Smart integration of cold plasma stream and surface discharge with ns laser ablation for composite nanomaterial

In this paper, smart integration of cold dielectric barrier discharge (DBD) plasma in various geometrical arrangements with laser ablation at atmospheric pressure for nanomaterial was described. A composite Co:ZnO target was ablated in an airflow by a nanosecond (ns) laser (wavelength: 1064 nm, pulse duration: 30 ns) using fluence of 5 J-cm-2 at a repetition rate of 10 Hz. The nanomaterial produced under vertical and oblique plasma streams, surface discharge and gas flow, were compared. Utilization surface discharge markedly improved the material adhesion by altering surface intrinsic behavior, inducing anticipated surface energy activation, chemical changes, and the formation of a densely packed solid structure. Under all conditions, the material consistently retained its crystalline nature, elemental composition, and ultraviolet emission characteristics. These preliminary findings hold promise for additional research, suggesting avenues for making complex materials in a flexible environment. Such new advancements could facilitate applications in the biomedical, catalysis, pharmaceutical, and surgical device domains.

Dual Applications of Cobalt-Oxide-Grafted Carbon Quantum Dot Nanocomposite for Two Electrode Asymmetric Supercapacitors and Photocatalytic Behavior

Carbon materials, such as graphene, carbon nanotubes, and quantum-dot-doped metal oxides, are highly attractive for energy storage and environmental applications. This is due to their large surface area and efficient optical and electrochemical activity. In this particular study, a composite material of cobalt oxide and carbon quantum dots (Co3O4-CQD) was prepared using cobalt nitrate and ascorbic acid (carbon source) through a simple one-pot hydrothermal method. The properties of the composite material, including the functional groups, composition, surface area, and surface morphology, were evaluated by using various methods such as ultraviolet, Fourier transform infrared, X-ray diffraction, Raman, X-ray photoelectron spectroscopy, Brunauer-Emmett-Teller, scanning electron microscopy, and transmission electron microscopy analysis. The electrochemical performance of the Co3O4-CQD composite has been studied using a three-electrode system. The results show that at 1 A g-1, the composite delivers a higher capacitance of 1209 F g-1. The asymmetric supercapacitor (Co3O4-CQD//AC) provided 13.88 W h kg-1 energy and 684.65 W kg-1 power density with a 96% capacitance retention. The Co3O4-CQD composite also demonstrated excellent photocatalytic activity (90% in 60 min) for the degradation of methylene blue dye under UV irradiation, which is higher than that of pristine Co3O4 and CQD. This demonstrates that the Co3O4-CQD composite is a promising material for commercial energy storage and environmental applications.

Synergistic cobalt oxide/reduced graphene oxide/biochar nano-composite catalyst: harnessing the power of the catalyst for sustainable remediation of organic dyes and chromium(vi)

The exponential growth of industrial activities has led to a significant rise in the release of organic effluents, containing hazardous heavy metals and dyes, into the environment. These pollutants exhibit resistance to conventional biodegradation processes and are associated with carcinogenic properties, posing a severe threat to living organisms. In this context, the present research endeavours to address this environmental challenge through the development of an affordable and efficient photocatalyst, the Co3O4/reduced graphene oxide/biochar (CBG-10) heterostructure. The structural analysis of CBG-10, conducted through various techniques such as XRD, XPS, SEM, and optical property measurements, demonstrates its potential as a highly effective and easily recoverable catalyst for the mineralization of persistent pollutants like methylene blue, malachite green, and hexavalent Cr(vi). The recyclability of CBG-10 was confirmed through XRD studies, highlighting its stability and practical usability in wastewater purification. The photocatalytic behaviour of the catalyst was attributed to the generation of hydroxyl (˙OH) and superoxide radicals (˙O2-) during visible light illumination, as revealed by quenching experiments. The cost-effectiveness and stability of CBG-10 position it as a promising solution for addressing the challenges associated with the removal of stubborn organic contaminants from wastewater, thereby contributing to environmental protection and public health.

Recent advances of modification effect in Co3O4-based catalyst towards highly efficient photocatalysis

Tricobalt tetroxide (Co3O4) has been developed as a promising photocatalyst material for various applications. Several reports have been published on the self-modification of Co3O4 to achieve optimal photocatalytic performance. The pristine Co3O4 alone is inadequate for photocatalysis due to the rapid recombination process of photogenerated (PG) charge carriers. The modification of Co3O4 can be extended through the introduction of doping elements, incorporation of supporting materials, surface functionalization, metal loading, and combination with other photocatalysts. The addition of doping elements and support materials may enhance the photocatalysis process, although these modifications have a slight effect on decreasing the recombination process of PG charge carriers. On the other hand, combining Co3O4 with other semiconductors results in a different PG charge carrier mechanism, leading to a decrease in the recombination process and an increase in photocatalytic activity. Therefore, this work discusses recent modifications of Co3O4 and their effects on its photocatalytic performance. Additionally, the modification effects, such as enhanced surface area, generation of oxygen vacancies, tuning the band gap, and formation of heterojunctions, are reviewed to demonstrate the feasibility of separating PG charge carriers. Finally, the formation and mechanism of these modification effects are also reviewed based on theoretical and experimental approaches to validate their formation and the transfer process of charge carriers.

Application of Co3O4 nanocrystal/rGO for simultaneous electrochemical detection of cadmium and lead in environmental waters

Sensing of cadmium (Cd) and lead (Pb) in environmental samples is crucial for identifying potential health risks associated with exposure to these heavy metals as well as understanding the extent of heavy metal contamination in different environments and its impact on the ecosystem. The present study elucidates the development of a novel electrochemical sensor that can detect Cd (II) and Pb (II) ions simultaneously. This sensor is fabricated using reduced graphene oxide (rGO) and cobalt oxide nanocrystals (Co₃O₄ nanocrystals/rGO). The characterization of Co₃O₄ nanocrystals/rGO was done by using various analytical techniques. The incorporation of cobalt oxide nanocrystals with intense absorption properties results in an amplification of the electrochemical current generated on the surface of the sensor by heavy metals. This, when coupled with the unique properties of the GO layer, enables the identification of trace levels of Cd (II) and Pb (II) in the surrounding environment. The electrochemical testing parameters were meticulously optimized to obtain high sensitivity and selectivity. The Co₃O₄ nanocrystals/rGO sensor exhibited exceptional performance in detecting Cd (II) and Pb (II) within a concentration range of 0.1-450 ppb. Notably, the limits of detection (LOD) for Pb (II) and Cd (II) were found to be highly impressive at 0.034 ppb and 0.062 ppb, respectively. The Co₃O₄ nanocrystals/rGO sensor integrated with the SWASV method displayed notable resistance to interference and exhibited consistent reproducibility and stability. Therefore, the suggested sensor has the potential to serve as a technique for detecting both ions in aqueous samples using SWASV analysis.

Rational optimization of g-C3N4/Co3O4 nanocomposite for enhanced photodegradation of Rhodamine B dye under visible light

Heterogeneous catalysis is widely known as an efficient, clean, and low-cost technology to mitigate the environmental pollution of industrial effluents. This research aimed at optimizing the preparation and characterization of efficient g-C₃N₄/Co₃O₄ nanocomposite for catalytic removal of Rhodamine B (Rh B) dye. The detected XRD peaks for the prepared nano-Co₃O₄ are matched with the cubic crystal structure. In contrast, the broad peak at 27.3° corresponding to the graphite reflection of hkl (002) was noticeably weakened in the XRD pattern of the g-C₃N₄/Co₃O₄ composite. FTIR spectra of g-C₃N₄/Co₃O₄ nanocomposites revealed the active vibrational modes of each Co₃O₄ and g-C₃N₄ component. The microstructure study of g-C₃N₄ showed the strong interlayer stacking of carbon nitride nanosheets, while the surface morphology of g-C₃N₄/Co₃O₄ nanocomposite revealed a hybrid particulate system. EDS analysis indicated that the spot area of g-C₃N₄/Co₃O₄ confirmed the chemical ratios of carbon, nitrogen, cobalt, and oxygen. BET measurements of g-C₃N₄/Co₃O₄ showed a significant increase in the surface area and pore volume of single components due to the lamination of stacked g-C₃N₄ nanosheets by the intercalated Co₃O₄ nanoparticles. The prepared 30% g-C₃N₄/Co₃O₄ revealed the lowest value of E_g ~1.2 eV and the highest light absorptivity suggesting strong promotion for the photocatalytic performance under visible light. The maximum photocatalytic activity of about 87% was achieved by 30% g-C₃N₄/Co₃O₄ due to the photonic enhancement, which reduces the recombination of excited electrons. The developed nanocomposite with a g-C₃N₄/Co₃O₄ ratio of 0.3 exhibited high stability in its photocatalytic performance after four recycling times, and a slight decrease of about 7% was estimated after the 5th reuse test.

Metal Oxide Wrapped by Reduced Graphene Oxide Nanocomposites as Anode Materials for Lithium-Ion Batteries

The reduced graphene oxide/iron oxide (rGO/Fe2O3) and reduced graphene oxide/cobalt oxide (rGO/Co3O4) composite anodes have been successfully prepared through a simple and scalable ball-milling synthesis. The substantial interaction of Fe2O3 and Co3O4 with the rGO matrix strengthens the electronic conductivity and limits the volume variation during cycling in the rGO/Fe2O3 and rGO/Co3O4 composites because reduced graphene oxide (rGO) helps the metal oxides (MOs) to attain a more efficient diffusion of Li-ions and leads to high specific capacities. As anode materials for LIBs, the rGO/Fe2O3 and rGO/Co3O4 composites demonstrate overall superb electrochemical properties, especially rGO/Fe2O3T-5 and rGO/Co3O4T-5, showcasing higher reversible capacities of 1021 and 773 mAhg-1 after 100 cycles at 100 mAg-1, accompanied by the significant rate performance. Because of their superior electrochemical efficiency, high capacity and low cost, the rGO/Fe2O3 and rGO/Co3O4 composites made by ball milling could be outstanding anode materials for LIBs. Due to the excellent electrochemical performance, the rGO/Fe2O3 and rGO/Co3O4 composites prepared via ball milling could be promising anode materials with a high capacity and low cost for LIBs. The findings may provide shed some light on how other metal oxides wrapped by rGO can be prepared for future applications.

Jellyfish-like few-layer graphene nanoflakes: high paramagnetic response alongside increased interlayer interaction

Jellyfish-like graphene nanoflakes (GNF), prepared by hydrocarbon pyrolysis, are studied with electron paramagnetic resonance (EPR) method. The results are supported by X-ray photoelectron spectroscopy (XPS) data. Oxidized (GNFox) and N-doped oxidized (N-GNFox) flakes exhibit an extremely high EPR response associated with a large interlayer interaction which is caused by the structure of nanoflakes and layer edges reached by oxygen. The GNFox and N-GNFox provide the localized and mobile paramagnetic centers which are silent in the pristine (GNF p ) and N-doped (N-GNF) samples. The change in the relative intensity of the line corresponding to delocalized electrons is parallel with the number of radicals in the quaternary N-group. The environment of localized and mobile electrons is different. The results can be important in GNF synthesis and for explanation of their features in applications, especially, in devices with high sensitivity to weak electromagnetic field.

Adsorptive removal of methylene blue (MB) and malachite green (MG) dyes from aqueous solutions using graphene oxide (GO)

Graphene oxide (GO) synthesized via modified Hummers method was studied for adsorption of methylene blue (MB) and malachite green (MG) dyes from aqueous solutions. It is hypothesized that electrostatic interactions between dye molecules and surface of GO will facilitate charge carrier movements and degrade the dye in an efficient way. The as synthesized GO was characterized using various characterization techniques such as XRD, Raman, FTIR, UV–Vis, SEM and EDAX. The experimental results suggest that dye removal percentage will increase with increase in adsorbent dosage, time as well as solution pH and the process was exothermic in nature. The adsorption data at 293 K could be fitted by Langmuir equation with a maximum adsorption amount of 119.04, 102.4 mg/g and Langmuir adsorption equilibrium constant of 1.58, 0.867 L/mg for MB and MG dyes, respectively. The outcomes of present article will help not only to understand the adsorption characteristics of GO on MB and MG dyes but also paves path towards development of highly oxidized GO surface for degradation of complex dyes.