Structural, optical and magnetic properties of Co-doped ZnO nanorods with hidden secondary phases

Cobalt-doped V2O5 hexagonal nanosheets for superior photocatalytic toxic pollutants degradation, Cr (VI) reduction, and photoelectrochemical water oxidation performance

The worldwide energy calamity and ecological disturbances demand materials that can remove harmful contaminants from the polluted water. Recently, semiconductor-based catalytic dye removal has created much consideration due to its high efficacy and eco-friendly contaminated water treatment processes. Vanadium oxide (V₂O₅) has attracted superior attention as a catalyst due to its robust oxidation power, chemical inertness, and stability against photodegradation. In this study, pristine and cobalt (Co)-doped V₂O₅ samples were synthesized by solvothermal method and examined for their photo-degradation activity and photoelectrochemical (PEC) water oxidation properties. The orthorhombic crystal phase was confirmed by X-ray diffraction (XRD), hexagonal-shaped morphology was observed by scanning electron microscope (SEM) and reduced optical band gap (2.01 eV) was noticed for doped V₂O₅ catalyst compared to the pristine (2.20 eV) catalyst. The doped V₂O₅ catalyst exhibited enhanced photodegradation of crystal violet CV (92.7%) and Cr (VI) reduction (90.5%) after 100 min of light irradiation. The doped photocatalyst exhibited approximately 2.1 and 1.9-fold enhancement of photodegradation of CV and Cr(VI) reduction, respectively. The doped electrode showed improved photocurrent density (0.54 mA/cm^-2) compared to pristine electrode (0.12 mA/cm^-2). Moreover, the doped electrode showed reduced charge-transfer resistance and enhanced charge-transfer properties compared to those of the pristine electrode. Hence, the prepared hexagonal-shaped V₂O₅ is a suitable material for the elimination of environmental contaminants from the polluted water as well as water splitting for hydrogen generation.

Structural, Morphological, Optical and Magnetic Studies of Cu-Doped ZnO Nanostructures

In the present work, Cu-doped ZnO nanostructures (Cu% = 0, 1, 5) have been prepared using microwave-assisted chemical route synthesis. The synthesized nanostructures were investigated through structural, morphological, optical, and magnetic characterizations. The results of the X-ray diffraction (XRD), high resolution transmission electron microscopy (HR-TEM), and selective area electron diffraction (SAED) patterns confirmed that all of the samples exhibit the single-phase polycrystalline hexagonal crystal structure. The XRD results infer a decrease in the lattice parameters (a/c) by increasing the Cu% doping into ZnO. The field emission scanning electron microscopy (FE-SEM) and energy dispersive x-ray (EDX) spectroscopic measurements revealed the formation of nanostructures, showing the major elemental presence of Zn and O in the samples. The photoluminescence (PL) spectra exhibited photoemission in the UV and blue-green regions. With the increase in the Cu%, the photoemission in the UV region is reduced, while it is enhanced in the blue-green region. Raman spectra of the Cu-doped ZnO nanostructures displayed a blue shift of the E2High mode and an increase in the peak intensity of E₁(LO), indicating the doping of Cu ion in the ZnO lattice. The dc magnetization measurements demonstrated the ferromagnetic behavior of all of the samples with an enhanced ferromagnetic character with increasing Cu%.

Preparation of surface-functionalized electrospun PVA nanowebs for potential remedy for SARS-CoV-2

Infections with coronaviruses remain a burden that is negatively affecting human life. The use of metal oxides to prevent and control the spread of severe acute respiratory syndrome coronavirus (SARS-CoV-2) has been widely studied. However, the use of metal oxides in masks to enhance the performances of barrier face coverings in trapping and neutralizing SARS-CoV-2 remained unexplored. In the present study, we explore the possibility of developing surface functional PVA/ZnO electrospun nanowebs to be used as a component of multilayer barrier face coverings. Polyvinyl alcohol (PVA) and zinc acetate (ZnA) nanowebs were electrospun as precursor samples. After calcination at 400 degrees centigrade under a controlled atmosphere of nitrogen gas, product nanowebs containing ZnO (PVA/ZnO) were obtained. The presence of ZnO was determined using an attenuated total reflectance Fourier Transform Infrared (FT-IR) spectrometer. This study inspired the possibility of developing surface-functional materials to produce enhanced performance masks against the spread of SARS-CoV-2.

Visible-light driven photocatalytic performance of eco-friendly cobalt-doped ZnO nanoarrays: Influence of morphology, cobalt doping, and photocatalytic efficiency

In order to remove the organic pollution from water environment, Co²⁺-doped ZnO nanoarray photocatalyst was prepared through a hydrothermal process. The influences of Co²⁺ doping amount and hydrothermal temperature on the nanostructure and photocatalytic performance of Co²⁺-doped ZnO nanoarray were discussed in detail. The standard ZnO structure and nanoarray morphology of Co²⁺-doped ZnO samples were achieved and the absorption of visible light was also realized through Co²⁺ doping. The 2% Co²⁺-doped ZnO nanoarray prepared at 95 °C exhibited excellent photocatalytic activity and could degrade 96% of methylene blue solution within 120 min under visible light. Furthermore, the as-prepared 2% Co²⁺-doped ZnO nanoarray still maintained 91% for removal rate after 3 cycles of photocatalytic degradation, showed good photocatalytic activity and recyclability. All results indicate that ZnO nanoarray with Co²⁺ doping has a potential application in visible light photocatalysis for environmental protection and pollution control.

A facile, sensitive and rapid sensing platform based on CoZnO for detection of fipronil; an environmental toxin

A sensitive detection of extremely toxic phenylpyrazole insecticide, 'Fipronil' is presented. Currently, the advancement of approaches for the detection of insecticides at low concentrations with less time is important for environmental safety assurance. Considering this fact, an effort has been made to develop an electrospun CoZnO nanofiber (NF) based label-free electrochemical system for the detection of fipronil. The CoZnO NF were characterized using different techniques including field emission scanning electron microscopy (FE-SEM), Energy Dispersive X-Ray Analysis (EDX), X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), and Raman Spectroscopy. Based on the experimental results, the proposed platform displayed a linear response for fipronil in the attogram/mL range despite the multiple interfering agents. The sensitivity of the device was found to be 3.99 Kῼ (g/ml)^-1 cm^-2. Limit of detection (LOD) and limit of quantification (LOQ) were calculated and found to be 112 ag mL^-1 and 340 ag mL^-1 respectively. Further, this proposed sensor will be implemented in the fields for the rapid and proficient detection of the real samples.

Study of structural, optical and magnetic properties of cobalt doped ZnO nanorods

Cobalt doped zinc oxide nanoparticles (NPs) and nanorods (NRs) were synthesized by a simple chemical method.

A sensitive and label-free photoelectrochemical aptasensor using Co-doped ZnO diluted magnetic semiconductor nanoparticles

Co-doped ZnO diluted magnetic semiconductor as a novel photoelectric beacon was first constructed for photoelectrochemical (PEC) aptasensor of acetamiprid. The fabricated PEC sensing is based on the specific binding of acetamiprid and its aptamer, which induces the decreasement of enhanced photocurrent produced by the electron donor of quercetin. Co(2+) doping has a beneficial effect in extending the band width of light absorption of ZnO into the visible region and to promote the separation of the photoinduced carriers due to the sp-d exchange interactions existing between the band electrons and the localized d electrons of Co(2+). The fabricated aptasensor was linear with the concentration of acetamiprid in the range of 0.5-800 nmolL(-1) with the detection limit of 0.18 nmolL(-1). The presence of same concentration of other conventional pesticides did not interfere in the detection of acetamiprid and the recovery is between 96.2% and 103.7%. This novel PEC aptasensor has good performances with high sensitivity, good selectivity, low cost and portable features. The strategy of Co-doped ZnO diluted magnetic semiconductor paves a new way to improve the performances of PEC aptasensor.

Raman scattering and interstitial Li defects induced polarization in co-doped multiferroic Zn0.96-yCo0.04LiyO (0.00 ≤ y ≤ 0.10) nanoparticles

Structural and Raman analysis confirmed a single phase wurtzite hexagonal crystalline structure of Li–Co co-doped ZnO nanoparticles.

Island nucleation, optical and ferromagnetic properties of vertically aligned secondary growth ZnO : Cu nanorod arrays

The paper reports an island nucleation and secondary growth of aligned ZnO : Cu nanorod arrays via thermal vapor phase transport. Results analysis indicates that the secondary segment is epitaxially grown on the ZnO : Cu nanorods with the radius strongly dependent on temperature and the concentration of zinc vapor. The modified characteristic radius (R(c)) model is used to explain the nucleation and secondary growth process. Temperature-dependent photoluminescence spectra indicate that the band gap emission of the secondary growth nanorods is greatly restrained. A controversial 3.31 eV emission (A line) and two different donor-acceptor pair (DAP) recombinations at 3.24 eV and 2.48 eV are observed at 13 K. The A line shows a different behavior from the two DAP emissions during the heat-up process. Intrinsic room temperature ferromagnetism (RTFM) is observed in the secondary growth ZnO : Cu nanorods and it can be explained by oxygen vacancy and copper defects related to bound magnetic polar (BMP) or double exchange mechanism.

STRUCTURE AND MAGNETIC PROPERTIES OF Co-DOPED SnO2 NANOWIRES

Co -doped SnO2 nanowires were grown by thermal evaporation of a mixture of Tin metal powder and CoCl2 · 6H2O in a tubular furnace. The growth occurs by vapor–solid growth mechanism. Nanowires grew along the sidewall of the alumina boat placed in the tubular furnace and the diameter of these nanowires (as was evident from scanning electron microscopy), was found to be in the range of 50 nm to 200 nm. Co was successfully doped in SnO2 lattice as revealed by X-ray diffraction data and was found to be in Co2+ state in the nanowires as detected by X-ray Photoelectron Spectroscopy measurements. Room temperature magnetic measurements, carried out using Vibrating Sample Magnetometer, indicated ferromagnetic behavior of the nanowires indicating their potential for spintronics applications. With increasing Co doping (upto 1%), the lattice parameters of SnO2 decreased and the saturation magnetization increased, suggesting a strong structure-magnetic property relationship.

Facile synthesis of highly uniform Mn/Co-codoped ZnO nanowires: optical, electrical, and magnetic properties

In this article, Co/Mn-codoped ZnO nanowires (NWs) were successfully synthesized on a silicon substrate by the thermal evaporation method with Au catalyst. The X-ray diffraction pattern indicated that the Co/Mn-codoped ZnO NWs are a hexagonal wurtzite structure without a second phase, and energy dispersive X-ray spectroscopy revealed that the Co and Mn ions were introduced into the ZnO NWs with the content of ∼0.8 at% and ∼1.2 at%, respectively. Photoluminescence spectra and Raman spectra showed that the Co/Mn were doped into the NWs and resulted in the shift of the near-band-edge emission. Moreover, the novel Raman peak at 519.3 cm(-1) has suggested that the two kinds of cations via doping could affect the local polarizability. Compared with the undoped ZnO NW, the electrical measurement showed that the Co/Mn-codoping enhanced the conductivity by an order of magnitude due to the presence of Co, Mn cations. The electron mobility and carrier concentration of a fabricated field effect transistor (FET) device is 679 cm2 V(-1) s(-1) and 2×10(18) cm(-3), respectively. Furthermore, the M-H curve demonstrated that the Co/Mn-codoped ZnO NWs have obvious ferromagnetic characteristics at room temperature. Our study enhances the understanding of the novel performances of transition-metal codoped ZnO NWs and also provides a potential way to fabricate optoelectronic devices.

Co-Doped ZnO nanoparticles: minireview

Diluted magnetic semiconductors with a Curie temperature exceeding 300 K are promising candidates for spintronic devices and spin-based electronic technologies. We review recent achievements in the field of one of them: Co-doped ZnO at the nanoparticulate scale.

Lattice variation and Raman spectroscopy in hierarchical heterostructures of zinc antimonate nanoislands on ZnO nanobelts

In ZnO hierarchical heterostructures of zinc antimonate nanoislands on ZnO nanobelts, the substitution of Sb(5+) for Zn(2+) induces lattice contraction and a variation in vacancy defects, and moreover the preferential accumulation and segregation of Sb in [001] planes results in the intense perturbation of atomic motion in the a-b plane. Under nonresonant conditions, nonpolar E(2)(high) and polar quasi-longitudinal optic (LO) modes decrease in frequency due to finite-size and phonon confinement effects. Under resonant conditions, localized excitons can ionize to free carriers and form plasmons at higher excitation power density, resulting in the transformation of scattering coupling from localized exciton-LO-phonon to LO-phonon-plasmon. The intensity ratio of 2LO/1LO decreases and multiphonon scattering shows a decrease in frequency with unequal neighboring interval, and moreover the scattering coupling between the continuum of electron-hole plasmon and the discrete LO phonons causes an asymmetric lineshape.

Intra-shell luminescence of transition-metal-implanted zinc oxide nanowires

Zinc oxide nanowires were grown by vapor transport using the vapor-liquid-solid growth mechanism. The zinc oxide nanowires were implanted with transition metals (Co, Fe or Ni) and subsequently annealed in air at 700 degrees C for 30 min. Energy-dispersive x-ray spectroscopy and electron energy loss spectroscopy measurements reveal a successful incorporation of the desired transition metals. Transmission electron microscopy analysis of implanted and annealed zinc oxide nanowires shows a strongly damaged zinc oxide lattice but no formation of transition metal-rich secondary phases. The as-grown nanowires show a strong and intensive near-band edge emission and a moderately structured green luminescence band. After ion implantation, the structured green luminescence band increases in intensity and new sharp luminescence lines appear in the red luminescence region. Those sharp transitions are due to intra-shell 3d transitions of iron and cobalt in the corresponding Fe- and Co-doped ZnO samples.