ZnO Samples Research Articles

UV Photoluminescence Microscopy of Individual ZnO Nanostructured Clusters

Ultraviolet (UV) photoluminescence (PL) spectra were acquired from individual nanostructured ZnO clusters less than 1 μm in size. The nanostructured clusters were formed by aggregation of a small number of nanoparticles. This analysis employed a microscopy apparatus specially designed for PL assessments of nanostructures at UV wavelengths with a spatial resolution of 0.395 μm. Atomic force microscopy was also employed to ascertain the sizes and morphologies of the nanostructured clusters. The ZnO samples were prepared by laser ablation in liquid (LAL) and comprised spherical, rhomboid, or gel-coated particles. PL emissions originating from free excitons (FX), FX phonon replicas, and defects were observed. The FX peak widths and positions were found to vary (with positions from 3.30 to 3.36 eV), suggesting that a range of particle sizes and morphologies was obtained from the LAL process. FX peaks at higher energies exhibited greater widths as a consequence of a quantum size effect originating from the crystallites comprising the nanostructured clusters. The rhomboid particles showed less-intense emissions related to defects compared with the other two types while also exhibiting the least intense emissions related to FX phonon replicas. This work also examined the mechanism by which nanoparticles were produced by LAL on the basis of the spectroscopic data. The information presented herein is expected to assist in the design and fabrication of semiconductor nanoparticles for future nanotechnology applications.

GO/Ag2S/ZnO nanorods coatings for non-enzymatic photoelectrochemical glycine determination at trace levels

Photoelectrochemical (PEC) detection as the accurate sensor detection technology was applied to monitor the low concentration of glycine based on GO/Ag2S/ZnO nanorods coatings, which were fabricated on stainless steel. The maximum photocurrent of 116.8 μA cm−2 was obtained for the samples with the deposition time of 120 s, which was indicating that GO/Ag2S/ZnO samples with the deposition time of 120 s had excellent photochemical properties compared to other samples, including Ag2S/ZnO and ZnO samples. The PEC sensing of GO/Ag2S/ZnO nanorods coatings electrodes against glycine were tested by i-t. The results showed that the GO/Ag2S/ZnO nanorods coatings electrodes have high sensitivity of 5.44 μA−1 nM−1 cm−2, big linear range of 5 nM–99.775 μM and low detection limit of 3 nM. Hence the obtained results confirmed the possibility of the GO/Ag2S/ZnO nanorods coatings electrodes used as PEC sensors for low concentration glycine measurements. If the sensor can be applied to clinical detection, it can not only monitor the content of glycine in patients in real time, but also greatly reduce the risk of kidney stones caused by excessive glycine (Gly) in humans.

Preparation-Height-Specific Surface Area of Flower-like ZnO for Norfloxacin Removal in Dialysis Wastewater

According to statistics, the number of patients with kidney dialysis is increasing every year, especially in Taiwan. The high content of antibiotics in kidney dialysis wastewater can create an environmental burden if not properly treated. Therefore, in this study, a new design for a flower-like ZnO catalyst that can effectively treat norfloxacin (NF) in dialysis wastewater is presented and its NF treatment efficiency is investigated under different operating parameters (including different dosages, pH, ambient temperatures, and pollutant concentrations). Scanning electron microscope results indicate that the ZnO sample consists of flower-like nanostructures with diameters of about 4.97 μm. The surface area, pore volume, and pore size of the flower-like ZnO were estimated to be 46.45 m2g−1, 0.132 cm3g−1, and 19.50 nm, respectively. The total removal efficiency increased with the increase in the initial pH value of NF, when the initial pH value of NF increased from 3.5 (38.1%) to 7.5 (82.5%). However, the total removal efficiency decreased with an increase in the initial pH value of NF, when the initial pH value of NF increased from 9.5 (79.5%) to 11.5 (32.9%). The second-order kinetic simulation results show that the linear relationship is better than that of the first-order kinetic, and the Rc2 values are all above 0.9.

Synthesis of Flower-like ZnO and Its Enhanced Sensitivity towards NO2 Gas Detection at Room Temperature

A flower-like ZnO was successfully synthesized via a simple chemical precipitation method at room temperature (RT) in distilled water, without the use of any catalysts or substrates. The sample’s structure was analyzed using various techniques including scanning electron microscopy (SEM), X-ray diffraction (XRD), transmission electron microscopy (FETEM), and X-ray photoelectron spectroscopy (XPS), which confirmed its hexagonal structure. UV–visible optical absorption measurements also revealed the presence of UV absorption at 365 nm. A reasonable growth mechanism for the formation of flower-like ZnO was proposed based on these analyses. The response of the sample to low concentrations of NO2 (1 ppm) was evaluated at different calcination temperatures, and the results showed that the best response was achieved when the sample was calcined at 600 °C. The flower-like ZnO sample labeled as 6ZnO showed the highest response of 54.18 when exposed to 1 ppm of NO2 gas at RT. Additionally, 6ZnO exhibited good response and recovery properties of 11 s and 93 s, respectively, at low concentrations of NO2 at 1 ppm. The gas sensing mechanism and the mechanism of the enhanced gas response of the flower-like ZnO are discussed.

Bottom-up self-assembly of macroporous ZnO nanostructures for photovoltaic applications

The present study utilized a template-assisted electrodeposition route for the bottom-up epitaxial growth of macroporous zinc oxide nanostructures. To this end, the ZnO seed layer was coated on the p-type silicon substrates using a radio frequency magnetron sputtering technique to form a p-n heterojunction. Then, polymer microspheres were implanted on ZnO/Si substrates to act as a template. Subsequently, ZnO nanostructures were electrodeposited through the interstitial spaces between the microspheres. After the deposition, the microspheres were removed by dissolving in chloroform solvent, forming a porous structure. The planar and cross-sectional electron microscopy analyses exhibited a uniform macroporous morphology with an average pore diameter of ∼1 μm. The pores were homogeneously distributed on the surface of the electrodeposited ZnO layer. The advantage of this technique over the top-down approaches, such as electrochemical etching, is that the porosity and size of pores can be easily adjusted by varying the concentration and diameter of microsphere templates. The optical investigations revealed enhancement in photon absorption and photoluminescence (PL) intensity due to multiple light scattering in the pore walls of the deposited ZnO nanostructures. For the templated sample, a PL blue shift was observed due to the reduction in crystallite size of ZnO nanostructures. A heterojunction thin film solar cell was designed by the metallization of ZnO/p-Si samples to study the power conversion capability of macroporous ZnO nanostructures. The photovoltaic performance of the developed devices was evaluated under a solar light simulator. The device based on the templated sample showed increased shunt resistance and reduced series resistance compared to the flat sample. The optoelectrical results indicated an efficiency improvement for the fabricated solar cells based on the macroporous ZnO sample due to its higher exposed area and increased rate of electron-hole generation.

Comparative study of structural, optical and electrical properties variation of pure, (Ag, Mg) doped and co-doped ZnO nanostructured thin films

Abstract Nanostructured thin films are one of the most valuable types of industrial semiconductors for a variety of optoelectronics and optical device applications, having recently been used as a transparent conductive oxide in solar cells. In this work, nanostructured thin films of pure ZnO, Ag doped ZnO, Mg doped ZnO and Ag–Mg co-doped ZnO were successfully synthesized on silicon and glass substrates, using rapid thermal evaporation. The impact of the doping elements on the surface morphology, structural, electrical, and optical properties of the deposited films were investigated. It was found that all films have polycrystalline hexagonal wurtzite structure using X-ray diffraction. Images obtained by scanning electron microscopy (SEM) revealed compact and smooth surfaces, with uniform coverage of all substrate regions. SEM images confirm the nanostructured nature of the surfaces with particle size varying as a function of doping. Raman spectroscopy showed A1(LO), E2(high) and LVM modes for all samples. The developed films’ optical transmission ranged from 74 % to 87 %, with an optical bandgap ranging from 3.09 for Mg:ZnO films to 3.8 eV for Ag:ZnO samples. Depending on the doping nature modification, these alterations were associated to structural and morphological changes in the films. All films were electrically conductive, while Ag:ZnO films exhibited the lowest resistivity value reaching 0.56 Ω cm.

Sargassum natans I Algae: An Alternative for a Greener Approach for the Synthesis of ZnO Nanostructures with Biological and Environmental Applications.

In this work, the influence of the Sargassum natans I alga extract on the morphological characteristics of synthesized ZnO nanostructures, with potential biological and environmental applications, was evaluated. For this purpose, different ZnO geometries were synthesized by the co-precipitation method, using Sargassum natans I alga extract as stabilizing agent. Four extract volumes (5, 10, 20, and 50 mL) were evaluated to obtain the different nanostructures. Moreover, a sample by chemical synthesis, without the addition of extract, was prepared. The characterization of the ZnO samples was carried out by UV-Vis spectroscopy, FT-IR spectroscopy, X-ray diffraction, and scanning electron microscopy. The results showed that the Sargassum alga extract has a fundamental role in the stabilization process of the ZnO nanoparticles. In addition, it was shown that the increase in the Sargassum alga extract leads to preferential growth and arrangement, obtaining well-defined shaped particles. ZnO nanostructures demonstrated significant anti-inflammatory response by the in vitro egg albumin protein denaturation for biological purposes. Additionally, quantitative antibacterial analysis (AA) showed that the ZnO nanostructures synthesized with 10 and 20 mL of extract demonstrated high AA against Gram (+) S. aureus and moderate AA behavior against Gram (-) P. aeruginosa, depending on the ZnO arrangement induced by the Sargassum natans I alga extract and the nanoparticles' concentration (ca. 3200 µg/mL). Additionally, ZnO samples were evaluated as photocatalytic materials through the degradation of organic dyes. Complete degradation of both methyl violet and malachite green were achieved using the ZnO sample synthesized with 50 mL of extract. In all cases, the well-defined morphology of ZnO induced by the Sargassum natans I alga extract played a key role in the combined biological/environmental performance.

Effect of Ni and Mn dopant on thermoelectric power generation performance of ZnO nanostructures synthesized via hydrothermal method

In this article, we have presented a low-cost hydrothermal approach to enhance the thermoelectric performance of ZnO nanostructures via modulation doping. For this purpose, we have prepared a series of pure and X:ZnO (X = Ni & Mn) samples. The Seebeck value of the Mn-doped samples possesses the maximum Seebeck coefficient of −36 μV/°C compared to the pure and Ni-doped samples (−22 μV/°C & −27 μV/°C) at room temperature. The highest value of the Seebeck coefficient for the Mn-doped samples is related to the formation of mid-gap energy band states due to the substitution of Mn2+ with Zn2+. These mid-band states induce an imbalance in the DOS, by producing a spin polarization effect that leads to a high Seebeck value. In terms of electrical conductivity, the Ni-doped ZnO sample exhibits the highest electrical conductivity of about 122 S/cm, due to the incorporation of Ni metal ions inside the ZnO matrix (confirmed by XRD) and leads to a high carrier concentration. However, the highest Seebeck value for the Mn-doped sample results in the maximum thermoelectric power factor ∼1.12 × 10−5 Wm−1C−2 at room temperature.

Preparation of tungsten-doped zinc oxide thin films by co-sputtering for micro-gas sensing devices

Synthesis of a good nanostructure is a vital part in regards to achieving proper gas sensing characteristics. In this study, Tungsten (W) doped ZnO nanostructure is synthesized on micro electro mechanical systems (MEMS) device by co-sputtering process. Appropriate doping concentration to the sensing material is crucial for sensing properties, therefore, 5 different doping concentrations ranging from 0% W to 4% W to the ZnO structure are developed. The structural properties of all the W doped ZnO samples were characterized by Scanning electron microscope (SEM), X-Ray diffraction (XRD) analysis and Energy-dispersive X-ray spectroscopy (EDS) analysis. Sensing properties were calculated with different concentrations of H2 gas ranging from 20 ppm to 100 ppm. All of the W doped ZnO sensors were tested for H2 gas at working temperatures varying from 100 °C to 300 °C to detect the optimal doping concentration and optimal working temperature. At 150 °C, 3% W doped ZnO revealed 67% gas sensing response for 100 ppm H2 gas. Selectivity test with 5 different gases displayed that W doped ZnO sensor has good selectivity over H2 gas at 150 °C.

Gamma irradiation induced surface modification of (PVC/HDPE)/ZnO nanocomposite for enhancing the oil removal and conductivity using COMSOL multiphysics

Blend nanocomposite film was prepared by loadings of irradiated ZnO in ratios of (5 wt%) inside the PVC/HDPE matrix using a hot-melt extruder technique. The physical and chemical properties of the irradiated and unirradiated ZnO samples are compared. The Vis–UV spectrum of ZnO shows an absorption peak at a wavelength of 373 nm that was slightly red-shifted to 375 nm for an irradiated sample of ZnO at a dose of 25 kGy due to the defect of crystal structure by the oxygen vacancy during gamma irradiations. This growth of the defect site leads to a decrease in energy gaps from 3.8 to 2.08 eV. AC conductivity of ZnO sample increased after the gamma irradiation process (25 kGy). The (PVC/HDPE)/ZnO nanocomposites were re-irradiated with γ rays at 25 kGy in the presence of four different media (silicon oil, sodium silicate, paraffin wax and water). FTIR and XRD were performed to monitor the changes in chemical composition. The new peak at 1723 cm−1 attributed to C=O groups was observed in irradiated (PVC/HDPE)ZnO samples at only sodium silicate and water media. This process induced new function groups on the surface of the (PVC/HDPE)/ZnO blend sample. This work aims to develop (PVC/HDPE)ZnO for oil/water separation. The highest oil adsorption capability was observed in samples functionalized by C=O groups based on the different tested oils. The results suggest that the surface characterization of the (PVC/HDPE)/ZnO can be modified to enhance the oil adsorption potential. Further, the gamma irradiation dose significantly enhanced the AC conductivity compared to the unirradiated sample. According to COMSOL Multiphysics, the irradiated sample (PVC/HDPE)ZnO in water shows perfect uniform electric field distribution in medium voltage cables (22.000 V).

Carrier Transport Mechanism of Pt Contacts to Atomic Layer Deposited ZnO on Glass Substrates

We grew ZnO films at different temperatures on glass substrates using thermal atomic layer deposition and investigated the current conduction mechanism of Pt/ZnO junctions. For ZnO samples grown at 46 and 96 °C, the current flow through the ZnO layer was not possible at low temperatures such as 298 and 320 K because the ZnO layer under Schottky contacts were wholly depleted. However, the current conduction was observed with increasing the temperature, which was found to be dominated by the Schottky emission at 360 and 380 K and the Poole–Frenkel emission at 380 and 400 K. For ZnO sample grown at 141 °C, the strong tunneling current could occur because very thin depletion region was formed because of the high carrier concentration of ZnO layer. The observed difference in the current conduction can provide a guidance how growth temperature of ZnO should be controlled to design the low-temperature grown ZnO based devices built on glass substrates.

Highly Active Nanocrystalline ZnO and Its Photo-Oxidative Properties towards Acetone Vapor.

Zinc oxide is one of the well-known photocatalysts, the potential applications of which are of great importance in photoactivated gas sensing, water and air purification, photocatalytic synthesis, among others. However, the photocatalytic performance of ZnO strongly depends on its morphology, composition of impurities, defect structure, and other parameters. In this paper, we present a route for the synthesis of highly active nanocrystalline ZnO using commercial ZnO micropowder and ammonium bicarbonate as starting precursors in aqueous solutions under mild conditions. As an intermediate product, hydrozincite is formed with a unique morphology of nanoplates with a thickness of about 14-15 nm, the thermal decomposition of which leads to the formation of uniform ZnO nanocrystals with an average size of 10-16 nm. The synthesized highly active ZnO powder has a mesoporous structure with a BET surface area of 79.5 ± 4.0 m2/g, an average pore size of 20 ± 2 nm, and a cumulative pore volume of 0.507 ± 0.051 cm3/g. The defect-related PL of the synthesized ZnO is represented by a broad band with a maximum at 575 nm. The crystal structure, Raman spectra, morphology, atomic charge state, and optical and photoluminescence properties of the synthesized compounds are also discussed. The photo-oxidation of acetone vapor over ZnO is studied by in situ mass spectrometry at room temperature and UV irradiation (λmax = 365 nm). The main products of the acetone photo-oxidation reaction, water and carbon dioxide, are detected by mass spectrometry, and the kinetics of their release under irradiation are studied. The effect of morphology and microstructure on the photo-oxidative activity of ZnO samples is demonstrated.

Chromium-doped ZnO nanoparticles synthesized via auto-combustion: Evaluation of concentration-dependent structural, band gap-narrowing effect, luminescence properties and photocatalytic activity

Herein we report the effect of the Cr3+ content on the distinctive features of the first-ever auto-combustion-synthesis-produced Cr3+ doped ZnO nanoparticles utilizing leucine as the fuel. To assess the impact of fuel and Cr3+ content on the structural, optical, and luminescence characteristics, as-synthesized powders were systematically examined using powder XRD, UV–Visible, and Photoluminescence spectroscopy. Structural studies show that the exothermicity of the redox mixture containing oxidizer and fuel combination leads to the development of polycrystalline, single-phase, and nanosized particles. XRD analysis shows that, reduced crystallite size with Cr3+ content. In contrast, other characteristics like lattice parameters, unit cell volume, strain, and dislocation density, were shown to increase linearly with Cr3+ concentration up to 7 mol%. Additionally, it is seen that the predicted Urbach energy values rise as Cr3+ is added to the ZnO host matrix, indicating that the substitution of Cr3+ for Zn in the host ZnO lattice has increased structural disorder. In contrast to the other samples, the 5 mol% Cr3+ doped ZnO sample exhibits the emission near the white region according to the PL emission measurements. Furthermore, the photocatalytic activity of the as-prepared Cr3+ doped ZnO NPs was examined. It was found that the as-prepared samples exhibit outstanding photocatalytic activity in the visible wavelength region against Malachite Green (MG) dye. Among all, 9 mol% Cr3+ doped ZnO has shown the maximum 95.4% degradation against MG dye. All the investigated results conclude that the produced Cr3+ doped ZnO nanoparticles could be exploited in a variety of upcoming optoelectronic and photocatalytic applications.

Assessment of flaws in cold‐sintered ZnO via acoustic wave speed and attenuation measurements

AbstractThe cold sintering process (CSP) is a low temperature processing technique that utilizes a transient phase to synthesize dense ceramics. However, some CSP parts contain microflaws that arise due to inhomogeneities in pressure, temperature, and transient phase. This work uses 20 MHz ultrasound to verify the presence of defects in CSP ZnO samples of varying densities (84%–97%). Acoustic metrics used in this work include wave speed, which is affected by differences in the effective elastic properties of the medium, and attenuation, which quantifies wave energy loss due to scattering from defects. Wave speed maps were inhomogeneous, suggesting density gradients which were verified with scanning electron microscopy. In addition, it was demonstrated that the pores produced by cold sintering are anisometric, which increases the anisotropy in the elastic properties. High attenuation regions (>300 Np/m) are present in all samples independent of relative density and correspond to defects identified in X‐ray computed tomography (XCT) which were as small as 38 µm in effective diameter. However, some high attenuation spots do not correspond to visible defects in XCT, which suggests the presence of features undetectable with XCT such as residual secondary phases at the grain boundaries.

Phase Transformation and Performance of Mg-Based Hydrogen Storage Material by Adding ZnO Nanoparticles.

ZnO nanoparticles in a spherical-like structure were synthesized via filtration and calcination methods, and different amounts of ZnO nanoparticles were added to MgH2 via ball milling. The SEM images revealed that the size of the composites was about 2 μm. The composites of different states were composed of large particles with small particles covering them. After the absorption and desorption cycle, the phase of composites changed. The MgH2-2.5 wt% ZnO composite reveals excellent performance among the three samples. The results show that the MgH2-2.5 wt% ZnO sample can swiftly absorb 3.77 wt% H2 in 20 min at 523 K and even at 473 K for 1 h can absorb 1.91 wt% H2. Meanwhile, the sample of MgH2-2.5 wt% ZnO can release 5.05 wt% H2 at 573 K within 30 min. Furthermore, the activation energies (Ea) of hydrogen absorption and desorption of the MgH2-2.5 wt% ZnO composite are 72.00 and 107.58 KJ/mol H2, respectively. This work reveals that the phase changes and the catalytic action of MgH2 in the cycle after the addition of ZnO, and the facile synthesis of the ZnO can provide direction for the better synthesis of catalyst materials.

Investigation of efficient photoconduction and enhanced luminescence characteristics of Ce-doped ZnO nanophosphors for UV sensors.

This study involves the single-step, mass-scale productive synthesis, photoconduction, and luminescence characteristics of pure and cerium rare-earth-ion-doped ZnO (CZO) nanophosphors with different Ce concentrations (Ce: 0, 2, 4, 6, and 8wt.%) synthesized using the solid-state reaction method. The synthesized nanophosphors were characterized for their structural, morphological, optical, and photoconductivity (PC) properties using X-ray diffraction (XRD), field-effect scanning electron microscopy (FE-SEM), energy dispersive spectroscopy, Fourier-transform infrared (FT-IR), photoluminescence (PL), and PC measurements. The sharp diffraction peaks of XRD results exhibit the formation of crystalline hexagonal wurtzite ZnO nanostructures. The decrease in diffraction peak intensities of CZO with an increase in Ce concentrations signifies the deterioration of the ZnO crystal. FE-SEM images exhibit the good crystalline quality of nanophosphors composed of spherical- and elongated-shaped nanoparticles that are distributed consistently on the surface. The energy dispersive X-ray pattern of the 4wt.% Ce-doped ZnO (CZO4 ) sample confirms the doping of Ce in ZnO. The presence of chemical bonds and functional groups corresponds to transmittance peaks established using FT-IR spectroscopy. Deconvoluted PL spectra show two major emission peaks, one in the UV region, which is near-band-edge, and the other in the visible region ranging from ~456 to 561 nm. In PC studies, current-voltage (I-V) and current-time (I-T) characteristics, that is, rise/decayin current under dark as well as UV light conditions, are also investigated. Efficient photoconduction is observed in CZO samples. The obtained results indicate the suitability to luminescent and photosensor applications.

Effective role of vibrational annealing in enhancing room temperature physical properties of Co doped ZnO nanoparticles by using novel TVA technique

Well-annealed nanocrystalline semiconductor materials in pellet or thin film form, composed of small grains with a high surface-to-volume ratio, are considered as promising candidates for multiple device applications. However, no such method is available yet that can control the grain size of such samples during heat treatment. In this present work, a novel thermo-vibrational annealing (TVA) setup for processing nanocrystalline materials was designed and fabricated in-house. Here both thermal and mechanical vibrational energy were simultaneously applied to the sample during annealing, followed by vibrational dry quenching in the presence of an inert gas environment. Co-doped ZnO pellets were synthesized by chemical route pyrophoric method followed by annealing at 800 °C for 4 h using this set up. For comparison, one pellet was annealed with vibration with calibrated vibration at a speed of 360 rpm, and another pellet was annealed without vibration. X-ray diffraction (XRD), Raman and Fourier transform Infrared (FTIR) spectroscopic studies showed the formation of a single crystalline phase with hexagonal wurtzite structure of both the samples and the proper incorporation of Co2+ ions into the ZnO matrix without any impurity phases, which was also confirmed by energy dispersive X-ray (EDX) spectroscopy studies. Scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM) studies confirmed the decrease in average grain and particle size of the sample when processed with the TVA setup. Ultraviolet–Visible spectra showed that the bandgap energy of the Co-doped ZnO sample varies inversely with particle size. Hall-effect measurements demonstrated the semiconducting nature of both samples with n-type charge carriers. The presence of Co2+ ions in the wurtzite ZnO lattice was confirmed by X-ray photoelectron spectroscopy (XPS). The magnetic properties were studied using a SQUID magnetometer, which confirmed that a Co doped ZnO sample annealed with the TVA technique exhibit better room temperature ferromagnetism properties compared to sample annealed without vibration. Based on these studies, it was believed that the sample annealed by mechanical vibrational energy with vibrational dry quenching has a great influence on several physical properties of any material and hence Co doped ZnO sample processed with this TVA technique can be used as a promising candidate for multiple sensor and magnetic storage devices.

Electronic, structural and optical properties of Gd-doped ZnO powder synthesized by solid-state reaction method

We explored the impact of Gd doping on the structural, electronic and optical characteristics of the ZnO powder. The Gd-doped ZnO (0, 2% and 5%) powder samples have been synthesized using the conventional solid-state reaction process with varied Gd concentrations. The XRD pattern confirmed that all the studied samples are in the hexagonal wurtzite crystalline structure. The morphology has been explored using SEM images, which exhibited an agglomerated rod-like particle structure. The XPS results indicate the presence of oxygen vacancies (Vo) in the Gd-doped ZnO samples and the Vo’s are found to increase with increasing Gd amount. According to PL findings, the intensity ratio of the green and ultra-violet emission peaks is found to increase from 0.090 to 0.418 with increasing Gd-doping concentrations, confirming that Vo’s are increasing with Gd-doping. The UV-visible spectroscopy results reveal that the energy band gap (Eg) decreased from 3.31 eV to 3.23 eV with increasing Gd-doping concentration. Bangladesh J. Sci. Ind. Res. 58(1), 53-64, 2023

Investigation of the simultaneous interactions of experimental variables and mechanism pathway in the photodegradation of methylene blue by binary ZnO/Cu2O photocatalyst

The pollution of water suppliers by various organic compounds, especially synthetic dyes, has been known as a critical global risk. An efficient removal technology is a heterogeneous photocatalysis based on the illumination of semiconducting materials, especially as coupled systems and on the nanoscale. This work synthesized and coupled ZnO and Cu2O nanoparticles (NPs) to enhance the photocatalytic activity due to the decreased electron/hole (e/h) pairs recombination. The pHpzc values of 8.5, 8.0, and 8.4 were estimated for ZnO, Cu2O, and Cu2O-ZnO samples. In the response surface methodology (RSM) study of methylene blue (MB) photodegradation, a significant model was confirmed based on model F-value of 55.8 > F0.05, 14, 15=3.18 and a lack-of-fit (LOF) of 2.52 < F0.05, 10, 5 =4.77. All correlation coefficients (R2 = 0.9812, the adjusted R2 = 0.9636, and the predicted R2 = 0.9109) are close to each other and unity. The optimal conditions run included pH 3, an illumination time of 45 min, and a binary catalyst dose of 0.55 g/L. In the presence of Na2CO3, ascorbic acid, Na2SO4, and NaCl, the initial degradation efficiency of 50.9% (in the absence of any scavenger) was decreased to 31.9%, respectively 36.3%, 39.7%, and 44.4%, respectively, within an irradiation time of 30 min. This order confirms the hydroxyl radicals, superoxide radicals, free electrons, and finally, the holes have relative importance in MB photodegradation process. Based on the results, a direct Z-scheme mechanism was suggested for the MB photodegradation. The direct Z-scheme is a favor to produce more hydroxyl and superoxide radicals as the main centers of MB photodegradation by the proposed system. The recovery percentages of 48, 45, 43, and 39% were obtained for the first to fourth reusing runs, respectively. The catalyst holds above 81% of its initial activity after four reusing runs, which is satisfactory.

Effect of Ni doping on structural, optical and gas sensing properties of ZnO films for the development of acetone sensor devices

The development of sensor materials for environmental air surveillance is very challenging. In order to meet the demand, the present study corelates the effect of nickel doping on structural, optical, morphological and gas sensing ability of zinc oxide thin films. The films were deposited on the glass substrates using spray pyrolysis technique. The crystalline character and morphological analysis of the films were characterized by X-ray diffraction (XRD) and Field emission scanning electron microscopy (FESEM). The hexagonal wurtzite structure of polycrystalline nature is observed from the XRD patterns. The preferred orientation is (101), however doping has significantly triggered (002) orientation. Systematic decrement in the lattice parameters and bond length have been observed which led to structural distortions as result of mismatch in ionic radii of dopant and host materials. FESEM analysis reveals that thin film samples exhibit nanoflake morphology. A well-defined morphology is observed with Ni doping. The compositional analysis (Energy dispersive X-ray spectroscopy) shows that the Ni content was increased with doping which confirm the successful Ni doping. Optical analysis of the samples was performed using UV–Vis spectroscopical analysis. Transmission spectra indicated the highest transmission value in the case of undoped ZnO samples (More than 80%). Gradually decreasing band gap values of ZnO films were observed with Ni doping. The sensor response was investigated for undoped and Ni doped ZnO samples at room temperature in the absence and presence of acetone with 50 ppm concentration. Optimum response (∼78%) is obtained for Ni doped ZnO (2% Ni) samples with response time of 33s. Spray synthesized 2% Ni doped ZnO thin film samples show promising approach to achieve high response at ambient temperature.