Structure Of Co3O4 Research Articles

Electron-Deficient Pd clusters induced by spontaneous reduction of support defect for selective phenol hydrogenation

A facile and green synthesis route to fabricate the stable and highly-dispersed Pd catalyst was reported by utilizing the reducibility and defect structure of Co3O4. Specifically, nanoshaped Co3O4 with different Co and O vacancies was prepared. Taking these as support, Pd2+ precursors were introduced and preferentially anchored in isolated Co vacancies, confirmed by density functional calculations. Notably, Pd2+ species were reduced by support without any reducing agent. More interestingly, as-obtained Pd catalysts exhibited different product distribution in selective phenol hydrogenation, whereas Pd/hexagonal Co3O4 only generated the cyclohexanol as product, while the cyclohexanone was dominant in rod and commercial Co3O4 supported Pd catalysts. This phenomenon was ascribed to electron-deficient Pd clusters influenced by Co vacancy in hexagonal Co3O4, facilitating further hydrogenation of reaction intermediate rather than desorption. This work provides a feasible way to construct well-distributed and electron-deficient Pd clusters, offering an opportunity to control product distribution in selective hydrogenation.

A novel hybridized needle-like Co3O4/N-CNO composite for superior energy storage asymmetric supercapacitors

The controlled growth of needle-like Co3O4 and composite formation with highly graphitic carbons such as N-CNOs is critically essential for obtaining high-performance energy storage supercapacitors. In this study, the needle-like Co3O4 and graphitic N-CNOs are synthesized by the simple solvothermal and pyrolysis methods, respectively. The Co3O4/N-CNO composite enhances the fast charge transfer by reducing ion diffusion. The Co3O4/N-CNO composite demonstrated an improved specific capacitance (3066 F g−1) than the needle-like structure of Co3O4 (2068 F g−1). The Co3O4/N-CNO composite exhibited very good rate capability and high capacitance retention of 82% at a high current density of 8 A g−1 meanwhile the Co3O4/N-CNO//AC ASC device shows high power and energy densities with capacitance retention of 78% and Coulombic efficiency of 100% over 2000 cycles. This attractive electrochemical performance of Co3O4/N-CNO composite makes it a favorable device for practical applications of supercapacitors.

Facile-synthesis and characterization of cobalt oxide (Co3O4) nanoparticles by using Arishta leaves assisted biological molecules and its antibacterial and antifungal activities

A novel biosynthesis of cobalt oxide nanoparticles (Co3O4 NPs) attains using Arishta leaves (Neem leaves) extract at disparate annealing temperature, (Untreated (RT), 200 °C, 400 °C, 600 °C, and 800 °C) was analysed. The structural and morphological analysis has been carried out by using different characterization techniques. The characterization techniques such as X ray diffraction and scanning electron microscopy reveals that the Arishta leaves extract act as a fundamental, oxidation-reductant in addition to mediated preserving compound. Also the transparent and nonporous pyramid like crystalline structure of Co3O4 is confirmed. The antibacterial and antifungal behaviour of synthesized nanoparticles was analysed against Staphylococcus aureus, Streptococcus mutans, Klebsilla pneumonia and Escherichia coli as well as Aspergillus species of A. flavus and A. Niger fungi by agar disc diffusion process. Because of the pH, reaction temperature, reaction time, and extract clustering during the synthesis of Co3O4 NPs, the synthesized neem Co3O4 NPs have a strong antibacterial and antifungal activity. These findings show that the leaf extract may effectively operate as a dynamic response medium for the formation of Co3O4 NPs, and that it can be used in a variety of biomedical by-products and nano devices due to its low cost and high efficiency.

Sensing of oxidizing and reducing gases by sensors prepared using nanoscale Co3O4 powders: A study through Cu substitution

We demonstrate the sensing-mechanism of both oxidising and reducing gases by nanoscale Co3O4 powders through a strategy of Cu-doping in Co3O4. The sensitivity towards both types of gases arises due to presence of Co2+ and Co3+ cations in the (nearly) normal spinel structure of Co3O4. Pellets made up of nanopowders were employed for the detection of ∼6.5 ppm CO gas present in either pure N2 or in a mixture of synthetic air as carrier gas (which represents the O2 sensing-gas too). The high sensitivity of Co3O4 nanoparticles to detect ∼6 ppm CO (in N2) arises due to the high surface area of nanopowders exposing a higher number of octahedral Co3+ cations as adsorption sites, whereas the sensitivity towards O2 arises due to partial presence (less number) of octahedral Co2+. To support this mechanism, octahedrally Cu2+ substituted Co3O4 specimens are investigated. The inactive Cu2+ at the octahedral site changes the unexposed tetrahedral Co2+ into Co3+. The presence of inactive Cu2+ at the octahedral site and the burial of the Co3+ at the tetrahedral sites reduce the adsorption sites for O2, thereby drastically reducing the overall O2-gas sensitivity shown by the Cu-substituted sample, although they have higher surface-area (nanoparticles).

X-ray Absorption Near-Edge Structure (XANES) at the O K-Edge of Bulk Co3O4: Experimental and Theoretical Studies.

We combine theoretical and experimental X-ray absorption near-edge spectroscopy (XANES) to probe the local environment around cationic sites of bulk spinel cobalt tetraoxide (CoO). Specifically, we analyse the oxygen K-edge spectrum. We find an excellent agreement between our calculated spectra based on the density functional theory and the projector augmented wave method, previous calculations as well as with the experiment. The oxygen K-edge spectrum shows a strong pre-edge peak which can be ascribed to dipole transitions from O to O states hybridized with the unoccupied states of cobalt atoms. Also, since CoO contains two types of Co atoms, i.e., Co and Co, we find that contribution of Co ions to the pre-edge peak is solely due to single spin-polarized orbitals (, , and ) while that of Co ions is due to spin-up and spin-down polarized orbitals ( and ). Furthermore, we deduce the magnetic moments on the Co and Co to be zero and 3.00 respectively. This is consistent with an earlier experimental study which found that the magnetic structure of CoO consists of antiferromagnetically ordered Co spins, each of which is surrounded by four nearest neighbours of oppositely directed spins.

Role of porosity and diffusion coefficient in porous electrode used in supercapacitors – Correlating theoretical and experimental studies

AbstractPorous electrodes are fast emerging as essential components for next‐generation supercapacitors. Using porous structures of Co3O4, Mn3O4, α‐Fe2O3, and carbon, their advantages over the solid counterpart is unequivocally established. The improved performance in porous architecture is linked to the enhanced active specific surface and direct channels leading to improved electrolyte interaction with the redox‐active sites. A theoretical model utilizing Fick's law is proposed, that can consistently explain the experimental data. The porous structures exhibit ∼50%–80% increment in specific capacitance, along with high rate capabilities and excellent cycling stability due to the higher diffusion coefficients.

Confined heterogeneous catalysis by boron nitride-Co3O4 nanosheet cluster for peroxymonosulfate oxidation toward ranitidine removal

Peroxymonosulfate (PMS) induced advanced oxidation processes hold great promise for heterogeneous oxidation reactions. In this study, boron nitride (BN)-Co3O4 nanosheet cluster (NC) was fabricated to facilitate PMS activation with a nanoconfined heterogeneous catalysis effect for the rapid removal of ranitidine (RAN) under mild conditions. The obtained BN-Co3O4 NC cluster exhibited efficient catalysis performance with a 99.5% removal efficiency for ranitidine in 5 min, and meanwhile this novel catalyst could be applied under a wide pH range (pH: 3–9) with still high degradation efficiencies. The porous structure of BN-Co3O4 NC provided a large number of channels for RAN and PMS molecules to enter the catalyst’s inner confinement space, resulting in a remarkable enhancement of catalytic performance. The kinetic rate constant for RAN degradation by the BN-Co3O4 NC/PMS system with 3–33 fold less catalyst dosage is much larger (1.58–213 fold) compared with the state-of-the-art. PMS activation by BN-Co3O4 NC was mainly due to the pathway of reduction via active radicals. Density functional theory calculations specified that the concomitant active radicals such as ∙OH and SO4∙− were mainly derived from PMS activation via O-O bond cleavage. This work provides a new perspective for regulating the structure of Co3O4 and elucidating the mechanism of PMS-induced heterogeneous catalytic oxidation.

A comprehensive study on structure, opto-nonlinear and photoluminescence properties of Co3O4 nanostructured thin films: An effect of Gd doping concentrations

Cobalt oxide (Co3O4) thin films with 0, 1.0, 3.0 and 5.0 wt% Gd doping concentrations were fabricated on glass substrates by spray pyrolysis method. X-ray diffraction pattern (XRD) of as-deposited thin films confirm spinel structure growth oriented along (311) plane. Crystallite sizes of the grown films decreases with the increase in Gd doping concentrations and found in range of ∼17.7–7.2 nm. Raman investigation of films further approves spinel growth of cobalt oxide films. Surface morphology of pure and Gd: Co3O4 thin films were analyzed using field emission scanning electron microscopy (FESEM) with round shape particles at nanoscale. Chemical compositions, elements, and their stoichiometry were observed by energy dispersive spectra (EDX). Tauc's plots of films clearly shows two direct optical band gaps, (1) in the range of 1.49–1.52 eV and (2) in the range of 2.01 eV–2.58 eV respectively. A significant impact of Gd doping was observed on second optical band gaps, which increases with Gd contents. Room temperature (RT) dependent photoluminescence (PL) spectra of the deposited films showed that emission peaks at 363, and 753 nm under excitation wavelength of 240 and 500 nm respectively. The third order nonlinear optical susceptibility χ(3) and nonlinear refractive n(2) which were calculated and found in range 4.46 × 10−13- 2.25 × 10−10 esu and 1.01 × 10−10-2.39 × 10−9 esu., respectively.

Two-dimensional self-assembled network structure of Co3O4 quantum-dot-decorated ZnO nanobeads for ppb-level acetone sensors

A two-dimensional self-assembled network structure of ZnO nanobeads (NBs) decorated with Co3O4 quantum dots (QDs) was fabricated by an alcohol-assisted Langmuir–Blodgett method for a highly sensitive acetone sensor. Owing to the formation of a p–n junction between the Co3O4 QDs and ZnO NBs and the catalytic activity of Co3O4 QDs for acetone oxidation, the operating temperature of the sensor decreased from 350 to 250 °C, and the response to 1 ppm acetone increased from 5.3 to 7.2. The response was 1.5 even to 40 ppb acetone. Furthermore, the sensor was applied to a commercial breath analyzer, and ppb-levels of acetone were successfully detected in the exhalation of an adult.

High performance humidity sensor based on 3D mesoporous Co3O4 hollow polyhedron for multifunctional applications

In this work, the three-dimensional (3D) hollow mesoporous Co3O4 was successfully prepared by calcining the Co-based zeolitic imidazolate framework-67 (ZIF-67). As-obtained Co3O4 inherited the rhombohedral framework structure of ZIF-67 and possessed mesoporous and hollow structure. Further, the humidity sensor based on Co3O4 was fabricated, and its humidity sensing properties were investigated at room temperature (25 °C). The results indicated that the Co3O4 humidity sensor exhibited high humidity sensing performance with a wide linear detection range (10%−95% relative humidity (RH)), small humidity hysteresis (2.6% RH), and fast response/recovery times (1.0/13.5 s). In particular, the Co3O4 humidity sensor was of high detection resolution (1% RH). The excellent performance was attributed to the strong hydrophilicity and the unique 3D porous structure of Co3O4. In addition, the potential applications of the fabricated Co3O4 humidity sensor in skin humidity, simulated diaper, human breathing, and non-contact switch were demonstrated. This work provides a promising humidity sensing material for fabricating high-performance humidity sensors.

A new strategy for designing highly efficient Co3O4 catalyst with the molecular space configurations for toluene catalytic combustion

Selective exposure of dominant molecular space configurations and controllable synthesis of nanocomposites microstructure are full of challenge in improving the catalyst activity and designing materials. Herein, we precisely designed the size of ZIFs growing on nanofibers by changing the distribution of surface N elements. N elements microenvironment of nanofibers surface influenced not only ZIFs’ growth mechanism, but also its derivatives’ molecular space configurations (octahedral and tetrahedral structure of Co3O4). To verify the influence of N element on space configurations, DFT were used to investigate structure preference energy (SPE). The result showed that the TEA (triethylamine)-induced method showed a big difference between octahedral and tetrahedral structure, indicating that this method was easier to generate octahedral complexes. Its derived Co3O4 catalysts with more Co3+ spieces showed the best catalytic performance (T90 only 220 °C). Based on this, exposure of molecular space configurations will no longer be random but manipulable. The establishment of this new strategy will play an important role in the future catalyst design and realize the adjustable and controllable catalyst.

Rapid synthesis and magnetic property characterization of Mg2+ doped Co3O4 nanostructures

Utilizing combustion method Mg substituted Co3O4 nanoparticles were prepared using the fuel L-alanine. The formation of the cubic spinel structure in the prepared undoped Co3O4 and Mg substituted Co3O4 is assured by X-ray diffraction (XRD) studies. The average crystallite size was observed to lie within 48.6 nm to 17.3 nm. The microstructural analysis shown that the prepared nanoparticles are porous in nature comprising of intragranular pores and melded grains with distinct grain boundaries. The bandgap values were determined using Kubelka–Munk (K–M) technique which was found to fall within 1.87–3.64 eV range. Interestingly, para-/superpara- magnetic characteristics was seen at ±15KOe by the magnetic studies. The FT-IR bands at 662 and 569 cm−1are attributed to the Co–O stretching mode of cubic spinel Co3O4 structure for the prepared samples. .

Synergistic co-doping induced high catalytic activities of La/Fe doped Co3O4 towards oxygen reduction/evolution reactions for Zn–air batteries

La/Fe co-doped Co3O4 nanoparticles supported on aminated CNTs have shown high catalytic activities for the ORR and OER. The specific La/Fe co-doped structure of Co3O4 is shown to be the main origin of their high catalytic activities.

The potential of Co3O4 nanoparticles attached to the surface of MnO2 nanorods as cathode catalyst for single-chamber microbial fuel cell

A simple two-step hydrothermal method was used to prepare the cathode catalyst of microbial fuel cell (MFC). MnO2@Co3O4 composite was successfully prepared by in-situ growth of nano-particle-like Co3O4 on nano-rod-like MnO2. The hybrid products had (121), (310), (311), (400) and (511) crystal planes, rod-like and point-like structures were observed. MnO2@Co3O4 nanohybrids were rich in a variety of metallic elements and provided rich electrochemically active sites. The maximum voltage of MnO2@Co3O4-MFC was 425 mV, the maximum stabilization time was 4 d. The maximum output power was 475 mW/m2, which was 2.24 times that of Co3O4-MFC (212 mW/m2) and 2.63 times of MnO2-MFC (180 mW/m2). The rod-like structure of MnO2 could effectively improve the ion flow efficiency and reduce the transfer resistance, and the point-like structure of Co3O4 can increase the specific surface area of the complex and provide more active sites.

Rational construction of core-branch Co3O4@CoNi-layered double hydroxide nanoarrays as efficient electrocatalysts for oxygen evolution reaction

Electrocatalytic water oxidation is a crucial process for many conversion and storage systems. Developing noble-metal-free oxygen evolution reaction (OER) electrocatalysts with high activity and long durability thus becomes immensely vital yet challenging. In this work, core-branch Co3O4 @CoNi-layered double hydroxide nanoarrays are developed on nickel foam with the assistance of metal-organic-frameworks template and atomic layer deposition technology, acting as active and durable electrocatalysts for OER. The introduction of CoNi-LDH significantly regulates the morphological and electronic structure of Co3O4, giving rise to high surface-active sites exposure, accelerated electron transfer, and optimal interaction with intermediate products. Together with the 3D self-supported and binder-free structure, the optimized Co3O4@CoNi-LDH/NF exhibits remarkable OER performances in terms of low overpotential, high OER current density, and low Tafel slope, which are even better than the benchmark IrO2 electrocatalyst. This study provides a new horizon for exploring biphasic core-branch materials for electrocatalysis and other energy-related applications.

Ag and MOFs-derived hollow Co3O4 decorated in the 3D g-C3N4 for creating dual transferring channels of electrons and holes to boost CO2 photoreduction performance

The rapid recombination of photoinduced charge carriers and low selectivity are still challenges for the CO2 photoreduction. Herein, we proposed that ZIF-67-derived Co3O4 hollow polyhedrons (CoHP) were embedded into NaCl-template-assisted synthesized 3D graphitic carbon nitride (NCN), subsequently, loading Ag by photo-deposition as efficient composites (CoHP@NCN@Ag) for CO2 photoreduction. This integration simultaneously constructs two heterojunctions: p-n junction between Co3O4 and g-C3N4 and metal–semiconductor junction between Ag and g-C3N4, in which Co3O4 and Ag serve as hole (h+) trapping sites and electron (e-) sinks, respectively, achieving spatial separation of charge carriers. The donor–acceptor structure design of NCN realize a good photogenerated e--h+ separation efficiency. The mesoporous structure of hollow Co3O4 facilitate gas-diffusion efficiency, light scattering and harvesting. And the introduction of plasmonic Ag further strengthens the light-harvesting and charge migration. Benefiting from the rational design, the optimized ternary heterostructures exhibit a high CO2-CO yield (562 μmol g−1), which is about 4-fold as high as that of the NCN (151 μmol g−1). Moreover, the conjectural mechanism was systematically summarized. We hope this study provides a promising strategy for designing efficient g-C3N4 systems for the CO2 photoreduction.

In-situ grown metal-organic framework-derived carbon-coated Fe-doped cobalt oxide nanocomposite on fluorine-doped tin oxide glass for acidic oxygen evolution reaction

Development of stable and efficient non-noble metal based electrocatalysts for oxygen evolution reaction (OER) in acidic media is of great importance for proton exchange membrane based water electrolysis, which is indispensable for green hydrogen production. Herein, iron-doped, carbon-coated Co3O4 nanocomposite derived from a cobalt metal-organic framework, is grown in-situ on fluorine-doped tin oxide (FTO) glass (Fe-Co3O4@C/FTO) as an efficient and a stable binder-free electrode for acidic OER. Fe doping enhances both catalytic efficiency and stability of carbon coated Co3O4 toward acidic OER, through inducing small primary particle sizes and suitably modulated electronic structure of Co3O4, and better catalyst/substrate adhesion. Fe-Co3O4@C/FTO exhibits impressive electrocatalytic performances in 0.5 M H2SO4, with a low overpotential of 396 mV at 10 mA cm−2 and a small Tafel slope of 68.6 mV dec−1. Its electrochemical performances remain stable for over 50 h at 10 mA cm−2, making it a promising non-noble metal based electrocatalyst for acidic OER.

Mechanochemically Prepared Co3O4-CeO2 Catalysts for Complete Benzene Oxidation

Considerable efforts to reduce the harmful emissions of volatile organic compounds (VOCs) have been directed towards the development of highly active and economically viable catalytic materials for complete hydrocarbon oxidation. The present study is focused on the complete benzene oxidation as a probe reaction for VOCs abatement over Co3O4-CeO2 mixed oxides (20, 30, and 40 wt.% of ceria) synthesized by the more sustainable, in terms of less waste, less energy and less hazard, mechanochemical mixing of cerium hydroxide and cobalt hydroxycarbonate precursors. The catalysts were characterized by BET, powder XRD, H2-TPR, UV resonance Raman spectroscopy, and XPS techniques. The mixed oxides exhibited superior catalytic activity in comparison with Co3O4, thus, confirming the promotional role of ceria. The close interaction between Co3O4 and CeO2 phases, induced by mechanochemical treatment, led to strained Co3O4 and CeO2 surface structures. The most significant surface defectiveness was attained for 70 wt.% Co3O4-30 wt.% CeO2. A trend of the highest surface amount of Co3+, Ce3+ and adsorbed oxygen species was evidenced for the sample with this optimal composition. The catalyst exhibited the best performance and 100% benzene conversion was reached at 200 °C (relatively low temperature for noble metal-free oxide catalysts). The catalytic activity at 200 °C was stable without any products of incomplete benzene oxidation. The results showed promising catalytic properties for effective VOCs elimination over low-cost Co3O4-CeO2 mixed oxides synthesized by simple and eco-friendly mechanochemical mixing.

Investigation of Co3O4 Activity and Stability in Amidation of Fatty Acid Methyl Esters

AbstractCo3O4 activity in amidation reaction between fatty acid methyl esters and 3‐(Dimethylamino)‐1‐propylamine was investigated for the first time. The catalytic effect was approved by comparison of non‐catalyzed and catalyzed reactions activation energies and connected with the unique structure of Co3O4. Using of Co3O4 allows decreasing of activation energy of amidation reaction up to 1.5 times (from 90 to 59 kJ/mol). During the recycling test no significant decrease in reaction rate and product yield was detected even after 5 cycles. Using various analysis methods (XRD, FTIR, EDS‐SEM) of fresh and spent catalyst it was fixed that Co3O4 has no transformation throughout the synthesis.

Synthesis of Ag/Co3O4 for High Sensitive Non-Enzymatic Glucose Sensor through Synergy of Surface/Interface Engineering

We reported an effective means to tailor electrocatalytic activity of Co3O4 for enhanced non-enzymatic glucose sensor by synthesizing three-dimensional porous structure decorated with Ag clusters and nanoparticles. The three-dimensional porous structure of Co3O4 is beneficial for glucose diffusion and contacting with active sites, and the presence of Ag nanoparticles on surface of Co3O4 not only increases electrochemical active area but also improves electronic conductivity. Therefore, the synergy between Co3O4 and Ag made the sensor exhibit outstanding electrocatalytic activity toward glucose with a wide linear range of 3 orders of magnitude, a high sensitivity of 1542.9 μA mM−1 cm−2 and a low detection limit of 0.3 μM.