Doped ZnO Nanostructures Research Articles

Enhanced Acetaldehyde Sensing Performance of Spherical Shaped Copper Doped ZnO Nanostructures

AbstractSpherical shape copper (Cu) doped ZnO nanostructures of various amount (3, 6, 9 and 12 %) were synthesized. The XRD, FTIR, UV‐Visible, HR‐TEM, FESEM, EDS, SAED and XPS were done to understand the structural, optical, morphology and shape of Cu doped ZnO nanostructures. To achieve the best gas reaction, doping concentration was optimized. ZnO and Cu doped ZnO nanostructures were exposed to various oxygenated volatile organic compounds (OVOCs) and found to be more selective towards acetaldehyde sensing. For 50 ppm acetaldehyde gas, temperature study was done at various temperatures (RT, 50, 100, 150, 200 °C) which showed optimal at 100°C for maximal gas response. The response and recovery time was 16.53 and 18.36 seconds for 50 ppm of acetaldehyde gas. The gas sensing study was carried out at different humidity rates (11, 32, 51, 63 and 84 %) using different saturated solutions. 9 % Cu doped ZnO shows maximum response (61.53 %) as compared to pure ZnO and 3, 6 and 12 % Cu doped ZnO. The spherical shape Cu doped ZnO sensing response was increases with increase in concentration of gas from 10 to 300 ppm. Acetaldehyde gas shows enhanced selectivity towards spherical shape Cu doped ZnO sensors as compared to the other OVOCs like acetone, ethyl methyl ketone, methanol, ethanol, n‐propanol, n‐butanol, formaldehyde, acetaldehyde, propionaldehyde and acrolein. The reproducibility of Cu doped ZnO was studied for 50 days. Also, after acetaldehyde gas sensing change in morphology study of sensor was done.

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.

Enhancement of Photocatalytic and Photoelectrochemical Performance of ZnO by Mg Doping: Experimental and Density Functional Theory Insights

Doped ZnO nanostructures have shown great potential for solar energy applications. Considering the compatible ionic radius, Mg atoms can be doped into ZnO at different concentrations. The current work reports a combined experimental and density functional theory study on the influence of the Mg dopant concentration on ZnO performance simultaneously for photocatalytic dye removal and photoelectrochemical water splitting. Among all the samples, Mg(3)-ZnO (3 at. % Mg) exhibits superior sunlight-driven photocatalytic performance. The optimal Mg-ZnO shows an 8-fold increase in the photocatalytic activity compared to the pristine ZnO. Likewise, the most active photocatalyst shows high photoelectrochemical performance with a photocurrent response of 1.54 mA at the lowest onset potential, 11 times higher than the pristine ZnO. Tuning of the Mg content results in the generation of extra charge carriers and a reduced recombination rate, which are the crucial factors responsible for enhanced photocatalytic and photoelectrochemical performance.

Effect and design of Mn2+ doped ZnO nanostructures for photodegradation and energy storage devices

Effect and design of Mn2+ doped ZnO nanostructures for photodegradation and energy storage devices

Probing structural, optical and magnetic properties of Sm-doped ZnO nanomaterials via experimental and DFT approach: Enhanced photocatalytic degradation and antibacterial performance

We prepared the pristine and Sm3+-doped ZnO nanostructures using an eco-friendly ball milling technique and investigated the physical properties of nanostructures by experimental methods and density functional theory approach. The reduction in crystallite size and increment in structural defects was witnessed due to Sm-doping. Decrease in band gap (from 3.27 to 3.02 eV) and enhancement of magnetic properties were observed with the increase in dopant concentration. The photocatalytic degradation potential of the samples towards the pollutants methylene blue (dye) and ciprofloxacin (antibiotic) improved with Sm3+ doping. The best performance was witnessed for the sample doped with 4 mol% of Sm2O3, which degraded the 93% and 95% of methylene blue (50 ppm) and ciprofloxacin (25 ppm) in 150 min and 210 min, respectively. Antibacterial activity towards the Escherichia coli and Staphylococcus aureus bacteria was also enhanced with the increase of Sm-content. Thus, Sm-doped ZnO nanostructures show good potential for photocatalytic and antibacterial applications.

Nd-Doped ZnO Nanostructures with Enhanced Photocatalytic Performance for Environmental Protection.

Neodymium (Nd)-doped ZnO nanostructures with different amounts of Nd were obtained by the electrospinning-calcination method. X-ray diffraction measurements indicated that the prepared nanostructures have a wurtzite structure without undesirable impurities. Nd doping changes the mean crystallite size as well the lattice strain, as proved by Williamson-Hall plots. The ZnO-based nanostructures were tested as photocatalysts for methylene blue (MB) dye and ciprofloxacin (CIP) drug pollutant degradations under visible light irradiation. Corroborating the obtained results, it was found that the reaction rate constant increased almost linearly with the mean crystallite size (from 2.235 × 10-2 to 3.482 × 10-2 min-1) with a variation in the mean crystallite size from 24.2 to 42.1 nm. Furthermore, the best catalyst sample (0.1% Nd-doped ZnO) was used to optimize the photodegradation process of ciprofloxacin, taking into account the pollutant concentration as well as the catalyst dose. The removal efficiency after 120 min was about 100%, with the rate constant of k = 5.291·10-2 min-1 (CIP) and k = 4.780·10-2 min-1 (MB) for the established optimal conditions. Considering the value of the rate constant, the half-life of the reaction (τ1/2 = ln2/k) was evaluated to be about τ1/2 =13 min for CIP and 14.5 min corresponding to MB. Several catalytic cycles were successfully performed without any loss of photocatalytic activity using these nanostructures, demonstrating that the obtained nanostructures have good stability in the leaching processes.

Synthesis and optical properties of phosphorus doped ZnO: X-ray absorption, X-ray emission, and X-ray excited optical luminescence studies

Abstract Over the past decades, zinc oxide semiconductor and its derivatives have been extensively developed because of its optoelectronic properties. Since ZnO is an intrinsic n-type semiconductor, how to synthesize high-quality p-type ZnO semiconductors and investigate their optoelectronic properties and local chemical structures are important and necessary. In this article, two studies of synthesizing both undoped and phosphorus-doped ZnO nanostructures by hydrothermal method and chemical vapor deposition (CVD) technique are presented. Scanning electron microscopy (SEM) and laboratory X-ray diffraction (XRD) are used to track the surface morphology and the crystalline structure of both undoped and phosphorus doped ZnO nanostructures, respectively. X-ray absorption near edge structures (XANES), X-ray emission spectroscopy (XES) and X-ray excited optical luminescence (XEOL) are also used to determine the local chemical information of both undoped and phosphorus-doped ZnO nano/microstructures such as local symmetry and optical properties. It is found that the phosphorus is successfully doped into the surface of ZnO and substituted the Zn. The phosphorus-doped ZnO products have better crystallinity and less oxygen vacancies on the surface. These two are correlated as one leads to the other. The XEOL results suggest that the average bandgap for undoped and phosphorus doped ZnO is the same, 3.24 eV. The second derivative of the absorption-emission spectra yields the fundamental bandgap for undoped ZnO and phosphorus-doped ZnO is 3.25 eV. The implication of this observation is discussed.

Aluminium doped ZnO nanostructures for efficient photodegradation of indigo carmine and azo carmine G in solar irradiation

Aluminium doped zinc oxide (AZO) nanomaterials (AlxZn1-xO) with x fraction varying as 0.02 and 0.04 were synthesized using the auto-combustion method using glycine as a fuel. The synthesized catalysts were characterized with X-ray diffraction (XRD), UV–Visible Spectroscopy (UV–Vis), Raman spectroscopy, Photoluminescence (PL) spectroscopy, and High Resolution Transmission Electron Microscopy (HR-TEM). XRD results showed that synthesized materials possessed good crystallinity, while UV–VIS was employed to find the band gaps of synthesized materials. Raman was used to determine the vibrational modes in the synthesized nanoparticles, while TEM analysis was performed to study the morphology of the samples. Industrial effluents such as indigo carmine and azo carmine G were used to test the photodegradation ability of synthesised catalysts. Parameters such as the effect of catalyst loading, dye concentration and pH were studied. The reduction in crystallite size, band gap and increased lattice strain for the 4% AZO was the primary reason for the degradation in visible irradiation, degrading 97 and 99% equimolar concentrations of indigo carmine and azo carmine G in 140 min. The Al doped ZnO was found to be effective in faster degradation of dyes as compared to pure ZnO in presence of natural sunlight.

Fabrication and study on the structural and photocatalytic characterization of Ag doped ZnO nanostructure materials

Fabrication and study on the structural and photocatalytic characterization of Ag doped ZnO nanostructure materials

Coexistence of ferromagnetic-antiferromagnetic ground state, exchange bias effect and bandgap narrowing in Cr-doped ZnO nanocrystals derived by simple chemical method.

A detailed investigation of the structural, optical and magnetic properties of Cr-doped ZnO nanostructures obtained via a simple chemical method has been carried out. The structural study using X-ray powder diffraction indicates the hexagonal wurtzite structure for undoped ZnO and ZnO doped with 1% Cr, whereas the appearance of a secondary cubic phase (ZnCr2O4) is witnessed with the incorporation of Cr content ≥3% in the ZnO compounds. Furthermore, the secondary phase is observed to increase systematically with the increase of the Cr concentration. Field emission scanning electron microscopy and high-resolution transmission electron microscopy studies indicate cuboid, hexagonal and rod-type structural morphology in all the nanocrystals. The presence of the cubic structure along with the hexagonal structure is further confirmed from the selected area electron diffraction pattern. Raman spectroscopy has been used to study the crystalline quality, defects and disorder present in the host lattice. UV-visible spectra were obtained to study the effect of Cr doping on the optical absorption and hence to determine the bandgap, and show a decrease in bandgap with increasing Cr concentration. PL spectra show near-band-edge emission along with visible emission, which decreases with a higher concentration of Cr-doped nanocrystals. X-ray photoelectron spectroscopy analysis indicates the incorporation of Cr3+ and Cr2+ ions in the ZnO lattice. Detailed magnetic studies reveal the co-existing ferromagnetic (FM) and antiferromagnetic (AFM) ground states, which result in the observation of an exchange bias (EB) effect in all the doped compounds. The observation of an EB effect arises from the coupling between the FM and AFM components in the Cr-containing ZnO nanocrystals, and provides a way to design new principles and materials platform that are useful for futuristic spintronic devices.

Green hydrothermal synthesis of Ga doping derived 3D ZnO nanosatellites for high sensitive gas sensors

A green hydrothermal synthesis methodology is employed for the synthesis of Ga3+ doped ZnO 3D nanosatellite structures. XRD technique exposed the hexagonal wurtzite type crystal structure of the 3D Ga3+ doped ZnO nanostructures. Ga3+ induced 3D morphology evolution in accordance to Ga doping concentration is realized via. the FESEM images. The FESEM images indicated one sided capped rod like structures (50–250 nm) in pristine ZnO, whereas 3D satellite kind of morphology (>500 nm) was observed in 5% Ga3+ doped ZnO structures. TEM images revealed physical specifications of 3D nanosatellite structures exposing the central rod of 500 nm length & 250 nm in width and the branch rods grown vertical to the central rod of length 300 nm and width of 50 nm. Further, optical absorbance and photoluminescence spectra confirmed the electron rich state of ZnO with Ga3+ doping. The gas sensing performance has shown selectivity toward CO gas at a working temperature of 250 ⁰C. High CO sensing was recorded for 5% Ga3+ doped ZnO 3D nanosatellites with attractive sensing characteristics such as good response, fast response time & fast recovery time.

Performance of 1D tin (Sn) decorated spherical shape ZnO nanostructures as an acetone gas sensor for room and high temperature

Spherical ZnO nanostructures doped with Sn nanoparticles (2 %, 5%, 7 %, and 10 %) were created using the hydrothermal technique. Characterizations included XRD, FTIR, XPS, HR-TEM, FESEM, SAED, EDS, BET and UV–Visible. Maximum gas response was achieved by optimising doping concentration. When ZnO and Sn doped ZnO nanostructures were examined at various temperatures (room temperature, 100, 150, 200, and 250 °C), it was discovered that 150 °C provided the best gas response. Using several saturated solutions, the gas sensing study was conducted at various humidity rates (11, 32, 51, 63, and 84 %). In comparison to the undoped and doped sensors (2, 7 and 10 %), the 5 % Sn doped ZnO sensor has the highest response (75 %). Compared to other gases, acetone gas exhibits improved selectivity towards Sn doped ZnO sensors. Response and recovery times for 5 % Sn doped ZnO are 30.19 and 63.54 s, respectively, and repeatability was examined for roughly 60 days.

Effect of Thermal Treatment on the Structure and Morphology of Vanadium Doped ZnO Nanostructures Obtained by Microwave Assisted Sol-Gel Method.

In this paper, we conducted a fundamental study concerning the effect of thermal treatment on the structure and morphology of 2 mol% vanadium doped ZnO nanopowders obtained by microwave assisted sol-gel method (MW). The samples were analyzed by DTA, FTIR, XRD, SEM, and UV-Vis spectroscopy. The DTA results showed that above 500 °C, there was no mass loss in the TG curves, and ZnO crystallization occurred. The XRD patterns of the thermally treated powders at 500 °C and 650 °C showed the crystallization of ZnO (zincite) belonging to the wurtzite-type structure. It was found that in the 650 °C thermally treated powder, aside from ZnO, traces of Zn3(VO4)2 existed. FTIR spectra of the annealed samples confirmed the formation of the ZnO crystalline phase and V-O bands. The micrographs revealed that the temperature influenced the morphology. The increase in the annealing temperature led to the grain growth. The SEM images of the MW powder thermally treated at 650 °C showed two types of grains: hexagonal grains and cylindrical nanorods. UV-Vis spectra showed that the absorption band also increased with the increasing temperature of thermal treatment. The MW sample annealed at 650 °C had the highest absorption in ultraviolet domain.

ZnO Nanostructures Doped with Various Chloride Ion Concentrations for Efficient Photocatalytic Degradation of Methylene Blue in Alkaline and Acidic Media.

In this study, chloride (Cl−) ions were successfully doped into ZnO nanostructures by the solvothermal method. The effect of various Cl− concentrations on the photocatalytic activity of ZnO towards the photodegradation of methylene blue (MB) under the illumination of ultraviolet light was studied. The as-prepared Cl−-doped ZnO nanostructures were analyzed in terms of morphology, structure, composition and optical properties. XRD data revealed an average crystallite size of 23 nm, and the XRD patterns were assigned to the wurtzite structure of ZnO even after doping with Cl−. Importantly, the optical band gap of various Cl ion-doped ZnO nanostructures was successively reduced from 3.42 to 3.16 eV. The photodegradation efficiency of various Cl− ion-doped ZnO nanostructures was studied for MB in aqueous solution, and the relative performance of each Cl ion-doped ZnO sample was as follows: 20% Cl−-doped ZnO > 15% Cl−-doped ZnO > 10% Cl−-doped ZnO > 5% Cl−-doped ZnO > pristine ZnO. Furthermore, the correlation of the pH of the MB solution and each Cl ion dopant concentration was also investigated. The combined results of varying dopant levels and the effect of the pH of the MB solution on the photodegradation process verified the crucial role of Cl− ions in activating the degradation kinetics of MB. Therefore, these newly developed photocatalysts could be considered as alternative materials for practical applications such as wastewater treatment.

Variation in band gap of antimony doped ZnO nanostructures with doping concentration

ZnO nanostructures were doped with antimony and characterized for structural and optical properties. ZnSbO thin films were fabricated by sol–gel spin coating technology. Structural properties of ZnSbO thin films were investigated by X-ray analysis and FESEM. For determination of transmittance and band gap, UV spectrophotometer characterization was done. XRD reveals single crystal wurtzite structure of ZnSbO thin films. Also results decrease in grain size with doping concentration of antimony in zinc oxide thin films. FESEM and EDAX shows the incorporation of antimony in ZnO. UV spectrophotometer shows increase in transmittance and band gap with doping concentration of antimony in zinc oxide.These results can explore in optoelectronics field.

Photocatalytic dye degradation efficiency of Co doped ZnO nanostructure

The influence of transition metal doping on the dye degradation efficiency of ZnO nanostructures are investigated by pristine and 3% Co doped ZnO nanostructures (Co: ZnO) grown by simple hydrothermal method. Phase purity and crystal structure of synthesized samples are revealed by X-ray diffraction (XRD) and the spectra confirms the phase pure material with hexagonal wurtzite structure. The crystalline size is found to decrease with Co doping. Optical characterization was done by UV-Visible absorption spectroscopy. Optical study confirms that the band gap energy of the samples during doping with Co decreases as compared to pure ZnO. The photocatalytic activity of the synthesized samples under sunlight over the Crystal Violet (CV)dye was investigated for pure and doped samples. The result showed that the pure ZnO samples act as an efficient material for photocatalysis as compared to 3% Co doped sample.

Characterization and antibacterial activity of Ti doped ZnO nanorods prepared by hydrazine assisted wet chemical route

In this study, a simple hydrazine assisted wet chemical method was used to prepare pure and Ti doped ZnO nanorods . The structural properties of pure and Ti doped ZnO nanorods were investigated by XRD analysis. Williamson-Hall (W–H) method was used to determine the crystallite size , strain and dislocation density of the samples. TEM analysis revealed rod like morphology for Ti doped ZnO nanoparticles . The presence of elements such as Zn, Ti and O of the doped sample was confirmed by EDS. XPS spectrum suggests that Ti 4+ ions well substitute Zn 2+ ions in doped nanocrystal . The Raman study further established the formation of ZnO wurtzite structure in both pure and Ti doped ZnO nanorods. The band gap of pure and Ti doped ZnO nanorods were estimated by the Tauc relation as 3.03 eV and 2.91 eV respectively. From the PL spectra, it is observed that the intensity of the polychromatic defect emissions of Ti doped ZnO nanorods is higher than pure ZnO, with some additional defect emissions. The antibacterial activity of Ti doped ZnO nanorods slightly decreased against gram-positive and gram-negative bacteria when compared to pure ZnO. • Synthesis of pure and Ti doped ZnO nanorods by a facile hydrazine assisted wet chemical method. • Confirmation of substitution of Ti 4+ ions into Zn 2+ ions in doped nanocrystal from XPS spectrum. • The band gap of pure and Ti doped ZnO nanorods were estimated by the Tauc relation as 3.03 eV and 2.91 eV. • Intensity of the polychromatic defect emissions of Ti doped ZnO nanorods is higher than pure ZnO. • The antibacterial activity of Ti doped ZnO nanorods is slightly lower than pure ZnO and higher than certain doped ZnO nanostructures.

Aloe barbadensis Mill leaf gel assisted combustion synthesized ZnO:Ni3+: Electrochemical sensor for ascorbic acid detection and photocatalysis

• Nickel (Ni 3+ ) doped ZnO were prepared by aloe vera gel assisted solution combustion technique. • Enhancement of Electrochemical properties in Ni 3+ doped ZnO have been investigated. • The photocatalytic degradation of Acid Orange (AO) and Direct Green (DG) dyes were analysed. A promising nanostructure of pure and Nickel (Ni 3+ ) doped ZnO was prepared by aloe vera gel-assisted solution combustion technique. Electrochemical and photocatalytic investigations of the resulting nanostructures were achieved using cyclic voltammetry and UV–Vis spectrophotometry respectively. Enhancement of electrochemical properties in Ni 3+ doped ZnO nanostructures was studied. The results suggest that the doped ZnO exhibits a dramatic electrocatalytic effect on the oxidation of ascorbic acid (AA). It was observed that 1 mol% Ni 3+ doped ZnO electrode can show a redox peak for 1 millimolar (mM) level AA. It has been shown that these modified electrodes can be used as a sensor for different concentrations of AA. The photocatalytic analysis was performed for the degradation of Acid Orange (AO) and Direct Green (DG) dyes. It shows that the AO and DG dyes are potential dyes for the degradation of textile dye pollutants and the elimination of secondary pollutants.

Review of Optoelectronic Properties of ZnO Photodetector

Photodetection has been gained a lot of attention in last years biased on military wide range and civil application. With essential properties of Zno which has the wide band gap, strong radiation hardness, low cost and good chemical stabilities. ZnO are considered as the most successful candidate for UV photodetector. The study of our report is to review photodetectors based on doped Zno nanostructures and the new advances in ZnO nanostructured generation technique including adjustment and doping methods with modifications of ZnO photodetector. Final part of this review is about literature reviews were reported in recent years about optoelectrical property of Zno nanostructures, due to the fact that Zinc oxide is an important semiconductor material for optoelectronic and industrial applications, such solar cell, photosensors and photodetectors.

Systematic Variations in Structural and Photoluminescence Properties Produced in Zn Oxide Nanostructures by Cu (0-5)% Substitution

Effects of Cu addition (0-5)% in ZnO are studied for structural and optical properties. The structural, photoluminescence properties and vibrational modes are strongly influenced with the Cu incorporation. Detailed investigations of the structural features of Cu doped ZnO nanostructures are reported. Our results show the systematic decrease in crystallite size (50.40 - 37.56 nm), lattice strain (1.82 - 1.49 micro), lattice stress (216.33 - 177.64 MPa) and energy density (196.78 - 132.69 KJ/m3) in the limit of small dopant concentration (0 < Cu ? 0.02). Decreasing trends are attributed to the smaller ionic size of Cu in comparison of Zn. Beyond Cu= 0.02 an increasing trend was noticed in crystallite size (41.67 - 70.67 nm), lattice strain (1.90 – 3.11 micro), lattice stress (226.32 – 369.35 MPa) and energy density (215.40 – 573.67KJ/m3. This increase in structural parameters is attributed to segregation of secondary phases for Cu content increase beyond 0.02. Two prominent regions in PL spectra were observed and the deconvoulution of these regions show a strong correlation with the structural changes observed within the limit of high and low dopant concentration. The FTIR spectra show shift of Zn-O vibrational mode toward higher frequency with increasing Cu concentration.