Cobalt Doped ZnO Nanoparticles Research Articles

Influence of cobalt doping on structural, optical, and electrical properties of zinc oxide nanoparticles prepared by polymeric precursor method

Cobalt-doped ZnO nanoparticles at different compositions have been obtained by the polymeric precursor method. The nanoparticles were obtained at the working pH from 8.3 to 8.5 and synthesized at 550 °C. The properties were studied using X-ray diffraction (XRD), vibrational spectroscopy (FTIR/Raman), diffuse reflectance absorbance spectroscopy (DR UV–Vis), photoluminescence spectroscopy (PL), scanning electron microscopy (SEM/EDS), and impedance spectroscopy. The lattice parameters were determined at room temperature by Rietveld refinement, confirming single-phase composition with a hexagonal wurtzite structure. FTIR and Raman analyzes identified the characteristic vibrations of the synthesized system and the typical deformations of the wurtzite-type hexagonal structure, corroborating the results obtained from XRD. A redshift in the optical energy band gap (Egopt) was observed with increasing cobalt content compared to the ZnO sample. Considering the doping percentage, Egopt value varied between 3.13 eV and 3.04 eV for pure ZnO and Co-doped ZnO with 5 at. %., indicating that the optical properties of the nanoparticles were affected by dopant concentration. PL and SEM/EDS characterization were used to determine the associated defects for each sample and the morphology and composition of the nanoparticles. PL results showed a strong blue emission at around 439 nm (2.83 eV), which is redshift with cobalt content (ΔE between 0.05 eV and 0.01 eV), attributed to the surface defects present in the doped samples. Conductivity analysis to temperature revealed a semiconductor behavior for all samples, and their respective activation energies determined. The results provide an easy method to obtain Co-doped ZnO nanoparticles with interesting properties for optoelectronics devices.

Structure and morphology modification of ZnO nanocrystals via substitutional cobalt doping for enhanced electrochemical activity

This study investigated the electrochemical performance of the morphologically and structurally modified Co-doped ZnO nanocrystals synthesized via the chemical co-precipitation method. The structural properties were characterized by XRD, where the lattice parameters and volume got smaller with the increasing amount of Cobalt doping. The compositional analyses showed that 1.5 and 2.5 at% of Cobalt was present in the Co-doped ZnO nanocrystals. The FT-IR analyses showed that Zn–O (tetrahedral) and Zn–O (octahedral) vibrational modes are present for the precipitated ZnO-based nanocrystals. Besides that, the characteristic Raman spectra mode for ZnO displayed redshift, and more modes were activated, which showed a change in the defect chemistry after the cobalt substitution into the ZnO host lattice. A significant change was observed in morphology where the pristine ZnO formed nanoflower composed of nanoflakes and the Co-doped ZnO nanoparticles formed nanospheres. Lastly, cyclic voltammetry was performed at different scan rates where typical Faradaic peaks were observed for all the samples, and the electrochemical performance was increased with the small amount of Co doping into the ZnO lattice. The samples showed improved pseudocapacitive behavior, suggesting that Cobalt doped ZnO nanoparticles synthesized via the chemical co-precipitation method can be a potential electrode material for pseudocapacitor applications.

Sol-Gel synthesis, characterization and photocatalytic activity of Cobalt doped ZnO nanoparticles

In the current study, Cobalt (Co) doped ZnO nanoparticles with different dopant concentrations are prepared using the sol-gel process. All the synthesized samples are characterised using a variety of instrumentation methods including XRD, FT-IR, UV-vis absorption spectroscopy, FE-SEM, EDAX, HRTEM and XPS. The XRD measurements revealed the crystallite sizes of the fabricated samples are reduced by increasing cobalt concentrations. The various functional groups present in the doped materials are identified using FT-IR spectra. According to the UV-vis absorption study, as Co dopant concentration rises, the energy band gap narrows down in comparison to pure ZnO. According to an FESEM image, Co doping in ZnO causes a shift in the morphology of the material, making for structures that resemble flowers almost exactly. The various elemental compositions are evaluated using EDAX. The results of analyses employing high-resonance transmission electron microscopy show that the two co-doped ZnO crystallites combine to produce spherical structures with a mean size of 16 nm. This is consistent with the crystallite size predicted by Scherrer's formula. According to the results of the XPS analysis, the Co ion was integrated into the ZnO lattice in a Co2+ oxidised form. The 0.3M Cobalt doped sample showed improved photocatalytic reaction efficiency of methylene blue. As the Co doping concentrations increased, the photocatalytic reaction's efficiency also increased.

Improved properties and salt rejection of polysulfone membrane by incorporation of hydrophilic cobalt-doped ZnO nanoparticles

In this study, the nanoparticles (NPs) of ZnO and Co2+ ions doped ZnO (doped ZnO) were incorporated into a matrix of polysulfone (PSf) membranes to enhance their surface properties prepared using a simple wet phase inversion technique. The hybrid PSf membranes were fabricated with 0.5 wt. % of ZnO and doped ZnO NPs. These membranes were characterized using XRD, TGA, FESEM-EDX, and salt rejection performance. The hydrophilicity of PSf membranes was improved by adding of ZnO and doped ZnO NPs which showed a decrease in contact angle values from 82° to 62° with an increased flux with water. Among the prepared membranes, doped ZnO NPs showed the highest salt rejection for both sodium chloride (NaCl) and sodium sulfate (Na2SO4) compared to pure PSf and PSf with ZnO NPs which confirm the improvement contact angle and water permeability. Overall, the results of this study showed that embedding a small amount of Co2+ ions doped ZnO NPs with PSf has significant potential to be applied in industrial-scale membrane applications.

Suppression of Visible Emission in Low-Temperature Synthesized Cobalt-Doped ZnO Nanoparticles and Their Photosensing Applications.

Cobalt (Co)-doped ZnO nanoparticles have been synthesized at 100 °C using a simple chemical technique, without post-deposition annealing. These nanoparticles are of excellent crystallinity and show a significant reduction in defect density upon Co-doping. By varying the Co solution concentration, it is observed that oxygen-vacancy-related defects are suppressed at lower Co-doping, while the defect density shows an increasing trend at higher doping densities. This suggests that mild doping can significantly suppress the defects in ZnO for electronic and optoelectronic applications. The effect of Co-doping is studied using X-ray photoelectron spectroscopy (XPS), photoluminescence (PL), electrical conductivity, and Mott-Schottky plots. Photodetectors fabricated using pure and Co-doped ZnO nanoparticles show a noticeable reduction in the response time upon Co-doping, which again affirms the reduction in the defect density after Co-doping.

Review on structure, optical and magnetic properties of cobalt doped ZnO nanoparticles

In recent years, semiconductor nanostructure gained much attention due to their application in next generation optoelectronics devices. In this article it is reviewed how cobalt doping impact zinc oxide nanoparticles structural, optical, and magnetic properties. The basic reason causing variation in structural parameter have been explored. The change in bandgap lead toward significant improvement in absorption and emission spectra. We explored how doping affects the optical property of ZnO and special attention have been paid to cobalt doping effect. The application of doped ZnO has been discussed in detail with the help of suitable table and figure. The synthesis process plays an important role to get the desired property for specific application. Therefore, the special attention has given to explore the entire synthesis route applicable to ZnO nanostructure fabrication. Investigation of the magnetic and optical characteristics of cobalt-doped ZnO nanoparticles shows its potential application in Dilute magnetic semiconductors and optoelectronic devices.

Microstructural, optical and Raman properties of Zn1-xCoxO nanoparticles for optoelectronics device applications

Undoped and cobalt doped ZnO nanoparticles have been synthesized using the co-precipitation method. Phase identification, morphological and quantitative analysis is carried out with the help of X-ray diffraction and FESEM-EDS analysis. As per the XRD results, samples have polycrystalline nature with a hexagonal wurtzite structure. The crystallite size has been increased with cobalt incorporation. FESEM analysis showed agglomerated particles. The significant change in morphology demonstrates successful doping into ZnO lattice. Redshift is observed in the absorbance peak. Raman spectra confirm the formation of wurtzite ZnO with the existence of all the characteristic peaks.

Application of visible light activated thiolated cobalt doped ZnO nanoparticles towards arsenic removal from aqueous systems

Populations at large are exposed towards Arsenic (As) contamination in water worldwide making it unfit for drinking and human consumption. This study was designed to assess As removal efficiency of newly developed thiolated chitosan cobalt-doped zinc oxide (CoZnO) nanoparticles (NP) under visible light spectrum. In this study the Co-ZnO NP of various sizes (40–60 nm) were prepared through the co-precipitation method. Removal of As with Co-ZnO NP was investigated in batch tests experiments alongside determining the optimal dose of NP, kinetic rates, effect of light, pH and ultra-sonication. This was followed by a continuous flow test with Co-ZnO layered on Whatman® grade 42 filter paper. Overall, the Co-ZnO NP effectively treated As i.e. in sunlight (100%), neutral pH (100%), ultra-sonication (100%) and in continuous-flow system (100%). The removal of As was maximum (88%) at NP:As ratio of < 1:5 and minimum (25%) at 1:100. Similarly, darkness (21.4%) and (11.1%) uptake at low and high pH respectively. It was found that Co-ZnO NP can efficiently reduce As to non-toxic state i.e. below the WHO permissible limit of (10 µg/L) in drinking water.

X-ray peaks profile analysis, optical and cathodoluminescence investigations of cobalt-doped ZnO nanoparticles

Effects of Co doping on the structural and optical properties of ZnO oxide nanoparticles (NPs) prepared by a solvothermal method are reported. X-ray diffraction examinations using Rietveld refinement confirms the hexagonal wurtzite symmetry ZnO phase nanostructure belonging to P63mc space group. No segregated secondary phases or Co rich clusters were detected. The X-ray diffraction peaks shifts towards higher angle gradually as the concentration of nominal Co content increases in ZnO. This shifting in peak position reflect that Co is well replaced Zn in ZnO matrix. With increasing the Co content to 3%, both lattice parameters a and c of the hexagonal ZnO tended to gradually decrease, suggesting substitutional doping of Co at the tetrahedral Zn2+sites. For Co loading of5%, these trends reversed and the lattice showed a gradual expansion, which is explained by additional interstitial incorporation of Co. The Williamson-Hall (W–H) method with various models i.e. uniform deformation model (UDM), uniform stress deformation model (USDM) and uniform deformation energy density model (UDEDM), as well as size-strain plot (SSP) method, and the morphological observations using transmission electron microscopy (TEM) image were used to evaluate the crystallite size as well as the lattice strain. Optical studies carried out by diffuse reflectance spectroscopy (DRS) indicated a decrease in the value of the band gap from 3.238 eV to 2.993 eV with increasing Co doping concentration. The obtained results are confirmed by cathodoluminescence technique.

Zero-field magnetic resonance of cobalt ion pairs in ZnO nanocrystals

Cobalt-doped ZnO nanoparticles (NPs) with different Co concentrations are investigated by means of $X$- and $Q$-band electron spin resonance (ESR) near liquid-helium temperature in both parallel and perpendicular modes. The high crystal quality of the NPs allows for the hyperfine-structure resolution within the single ${\mathrm{Co}}^{2+}$ ions' ESR powder spectra. Depending on cobalt concentration, common additional weak ESR lines are detected which are here demonstrated to arise from some ${\mathrm{Co}}^{2+}$ high-spin pairs with a distance of about 4--6 \AA{}. ESR simulations show that these 3/2 spin pairs are weakly coupled by an isotropic Heisenberg Hamiltonian with either ferromagnetic or antiferromagnetic $J$ coupling constants, almost identical to those previously detected in bulk and microwire ZnO:Co. The presence of substantial (axial) single-ion anisotropy in ZnO:Co makes the different pairs' resonance positions strongly depending on the $J$ value. For resonance frequency $\ensuremath{\nu}$ in the microwave range, four cobalt pairs can satisfy the condition $|J|\ensuremath{\sim}h\ensuremath{\nu}/3$ to resonate at almost zero magnetic field. Such near-zero-field transitions notably resonate in the parallel ESR mode, which is the signature of the gapped nonlinear Zeeman effect, which is of particular interest for highly stable atomic-clock transitions.

Plasma assisted synthesis of cobalt-doped ZnO nanoparticles in liquid

Cobalt-doped ZnO nanoparticles were synthesized by electrical discharge treatment of a mixture of metallic zinc and cobalt micropowders (with Co atomic concentration of 10%) in distilled water. The results of the characterization of inner structure, phase composition and morphology of the prepared samples performed by means of TEM, XRD, FTIR and UV–Vis spectroscopy proved the formation of near-spherical doped ZnO:Co nanocrystals under the found optimized experimental conditions. The band gap of the Co-doped ZnO nanoparticles was estimated to be 2.88 eV in comparison to the pure ZnO – 3.28 eV. The broad luminescence band associated with the formation of defect levels in Co-doped ZnO was observed the range from 450 nm to 750 nm. The prepared Co-doped ZnO nanocrystals exhibited ferromagnetic behavior at room temperature that can be useful for their application in spintronics.

Co-precipitation synthesis of cobalt doped ZnO nanoparticles: Characterization and their applications for biosensing and antibacterial studies

A new modified sensor based on carbon paste electrode (CPE) was developed using cobalt doped ZnO (Co-ZnO) nanoparticles (NPs). In this work, we demonstrated the analytical behavior and applications of CPE modified with Co-ZnO/MCPE for the simultaneous determination of uric acid (UA) and adrenaline (AD) with highly selective and sensitive using voltammetric techniques. The synthesized Co-ZnO NPs were characterized by utilizing XRD, FTIR, FESEM with EDX, TEM, UV–Vis and photoluminescence spectroscopy. XRD suggests that the average size of these NPs was between 21 and 35 nm with a hexagonal wurtzite structure. Tauc plot exhibited that the optical energy bandgap of ZnO NPs gradually decreases with Co doping. Compared with undoped ZnO, Co-ZnO modified carbon paste electrode (Co-ZnO/MCPE) exhibits excellent electrochemical performance towards the oxidation of UA. Influencing factors, including scan rate, concentration, and pH values were optimized. Under the optimal condition, the Co-ZnO/MCPE responded to UA linearly with a detection limit of 3.37 µM and the fabricated sensor exposes diffusion-controlled electrode process. The developed Co-ZnO/MCPC has capable of determination of both UA and AD simultaneously with two different oxidation peaks. The sensitivity, long-term stability and reproducibility of the developed sensor were estimated. The bacterial efficiency of undoped and Co-ZnO NPs was inspected against gram-negative (Escherichia coli) and gram-positive (Enterococcus faecalis) bacteria.

Photocatalytic Activities of Cobalt-Doped ZnO Nanoparticles by Hydrothermal Method

Photocatalytically active cobalt-doped ZnO (Co: ZnO) hexagonal nanoparticles have been prepared by hydrothermal process. X-ray diffraction, SEM, FTIR and UV–vis spectroscopy confirmed that the dopant ions substitute for some of the lattice zinc ions, and furthermore, that Co2+ ion exists. The as-prepared Co: ZnO samples have an extended light absorption range compared with pure ZnO and showed highly efficient photocatalytic activity, only requiring 120 min to decompose ~90% of MB dye under sun light irradiation. The results indicated that a strong electronic interaction between the Co and ZnO was present, and that the incorporation of Co promoted the charge separation and enhanced the charge transfer ability and, at the same time, effectively inhibited the recombination of photogenerated charge carriers in ZnO, resulting in high visible light photocatalytic activity.

Structural and optical investigation of Co-doped ZnO nanoparticles for nanooptoelectronic devices

Cobalt-doped ZnO nanoparticles (NPs), with concentration of Co2+ varying between 1 and 5%, have been synthesized by a sol–gel procedure. The structural, morphological and optical properties of these nanoparticles were investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM) and ultraviolet–visible (UV–Vis) measurements. The X-ray diffraction shows that these semiconductors crystallize in a wurtzite single crystalline phase with P63mc space group. In this structure, the cobalt ion Co2+ substitutes for a Zinc ion Zn2+ in a ZnO semiconductor and occupies a tetrahedral Td site symmetry surrounded by four oxygen atoms with a slight distortion. The TEM images characterize the morphology and crystalline structure of these semiconductors. From the UV spectra, a direct bandgap semiconductor was assumed for ZnO:Co2+ NPs. The bandgap energy of the ZnO lattice gradually decreases following the addition of Co2+ ions. The red absorption spectra are ascribed to the electronic transitions of Co2+ ion in ZnO. To determine the electronic structure of the transition ion Co2+, the crystal field theory is applied for the visible spectrum associated with the d–d transitions of this ion located at a Td site symmetry in ZnO NPs. The experimental and theoretical results of energy levels are in agreement. The results were compared to that published for the Co2+ ion in NP ZnO.

Effect of cobalt doping on optical, magnetic and photocatalytic properties of ZnO nanoparticles

Cobalt doped ZnO nanoparticles (Zn1-xCoxO(0.00≤x≤0.1)) was synthesized by a two-step coprecipitation method using oxalic acid and ammonium hydroxide. The effect of Co doping on the crystallite structure, optical, magnetic and photocatalytic properties of ZnO was investigated. The X-ray powder diffraction (XRD) patterns confirmed that all Zn1-xCoxO samples exhibited hexagonal wurtzite structure. Further, the lattice parameters revealed an increasing trend in doped samples which indicated the incorporation of Co ions into the ZnO lattice. The X-ray photoelectron spectroscopic (XPS) survey suggested that Co ion incorporated into the ZnO lattice with a Co2+ oxidization state. The scanning electron micrograph (SEM) showed that the average size decreased with increasing doping concentration. Photoluminescence (PL) showed blue emission peak at 475 nm, green emission peak at 545 nm and yellow emission peak at 580 nm, respectively. UV–vis spectral illustrated the substitution of Co2+ in ZnO leaded to band gap narrowing. Vibrating sample magnetometer (VSM) demonstrated doped samples exhibited ferromagnetism behavior at room temperature. The Zn0.96Co0.04O sample showed enhancement in the photocatalytic degradation efficiency of methylene blue as compared to the pure ZnO. However, increasing doping concentrations of Co leaded to a decrease of photocatalytic efficiency.

Effective Mass Model Supported Band Gap Variation in Cobalt-Doped ZnO Nanoparticles Obtained by Co-Precipitation

Zn1 –xCoxO (x = 0, 0.01, 0.03, 0.05) nanoparticles were synthesized using co-precipitation method. Shift in peaks of XRD patterns for 2θ values has been observed. The changes in 2θ value for different peaks for different samples are studied systematically. Dislocation densities (δ) for the samples are calculated and correlated with observed shift in 2θ values for all the samples. UV-Vis study has been performed to understand the effect of cobalt doping on optical band gap. The band gap shows a cubic variation with dopant concentration (x). The nature of band gap variation has been explained and supported by effective mass model. Samples are also characterized by SEM and EDX to understand the surface morphology and elemental composition.

Cobalt-doped ZnO nanoparticles derived from zeolite imidazole frameworks: Synthesis, characterization, and application for the detection of an exhaled diabetes biomarker

Metal−organic frameworks (MOFs) with porous structures, high surface areas, diverse compositions, and functional linkers are promising materials and good carriers for building high-performance devices. In this work, uniform cobalt-doped ZnO nanoparticles (Co-doped ZnO NPs) derived from a MOF mold were synthesized, demonstrating the first example of synthesizing doped semiconductor metal oxide nanostructures using such strategy. The synthesis method produced Co-doped ZnO NPs that had a controllable doping mode, adjustable surface status, good dispensability, ferromagnetism and catalytic activity. The Co-doped ZnO NPs were evaluated as a sensing material for diabetes biomarker detection; the obtained sensors showed a high response to trace acetone (18.2 at 5 ppm), fast response/recovery times, a low detection limit (170 ppb), and long-term stability for 4 months. The enhanced sensing performance can be attributed to the increased number of active sites, additional impurity energy levels, and the catalytic ability of elemental Co. Moreover, the optimized sensor could distinguish between simulated diabetic breath and healthy human breath samples. The MOF-derived Co-doped ZnO NPs are a good candidate for the low-cost and noninvasive diagnosis of diabetes, and the proposed synthesis strategy can be extended to other types of extrinsically doped oxide materials.

Correlation among oxygen vacancy and doping concentration in controlling the properties of cobalt doped ZnO nanoparticles

We have observed ferromagnetism at room temperature in 2% cobalt doped ZnO nanoparticles prepared by a simple chemical precipitation method. This can be described as a consequence of bound magnetic polaron (BMP) resulting from the occurrence of oxygen vacancies and surface defects in the sample. Photoluminescence and Raman measurements indicate the existence of such defects in the sample. Electron Spin Resonance (ESR) studies are done to probe into the magnetic nature of the doped samples further. Redshift in the band gap and formation of characteristic absorption bands after Co doping shows that Co ions are incorporated in the host ZnO lattice. The infrared sensitive vibrational modes are identified with Fourier Transform Infrared Spectroscopy (FTIR) measurements. The spin-orbital splitting in X- ray Photoelectron Spectroscopic (XPS) measurements show the matching oxidation (divalent) state among the dopant and the host. Local structural studies after Co doping by the Extended X-ray Absorption Fine Structure (EXAFS), shows the Co2+ integration in the ZnO lattice without any impurity states. Photocatalytic measurements show that ZnO is a very promising degrading agent for Rhodamine B dye solution under UV as well as solar irradiation.

Effect of cobalt doping on microstructures and dielectric properties of ZnO

Pure and cobalt-doped ZnO nanoparticles (2.5, 5, 7.5, and 10 atom % Co) are synthesized by sol–gel method. The as-synthesized nanoparticles are characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and field emission scanning electron microscopy (FE-SEM) analysis. The nanoparticles of 0, 2.5, and 5 atom % Co-doped ZnO exhibited hexagonal wurtzite structure and have no other phases. Moreover, the (101) diffraction peaks position of Co-doped ZnO shift toward a smaller value of diffraction angle compared with pure ZnO powders. The results confirm that Co ions were well incorporated into ZnO crystal lattice. Simultaneously, Co doping also inhibited the growth of particles, and the crystallite size decreased from 43.11 nm to 36.63 nm with the increase in doping concentration from 0 to 10 atom %. The values of the optical band gap of all Co-doped ZnO nanoparticles gradually decreased from 3.09 eV to 2.66 eV with increasing Co content. Particular, the dielectric constant of all Co-doped ZnO ceramics gradually increased from 1.62 × 103 to 20.52 × 103, and the dielectric loss decreased from 2.36 to 1.28 when Co content increased from 0 to 10 atom %.

Photo-inactivation and efflux pump inhibition of methicillin resistant Staphylococcus aureus using thiolated cobalt doped ZnO nanoparticles

Multidrug resistance (MDR) in bacteria is a major concern these days. One of the reasons is the mutation in efflux pump that prevents the retention of antibiotics and drugs in the bacterial cell. The current work is a step to overcome MDR in bacteria via inhibition of efflux pump and further photoinhibition by thiolated chitosan coated cobalt doped zinc oxide nanoparticles (Co-ZnO) in visible light. Co-ZnO were synthesized in a size range of 40–60 nm. Antibacterial activity of the Co-ZnO against methicillin resistant Staphylococcus aureus (MRSA) was found 100% at a concentration of 10 μg/ml upon activation in sunlight for 15 min. Interestingly, it was found that cobalt as a dopant was able to increase the photodynamic and photothermal activity of Co-ZnO, as in dark conditions, there was only 3–5% of inhibition at 10 μg/ml of nanoparticle concentration. Upon excitation in light, these nanoparticles were able to generate reactive oxygen species (ROS) with a quantum yield of 0.23 ± 0.034. The nanoparticles were also generating heat, Because of the magnetic nature, thus helping in more killing. Thiolated chitosan further helped in blocking the efflux pump of MRSA. The current nanoparticles were also found biocompatible on human red blood cells (LD50 = 214 μg/ml). These data suggest that the MRSA killing ability was facilitated through efflux inhibition and oxidative stress upon excitation in visible light hence, were in accordance with previous findings.