Doped Zinc Oxide Nanowires Research Articles

Synthesis of Ag Doped ZnO Nanowire by Hydrothermal Method and its Characterization

This research is mainly focused over synthesizing zinc oxide (ZnO) nanowire (NW) and silver doped zinc oxide nanowires (Ag/ZnO) using two step hydrothermal method which comprises of seed layer deposition and hydrothermal nanowire growth step. Hydrothermally grown nanowires are of great significance. The synthesized nanowires were characterized by UV-Vis Spectroscopy (UV-Vis), X- ray Diffraction Spectroscopy (XRD), Energy Dispersive Spectroscopy (EDS), Field Emission Scanning Electron Microscopy (FE-SEM) and High-Resolution Transmission Electron Spectroscopy (HR-TEM). XRD pattern revealed as-synthesized materials are of crystalline nature having crystallite size of 166.27 nm and 42.32 nm for ZnO nanowire and Ag doped nanowire, respectively. Further confirmation was done by EDS, SEM and TEM. The microscopic images of SEM and TEM evidenced for successful fabrication of nanowires.

Chemiresistive room temperature NO2 sensor based on nitrogen doped zinc oxide nanowires

The prevalence of nitrogen dioxide (NO2) in the atmosphere is causing a steady increase in air pollution. As such, there is an urgent need to create a sensitive and energy-efficient NO2 gas sensor to ensure environmental and health safety. In this study, we explore the effectiveness of nitrogen-doped zinc oxide nanowires in detecting harmful NO2 gas. Through the hydrothermal method, we synthesized zinc oxide (NW-0) and nitrogen-doped zinc oxide nanowire sensors (NW-1, NW-2 & NW-4). The introduction of nitrogen induced changes in both the crystallite size and nanowire density in ZnO. Additionally, an increase in oxygen vacancy concentration was observed with nitrogen doping. At room temperature, the NW-2 sensor exhibited exceptional NO2 sensing performance (response of 110) compared to NW-0 sensor (response of 1.9) for 10 ppm of gas. The NW-2 sensor also demonstrated a rapid response/recovery time of 50 s/5 s for a 10 ppm NO2 concentration. Moreover, the sensor showed stability over an extended period, minimal response variation with changes in relative humidity, and selectivity towards NO2 over other gases. Complementing the experimental findings, density functional theory (DFT) calculations were employed to estimate the adsorption energies of NO2 on the sensor surface.

Spatially Resolved Dynamics of Cobalt Color Centers in ZnO Nanowires.

The dynamics of color centers, being a promising quantum technology, is strongly dependent on the local environment. A synergistic approach of X-ray fluorescence analysis and X-ray excited optical luminescence (XEOL) using a hard X-ray nanoprobe is applied. The simultaneous acquisition provides insights into compositional and functional variations at the nanoscale demonstrating the extraordinary capabilities of these combined techniques. The findings on cobalt doped zinc oxide nanowires show an anticorrelation between the band edge emission of the zinc oxide host and the intra-3d cobalt luminescence, indicating two competing recombination paths. Moreover, time-resolved XEOL measurements reveal two exponential decays of the cobalt luminescence. The fast and newly observed one can be attributed to a recombination cascade within the cobalt atom, resulting from direct excitation. Thus, this opens a new fast timescale for potential devices based on cobalt color centers in ZnO nanowires in photonic circuits.

High Current Field Emission from Large-Area Indium Doped ZnO Nanowire Field Emitter Arrays for Flat-Panel X-ray Source Application.

Large-area zinc oxide (ZnO) nanowire arrays have important applications in flat-panel X-ray sources and detectors. Doping is an effective way to enhance the emission current by changing the nanowire conductivity and the lattice structure. In this paper, large-area indium-doped ZnO nanowire arrays were prepared on indium-tin-oxide-coated glass substrates by the thermal oxidation method. Doping with indium concentrations up to 1 at% was achieved by directly oxidizing the In-Zn alloy thin film. The growth process was subsequently explained using a self-catalytic vapor-liquid-solid growth mechanism. The field emission measurements show that a high emission current of ~20 mA could be obtained from large-area In-doped sample with a 4.8 × 4.8 cm2 area. This high emission current was attributed to the high crystallinity and conductivity change induced by the indium dopants. Furthermore, the application of these In-doped ZnO nanowire arrays in a flat-panel X-ray source was realized and distinct X-ray imaging was demonstrated.

Current trends of Silver doped Zinc oxide nanowires photocatalytic degradation for energy and environmental application

A simple phyto-assisted synthesis of zinc oxide nanowires (ZnO NWs) employing urinary tract infection (UTI) controlling traditional medicinal plant Pedalium murex L. mucilage, their silver (Ag) doping by co-precipitation method has been reported. The synthesized Ag-doped ZnO NWs photocatalytic action on the UTI antibiotic nitrofurantoin (NFT) and the dye methylene blue (MB) has been reported. The synthesized NPs optical, biocomponents, structural and chemical properties were determined by UV-vis spectroscopy, FTIR, XRD, SEM, TEM, EDAX, particle size analyzer. Photocatalytic activity of the phyto-assisted synthetic Ag-doped ZnO NWs was investigated on the degradation of the antibiotic NFT and the dye MB. The percentage of degradation, as well as dye removal efficiency was calculated. The UV-vis absorption spectrum showed a surface plasmon resonance (SPR) band at 370 nm - 400 nm with blue and redshift. The vast bandgap energy (3.37 eV - 2.75 eV) reduction indicated the inclination of noble metal Ag on the surface of ZnO NWs. XRD diffractogram revealed the crystalline hexagonal wurtzite structure and c-axis oriented growth of the synthesized ZnO nanowires. FTIR spectra functional groups exposed the possible contribution of plant phytochemicals in the formation of nanowires. TEM micrographs showed the agglomerations of zinc cite crystal structure nanowire with silver inclination on their surface. EDX and SAED confirmed the elemental composition and purity of the synthesized Ag/ZnO nanowires. The synthesized Ag-doped ZnO nanowires achieved photocatalytic degradation of about 78.51% of the antibiotic NFT and 92.43% of MB dye in 150 min under UV irradiation. The present study establishes the likelihood of photocatalytic degenerative potency of the antibiotic nitrofurantoin and methylene blue employing photosynthesized phytosynthesized zinc oxide nanowires.

Sm Doped ZnO Nanowires@PAN Nanofibrous Membranes for Photocatalytic Degradation of Dye.

Wastewater involving a lot of contaminants like organic dyes from the textile finishing industry causes a greater adverse impact on human beings. There are many patents on nanofibers involved metallic oxides, this paper studies photocatalytic degradation of free-pollution Zinc Oxide (ZnO) nanomaterials on dye decontamination. Polyacrylonitrile (PAN) nanofibrous membranes loaded with Zinc Oxide (ZnO) nanowires were fabricated and evaluated for photocatalytic degradation. In this work, Polyacrylonitrile (PAN) nanofibrous membranes loaded with ZnO seeds were prepared by electrospinning PAN/Zn (Ac)2 solution followed by a thermal decomposition process. ZnO nanowires were hydrothermally grown on the surface of PAN nanofibers. The effects of the ratio of PAN and zinc acetate in a solution, decomposition temperature and ammonia (NH4OH) on the morphologies of ZnO nanowires were observed. ZnO nanowires showed the optimum morphologies when the ratio of PAN/Zn (Ac)2 was 10:1.5. The decomposition temperature was 150oC, and NH4OH was added in the hydrothermal reaction. The photocatalytic degradation of Rhodamine B solution under UV irradiation was used as a model reaction. The photodegradation ability of the ZnO @PAN membrane doped with cerium (Sm) was also investigated. Slight Sm doping increased the photocatalytic degradation rate from 57% to 89% under ultraviolet light irradiation for 2h. After 5 times of cycling under the same conditions, it still maintained the dye decolorization rate that was above 65%. Sm doped ZnO nanowires @PAN nanofibrous membranes were easily produced and could provide a novel process for the degradation of dye decontamination.

Ag+ driven antimicrobial activity of Ag+: ZnO nanowires immobilized on paper matrices

The prevalence of infectious disease causing microbes in the environment is a worldwide critical concern. This is prevalent both in air and water bodies. Thus, fabricating cellulose based materials with superior antimicrobial activity is highly significant in day-to-day life. Herein, Ag/Ag+ doped zinc oxide nanowires have been immobilized on the cellulose fibers of the paper matrices using facile one step scalable autoclave technology. The incorporation of Ag+ in the ZnO lattice has indicated a synergy in the antimicrobial activity. The present work has demonstrated significant enhancement in antimicrobial activity with increased Ag+ contents at the Zn sites of the wurtzite ZnO. Within a short time period of 2 h only, the Escherichia coli (E. coli) count of the order of 108 has been deactivated under the exposure of visible light. The synthesized paper matrices have also resisted the degradation even in the presence of Gloeophyllum trabeum (G. trabeum), a cellulose eating fungus. The paper remains intact even after the incubation for 7 days, which is unprecedented. The thorough characterization of the paper matrices along with their superior antimicrobial activities makes them a potential candidate for applications in healthcare and to produce pathogen free safe drinking water using a cheap point of use system.

Ag and Cu doped ZnO nanowires: A pH-Controlled synthesis via chemical bath deposition

Synthesizing and doping process of p-type zinc oxide (ZnO) nanowire arrays (NWAs) through chemical bath deposition is still a challenge. We systematically investigate the growth of ZnO NWAs in a pH-controlled aqueous media. This study helps us to successfully grow copper (Cu) and silver (Ag) incorporated NWAs. The optimum pH values for NWA growth and doping are 6.8 and 10.8. Field emission scanning electron microscopy (FESEM) images reveal the finest ZnO NWAs with the length of 1.3 µm (70 nm in diameter) for pH = 6.8 and 8.2 µm (170 nm in diameter) for pH = 10.8, respectively. Moreover, high-resolution X-ray photoelectron spectroscopy (HRXPS) demonstrates the peaks of Cu and Ag at their specific binding energies especially in pH of 6.8. A slight shift to lower angles of (002) peak in X-ray diffraction (XRD) pattern of doped samples is also detected relative to the presence of Ag+ (rAg+ = 115 pm) and Cu+ (rCu+ = 77 pm) which have higher ionic radii than Zn2+ (rZn2+ = 74 pm). A lattice expansion is also observed by high-resolution transmission electron microscope (HRTEM) confirming an average increase in interplanar spacing of 5 pm and 20 pm for copper and silver-doped samples, respectively. Finally, diffused reflectance spectroscopy (DRS) graphs show a red-shift in the UV-absorption of doped samples regarding to obtaining Ag or Cu doped NWAs.

Theoretical investigation of the cathodoluminescence spectra of Co-doped ZnO nanowires

The morphology, structural and optical properties of the Co2+ ions doped in ZnO nanowires were investigated by S. Geburt et al. (2013) [1]. The cathodoluminescence CL spectrum is composed of the ZnO near-band-edge NBE (ultraviolet emission), green emission band attributed to the recombination of carriers at intrinsic ZnO defects and sharp red emission assigned to the Co2+ intra-3d luminescence. The photoluminescence excitation PLE spectrum shows the direct transitions from the ground state of Co2+ occupying Td site to the higher excited states. The visible region provides important information about the electronic structure of the Co2+ doped zinc oxide nanowires. This work investigates an interpretation of the origin of the ultraviolet NBE and discusses the defects involved in the broad green emission band. A theoretical crystal-field analysis of the visible lines, associated to the Co2+ ion transition occupying Td site symmetry in ZnO host crystal, is also realized which leads to a satisfactory correlation between experimental and calculated energy levels. The electronic structure was compared to the structure reported for Co2+ ion doped in ZnO nanocrystalline (nanorods, nanoparticles) and bulk crystals. The quantum confinement effect of ZnO nanowires is interpreted.

Effect of cerium composition on optical and structural properties of cerium doped ZnO nanowires

Synthesis of cerium (Ce) doped zinc oxide (ZnO) nanowire has been carried out using chemical bath deposition over seed layer. The seed layer of Ce doped ZnO thin film was deposited by spin coating method. Effect of Ce doping on optical and structural properties of nanowire has been explored to optimize the performance of nanowires for their applicability in light emitting devices. High resolution field emission scanning electron microscopy (FESEM) clearly reveals nanowire growth for 15% of Ce in ZnO. Optical band gap of the films was found to increase with an increase in Ce concentration in ZnO. All Ce doped ZnO thin films exhibits more than 90% transparency in the visible region and show absorption sharply in ultra-violet region at approximate 375 nm. Transmittance of the nanowire in visible region is showing an average transmittance of 61%. The photoluminescence (PL) spectra in all samples exhibit a strong ultraviolet emission at the near band edge centered at 389 nm due to free exciton recombination. A broad blue visible emission peak for all the samples located at 467 nm was seen to be originated due to the interstitial position of Zn2+ ions.

Synthesis of copper doped Zinc oxide nanowires with enhanced ultraviolet photoresponse behavior

This work mainly focused on the synthesis of copper doped zinc oxide nanowires by hydrothermal method, their characterization and their ultraviolet (UV) light sensing response at room temperature. The structural and morphological characterization was carried out using X-ray diffraction and scanning electron microscopy. Enhanced ultraviolet (UV) photodetection property has been achieved for a dopant concentration of 2.5wt% and 5wt% showing UV photosensitivity values (photo-to-dark current ratio) of around 800 and 1800, respectively. This is an order of magnitude higher than the undoped ZnO nanowires. High photocurrent gain is attributed to the trapping of carriers under dark and detrapping them under UV illumination by Cu-related defects. Enhancement in photosensitivity indicates that Cu-doped ZnO nanowires are promising candidates for UV photodetection applications.

Quantum chemical simulations of doped ZnO nanowires for photocatalytic hydrogen generation

Zinc oxide (ZnO) is considered in general as a promising material for solar water splitting. Its wurtzite‐structured bulk samples, however, can be considered as active for photocatalytic applications only under UV irradiation, where they possess ∼1% efficiency of sunlight energy conversion due to their wide band gap (3.4 eV). Although pristine ZnO nanowires (NWs) possess noticeably narrower band gaps than the bulk, the tendency of band gap reduction with increasing NW diameter is insufficient, and further modification is required. We have contributed to filling this gap by performing a series of ab initio calculations on ZnO NWs of different diameters (dNW), which are mono‐doped by metal (Ag) and non‐metal atoms (C, N) or contain oxygen vacancies with varied concentration (∼3 vs. ∼6%). To reproduce qualitatively the energies of one‐electron states of nanowires in our calculations, the hybrid DFT + HF Hamiltonian has been used, based on the PBE0 exchange‐correlation functional. We have analyzed changes in the electronic structure induced in a few defect composition scenarios, showing that, for specific concentrations and locations of the dopants, the optical absorption peak of doped ZnO can be shifted to the visible light range with promising efficiency. In agreement with experimental observation, the most significant results have been achieved for carbon‐doped ZnO nanowires. They possess the highest photocatalytic suitability, since the band gap is reduced in this case down to 2.1–2.2 eV (for nanowire diameters of 2.9–3.5 nm), which corresponds to optimal 15–17% efficiency of solar energy conversion.

All Solution‐Based Fabrication of Copper Oxide Thin Film/Cobalt‐Doped Zinc Oxide Nanowire Heterojunctions

Versatile and intriguing solution‐based processes are utilized to synthesize nanostructured materials for device applications to reduce material production and device fabrication costs. This study presents results on the fabrication and characterization of copper oxide (CuO) coated cobalt‐doped zinc oxide nanowires (Co‐doped ZnO NWs)‐based heterojunction diodes prepared by a two‐step synthesis route through combined hydrothermal growth and sol–gel spin coating. Highly dense, well‐ordered, undoped, and Co‐doped ZnO NWs were successfully grown by hydrothermal method. Complementary CuO thin films were synthesized by sol–gel method and subsequently coated onto both undoped and Co‐doped ZnO NWs through spin‐coating technique. Enhanced diode properties with a rectification ratio of 103 at ±2 V and an ideality factor of n = 2.4 (in dark) were obtained for Co‐doped ZnO NWs‐based heterojunction diodes. The obtained results demonstrated that the investigated heterojunction diode structure fabricated by facile and cost‐effective solution‐based processes can be a promising candidate for the next generation optoelectronic devices.

Nanosimulation of electron confinement in cerium doped zinc oxide nanowire structure for light emitting devices

Nanosimulation of Cerium (Ce) doped Zinc Oxide (ZnO) nanowire has been carried out for nanowires structure of Ce doped ZnO/MgxZn1−xO using MATLAB. Electron confinement in Ce doped ZnO nanowire has been achieved by deducing wave function intensity from the solutions of Schrodinger equation. Eigen energy has been computed using the Transfer Matrix Method (TMM). It is revealed from our analysis that increasing mole fraction of magnesium (Mg) increases Eigen energy. For 10% magnesium, Eigen energy was found to be 0.07eV and for 30% magnesium, it has got increased up to 0.09eV. Effect of Mg mole composition in barrier region on confinement of electron wave function spread has been investigated. Better confinement was obtained for increasing values of Mg mole composition.

Fluorine doped zinc oxide nanowires: Enhanced photocatalysts degrade malachite green dye under visible light conditions

Enhanced visible-light absorption of 4at% fluorine (F) doped zinc oxide (ZnO) nanowires (F:ZnO) produced via a hydrothermal method with 15M sodium hydroxide (NaOH) is explored with various characterization techniques: XRD, TEM, UV–vis spectra, Pl spectra, XPS, and surface area analysis. Moreover, photocatalytic performance of as-prepared samples is studied via degradation of malachite green dye under visible light irradiation. Finally, the photocatalyst’s optimal amount to use is determined as well as its recyclability. Results show that band gaps of ZnO nanostructures depend on NaOH concentration, doping 15M NaOH resultant ZnO nanowires with 4at% F further narrows the band gap, F:ZnO nanowires perform 1.6 times better than the pure ZnO nanowires in malachite green dye (MG) degradation tests, overloading the solution with the photocatalyst actually hinders degradation performance, and the F:ZnO photocatalyst remains a robust performer even after five cycles.

VLS-grown diffusion doped ZnO nanowires and their luminescence properties

Zinc Oxide (ZnO) nanowires were deposited by vapor–liquid–solid (VLS) method on to aluminum doped ZnO (AZO) thin films grown by sol-gel technique. For various device applications, current injection into such nanowires is critical. This is expected to be more efficient for ZnO nanowires deposited on to AZO compared to those deposited on to a foreign substrate such as silicon. In this work we compare the morphological and optical properties of nanowires grown on AZO with those grown under similar conditions on silicon (Si) wafers. For nanowires grown on silicon, diameters around 44 nm with heights around 2.2 μm were obtained. For the growth on to AZO, the diameters were around 90 nm while the heights were around 520 nm. Room temperature photoluminescence (RT-PL) measurements show improved near band-edge emission for nanowires grown on to AZO, indicating higher material quality. This is further established by low temperature photoluminescence (LT-PL) measurements where excitonic transitions with width as small as 14 meV have been obtained at 4 K for such structures. Electron energy loss spectroscopy (EELS) studies indicate the presence of Al in the nanowires, indicating a new technique for introduction of dopants into these structures. These results indicate that ZnO nanowires on sol-gel grown AZO thin films show promise in the development of various optoelectronic devices.

Simple strategy for production of aluminium/nitrogen co doped zinc oxide nanowires

In this study, a novel ZnO homojunction was produced using hydrothermally grown n-type ZnO nanowires coated with p-type ZnO:Al:N [Zn (98 at.%), Al (1 at.%) and N (1 at.%)]. The fabricated homojunction was extensively characterized by scanning electron microscopy, energy dispersive spectroscopy, photoluminescence emission measurements and current voltage measurements. It was found that the p-type ZnO:Al:N affected the vertically aligned ZnO nanowires due to the incorporated dopant and very large capillary force during the drying process. PL emission measurements indicated that the p-type ZnO:Al:N coating suppressed the UV emission peak without degrading the visible emission peak. In terms of solar cell performances, the homojunctional device exhibits photovoltaic behavior with power conversion efficiency ~0.001576 %.

Comparative Organics Remediation Properties of Nanostructured Graphene Doped Titanium Oxide and Graphene Doped Zinc Oxide Photocatalysts

In recent years, we have accomplished effective organics remediation using titanium oxide (TiO2) doped transition metals, zinc oxide (ZnO) nanowires and silver & palladium doped ZnO nanowires. The present manuscript displays the advantage of organic remediation in both UV and visible radiation using graphene (G) doped TiO2 nanoparticles, G doped ZnO nanowires. The nanostructured G-TiO2 nanoparticles and G-ZnO nanowires were synthesized using sol-gel and hydrothermal methods. The nanostructured materials were characterized using scanning electron microscopy (SEM) and X-Ray diffraction (XRD), procedures. The remediation of organic compounds (naphthalene, methyl orange) in water was achieved under both UV and visible radiation using graphene doped nanostructured photocatalytic materials. The advantage of graphene doped ZnO nanowires as well as G-TiO2 nanoparticles has revealed organics remediation in both UV and visible radiation of light.

Enhanced photocatalytic activity of iron doped zinc oxide nanowires for water decontamination

Zinc oxide (ZnO) and iron doped zinc oxide (ZnO/Fe) nanowires were synthesized on glass substrates through a conventional hydrothermal method and the nanowires were characterized by UV–visible spectrum, scanning electron microscope (SEM), X-ray diffraction (XRD), and Raman spectroscopy techniques, respectively. Photocatalytic activities of ZnO and ZnO/Fe nanowires were investigated in both UV and white light for degradation of organic contaminants (1, 2-dichlorobenzene ‘DCB’ and methyl orange ‘MO’) in water. The ZnO/Fe nanowires exhibit an improved photocatalytic activity compared to ZnO nanowires. The photocatalytic performance of the nanowires is also compared to P25 titanium oxide (TiO2) for degradation of DCB and MO. Interestingly, ZnO/Fe nanowires show superior photocatalytic activity than TiO2 in white light and a similar activity level under UV light. The results indicate that this photocatalyst is suitable for the decontamination of organic materials under solar radiation.

Effect of the Deposition Conditions on the Optical Properties of Samarium and Samarium-Cobalt Doped Zinc Oxide Nanowires

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