Cobalt Doping Research Articles

COMPARATIVE CATALYTIC STUDY OF PURE COBALT OXIDE SPINEL AND NON-NOBLE METAL DOPED COBALT OXIDE SPINEL FOR SELECTIVE OXIDATION OF ALCOHOL TO ALDEHYDE: A REVIEW

The selective oxidation of alcohol by heterogeneous catalysts, such as noble and non-noble metal oxide spinels and doped metal oxide spinels, is one of the challenging and interesting routes in catalysis. In this review, the selective oxidation mechanism of non-noble cobalt oxide spinel and various metal-doped cobalt oxide spinel-based catalyst systems are examined. Selective oxidation of alcohol to aldehyde by using cobalt oxide spinel (Co<sub>3</sub>O<sub>4</sub>) and various metal-doped cobalt oxide spinels (Fe, Mn, Ni, Al, Cu, Sr) has been reviewed carefully. The selective oxidation by pure cobalt oxide spinel showed higher activity. However, a large number of studies have also been devoted to selective oxidation by various metal-doped cobalt oxide spinels. The metal-doped Co<sub>3</sub>O<sub>4</sub> showed higher selective oxidation activity compared to the pure spinel Co<sub>3</sub>O<sub>4</sub>. The mechanistic aspects and the role of cobalt and doping metal in the selective oxidation of alcohol have been studied thoroughly.

Chromium doping enabled improvement in alkaline seawater oxidation over cobalt carbonate hydroxide nanowire array.

The presence of chlorine species in seawater can cause severe anode corrosion, highlighting the critical need for the design of efficient and robust electrocatalysts towards the oxygen evolution reaction (OER) for hydrogen production. Herein, we present a chromium doped cobalt carbonate hydroxide nanowire array on nickel foam (Cr-CoCH/NF) as an effective OER electrocatalyst in seawater. In alkaline conditions, Cr-CoCH/NF exhibits a low overpotential of 450 mV to achieve 500 mA cm-2, surpassing that of CoCH/NF (614 mV). Additionally, it demonstrates 200 h of continuous oxygen evolution testing.

Role of Cobalt Doping on the Physical Properties of CdO Nanocrystalline Thin Films for Optoelectronic Applications

In the current work, the authors aim to present an insight on the role of cobalt (Co) doping for the structural, morphological, and linear and nonlinear optical (NLO) properties of CdO thin films. The films were prepared using the spray pyrolysis (SP) technique, and the weight % of Co (x) was varied from 0–10. The structural properties of the films were confirmed by the powder X-ray diffraction (P-XRD) studies and are polycrystalline with a cubic structure and a lattice parameter of 0.4658 nm. As Co content in CdO films increases, cluster grain size and porosity decrease significantly, as seen in surface topographic and nanostructural analysis. Through the Burstein–Moss shift, the optical band gap “Eg” in Co: CdO film decreases from 2.52 to 2.05 eV with the increase in Co-doping. To study the NLO parameters, open aperture (OA) and closed aperture (CA) Z-scan measurements were performed using the diode-pumped solid-state continuous wave laser excitation (532 nm), and with the increased Co-content, the NLO parameters—nonlinear absorption coefficient (β∼10−3 cm/W), nonlinear refractive index n 2 ∼ 10−8 cm2/W), and the 3rd-order NLO susceptibility χ 3 ∼ 10−7 to 10−6 e.s.u.) values were determined and found to be enhanced. The maximum NLO parameters achieved in the present study with increasing Co concentration on CdO nanostructures prepared by the SP method are found to be the highest among the reported values and suggest that processed films are a capable material for optoelectronic sensor applications.

Co-doped ZnO nanowires: Synthesis, photocatalytic performance, and cytotoxic activity against human brain glioblastoma cells

In this paper, we introduced a green method for the preparation of pure and 1, 3, 7, and 10 % cobalt doped zinc oxide (Co-doped ZnO) Nanowires through the application of Salvadora persica aqueous extract. The synthesis of nanorods was confirmed by the results of PXRD, UV–vis, FESEM, EDX, and Raman analyses. The existence of well doped cobalt within the structure of zinc oxide was affirmed by the results of PXRD, EDX, and UV–vis. The FESEM analysis displayed the length and diameter of pure ZnO Nanowires to be 500 ± 0.2 nm and 25 ± 5 nm, while an enlargement was observed in the length and diameter of doped Nanowires due to the doping of cobalt into ZnO. The photocatalytic activity of synthesized samples indicated the culmination of doped cobalt into ZnO in increasing the rate of photocatalyst performance. The optimum sample was 1 % Co-doped ZnO Nanowires that eliminated 89 % of MB with a concentration of 20 mg/Lit in pH = 7. The toxicity effect of synthesized Nanowires on brain glioblastoma cells (U87) was investigated by the means of WST-1 test. Accordingly, the doped ZnO Nanowires induced a more toxic impact on U87 cells when compared to the case of pure zinc oxide Nanowires. Thus, performing a doping process on the nanostructure of ZnO led to increasing its inhibitory effect against U87 cells and intensifying its photocatalytic activity on MB dye.

Mn2+ Doped Cobalt Oxide and Its Composite with Carbon Nanotubes for Adsorption-Assisted Photocatalytic Applications

In this study, cobalt oxide (Co3O4), Mn-doped Co3O4 (MDCO), and Mn-doped Co3O4-functionalized carbon nanotube (MDCO-CNTs) were synthesized via the co-precipitation method using cobalt nitrate and manganese nitrate as a cobalt and manganese precursor, respectively. Synthesized materials were assessed using different characterization techniques like scanning electron microscopy, X-ray diffraction, and UV-visible spectroscopy. Congo red in an aqueous solution was adopted as the model dye to estimate the adsorption-assisted photocatalytic efficiency of the synthesized materials. The samples studied for adsorpsstion-assisted photocatalysis were found to be highly effective and among all the samples, the best removal performance (80%) was obtained by treating the MDCO-CNTs composite for 50 min at 50 °C. Mathematical modeling shows that all of the samples followed a pseudo-second-order kinetic model and data best fitted to a Langmuir isotherm, implying that the process involved in the removal of Congo red dye is chemisorption.

A High Catalytic Activity Nanozyme Based on Cobalt-Doped Carbon Dots for Biosensor and Anticancer Cell Effect

Nanozyme technology as an emerging field has been successfully applied to chemical sensing, biomedicine, and environmental monitoring. It is very significant for the advance of this field to construct nanozymes with high catalytic activity by a simple method and to develop their multifunctional applications. Here, a new type of cobalt-doped carbon dots (Co-CDs) nanozymes was designed using vitamin B12 and citric acid as the precursors. The homogeneous cobalt doping at carbon nuclear led the Co-CDs to show significant peroxidase-like activity resembling natural metalloenzymes. Based on the high affinity of Co-CDs to H2O2 (Km = 0.0598 mM), a colorimetric sensor for glucose detection was constructed by combining Co-CDs with glucose oxidase. On account of the high catalytic activity of nanozymes and the cascade strategy, a good linear relationship was obtained from 0.500 to 200 μM, with a detection limit of 0.145 μM. The biosensor has realized the accurate detection of glucose in human serum samples. Moreover, Co-CDs could specifically catalyze H2O2 in cancer cells to generate a variety of reactive oxygen species, leading to the death of cancer cells, which has useful application potential in tumor catalytic therapy. In this work, the catalytic activity of Co-CDs has been adequately exploited, which extends the application of carbon dots in multiple biotechnologies, including biosensing, disease diagnosis, and treatment.

Nanohybrid material of Co–TiO2 and optical performance on methylene blue dye under visible light illumination

The present study explores the sonochemical route for preparing Cobalt doped Titania (CTN) nanoparticles (NPs). As-prepared CTN NPs were characterized by analytical instruments such as X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), Brunauer–Emmett–Teller (BET), UV–Visible Diffuse Reflectance Spectroscopy (UV–Vis DRS), and Fourier Transform Infrared Spectroscopy (FTIR) to study their structural, optical and morphological properties. The characterisation results confirmed the pure phase of prepared CTN NPs by doping Cobalt into TiO2 nanoparticles via a sonochemical route. Further studies were conducted to characterise CTN NPs and investigated their photocatalytic performance over the decolourisation of model dye pollutant Methylene blue (MB) under visible light illumination. Cobalt doping into TiO2 NPs has led to the reduced bandgap, which possesses excellent pore area (56 ​m2/g), thus CTN NPs acts as a benign visible-light-driven photocatalyst over MB dye that completely degraded (99%) in 75 ​min without oxidising agents. The photodegradation results of CTN NPs were compared with previous reports of other metal-doped TiO2 nanoparticles and found that CTN NPs is the best photocatalyst for the degradation of MB dye.

Synthesis and properties of ultra-small BiFeO3 nanoparticles doped with cobalt

Bismuth ferrite (BiFeO3, BFO) is the most promising material in the field of multiferroics. Additionally, it has excellent potential in photocatalysis applications due to its relatively small bandgap, stable structure, and low cost. Doping this material and enhancing its particle size showed promising results in many applications, especially photocatalysis, but the effect of both parameters has never been combined and studied before.In the present work, we report on the effect of cobalt doping of bismuth ferrite Bi Fe1-xCoxO3 x (with x = 0, 0.02, 0.04, 0.06 and 0.08) synthesized by hydrothermal route. The crystalline phase was obtained at a temperature as low as 200 °C. Rietveld's refinement of X-ray diffraction (XRD) confirmed the rhombohedral structure of the crystalline powders. Transmission Electron Microscopy (TEM) alongside High-Resolution Transmission Electron Microscopy (HRTEM) was conducted to probe microstructural features and showed a remarkable decrease in particle size from 12.5 nm to only 4.5 nm, when increasing the cobalt concentration to 8%. The material's optical properties were also studied and showed an increase in band gap values from 2.12 to 2.33eV.The application of the samples to the photodecomposition of methylene blue (MB) under direct sunlight irradiation was reported and have shown unusual results that were explained by the unique sizes of the samples and the phenomena that can occur at that order of magnitude.

Low temperature synthesis of In doped cobalt ferrite and investigations of structural, magnetic and dielectric properties

The present paper deals with the low temperature synthesis of In3+ doped cobalt ferrite (CoFe2-xInxO4, x = 0.00, 0.02, 0.04, 0.06, 0.08 and 0.10) using sol-gel auto-combustion method operated at low temperature. The prepared samples were well characterized for crystal structure and phase purity using X-ray diffraction technique which shows the formation of single-phase cubic spinel structure. The FE-SEM images of the typical samples show the well formation of spherical grains of average grain size 36 nm. The particle size determined from TEM histogram is found to be 35 to 32 nm. M − H plot recorded at room temperature reflects that the saturation magnetization overall decreases with doping due to the decreasing A-B interaction. The real and imaginary part of dielectric constant varies exponentially with frequency. The dielectric constant decreases with In3+ doping.

Chemical-substitution dependence of magnetization strength in room- temperature ferromagnetism of dilute magnetic oxides: Valence and spin state of slightly doped cobalt in (In,Al)2O3

This study investigates the valence and spin states of cobalt ions and the magnitude of room-temperature ferromagnetic magnetization in In1.9−xAlxCo0.1O3 (0≤x≤0.3) prepared by a chemical solution method. According to X-ray photoelectron spectroscopy, the Co ions in the Al-free sample (x=0) existed in a mixed state of trivalent Co3+ and divalent Co2+. The abundance ratio of Co2+ increased with Al content, and only divalent ions were present at x=0.3. A magnetic susceptibility analysis showed that both the spin and orbital degrees of freedom were magnetized in Co2+, whereas Co3+ was in a low-spin state. Co3+ was converted to Co2+ by vacuum annealing. The higher the conversion ratio of Co3+ to Co2+, the stronger was the room-temperature ferromagnetism.

Spray-deposited cobalt-doped RuO2 electrodes for high-performance supercapacitors

RuO2 is widely used as the material in supercapacitors; however, there is little information on the doping RuO2 with cobalt using an aqueous/organic solvent mixture in the spray pyrolysis technique. The phase purity and rutile crystal structure of cobalt-doped RuO2 were validated using X-ray diffraction. Optical studies indicated that the bandgap can be decreased from 1.80 eV to 1.70 eV by doping the RuO2 with cobalt. In this study, the performance of electrochemical supercapacitors and their morphology are both significantly altered by cobalt doping. 1.00 mol% cobalt-doped RuO2 displays a high specific capacitance (1072 F g−1 at a 5 mV s−1 scan rate) compared with that of undoped RuO2 (893 F g−1 at a 5 mV s−1 scan rate). 1.00 mol% cobalt-doped RuO2 had the highest specific energy (96.02 W h kg−1) at a specific power value of 1.702 kW kg−1. The specific capacitance was improved (1158 F g−1 at 0.5 A g−1) in a 0.5 M H2SO4 electrolyte. After 1000 charge–discharge cycles, 94% of the capacity of a 1.00 mol% cobalt-doped RuO2 electrode was preserved, indicating outstanding long-term cyclic stability. This study endorses the view that 1.00 mol% cobalt-doped RuO2 is a promising material for supercapacitor applications.

Rare earth effect on laser produced plasma dynamics during pulsed laser deposition of doped cobalt ferrite

The addition of rare earth elements the ferrites can lead to significant changes in structural, magnetic and electric properties of bulk materials and also of thin films deposited by pulsed laser deposition. The present study relies on the analysis of the laser induced plasma of three sets of cobalt ferrite targets doped with various concentrations of RE elements (Dy, Gd, Yb) and proposes a correlation of the derived results with structural investigations of the films obtained during the same experiment. ICCD imaging and space-and time-resolved optical emission spectroscopy techniques were used to obtain information on the dynamics and excitation temperatures of various species found in the laser produced plasmas (LPP). Initial investigations on the global behavior of the LPP revealed that the addition of RE reduced the drift velocities of the formed plasma structures, the lowest ones being observed for the targets doped with the heaviest RE (Yb). Space-and time-resolved spectroscopy measurements applied for all main elements (Fe, Co and RE - both neutral and ionic species) showed a complex dynamic system, with decreased/increased kinetic energies for neutrals/ions at high dopant concentrations, suggesting a possible re-sputtering effect at the films surface. The individual excitation temperatures of the main elements derived from Boltzmann plots increased as the RE content was augmented via radiative collision events due to their larger diameters compared with Co, Fe or O. The spatial distribution of electron temperature can be explained by the charge separation occurring with the addition of RE in the investigated systems.

Study of Co-Doped K2Ti6O13 Lead-Free Ceramic for Positive Temperature Coefficient Thermistor Applications

Cobalt-doped potassium hexa-titanate (Cox:K2Ti6O13 (x = 0.05, 0.10, 0.15 mole%)) ceramics were synthesized by the solid-state reaction method. The XRD patterns confirmed single-phase development in a monoclinic symmetry of various samples, and they were used for different structural calculations of Cox:K2Ti6O13 ceramics. The dielectric constant, tanδ, electrical modulus, and ac conductivity of Co-doped K2Ti6O13 were studied in the temperature range of 100–500 °C. Anomalies were observed in graphs of the dielectric constant versus temperature, showing the transition phase in the studied samples. Dielectric peaks at transition temperature decreased with an increasing frequency, and the peaks shifted toward higher temperatures, illustrating the relaxation of the dielectric materials. The composition with x = 0.10 showed low dielectric loss and a higher dielectric constant and can be utilized for high-temperature dielectric material. Small doping of cobalt improved the ac conductivity of K2Ti6O13 ceramics due to the increase in the spin–phonon interaction and dominant electron hopping conduction; however, the conductivity diminished with substantial doping because of the contraction of the tunnel space and ambushing of conduction electrons. The uniqueness of this study is in the high dielectric optimization of lead-free ceramic Cox:K2Ti6O13 and the discovery of positive temperature coefficients of the resistivity of these ceramic samples.

Effect of cobalt incorporation on the photocatalytic degradation of brilliant green using SnO2 nanoparticles under visible light irradiation

• Bare and Co-doped nanocrystals of SnO 2 were synthesized by a simple chemical precipitation method. • The result of UV-DRS proposed a band gap narrowing effect on SnO 2 with cobalt doping. • The defects and vacancies induced band gap reduction and increased BET surface area on cobalt doping, have played a vital role in the photochemistry of SnO 2 . Suggested here are a simple chemical precipitation method in order to synthesize bare and various levels of Co doping samples. The harvested samples were tested for their structural, optical, morphological and photocatalytic properties. The optical study shows a decline in the band gap of SnO 2 on 0.075 M of cobalt doping. The tuned band gap of SnO 2 on doping utilizes the visible light for the photodegradation of brilliant green (BG) and recommends the usage of the optimum level of Co-doped SnO 2 in environmental remediation applications.

Investigation of Co-doped Mn oxide catalyst for NH3-SCR activity and SO2/H2O resistance

A series of Co-doped Mn oxide catalysts with different Co/Mn molar ratios were prepared by co-precipitation method, which was systematically characterized by XRD, SEM, H2-TPR and NH3-TPD etc. Co-doped Mn oxide catalysts are evaluated for NH3-SCR activity and resistance to SO2 and/or H2O, and the Co(1)-MnOx catalyst with Mn/Co molar ratio of 1:1 performs the best catalytic performance, which achieved higher than 90% NOx conversion in the temperature range of 100−275 °C and possessed better SO2 and H2O resistance. The Co(1)-MnOx catalyst presented a sphere-like structure possessing a relatively large surface area. Doping of cobalt greatly improved the high-valent metal ions and chemisorbed oxygen content of Co(1)-MnOx catalyst surface, and the catalyst possessed abundant active species and acid sites and apparent activation energy of the catalyst was reduced, which makes Co(1)-MnOx a highly effective NH3-SCR catalyst.

Effect of slight cobalt incorporation on the chemical, structural, morphological, optoelectronic, and photocatalytic properties of ZnO thin film

In this study, the effect of low-content cobalt doping on the chemical, structural, morphological, optoelectronic, and photocatalytic properties of ZnO was systematically investigated via XRD, XPS, AES, UPS, PL, UV-vis, and AFM techniques. In this regard, pure and Co (1 at%, 3 at%)-doped ZnO (Co-ZnO#1, Co-ZnO#3) thin films were synthesized using the ultrasonic spray pyrolysis technique. Similarly, the samples were used to coat the inner walls of transparent tubes for MB photocatalytic degradation. AFM-images reveal a high tendency for crystalline grains of both CoZnO surfaces to aggregate to form large ones, increasing the mean roughness. XRD, XPS, and AES, as sensitive and complementary techniques, substantiate the successful Co incorporation as a substitute for Zn, especially with low content (1 at%). UV-vis, PL, and UPS were adopted to study the influence of Co substituting Zn on the optoelectronic properties of ZnO, including the valence band electronic structure, bandgap, mid-bandgap states, excitonic emission, work function, Fermi level, and ionization potential. Besides, PL spectra of both Co-ZnO films reveal the participation of band-to-band transition in UV emissions and a useful intense red-emission at 685 nm, due to the Co incorporation. However, bandgap narrowing, Fermi level lowering, a redshift with considerable fluctuations in excitonic emission, and a perfect quenching of visible emission (400–640 nm) were observed only with Co(1 at%)-doping. These factors combined with the increased grain size, the decreased microstrain, and the low ionization potential (6.80 eV) are suggested to be responsible for improving the photocatalytic efficiency in Co-ZnO#1.

Effect of air introduction on filamentous coke during CO2 reforming of tar with core-shell catalysts

The coke accumulation is the main factor affecting the activity of nickel-based catalysts during the CO2 reforming of tar. In this work, toluene is chosen to study the influence of filamentous coke on the coke-forming mechanism of the Ni/La2O3 @SiO2 catalyst. Two methods are proposed to address the problem of reduced tar conversion of Ni/La2O3 @SiO2 due to coke deposition. The Ni/La2O3 @SiO2 is first modified with cobalt doping to improve the resistance to coke accumulation. The Ni8Co/La2O3 @SiO2 catalyst showed higher carbon conversion (50–75%) and hydrogen conversion (35–55%) than Ni/La2O3 @SiO2 within the 5 h tar reforming process. And the used Ni8Co/La2O3 @SiO2 catalysts had only 0.1 g/g of filamentous coke after reforming reaction. Next, air is introduced to oxidize the deposited coke to address the problem of coke accumulation affecting catalyst activity. An appropriate air flow rate could provide oxidation of the coke and prolong the reaction activity of the catalyst from 5 h to 10 h.

Engineering manganese-rich phospho-olivine cathode materials with exposed crystal {0 1 0} facets for practical Li-ion batteries

Manganese-rich LiMn1-yFeyPO4 (e.g., LiMn0.7Fe0.3PO4) is emerging as the most promising olivine cathode material after LiFePO4, which has a current market demand of >500000 tons per year. However, its commercial application is challenging because of its poor kinetic properties. Although nanocrystallization is a transformative paradigm for improving the kinetics, it results in the concomitant problem of increasing the specific surface area of the material, which leads to more interfacial side reactions. Here, we develop a polyol solvothermal method to boost the particle size (decrease the specific surface area) whilst simultaneously regulating the crystal orientation (improving the kinetics) of LiMn0.7Fe0.3PO4. Importantly, the synthesis can be used at the ton scale, with the off-take potential reaching 1000 tons per year. Cobalt doping and carbon coating are combined to further increase the kinetic properties. Electrochemical measurements demonstrate that the diffusion of the Li+ kinetics is increased by 58.6 % and 46.1 % for the Fe2+/3+ and Mn2+/3+ redox couple during charging and 92.0 % and 21.2 % during discharging, respectively. A capacity of 150 mAh g−1 at a 5C rate is then delivered. In full batteries (14000 mAh), the capacity retention reaches 89.6 % over 1000 cycles at a 1C rate.

Influence of La3+ substitutions on structural, dielectric and electrical properties of spinel cobalt ferrite

La3+ doped cobalt ferrites with composition CoLaxFe2−xO4 (0.00 ≤ x ≤ 0.20) were synthesized by a co-precipitation method. X-ray diffraction (XRD) analysis confirm the formation of single-phased spinel structure for all synthesized samples. The result of La3+ doping on dielectric and electrical properties of cobalt ferrites was investigated. Dielectric constant and dielectric loss decrease with increasing frequency whereas alternating current (AC) electrical conductivity increases with increasing frequency. The AC electrical conductivities were effectively modeled by employing the Jonscher’s power law. Role of grain and grain boundary on impedance has been explored from nyquist plots and equivalent electrical circuits were proposed to clarify the impedance spectroscopy results. The Direct Current (DC) electrical resistivities were estimated by two probe method within the temperature range of 303K–700K. DC electrical resistivity decreases with increasing temperature and explained by hopping mechanism. DC electrical resistivity and drift mobility decreases with La3+ doping. Activation energies were calculated by employing the Arrhenius plot. Activation energy found to increases with La3+ substitutions. Maximum value of DC electrical resistivity achieved was 9.26 x 10+8 (Ω-cm) with crystallite size 17 nm. Current-Voltage (I–V) measurements were carried out within 0→6V→0V→ –6V→0V voltage range. It is worth mentioning that all doped sample exhibited remarkable and improved nonlinear hysteresis loop-type behavior than pour sample. Variation in resistance, in current-voltage loops, is clarified by considering space charge limited conduction (SCLC) model and oxygen vacancies migration across the metal-semiconductor interface. Out study suggest that La3+ doped cobalt ferrites may be tested as an active material for possible applications in non-volatile memory devices and neuromorphic applications.

Synthesis of Co-doped Fe metal–organic framework MIL-101(Fe,Co) and efficient degradation of organic dyes in water

In order to further improve the catalytic performance of MIL-101, cobalt-doped MIL-101(Fe,Co) was synthesized by solvothermal method. By adjusting the ratio of cobalt doping, the MIL-101(Fe,Co20%) with the best catalytic activity was obtained. The activation performance of MIL-101(Fe,Co20%) for peroxymonosulfate (PMS) was studied using Rhodamine B (RhB) as a pollutant model. The experimental results proved MIL-101(Fe,Co20%) with much better catalytic performance than MIL-101(Fe), which can degrade more than 99% of RhB within 15 min. The effects of initial solution pH and coexisting anions in water on the degradation of RhB were further discussed. The results showed that MIL-101(Fe,Co20%) was with excellent stability and degradation efficiency can still keep above 90% after five cycles. The free radical quenching experiments were further studied to explore the degradation mechanism. It can be concluded that SO4-· was the main active free radical for the degradation of RhB. The possible intermediate products in the degradation process of RhB were analyzed by LC-MS. Combined with the comparison of XPS before and after the reaction, the possible reaction mechanism of RhB degradation process was inferred.