Wurtzite Structure Of Zinc Oxide Research Articles

Multifunctional Applications of Gd‐Doped ZnO Nanoparticles Prepared Easily by the Coprecipitation Method

AbstractThe present work involves the preparation of pure ZnO and gadolinium‐doped ZnO nanoparticles with the general formula GdxZn1−xO (X = 0–0.05) by wet chemical coprecipitation technique. XRD outcomes confirmed that these nanoparticles exhibited a hexagonal wurtzite structure of zinc oxide lacking any secondary phase. The calculated average crystallite size declined from 33 to 28 nm. Through SEM analysis, the shape and morphology of the sample were determined, which showed nanoflakes‐like structures, and EDS analysis confirmed the elemental composition of Gd‐doped ZnO nanoparticles. UV–vis DRS spectral studies indicate good optical capabilities with a decline in the bandgap from 3.4 to 2.6 eV with an incline in doping concentration. Photoluminescence studies exhibited a green emission peak at 378 nm. Additionally, photodegradation of these nanoparticles was assessed through degradation of MB dye, which showed 94% of dye degradation. Synthesized nanoparticles show good electrochemical performance in CV studies. Pure ZnO and Gd‐ZnO were examined against Gram‐positive Enterococcus faecalis and Gram‐negative Escherichia coli bacteria, and it was initiated that the zone of inhibition of antibacterial activity improved with gadolinium doping compared to the pure ZnO nanoparticles.

Low-cost fabrication methods of ZnO nanorods and their physical and photoelectrochemical properties for optoelectronic applications

Zinc Oxide (ZnO) nanorods have great potential in several applications including gas sensors, light-emitting diodes, and solar cells because of their unique properties. Here, three low cost and ecofriendly techniques were used to produce ZnO nanorods on FTO substrates: hydrothermal, chemical bath deposition (CBD), and electrochemical deposition (ECD). This study explores the impact of such methods on the optical, structural, electrical, morphological, and photoelectrochemical properties of nanorods using various measurements. XRD analysis confirmed the hexagonal wurtzite structure of ZnO nanorods in all three methods, with hydrothermal showing a preferred orientation (002) and CBD and ECD samples showing multiple growth directions, with average particle sizes of 31 nm, 34 nm, and 33 nm, respectively. Raman spectra revealed hexagonal Wurtzite structure of ZnO, with hydrothermal method exhibiting higher E2 (high) peak at 438 cm−1 than CBD and ECD methods. SEM results revealed hexagonal ZnO nanorods became more regular and thicker for the hydrothermal method, while CBD and ECD led to less uniform with voids. UV-vis spectra showed absorption lines between 390 nm and 360 nm. Optical bandgap energies were calculated as 3.32 eV, 3.22 eV, and 3.23 eV for hydrothermal, CBD, and ECD samples, respectively. PL spectra revealed UV emission band with a small intensity peak around 389 nm and visible emission peaks at 580 nm. Temperature dependent PL measurements for ZnO nanorods indicated that the intensities ratio between bound exciton and free exciton decreases with temperature increases for the three methods. Photocurrent measurements revealed ZnO nanorod films as n-type semiconductors, with photocurrent values of 2.25 µA, 0.28 µA, and 0.3 µA for hydrothermal, CBD, and ECD samples, and photosensitivity values of 8.01, 2.79, and 3.56 respectively. Our results suggest that the hydrothermal method is the most effective approach for fabricating high-quality ZnO nanorods for optoelectronic applications.

Effect of various processing parameters on the properties of ZnO thin films

Zinc oxide (ZnO) thin films are essential in opto-/piezo-electronics due to their transparency, high electron mobility, wide bandgap (∼3.37 eV), and high excitonic binding energy (60 meV). Effects of processing parameters on ZnO thin films, such as the molarity, ageing, thickness, and calcination temperature, on the microstructural and optical properties deposited by sol-gel spin-coating are investigated under one roof. X-ray diffraction (XRD) confirmed the polycrystalline nature of all films, along with a dominant orientation (002) plane, indicating the formation of a c-axis oriented hexagonal wurtzite structure of ZnO regardless of the processing parameters. Peak intensities varied for all samples and exhibited the highest peak intensity annealed at 500 °C, which correlates with the increase in crystallite size from 15.93 to 16.41 nm due to a decrease in defect density via the thermal expansion. 0.4 M aged solution over 70 h showed the variation in the crystallite size and dislocation density, indicating the improvements in the thin film quality. Thickness-dependent ZnO thin films also improved the crystallinity, which was confirmed by high peak intensities. Decreasing the Urbach energy (Eu) of 0.4 M solution indicates reduced lattice imperfections/defects and high electronic quality of thin-film materials. Deposited ZnO films with an ageing time of 70 h and thickness of 109 nm exhibit the highest refractive index of 3.9 and 2.6, indicating light interaction and optimal density. The optimized conditions of sol-gel derived ZnO thin films augment the ease of development of economic devices for practical implications in opto-/piezo-electronics.

ZnO nanostructures grown from spent batteries: Ambient catalytic aspects and novel mechanistic insights

The present work includes a facile and economic microwave assisted hydrothermal synthesis of Zinc Oxide (ZnO), Diethylene Triamine Pentaacetic Acid (DTPA) stabilized Zinc Oxide (ZD) and DTPA stabilized Silver doped Zinc Oxide (ZAD) nanostructures using Zn from spent alkaline batteries. The synthesised nanostructures were well characterised using electronic, vibrational and X-Ray spectroscopic techniques as well as thermal and microscopic techniques revealing the successful stabilisation of DTPA in ZD and doping of Ag in ZAD. The Fourier Transform Infrared Spectroscopy (FTIR) spectra showed peaks characteristic to the presence of ZnO in the fingerprint region and those to the presence of DTPA. The X-Ray Diffraction Spectroscopy (XRD) pattern of ZnO, ZD and ZAD indicated the hexagonal wurtzite structure of ZnO and face centred cubic metallic Ag in ZAD. The Transmission Electron Microscopy (TEM) images revealed rod shaped morphology for ZnO and spherical morphologies for ZD and ZAD. The nanostructures proved to be efficient catalysts to achieve 100 % degradation of Malachite Green, Crystal Violet and Reactive Blue-21 and their binary mixtures under ambient conditions in presence of Hydrogen peroxide (H2O2). ZAD exhibited relatively rapid degradation with rate constants 0.754 min−1, 0.187 min−1 and 0.0150 min−1 for MG, CV, and RB-21 respectively as well as 99 % reduction in Chemical Oxygen Demand (COD) value of the dye solutions. Scavenging studies and Electron Paramagnetic Resonance (EPR) studies using different spin trapping agents revealed the involvement of singlet oxygen species, hydroxyl radicals (OH.) and superoxide radicals (O2.-) in the degradation process. This work aligns with Sustainable Development Goals 6, 12 and 13.

Eco-friendly synthesis of indole-4-hydroxy-chromen-2-ones using green zinc oxide nanocatalyst and its assessment of anti-cancer studies against A549 cells

Zinc oxide (ZnO) nanoparticles have significant attention in the field of photocatalyst, super capacitor, battery and biomedicine due to their versatile potential and diverse applications. In the present study, ZnO was synthesized using Celastruspaniulatus leaf extract as a green fuel through combustion method. The morphological and structural studies of ZnO were characterized using XRD, FTIR, UV–Vis, SEM and TEM analysis. The PXRD pattern of ZnO as shown diffraction peaks of ZnO planes (100), (002), (102), (110), (103) and (112) are hexagonal Wurtzite ZnO structure. ZnO is formed in a discrete irregular hexagonal shape was confirmed by SEM analysis. The application of ZnO is achieved for the synthesis of (4-hydroxy3-(1H-indol-3-yl)-phenyl-methyl-chromen-2-one) and its derivatives via Knoevenagel/Michael addition reaction. All synthesized compounds showed good yield and are characterized using 1H NMR, 13C NMR and ESI-MS spectral studies. The reusability of the ZnO catalyst is tested and documented. Some of the synthesized chromenone compounds show promising anticancer activity against A549 cells with less concentration.

Green synthesis and studies on citrus medica leaf extract-mediated Au–ZnO nanocomposites: A sustainable approach for efficient photocatalytic degradation of rhodamine B dye in aqueous media

Abstract Incorporating narrow band gap oxide semiconductors and metals into zinc oxide (ZnO) nanostructures broadens the range of light sensitivity to include visible wavelengths. In this study, the photocatalytic degradation of rhodamine B (RhB) dye was studied as a model for environmental pollution in aqueous media. This study describes the use of photodegradation catalysts, including gold (Au), ZnO, and Au–ZnO nanocomposites (prepared in ratios of 90:10 and 95:5) using the extract of Citrus medica leaves. X-ray diffraction (XRD) findings have shown that ZnO nanoparticles (NPs) have a hexagonal wurtzite structure. Field emission-scanning electron microscopy findings have depicted that ZnO NPs have diverse shapes, including spherical, quasi-spherical, hexagonal, and anisotropic, with some clumping. Au exhibits consistent spherical shapes and sizes with even distribution. Au–ZnO (90:10) shows quasi-spherical NPs with interconnected spherical Au, forming a porous and uneven surface. Au–ZnO (95:5) has spherical gold nanoparticles (Au NPs) dispersed on a textured ZnO surface, with some clustering and size variation as evident from the transmission electron microscopy, atomic force microscopy, and diffuse reflectance UV-visible spectroscopy analysis. The characterization results have demonstrated the uniform distribution of Au across the ZnO lattice. Additionally, the XRD patterns confirmed the hexagonal wurtzite structure of ZnO. Furthermore, energy-dispersive analysis of X-ray (EDX)-mapping verified the inclusion of zinc, oxygen, and Au in the hybrid Au–ZnO nanocomposites and their effective distribution. The topological analysis revealed a rough surface for the generated nanostructures. By comparing the results of various techniques, EDX analysis using atomic and weight ratios confirmed the presence of oxygen and Au in the nanocomposite. Additionally, the surface area analysis (BET) test has reported that the adsorption and desorption of nitrogen follow a Type III isotherm. The presence of an H3-type hysteresis loop further confirms the mesoporous nature of the composites, which reports the presence of wedge-shaped pores. The Au–ZnO (90:10) nanocomposite exhibits a higher surface roughness compared to other composites. In addition, this UV-visible diffuse reflectance spectroscopy has enumerated the band gaps of various nanomaterials using UV-visible spectroscopy. Moreover, the analysis has unveiled that combining ZnO with Au NPs (doping) improved the photocatalytic performance of ZnO. This improvement is attributed to the formation of additional energy levels within the ZnO band gap due to the presence of Au ions. Experimental investigation of the breakdown of RhB dye under visible light irradiation revealed superior photocatalytic activity for the Au–ZnO (90:10) nanocomposite compared to both Au–ZnO (95:5) and pure ZnO and Au counterparts. Multiple experiments confirmed the effective photodegradation and removal of RhB dye from the aqueous medium using the nanocatalyst under visible light irradiation. Under optimal conditions (1.0 g·L−1 photocatalyst, 10 ppm RhB, and pH 10), 99% photodegradation efficiency was reached within 50 min of irradiation. Investigation of reactive species revealed that the increased effectiveness of photodegradation in Au–ZnO (90:10) stems from the presence of photogenerated holes and hydroxyl radicals. The study also analyzed the reaction kinetics and order, and the reusability of the best photocatalyst Au–ZnO (90:10)) was confirmed through five consecutive cycles, demonstrating its sustained effectiveness in photodegradation. These findings highlight the potential of Au–ZnO (90:10) nanocomposite as a promising material for photocatalytic degradation of organic dyes.

Noticeable influence of V-dopant on optoelectronic properties of ZnO films prepared by SILAR technique

Wide bandgap semiconductors such as Zinc Oxide (ZnO) have earned much attention on account of its interesting optical and electrical properties. Also, doping ZnO with suitable transition elements enables to tune its properties, making it suitable for applications like transparent conducting oxides and LEDs. To this aim, Vanadium-doped ZnO (V:ZnO) thin films are fabricated using the SILAR method and studied the structural, optical, vibrational, photophysical and electrical properties. Introducing vanadium creates lattice relaxation in the ZnO wurtzite structure, influencing its electronic band structure. The X-ray diffraction (XRD) analyses have verified the structural integrity of the vanadium-doped zinc oxide (V:ZnO) films, revealing their polycrystalline composition. The Raman spectroscopy shows the reduced phonon line widths due to the improved crystallite quality with the presence of vanadium. Furthermore, it has been noted that optical characteristics such as the bandgap and refractive index are sensitive to vanadium doping as a consequence of modified electronic structures. Hall-effect experiments have shown that undoped ZnO films possess a mobility of 1.31 cm2/Vs and a charge carrier density of 5.58 × 1013 cm−3. It has been observed that doping with V markedly influences these parameters of ZnO films. Then, the time-resolved photoluminescence measurements reveal the increased carrier lifetimes, suggesting the introduction of dopants mitigates carrier-phonon interactions. Such interactions need to be minimized to prevent the dissipation of carrier energy. In essence, the reported work demonstrates the potential of V:ZnO for optoelectronic applications.

Synthesis and characterization of efficient Sr-doped ZnO nanostructures for optoelectronic, and photocatalytic applications

With increasing technological advancements, optoelectronics emergence is inevitable. Various metal oxides are explored for optoelectronics properties and Zinc oxide-based nanostructures have various advantages that can be explored in optoelectronic devices. Nanomaterials that are undoped and Strontium doped were synthesized via a simple wet chemistry route. The study set out to quantify the impact of Strontium doping in Zinc Oxide on optical and photocatalytic properties. The doping of strontium concentration within ZnO varied from 0 % to 3 % by weight of the total molar ratio. The characterization of SZO nanomaterials was done using measurements of X-ray diffraction, Raman Spectroscopy, SEM, Hall effect measurements, UV/Vis, and PL regarding their structural properties, morphological properties, optical properties, and electrical characteristics. X-ray diffraction analysis showed that the Sr-doped ZnO had the hexagonal wurtzite structure of zinc oxide. SEM showed that the morphology of Sr-doped ZnO thin films changed by increasing Sr concentration. Meanwhile, the film’s surface was smooth and crack-free. In UV–Vis experiments, the concentration of Sr doping reduced the optical band gap ranges from 3.27 eV to 2.98 eV. All the samples exhibited n-type conductivity in the Hall Effect. Photocatalytic degradation Methylene Blue was studied and SZO (3 at. %) was best for degradation with efficiency over 80 %.

Photodegradation of methylene blue dye using graphene oxide incorporated, post-transition metal doped zinc oxide thin films by spray pyrolysis

Photocatalytic activity of graphene oxide incorporated pure and metal doped zinc oxide thin films were studied against methylene blue dye under simulated solar irradiation. Thin films were deposited on a glass substrate using an automated spray pyrolysis technique at a temperature of 425 °C. Aluminium, gallium, and indium were the post-transition metals used for doping. Graphene oxide content in the precursor solution was fixed at 0.00375 g/l. The formation of the wurtzite structure of zinc oxide has been confirmed using structural analysis. The average crystallite size of all the thin film samples was found to be in the range of 45–55 nm. The morphology and elemental composition of the films were studied using scanning electron microscopy and energy-dispersive x-ray spectroscopy. The energy band gap of the material was determined from UV–vis-NIR spectroscopic measurements using Tauc’s plot and it is in the range of 3.25–3.28 eV. Photoluminescence spectra of the as-deposited films were recorded. Intensity of the near band emission at 395 nm was found to decrease upon metal doping, indicating a better photocatalytic property. All the films were used for heterogeneous photocatalysis and the indium doped zinc oxide thin film incorporated with graphene oxide was found to be a better catalyst with an efficiency of 94.9% for degrading methylene blue dye in 180 min.

Photocatalytic evaluation of disperse purple dye using Polyvinylpyrrolidone capped bare and Cu+2/Fe+3 codoped ZnO nano catalysts

Polyvinylpyrrolidone capped bare zinc oxide and codoped with cupric and ferric ions, have been fabricated by a facile polyol reduction method with ethylene glycol. The as-fabricated nanoparticles were calcinated to control their size and morphology. The fabricated nanoparticles were characterized using various techniques including X-ray diffraction, scanning electron microscopy, energy dispersion X-rays, UV–Vis spectroscopy, and Fourier transform infrared Spectroscopy. The results showed phase pure nanoparticles with wurtzite zinc oxide structure, and a blue shift in absorbance spectrum when zinc oxide was codoped with cupric and ferric ions.The study examined the degradation rate of disperse purple dye using bare and codoped zinc oxide nanoparticles in the solar region. Codoped nanocatalysts showed superior efficiency compared to bare zinc oxide. The kinetic analysis of the dye was conducted, revealing that the degradation of the dye followed a pseudo-first-order kinetics pattern. Furthermore, about 99 % degradation of the dye solution in 110 min by codoped zinc oxide as compared to bare zinc oxide (84 %) under solar light suggests Cu+2/Fe+3 codoped zinc oxide is an emerging tool for environmental remediation.

Synthesis and characterization of P3HT:ZnO-FWCNTs for possible application in organic solar cells

Zinc oxide (ZnO) and few-walled carbon nanotubes (FWCNTs) mixed in poly(3-hexylthiophene-2,5-diyl) (P3HT) were prepared for application in organic solar cells (OSCs) as photoactive materials. ZnO was synthesized by microwave-assisted sol-gel method. Improved properties were found for the nanocomposite with 3 wt% of FWCNTs concentration. XRD revealed the hexagonal wurtzite structure of ZnO and the nanocomposites (ZnO-FWCNTs) showed both hexagonal wurtzite and carbon structure. UV/Vis/NIR and PL studies revealed a relatively higher photon absorption efficiency and emission intensity from the ZnO-3% FWCNTs. PL intensity of P3HT was quenched from the sample P3HT:ZnO-3% FWCNTs with the ratio of 1:1, indicating charge transfer phenomena between the electron donor (P3HT) and an acceptor (ZnO-FWCNTs) materials. FESEM showed well-mixed ZnO nanorods with P3HT. Current-voltage measurements indicated an improved electrical conductivity for P3HT:ZnO-3% FWCNTs (ratio 1:1). The obtained results suggest that this sample can potentially improve the photoelectrical conversion efficiency of the OSCs.

Hydrothermal synthesis of ZnO Crystals: Diverse morphologies and characterization of the photocatalytic properties

Zinc oxide (ZnO) microstructures including the ZnO nanorods (R-ZnO), ZnO nanopillars (C-ZnO), and multistage microspheres composed of ZnO nanosheets (M-ZnO) have been synthesized using a two-step hydrothermal approach by adjusting the concentrations of the growth solution. Scanning Electron Microscopy (SEM) was employed to observe the surface morphology of the fabricated samples. X-ray diffraction (XRD) was utilized for the structure characterization, which the results reveal a hexagonal wurtzite ZnO structure in all three samples with different microstructures. X-ray Photoelectron Spectroscopy (XPS) was used to investigate their defects, indicating that the oxygen vacancy ratios were 34.3 %, 21.8 %, and 51.5 % respectively for R-ZnO, C-ZnO, and M-ZnO. The band gaps of R-ZnO, C-ZnO, and M-ZnO, determined through Ultraviolet–Visible Absorption Spectroscopy (UV–Vis), were found to be 3.35 eV, 3.6 eV, and 3.19 eV, respectively. Finally, the photocatalytic performances of the prepared ZnO samples were investigated under simulated sunlight irradiation by observing the degradation of methyl orange, which the M-ZnO samples obtained a superior photocatalytic efficiency of 79 %.

Plant extract-mediated synthesis Cobalt doping in zinc oxide nanoparticles and their in vitro cytotoxicity and antibacterial performance

In this research, zinc oxide (ZnO) nanoparticles doped with different percentages of produced cobalt using the green synthesis method. ZnO nanoparticles showed good cellular and microbial toxicity due to their high surface-to-volume ratio. Adding cobalt metal to the nanostructure can lead to the appearance of a new feature. To investigate the effect of adding cobalt metal, synthesized ZnO nanoparticles containing 3 and 6% cobalt were synthesized using plant extract. The resulting nanostructures were characterized by a Raman spectroscopy, UV–Visible spectrometer, X-ray diffraction, and Field emission scanning electron microscopy. Ultimately, the synthesized samples' cytotoxicity and antimicrobial tests were performed. XRD confirmed the formation of a hexagonal wurtzite ZnO structure. XRD and electron imaging showed that doping resulted in a decrease in average crystal size. The results showed that with cobalt doping, the particle size decreased slightly. The cytotoxicity and antimicrobial effects results showed that in all three studies, cobalt doping leads to an increase in the toxicity of this nanostructure compared to non-doped nanoparticles.

Graphene Oxide Incorporated Zinc Oxide Thin Films by Spray Pyrolysis for Efficient Photodegradation of Methylene Blue

AbstractPhotodegradation of methylene blue dye was studied with pure and graphene oxide incorporated zinc oxide thin films as catalysts. Graphene oxide content in the precursor solution was varied from 0.0005 to 0.005 g/L. Thin films were prepared by automated spray pyrolysis technique at a substrate temperature of 425 °C. Structural studies revealed the formation of hexagonal wurtzite structure of zinc oxide. Carbon presence in the films was confirmed with energy‐dispersive spectroscopy. Optical band gap of the samples was determined using Tauc method. Intensity of the near band emission of photoluminescence spectrum was found to decrease upon increasing graphene oxide concentration. Photocatalytic activity of all the films has been studied against methylene blue dye under solar irradiation for 180 minutes and it is found that the highest graphene oxide content attributes to better degradation efficiency of 91.2 %.

In vitro Evaluation of Antibacterial Activity of Synthetic Zeolite Supported AgZno Nanoparticle Against a Selected Group of Bacteria.

The development of novel and intriguing nanoparticle (NP)-based materials with antibacterial activity has recently received attention due to the problem of bacterial resistance to conventional antibiotics becoming more and more frequent. Thus, this study aimed to investigate the antibacterial effectiveness of a synthetic zeolite-supported AgZnO nanoparticle against selected bacteria in vitro. Using the disc diffusion method, the antibacterial activity of synthetic zeolite-supported AgZnO nanoparticles was assessed against Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli). Zinc oxide (ZnO) and Ag/ZnO nanoparticles were used to create the zeolite-supported Ag/ZnO composite. Chloramphenicol was used as a standard drug. The nanoparticles and composites were characterized using powder X-ray diffraction (XRD), Fourier transform infrared (FTIR), and atomic absorption spectroscopy (AAS). Synthetic zeolite-supported AgZnO nanoparticles showed promising antibacterial properties with the largest zone of inhibition against S. aureus bacteria in comparison to E. coli. The synthetic zeolite-supported AgZnO nanoparticle displayed a zone of inhibition against S. aureus and E. coli without a remarkable difference compared to the respective standard drug (Chloramphenicol). Zinc peaks were visible in the X-ray diffractograms, which supported the theory that the characteristic hexagonal wurtzite structure of zinc oxide was present. All types of ZnO, AgZnO, and AgZnO-Zeolite showed wide-spectrum activity with better effect against gram-positive bacteria, while the Zeolite-Ag/ZnO composite showed even better antibacterial activity. The findings suggest a potential bactericide that needs further evaluation in future studies was observed in synthetic zeolite-supported Ag/ZnO nanoparticles.

New insights into the photocatalytic mechanism of pristine ZnO nanocrystals: From experiments to DFT calculations

Zinc oxide (ZnO) has been regarded as a promising photocatalytic candidate for the purification of wastewaters containing organic contaminants. In this study, six ZnO nanocrystals with the shapes of granule, flake, rod, porous flake, nanosheet-assembled flower, and nanorod-assembled flower were designed and synthesized to investigate the relationship between their photocatalytic activities and morphological features. All these different morphological samples had high-degree of crystallization and belonged to the hexagonal wurtzite structure of ZnO. The morphology had little effect on the light absorption threshold and band gap of these samples, but showed great effect on their adsorption performance, photocatalytic activity, and separation efficiency of photogenerated electrons and holes. The main reactive radicals generated during the photocatalytic process were O2–, OH, and holes. The theoretical calculations revealed that the polar crystal plane could facilitate the separation of charge carriers. The adsorption and distortion energies for O2 adsorbed onto different crystal planes were found to be much higher than those for H2O. These findings theoretically confirmed why O2– was the dominant group of reactive radicals.

Simultaneous removal of Cu (II) and Cr (VI) ions from petroleum refinery wastewater using ZnO/Fe3O4 nanocomposite

The presence and removal of heavy metals such as Cu(II) as well as Cr(VI) in petroleum refinery wastewater calls for concerted efforts due to their mobility, toxicity, bioaccumulation, and non-biodegradability in the environment. In this present work, zinc oxide (ZnO), iron oxide (Fe3O4) nanoparticles and ZnO/Fe3O4 nanocomposites were synthesized via simple sol-gel and chemical reduction methods; characterized using different analytical tools and then applied as nanoadsorbent to sequester Cu(II) and Cr(VI) ions from Petroleum Refinery wastewater via batch adsorption process. Cu(II) and Cr(VI) adsorption processes were examined with respect to contact time (kinetic effect), nanoadsorbent dosage, isotherm equilibrium, and thermodynamic parameters. ZnO/Fe3O4 nanocomposites with higher surface area (39.450 m2/g) have a mixture of rod-like and spherical shapes as compared to ZnO and Fe3O4 nanoparticles with spherical shape only and surface areas of 8.62 m2/g and 7.86 m2/g) according to the high-resolution scanning electron microscopy (HRSEM) and Brunauer–Emmett–Teller (BET) analysis. The X-ray diffractometer (XRD) results revealed the formation of hexagonal wurtzite structure of ZnO and the face-centered cubic structure phase of Fe3O4 nanoparticles, after the formation of the ZnO/Fe3O4 nanocomposites the phases of the nanoparticles were not affected but the diffraction peaks shifted to higher 2θ degree. The average crystallite size of ZnO and Fe3O4 nanoparticles and ZnO/Fe3O4 nanocomposites were 20.12, 26.36 and 14.50 nm respectively. The maximum removal efficiency of Cu (II) (92.99%) and Cr (VI) (77.60%) by ZnO/Fe3O4 nanocomposites was higher than 85.83%; 65.19% for Cu (II) and 80.57%; 62.53 for Cr (VI) using ZnO and Fe3O4 nanoadsorbents individually under the following conditions: contact time (15), dosage (0.08 g) and temperature (30 °C). The experimental data for Cu (II) and Cr (VI) ion removal fitted well to the pseudo-second-order kinetic and Langmuir isotherm models. The thermodynamic study suggested that the removal of the two metal ions from petroleum wastewater was endothermic. The reusability study after the fourth adsorption-desorption cycle indicated the stability of ZnO/Fe3O4 nanocomposites with 85.51% and 69.42% removal efficiency of Cu (II) and Cr (VI). The results showed that ZnO/Fe3O4 nanocomposite achieves higher performance than ZnO and Fe3O4 alone in the removal of Cu (II) and Cr (VI) ions from the petroleum refinery wastewater.

Effect of Carrier Gas Flow Rates on the Structural and Optical Properties of ZnO Films Deposited Using an Aerosol Deposition Technique

Aerosol deposition (AD) is a simple, dry raw-powder deposition process in which the targeted film is formed by direct bombardment of accelerated starting powder onto the substrate surface at room temperature. Despite the increased interest in AD film formation, no work has been completed to systematically investigate the formation of dense zinc oxide (ZnO) films using the AD method and their optical properties. Therefore, this study was carried out to investigate the effect of AD gas flow rate on the formation of AD films and the optical properties of aerosol-deposited ZnO films. ZnO films with nanosized (<40 nm) crystallites were successfully deposited on FTO substrates at room temperature. A dense and uniform layer of aerosol-deposited ZnO films with a roughened surface was obtained without subsequent heat treatment. With the increase in the AD gas flow rate, the crystal size and the AD film’s thickness were reduced. The Raman spectroscopy verified that the thin film was of a ZnO wurtzite structure. The room temperature photoluminescence of the ZnO thin film produced strong visible emissions. The findings of this work demonstrated that AD can be an alternative technique for the rapid deposition of dense and thick ZnO films for optoelectronic applications.

Hydrothermal growth and ultraviolet sensing performance of well-aligned Ga-doped ZnO nanowire arrays

Herein, gallium (Ga)-doped zinc oxide (ZnO) nanowire arrays (GZNWAs) with different Ga doping concentrations (Ga/Zn = 0–4 atom%) were grown on the interdigital patterned fluoro-doped tin oxide glass substrates by a hydrothermal technique, their crystalline structure, morphology and ultraviolet (UV) sensing performance were focused on investigating. The results showed that all the as-grown samples were hexagonal wurtzite structure of ZnO. When the Ga doping concentration was below 4%, well-aligned GZNWAs were achieved. Furthermore, five UV photodetectors (PDs) were prepared using the GZNWAs as photoactive layers, all the devices were found to be excellent responses towards 365 nm light. Among these devices, the GZNWAs UV PD (1% Ga) maintained the optimal performance, its responsivity, sensitivity, detectivity, external quantum efficiency, response time and decay time were 72.8 A/W at 5 V, 747.8 at 0 V, 5.5 × 1012 Jones, 2.5 × 104%, 10.6 s and 45.6 s, respectively.

Ultraviolet photoconductivity and photoluminescence properties of spray pyrolyzed ZnO nanostructure: Effect of deposition temperature

The current investigation focuses on the influence of substrate temperature on Zinc Oxide (ZnO) thin films synthesized on glass substrates using 0.1 M precursor solution by low-cost spray pyrolysis technique. The x-ray diffraction peaks matched the hexagonal wurtzite structure of ZnO with the highest intensity along the (1 0 1) plane. Estimated the crystallite size, dislocation density, micro-strain, and the number of crystallites in the deposits using X ray diffraction (XRD) data. The crystallinity of the films deposited at 450 °C was maximum. Fibrous surface morphology is altered by varying the deposition temperature. The enhancement of optical transmittance and energy bandgap of the deposits with deposition temperature. The reduction of Urbach energy with an increase in the substrate temperature confirmed the improvement of crystallinity. The photoluminescence study revealed peaks associated with electron-hole pair recombination, zinc, and oxygen-related defects. The samples deposited at 450 °C showed minimum defects. Commission Internationale de l'éclairage (CIE) chromaticity diagram showed white light emission for sample deposited at 450 °C with the color temperature equal to 5378 °C which is agreeing with the temperature of a normal white light source. Improvement of free carrier concentration and n-type conductivity due to the enhancement of crystallinity was observed. ZnO thin films deposited at 450 °C showed maximum photocurrent when illuminated with UV light and faster rise and fall of photo resistance due to the improvement in the crystallinity and carrier concentration. The maximum photosensitivity was observed for the samples synthesized at 450 °C. Hence the ZnO thin films deposited at 450 °C can be used as ultraviolet photodetector material.