Hydrothermal Synthesis of Co3O4 Urchin-Like and their Catalytic Properties in Co Oxidation
Sami Barkaoui1 and Gunel Imanova2*
1Laboratory Materials Treatment and Analysis, National Institute for Research and Physico-chemical Analysis (INRAP), Tunisia
2Institute of Radiation Problems, Azerbaijan National Academy of Sciences, Azerbaijan
Submitted: April 07, 2022; Published: April 19, 2022
*Corresponding author: Gunel Imanova, Institute of Radiation Problems, Azerbaijan National Academy of Sciences, Azerbaijan
How to cite this article: Sami B, Gunel I. Enhanced Antiangiogenic Activity of Silver Nano-Particles Grafted on Graphene Oxide. JOJ Material Sci. 2022; 7(1): 555704. DOI:10.19080/JOJMS.2022.07.555704
Abstract
Urchin-like nanocrystalline Co3O4 has been success fully prepared through a hydrothermal synthesis route via a simple and elegant route at low temperature, and was characterized by thermal analysis (TGA), X-ray diffraction (XRD), scanning electron microscopy (SEM), Raman spectroscopy, nitrogen adsorption/desorption isotherms and X-ray photoelectron spectroscopy (XPS). The light-off temperature (10% conversion) of CO oxidation on Co3O4 ursin-like catalyst was at 60°C and when the temperature reaches 120°C, the CO conversion ratio reaches 100%. The high relative concentration surface-adsorbed oxygen on the Co3O4 ursin-like is highly active in CO oxidation reaction due to its higher mobility than lattice oxygen. The study it has been shown that the high catalytic activity and stability for CO oxidation can be attributed to its higher mobility than lattice oxygen. In addition, the oxide defects can adsorb and activate gaseous O2 to form active oxygen species, which is beneficial to promote the CO oxidation reaction. The as-obtained results make the Co3O4 nanomaterial possible candidate to be used as catalyst for CO oxidation.
Keywords: Hydrothermal Synthesis; Urchin-Like; Nanocrystalline Co3O4; Catalytic Properties; Oxidation
Abbreviations: TGA: Thermal Analysis; XRD: X-ray Diffraction; SEM: Scanning Electron Microscopy; XPS: X-ray Photoelectron Spectroscopy; CO: Carbone monoxide; TCD: Thermal Conductivity Detector; BET: Brunauer-Emmett-Teller
Introduction
Carbone monoxide (CO), emission from mobile and stationary combustion sources is harmful to the environment, one of the major air pollutants and its presence even in traces may cause serious environmental and health problems. Therefore, the elimination of CO became important, and the oxidation of CO is a promising route to cleaning the air and lowering automotive emissions. Tricobalttetraoxide (Co3O4), a typical spinel-structure transition metal oxide, shows a strong morphology-dependence in the chemical reactions such as CO oxidation [1-6], CH4combustion [7], and selective reduction of NO with NH3 [8]. For example, in 2009, it has been developed Co3O4 nanorods containing substantial amounts of exposed (110) planes exhibited superior catalytic activity for low-temperature CO oxidation to the spherical particles mainly enclosed by the (111) facets [1]. Also, Co3O4 nanotubes [9], nanosheets [3], nanowires [4], and nanocubes [10] similarly showed a distinct shape effect in CO oxidation. These results clearly confirm that controlling the morphology of nanostructured cobalt oxides is beneficial to expose more catalytically active sites.
Development of catalysts with desirable dimensions andmorphology is an interesting and challenging task owing to their improved catalytic activity and increasing applications in various fields [11-13]. Hierarchical 3D urchin-like nanostructures are promising for wastewater treatment through heterogeneous photo-catalysis because of their high surface area which facilitates catalysis by providing a larger solid-liquid interface. As can be seen from the writing information, radiation-heterogeneous forms in contact of to begin with radiation-oxidative treated zirconium and nano-zirconium oxide with water causes a alter within the sum of surface oxide film. The arrangement of an oxide film, in turn, changes the radiation-catalytic movement and physicochemical properties, which influence the dynamic parameters. One of them, the foremost delicate is the electro physical and optical properties of metal surfaces [14-22].
In this study, we report on the hydrothermal synthesis and physicochemical characterization of urchin-like nanostructures of Co3O4 with a surface area of 43m2/g and their application in the CO reaction. The nanomaterial was synthesized using PEG-400 as a template. The Co3O4 morphology proved to be stable and did not collapse after calcination at 300°C for 2h. XRD measurements showed that the Co3O4 average particle size is 44nm. The assynthesized C Co3O4 ursin-like exhibited superior catalytic activity and durability in CO oxidation at room temperature. It has been shown that when the temperature reaches to 120°C, the CO conversion ratio reaches 100%.
Experimental Details
Hydrothermal synthesis
The Co3O4 were synthesized by the typical procedures reported in the literature [23]. 0.77 mmol of CoCl2.6H2O was dissolved in distilled water (27mL), followed by the addition of 0.25 mmol of PEG-400 then 8 mL of H2O2 (30%). The solution was transferred into a Teflon-lined stainless-steel autoclave which was sealed and maintained at 100°C for 12h. The autoclave was then cooled to 25°C, 2.25 mmol of urea was added and the autoclave was heated at 150°C for 16h. The precipitate was filtered, washed several times with deionized water and ethanol until free of chloride ions (AgNO3 test) and dried overnight at 80°C under vacuum. Then, it was calcined in air at 300°C for 2h.
Characterization
TGA was performed using a Setaramsetsys 1750 apparatus at a heating rate of 2°C/min from RT to 700°C. XRD data were collected on a Panalytical X’Pert Pro diffractometer with CuK α radiation (λ = 1.5406 Å) and a graphite monochromator by applying a step scanning method (2θ range from 10 to 70°). Raman spectroscopy was performed using a Jobin-Yvon T64000 spectrometer with a laser wavelength of 785 nm and a laser power of 3m W and taken after 60 seconds of exposure. The morphology of the sample was studied using an FEI Quanta 200 Environmental SEM and H2-TPR profiles were obtained on a Micromeritics Autochem analyzer, in a Pyrex U-tube reactor and an on-line thermal conductivity detector (TCD). The calcined sample (50 mg) was first purged with an argon flow of 20 mL/min at a ramp rate of 10 °C/min to 350°C for 30 min to remove the traces of water, followed by cooling to room temperature. Then the sample was reduced by 4% vol. hydrogen and argon mixture (30 mL/min) at a temperature ramp rate of 5°C/min. The effluent gas was passed through a cooling trap to condense and collect the water produced during the reductions. The Brunauer-Emmett-Teller (BET) specific surface area, average pore diameter and pore size distributions were determined by N2- physisorption at 77K using a Micrometrics ASAP-2020 instrument.
Catalytic investigation
CO oxidation was tested in a flow reactor. Before the reactions, Co3O4 was activated at 300°C for 1h at 5%O2/He. After the sample was cooled down to room temperature, a feed gas (1%CO/20%O2/ He) was passed over the catalyst with a flow rate of 30 mL/min. 50 mg of the catalyst was heated to the desired reaction temperature and then kept for 1 hour until the catalyst reaction reached a steady state. The amounts of CO, CO2 and O2 in the inlet and outlet streams were analyzed by an online gas chromatograph. CO conversion was calculated from the measured CO concentration using the formula CO conversion = [(Coin - COout)/COin], where COin and COout were the inlet and outlet CO concentration, respectively.
Result and Discussion
Thermo gravimetric analysis (TGA)
The thermal behavior of the hydrothermally as-prepared sample was examined using TGA in order to determine the appropriate calcination temperature. As depicted in Figure 1, a sharp decrease with a total weight loss of 11.2% around 260°C which indicated that a temperature of 300°C was chosen to completely decompose of cobalt chloride carbonate hydroxide hydrate decomposed completely into Co3O4, CO2, Cl2 and H2O.
X-ray diffraction (XRD)
The diffraction patterns (XRD) are given in Figure 2. All the diffraction peaks displayed in the diffractogram (a) can be perfectly indexed to the cobalt chloride carbonate hydroxide hydrate [JCPDS 00-038-0547, Co (CO3)0.35Cl0.20(OH)1.10.1.74H2O] and those in (b) with cobalt oxide [JCPDS 01-076-1802, Co3O4]. The second XRD pattern shows that the main peaks of the final products could be indexed to a cubic phase cobalt oxide and no peaks of other phases are observed. All the peaks can be indexed to the diffraction from the (111), (220), (311), (222), (400), (422), (511) and (440) planes of cubic Co3O4, respectively. Crystallite sizes (DXRD) for Co3O4 after heating in air at 300°C was estimated from the broadening of the most intense XRD peak (311) using the Debye-Scherrer approximation [24]. The average particle size of Co3O4 catalyst was calculated to be 44nm.
Raman spectroscopy
Raman spectroscopy of Co3O4 nanostructure is displayed in Figure 3. The Raman spectrum of the Co3O4 in the range of 100- 800 cm-1 shows five obvious peaks (A1g + Eg + 3F2g) located at around 187, 495, 505, 597 and 658 cm-1, corresponding to the five Raman-active modes of Co3O4. The peak at 187 cm-1 is attributed to the F(3)2g mode of tetrahedral sites (CoO4). The peaks at 459 and 505 cm-1 are assigned to the Eg and F(2) 2g symmetry, respectively. Whereas the peak at 597cm-1 is attributed to the F(1)2g symmetry. The strong band at 658 cm-1 with A1g symmetry is attributed to the characteristics of octahedral CoO6 sites corresponding to the unique characteristics of spinel-type cubic Co3O4 phase [25,26] and no additional peaks assigned to other impurities such as Co2O3 and CoO have been found in good agreement with the XRD result. The Raman shifts are consistent with those of pure crystalline Co3O4, indicating that the Co3O4 catalyst has a similar crystal structure of the bulk Co3O4.
Scanning electronic microscopy (SEM)
Figures 4a & 4b shows the SEM images of the as-prepared precursor obtained by hydrothermal treatment at 150°C and after calcination at 300°C. As shown in Figure 4b, The Co3O4 morphology proved to be stable and did not collapse after calcination at 300°C in air for 2h. Polyethylene glycol (PEG) was used as a surfactant, which can modify the surface energy of the crystallographic surface. Co3O4 has a uniform urchin-like structure covered with dense nanowires starting from the center with an average of diameter of 4-6μm. The nanowires appear to have a common center and grow to the outside along the radial direction.
H2-TPR studies
nostructures, TPR measurements were carried out and shown in Figure 5. The H2-TPR profile of the catalyst shows two main reduction peaks at about 360°C and 440°C, which can be attributed to the reduction of Co3O4 into CoO and from CoO to metallic Co [27], respectively. The narrow peaks indicate the reduction process was fast. The curve exhibits Co3+ is reduced at first, and then the produced Co2+ and Co2+ in the catalyst itself are further reduced into metallic Co.
Nitrogen adsorption-desorption
As shown in Figure 6, The N2 adsorption-desorption isotherms at 77 K which is close to type IV of the IUPAC classification [28] with an evident hysteresis loop in the 0.5 to 1.0 range suggesting that the Co3O4 ursin-like is basically mesoporous.
The specific area of the sample calculated by BET to be 43m2/g and the average pore diameters is 16 nm. These porous structures can be helpful for CO molecules to rapidly penetrate into the pores and contact to active sites during the catalytic process [29,30].
X-ray photoelectron spectroscopy (XPS)
XPS analysis was employed to investigate the surface elemental composition and chemical state of the as-obtained Co3O4-ursin like a catalyst, as shown in Figure 7. The XPS survey spectrum (Figure 7a) reveals that the sample only consists of cobalt and oxygen (the C1s peak was appeared, which could be due to the support used to prepare a sample for XPS analysis).The Co2p spectra in Figure 7b exhibited two major peaks with binding energies at around 780.0 eV and 795.1 eV corresponding to the Co2p3/2 and Co2p1/2, respectively, suggesting that the cobalt oxide was present in the form of Co3O4 [31,32].
Next, Co2p3/2 peaks in Figures 7b & 7c were fitted and de convoluted into two peaks of 780.8 and 779.5 eV, which are attributed to Co2+ and Co3+ respectively. As shown in Figure 7d, the O 1s electronic levels also were examined. The asymmetric O 1s could be de convoluted to two components at 531.5 and 529.5 eV. The XPS peak at 529.5 eV was attributed to the surface lattice oxygen (Olatt) species, and the 531.5 eV peak was ascribed to the surface adsorbed oxygen (Oads) species in Co3O4 [33,34]. The O1s peak at 531.5 eV in the spectrum indicates the presence of surface adsorbed oxygen such as O22- or O-, belonging to defect-oxide or hydroxyl-like group [35,36]. The presence of surface hydroxyl like groups can result from oxygen vacancy on the surface of the Co3O4 catalyst originating from the dissociative adsorption of H2O molecules. The oxide defects can adsorb and activate gaseous O2 to form active oxygen species, which is beneficial to promote the oxidation reaction. Furthermore, Co3O4 ursin-like had the Oads/ Olatt ratio about 1.7 proving that its surface possesses the largest amount of facile and reactive oxygen species, which is beneficial to promote the CO oxidation reaction [37].
Catalytic properties of Co3O4 ursin-like in CO oxidation
As a typical probe reaction of numerous novel catalytic materials, CO oxidation was carried out to evaluate the catalytic activity of the as-prepared Co3O4 ursin-like. As shown in Figure 8a, the light-off temperature (10% conversion rate) at 60°C and when the temperature reaches to 120°C, the CO conversion ratio reaches 100%, which exhibits higher catalytic activity than that of the Co3O4 nanowires [4] and Co3O4 nanorods [38]. The longterm stability of the catalyst is important in practical applications. Furthermore, the stability test for CO oxidation was performed over the period of 20 h at T=120°C, as shown in Figure 8b. The high catalytic activity and stability for CO oxidation can be attributed to its higher mobility than lattice oxygen. In addition, the oxide defects can adsorb and activate gaseous O22 to form active oxygen species, which is beneficial to promote the CO oxidation reaction.
Scanning electronic microscopy of the spent catalyst
As shown in Figure 9, the morphology of the spent catalyst after 20 h on stream reaction still retains ursin-like shape.
It can be shown that excellent catalytic performance and long-term stability for CO oxidation make the Co3O4 nanomaterial possible candidate to be used as a catalyst for CO oxidation.
Conclusion
In this paper, we have obtained Co3O4 precursor by a lowtemperature hydrothermal method. The product Co3O4 has a uniform urchin-like structure covered with dense nanowires starting from the center with an average of diameter of 4-6 μm by PEG-400 as a template. The light-off temperature (10% conversion) of CO oxidation on Co3O4 ursin-like catalyst was at 60°C and when the temperature reaches to 120°C, the CO conversion ratio reaches 100%. The stability test for CO oxidation was performed over the period of 20h at T = 120°C. It has been shown that the high catalytic activity and stability for CO oxidation can be attributed to its higher mobility than lattice oxygen. In addition, the oxide defects can adsorb and activate gaseous O2 to form active oxygen species, which is beneficial to promote the CO oxidation reaction. The as-obtained results make the Co3O4 nanomaterial possible candidate to be used as catalyst for CO oxidation.
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