Effect of Urea on the Morphology of Co3O4Nanostructures and Their Application for Potentiometric Glucose Biosensor

Honeycomb-like holey Co3O4 membrane triggered peroxymonosulfate activation for rapid degradation of organic contaminants

Heterogeneous advanced oxidation processes (AOPs) are commonly employed for the degradation of recalcitrant contaminants, however, practical application of heterogeneous AOPs has been limited by their low activation efficiency and inefficient utilization of radicals. Herein, this study demonstrates for the first time that 2D honeycomb-like holey membranes assembled by Co₃O₄ nanosheets, serve as an excellent activator for peroxymonosulfate (PMS) and aid in rapid pollutant removal. The Co₃O₄ membrane achieved 100% target pollutant ranitidine removal and a membrane retention time of only ~385 ms with the degradation rate 3-5 orders of magnitude faster than that achieved by conventional heterogeneous catalysis. Ranitidine degradation was maintained at >90% for 13 h of continuous-flow operation at a high flux of 176 L m^-2 h^-1 bar^-1. Furthermore, the Co₃O₄ membrane could also effectively degrade several recalcitrant pollutants, including pharmaceutical personal care products, phenols, and dyes. SO₄^•- and •OH were identified as the primary reactive oxygen species in the Co₃O₄ membrane/PMS system, with Co providing the active site for PMS activation. This strategy of membrane-based AOP treatment offers helpful guidance for the design of other efficient heterogeneous catalytic systems and presents a novel approach to overcoming the limitations of conventional heterogeneous catalysis.

Synthesis, Characterization and Applications of Spinel Cobaltite Nanomaterials

Recently, spinel structures (AB₂O₄) Nanoparticles (NPs) having binary and ternary mixtures of metal oxides have been established as promising redox catalysts. Due to the presence of two mixed valence metal cations, transport of electrons takes place easily between multiple transition-metal cations with relatively low energy of activation. Among these, spinel cobaltite (MCo₂O₄) is very attractive due to its low cost, non-toxicity, higher stability, higher electronic conductivity and electrochemical property. To date, MCo₂O₄ has been used in the fabrication of supercapacitors, electrodes for oxygen evolution reaction, and electrochemical sensors for glucose. A variety of MMCo₂O₄materials have been synthesized, characterized, and utilized in the fabrication of super capacitors, electrodes for oxygen evolution reaction, and electrochemical sensors for glucose. The progress in the field of the spinel MCo₂O₄ materials opens the door to novel and efficient applications in the nanoscience and nanotechnology, and elctrochemistry.

Juglans Sporopollenin for High-Performance Supercapacitor Electrode Design

Recently, plant pollen has been used as a source of activated carbon to produce carbon-containing supercapacitor electrodes. However, in this study, pollen was used as a biotemplate with a completely different approach. As a biotemplate, pollen offers a wide range of varieties in terms of exterior, porosity, shape, and size. An electrode formed by the use of metal oxide grown on the pollen exine layer (sporopollenin microcapsules) as the active substance will inevitably exhibit good electrochemical capacitive properties. Juglans male flowers have been distinguished by dissection from anthers. Isolation of pollen grains from anthers was carried out using sieving from suitable sieves (45-200 μm). Juglans sporopollenin exine microcapsules (SECs) were separated from the intine and protoplasm by acetolysis in combination with reflux. The solution containing SECs, metal ions, and Ni foam was put into a Teflon-lined hydrothermal container, and then, it was reacted at 120 °C for 15 h. The resulting precipitate, as well as the Ni foam, was heat-treated at 300 and 360 °C for 3 h in air. The raw pollen, chemically treated pollen, and cobalt-coated SEC (CoSEC) and CoSEC/Ni foam were characterized using scanning electron microscopy, Brunauer-Emmett-Teller surface area analysis, thermogravimetric analysis, and X-ray diffraction techniques. Two different types of supercapacitor electrode designs, with the use of exine microcapsules of Juglans sporopollenin, were performed for the first time. The maximum specific capacitance was up to 1691 F g^-1 at 5 A g^-1.

Development of 3-dimensional Co3O4 catalysts with various morphologies for activation of Oxone to degrade 5-sulfosalicylic acid in water

Since 5-sulfosalicylic acid (SFA) has been increasingly released to the environment, SO₄^--based oxidation processes using Oxone have been considered as useful methods to eliminate SFA. As Co₃O₄ has been a promising material for OX activation, the four 3D Co₃O₄ catalysts with distinct morphologies, including Co₃O₄-C (with cubes), Co₃O₄-P (with plates), Co₃O₄-N (with needles) and Co₃O₄-F (with floral structures), are fabricated for activating OX to degrade SFA. In particular, Co₃O₄-F not only exhibits the highest surface area but also possesses the abundant Co²⁺ and more reactive surface, making Co₃O₄-F the most advantageous 3D Co₃O₄ catalyst for OX activation to degrade SFA. The mechanism of SFA by this 3D Co₃O₄/OX is also investigated and the corresponding SFA degradation pathway has been elucidated. The catalytic activities of Co₃O₄ catalysts can be correlated to physical and chemical properties which were associated with particular morphologies to provide insights into design of 3D Co₃O₄-based catalysts for OX-based technology to degrade emerging contaminants, such as SFA.

Synthesis and Electrochemical Study of Mesoporous Nickel-Cobalt Oxides for Efficient Oxygen Reduction

Development of a cost-effective and efficient electrocatalyst for the sluggish oxygen reduction reaction (ORR) is a crucial challenge for clean energy technologies. In this study, we have synthesized various Ni and Co oxide (NCO) nanomaterials via a facile coprecipitation, followed by the calcination method. The morphology of the formed NCO nanomaterials was controlled by varying the percentage of the Ni and Co precursors, leading to the formation of a template-free mesoporous spinel phase structure of Ni _xCo_{3- x}O₄. It was found that the number of the octahedral site cations and the defect sites with lower oxygen in the spinel oxides can be tunable by taking appropriate ratios of the Ni and Co precursors. The optimized NCO nanomaterial exhibits superior electrocatalytic activity compared to the mono-metal oxides of NiO and Co₃O₄ with over 3 times higher current density and ∼0.250 V lower onset potential toward ORR in a 0.1 M KOH solution. Scanning electrochemical microscopy was utilized in mapping the activity of the catalyst and monitoring the ORR products, further confirming that a four-electron transfer pathway was facilitated by the NCO nanomaterial. Moreover, the developed mesoporous NCO nanomaterial exhibits a high methanol tolerance capability and long-term stability when compared to the commercial state-of-the-art Pt/C electrocatalyst. The improvement of the catalytic activity and stability of this advanced NCO nanomaterial toward ORR may be attributed to the facile accessible mesoporous structure, and the abundance of octahedral site cations and defective oxygen sites.

Co3O4/TiO2 hetero-structure for methyl orange dye degradation

Advanced oxidation processes based on sulphate radical generated by peroxymonosulphate (PMS) activation is a promising area for environmental remediation. One of the biggest drawbacks of heterogeneous PMS activation is catalyst instability and metal ion leaching. In this study, a simple organic binder mediated route was explored to substitute Ti⁴⁺ ions into the Co₃O₄ host lattice structure to create a Co-O-Ti bond to minimise cobalt leaching during methyl orange degradation. The catalyst was characterised by X-ray diffraction, and scanning and transmission electron microscopy. The as-prepared catalysts with Co₃O₄:TiO₂ ratio of 70:30 exhibited minimal leaching (0.9 mg/L) compared to other ratios studied. However, the pristine Co₃O₄ exhibited highest catalytic activity (rate constant = 0.41 min^-1) and leaching (26.7 mg/L) compared to composite material (70:30 Co₃O₄:TiO₂). Interestingly, the morphology of the composite and leaching of Co²⁺ ions were found to be temperature dependent, as an optimum temperature ensured strong Co-O-Ti bond for prevention of Co²⁺ leaching. The classical quenching test was utilised to determine the presence and role of radical species on methyl orange degradation. The fabricated catalyst also exhibited good catalytic activity in degrading mixed dyes and good recyclability, making it a potential candidate for commercial application.

Synthesis of hydrous cobalt phosphate electro-catalysts by a facile hydrothermal method for enhanced oxygen evolution reaction: effect of urea variation

Highly active hydrous cobalt phosphate thin film electro-catalysts were synthesized by one-pot hydrothermal method and were evaluated for the oxygen evolution reaction (OER).

Highly active 3-dimensional cobalt oxide nanostructures on the flexible carbon substrates for enzymeless glucose sensing

3-Dimensional cobalt oxide nanostructures on the flexible carbon substrates for enzymeless glucose sensing.

Sol-Gel Synthesis of Carbon Xerogel-ZnO Composite for Detection of Catechol

Carbon xerogel-zinc oxide (CXZnO) composites were synthesized by a simple method of sol-gel condensation polymerization of formaldehyde and resorcinol solution containing zinc salt followed by drying and thermal treatment. ZnO nanoparticles were observed to be evenly dispersed on the surfaces of the carbon xerogel microspheres. The as-prepared CXZnO composites were mixed with laccase (Lac) and Nafion to obtain a mixture solution, which was further modified on an electrode surface to construct a novel biosensing platform. Finally, the prepared electrochemical biosensor was employed to detect the environmental pollutant, catechol. The analysis result was satisfactory, the sensor showed excellent electrocatalysis towards catechol with high sensitivity (31.2 µA·mM⁻¹), a low detection limit (2.17 µM), and a wide linear range (6.91–453 µM). Moreover, the biosensor also displayed favorable repeatability, reproducibility, selectivity, and stability besides being successfully used in the trace detection of catechol existing in lake water environments.

Advances in non-enzymatic glucose sensors based on metal oxides

This review summarizes the advances in non-enzymatic glucose sensors based on different metal oxides (ZnO, CuO/Cu₂O, NiO,etc.) and their composites.

An enzyme-free glucose sensor based on a difunctional diboronic acid for molecular recognition and potentiometric transduction

Based on a diboronic acid for specific recognition of glucose, an enzyme-free potentiometric glucose sensor was developed.

Rapid and large-scale synthesis of Co3O4 octahedron particles with very high catalytic activity, good supercapacitance and unique magnetic properties

Octahedron Co₃O₄ particles with very high catalytic activity, good supercapacitance, and unique magnetic properties.