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Magnetic Cobalt Oxide (CoO/Co₂O₃/Co₃${\text{O}}_4)$ and Nickel Oxide (NiO) Nanoparticles have been widely reported as heterogeneous catalysts for the preparation of derivatives of heterocycles. These are abundant, eco-friendly, relatively nontoxic and inexpensive catalysts. This review consists of the previous 10-year publications on the catalytic applications of Cobalt Oxide and Nickel Oxide Nanoparticles for the synthesis of heterocycles and their derivatives. Among the various metal oxide nanomaterials reported in the literature as catalyst materials for the synthesis of varied heterocycles and their derivatives, we have kept our focus on the key materials viz. Cobalt Oxide and Nickel Oxide Nanoparticles. In the conclusion part, we have also commented on the better options for the catalyst selection among the reports covered in this paper. This paper will definitely be useful for new researchers in the metal oxide nanomaterials-based catalytic applications for synthetic heterocyclic compounds.

We report imaging of human lung epithelial cells exposed to cobalt oxide (${Co}_3{\mathrm{O}}_4$) microparticles using three-dimensional (3D) particle-induced X-ray emission microcomputed tomography ($PIXE\mu CT$). The use of energy-selectable quasi-monochromatic low-energy X-rays generated via proton microbeam bombardment led to high-quality images. We also carried out two-dimensional (2D) micro-PIXE imaging. The 3D $PIXE\mu CT$ imaging data are complementary with 2D micro-PIXE images and the CT value ratios of the cells show that the strong absorption stems from ${Co}_3{\mathrm{O}}_4$. The 2D micro-PIXE analysis provides projection images of the elemental distribution, and this in combination with the 3D $PIXE\mu CT$ imaging revealed details of the internal distribution of ${Co}_3{\mathrm{O}}_4$, and hence provides insight into the mechanisms of ${Co}_3{\mathrm{O}}_4$ toxicity via intracellular perinuclear accumulation.

The cobalt oxide and boron-doped cobalt oxide thin films were produced by spray deposition method. All films were obtained onto glass and fluorine-doped tin oxide (FTO) substrates at 400${}^{\circ }$C and annealed at 550${}^{\circ }$C. We present detailed analysis of the morphological and optical properties of films. XRD results show that boron doping disrupts the structure of the films. Morphologies of the films were investigated by using a scanning electron microscopy (SEM). Optical measurements indicate that the band gap energies of the films change with boron concentrations. The electrochemical supercapacitor performance test has been studied in aqueous 6 M KOH electrolyte and with scan rate of 5 mV/s. Measurements show that the largest capacitance is obtained for 3% boron-doped cobalt oxide film.

Here, we report single step synthesis of hydrophobic and hydrophilic Fe₃O₄, ZnO, CoO and Y₂O₃:Eu nanoparticles via thermal decomposition of different organometallic complexes in oleylamine (OM) and tri(ethyleneglycol) (TREG) media, respectively. The crystal structure of the as-prepared nanoparticles is identified using X-ray diffraction, Fourier transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA). Morphology of the nanoparticles is determined by transmission electron microscopy (TEM) while the magnetic properties are measured using vibrating sample magnetometer (VSM). Thermolysis of appropriate precursors in OM and TREG medium are very capable of producing the highly dispresed hydrophobic and hydrophilic nanoparticles with diverse morphologies.

The structural, electronic and magnetic properties of the neutral and cationic cobalt oxide clusters (CoO)${}_n^q$ ($n=3-10$, $q=0,+1$) have been studied using a modified basin-hopping Monte Carlo (BHMC) algorithm refined by spin-polarized DFT. A systematic search of global minimum structures predicts new global minima of (CoO)${}_9^{0∕+}$ and reproduced other minima that are in excellent agreement with previous works. For most low-spin and high-spin states, the structural transition from planar-like to compact structure occurs at (CoO)${}_5^{0∕+}$, which is in contrast with the general notion that the structural changes at (CoO)${}_6^{0∕+}$. Supported by the results of the binding energy, second-order total energy difference, chemical hardness, chemical potential and HOMO-LUMO gap confirms the stability of (CoO)₄. Results of the spin magnetic moments for the global minima show that (CoO)₄ and (CoO)₈ spin configurations exhibit a fully antiferromagnetic (AFM) ordering, while (CoO)₉ spin displays the highest ferromagnetic (FM) ordering. Interestingly, elongation of Co–Co bond in (CoO)₄ causes O being polarized by the neighboring Co atoms that accordingly follows the Goodenough-Kanamori-Anderson rule of FM super-exchange coupling for the Co-O-Co structural rearrangement to 90^∘ ($D_{4h}$ structure) in order to accommodate the spin magnetic ordering changes. This rearrangement is a result of the valence band being shifted away from the Fermi level to lower energy causing high population of the spin-up density of state and leading to the asymmetrical polarization of the whole (CoO)₄ structure. As far as the dissociation energy surfaces are concerned, the first ever such surfaces are constructed corresponding to ${(\mathrm{\text{CoO}})}_n^q\to {(\mathrm{\text{CoO}})}_m^q+{(\mathrm{\text{CoO}})}_{(n-m)}$, which identify a complete dissociation pathway linking the cationic and neutral clusters and finally confirm (CoO)${}_4^{0∕+}$ as the most stable cluster compared to the rest.

In this paper, three-dimensional (3D) Co₃O₄ flower-like microspheres have been successfully synthesized via a facile ethylene glycol (EG)-mediated solvothermal method followed by calcination. The as-prepared flower-like precursors microspheres are formed from the assembly of 2D nanosheets in the presence of hexadecyltrimethylammonium bromide (CTAB). The flower-like architectures of the prepared precursors could be tailored by changing the amount of CTAB. Furthermore, when evaluated as a gas sensor, the obtained Co₃O₄ flower-like microspheres exhibit a good response and sensitivity toward ethanol gas, suggesting their promising potential for gas sensors application.

As one of the electrode materials for supercapacitor, Co₃O₄/graphene composite was mainly synthesized via two-steps method. Here, a facile one-pot method was used for Co₃O₄/graphene composite, and the performances of one-pot-synthesized Co₃O₄/graphene composite were carefully investigated. Liquid-phase exfoliation was used for graphene and the $D$-band/$G$-band ratio of liquid-phase exfoliated graphene was only 0.094, which indicated that the graphene had low defect density and enhanced electrical conductivity. Morphologies investigation of Co₃O₄/graphene composites indicated that Co₃O₄ nanoparticles with mean diameter of 14nm were uniformly anchored on graphene sheets. The facile one-pot method associated with liquid-phase exfoliated graphene induced Co₃O₄/graphene composite with enhanced specific capacitance of 392 F$\cdot$g${}^{-1}$ at a current density of 1 A$\cdot$g${}^{-1}$. The Co₃O₄/graphene composite also expressed relatively small internal resistance and diffusion resistance (0.36$\mathrm{\Omega }$ and 0.45$\mathrm{\Omega }$, respectively). Moreover, the synthesized Co₃O₄/graphene composite yielded excellent rate performances with only 9.5% capacitance loss when current density was increased by a factor of 10.

Developing a general, green and effective strategy to improve the hydrogen evolution reaction (HER) electrocatalyst is urgently needed but challenging. Herein, we report a novel conducting polymer/metal/metal oxide composite as HER catalyst prepared by a two-step strategy, in which the Au/Co₃O₄ is synthesized by a one-pot hydrothermal method, subsequently, cyclic voltammetry is employed to electropolymerize polythionine on the Au/Co₃O₄. It is demonstrated that the HER electrocatalytic activity of Au/Co₃O₄ is effectively improved by the coating polythionine layer. The optimal polythionine/Au/Co₃O₄ displays an excellent electrocatalytic ability towards HER with an overpotential of 168mV at $10\mathrm{\text{mA}}\cdot {\mathrm{\text{cm}}}^{-2}$ and low Tafel slope of 79mV$\cdot$dec${}^{-1}$ in 0.5M H₂SO₄, which is greatly superior to those of the Au/Co₃O₄ (an overpotential of 300mV at $10\mathrm{\text{mA}}\cdot {\mathrm{\text{cm}}}^{-2}$ and tafel slope of $157\mathrm{\text{mV}}\cdot {\mathrm{\text{dec}}}^{-1})$. Interestingly, the HER performance of N-doped reduced graphene (N-rGO) can also be significantly boosted by the coating polythionine layers, indicating the multifunctionality of polythionine in the enhancement of HER performance of nano electrocatalysts.