO nanostructures

In the current experimental work, pure ZnO and Ba-doped ZnO nanorods have been prepared by implementing a facile wet chemical technique. XRD study reveals the formation of the hexagonal wurtzite phase of pure ZnO and Ba-doped ZnO nanorods. Interestingly, Ba-doped ZnO nanorods show very good absorption in the UVA (93% at 351 nm), UVB (90% at 300 nm) and UVC (61% at 220 nm) regions. The obtained results of the UV–visible absorbance study validate in such a way that the Ba-doped ZnO nanorods could be a better bet to be utilized as a UV blocker for the next generation of UV shielding materials. The Photoluminescence spectrum of Ba-doped ZnO nanoparticles reveals widespread UV–Visible bands between 350 and 600 nm. Also, the zone of inhibition is found to be 15 nm for both bacterial strains S.aures and E.coli and implies excellent antibacterial activity. Interestingly, the outcome as observed in the zone of inhibition towards S. aureus and E. coli in the present study is found to be higher than many doped ZnO and Ba-doped metal oxide nanostructures. The observed experimental results via the aforementioned characterizations imply that the synthesized samples possess the potential ingredients required for the applications related to the field of health care.

Effect of Ga Concentration on the Output Performance of ZnO Piezoelectric Nanorods Nanogenerator

In this study, a self-assembled monolayer of octyltriethoxysilane was grown on ITO glass. Subsequently, a hydrothermal method was employed to grow low-density gallium (Ga)-doped zinc oxide (ZnO) nanorod structures. In this growth process, the undoped pure ZnO nanorods and ZnO nanorods doped with five different Ga concentrations were developed. After growing the nanorods, X-ray diffraction (XRD) analysis was conducted on both undoped pure ZnO and Ga-doped ZnO nanorods to observe the influence of Ga concentration on the crystalline structure of the ZnO nanorods. Additionally, scanning electron microscopy (SEM) was utilized to examine changes in the surface and cross-sectional growth of ZnO nanorods with varying Ga concentrations, thereby investigating the impact of Ga concentration on the growth of ZnO nanorods. Finally, a thin Pt film was sputtered onto the ZnO nanorod structures to assemble nanogenerators. Ultrasonic excitation was applied to develop these nanogenerators for electrical measurements, allowing us to explore the effects of metal doping on the nanorods’ electrical properties.

Effect of yttrium doping on the crystal structure, optical, and photocatalytic properties of hydrothermally synthesized ZnO nanorods

The hydrothermal technique was utilized to fabricate yttrium doped ZnO nanorods (Y-doped ZnO). Various spectroscopic approaches were used to examine the effect of yttrium doping on the crystal structure, shape, energy bandgap, and photocatalytic performance of ZnO nanorods. The fact that Y-doped ZnO nanocatalysts had the same hexagonal wurtzite crystal structure and nanorod shape as like undoped ZnO, signifying that doped yttrium ions have no effect on the structural as well as morphological features of ZnO nanorods. By doping yttrium into the ZnO sites, the bandgap energy of the ZnO nanorods was significantly altered, and the photodegradation activity was improved. The absorption edge of the Y-doped ZnO nanorods was shifted towards the higher wavelengths and blue shift in bandgap was observed. It has been confirmed that yttrium doping increases the light sensitivity of ZnO in the visible region while providing several active charge transporters on the nanorods surface as well. The photocatalytic activity of Y-doped ZnO nanocatalysts was significantly increased by generated charge carriers. For doping concentrations of 1 %, 3 % and 5 %, the photodegradation activity of Y-doped ZnO nanorods is 71 %, 97 %, and 82 %, respectively, whereas the photodegradation efficiency of pure ZnO nanorods is 22 %. The photodegradation efficiency of ZnO:Y3 was found to be 4.4 times higher than the pristine ZnO nanorods. In addition to the photodegradation, the Y-doped ZnO nanorods are anticipated to offer a valued platform to the widespread applications in the field of photocatalysis like electrochemical water splitting, hydrogen production and supercapacitors.

Photocatalytic degradation of model pollutants using ZnO/Ag3PO4 heterostructure thin films under visible and solar irradiation

ZnO/Ag3PO4 heterostructure-based thin films were prepared by hydrothermal and SILAR deposition processes. The prepared samples were characterized for their morphology, structure, and optical properties using SEM, XRD, EDS, UV–Vis spectroscopy, and PL spectroscopy. Ag3PO4 modifies the light absorption characteristics significantly, with a considerable absorbance in the visible region found for ZnO. Under visible light and sunlight irradiation, Ag3PO4–ZnO nanorod-based heterostructure displayed substantially more substantial photocatalytic activity toward MB degradation, as well as superior recyclability and stability than pure ZnO nanorods. The Ag3PO4–ZnO nanorod combination with a 5 times dip of Ag3PO4 had the excellent photodegradation efficiency of MB (86%) compared to pure ZnO nanorods (60%) under visible irradiation.

Synthesis and antibacterial activity of nanoenhanced conjugate of Ag-doped ZnO nanorods with graphene oxide

In this paper, we report a successful synthesis of ZnO nanorods using the microwave-assisted technique, solid-state reaction method was utilized for the preparation of Zn1-xAgxO (x = 0.05, 0.1), Hummer’s modified method for graphene oxide (GO) along with the sonication method to prepare GO-based Ag-doped ZnO (Zn1-xAgxO/GO: x = 0.05, 0.1) nanocomposites. These nanorods and nanocomposites were characterized by X-ray diffraction (XRD), Fourier-transform infrared (FTIR), high-resolution transmission electron microscopy (HRTEM), and Raman spectroscopy for structural properties, scanning electron microscopy (SEM) along with energy dispersive X-ray (EDX) spectroscopy for morphological analysis, and UV–Vis spectroscopy for optical properties. XRD, FTIR, and Raman measurements substantiated that each sample is well crystallized in the single-phase polycrystalline wurtzite hexagonal structure of ZnO. The average crystallite size is found to be in decreasing order ranges 40 nm to 29 nm, respectively, along with a significant reduction in the optical bandgap. The SEM images showed a clear evidence of nanorods of ZnO, while the EDX spectra verified the presence of Zn, Ag, O, and C elements in the synthesized samples with their nominal percentage. Furthermore, the prepared nanocomposites effectively inhibited the growth ofStaphylococcus aureus and Escherichia coli. In comparison to pure ZnO nanorods, GO-based Ag-doped ZnO nanorods showed improved antibacterial activity against both S. aureus and E. coli.

ZnO/g-C3N4 heterostructures: Synthesis, characterization and application as photoanode in dye sensitized solar cells

A simple low-temperature hydrothermal route was adopted to prepare the binary ZnO/g-C3N4 heterostructures, which were thoroughly characterized by various spectroscopic and microscopic probes. The clearly visible interfaces between the ZnO NRs and g-C3N4 in the HRTEM micrograph verify the formation of ZnO/g-C3N4 heterojunction structures, which, combined with N3 dye, deliver increased optical absorption extending from UV to the visible range. The binary ZnO/g-C3N4 heterostructures are used as the photoanode in the DSSC application. Improvement in the DSSC performance arises because of the growth of the g-C3N4 layer on the ZnO nanorods surface, which efficiently delays the reverse recombination of electrons from ZnO to the electrolyte. The g-C3N4 layer also increases the electron concentration in the photoelectrode and, thereby, directly contributes to the improved performance of the DSSC device. The optimal DSSC based on the ZnO/g-C3N4 photoanode delivers its characteristic JSC ∼14.18 mA/cm2, VOC ∼544 mV, FF ∼0.586 and η ∼4.52%, which is about 2.3 times greater than the DSSC efficiency based on pure ZnO nanorod photoelectrode and retains the spirit of generating the green energy following the photovoltaic endeavor.

One-step electrodeposition of ZnO/graphene composites with enhanced capability for photocatalytic degradation of organic dyes.

Zinc oxide is a popular semiconductor used in catalysts due to its wide bandgap and high exciton binding energy. However, the photocatalytic performance of ZnO was compromised by its insufficient electron-hole separation efficiency and electron transfer rate. Herein, ZnO-reduced graphene oxide (rGO) composite solid catalyst was synthesized by one-step electrodeposition method on FTO substrate using lithium perchlorate (LiClO4) as the supporting electrolyte. Scanning electron microscopy, Raman, Fourier Transform Infrared, and XRD characterizations confirmed the deposition of ZnO and the reduction of graphene oxide Owing to the cooperative effect between rGO and ZnO, the as-prepared ZnO-rGO composites show much enhanced photocatalytic degradation ability compared with pure ZnO nanorods. By optimizing the conditions of electrodeposition of ZnO-rGO composites, the degradation rate of methylene blue can reach 99.1% within 120min. Thus, the simple preparation and the excellent performance could endow the ZnO-rGO composites with promising application in practical dye-polluted water treatment.

PH Controlled Nanostructure and Optical Properties of ZnO and Al-Doped ZnO Nanorod Arrays Grown by Microwave-Assisted Hydrothermal Method.

The low-temperature microwave-assisted hydrothermal method was used to successfully grow pure and Al-doped ZnO (AZO) nanorod (NR) arrays on glass substrates. The combined effects of doping and pH on the structural properties, surface chemistry, and optical properties of all samples were investigated. Thermodynamic-based simulations of the growth solution were performed and a growth mechanism, that considers the effects of both the pH and Al-doping, is proposed, and discussed. Tuning the solution pH is key parameter to grow well-aligned, single crystal, highly packed, and high aspect ratio nanorod arrays. Moreover, the optical absorption in the visible range is enhanced by controlling the pH value. The PL spectra reveal a shift of the main radiative emission from the band-to-band into a transition involving deep defect levels of Zinc interstitial Zni. This shift is caused by an enhancement of the non-radiative components (phonon relaxation) at high pH values. The production of well-ordered ZnO and AZO nanorod arrays with visible-active absorption/emission centers would increase their potential use in various applications.

Photoconversion efficiency of In2S3/ZnO core-shell heterostructures nanorod arrays deposited via controlled SILAR cycles

This paper reports the structures, morphologies, optical properties, and photoconversion efficiency (η%) of the In2S3/ZnO core-shell heterostructures nanorod arrays (IZCSHNRAs) produced via the controlled successive ionic layer absorption and reaction (SILAR) cycles. As-produced samples were characterized using XRD, FESEM, TEM, UV-Vis, PL, XPS and FTIR techniques. The proposed IZCSHNRAs revealed nearly double photocurrent density and η% values compared to the pure ZnO nanorod arrays (ZNRAs). In addition, the light absorption, crystallinity and microstructures of the specimens were appreciably improved with the increase of the SILAR cycles. The deposited nanoparticles of In2S3 (ISNPs) on the ZNRAs surface was responsible for the improvement in the heterostructures, light absorption and photogenerated electron–hole pairs separation, thus enhancing the photoconversion performance. It is established that a simple SILAR approach can be very useful to produce good quality IZCSHNRAs-based photoelectrodes required for the future development of high performance photoelectrochemical cells (PECs).

Phenol removal and hydrogen production from water: Silver nanoparticles decorated on polyaniline wrapped zinc oxide nanorods

The toxic and carcinogenic organic compounds discharge from industries, contaminate the natural reservoirs of water and air which eventually pose a global threat not only to the aquatic life but also to the humanity. Herein, ternary nanocomposites of silver-nanoparticle (AgNPs)-decorated on polyaniline (Pani)-wrapped zinc oxide nanorods (AgNPs@Pani/ZnO) were prepared via a facile approach. The nanocomposite degraded 97.91% phenol with an optimized dosage and concentration of H2O2. Moreover, the apparent rate constant for phenol degradation was 3.69 times higher than for pure ZnO nanorods. The hydrogen production from AgNPs@Pani/ZnO was 1.58 and 2.74 times higher than Pani/ZnO and ZnO, respectively. The enhanced phenol degradation and hydrogen production is attributed to the transfer of holes to the Pani, from which the electrons were transferred to the conduction band of ZnO and eventually to the conduction band of the AgNPs, where they accelerated the redox reactions for rapid photolysis of water and phenol. The concentration of the catalyst dosage affected the rate of phenol degradation. Further, response surface methodology was also applied in order to design 13 sets of random experiments in which the catalyst dosage and degradation time were varied to predict the phenol degradation.

Application of Ni-doped ZnO nanorods in surface acoustic wave ultraviolet photodetectors

A surface acoustic wave ultraviolet photodetector was fabricated on a ZnO thin film with pure and Ni-doped ZnO nanorods deposited on a Si substrate. Piezoelectric ZnO thin films were grown on Si through radio-frequency magnetron sputtering, and ZnO nanorods were synthesized on ZnO thin films by using the hydrothermal method. The crystalline structure, surface morphology, and luminescent characteristics of ZnO films and nanorods were examined using X-ray diffraction and photoluminescence spectrometers and scanning electron microscope. The performance of the surface acoustic wave photodetector was evaluated using the variations in surface capacitance, insertion loss, and phase shift. ZnO nanorods became shorter and thicker with an increase in the concentration of Ni doping; however, the variations in surface capacitance of Ni-doped ZnO nanorods were greater than those of pure ZnO nanorods obtained under ultraviolet irradiation. Devices with Ni-doped ZnO nanorods exhibited larger shifts in insertion loss and phase than those with pure ZnO nanorods did.

Structural and Electrical Characterization of Pure and Al-Doped ZnO Nanorods.

Pure and Al-doped (3 at.%) ZnO nanorods were prepared by two-step synthesis. In the first step, ZnO thin films were deposited on silicon wafers by spin coating; then, ZnO nanorods (NR) and Al-doped ZnO NR were grown using a chemical bath method. The structural properties of zincite nanorods were determined by X-ray diffraction (XRD) and corroborated well with the morphologic properties obtained by field-emission gun scanning electron microscopy (FEG SEM) with energy-dispersive X-ray spectroscopy (EDS). Morphology results revealed a minute change in the nanorod geometry upon doping, which was also visible by Kelvin probe force microscopy (KPFM). KPFM also showed preliminary electrical properties. Detailed electrical characterization of pure and Al-doped ZnO NR was conducted by temperature-dependent current–voltage (I–V) measurements on Au/(Al)ZnO NR/n-Si junctions. It was shown that Al doping increases the conductivity of ZnO NR by an order of magnitude. The I–V characteristics of pure and Al-doped ZnO NR followed the ohmic regime for lower voltages, whereas, for the higher voltages, significant changes in electric conduction mechanisms were detected and ascribed to Al-doping. In conclusion, for future applications, one should consider the possible influence of the geometry change of (Al)ZnO NRs on their overall electric transport properties.