3D Cobalt Research Articles

Harnessing 3D Porous Cobalt Oxide Nanoflakes Grown on Metal for Exceptional Adhesion between Aluminum Surfaces and the Epoxy Matrix

The developments in the automotive and aerospace sectors require alternative structures to metals for diverse applications; therefore, lightweight polymer–metal hybrid composites with outstanding mechanical characteristics are synthesized. Herein, the modern nanoperfusion technology, which involves the in situ growth of 3D porous cobalt oxide nanoflakes (Co3O4 NFs) on the porous aluminum surface, is used. A rough surface with corresponding surface porosities of 21, 48.1, and 49.8% can be produced by anodization of aluminum at 8, 10, and 12 V, respectively. The samples anodized at 10 V are selected as a structure for the growth of 3D Co3O4 NFs at different hydrothermal temperatures (90, 120, and 160 °C). The bond strength and modulus of the toughness of the sample combining aluminum and 3D Co3O4 NF growth at 120 °C exhibit a substantial bonding strength, reaching a value of 14.27 MPa and 3.56 kJ m−3, respectively. The porous nature of the manufactured cobalt oxide nanoflakes allows the epoxy to penetrate, which enhances the bonding strength and thus improves the mechanical properties of the manufactured joints.

Enhancement in Magnetic and Magnetocaloric Properties of CoFe2O4 Nanofibers at Lower Temperatures

AbstractThis research paper investigates new and first insights into the magnetic and magnetocaloric properties of one-dimensional (1D) cobalt ferrite CoFe2O4 (CFO) nanofibers (NFs) fabricated using a sol–gel-based electrospinning technique, focusing in particular on their behavior at low temperatures for specific applications. The microstructural, structural, magnetic, and magnetocaloric properties of the calcined CFO NFs were explored. The microstructure of the NFs, with an average diameter of 210 nm, was examined by scanning and transmission electron microscopy (SEM, TEM). The x-ray diffraction (XRD) of the CFO NFs showed a pure cubic close-packed (ccp) spinel crystalline structure with the Fd$$\overline{3}$$ 3 ¯ m space group. The Raman spectroscopic studies further confirm the cubic inverse spinel phase. The magnetic properties were explored as a function of temperature, ranging from 10 K to 300 K, and ferromagnetic behavior was observed with the highest saturation magnetization of 75.87 emu/g and coercivity of 723 Oe at room temperature. The variation of the magnetic entropy was measured indirectly using the Maxwell approach with an increasing magnetic field. A maximum of $$\left| {\Delta S} \right|$$ Δ S = 1.71 J/K was reached around 32 K. At 180 K, the associated adiabatic temperature change, ΔTmax, was 0.93 K, with a large RCP value of 7.58 J/kg, which is reasonably high for the corresponding nanoparticles (NPs). This work suggests that 1D CFO NFs offer a promising route for the production of nanostructured magnetic materials, potentially impacting various electronic and electromagnetic device applications at low temperatures.

Integration of vanadium diphosphide with 2D cobalt phosphide architected as an extensible redox active positrode for alkaline supercapacitor

Metal phosphides in the form of rationally constructed two-dimensional (2D) nanosheets hold significant promise as versatile materials for energy storage applications. This study introduces a novel hybrid supercapacitor electrode, composed of a binder-free vanadium phosphide integrated cobalt phosphide (VP@CP) on a nickel foam substrate. The fabrication process involves the hydrothermal growth of Co2(OH)2BDC (BDC- 1,4-benzenedicarboxylate) nanosheets on a Ni-foam substrate (CMF-Ni), followed by the deposition of VO2 on CMF nanosheets (VO@CMF-Ni) using chronoamperometry and phosphorization of the VO@CMF-Ni to yield VP@CP-Ni nanosheets. Particularly, the density functional theory (DFT) results show that the VP2 integrated Co2P sample provides metallic behavior and low adsorption energy of OH− ions, resulting in improved electrochemical redox process. These bimetallic phosphides exhibit outstanding properties, including enhanced pathways for rapid ion transport and storage, increased electronic conductivity, and expanded electroactive regions facilitating the faradaic charge storage process. Due to the presence of vanadium and cobalt coupled sites, the fabricated VP@CP-Ni electrode was able to attain a maximum areal capacity (CAR) of 971 mA h cm−2 at 6 mA cm−2. Additionally, the fabricated hybrid device (HDC) exhibits an impressive specific energy (SE) of 30.9 Wh kg−1 at a specific power (SP) of 1344 W kg−1, and excellent cyclic durability. These remarkable results stimulate the exploration of such possible 2D VP@CP-Ni nanosheets with promising charge storage electrode capabilities to develop a future era of energy storage devices.

Two new 3D cobalt(II) coordination polymers constructed by semi-rigid carboxylic acid ligand: Syntheses, structures and properties

Two novel coordination polymers, {[Co2(L)(H2O)5]·H2O}n (1), and {[Co5(L)2(H2O)6(μ3-OH)2]·2C3H7NO·2H2O}n (2) (H4L = 3, 3′, 5, 5′-diphenyl ether tetracarboxylic acid, C16H10O9) have been synthesized by assembling semi-rigid aromatic polycarboxylic acids with transition-metal cobalt salts, and structurally characterized by elemental analysis, thermogravimetric analysis, IR spectrum, powder X-ray diffraction, and single crystal X-ray diffraction analysis. Structural analysis showed both the L ligands in CP 1 and CP 2 were regarded as 4 connection points, while the binuclear clusters in CP 1 and the pentanuclear clusters in CP 2 were regarded as 4 connection points and 8 connection points, respectively. Finally, both CP 1 and CP 2 were 3D network structures connected by two nodes (4, 4-connected for CP 1 and 4, 8-connected for CP 2). In addition, temperature-dependent susceptibilities have been measured in the range of 2 to 300 K, indicating that both CP 1 and CP 2 have antiferromagnetic coupling between adjacent Co(II) ions. Finally, Electrochemical experiments show that the CP 1 and CP 2 have good electrochemical behaviors.

Pt atomic clusters/MoS2 nanosheets/Co-doped hollow carbon nanofibers for high-current–density alkaline hydrogen production

The application of layered molybdenum disulfide (MoS2) in catalytic hydrogen production has attracted great interest, while their catalytic properties are limited by poor electron conductivity and a few catalytically active sites. In this work, we demonstrated a highly active electrocatalyst for large-scale hydrogen production, consisting of two-dimensional (2D) Pt-MoS2 nanosheets along one-dimensional (1D) cobalt nanoparticle integrated carbon hollow nanofibers (Co@CHNF). The as-prepared Pt-MoS2-Co@CHNF had a large specific surface area (44.5 m2 g−1). X-ray photoelectron spectrometer (XPS) and spherical aberration corrected transmission electron microscope (AC-STEM) demonstrated that Pt atomic clusters (Pt ACs) were doped on MoS2 nanosheets by thermodynamically induced spontaneous interfacial redox between MoS2 and H₂PtCl₆. The Pt-MoS2-Co@CHNF based catalysts exhibited an overpotential as low as 91 mV for 10 mA cm−2 and 258 mV for 200 mA cm−2 in 1 M KOH electrolyte, and there is no significant floating for catalytic active with 14 h continuous operation, which demonstrates its excellent long-term operation durability, significantly superior to the previously reported state-of-the-art Co-based or Mo-based catalysts. In particular, the self-supporting binder-free Pt-MoS2-Co@CHNF catalyst-based electrode showed an ultra-high current density of 500 mA cm−2 at a low overpotential of 301 mV, without any decrease after 24 h operation at 500 mA cm−2 in 1 M KOH seawater electrolyte, representing a great potential for large-scale seawater hydrogen production.

Construction of 3D spinel binary metal oxide flower decorated 1D halloysite nanotube electrocatalyst for the selective detection of arsenic drug pollutant roxarsone

Heavy metals, including arsenic (As), are categorized as a Group I toxic carcinogen and pose significant threats to the environment and habitats. Roxarsone (RXN) is an organoarsenic antibiotic drug commonly employed as a veterinary curative agent and growth promoter for poultry. Due to its widespread use, it substantially contributes to the accumulation of As in humans and ecosystems. Therefore, it is essential to monitor this potential drug in various real-world samples with high accuracy. Consequently, we have designed 3D zinc cobalt oxide (ZCO) with a 1D halloysite nanotube (HNT) based electrochemical sensor. The functional and morphological features of the electrocatalysts were evaluated with numerous analytic methods. The electrocatalytic property was investigated with different voltammetric measurements. Based on the outcomes, our ZCO/HNT-modified sensor displayed good linear ranges (0.01 to 127 μM and 127 μM to 1147 μM), low detection (1.6 nM), and quantification (5.2 nM) limits, optimal sensitivity (0.465 μA μM−1 cm−2), good selectivity, remarkable performance, and good stability results. Further, this sensor was applied to monitor RXN in various real-world samples and consequently, obtained the well-resolved results. Hence, our ZCO/HNT is an efficacious electrocatalyst for the precise detection of RXN.

New robust 2D cobalt (II) coordination polymer as an effective turn-on luminescent sensor to detect Tb3+ and pefloxacin

It is necessary to employ highly sensitive and rapid detection of antibiotics and heavy ions in the environment. A mixed-ligands ternary Co (II) coordination polymer containing new L ligands, {[Co(L)(mip)(H2O)]·2H2O}n (1), (L = 2,2′-bis-(2-pyridin-3-yl-vinyl)-3H,3′H-[5,5]bibenzoimidazole, H2mip= 5-methylisophthalic acid) was synthesized under solvothermal condition. Compound 1 displays a sql 2D layer with the point symbol of {44.62}. Compound 1 owns excellent thermal and pH stability and can effectively sensitize the luminescence of Tb3+ ions through the “antenna effect”. Compound 1 can serve as luminescent probe for detecting pefloxacin and Tb3+ with low detection limits. Especially Compound 1 is the first turn-on sensor for the detecting Tb3+ ions and pefloxacin via fluorescence enhancement. In addition, the sensing mechanism is discussed in detail.

Polyoxovanadate-Based Metal-Organic Frameworks with Dual Active Sites for the Synthesis of p-Benzoquinones.

p-Benzoquinones are important organic intermediates in the synthesis of biopharmaceuticals and fine chemicals. In this study, two crystalline 3D polyoxovanadate-based metal-organic frameworks, H[Cu(tpi)2]{Cu2V7O21}·H2O (1, tpi = C18N5H13) and [Co(Htpi)2]{V4O12} (2, Htpi = C18N5H14), were synthesized, which as heterogeneous catalysts showed excellent catalytic activities for the synthesis of p-benzoquinones. Both compounds were characterized by IR, UV-vis diffuse reflectance spectroscopy, TG, XPS, X-ray diffraction, etc. In 1, {Cu2V7} clusters are connected together by copper cations and 1D Cu-organic coordination chains to yield a 3D polyoxometalate-based metal-organic framework (POMOF); in 2, adjacent 2D bimetallic oxide layers, constructed from 1D polyoxovanadate chains and cobalt ions, are further connected by 1D Co-organic coordination chains to form a 3D POMOF. Noteworthily, in the synthesis of trimethyl-p-benzoquinone, the key intermediate of vitamin E, using 2,3,6-trimethylphenol as the model substrate, the turnover frequency values for compounds 1 and 2 can, respectively, reach 607 and 380 h-1 in 8 min. Furthermore, both compounds demonstrated excellent recyclability and structural stability, characterized by PXRD and IR. The catalytic mechanism reveals that both the homolytic radical mechanism and heterolytic oxygen atom transfer mechanism are involved.

Two-Dimensional Cobalt(II) Benzoquinone Frameworks for Putative Kitaev Quantum Spin Liquid Candidates.

The realization and discovery of quantum spin liquid (QSL) candidate materials are crucial for exploring exotic quantum phenomena and applications associated with QSLs. Most existing metal-organic two-dimensional (2D) quantum spin liquid candidates have structures with spins arranged on the triangular or kagome lattices, whereas honeycomb-structured metal-organic compounds with QSL characteristics are rare. Here, we report the use of 2,5-dihydroxy-1,4-benzoquinone (X2dhbq, X = Cl, Br, H) as the linkers to construct cobalt(II) honeycomb lattices (NEt4)2[Co2(X2dhbq)3] as promising Kitaev-type QSL candidate materials. The high-spin d7 Co2+ has pseudospin-1/2 ground-state doublets, and benzoquinone-based linkers not only provide two separate superexchange pathways that create bond-dependent frustrated interactions but also allow for chemical tunability to mediate magnetic coupling. Our magnetization data show antiferromagnetic interactions between neighboring metal centers with Weiss constants from -5.1 to -8.5 K depending on the X functional group in X2dhbq linkers (X = Cl, Br, H). No magnetic transition or spin freezing could be observed down to 2 K. Low-temperature susceptibility (down to 0.3 K) and specific heat (down to 0.055 K) of (NEt4)2[Co2(H2dhbq)3] were further analyzed. Heat capacity measurements confirmed no long-range order down to 0.055 K, evidenced by the broad peak instead of the λ-like anomaly. Our results indicate that these 2D cobalt benzoquinone frameworks are promising Kitaev QSL candidates with chemical tunability through ligands that can vary the magnetic coupling and frustration.

Experimental optimization of the sono-photocatalytic hydrogen evolution reaction (HER) using 1D ZnO and cobalt phthalocyanine

This study presents the sono-photocatalytic hydrogen generation (HER), using ZnO and theraphthal, a water-soluble sodium salt of cobalt 4,5-carboxyphthalocyanine (TP). HER efficiency was optimized by a multivariable design of experiments modifying 5 factors (additives): (i) ascorbic acid, (ii) zinc oxide load, (iii) ultrasound power, (iv) ethanol, and (v) theraphthal under UV irradiation. Differences in hydrogen production according to the variable employed factors were observed in the reactions, resulting in higher yields when larger amounts of ethanol were used. Hydrogen evolution reached a maximum concentration near to 67 μmol (669 μmol g−1) in the HER process, when zinc oxide, theraphthal, and ascorbic acid in water/ethanol mixture were combined. Statistical analysis suggests that the H2 production was influenced mainly by the presence of alcohol in the reaction medium.

Room-temperature olefin epoxidation reaction by two 2D cobalt metal-organic complexes under O2 atmosphere: coordination and structural regulation

Room-temperature olefin epoxidation reaction by two 2D cobalt metal-organic complexes under O2 atmosphere: coordination and structural regulation

3D-Cobalt-Dicyanamide-Derived 2D-Layered-Co(OH)2-Based Catalyst for Light-Driven Hydrogen Evolution.

Derivation of 3D coordination polymers to produce active catalysts has been a feasible strategy to achieve a precise coordination sphere for the catalytic site. This study demonstrates the partial conversion of a 3D cobalt dicyanamide coordination polymer, Co-dca, to a 2D layered hydroxide-oxyhydroxide structure under photocatalytic conditions. The catalyst exhibits an activity as high as 28.3 mmol h-1 g-1 in the presence of a [Ru(bpy)3]2+/triethylamine (TEA) couple to maintain it for at least 12 h. Photocatalytic and characterization studies reveal that the dicyanamide ligand within the coordination polymer is crucial for governing modification and achieving a superior H2 evolution rate. Moreover, we observed the critical role of TEA as the hydrolyzing agent for the transformation process. This study displays that the metal dicyanamides can be utilized as templates for preparing active and robust catalysts.

A comparison between 2D and 3D cobalt–organic framework as catalysts for electrochemical CO2 reduction

Electrocatalytic CO2 reduction, as an effective way to reduce the CO2 concentration, has gained attention. In this study, we prepared ZIF-67 nanoparticles and nanosheets and investigated them as electrocatalysts for CO2 reduction. It was found that ZIF-67 nanosheets, because of their two–dimensional morphologies, provide more under–coordinated cobalt nodes and have lower overpotentials for both hydrogen evolution and CO2 reduction reactions. Also, the rate–determining step for hydrogen evolution changes from Volmer for ZIF-67 nanoparticles to Hyrovsky for ZIF-67 nanosheets. Also, the presence of Mg2+ ions in solution causes more facile CO2 reduction, especially for ZIF-67 nanosheets.

Emerging 2D Cobalt Telluride (CoxTey): from Theory to Applications

AbstractCobalt telluride, with tunable magnetism and ferromagnetism that hinged upon the stoichiometric ratio, has emerged as a new member of 2D materials in the last decade. Metallic doping by sodium (Na) and platinum (Pt) atoms below critical concentrations is found to enhance the magnetism of cobalt telluride. After thinning cobalt telluride down to few‐layer, the saturation magnetism is improved by two order of magnitudes because of the oxidation state of cobalt (Co) and reduced coordination number of the surface atoms. In 2D limit, cobalt di‐telluride possesses Dirac band structure with many nodal lines that correlate with quantum criticality and other fantastic physics. In this mini‐review, the crystal and band structures of cobalt telluride categorized by stoichiometric ratio are overviewed after briefing the introduction. Both top‐down and bottom‐up methods are then discussed to offer optimum solutions for each specified application scenario. Afterward, emerging magnetic and electronic properties and credit enhancements are launched accompanied with their key advances. Beyond these, the faced challenges and possible directions of future research are also provided, attempting to boost both fundamental physics and device applications based on 2D cobalt telluride.

Two-dimensional cobalt ferrite through direct chemical vapor deposition for efficient oxygen evolution reaction

Two-dimensional (2D) transition metal oxides (TMOs) are promising electrocatalysts for the new energy industry, owing to their earth-abundancy, excellent performance, and unique physicochemical properties. However, microscopic electrochemical study for 2D TMOs is still lacking to provide detailed electrocatalytic mechanisms due to the challenges in synthesizing 2D TMOs with high quality and controlled thickness, which is indispensable for the microscopic studies. In this study, we report the direct synthesis of 2D cobalt ferrite (CoFeO) using a chemical vapor deposition (CVD) method. The as-synthesized 2D CoFeO possesses a well-crystallized spinel structure with an ultrathin thickness of 6.8 nm. Its oxygen evolution reaction (OER) properties under alkaline conditions were accurately assessed using an ultra-microelectrode testing platform. The (111) facet of the 2D CoFeO exhibits a low overpotential of 330 mV at a current density of 10 mA cm–2 and a high current density of ~142 mA cm–2 at an overpotential of 570 mV. The OER mechanism of the 2D CoFeO was analyzed using density functional theory (DFT) calculations, which reveal the bimetallic sites on the surface reduce the energy barrier and facilitate the reaction. Moreover, we demonstrate the reduced thickness of 2D CoFeO improves the OER activity by lowering the bulk resistance and improving the utilization of active sites, which was confirmed by the thickness-activity dependency (6.8 to 35 nm) tests using the ultra-microelectrode platform. Furthermore, the practical values of the as-prepared 2D CoFeO was demonstrated by synthesizing a large-area continuous film and collecting high OER activity and superb durability from macro-electrochemical experiments. Our study provides new solutions for the controlled synthesis of 2D TMOs electrocatalysts and uncovers the electrocatalytic mechanisms with the ultra-microelectrode platform, which provides new insights for exploring the inherent properties and applications of 2D materials in electrocatalysis.

Hierarchical 3D porous trimetallic palladium-iron and cobalt on nickel foam as electrocatalyst for large current density oxygen evolution reaction in alkaline seawater

Electrolysis in seawater is a low-cost but difficult method of producing hydrogen. Herein, self-assembled hierarchical three-dimensional (3D) porous trimetallic palladium-iron and cobalt oxide anchored on a cheap and high surface area nickel foam (NF) (PdFeCo3−xO4/NF) were synthesized using a simple and low-cost impregnation-hydrothermal and thermal reduction strategy. The as-fabricated PdFeCo3−xO4/NF electrode showed both superhydrophilic and superaerophobic properties, which favored the fat removal of oxygen bubbles from the electrode surface owing to the close interaction between the electrode and electrolyte. Furthermore, the significant synergistic effect of trimetallics and the NF-matrix resulted in substantially enhanced oxygen evolution reaction (OER) intrinsic activity. The self-assembled PdFeCo3−xO4/NF catalyst exhibited critical low overpotentials of 300 and 340 mV to achieve an extremely large current density of 100 mA cm−2 in 1 M KOH solution and 1 M KOH seawater. Cell voltages as low as 1.44 and 1.51 V were required to drive 10 mA cm−2 in alkaline solution and seawater electrolytes for the full cell overall water splitting performance. This work suggests a promising strategy for developing next-generation electrocatalysts appropriate for natural seawater with cost-effective.

Promoting homogeneous lithium deposition by facet-specific absorption of CoIn3 for dendrite-free lithium metal anodes

Lithium metal is expected to be an ideal anode material for future high-energy density lithium batteries. However, the uncontrollable growth of lithium dendrites resulting in a short circuit inside the battery and battery failure has become an obstacle to commercializing lithium metal batteries. In this work, a surface with lithiophilic CoIn3 nucleation sites is developed to achieve a uniform lithium deposition by low temperature thermal treatment of super lithiophilic indium foil with three-dimensional (3D) cobalt foam (CoIn3 @CF). The CoIn3 @CF with 3D porous structure provide channels for rapid Li-ions (Li+) transport and inhibit the volume expansion, while the synergistic effect of lithiophilic CoIn3 alloys caused by the multi-facet orientation relationship promote the formation of homogeneous Li+ diffusion. As a result, the CoIn3@CF host exhibits long cycling over 2400 h at 40 mA cm−2/1 mA cm−2 in symmetric cells. Moreover, a full cell with the Li/CoIn3 @CF as anode and LiFePO4 as cathode delivers a columbic efficiency more than 99.3% over 800 cycles. This work provides a new perspective for the design of high energy Li anodes.

Anchoring 0D ZnO on 1D cobalt molybdate support for selective removal of heavy metal ion

The health of people and the environmental ecosystem are severely threatened by pollutants. Photocatalysis a desirable and effective method for pollutants removal that is associated with the adsorption phenomenon. The CoMoO4/ZnO photocatalysts were fabricated by facile template free methods. 1D-0D of CoMoO4/ZnO was fully characterized by different techniques for investigation of Pb+2, Cd+2 and Zn+2 removal in aqueous medium. Although the support photocatalyst did not show proper activity, the formation of the heterostructure led to the significant removal of Pb+2 ion. Adequate adsorption of Pb+2 ion was accompanied by photocatalytic process of visible-light-driven n-n CoMoO4/ZnO heterojunction, caused to high performance. Effect of different parameters on photoactivity, and kinetics and thermodynamic were considered. The synergistic effect induced by formation of 1D CoMoO4 containing 0D ZnO particles drastically improve the charge carrier generation, transfer and separation. Consequently, the prepared CoMoO4/ZnO composites are considered good candidates for wastewater treatment.

One-pot cocrystallization of mononuclear and 1D cobalt(II) complexes based on flexible triclopyr and 2,2′-bipyridine coligands: Structural analyses, conformation comparison, non-covalent interactions and magnetic properties

A pair of cobalt(II) complexes with formulas of [Co(3,5,6-tcpa)(2,2′-bpy)Cl] (1A) and [Co(3,5,6-tcpa)2(2,2′-bpy)]n (1B) have been cocrystallized by the solvothermal reaction of cobalt chloride hexahydrate with triclopyr (systematic name 2-((3,5,6-trichloropyridin-2-yl) oxy)acetic acid, abbreviation 3,5,6-Htcpa) and 2,2′-bipyridine (2,2′-bpy). Single-crystal X-ray diffraction analysis indicated that both 1A and 1B crystallized in triclinic system, space group P1¯ (no. 2). Compound 1A is mononuclear and 3,5,6-tcpa anion in it is a bidentate chelate ligand. In contrast, 1B is a 1D double-stranded chain structure in which 3,5,6-tcpa are bidentate bridging-μ2 linkers. The non-covalent interactions of Cl···Cl halogen bonds, C–H···O/Cl hydrogen bonds as well as π···π stacking interactions play an important part in their crystal packing, which have been confirmed by the careful Hirshfeld surface analyses. After deeply structural analyses, it was proposed that flexible conformation alteration of 3,5,6-tcpa might be in charge of the cocrystallization phenomenon of 1A and 1B. In addition, the magnetic characterizations suggested antiferromagnetic coupling between neighbouring cobalt(II) centers in 1B.

Bi-functional two-dimensional cobalt silicate catalyst for selective catalytic oxidation of ammonia

We have newly synthesized the zeolitic cobalt silicate catalysts via a simple hydrothermal treatment of borosilicate MWW precursor with Co precursor solution. As the hydrothermal temperature increased, a structural transformation occurred, shifting from three-dimensional (3D) to two-dimensional (2D) delaminated MWW layers (DML), and further to 2D amorphous phyllosilicate, accompanied by a continuous increase in Co content. The synthesized bi-functional 2D cobalt silicate facilitates the selective catalytic oxidation of NH3 (NH3-SCO), a process that requires both surface acidity and redox characteristics. In particular, Co-DML-160 prepared by hydrothermal treatment at 160 °C exhibited the coexistence of Co3O4 and framework Co species resulting in a strong redox ability and high Lewis acidity, respectively, due to their synergetic effect.