Nano-sized Co3O4 Research Articles

One-step combustion synthesis of high-performance nanosized Co3O4 and Ag-Co3O4 catalysts for propane total oxidation

Devising an effective strategy to refine the physicochemical properties of Co3O4 and tune the Ag-Co interaction is pivotal for developing superior Ag-Co3O4 catalysts targeting VOCs abatement. In this study, nanosized Co3O4 and Ag-Co3O4 (Ag content of 0.5–5.0 wt%) catalysts were prepared via a facile one-pot urea combustion method. The as-prepared catalysts were characterized using various techniques and their performance in propane total oxidation was evaluated. Compared to its counterpart obtained through the direct decomposition of cobalt nitrate, the nanosized Co3O4 exhibited a larger surface area, more oxygen vacancies, better reducibility, and thus superior propane oxidation activity. The addition of Ag can further enhance the catalytic performance by significantly improving the redox properties of Co3O4. The best performance was achieved with the catalyst 3.5 wt% Ag-Co3O4, which mineralized 90 % of propane into CO2 at 200 °C and exhibited excellent cycling stability and long-term durability. In addition, 3.5 wt% Ag-Co3O4 demonstrated high activity under various conditions, including high propane concentration (6000 ppm), high space velocity (160,000 mL g−1h−1), and high water content (10 vol%), making it a promising candidate for practical VOCs removal.

Synthesis and Electrochemical Properties of Co3O4@Reduced Graphene Oxides Derived from MOF as Anodes for Lithium-Ion Battery Applications

In this study, we utilized nano-sized Co3O4 and reduced graphene oxides (rGOs) as composite anode materials for Li-ion batteries. The Co3O4/C composite anode was derived from ZIF67 (Zeolitic Imidazolate Framework-67) and was wrapped in rGOs through precipitation. X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) were used to identify the crystal structure, phase purity, and surface morphology of the composite. The composition-optimized Co3O4/rGO/C composite anode exhibited a reversible capacity of 1326 mAh/g in the first cycle, which was higher than that of the Co3O4/C composite anode with a capacity of 900 mAh/g at a current density of 200 mA/g. Moreover, after 80 cycles, Co3O4/rGO/C maintained a capacity of 1251 mAh/g at the same current density, which was also higher than the bare Co3O4/C composite (595 mAh/g). Additionally, the Co3O4/rGO/C composite exhibited a good capacity retention of 98% after 90 cycles, indicating its excellent cycling stability and high capacity. Therefore, the Co3O4/rGO/C electrode has great potential as a promising anode material for Li-ion batteries.

Efficient electrocatalytic chlorine evolution under neutral seawater conditions enabled by highly dispersed Co3O4 catalysts on porous carbon

Chlorine evolution reaction (CER) is fundamental and critical for the conversion of Cl- to Cl2 in a seawater environment. However, the selectivity and electrocatalytic activity of non-precious metal-based catalysts in CER remain unsatisfactory. It is still a challenge to develop cost-effective and efficient CER electrocatalysts that can be produced in large scale. Herein, we proposed a metal-organic framework (ZIF-67) as a precursor for the synthesis of Co3O4 with a high specific surface area (SSA) and porous nano-sized. We then demonstrated for the first time that the porous nano-sized Co3O4 has high chlorine precipitation activity and stability. The potential (vs. Ag/AgCl) increased slightly from 1.225 to 1.258 V within 24 h of electrocatalytic reaction, and the Faraday efficiencies were higher than 80% at different current densities, indicating significant stability and selectivity. CER mechanism of the Co3O4 material under neutral seawater conditions was verified to be the Krishtalik mechanism by theoretical calculations.

Impacts of Nano-Sized Co3O4 on Ignition and Oxidation Performance of N-Decane and N-Decane/1,2,4-Trimethylbenzene Mixtures

ABSTRACT Nano-sized Co3O4 is an effective catalyst for fuel oxidation due to its high capacity of oxygen storage, and it is thus frequently applied in improving the oxidation performance of hydrocarbon fuels. In our present work, attempts were made to study the catalytic performance of Co3O4 for the oxidation of liquid fuels over a wide temperature range. Neat n-decane and n-decane/1,2,4-trimethylbenzene mixtures were chosen because they are typical liquid hydrocarbon fuels. The evidences from this study suggest that the temperatures of both fuel ignition and full conversion are significantly decreased by Co3O4 catalyst. CO2 is the only product detected in the catalytic oxidation, which also proves the complete oxidation of the liquid fuels. Furthermore, to explore the possible reaction pathways on the catalyst surface, temperature-dependent and time-dependent in situ DRIFTS were employed to identify surface species and analyze catalytic mechanism. Various surface intermediates including bidentate, monodentate carbonate species, carboxylate species and molecular adsorbed n-decane have been observed. The experimental results indicate that n-decane oxidation over Co3O4 proceeds via the Mars-van Krevelen mechanism where lattice oxygen plays a critical role in the fuel oxidation.

Enhanced catalytic properties of cobaltosic oxide through constructing MXene-supported nanocomposites for ammonium perchlorate thermal decomposition

The novel Co3O4@MXene nanocomposites (CMNs) were fabricated by a facile, green and highly tunable strategy without using any chemical modifiers. Various characterization results proved that nano-size Co3O4 was loaded on MXene nanosheets and CMNs exhibited a large specific surface area, especially for CMNs-3 (76.9 m2·g−1). The catalytic properties of CMNs for ammonium perchlorate (AP) thermal decomposition were investigated by a series of catalytic experiments. The results showed that the high-temperature decomposition (HTD) temperature and decomposition heat of AP mixed with CMNs-3 (2 wt%) could significantly decrease to 316.3 °C and remarkably increase to 1457.9 J·g−1, respectively. Moreover, the CMNs-3 could significantly reduce the apparent activation energy of AP by 49.1% and increase the value of reaction rate constant of AP by 482.0%. As for the effects of mass content of CMNs-3 on AP decomposition, the HTD temperature could decrease by as high as 128.0 °C with ratios of 10.0 wt% CMNs-3. It could be predicted that CMNs-3 with excellent catalytic performance would be a potential catalyst to promote AP decomposition and the synthesis method of CMNs-3 could provide an idea for the preparation of other metal oxide nanomaterials with high catalytic activity.

A novel nano-sized Co3O4@C catalyst derived from Co-MOF template for efficient Hg0 removal at low temperatures with outstanding SO2 resistance.

Co3O4 is a promising Hg0 removal catalyst for industrial application. Operating temperature and low sulfur resistance are two of the main problems that hinder its industrial application in Hg0 removal. Herein, a metal-organic framework (Co-BDC) was introduced as a sacrificial template to obtain the catalyst nano-sized Co3O4@C by calcination. Part of the organic ligands is carbonized during the calcination. Carbon wrapped Co3O4 and reduced metal agglomeration. The optimal Hg0 removal temperature of the existing cobalt oxide catalysts was always around 150 °C, but H2-TPR showed that the oxygen atoms on the Co3O4@C were more active than those on Co3O4, causing the Hg0 removal temperature window of Co3O4@C to shift to lower temperatures. The Hg0 removal efficiency of Co3O4@C could reach almost 100% even at 25 °C. In the meanwhile, Co3O4@C also showed a strong SO2 resistance at ambient temperature. Experimental results and characterization proved that SO2 did not compete with Hg0 on the surface of Co3O4 at low temperatures. On the contrary, it participated in the oxidation of Hg0. This is a great improvement for Co3O4 catalyst in Hg0 removal. It reduces the restrictions on the application of Co3O4 in Hg0 removal. Co3O4@C shows considerable potential as an Hg0 removal catalyst.

ZIF-67-derived Co3O4 hollow nanocage with efficient peroxidase mimicking characteristic for sensitive colorimetric biosensing of dopamine.

Co3O4 hollow nanocages (Co3O4 HNCs) were prepared by simple calcination with ZIF-67 as the precursor. Compared with ordinary nano-sized Co3O4, skeletal Co3O4 HNCs have a larger specific surface area and porosity, lead to better dispersion, which can expose more catalytic active sites, and obtain higher catalytic activity. Experiments indicate that Co3O4 HNCs are used as a catalyst to make H2O2 generate O2. At the same time, Co3O4 HNCs act as bridge to accelerate the electrons transfer from the chromogenic substrate 3,3',5,5'-tetramethylbenzidine (TMB) to the dissolved oxygen and efficiently obtain blue oxidized TMB (oxTMB) at low concentration of H2O2. Steady-state kinetic analysis shows a lower Km and a higher Vmax value than other materials, indicating its excellent affinity and high catalytic efficiency. Based on the inhibitory effect of dopamine (DA) on TMB oxidation in the system, a sensitive, visual colorimetric biosensing method is developed. The calibration curve of DA has a good linear response at both high and low concentrations. Compared with other system, it has the unique advantage of very low detection limit, while retaining a wide detection range, and realizes the accurate detection of actual samples with different concentrations.

Nanosized Co3O4–MoS2 heterostructure electrodes for improving the oxygen evolution reaction in an alkaline medium

Nano-sized Co3O4–MoS2/Ni foam heterostructure electrodes were fabricated using a vacuum kinetic spray technique with microparticles of Co3O4 and MoS2. The deposited films were utilized to study the oxygen evolution reaction (OER) at various MoS2 contents (25, 50, 75 wt.%). The surface state of the obtained heterostructure electrodes was characterized using various surfaces sensitive techniques such as scanning electron microscopy (SEM), Raman spectroscopy, and x-ray photoelectron spectroscopy (XPS). SEM images exhibited the fragmentation of the microparticles to smaller sizes in the nanoscale range. An analysis of the XPS spectra revealed the improvement in the cumulative synergy between the nanostructured Co3O4 and MoS2 in the heterostructured Co3O4–MoS2 electrocatalyst. We found that the gradual addition of MoS2 caused an enhancement in the OER activity due to improved charge transfer kinetics. Moreover, the heterostructure electrode with 75 wt.% MoS2 showed the highest activity with the lowest OER overpotential value of 298 mV at 10 mA··cm−2 and the smallest Tafel slope value of 46 mV·dec−1, as well as, 50 h OER stability at a current density of 50 mA·cm−2.

Self-reconstructed interlayer derived by in-situ Mn diffusion from La0.5Sr0.5MnO3via atomic layer deposition for an efficient bi-functional electrocatalyst

The development of efficient electrocatalyst is crucial to realize a sustainable energy conversion and storage system. Herein, we have applied atomic layer deposition (ALD) to depositing nano-sized Co3O4 onto La0.5Sr0.5MnO3 (LSM). Interestingly, an in-situ Mn diffusion from LSM during ALD process gives a self-reconstructed MnCo2O4 spinel interlayer between LSM and Co3O4. The X-ray absorption fine structure (XAFS) of LSM with 20 ALD cycles of Co3O4 (LSM-20-Co) showed a partially left-shifted white line of Co K-edge compared to the that of Co3O4, confirming the existence of the MnCo2O4 interlayer. Notably, the LSM-20-Co catalyst showed comparable Tafel slope for both the ORR (65 mV dec−1) and the OER (82 mV dec−1) comparing with the Pt/C (58 mV dec−1) and IrO2 (114 mV dec−1), along with stable cycling performance over 450 min for alkaline Zinc-air battery. This work provides the rational design strategy of self-constructed interlayer via ALD process for efficient bi-functional electrocatalyst.

Unique Double Carbon Protection Structured Co<sub>3</sub>O<sub>4</sub> Anode for Lithium Ion Battery

In this study, novel Carbon aerogel (CA)/Co3O4/Carbon (C) composites with a double protective structure are synthesized through a solvothermal method and in-situ polymerization. The morphology and structure are characterized by X-ray diffraction, scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), and Fourier transform infrared spectroscopy (FTIR). The loading content of active anode material Co3O4 in the composite is investigated by thermogravimetry, and the electrochemical properties of the composite are characterized by electrochemical impedance spectroscopy (EIS). The SEM results show that the nano-sized spherical Co3O4 particle is adhered to the inner Carbon aerogel (CA). The HRTEM result indicates the thickness of the prepared Carbon (C) up to 40 nm. Nano-sheet is coated on the surface of the Co3O4 particle. Compared with the pure Co3O4 anode materials, the Carbon aerogel (CA)/Co3O4/Carbon (C) composites have better transport kinetics for both electron and lithium-ion in EIS testing results, which may contribute to its higher specific capacity and higher first coulomb efficiency. Due to the unique structure of the composite material with double protection against the volume expansion of Co3O4 when charged, the Carbon aerogel (CA)/Co3O4/Carbon (C) composite material exhibits better cycle stability with a discharge capacity of 1180 mAh/g after 50 cycles. Therefore, the double protection strategy is verified as an effective method to improve the electrochemical performance of transition metal oxide with carbon composite as an anode material in lithium battery.

A bio-inspired nanofibrous Co3O4/TiO2/carbon composite as high-performance anodic material for lithium-ion batteries

A bio-inspired nanofibrous Co3O4/TiO2/carbon composite was fabricated using natural cellulose substrate (laboratory filter paper) as both the carbon source and the structural scaffold. Employing a surface sol–gel process to form a thin TiO2 gel layer coating on each cellulose nanofiber of the filter paper, the resulted composite sheet was successively carbonized in inert atmosphere to give a nanofibrous TiO2/carbon composite; afterwards, nano-sized Co3O4 particles (10–30 nm) were uniformly deposited onto the yielded composite fibers via a simple hydrothermal method, resulting in the Co3O4/TiO2/carbon hybrid. The ternary composite possessed a unique hierarchically three-dimensional porous structure which inherited precisely from the initial filter paper. This special structure with the internal conductive carbon fiber and the external nano-sized Co3O4 particles offered the nanocomposite with an excellent electrochemical performance as anodic material for lithium-ion batteries. The optimal sample with a Co3O4 mass content of 50.6% delivered an initial discharge capacity of 1239 mAh g−1 at a current density of 100 mA g−1, which was far exceeded the theoretical capacity of Co3O4. The extra capacity is ascribed to the additional lithium storage sites provided by the large specific surface area of the composite, and the formation of the solid electrolyte interface (SEI) layer in the initial discharge process causing a large consumption of Li+ which results in some irreversible capacity. And after 200 discharge/charge cycles, a high reversible capacity of 764 mAh g−1 was maintained, which is higher than most of the Co3O4/carbon hybrid materials reported. This work provided a simple and efficient strategy for designing and preparing nanoscale metal-oxide/carbon composite material with considerable potential in energy storage and conversion.

Synthesis of highly active Cobalt catalysts for low temperature CO oxidation

Abstract Cobalt-oxide catalysts has shown a huge potential for CO oxidation in a catalytic converter for their high thermal stability and tailoring flexibility. A novel route of reactive calcination (RC) of Co-salts (oxalate = O, oxalate synthesize by reactive grinding = ORG, carbonate basic = C, acetate = A, nitrate = N) for the preparation of highly active catalysts was studied. The route concerned feeding a low concentration of chemically reactive CO–Air mixture over the cobalt salts at a low temperature. The RC of the precursor produced cobalt species (Co3O4 and CoO) in thermodynamic equilibrium, with the major nano-size Co3O4 phase having a large surface area, while applying in a stagnant air at 400 °C resulted in a CoO phase of better crystallites with the poorer surface area. The amazing performances of novel catalysts over conventional ones (obtained by calcination of the precursors in stagnant air and flowing air) in CO oxidation was associated with the presence of Co3O4 and its unusual morphology as evidenced by XRD, SEM-EDX, XPS and FTIR characterization. The catalysts obtained by RC of various precursors showed activities for CO oxidation in the following order: Cat-ORGr>Cat-Or>Cat-Cr> Cat-Ar>Cat-Nr between (60–130 °C) while the traditional route of catalysts followed the same activity order but at the higher temperatures (75–170 °C). Further, the activity order of the catalysts obtained by various calcination conditions was as follows: RC> flowing-air>stagnant-air. The current research focused highly active Co3O4 catalysts would be applied in wide range of reactions for commercial importance, as well as those associated with environmental cleanliness and production of clean energy sources etc.

Co(II, III) Hydroxides Supported on Zeolite Acting as an Efficient and Robust Catalyst for Catalytic Water Oxidation with Ru(bpy)33+

A novel highly efficient and stable for many cycles catalyst (1% Со-ZSM-5(17)) for water oxidation was developed using the method of polycondensation for stabilization of oxo/hydroxo complexes of cobalt (II, III) and nanosize Co3O4 in zeolite channels. In a weak-alkaline medium (pH 8.0, 9.2, 10.0) in the presence of a one-electron oxidant (Ru(bpy)33+), the catalyst provided the yield of oxygen as high as 56, 73 и 78% of the stoichiometric quantity, respectively. Catalysts based on ZSM-5 zeolite exhibited higher catalytic activity as compared to the catalysts based on the MOR, BEA, Y. Inspection of the electron states of cobalt in the Co-containing zeolite-based catalysts using TPR-H2 and UV–Vis DR techniques revealed that α-Co(OH)2-like polynuclear clusters and hydrocomplexes stabilized in the zeolite channels were most active to catalytic oxidation of water, while their transformation to Co3O4-like clusters/nanoparticles and Co2+ oxocomplexes, respectively, during thermal treatment led to some decrease in the catalyst efficiency. Coarsening of Co3O4-like clusters/nanoparticles caused the further decrease in the system efficiency. The minimal activity was observed with the catalysts containing predominantly isolated Co2 +Oh ions. The result obtained indicates a kind of at least polynuclear structure of the catalytically active center ConOx, where n > 2.

Zinc/Nickel-Doped Hollow Core-Shell Co3 O4 Derived from a Metal-Organic Framework with High Capacity, Stability, and Rate Performance in Lithium/Sodium-Ion Batteries.

Transition-metal oxides are one of the most promising anode materials for energy storage in lithium- and sodium-ion batteries (LIBs and NIBs, respectively). To improve the electrochemical performance of metal oxides (e.g., Co3 O4 ), such as capacity and cyclability, a convenient strategy (with a metal-organic framework as a template) is introduced to generate Zn- or Ni-doped Co3 O4 . The obtained hollow core-shell nanosized Co3 O4 (denoted as Zn/Ni-Co-Oxide) derived from pyrolyzing zinc or nickel co-doped ZIF-67 (Co(mIm)2 ; mIm=methylimidazole) shows a drastically enhanced capacity of 1300 mAh g-1 at a high current density of 5000 mA g-1 , compared with that of pristine cobalt oxide (800 mAh g-1 ) in LIBs. A zinc-doped Zn-Co-Oxide demonstrates a stable capacity of 1600 mAh g-1 at 1000 mA g-1 for 700 cycles and an excellent performance in full coin cells (cycled with LiNi0.5 Co0.3 Mn0.2 O2 ). Moreover, NIB tests show a stable capacity of 300 mAh g-1 for more than 250 cycles.

Promotion of low temperature oxidation of toluene vapor derived from the combination of microwave radiation and nano-size Co3O4

Co3O4 nano-particles were prepared deriving from the complexation reaction of ultrasonic treatment at room temperature and atmospheric pressure for low temperature oxidation of toluene under microwave radiation. Differences of catalytic performance of nano- and bulk Co3O4 under microwave radiation and conductive heating were investigated using the removal rate and the mineralization rate as assessment criteria. The result shows that the low temperature oxidation of toluene was promoted apparently by the combination of microwave radiation and nano-Co3O4. For effects of microwave radiation, maximum increases of removal rate and mineralization rate are 4.76 and 95.93 times respectively. FTIR spectra of the surface of the post-reaction catalyst shows that the amount of OH and H2O is larger under microwave heating and residual toluene or by-product of the incomplete decomposition is detected under conductive heating, which the results may be explained by the hypothesis of “hot spots” induced by microwave radiation. For effects of the nano-Co3O4 material properties, maximum increases of removal rate and mineralization rate are 1.84 and 220.9 times, respectively. Though XRD patterns of both nano- and bulk Co3O4 present a pure phase of Co3O4, catalytic activity of nano-Co3O4 is higher, because of smaller the particle size distribution, larger the surface area, higher levels of the Co2+/Co3+ and the Olatt/Oads, which may be due to reciprocal action between complexation reaction and ultrasonic treatment. Moreover, for integrated advantages of both microwave radiation and nano-Co3O4, maximum increases of removal rate and mineralization rate are 3.54 and 220.9 times, respectively.

Sonochemical synthesis of porous nanowall Co3O4/nitrogen-doped reduced graphene oxide as an efficient electrode material for supercapacitors

A composite of nitrogen-doped reduced graphene oxide (NRGO) with nano-sized Co3O4 was prepared using a sonochemical method. The prepared Co3O4/NRGO samples were assessed through field emission scanning electron microscopy, X-ray diffraction, X-ray photoemission spectroscopy, and Raman spectroscopy to obtain chemical, structural and morphological information. The resulting composite (Co3O4/NRGO) was evaluated as a candidate for building supercapacitor electrodes. In this line the electrochemical performance of the tested materials were studied through cyclic voltammetry, galvanostatic charge/discharge, electrochemical impedance spectroscopy, and continues cyclic voltammetry. The electrochemical tests were performed using 3 M KCl solutions as the electrolyte. The evaluations on Co3O4/NRGO-based electrodes revealed the material to have a specific capacitance (SC) of 763 F g−1 at a scan rate of 2 mV s−1, an energy density (ED) of 138 W h kg−1, and a high rate capability. Continues cyclic voltammetry evaluations using Co3O4/NRGO-based electrodes proved the electrodes to be capable of maintaining almost 98.9% of its initial SC after 4000 cycles. Based on the electrochemical evaluations the synthesized nanocomposite was proven to possess the merits of both of its ingredients.

Synthesis, characterization, and biological activity of some novel Schiff bases and their Co(II) and Ni(II) complexes: A new route for Co3O4 and NiO nanoparticles for photocatalytic degradation of methylene blue dye

Six novel Co(II) and Ni(II)-triazole Schiff base complexes have been successfully synthesized by refluxing the prepared triazole Schiff bases with CoCl2·6H2O or NiCl2·6H2O. The Schiff base ligands were prepared through condensation of 3-R-4-amino-5-hydrazino-1,2,4-triazole with dibenzoylmethane [RH, CH3, and CH2CH3; namely, L1, L2, and L3, respectively]. The prepared Co(II) and Ni(II) complexes have been identified using elemental analysis, FT-IR, UV–Vis, magnetic moment, conductivity, and thermal analysis. On the basis of the conductance results, it was concluded that all the prepared complexes are nonelectrolytes. Interestingly, the prepared Co(II) and Ni(II) complexes were employed as precursors for producing of Co3O4 and NiO nanoparticles, respectively. The produced nanostructures have been identified by XRD, HR-TEM, FT-IR and UV–Vis spectra. The produced nanoparticles revealed good photocatalytic activity for the degradation of methylene blue dye under UV illumination in presence of hydrogen peroxide. The percent of degradation was estimated to be 55.71% in 420.0 min and 90.43% in 360.0 min for Co3O4 and NiO, respectively. Moreover, the synthesized complexes, nano-sized Co3O4, and NiO products have been examined, employing modified Bauer- Kirby method, for antifungal (Candida albicans and Aspergillus flavus) and antibacterial (Staphylococcus aureus and Escherichia coli) activities.

Dispersion–precipitation synthesis of highly active nanosized Co3O4 for catalytic oxidation of carbon monoxide and propane

Nanosized Co3O4 catalyst was prepared through a dispersion–precipitation method involving a reaction between wet cobalt hydroxide and acetic acid, which forms a colloidal dispersion, and subsequent dilution, which destabilizes and precipitates the colloidal particles. The catalyst had a particle size of 5–15nm and a specific surface area of 82m2/g. Compared with the analogue prepared by conventional alkali-induced precipitation method, the nanosized catalyst was more reducible and contained a larger amount of active surface oxygen species, as revealed by experiments using temperature-programmed reduction in hydrogen and temperature-programmed desorption of oxygen. The oxygen species could contribute to the observed higher activity in the catalytic oxidation of carbon monoxide and propane. In addition, a kinetics study revealed that the apparent activation energies for carbon monoxide and propane oxidation over the catalyst were 34.0 and 49.5kJ/mol, respectively, much lower than those over the analogue (54.7 and 71.1kJ/mol, respectively). Furthermore, a long-term test (76h) showed that the nanosized catalyst is highly stable.

Synthesis of Co(II) and Cr(III) salicylidenic Schiff base complexes derived from thiourea as precursors for nano-sized Co3O4 and Cr2O3 and their catalytic, antibacterial properties

This study focuses on the synthesis of Co(II) and Cr(III) Schiff base complexes obtained from thiourea. The complexes were synthesized by template method and characterized by elemental analysis (CHNS), FT-IR, UV–vis spectroscopy, conductivity measurement and magnetic moment. The spectroscopic studies suggested the octahedral and square-pyramidal structures for Co(II) and Cr(III) complexes, respectively. Then the complexes were used as precursors for preparation of Co3O4 and Cr2O3 nanoparticles via solid-state thermal decomposition without using a catalyst, toxic solvent, template or surfactant and complicated equipment, which makes it efficient, one-step, simple and environment-friendly. The chemical structure of the metal oxides is studied by FT-IR, XRD and SEM. To investigate the applications of the synthesized complexes, in the next step, the complexes were screened for antibacterial activity against clinically important bacteria such as Escherichia coli, Staphylococcus aureus, and Bacillus subtilis. The Cr(III) and Co(II) complexes showed good biological activity against all the tested bacteria. Also, the catalytic activities of the complexes were studied in toluene using non-toxic hydrogen peroxide as the oxidant. The results showed that Co(II) complex has catalytic activity for oxidation of toluene, but Cr(III) complex did not show any catalytic activity.

Production of Nano-Sized Co<sub>3</sub>O<sub>4</sub> by Pyrolysis of Organic Extracts

The most promising application field of materials based on nano-sized Co3O4 is catalysis. The method of production is one of the factors, which greatly affects the catalytic activity of Co3O4 catalysts. The aim of this research is to study possibilities of a new promising extractive-pyrolytic method (EPM) for the production of Co3O4 nanopowders and silica- and ceria-supported Co3O4 nanocomposites. Solutions of cobalt hexanoate in hexanoic acid and trioctylammonium tetrachlorocobaltate in toluene preliminary produced by solvent extraction were used as precursors. The precursors’ thermal stability, phase composition, morphology and the magnetic properties of the final products of pyrolysis were studied. The performed investigations have shown that the mean size of the Co3O4 crystallites in the materials produced by the EPM varies from amorphous to 55 nm due to the production conditions.