A novel kind of self-assembled graphene quantum dots-Co3O4 (GQDs-Co3O4) nanocomposite was successfully manufactured through a hydrothermal approach and used as an extremely effectual oxygen evolution reaction (OER) electrocatalyst. The characterization of morphology with scanning electron microscopy (SEM) and transmission electron microscopy (TEM) showed that Co3O4 nanosheets combined with graphene quantum dots (GQDs) had a new type of hexagonal lamellar selfassembly structure. The GQDs-Co3O4 electrocatalyst showed enhanced electrochemical catalytic properties in an alkaline solution. The start potential of the OER was 0.543 V (vs SCE) in 1 M KOH solution, and 0.577 V (vs SCE) in 0.1 M KOH solution correspondingly. The current density of 10 mA cm− 2 had been attained at the overpotential of 321 mV in 1 M KOH solution and 450 mV in 0.1 M KOH solution. Furthermore, the current density can reach 171 mA cm− 2 in 1 M KOH solution and 21.4 mA cm− 2 in 0.1 M KOH solution at 0.8 V. Moreover, the GQDs-Co3O4 nanocomposite also maintained an ideal constancy in an alkaline solution with only a small deterioration of the activity (7%) compared with the original value after repeating potential cycling for 1000 cycles.

The disposal of organic pollutants is one of the important research topics. Some of the studies in this field are based on the degradation of organic pollutants with a catalytic agent. The cobalt tetraoxide/peroxymonosulfate system is an important catalytic system used for the radical degradation of organic pollutants. To increase the catalytic efficiency of such reactions, graphitization of activated carbon used as a support solid and nitrogen doping to the carbon structure are commonly used methods. In this study, cobalt tetraoxide production, N-doping and graphitization were carried out in a single step by heat treatment of activated carbon doped with the phthlocyanine cobalt (II) complex. The catalytic performance of the catalyst/ peroxymonosulfate system was investigated by changing the pH, catalyst, and PMS concentration parameters on rhodamine B and 1,3,5 trichlorophenol, which were used as models. It was seen that the catalysts had 97% activity on rhodamine B in 16 min and 100% on 1,3,5 trichlorophenol in 6 min. It was observed that the catalysts continued to show high catalytic activity for five cycles in reusability studies and had a very low cobalt leaching rate. These results are in good agreement with previously published studies. In line with these results, the synthesized N-doped graphitic carbon/Co3O4 catalyst can be used as an effective catalyst for wastewater treatments.

Herein, a new and generic strategy has been proposed to introduce uniformly distributed graphitic carbon into the nanostructured metal oxide. A facile and generic synthetic protocol has been proposed to introduce uniformly distributed conducting graphitic carbon into the Co3O4 nanoparticles ( Co3O4 NPs@graphitic carbon). The prepared Co3O4 NPs@graphitic carbon has been drop casted onto the portable screen-printed electrode (SPE) to realize its potential application in the individual and simultaneous quantification of toxic Pb(II) and Cd(II) ions present in aqueous solution. The proposed Co3O4 NPs@graphitic carbon-based electrochemical sensor exhibits a wide linear range from 0 to 120 ppb with limit of detection of 3.2 and 3.5 ppb towards the simultaneous detection of Pb(II) and Cd(II), which falls well below threshold limit prescribed by WHO.

The hydrogen reduction behavior of the CuO-Co3O4 powder mixture for the synthesis of the homogeneous Cu-15at%Co composite powder has been investigated. The composite powder is prepared by ball milling the oxide powders, followed by a hydrogen reduction process. The reduction behavior of the ball-milled powder mixture is analyzed by X-ray diffraction (XRD) and temperature-programmed reduction at different heating rates in an Ar-10%H2 atmosphere. The scanning electron microscopy and XRD results reveal that the hydrogen-reduced powder mixture is composed of fine agglomerates of nanosized Cu and Co particles. The hydrogen reduction kinetics is studied by determining the degree of peak shift as a function of the heating rate. The activation energies for the reduction of the oxide powders estimated from the slopes of the Kissinger plots are 58.1 kJ/mol and 65.8 kJ/mol, depending on the reduction reaction: CuO to Cu and Co3O4 to Co, respectively. The measured temperature and activation energy for the reduction of Co3O4 are explained on the basis of the effect of pre-reduced Cu particles.

Octahedral Co3O4/carbon nanofiber (CNF) composites are fabricated using electrospinning and hydrothermal methods. Their morphological characteristics, chemical bonding states, and electrochemical properties are used to demonstrate the improved photovoltaic properties of the samples. Octahedral Co3O4 grown on CNFs is based on metallic Co nanoparticles acting as seeds in the CNFs, which seeds are directly related to the high performance of DSSCs. The octahedral Co3O4/CNFs composites exhibit high photocurrent density (12.73 mA/m2), superb fill factor (62.1 %), and excellent power conversion efficiency (5.61 %) compared to those characteristics of commercial Co3O4, conventional CNFs, and metallic Co-seed/CNFs. These results can be described as stemmnig from the synergistic effect of the porous and graphitized matrix formed by catalytic graphitization using the metal cobalt catalyst on CNFs, which leads to an increase in the catalytic activity for the reduction of triiodide ions. Therefore, octahedral Co3O4/CNFs composites can be used as a counter electrode for Pt-free dye-sensitized solar cells.

In this study we aimed to examine the co-doping effects of 1/6mol% Co3O4 and 1/4mol% Cr2O3 (Co:Cr=1:1)on the reaction, microstructure, and electrical properties, such as the bulk defects and the grain boundary properties, of ZnO-Bi2O3-Sb2O3 (ZBS; Sb/Bi=0.5, 1.0, and 2.0) varistors. The sintering and electrical properties of Co,Cr-doped ZBS, ZBS(CoCr)varistors were controlled using the Sb/Bi ratio. Pyrochlore (Zn2Bi3Sb3O14), α-spinel (Zn7Sb2O12), and δ-Bi2O3 were formed inall systems. Pyrochlore was decomposed and promoted densification at lower temperature on heating in Sb/Bi=1.0 by Cr ratherthan Co. A more homogeneous microstructure was obtained in all systems affected by α-spinel. In ZBS(CoCr), the varistorcharacteristics were improved (non-linear coefficient, α=20~63), and seemed to form Zni..(0.20eV) and Vo.(0.33eV) asdominant defects. From impedance and modulus spectroscopy, the grain boundaries were found to be composed of anelectrically single barrier (0.94~1.1eV) that is, however, somewhat sensitive to ambient oxygen with temperature. The phasedevelopment, densification, and microstructure were controlled by Cr rather than by Co but the electrical and grain boundaryproperties were controlled by Co rather than by Cr.

Co3O4, Al2O3 and Co3O4/Al2O3 mesoporous powders were prepared by a sol-gel method with starting matierals ofaluminum isopropoxide and cobalt (II) nitrate. A P123 template is employed as an active organic additive for improving thespecific surface area of the mixed oxide by forming surfactant micelles. A transition metal cobalt oxide supported on aluminawith and without P123 was tested to find the most active and selective conditions as a heterogeneous catalyst in the reactionof styrene epoxidation. A bBlock copolymer-P123 template was added to the staring materials to control physical and chemicalproperties. The properties of Co3O4/Al2O3 powder with and without P123 were characterized using an X-ray diffractometer(XRD), a Field-Emission Scanning Electron Microscope (FE-SEM), a Bruner-Emmertt-Teller (BET) surface analyzer, and 27AlMAS NMR spectroscopy. Powders with and without P123 were compared in catalytic tests. The catalytic activity and selectivitywere monitored by GC/MS, 1H, and 13C-NMR spectroscopy. The performance for the reaction of epoxidation of styrene wasobserved to be in the following order: [Co3O4/Al2O3 with P123-1173 K>Co3O4/Al2O3 with P123-973 K>Co3O4-973K>Co3O4/Al2O3-973 K>Co3O4/Al2O3 with P123-1473 K>Al2O3-973 K]. The existence of γ-alumina and the nature of thesurface morphology are related to catalytic activity.

We synthesized porous Co3O4/RuO2 composite using the soft template method. Cetyl trimethyl ammonium bromide (CTAB) was used to make micell as a cation surfactant. The precipitation of cobalt ion and ruthenium ion for making porosity in particles was induced by OH- ion. The porous Co3O4/RuO2 composite was completely synthesiszed after anealing until 250˚C at 3˚C/min. From the XRD ananysis, we were able to determine that the porous Co3O4/RuO2 composite was comprised of nanoparticles with low crystallinity. The shape or structure of the porous Co3O4/RuO2 composite was studied by FE-SEM and FE-TEM. The size of the porous Co3O4/RuO2 composite was 20~40 nm. From the FE-TEM, we were able to determine that porous cavities were formed in the composite particles. The electrochemical performance of the porous Co3O4/RuO2 composite was measured by CV and charge-discharge methods. The specific capacitances, determined through cyclic voltammetry (CV) measurement, were ~51, ~47, ~42, and ~33 F/g at 5, 10, 20, and 50 mV/sec scan rates, respectively. The specific capacitance through charge-discharge measurement was ~63 F/g in the range of 0.0~1.0 V cutoff voltage and 50 mAh/g current density.

Sr 페라이트 자석의 자기적 특성을 향상시키기 위하여 화학량론적 조건인 SrFe 12O19 [SrM]에서 11.7CoSrFe0.3 O19[Co0.3 -SrM]/ 및 Sr0.7 La0.3F e11.7 Co0.3 O19 /[(La-Co)0.3-SrM] 조성으로 혼합후 공기중 하소를 실시하여 하소분의 특성을 조사하였고, 소결조제와 함께 미분쇄한 후 공기 중에서 소결하여 페라이트 자석을 제조한 후 자기특성 변화를 조사하였다. 화학량론적인 조성에서 (La-Co)0.3-SrM 조성으로 원소치환을 실시한 하소분말을 사용하여 제조한 페라이트 자석의 소결특성은 포화자화 (Ms ) 71.08 emu/g, 보자력 (iHC ) 4.38 kOe 및 잔류자속밀도 (Br ) 4.18 kG, 보자력 (iHC ) 4.35 kOe, 최대에너지적(BHmax ) 4.3 MGOe으로 화학량론적인 조건에 비해 B Hmax가 10% 이상 더 큰 자기특성값을 나타내었다.나타내었다.다.

TiO2- and SiO2-supported Co3O4, Pt and Co3O4-Pt catalysts have been studied for CO and C3H8 oxidations at temperatures less than 250℃ which is a lower limit of light-off temperatures to oxidize them during emission test cycles of gasoline-fueled automotives with TWCs (three-way catalytic converters) consisting mainly of Pt, Pd and Rh. All the catalysts after appropriate activation such as calcination at 350℃ and reduction at 400℃ exhibited significant dependence on both their preparation techniques and supports upon CO oxidation at chosen temperatures. A Pt/TiO2 catalyst prepared by using an ion-exchange method (IE) has much better activity for such CO oxidation because of smaller Pt nanoparticles, compared to a supported Pt obtained via an incipient wetness (IW). Supported Co3O4-only catalysts are very active for CO oxidation even at 100℃, but the use of TiO2 as a support and the IW technique give the best performances. These effects on supports and preparation methods were indicated for Co3O4-Pt catalysts. Based on activity profiles of CO oxidation at 100℃ over a physical mixture of supported Pt and Co3O4 after activation under different conditions, and typical light-off temperatures of CO and unburned hydrocarbons in common TWCs as tested for C3H8 oxidation at 250℃ with a Pt-exchanged SiO2 catalyst, this study may offer an useful approach to substitute Co3O4 for a part of platinum group metals, particularly Pt, thereby lowering the usage of the precious metals.