Synthesis, structural, morphological, optical and magnetic characterization of iron oxide (α-Fe2O3) nanoparticles by precipitation method: Effect of varying the nature of precursor
Graphical abstract
Introduction
Magnetic nanocrystals can exhibit many unique properties such as electrical, chemical, optical and magnetic properties [1], [2] which are advantageous towards a variety of the applications. The three main types of iron oxide nanoparticles are FeO, Fe2O3 and Fe3O4. They are considered to be important materials due to their catalytic activity, biocompatibility, low-cost, nontoxicity and environmentally friendly nature. Fe2O3, the ferric oxide has four crystallographic phases, namely hematite (α-Fe2O3), β-Fe2O3, maghemite (γ-Fe2O3) and ε-Fe2O3 [3].
Hematite is plentiful in nature, for example, in aquatic systems, sediments and soils. α−Fe2O3 is the most stable iron oxide under ambient conditions and has been studied extensively for its broad range of application. It crystallizes in the rhombohedral crystal system with n-type semiconducting properties (the optical band gap is 2.1 eV) [4].
The synthesis of hematite particles (α-Fe2O3) of various sizes and shapes was thoroughly examined because their new chemical and physical properties correlated to bulk materials, and their potential applications in inorganic pigments [5], catalysts [6], gas and humidity sensors [7], [8], photoanode for photo-electrochemical cells [9], photoelectrolysis reactors [10], water treatment [11], and lithium ion batteries [12]. Different techniques have been developed to synthesis hematite particles, such as polyol method [13], sol–gel method [14], [15], [16], spray pyrolysis [17], [18], [19], hydrothermal technique [20], chemical vapor deposition [21], pulsed laser deposition [22], co-precipitation [23], [24] and high vacuum evaporation [23]. In these synthesis methods, size and shape of the compounds modify depending on the synthesis parameters, such as the reactant concentration, time and temperature reaction, pH solution, the surfactant, ionic strength, the anions and the nature of iron salts [25], [26], [27], [28], [29], [30]. Moreover, the chemical precipitation method is particularly attractive due to its short preparation time, high purity, high homogeneity, low cost, well-crystallized product and relatively low reaction temperature. Liu et al. [31], [32] successfully obtained nearly spherical nanoparticles of hematite with a diameter of 60–80 nm.
However, in this work we have attempted to explore the effects of changes in the nature of the precursor used in the synthesis of hematite nanoparticles at the level of size, morphology and optical band gap. We have used precipitation method which stands for a simple procedure to synthesize α-Fe2O3 nanoparticles. The nanoparticles are well characterized for their structural, morphological and optical properties by various characterization techniques such as the X-ray diffraction (XRD), Transmission Electron Microscopy (TEM), Scanning Electron Microscopy (SEM), Fourier Transform Infra-Red (FT-IR) spectroscopy, Raman spectroscopy, Thermogravimetric Analysis (TGA), Differential Thermal Analysis (DTA), Ultraviolet–Visible (UV–Vis) analysis and Vibrating Sample Magnetometer (VSM).
Section snippets
Materials
Iron (III) chloride hexahydrate (FeCl3, 6H2O) (Sigma–Aldrich), iron (III) acetylacetonate (Fe (C5H7O2)3) (Sigma–Aldrich) and iron (III) nitrate nonahydrate (Fe (NO3)3, 9H2O) (Sigma–Aldrich) were used as the precursors. Ammonium hydroxide 25 wt% NH3 in water (Sigma–Aldrich) was used as the precipitating agent. Ethanol (C2H6O) (Sigma–Aldrich) was used for washing. All of the materials were used without further purification. All solutions were prepared with deoxygenated distilled water.
Synthesis of α-Fe2O3 nanoparticles
Hematite
X-ray diffraction analysis
The XRD pattern (Fig. 2) of the synthesized product is in good agreement with that of hematite in the literature (JCPDS Card No. 330664) [33], [34], which appears the rhombohedral (hexagonal) structure of pure α-Fe2O3 with a lattice parameter of a = 0.5034 nm and c = 1.375 nm. No peaks of Fe3O4, metal hydroxides, or other impurities were detected, suggesting the complete formation of α-Fe2O3. The peaks appearing at a 2ϴ range of 24.16°, 33.12°, 35.63°, 40.64°, 49.47°, 54.08° and 57.42° can be
Conclusion
To sum up, we successfully synthesized α-Fe2O3 nanoparticles using the precipitation method. The XRD, TEM and SEM measurements revealed the nanocrystalline nature of α-Fe2O3, spherically shaped particle morphology, average nanoparticles size of hematite synthesis with FeCl3, 6H2O (of about 21 nm). Besides, FT-IR spectroscopy allowed the observation of hematite bands of FeO (527 and 434 cm−1). Furthermore, Raman spectroscopy helped verify hematite synthesis and determine its phonon modes: two A1g
Acknowledgments
The present work was supported by the Research Funds of Electrochemistry, Materials and Environment Research Unit UREME (UR17ES45), Faculty of Sciences Gabes University, Tunisia and Structures, Properties and Modeling of Solids (SPMS) Laboratory, Ecole Centrale Paris, France.
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