Cobalt Doping Levels Research Articles

The Role of PbCoS Quantum Dots in Improved Photovoltaic Efficiency

<p>The quest for efficient, sustainable solar energy solutions has propelled the exploration of novel materials with enhanced photovoltaic properties. This study delves into the synthesis, characterization, and photovoltaic application of cobalt-doped lead sulfide (PbCoS) quantum dots (QDs) deposited on titanium dioxide (TiO2) substrates. Employing a hot-injection method, we synthesized PbCoS QDs and characterized their structural, compositional, and optical properties using X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDX), and UV-Visible absorption spectroscopy. The QDs demonstrated a cubic crystal structure with an average size of 20.12 nm and exhibited a direct band gap of 1.91 eV, indicative of quantum confinement effects and improved absorption in the visible spectrum. The photovoltaic performance of quantum dot-sensitized solar cells (QDSSCs) incorporating PbCoS QDs was assessed through current density-voltage (J-V) measurements, revealing a power conversion efficiency (PCE) of 2.17%. This efficiency highlights the potential of PbCoS QDs to enhance the performance of QDSSCs, partly attributed to the impact of cobalt doping on the electronic structure and photovoltaic properties of the material. The study identifies gaps in current research, such as the optimization of cobalt doping levels and the exploration of interface engineering between QDs and substrates, pointing towards future directions for enhancing the efficiency and applicability of PbCoS-based photovoltaic devices.</p>

Rapid preparation of cobalt doped GdBa2Cu3O7-δ films by non-fluorine chemical solution deposition method

The efficient preparation of superconducting layer is significant for large-scale applications of REBa2Cu3O7-δ coated conductors. In this work, a series of GdBa2Cu3-xCoxO7-δ films were prepared on LaAlO3 (00 l) substrates by non-fluorine metal organic deposition method. The influence of polymers on the pyrolysis process of the gel film was investigated, and the effect of cobalt doping on the epitaxial growth of the precursor film was analyzed. It was found that smooth and dense precursor film was obtained after decomposition at a high rate of 15 ℃/min. The rapid c-axis textured growth of the precursor film was achieved by optimizing the cobalt doping level for only ten minutes of firing. The optimal film possesses better texture, denser microstructure and larger critical current density (77 K, self-field) up to 1.3 MA/cm2.

Heterogeneous activation of peroxymonosulfate by Co-doped Fe2O3 nanospheres for degradation of p-hydroxybenzoic acid

Environmental remediation has become more effective when using nanotechnologies. In this study, iron oxide (α-Fe2O3) nanospheres with different cobalt doping levels (xCo-Fe2O3) were synthesised and applied in the heterogeneous activation of peroxymonosulfate (PMS) for the degradation of p-hydroxybenzoic acid (p-HBA). The catalyst (3Co-Fe2O3) with 3% Co doping exhibits the best performance for PMS activation, possibly because of the larger specific surface area and the tailored catalyst surface as confirmed by X-ray photoelectron spectroscopy (XPS). Reaction parameters were investigated to optimise the degradation efficiency. The metal ions leaching tests confirmed the higher stability of the catalyst, thanks to the leaching suppression by the doping of Co2+. The main contribution of free radicals (SO4•- and •OH) was confirmed by electron paramagnetic resonance (EPR) spectra, whereas partial contribution of oxygen anions and singlet oxygen (O2•-, 1O2) was observed during the quenching tests. Finally, a radical based degradation mechanism was proposed for the removal of p-HBA. It is expected to open up a novel perspective for the application of iron oxide as a potential catalyst for the removal of emerging contaminants.

Ternary heterojunction stabilized photocatalyst of Co-TiO2/g-C3N4 in boosting sulfite oxidation during wet desulfurization

Visible light can promote a catalyst to generate a large number of oxidative free radicals. The photocatalysis of sulfite oxidation is an efficient and economical approach for reclaiming wet desulfurization byproducts. In the present study, a cost-effective photocatalyst with a low metal concentration, namely Co-TiO2/g-C3N4 (CTO/CN), was synthesized using a simplified one-pot hydrothermal procedure. The structure and characteristics of this photocatalyst were assessed using various characterization methods. The as-prepared CTO/CN exhibited enhanced photocatalytic activities for the oxidation of MgSO3, which was 11-fold higher than that of the uncatalyzed benchmark. Under irradiation, ternary heterojunction photocatalyst accelerated the charge transfer, reduced the band gap and enhanced the production of strong oxidizing species (·O2−, ·OH and h+), which promote the formation of the ·SO5− radical, the active species in the MgSO3 oxidation. The as-prepared CTO/CN increased the critical mass concentration of magnesium sulfate from 10% to 19.9%, which reduced the recovery cost of magnesium sulfate. This paper proposes an environmentally friendly strategy for improving the overall performance of wet desulfurization with low cobalt doping levels for photocatalytic oxidation reactions under visible light.

Influence of cobalt doping level for distinct numbers of dipping with heat-treatment temperature on dip-coated TiO2 thin films elaborated via sol-gel technique on structural optical and electrical characterizations

The influence of cobalt doping level for distinct numbers of dipping with heat-treatment temperature (400, 450, and 500 °C) on the characterization of Ti1-xCOxO2 (x = 0, 0.03, 0.05, and 0.07) thin layers have been focused on this investigation. The specimens were studied using Differential scanning Calorimetry, Spectroscopic ellipsometry (SE), X-ray diffraction (XRD), and atomic force microscopy (AFM). Structural properties revealed that deposited thin films display both tetragonal anatase and orthorhombic brookite crystal structure. The surface morphologies of Ti1-xCOxO2 are smoother relative to undoped TiO2 films. The optical transmittance of Ti1-xCOxO2 thin films is around 60–75% in the visible region with an energy band that reduction of 3.29 to 2.95 eV at 500 °C for 7 % at showing their possible feasibility for optoelectronic and photovoltaic gadgets. The electrical characterization reveals a minimum electrical conductivity of 7.90 10−9 (Ω. cm)-1 picked up for the film doped with 5% at Co at 450 °C.

Water stability of cobalt doped ZIF-8: a quantitative study using optical analyses

Zeolitic imidazolate frameworks (ZIFs), in particular ZIF-8 (made of Zn2+ and 2-methyilimidazolate) and cobalt-doped-ZIF-8, are found important for many energy and environmental applications. It was reported that ZIFs show excellent structural stability in water and thus ideal for aqueous applications. However, recent studies also found some evidence that ZIF-8 undergoes hydrolysis in water. Despite the importance of ZIF's stability in many aqueous applications, the extent of ZIFs' degradation in water is still not yet fully understood. In this study, we report a quantitative study of the water stability of 0–100 at% cobalt-doped ZIF-8, using a new combination of analytical tools. The study demonstrated the importance of analyzing both filtered powders and the filtrate liquid systematically, in particular by using UV–Vis spectroscopy and thermogravimetric analysis. The combination of analytical tools allowed the study on the effects of ZIF concentrations in water, cobalt doping levels, and amounts of ligands in water on the water stability of ZIF samples. The effect of cobalt-doping was investigated by using ZIF particles with identical sizes (200–400 nm), in order to eliminate the effects of particle size on hydrolysis. Unlike other synthesis methods, a mechanochemical ball milling method allowed the production of nano-scale ZIF-8 particles with similar sizes, independent of cobalt-doping levels. The proposed combination of analytical tools including UV–Vis spectroscopy can be applied to the study of the water stability of other MOF materials.

Development of Bimetallic Non-Platinum Group Metal Catalysts Based on Metal Organic Framework Precursors

It has been postulated that platinum group metal free (PGM-free) catalysts for the oxygen reduction reaction (ORR) must meet four criteria: metal, carbon, nitrogen, and pyrolysis. Results from multiple studies indicate that metals surrounded by four pyridinic nitrogen atoms form at least part of the active site. Other groups have demonstrated enhanced activity in bimetallic catalysts using first and second-row non-PGM transition metals in metal-nitrogen-carbon (M-N4-C) coordination environments. The precise nature of the active site remains under debate. Many permutations of metal, nitrogen, and carbon are formed during pyrolysis, only a few of which are active. In nature, however, there is no known example of four electron reduction of oxygen at a single metal center. It may be that only multiple-metal centers, metals situated close enough to work cooperatively, are able to catalyze ORR. It stands to reason that the greater the number of M-N4-C sites formed, the greater the probability of producing centers close to one another. However, nanoparticle formation tends to compete as the metal content increases. The present research focuses on the use of zeolitic imidazolate frameworks (ZIFs), a subset of metal organic frameworks, as catalyst precursors. ZIFs are of interest because they are highly porous, contain a high density of M-N4-C centers, and are simple to prepare. Cobalt doping in ZIF precursors affects the porosity and graphitization of the pyrolyzed material. This research investigates the effect of cobalt doping level in ZIF precursors and non-PGM metal pairs (e.g. cobalt adjacent to iron) on catalytic activity. It is hypothesized that graphitization formed during pyrolysis will facilitate the cooperation of proximal metal sites in electron transfer to oxygen. This will be investigated by evaluating bimetallic Co-containing catalysts in ORR by varying the degree of graphitization while holding the ratio of Co and another metal (e.g. iron) constant. Comparison with similar catalysts prepared from amorphous ZIF precursors will elucidate the importance of local carbon structure in electron transfer between metal centers.

Thermo-Optical Properties of Cobalt-Doped Zinc Oxide (ZnO) Nanorods.

Thermo-optical and structural properties of cobalt-doped zinc oxide (ZnO) nanorods grown by chemical bath deposition were investigated. The average nanorods diameter was found to increase with cobalt doping. X-ray diffraction (XRD), Raman, and Fourier Transform Infrared (FTIR) analysis confirm the substitution of cobalt into ZnO lattice without forming any impurities at higher doping and preserving the hexagonal wurtzite structure. Variations in the absorption spectrum, band gap, photoluminescence, electronic structure by X-ray photoelectron spectroscopy (XPS), and index of refraction were analyzed at different cobalt doping levels and annealing temperatures. The thermooptic coefficient of ZnO nanorods was extracted and explained regarding cobalt doping. We will also discuss the nature of cobalt incorporation in ZnO nanorods at various doping levels.

Study on the effect of some surface phenomena on the properties of citrate capped cobalt doped ferrites

Magnetic nanoparticles for applications in life sciences require their uniform dispersion in water which involves surface modification with organic hydrophylic molecules. This study was focused on cobalt doped ferrite nanoparticles known mainly for their usefulness in experimental oncologic thermotherapy. The influence of cobalt doping level was analyzed with focus on crystallinity, granularity and saturation magnetization, based mainly on experimental data provided by X-ray diffractometry, Transmission Electron Microscopy, Vibrating Sample Magnetometry, as well as on the mathematical modeling of data resulted from Small Angle X-ray Scattering measurements.The features of spinel crystallization system of citrate capped cobalt ferrite powders were described with X-ray diffractometry while magnetic core morphology and size polydispersity were evidenced by Transmission Electron Microscopy. Small Angle X-ray Scattering, carried out on fluid samples, revealed theoretically different particle associations for iron oxide and cobalt doped nanoparticles that could be discussed assuming different citrate binding in case of irregular surface. Magnetic properties were studied with Vibrating Sample Magnetometry, revealing superparamagnetism in all samples and also coercivity for cobalt doped ferrites; discussion was developed on the influence of surface crystal defects on saturation magnetization. Citrate ion interaction with magnetic core surface was confirmed by FTIR recordings. The interpretation of cobalt influence on the microstructural and magnetic properties of the nanoparticle series of CoxFe3-xO4 (x = 0; 0.25; 0.50; 0.75; 1) was based on different binding of citrate at the surface metal ions for magnetite and cobalt ferrites.

Characterization of transparent semiconducting cobalt doped titanium dioxide thin films prepared by sol–gel process

We report the synthesis of TiO2 and Cobalt doped TiO2 (CoT) thin films by sol–gel process and the influence of dopant incorporation onto the structural, optical and electrical properties of the host lattice is analysed. The XRD analysis shows the reduction of crystal size with increasing Co dopant concentration. FESEM analysis confirmed the agglomeration of particles in CoT films upon Co doping. Vibrational modes of the anatase phase of TiO2 along with the weak intensity peaks for cobalt doped samples have been identified in Raman spectroscopy. The average transmittance of the films decreases with an increase in the surface roughness and decrease in the crystallinity of the films. Red shift in the energy gap is observed with the increase in the cobalt dopant concentration due to the defect state formation in the band gap. Surface roughness of the samples increases from 0.646 to 6.486 nm. Room temperature photoluminescence (PL) measurements confirmed the increase of F+ colour centres in cobalt doped films. I–V measurements indicate the ohmic behaviour of TiO2 films with the increase of resistivity from 2.707 × 103 to 7.699 × 103 Ω-cm for the samples with cobalt content. The increase in resistivity due to dopant incorporation is significant from its application point of view and is evaluated using grain boundary model. It was observed that by increasing cobalt doping level in TiO2 the surface trap density increases and implicitly the conductivity decreases.

Structure Evolution and Multiferroic Properties in Cobalt Doped Bi4NdTi3Fe1-xCoxO15-Bi3NdTi2Fe1-xCoxO12-\u03b4 Intergrowth Aurivillius Compounds

Here, we report the structure evolution, magnetic and ferroelectric properties in Co-doped 4- and 3-layered intergrowth Aurivillius compounds Bi4NdTi3Fe1-xCoxO15-Bi3NdTi2Fe1-xCoxO12-δ. The compounds suffer a structure evolution from the parent 4-layered phase (Bi4NdTi3FeO15) to 3-layered phase (Bi3NdTi2CoO12-δ) with increasing cobalt doping level from 0 to 1. Meanwhile the remanent magnetization and polarization show opposite variation tendencies against the doping level, and the sample with x = 0.3 has the largest remanent magnetization and the smallest polarization. It is believed that the Co concentration dependent magnetic properties are related to the population of the Fe3+ -O-Co3+ bonds, while the suppressed ferroelectric polarization is due to the enhanced leakage current caused by the increasing Co concentration. Furthermore, the samples (x = 0.1–0.7) with ferromagnetism show magnetoelectric coupling effects at room temperature. The results indicate that it is an effective method to create new multiferroic materials through modifying natural superlattices.

Effect of cobalt doping level of ferrites in enhancing sensitivity of analytical performances of carbon paste electrode for simultaneous determination of catechol and hydroquinone

This work presents the simultaneous determination of catechol (CC) and hydroquinone (HQ), employing a modified carbon paste electrode (CPE) with ferrite nanomaterial. Ferrite nanomaterial was doped with different amount of cobalt and this was investigated toward simultaneous oxidation of CC and HQ. It was shown that this modification strongly increases electrochemical characteristics of the CPE. Also, electrocatalytic activity of such materials strongly depends on the level of substituted Co in the ferrite nanoparticles. The modified electrodes, labeled as CoFerrite/CPE, showed two pairs of well-defined redox peaks for the electrochemical processes of catechol and hydroquinone. Involving of ferrite material in the structure of CPE, cause increase in the potentials differences between redox couples of the investigated compounds, accompanied with increases in peaks currents. Several important parameters were optimized and calibration curves, with limits of detection (LOD) of 0.15 and 0.3µM for catechol and hydroquinone, respectively, were constructed by employing amperometric detection. Effect of possible interfering compounds was also studied, and proposed method was successfully applied for CC and HQ quantification in real samples.

RETRACTED: Structural, optical, and electrical properties of Schottky diodes based on undoped and cobalt-doped ZnO nanorods prepared by RF-magnetron sputtering

Cobalt-doped ZnO nanorods were successfully synthesized on Si/SiO2 substrate using RF-magnetron sputtering at room temperature. The undoped and Co-doped ZnO nanostructures were characterized by XRD, FE-SEM, AFM, and PL spectra. The results showed that Co2+ replaced Zn2+ in the ZnO lattice without changing the wurtzite structure. The ZnO structure became high crystallite and was gradually converted into nanorods without extra phases as increased cobalt doping levels to 3 at.% and 4 at.%. The as-synthesized nanorod arrays were dense and vertically grew on the substrate with lengths of approximately 341 and 382.3 nm for 3 at.% and 4 at.% CO, respectively. PL analysis revealed that the ultraviolet (UV) emission intensity decreased and exhibited a blue shift with increased Co atomic percentage. This result was consistent with the energy bandgap values (3.26–3.3 eV) obtained from UV–vis spectra. The I–V characteristics revealed that the Shottky diodes based on Co-doped ZnO nanostructure with Pd electrodes have high barrier height (0.715–0.797 eV) and low saturation current (0.035–0.841 μA). The barrier height decreased after annealing the diodes at 500 °C for 2 h. To the best of our knowledge, Schottky diodes based on Co-doped ZnO nanorods prepared by RF-magnetron sputtering have not yet been reported.

Effect of Co-doping on the structure and optical properties of ZnO nanostructure prepared by RF-magnetron sputtering

Cobalt-doped ZnO nanorods were successfully synthesized on SiO2/Si substrate using RF-magnetron sputtering at room temperature. The undoped and Co-doped ZnO nanostructures were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), and atomic force microscopy (AFM). The results showed that Co2+ replaced Zn2+ in the ZnO lattice without changing the wurtzite structure. The ZnO structure became high crystallite and was gradually converted into nanorods without extra phases as increased cobalt doping levels to 3at.% and 4at.%. The as-synthesized nanorod arrays were dense and vertically grew on the substrate with lengths of approximately 341 and 382.3nm for 3at.% and 4at.% CO, respectively. The energy bandgap values increased as the Co concentration increased to 4at.% to reach 3.3eV compared with undoped ZnO (3.26eV).

Giant temperature coefficient of resistance in Co-doped ZnO thin films

A novel high-performance thermistor material based on Co-doped ZnO thin films is presented. The films were deposited by the pulsed laser deposition technique on Si (111) single-crystal substrates. The structural and electronic transport properties were correlated as a function of parameters such as substrate temperature and Co-doped content for Zn1−xCoxO (x=0.005,0.05,0.10 and 0.15) to prepare these films. The Zn1−xCoxO films were deposited at various substrate temperatures between 20 and 280 °C. A value of 20 %/K for the negative temperature coefficient of resistance (TCR) with a wide range near room temperature was obtained. It was found that both TCR vs. temperature behavior and TCR value were strongly affected by cobalt doping level and substrate temperature. In addition, a maximal TCR value of over 20 % K−1 having a resistivity value of 3.6 Ω cm was observed in a Zn0.9Co0.1O film near 260 °C, which was deposited at 120 °C and shown to be amorphous by X-ray diffraction. The result proved that the optimal Co concentration could help us to achieve giant TCR in Co-doped ZnO films. Meanwhile, the resistivities of the films ranged from 0.4 to 270 Ω cm. A Co-doped ZnO/Si film is a strong candidate of thermometric materials for non-cooling and high-performance bolometric applications.

Microwave absorption study of pinning regimes in Ba(Fe1−xCox)2As2 single crystals

Magnetic field dependent modulated microwave absorption (MMWA) measurements have been carried out to investigate vortex pinning effects in single crystals of the iron-based high-Tc superconductor Ba(Fe1−xCox)2As2 with three different cobalt doping levels of x = 0.07, 0.09 and 0.11. The dependence of the MMWA hysteresis loops on temperature, magnetic field and Co concentration have been measured and analyzed using a theoretical model of microwave absorption in superconductors. The analysis reveals that in the underdoped crystal (x = 0.07) the so called δTc-pinning due to magnetically ordered regions defines the temperature dependence of the critical current density, while in the optimally doped (x = 0.09) and overdoped (x = 0.11) samples the pinning is governed by structural imperfections due to the inhomogeneous distribution of the cobalt dopant and has the so called δl character.

Electrical transport measurements under pressure forBaFe2As2 compounds doped with Co, Cr, or Sn

We investigate the in-plane resistivity of single crystalline samples ofBa(Fe1 − xCox)2As2 (x = 0.038, 0.047, 0.074, 0.1and 0.114), Ba(Fe0.973Cr0.027)2As2 andslightly tin-doped BaFe2As2 under various pressures up to 7.5 GPa, in order to establish temperature–pressure,T(P), phase diagrams and to compare the influence of pressure and doping onsuperconductivity. At ambient pressure, cobalt doping is known to lead to adecrease in the combined magnetic and structural transition temperatureT0. Likewise, an increase of pressure tends to have the same effect forBa(Fe1 − xCox)2As2 for the various values ofx. As was seen in theT(P) phase diagram ofBaFe2As2, a superconductingdome is observed for Ba(Fe1 − xCox)2As2 samples with the dome shifted to lower temperatures and pressures withincreased cobalt doping levels. A very different behaviour is noticed forBa(Fe0.973Cr0.027)2As2 and the slightlytin-doped BaFe2As2 withthe decrease of T0 being close to linear down to 2 K, and no obvious sign of superconductivity in the pressurerange investigated.

Structure and magnetism of cobalt-doped ZnO thin films

The structure and magnetic properties of Co-doped ZnO films are discussed in relation to cobalt doping levels and growth conditions. Films were deposited by pulsed-laser deposition (PLD) from ZnO targets containing cobalt concentrations from 0 to 30 at.%. The structure of the films is examined by x-ray diffraction (XRD) and transmission electron microscopy (TEM), and optical absorption is used to infer the substitution of cobalt inside the ZnO lattice. Magnetic properties are characterized by superconducting quantum interference device (SQUID) magnetometry. Films doped with cobalt concentrations of a few per cent appear to be composed of two magnetic components: a paramagnetic component and a low-field ferromagnetic component. Films doped with 30% cobalt show a larger FM signature at room temperature with clear hysteretic shape, but films grown at low pressure are plagued by the precipitation of metallic cobalt nanoparticles within the lattice which can be easily detected by XRD. These particles are well oriented with the ZnO crystal structure. By increasing the base pressure of the vacuum chamber to pressures above 1×10−5 Torr, metallic cobalt precipitates are undetectable in XRD scans, whereas the films still show an FM signature of ∼0.08 μB/Co. Depositions in the presence of oxygen background gas at 0.02 mTorr decreases the magnetization. The decreased magnetization with oxygen suggests that the activation of ferromagnetism depends on defects, such as oxygen vacancies, created during growth. Optical absorption measurements show a sequential increase in the Co+2 absorption peaks in these films, along with an almost linearly increasing bandgap with cobalt concentration suggesting a large solubility of cobalt in ZnO. Bright-field TEM imaging and electron diffraction do not show signs of precipitation; however, dark-field imaging shows circular areas of varying contrast which could be associated with cobalt precipitation. Therefore, the possibility that ferromagnetism results from secondary phases cannot be ruled out.

Infrared-active phonons of perovskite HoMn/sub 1-x/Co/sub x/O/sub 3/ (x=0--0.8)

Polycrystalline perovskites compounds HoMn/sub 1-x/Co/sub x/O/sub 3/ (x=0--0.8) have been prepared by conventional solid-state reaction. Here, we used far-infrared (FIR) spectroscopy to study infrared active phonon modes and present a comparative analysis of infrared transmission spectra of polycrystalline HoMn/sub 1-x/Co/sub x/O/sub 3/ (x=0--0.8). The data indicated that phonon modes significantly changed with increase of cobalt doping level. Four main bands were assigned as external, torsional, bending and stretching bands. The external vibration energy remain same at /spl omega//sub 1//spl sim/190 cm/sup -1/ for Co doping x/spl les/0.5 and shift to higher energy for x>0.5. Torsional and bending bands exhibit splitting. The stretching band is at 600 cm/sup -1/ for all samples, but the bandwidth is reduced as Co doping increased. The transmission spectrum of HoMn/sub 4/5/Co/sub 1/5/O/sub 3/ was analyzed to obtain the spectrum of optical density. The minimum number of oscillators to obtain a reliable fit is 5 by using a sum of noninteracting harmonic oscillators.

Non-locality and the flux line lattice square to hexagonal symmetry transition in the borocarbide superconductors

Using small angle neutron scattering we have studied the square to hexagonal flux line lattice symmetry transition in different members of the borocarbide superconductors. The studies were performed using samples of ErNi 2B 2C, Lu(Ni 1− x Co x ) 2B 2C with cobalt doping levels x=1.5–9% and Y 0.64Lu 0.36Ni 2B 2C. We find that the onset field of the symmetry transition can be shifted more than an order of magnitude due to changes in the range of the non-local electrodynamics. Comparing the results to transport measurements of the electronic mean free path and the superconducting coherence length we find that the transition onset follows a model by V. Kogan et al., which includes non-local corrections to the London model due to the Fermi surface anisotropy of the borocarbides.