A simple and straightforward approach was used to prepare Fe2O3/graphene nanocomposites with different temperature conditions. The nanocomposites were characterized by X-ray diffraction (XRD), Raman spectroscopy, field emission scanning microscopy (FESEM), transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS) and photoluminescence (PL).
Vietnam Journal of Science and Technology 57 (3A) (2019) 150-159 doi:10.15625/2525-2518/57/3A/14105 EFFECT OF TEMPERATURE ON THE STRUCTURE AND PROPERTIES OF Fe2O3/GRAPHENE NANOCOMPOSITES SYNTHESIZED BY HYDROTHERMAL METHOD Tran Van Khai1, 2, * Nguyen Quang Vinh 1, Le Van Thang1, 2, Mai Thanh Phong3 Faculty of Materials Technology, Ho Chi Minh City University of Technology, Vietnam National University Ho Chi Minh City, 268 Ly Thuong Kiet street, Ward 14, District 10, Ho Chi Minh City Material Technologies Laboratory, Ho Chi Minh City University of Technology, Vietnam National University Ho Chi Minh City, 268 Ly Thuong Kiet street, Ward 14, District 10, Ho Chi Minh City Ho Chi Minh City University of Technology, Vietnam National University Ho Chi Minh City, 268 Ly Thuong Kiet street, Ward 14, District 10, Ho Chi Minh City * Email: tvkhai1509@hcmut.edu.vn Received: August 2019, Accepted for publication: 30 September 2019 Abstract A simple and straightforward approach was used to prepare Fe2O3/graphene nanocomposites with different temperature conditions The nanocomposites were characterized by X-ray diffraction (XRD), Raman spectroscopy, field emission scanning microscopy (FESEM), transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS) and photoluminescence (PL) The results show that Fe2O3 nanoparticles with size in range of 60-100 nm are anchored on the surface and filled between the graphene nanosheets at hydrothermal reaction The PL spectrum exhibits the emission peaks appeared at ~ 650 nm and ~ 720 nm Keywords: Fe2O3/graphene, nanocomposite, graphene, hydrothermal method Classification numbers: 2.1.1, 2.4.4, 2.9.4 INTRODUCTION Over the past few years, a lot of carbon-based materials have been synthesized and investigated for potential applications [1-3] Graphene, a single layer of carbon atoms densely packed into a two-dimensional (2D) honeycomb sp2 carbon lattice, has attracted a great deal of research attention due to its unique electrical, physical, and chemical properties [4, 5] It has unmatched thermal conductivity (~ 5000 W/mK), very high electron mobility (μ ~ 200,000 cm2 V-1.s-1), a theoretical specific surface area (~ 2630 m2/g) as well as excellent mechanical properties (Young’s modulus ~ 1.1 TPa), which makes it promising for applications in various fields such as solar-cells, energy storage, field effect transistors, catalyst support, sensors, supercapacitors, electrodes, separation and nanocomposites [6-9] Up to now, a number of facile and low-cost methods have been used to prepare graphene in bulk quantities [10] Among the many methods proposed, most people produced graphene sheets by chemical reduction of exfoliated graphene oxides [11] Many graphene nanocomposites based on the hybridization with nanoparticles fabricated are of highly versatile in electronics [12], photonics [13], energy Effect of temperature on the structure and properties of Fe2O3/graphene nanocomposites… storage [14, 15], sensors [16], catalysis [17] and bioapplication [18] Although these exciting results concerning the graphene based materials in these fields, there are still some issues remained for further consideration Recently, transition metal oxides have been widely studied in various fields to constitute composite materials with graphene in order to enhance its properties in application Among the various transition metal oxides, such as ZnO [19], TiO2 [20], Fe3O4 [21], CuO [22], SnO2 [23]; Fe2O3 is one of the most common oxides in the natural world Due to its low cost, environmental friendliness, chemical stability and nontoxic, Fe2O3 has been extensively studied in lithium batteries [24], catalysis [25], sensors [16], magnetic materials [26], biological and medical fields [27] It has been differently synthesized dimensional nanostructures (1D), such as nanorods [28], nanobelts [29], nanowires [30], nanotubes [31], porous structures) [32], core–shell structures [33], and so on In terms of Fe2O3, several ways, including precipitation methods [34], hydrothermal methods [35], solvothermal methods [36], hydrolysis [37], microwave methods [38], were utilized in preparation of its graphene composites Herein, we adopted one-step hydrothermal method to synthesize Fe2O3/graphene nanocomposites with different temperature condition Under the hydrothermal condition, graphene oxide (GO) is simultaneously reduced to graphene along with the homogeneous precipitation of Fe2O3 nanoparticles Compared to GO and reduced graphene oxide (rGO), Fe2O3/graphene composites can be easily separated from the solution after adsorption EXPERIMENTS 2.1 Materials All chemicals used in this study were purchased from Xilong Scientific Co., Ltd., including graphite flakes (~5 μm, 99.8 %), H2SO4 (98 %), H3PO4 (85 %), KMnO4 (98 %), H2O2 (30 wt %), FeCl3.6H2O and CO(NH2)2 The starting GO nanosheets were prepared by modified Hummors method 2.2 Synthesis of Fe2O3/graphene nanocomposites The Fe2O3/graphene nanocomposites were prepared via a one-pot hydrothermal method First, 0.41 g of FeCl3.6H2O and 1.55 g of CO(NH2)2 were added into 10 mL of a 1.825 mg/mL graphene oxide (GO) aqueous solution while stirring for 30 at room temperature, and the above mixture was sonicated for 20 to obtain a uniform suspension After adding distilled water to about 90 mL, the mixture solution was transferred to a 100 mL Teflon-lined stainless steel autoclave and maintained for h at several different temperatures in an electric oven After being cooled to room temperature naturally, the resulting black product was centrifuged and washed with distilled water and ethanol several times, and Fe2O3/graphene composites were finally dried at 35 °C for h 2.3 Characterization The X-ray diffraction (XRD) patterns were recorded using a D8 advance (Bruker-AXS) diffractometer with Cu Kα radiation (λ= 0.1546 nm) The morphologies of the as-prepared products were observed by field emission scanning electron microscopy (FESEM Hitachi S4800), using an acceleration voltage of 10 kV, and transmission electron microscopy (TEM: 151 Tran Van Khai et al JEOL JEM-100CX II) at 100 kV TEM specimens were prepared by drop casting the dispersions on a carbon-coated copper grid, followed by drying under vacuum for 24 h at 50 °C Raman measurements were carried out using Horiba XploRA One spectrometer equipped with an Olympus BX50 microscope attachment to focus the laser beam on a 180×120 μm2 selected area of the sample, a 15 mW green argon laser (λ = 532 nm) were used as an excitation source with exposition time of 15 s along with a 900 lines per mm grating monochromator with liquid nitrogen-cooled CCD The room-temperature photoluminescence (PL) used a He-Cd laser line with the excitation source of 325 nm RESULTS AND DISCUSSION The Fe2O3 nanoparticles are grown on the surfaces of the graphene nanosheets through a reduction process of the pristine GO to reduce graphene under a hydrothermal treatment Urea can release CO2 and OH- when the temperature of the solution exceeds 80°C, as a result, Fe(OH)3 particles anchor onto the surfaces of GO sheets uniformly The formation of Fe2O3/graphene composite under the action of urea can be represented as following: CO(NH2)2 + 3H2O 2NH3.H2O + CO2 NH3.H2O NH4++ OH− Fe3+ + 3OH− Fe(OH)3 2Fe(OH)3 Fe2O3 + 3H2O c ) Figure FE-SEM images of Fe2O3/graphene composites grown at different temperatures: (a) 120 °C, (b) 150 °C, (c) 180 °C, (d) 210 °C, (e) 240 °C for h and (g) EDS analyses of the composites The morphologies and structure of the Fe2O3/graphene composites grown at different temperatures were observed by FE-SEM As can be seen in Figure 1(a-e), the Fe2O3 nanoparticles are uniformly anchored on the surface and filled between the graphene nanosheets Furthermore, there are no free or independent Fe2O3 nanoparticles outside the graphene sheets, demonstrating that all of the nanoparticles are completely attached to the almost transparent 152 Effect of temperature on the structure and properties of Fe2O3/graphene nanocomposites… graphene sheets Figure 1(g) confirms the presence of C, O and Fe elements in the products, proving the formation of Fe2O3/graphene composites again TEM images (Figure 2) illustrate the presence of interface between Fe 2O3 particles and graphene with good size distribution The almost transparent graphene sheets are fully decorated with Fe2O3 particles with average diameters of 60 nm Even after a long duration of sonication during the preparation of the TEM specimen, Fe2O3 particles are still adsorbed on the surface of graphene nanosheets, proving the formation of Fe2O3/graphene composites again Most carboxyl and hydroxyl groups, which can act as anchor sites, are decorated on the edges of GO, leading to in situ formation of Fe2O3 nanoparticles attached on the edges of GO sheets [34] Similar to the dopamine molecule, GO has a large quantity of phenolic hydroxyl groups that can coordinate with Fe2O3 nanoparticles [40] Herein, the nanoparticles directly disperse on the surface and alternate between graphene sheets, which could efficiently prevent from agglomerating of graphene sheets Figure TEM images of Fe2O3/graphene composites grown at 180°C for 8h at different scales XRD diffraction patterns of GO, reduced graphene oxide (rGO) and Fe 2O3/graphene nanocomposites are shown in Figure In the case of GO (Figure 3a), a strong diffraction peak at 2θ of 11.2°, which is associated with (002), showing the complete oxidation of graphite to the graphite oxide due to the introduction of oxygen-containing functional groups on the graphite sheets [41,42] For the XRD pattern of rGO, after reduction, the peak located at 11.2° disappears, while a broad diffraction peak (002) appears at 25° The basal spacing of rGO is a little larger than that of GO, revealing the great reduction of GO and exfoliation of layered graphene sheets For Fe2O3/graphene nanocomposites, the XRD pattern is shown in Figure 3b and diffraction peaks are consistent with the standard card (JCPDS card No 33-0644) The 153 Tran Van Khai et al peaks at 2θ value of 24.2, 33.2, 35.5, 40.9, 43.5, 49.5, 54.1, 57.6, 62.4, and 64.0° can be indexed as (012), (104), (110), (113), (202), (024), (116), (018), (214) and (330) crystal planes of hexagonal iron oxide, respectively The strong and sharp diffraction peaks show that the obtained products are well crystallized The disappearance of GO peak is attributed that the regular layer stacking of GO can be destroyed by the ultrasonic process and the crystal growth of Fe2O3 during the hydrothermal reaction, leading to the exfoliation of GO sheets On the other hand, as reported previously in many literatures, GO sheets can be reduced under hydrothermal conditions [43] and the obtained graphene sheets can be further exfoliated by decorating Fe 2O3 nanoparticles, resulting in the disappearance of diffraction peak of GO Figure XRD patterns of a) GO and rGO, b) Fe2O3/graphene composites synthesized at 120, 150, 180, 210 and 240 oC for h The Raman spectra of GO, rGO and Fe2O3/graphene nanocomposites are presented in Figure In the case of GO, there are two peaks observed at 1330 and 1590 cm-1, corresponding to the disorder band associated with structural defects, amorphous carbon created in graphene (D-band) and well ordered scattering of the E2g phonon of sp2 C atoms of graphene (G-band), respectively [44] The intensity of D-band is stronger than that of G-band, meaning the presence of high density of defects and structure disorder in GO Moreover, the ID/IG intensity ratio, as a vital parameter to evaluate disorder and defects of carbon materials, presents a negative correlation with the degree of ordering in the carbon materials The ID/IG of GO is about 1.07 After hydrothermal reduction, the ID/IG of rGO is increased to 1.25, indicating the presence of localized sp3 defects with the sp2 carbon network after a reduction in the exfoliated rGO For the Fe2O3/graphene composites (180 oC), the Raman spectrum shows the typical peaks of hematite and the D and G bands of graphene, which implies the formation of Fe 2O3/graphene composite Moreover, the Raman peaks at about 220 cm-1 is assigned to the A1g mode and 285 cm-1 can be ascribed to the Eg mode of Fe2O3, suggesting the combination of Fe2O3 nanoparticles with the graphene layer The calculated ID/IG ratios of Fe2O3/graphene composite with different temperature condition 120 °C, 150 °C, 180 °C, 210 °C, 240 °C are 1.22, 1.27, 1.27, 1.28 and 1.25, respectively No other features corresponding to different iron oxide phases were detected, indicative of high purity of the products 154 Effect of temperature on the structure and properties of Fe2O3/graphene nanocomposites… Figure Raman spectra of a) GO and rGO, b) Fe2O3/graphene composites Figure Photoluminescence spectrum of Fe2O3/graphene composite synthesized at 180 oC for h Photoluminescence (PL) spectrum is a well known technique to study of the interface charge carrier transfer as well as the recombination process involving the electron-hole pairs in semiconductor particles [45] and PL emission results from the radiative recombination of excited electrons and holes Figure shows the PL spectrum of Fe2O3/graphene composites at the excitation wavelength of 448 nm The emission of Fe2O3 is positioned at 650 nm and 720 nm, assigned to 6A1 4T2 (4G) ligand filed transitions of Fe3+ [46] Furthermore, by using the formula Eg = 1240/λ, the Fe2O3/graphene nanocomposites provide band gap of around 1.7 eV and 1.9 eV 155 Tran Van Khai et al CONCLUSSION In summary, Fe2O3/graphene nanocomposites have been successfully prepared by a onestep hydrothermal method with different temperature condition The structure and morphologies of the Fe2O3/graphene nanocomposites are well investigated and provided some positive achievements to any further applications In these different temperature conditions, the experiment was prepared at a temperature of 180°C for h, giving the best results 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Nanotechnology 18 (2007) 275608 159 ... the regular layer stacking of GO can be destroyed by the ultrasonic process and the crystal growth of Fe2O3 during the hydrothermal reaction, leading to the exfoliation of GO sheets On the other... 152 Effect of temperature on the structure and properties of Fe2O3/graphene nanocomposites graphene sheets Figure 1(g) confirms the presence of C, O and Fe elements in the products, proving the. .. preparation of its graphene composites Herein, we adopted one-step hydrothermal method to synthesize Fe2O3/graphene nanocomposites with different temperature condition Under the hydrothermal condition,