Co3O4 Nanoparticles Research Articles

CoO embedded porous biomass-derived carbon as dual-functional host material for lithium-sulfur batteries

A new strategy is developed to fabricate sulfur electrode by infusing sulfur into a conductive biochar decorated with highly dispersed CoO nanoparticles. The loading of the CoO nanoparticles, as the active sites for reactions, is efficiently increased by using the microwave-assisted diffusion method. It is demonstrated that biochar can serve as an excellent conductive framework to effectively activate sulfur. Simultaneously, the CoO nanoparticles possessing excellent capability to adsorb polysulfides can remarkably alleviate the dissolution of polysulfides, and greatly enhance the conversion kinetics between the polysulfides and Li2S2/Li2S in the charge/discharge processes. The sulfur electrode dual-functionalized with biochar and CoO nanoparticles exhibits excellent electrochemical performance, including high initial discharge specific capacity of 930.5 mAh g−1 and low capacity decay rate of 0.069 % per cycle during 800 cycles at 1C rate. It is particularly interesting that the CoO nanoparticles distinctively enhance the Li+ diffusion during the charge process, endowing the material with excellent high-rate charging performance. This could be beneficial for the development of Li-S batteries with fast charging feature.

Green Synthesis and Characterizations of Cobalt Oxide Nanoparticles and Their Coherent Photocatalytic and Antibacterial Investigations

Water pollution is a serious concern for developing and undeveloped countries. Photocatalytic degradation of organic pollutants is an effective degradation method to restrain the green ecosystem. This research article presents a green, low-cost, and benevolent eco-friendly biosynthesis of cobalt oxide (Co3O4) nanoparticles using Curcuma longa plant extract. The UV and visible region absorbance of Co3O4 nanoparticles estimated the Co2+ and Co3+ transitions on the lattice oxygen, and their bandgap of 2.2 eV was confirmed from the UV-DRS spectroscopy. The cubic structure and spherical shape of Co3O4 nanoparticles were estimated by using XRD and TEM characterizations. Plant molecules aggregation and their agglomerations on the nanoparticles were established from FTIR and EDX spectroscopy. Multiple cobalt valences on the oxygen surfaces and their reaction, bonding, and binding energies were analyzed from XPS measurements. The biogenic Co3O4 nanoparticles were executed against gram-positive (Staphylococcus aureus—S. aureus) and gram-negative (Escherichia coli—E. coli) bacteria. A gram-positive bacterial strain exhibited great resistivity on Co3O4 nanoparticles. Degradation of organic dye pollutants on the Co3O4 nanoparticles was performed against methylene blue (MB) dye under the conditions of visible light irradiation. Dye degradation efficiency pseudo-first-order kinetics on the pseudo-first-order kinetics denotes the rate of degradation over the MB dye. This research work achieved enhanced degradation potency against toxic organic dye and their radicals are excited from visible light irradiations. Absorption light and charged particle recombinations are reformed and provoked by the plant extract bio-molecules. In this process, there is no inferior yield development, and electrons are robustly stimulated. Furthermore, the biosynthesized Co3O4 nanoparticles determined the potency of bacterial susceptibility and catalytic efficacy over the industrial dye pollutants.

Nanocriticality in the magnetic phase transition of CoO nanoparticles

The universal theory of critical phase transitions describes the critical behavior at second-order phase transitions in infinitely large systems. With the increased contemporary interest in nanoscale materials, we investigated CoO nanoparticles by means of neutron scattering and found how the theory of critical phenomena breaks down in the nanoscale regime. Using CoO as a model system, we have identified a size-dependent nanocritical temperature region close to the antiferromagnetic phase transition where the magnetic correlation length of the nanoparticles converges to a constant value, which is significantly smaller than that of the saturated state found at low temperatures. This is in clear contrast to the divergence around $T_{\rm N}$ observed for bulk systems. Our findings of nanocriticality in the magnetic phase transition is of great importance for the understanding of phase transitions at the nanoscale.

Ordered mesoporous Co3O4-Al2O3 bimetal oxides for CO2 hydrogenation to synthetic natural gas: Effects of surface Al2O3 distribution

The highly ordered mesoporous structures of Co3O4-Al2O3 mixed metal oxide, prepared by using a hard template of the mesoporous KIT-6, revealed a higher catalytic activity and stability for CO2 hydrogenation to synthetic methane at an optimal surface Al content with ∼6 wt% (m-CoAl(1)). The higher CO2 conversion (42.5%) and CH4 selectivity (96.7%) were attributed to the adjusted surface hydrophobicity with optimal amount of spinel CoAl2O4 phases, where the CoAl2O4 phases mainly acted as structural stabilizing components in the ordered mesoporous Co3O4-Al2O3 matrices by suppressing the aggregations of Co3O4 nanoparticles as well as by generating more hydrophobic surfaces. At an optimal surface Al2O3 content (m-CoAl(1)), the stronger interactions of Co3O4-Al2O3 were selectively formed with the help of an optimal amount of the spinel CoAl2O4 phases, which further enhanced the surface hydrophobicity and oxygen vacant sites to effectively suppress competitive adsorption of water formed by CO2 hydrogenation.

Co supported on N and S dual-doped reduced graphene oxide as highly active oxygen-reduction catalyst for direct ethanol fuel cells

Oxygen reduction reaction (ORR) is one of the key features for the efficient functioning of several energy conversion devices such as fuel cells, appearing the necessity of development of new low-cost catalyst materials. Heteroatom-doped carbon materials have attracted attention in this field due to its physicochemical and electronic properties. In this work, a nitrogen and sulfur doped material with anchored Co3O4 nanoparticles (Co/SN-rGO) is proposed as cathode catalyst for direct ethanol fuel cells (DEFCs) and results are compared with different doped graphene nanomaterials (GMs). The effect of the heteroatoms and cobalt oxide nanoparticles in the final efficiency was studied. Synthesized materials were characterized and the activity of Co/SN-rGO and GMs for the ORR was studied. Co/SN-rGO presents high ORR performance in terms of onset potential (Eonset), 0.86 V (vs RHE) and half-wave potential (E1/2) 0.72 V (vs RHE). Tafel analysis shows 60 mV dec-1 at low overpotential for potential dependent ORR mechanism. Besides, when Co/SN-rGO performance is evaluated in a DEFC using a fuel cell test station, main results indicate higher catalytic activity, stability, and ethanol tolerance of Co/SN-rGO in comparison to a carbon-supported Pt catalyst.

Enhancing pseudocapacitive properties of cobalt oxide hierarchical nanostructures via iron doping

Through co-precipitation and post-heat processing, nanostructured Fe-doped Co3O4 nanoparticles (NPs) were developed. Using the SEM, XRD, BET, FTIR, TGA/DTA, UV–Vis, and techniques were examined. The XRD analysis presented that Co3O4 and Co3O4 nanoparticles that had been doped with 0.25 M Fe formed single cubic phase Co3O4 NPs with average crystallite sizes of 19.37 nm and 14.09 nm, respectively. The as prepared NPs have porous architectures via SEM analyses. The BET surface areas of Co3O4 and 0.25 M Fe-doped Co3O4 NPs were 53.06 m2/g and 351.56 m2/g, respectively. Co3O4 NPs have a band gap energy of 2.96 eV and an extra sub-band gap energy of 1.95 eV. Fe-doped Co3O4 NPs were also found to have band gap energies between 2.54 and 1.46 eV. FTIR spectroscopy was used to determine whether M–O bonds (M = Co, Fe) were present. The doping impact of iron results in the doped Co3O4 samples having better thermal characteristics. The highest specific capacitance was achieved using 0.25 M Fe-doped Co3O4 NPs at 5 mV/s, which corresponding to 588.5 F/g via CV analysis. Additionally, 0.25 M Fe-doped Co3O4 NPs had energy and power densities of 9.17 W h/kg and 472.1 W/kg, correspondingly.

Magnetized homann flow comprising GO and Co3O4 nanoparticles past a biaxially stretching surface

The usage of hybrid nanofluid due to their outstanding thermal conductivity has become a fascinating topic in research. This study considers the suspension of graphene oxide and cobalt oxide in ethylene glycol on a biaxially, planarly, and perpendicularly stretching surface. The influence of heat Cattaneo-Christov double diffusion with generation/absorption, Joule heating, and shapes of nanoparticles is scrutinized. The similarity conversions are assumed, which determine dimensionless ordinary equations. The collocation method, bvp4c routine is utilized to determine the numerical and asymptotic behavior of the problem. Because of better thermal and electrical conductivity of nanoparticles under consideration, this research can be used for energy storage, electronics, catalytic supports, and cooling of a system. The thermophysical properties are scrutinized via the Hamilton-Crosser model of nanofluids, which is significant as it provides a quantitative understanding of the heat transfer behavior of nanofluids, enabling the design and optimization of nanofluid-based heat transfer systems. Due to the magnetic field, temperature distribution is increased; however, velocities diminish. Moreover, energy transport is maximum for spherical-shaped nanoparticles, while it is lowest for blade-shaped nanoparticles. By incrementing volume fraction, the intermolecular motion amongst the particles becomes disorderly and erratic, which enhances the flow and thermal transport. The wall stress parameter along the x-axis is augmented due to an increment in the stretching parameter, while the opposite trend is seen for the wall stress parameter along the y-axis.

A combined experimental and theoretical study on the structural, optical and electronic properties of hetero interface-functionalized MoS2 /Co3O4 nanocomposite

Co3O4 decorated MoS2 nanoflower (MoS2/Co3O4) has been successfully synthesized by a simple hydrothermal method. A combined experimental and theoretical investigation was performed to comprehend the effect of Co3O4 on the structural, optical, and electronic properties of MoS2 nanoflowers. A number of characterization techniques have been used to study the surface morphologies, structural properties, chemical constitution, and optical properties of the nanocomposites including, FE-SEM, TEM, XRD, XPS, and UV–VIS spectroscopy. Flower-like structures of MoS2 and MoS2/Co3O4 have been observed from the FE-SEM and TEM images. The Rietveld refinement of the X-ray diffraction (XRD) pattern was used to estimate the various structural parameters of the nanoflowers which also confirms the phase purity of the MoS2 nanoflower. X-ray photoelectron spectroscopy (XPS) results revealed strong electronic interaction between Mo–S and Co–O in the nanocomposites. The optical bandgap of the as-prepared samples was estimated using diffusive reflectance spectra and was found to be varied between 1.44 eV to 1.27 eV nanostructure due to the incorporation of Co3O4 nanoparticle. To fully understand and validate the structural, optical, and electrical characteristics of the samples, density functional theory (DFT) calculations were carried out. DFT results revealed that the Mo-4d and Co-3d orbital-orbital interactions occur due to the incorporation of Co3O4 into MoS2, leading to a decrease in the band gap. Moreover, a charge redistribution occurred between MoS2 and Co3O4 interface, creating more active sites for electro and opto-catalytic reactions. Among the results, the red shift of the optical absorbance spectra is the most obvious one enabling our synthesized nanocomposite to absorb in the near-infrared range. This study will offer a new insight into the fabrication of transition oxide-based hetero-interface influenced MoS2 functional devices for diverse applications.

Green synthesis of Co3O4 nanoparticles using psyllium husk (Plantago Ovata) and application as electrocatalyst for oxygen evolution reaction

The continuous supply of hydrogen from renewable sources through water electrolysis technology is a key issue for the development of humanity. To meet this purpose, catalysts based on transition metals (Ni, Fe and Co) are promising candidates for the hydrogen and oxygen evolution reactions. Therefore, in this work, nanocrystalline Co3O4 with a spinel-like cubic structure was prepared by a proteic sol–gel synthesis using psyllium husk as a polymerizing agent, and later tested as an electrocatalyst for the oxygen evolution reaction (OER). The purity of the Co3O4 phase was confirmed by several characterization techniques, including X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), Raman spectroscopy and X-ray Photoelectron Spectroscopy (XPS). The size of crystallites and particles obtained from Rietveld refinement of X-ray diffraction patterns ranged from 16.5 nm to 25.3 nm for powders calcinated at 400 °C and 600 °C, respectively, confirming nanometric Co3O4 powders. Scanning electron microscopy shows nanostructures with predominantly spherical morphology. From the electrocatalytic point of view, it was observed that the larger particle size impairs the oxygen evolution reaction. The Co3O4 calcined at 400 °C showed superior electrocatalytic performance, with an overpotential of 328 mV at 10 mA cm−2, Tafel slope of 71 mV dec-1, CDL of 5.46 mF cm−2, ECSA of 91 cm2, specific activity of 4.73 mA cm−2 and mass activity of 718 A g−1.

Synthesis and Biological Activity Study of Co and Cr Complexes with α-(2-Salsayl)-<i>N</i>-phenyl Nitrone and Oxide Nanoparticles

This paper describes the synthesis of two complexes from the ligand α-(2-Salsayl)-N-phenyl nitrone with CoCl2 and CrCl2. The ligand was characterized by several spectroscopic techniques (ultraviolet/visible (UV/Vis), nuclear magnetic resonance (1H-NMR and 13C-NMR), Fourier-transform infrared spectroscopy (FTIR), and mass spectrometry (MS). While infrared, ultraviolet-visible (UV-Vis), thermal analysis, and job method studies were used to reveal the structure of the complexes. The synthesized complexes were then synthesized by the sonochemical method, and the copper and chromium oxide nanoparticles were produced using the thermal decomposition method. Scanning electron microscopy (SEM), Energy dispersive X-ray spectroscopy (EDX), and X-ray diffraction (XRD) characterization confirmed the formation of Co3O4 and Cr2O3 nanoparticles. Antimicrobial studies of the complexes against some microorganisms, such as Staphylococcus epidermis and Escherichia coli, utilizing the disk diffusion method, revealed the antibacterial activity of the complexes.

Efficient Conversion of Biomass‐Derived Furfural to Tetrahydrofurfuryl Alcohol over Co3O4−C Nanocomposite Catalyst at Mild Conditions

AbstractDue to the depletion of fossil fuel resources, catalytic conversion of biomass into liquid fuels and valuable compounds has become an attractive field of research. Tetrahydrofurfuryl alcohol (THFAL) is an important platform molecule in both industrial and pharmacological fields, and catalytic hydrogenation of furfural (FA) to THFAL is a sustainable process. However, an active and stable catalyst for the direct hydrogenation of FA to THFAL under milder conditions is still a challenge. Accordingly, herein, we investigated a high‐valence metal catalyst (Co3O4−C) for the hydrogenation of FA to THFAL using sodium borohydride (NaBH4) as the H source. Under optimal reaction conditions (that is, 0.05 g Co3O4−C‐700 in an aqueous solution, 5 mmol NaBH4, 60 °C, and 3 h), 88.5 % THFAL was produced over Co3O4−C‐700. The kinetic study revealed that furfuryl alcohol was generated as an intermediate during the hydrogenation of FA. Additionally, the reaction followed pseudo‐first order kinetics, and the reaction rate constant (k) values were .80, 3.41, 3.45, and 5.55 h−1 at 30, 40, 45, 50, and 60 °C, respectively. From the slopes of the Arrhenius plot, the activation energy was determined to be 22.02 kJ mol−1, indicating high activity of the catalyst for the reaction. Moreover, Co3+ and smaller sizes of Co3O4 nanoparticles contributed to the activity of Co3O4−C‐700. We believe that the metal oxide catalyst developed herein can be used for various biomass conversions.

Unraveling Sequential Oxidation Kinetics and Determining Roles of Multi-Cobalt Active Sites on Co3O4 Catalyst for Water Oxidation

The multi-redox mechanism involving multi-sites has great implications to dictate the catalytic water oxidation. Understanding the sequential dynamics of multi-steps in oxygen evolution reaction (OER) cycles on working catalysts is a highly important but challenging issue. Here, using quasi-operando transient absorption (TA) spectroscopy and a typical photosensitization strategy, we succeeded in resolving the sequential oxidation kinetics involving multi-active sites for water oxidation in OER catalytic cycle, with Co3O4 nanoparticles as model catalysts. When OER initiates from fast oxidation of surface Co2+ ions, both surface Co2+ and Co3+ ions are active sites of the multi-cobalt centers for water oxidation. In the sequential kinetics (Co2+ → Co3+ → Co4+), the key characteristic is fast oxidation and slow consumption for all the cobalt species. Due to this characteristic, the Co4+ intermediate distribution plays a determining role in OER activity and results in the slow overall OER kinetics. These insights shed light on the kinetic understanding of water oxidation on heterogeneous catalysts with multi-sites.

A multifunctional heterogeneous superwettable coating for water collection, oil/water separation and oil absorption.

Herein, inspired by desert beetles, we fabricated a multifunctional heterogeneous superwettable coating (MHSC) for water collection and oily wastewater cleanup. The selective modifications of 1-octadecanethiol (ODT) treated CoO and P25 TiO2 nanoparticles (NPs) were prepared, so hydrophobic CoO NPs and superhydrophilic P25 NPs were combined on the MHSC, showing the water contact angle (WCA) of 156.5° and rolling-off angle (RA) of 6.4°. With the aid of waterborne polyurethane (WPU), five kinds of substrates (i.e., glass slide, dish, wood, fabric, sponge) spray-coated by MHSC displayed high-efficiency water collection rates (WCRs) of 18.1±0.7mgmin-1 cm-2. Moreover, MHSC coated fabric manifested robust oil/water separations with separation efficiencies (SEs) >99.7 % and fluxes ranged from 9.7 to 11.0Lm-2 s-1. Efficient oil sorption from oily water was obtained by MHSC coated sponge with oil absorption capacities (OACs) of 6.5-29.5gg-1. Further, even dealt with the treatments of mechanical destructions, extreme temperature and UV illumination, the coated materials remained stable performances.

Ag doped Co3O4 nanoparticles for high-performance supercapacitor application

Ag doped Co3O4 nanoparticles (NPs) were synthesized via a co-precipitation method changing the concentration of Ag. The crystal structure, morphology, surface area, functional group, optical band gap, and thermal property were investigated by XRD, SEM, BET, FTIR, UV–Vis, and TGA/DTA techniques. The XRD results showed the formation of single-cubic Co3O4 nanostructured materials with an average crystal size of 19.37 nm and 12.98 nm for pristine Co3O4 and 0.25 M Ag-doped Co3O4 NPs. Morphological studies showed that pristine Co3O4 and 0.25 M Ag-doped Co3O4 NPs having a porous structure with small spherical grains, porous structures with sponge-like structures, and loosely packed porous structures, respectively. The pristine and 0.25 M Ag-doped Co3O4 NPs showed BET surface areas of 53.06 m2/g, and 407.33 m2/g, respectively. The band gap energy of Co3O4 NPs were 2.96 eV, with additional sub-bandgap energy of 1.95 eV. Additionally, it was discovered that the band gap energies of 0.25 M Ag-doped Co3O4 NPs ranged from 2.2 to 2.75 eV, with an extra sub-band with energies ranging from 1.43 to 1.94 eV for all as-prepared samples. The Ag-doped Co3O4 as prepared samples show improved thermal properties due to the doping effect of silver. The CV test confirmed that the 0.25 M Ag-doped Co3O4 NPs exhibited the highest specific capacitance value of 992.7 F/g at 5 mV/s in a 0.1 M KOH electrolyte solution. The energy density and power density of 0.25 M Ag-doped Co3O4 NPs were 27.9 W h/kg and 3816.1 W/kg, respectively.

Enhanced gas sensing property of Co3O4 matrix nanocomposites with halloysite nanotubes toward triethylamine

Despite their high surface reactivity, the gas sensor based on Co3O4 nanoparticles frequently suffers from a low response to volatile organic compounds (VOCs) due to high-temperature sintering and inefficient resistance modulation. Herein, halloysite nanotubes (HNTs) were incorporated as the additive into the Co3O4 nanoparticle matrix to enhance the sensing property toward VOCs in terms of gas response (Rg/Ra) and operation stability. Co3O4 nanoparticles intimately attached on HNTs were achieved by a facile deposition-precipitation method followed by calcination. The best-performing Co3O4/0.3HNTs-based sensor had a high gas response of 22.9 to 50 ppm triethylamine at 240 °C, which was 4.9 times than that of Co3O4 alone. The enhanced sensitivity could be attributed to the HNT incorporation that facilitated effective resistance modulation, surface property tuning, as well as surface defect formation. These results bring new insight into an enhancement of gas sensing property of a p-type metal oxide with insensitive materials. They also provide a potential to expand the application of aluminosilicate clays to gas sensors.

Cobalt oxide functionalized ceramic membrane for 4-hydroxybenzoic acid degradation via peroxymonosulfate activation

Membrane separation and sulfate radicals-based advanced oxidation processes (SR-AOPs) can be combined as an efficient technique for the elimination of organic pollutants. The immobilization of metal oxide catalysts on ceramic membranes can enrich the membrane separation technology with catalytic oxidation avoiding recovering suspended catalysts. Herein, nanostructured Co3O4 ceramic catalytic membranes with different Co loadings were fabricated via a simple ball-milling and calcination process. Uniform distribution of Co3O4 nanoparticles in the membrane provided sufficient active sites for catalytic oxidation of 4-hydroxybenzoic acid (HBA). Mechanistic studies were conducted to determine the reactive radicals and showed that both SO4•− and •OH were present in the catalytic process while SO4•− plays the dominant role. The anti-fouling performance of the composite Co@Al2O3 membranes was also evaluated, showing that a great flux recovery was achieved with the addition of PMS for the fouling caused by humic acid (HA).

Effect of surface modification by KOH activation on the electrochemical performance of Co3O4 nanoparticles

In this work, the effects of different Co3O4:KOH mass ratios on the microstructure, chemical state, and surface properties of Co3O4 nanoparticles were investigated and discussed. The different KOH contents in the activation process affecting the electrochemical properties of the samples were determined in a three-electrode configuration. The results showed that the sample with a Co3O4:KOH mass ratio of 1:0.5 (Co@0.5KOH) exhibited the highest specific capacitance of 204.0 F/g at a current density of 1 A/g. The excellent capacitance retention of 97.7% was observed after a 5000 cycle galvanostatic charge/discharge test. A symmetrical two-electrode system was set up, and the results showed that the Co@0.5KOH sample had a superior energy density of 3.5 Wh/kg and a power density of 276.0 W/kg at a current density of 1 A/g. The KOH activation method was effective and could be extended to other metal oxides to obtain better electrode materials for supercapacitors.

Plasma modified Co3O4 nanoparticles for catalytic degradation process through enhanced peroxidase-like activity

This study highlights a simple and efficient nanochemistry-based approach for the effective degradation of triphenylmethane and toxic dye, malachite green (MG) using Argon cold plasma-modified cobalt oxide nanoparticles (Ar-Co3O4-NPs). Synthesized particles were characterized using scanning electron microscope, X-ray diffraction, and Fourier-transform infrared spectroscopy. The peroxidase-mimic activity of Co3O4-NPs was evaluated, and the results confirmed that the catalytic activity of Co3O4-NPs was enhanced after plasma modification. The decomposition of MG was tested using the improved catalytic activity of Ar-Co3O4-NPs in model aqueous solution. The results indicated the ability of 0.16 g/mL Ar-Co3O4-NPs to completely degrade 40 µM MG within 70 min with a decolorization efficiency of 96.78%. Experimental conditions were optimized for maximum MG removal. Gas chromatography-mass spectrometry was used to determine the byproducts of MG degradation, and the findings indicated the production of less toxic products. The toxicity of the resultant metabolites of MG degradation was evaluated against E. coli and B. subtilis and the results confirmed less toxic product formation. Artificial neural networks (ANNs) were used to model the catalytic degradation data, and the strong correlation between experimental observations and ANN model predictions suggested that the designed model could accurately predict MG dye removal efficiency under different operating conditions.

Multifunctional cobalt oxide nanocomposites for efficient removal of heavy metals from aqueous solutions

In this study, co-precipitation synthesis of natural clay (NC) with Co3O4 nanoparticles (NPs) is carried out to elaborate the super NC@Co3O4 nanocomposites with admirable salinity confrontation, environmental stability and reusability, to eliminate heavy metal pollution such as toxic Pb(II) and Cd(II) ions. The advantages of using the NC@Co3O4 adsorbent are easy synthesis and biocompatibility. In addition, NC@Co3O4 can keep an excellent adsorption capacity by taking into account various environmental parameters such as the pH solution, NC@Co3O4 dose, adsorption process time and the initial heavy metals concentration. Furthermore, FTIR, XRD, TGA, SEM-EDS, TEM and AFM analyses were performed to confirm NC@Co3O4 nanocomposites synthesis and characterisation. The adsorption efficiencies of Pb(II) and Cd(II) ions by NC@Co3O4 nanocomposites were demonstrated to be up to 86.89% and 82.06% respectively. Regarding the adsorption from water onto the NC@Co3O4 nanocomposites, kinetics data were well fitted with PSO kinetic model, whereas a good agreement was found between the equilibrium adsorption and theoretical Langmuir isotherm model leading to maximum adsorption capacities of 55.24 and 52.91 mg/g, for Pb(II) and Cd(II) respectively. Monte Carlo (MC) simulations confirmed the spontaneous of this adsorption based on the negative values of Eads. The MC simulations were performed to highlight the interactions occurring between heavy metal ions and the surface of NC@Co3O4 nanocomposites, these were well correlated with the experimental results. Overall the study showed that NC@Co3O4 nanoadsorbents have strongly versatile applications and are well designed for pollutant removal from wastewater due to their unique adsorptive properties.

Speciation of Oxygen Functional Groups on the Carbon Support Controls the Electrocatalytic Activity of Cobalt Oxide Nanoparticles in the Oxygen Evolution Reaction.

The effective use of the active phase is the main goal of the optimization of supported catalysts. However, carbon supports do not interact strongly with metal oxides, thus, oxidative treatment is often used to enhance the number of anchoring sites for deposited particles. In this study, we set out to investigate whether the oxidation pretreatment of mesoporous carbon allows the depositing of a higher loading and a more dispersed cobalt active phase. We used graphitic ordered mesoporous carbon obtained by a hard-template method as active phase support. To obtain different surface concentrations and speciation of oxygen functional groups, we used a low-temperature oxygen plasma. The main methods used to characterize the studied materials were X-ray photoelectron spectroscopy, transmission electron microscopy, and electrocatalytic tests in the oxygen evolution reaction. We have found that the oxidative pretreatment of mesoporous carbon influences the speciation of the deposited cobalt oxide phase. Moreover, the activity of the electrocatalysts in oxygen evolution is positively correlated with the relative content of the COO-type groups and negatively correlated with the C═O-type groups on the carbon support. Furthermore, the high relative content of COO-type groups on the carbon support is correlated with the presence of well-dispersed Co3O4 nanoparticles. The results obtained indicate that to achieve a better dispersed and thus more catalytically active material, it is more important to control the speciation of the oxygen functional groups rather than to maximize their total concentration.