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Vol. 8. Issue 2.
Pages 2164-2169 (April 2019)
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Vol. 8. Issue 2.
Pages 2164-2169 (April 2019)
Original Article
DOI: 10.1016/j.jmrt.2019.02.004
Open Access
Annealing temperature effect on structural and optical investigations of Fe2O3 nanostructure
Yarub Al-Douria,b,c,
Corresponding author
, Noureddine Amraned, Mohd Rafie Johanb
a University Research Center, Cihan University Sulaimaniya, 46002, Iraq
b Nanotechnology and Catalysis Research Center (NANOCAT), University of Malaya, 50603 Kuala Lumpur, Malaysia
c Department of Mechatronics Engineering, Faculty of Engineering and Natural Sciences, Bahcesehir University, 34349 Besiktas, Istanbul, Turkey
d Department of Physics, United Arab Emirates University, P.O. Box 17551, Al-Ain, United Arab Emirates
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Figures (4)
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Tables (2)
Table 1. Structural parameter of annealed α-Fe2O3 nanostructure.
Table 2. Optical properties of annealed α-Fe2O3 nanostructure.
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Ferric oxide (Fe2O3) was synthesized at different temperatures (TS) between 300 and 500°C by spray pyrolysis technique. Surface of annealed Fe2O3 nanostructure was characterized by field emission scanning electron microscopic (FESEM). Annealed Fe2O3 nanostructure has showed rhombohedral hexagonal structure with the preferred orientation along (104) plane in X-ray diffraction patterns (XRD). Crystallite size was increased from 43 to 63nm with increasing of TS between 300 and 500°C. The maximum transmittance was found to be 72% for Fe2O3 nanostructure at TS=300°C. The energy gap for direct band transitions was measured to be 2.05–2.09eV. Refractive index of Fe2O3 nanostructure in the visible region was found in the range of 2.37–2.62. Fe2O3 nanostructure has showed n-type electrical conductivity and electrical resistivity was found in the range of 1.02×103–6.23×103Ωm. Formation of transparent Fe2O3 nanostructure with band gap and high refractive index suggests the suitability of Fe2O3 nanostructure in gas sensors.

Ferric oxide
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Nowadays semiconductor metal oxide nanoparticles are attractive due to their differences in electric, dielectric, optical, bio-medical, photo-catalytic and magnetic properties respect to their same bulk counterparts [1–5]. α-Fe2O3 is very popular due to its non-toxicity, less costly, abundance, thermal and chemical stability at ambient temperature and environmentally friendly [6–9]. It is an intrinsically n-type semiconductor with rhombohedral crystal structure, high refractive index and direct band gap around 1.9 and 2.2eV [10]. Fascinating properties of α-Fe2O3 makes it suitable for various electronic and optoelectronic applications like gas-sensors, vapor sensors, microwave devices, high-density recording media, solid state lithium ion batteries, supercapacitors, water splitting for hydrogen production, solar cells and antibacterial coating [11,12]. α-Fe2O3 is synthesized by several techniques as successive ionic layer adsorption and reaction method [10], sol–gel [12] and chemical vapor deposition [13] to report the optical and structural properties of α-Fe2O3 nanostructure via aqueous solution of Fe(NO3)3·9H2O varied with TS and deposition time.

Yadav et al. [14] have prepared electrochemical supercapacitor performance Hematite α-Fe2O3 by spray pyrolysis from non-aqueous medium. They have studied structural, morphological optical and electrochemical properties of α-Fe2O3. They have revealed that α-Fe2O3 has well covered nanoporous surface. The as prepared films exhibited a direct band gap energy varying from 2.36 to 2.14eV. The α-Fe2O3 has showed a maximum specific capacitance 451g−1 within potential window −1.1 to 0.2V in aqueous 2M KOH electrolyte. Such nanoporous α-Fe2O3 with high performance may be used as a promising material for electrochemical supercapacitors. Hierarchical oxide nanostructure had proved by Jia et al. [15] a promising feature in gas sensing due to their high surface areas and well-aligned nanoporous structures containing less agglomerated configurations. They have developed a facile method to prepare Ag/α-Fe2O3 microspheres using α-FeOOH microspheres as precursor and AgNO3 as Ag resource. Their results revealed that Ag nanoparticles with diameter 5nm formed on the surface of hollow α-Fe2O3 spheres were composed of primary nano-sized particles. The addition of Ag served as an active catalyst, creating more active sites believed crucial for enhancing sensitivity. Li et al. [16] have observed two modulated structures caused by long-range ordering of oxygen vacancies in α-Fe2O3 nanowires (NWs) produced after oxidation of Fe. Both types of oxygen vacancy ordering structures have a similar modulation periodicity of 1.45 or 1.50nm with corresponding atomic ratios of Fe and O (Fe/O) of 0.7407 and 0.7273, respectively. They have studied electron energy-loss spectroscopy to show the Fe/O ratio of NWs is close to that of Fe3O4 when oxygen atoms are not sufficient, which makes the NWs energetically favorable.

Although various studies have been performed, but still there is a lot of studies of effect of annealing temperature on specific properties of α-Fe2O3 nanostructure. Spray pyrolysis technique (SPT) is simple and less expensive technique for preparation of dense and uniform nanostructure via a simple chemical route. There are various deposition parameters such as precursor, solvent concentration, substrate temperature (TS), spray rate, pressure of carrier gas and nozzle to substrate distance. TS is necessary parameter since growth kinetics strongly depends on the temperature at which pyrolysis occurs. Effect of TS on the properties of α-Fe2O3 nanostructure has been reported by few researchers [14–16]. In the present work, structural, morphological and optical properties of annealed α-Fe2O3 nanostructure deposited by SPT under specific conditions different than others [14–16] are investigated. The prime novelty is to interconnect the results obtained from various investigations and point out the effect of TS on the various properties of annealed α-Fe2O3 nanostructure and hence to find out the suitability for gas sensing applications. This work is organized as the followings: Section 2 details the experimental procedure, while the results and discussion are explained in Section 3. The conclusions are summarized in Section 4.

2Experimental process

Spray pyrolysis reactor was used for preparation of α-Fe2O3 nanostructure 0.1M aqueous solution of iron (III) chloride hexahydrate (FeCl3·6H2O, purity 99% MERCK, Germany). The precursor salt was dissolved in distilled water by stirring the mixture with a magnetic stirrer for 60min in order to acquire a homogeneous solution and a few drops of ethanol was added to the solution to ensure better crystallinity. The pH value of solution was about 4. Ultrasonically and chemically cleaned glass slides were used for deposition. An ebonite spray gun with outlet aperture diameter, 0.001m was utilized. The nozzle for substrate separation was arranged constant at 25cm during process of spray. The air has used as carrier gas and air pressure was maintained at 0.50. Spray rate was kept constant at 5mL/min during deposition. α-Fe2O3 was deposited for 10min at various TS between 300 and 500°C. α-Fe2O3 nanostructure was annealed at 450°C for 60min in a tubular furnace (Carbolite SHEFFIELD, UK). The surface morphology of α-Fe2O3 nanostructure was studied by field emission scanning electron microscope (FESEM) (JEOL JSM-7600F, Japan). The FESEM images were taken at 30,000 (×30K) magnification.

Structure of annealed α-Fe2O3 nanostructure was analyzed by X-ray powder diffractometer (XRD, PANalytical EMPYREAN SERIES 2, Netherlands) for wavelength, 1.5406Å as Cu Kα operated target in power input, 60kV. “X’Pert Highscore” computer software was utilized to research 2θ values, spacing of interplanar (d) value and FWHM is full width at half maximum. These parameters of structure were compared with standard data of α-Fe2O3 (JCPDS card: 24-0072). Optical transmittance and absorbance of α-Fe2O3 nanostructure were tested at ambient temperature via UV–vis spectrophotometer (Dynamica Halo DB-20, Australia) in the wavelength range, 200–1100nm.

3Results and discussion3.1Structural properties

The morphology of annealed Fe2O3 nanostructure prepared at various TS captured at ×30K magnification is represented by FESEM images as shown in Fig. 1. FESEM images are comprised of clusters of nanoparticles and film surface and getting roughness with rising TS from 350 to 500°C. Increasing of surface roughness may be associated with the fact that film growth kinetics is governed by chemical reaction in vapor state of spray solution at higher TS[17]. After annealing the Fe2O3 nanostructure, nanoparticle agglomerates to be more distinguishable as observed in Fig. 1. Among the four FESEM images, Fig. 1(a) represents uniformity and even distribution of nanoparticles on the film surface; the reason of uniformity may be attributed to removal of oxide layers and rearrangements of particles via annealing process. This is may be due to the temperature effect [18–20]. The surface morphology of Fe2O3 nanostructure deposited at TS, 400°C is not much changed due to low annealing process for removal of fine cracks. At TS, 400, 450 and 500°C, the particle agglomerates and found more clearly visible as seen in Fig. 1(b), (c) and (d), respectively. Fig. 1(d) exhibits the nanoparticle-agglomerates to be more closely spaced on the film surface, porous and forming a rock-like morphology. It can be said that the surface roughness of annealed Fe2O3 nanostructure is found to be increased with TS. Similar annealing effect on surface morphology is observed for Fe2O3 nanostructure [21]. The surface morphology of Fe2O3 nanostructure is observed of porous nature which is strongly influenced by TS and annealing. Response of Fe2O3 nanostructure-based gas sensor depends very strongly on the surface morphology [22].

Fig. 1.

FESEM images of annealed α-Fe2O3 nanostructure at TS (a) 350, (b) 400, (c) 450 and (d) 500°C, taken at 30K magnification.


XRD patterns of annealed α-Fe2O3 nanostructure in Fig. 2 show improvement in polycrystalline rhombohedral hexagonal crystal structure with the peaks (104), (110), (006), (300), (122). Among all these peaks, (104) is the predominant one indicating high orientation along that crystal plane. The XRD patterns are matching the standard data of α-Fe2O3 (JCPDS card: 24-0072) [23]. No peak corresponding to non-stoichiometric or any other phase of α-Fe2O3 is found. Intensity of (104) peak increases with increasing of TS and indicating the betterment of crystallinity of α-Fe2O3 nanostructure via annealing which is in good agreement with other [23,24]. The intensity of (104) peaks is rising with the rise of TS. The other peaks are appearing in XRD patterns of annealed α-Fe2O3 nanostructure in an irregular manner. This may be affirmed as the difference in surface morphological features as shown in Fig. 1.

Fig. 2.

XRD patterns of annealed α-Fe2O3 nanostructure at TS (a) 300, (b) 350 (c) 400 and (d) 500°C.


Crystallite size (D) and dislocation density (δ) of α-Fe2O3 nanostructure have been evaluated by Scherrer formula [25]. The strain (ɛ) and lattice constants (a and c) of α-Fe2O3 nanostructure are calculated using the relations given in the references [26,27], respectively. Texture coefficient (TC) for the preferential (104) peak in the XRD pattern of α-Fe2O3 nanostructure is evaluated using the equation mentioned elsewhere [28]. Porosity of α-Fe2O3 nanostructure is computed using the relation [29],

where ρexpt and ρstd are the experimental and standard density of α-Fe2O3. Table 1 presents the structural parameters of annealed α-Fe2O3 nanostructure. Increasing of D with TS can be correlated directly as found in FESEM images. Decreasing of ɛ and δ values with rising of TS occurs as a consequence of rising D value. There is an increasing in a value excepting for case at 400°C and decreasing in c value, followed by c/a ratio reduces indicating a reduction of size of unit cell and lowering the growth along c-axis. Rise of TC (104) is a strong evidence of promotion of growth along (104) plane. Increment in porosity of annealed α-Fe2O3 nanostructure may occur as a result of removal of oxide layers and rearrangements of particles via annealing that correlate directly. D values of annealed α-Fe2O3 nanostructure are found in few nm, which is very much suitable for gas sensing applications. Small particle size ensures large specific surface area and excellent sensitivity to gases [30].

Table 1.

Structural parameter of annealed α-Fe2O3 nanostructure.

TS (°C)  D (nm)  ɛ 10−4  δ 10−4 (nm−2a (Å)  c (Å)  c/a  TC (104)  Porosity (%) 
300  43  9.22  6.90  5.0157  13.8334  2.76  0.36  0.30 
350  44  9.08  6.87  5.0217  13.8013  2.75  0.38  0.35 
400  45  8.57  5.95  5.0120  13.6957  2.73  0.43  0.67 
500  63  7.13  4.39  5.0312  13.6775  2.72  0.52  0.76 
3.2Optical properties

Optical transmittance (T) of annealed α-Fe2O3 nanostructure is plotted against photon wavelength as displayed in Fig. 3. The annealed α-FeO nanostructure is found transparent in UV–vis. In Fig. 3, T increases slightly with increasing of TS in the range 300–500°C. Maximum T is found to be 72% for α-Fe2O3 nanostructure deposited at the TS, 300°C. Clearer porosity at low TS is more effective than high TS and corresponding to small D, that causes an increasing of T as proved in Table 1. Reduction in T of α-Fe2O3 nanostructure deposited at TS, 500°C may be attributed to higher surface roughness and changes in the structure and morphology [31].

Fig. 3.

Variations of transmittance (T%) of annealed Fe2O3 nanostructure.


Extinction coefficient (k) is calculated using the formula [32] as displayed in Table 2. The optical band gap for direct transition (Eg) is calculated using Tauc formula [33] and refractive index (η) is evaluated using the formula [32]. Eg of annealed α-Fe2O3 nanostructure is evaluated using the Tauc plots as shown in Fig. 4. Eg value decreases with increasing TS which may be attributed to the change in surface morphological and structural features. Band gap values are in accordance with values of α-Fe2O3[2,14].

Table 2.

Optical properties of annealed α-Fe2O3 nanostructure.

TS (°C)  Eg (eV)  η (at 650nm)  k (at 650nm) 
300  2.090  2.37  0.16 
350  2.084  2.38  0.17 
400  2.076  2.54  0.21 
500  2.058  2.62  0.26 
Fig. 4.

Tauc plots of annealed α-Fe2O3 nanostructure.


The structure, morphology and optical properties of α-Fe2O3 nanostructure synthesized at different TS in the range of 300–500°C are investigated by SPT. Annealed hexagonal rhombohedral structure is highly improved with enhancement of intensity of (104) peak in XRD patterns, the porous structure is more regulated with increasing of roughness. The annealed α-Fe2O3 nanostructure was transparent. Optical band gap, refractive index and extinction coefficient of annealed α-Fe2O3 nanostructure correlated inversely and directly with TS, respectively. The α-Fe2O3 nanostructure deposited at TS, 500°C shows less transmittance, high refractive index and high extinction coefficient due to its high roughness. It can be stated that highly absorbing, better crystalline structure and porous surface of α-Fe2O3 nanostructure are possible to achieve at TS, 300°C. It is expected that α-Fe2O3 nanostructure is a suitable candidate for gas sensors.

Conflicts of interest

The authors declare no conflicts of interest.


It is pleasure to present our sincere acknowledgments to University of Malaya of grant number RU2018 NANOCAT.

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Recent trends in nano-based drug delivery systems for efficient delivery of phytochemicals in chemotherapy.
RSC Adv, 6 (2016), pp. 48294-48314
A. Godlyn Abraham, A. Manikandan, E. Manikandan, S.K. Jaganathan, A. Baykal, P. Sri Renganathan.
Enhanced opto-magneto properties of NixMg1−xFe2O4 (0.0<x<1.0) ferrites nano-catalysts.
J Nanoelectron Optoelectron, 12 (2017), pp. 1326-1333
B. Li, W. Shang, D. Zhang, M. He.
Influences of different precursors upon humidity sensing properties of BaTiO3 nanowires prepared by molten salt synthesis method.
J Nanosci Nanotechnol, 16 (2016), pp. 7325-7336
K. Chitra, K. Reena, A. Manikandan, S. Arul Antony.
Antibacterial studies and effect of poloxamer on gold nanoparticles by Zingiber officinale extracted green synthesis.
J Nanosci Nanotechnol, 15 (2015), pp. 4984-4991
B. Meenatchi, V. Renuga, A. Manikandan.
Size-controlled synthesis of chalcogen and chalcogenide nanoparticles using protic ionic liquids with imidazolium cation.
Korean J Chem Eng, 33 (2016), pp. 934-944
A. Manikandan, A. Saravanan, S. Arul Antony, M. Bououdina.
One-pot low temperature synthesis and characterization studies of nanocrystalline α-Fe2O3 based dye sensitized solar cells.
J Nanosci Nanotechnol, 15 (2015), pp. 4358-4366
A. Manikandan, J. Judith Vijaya, L. John Kennedy.
Structural, optical and magnetic properties of porous α-Fe2O3 nanostructures prepared by rapid combustion method.
J Nanosci Nanotechnol, 13 (2013), pp. 2986-2992
A. Manikandan, J. Judith Vijaya, J. Arul Mary, L. John Kennedy, A. Dinesh.
Structural, optical and magnetic properties of Fe3O4 nanoparticles prepared by a facile microwave combustion method.
J Ind Eng Chem, 20 (2014), pp. 2077-2085
K. Chinnaraj, A. Manikandan, P. Ramu, S. Arul Antony, P. Neeraja.
Comparative studies of microwave- and sol–gel-assisted combustion methods of Fe3O4 nanostructures: structural, morphological, optical, magnetic, and catalytic properties.
J Supercond Novel Magn, 28 (2015), pp. 179-190
C. Xia, Y. Jia, M. Tao, Q. Zhang.
Tuning the band gap of hematite α-Fe2O3 by sulfur doping.
Phys Lett A, 377 (2013), pp. 1943-1947
L. Yu, Y. Zhang, J. He, H. Zhu, X. Zhou, M. Li, et al.
Enhanced photoelectrochemical properties of α-Fe2O3 nanoarrays for water splitting.
J Alloys Compd, 753 (2018), pp. 601-606
M. Cavas, R.K. Gupta, A.A. Al-Ghamdi, Z.H. Gafer, F. El-Tantawy, F. Yakuphanoglu.
Preparation and characterization of dye sensitized solar cell based on nanostructured Fe2O3.
Mater Lett, 105 (2013), pp. 106-110
S. Osaka, O. Kubo, K. Takahashi, M. Oda, K. Kaneko, H. Tabata, et al.
Unpredicted surface termination of α-Fe2O3(0001) film grown by mist chemical vapor deposition.
Surf Sci, 660 (2017), pp. 9-15
A.A. Yadav, T.B. Deshmukh, R.V. Deshmukh, D.D. Patil, U.J. Chavan.
Electrochemical supercapacitive performance of Hematite α-Fe2O3 thin films prepared by spray pyrolysis from non-aqueous medium.
Thin Solid Films, 616 (2016), pp. 351-358
X. Jia, X. Yu, L. Xia, Y. Sun, H. Song.
Synthesis and characterization of Ag/α-Fe2O3 microspheres and their application to highly sensitive and selective detection of ethanol.
Appl Surf Sci, 462 (2018), pp. 29-37
T. Li, H. Feng, Y. Wang, C. Wang, W. Zhu, L. Yuan, et al.
Formation of modulated structures induced by oxygen vacancies in α-Fe2O3 nanowires.
J Cryst Growth, 498 (2018), pp. 10-16
H. Alijani, Z. Shariatinia.
Effective aqueous arsenic removal using zero valent iron doped MWCNT synthesized by in situ CVD method using natural α-Fe2O3 as a precursor.
Chemosphere, 171 (2017), pp. 502-511
A. Silambarasu, A. Manikandan, K. Balakrishnan.
Room-temperature superparamagnetism and enhanced photocatalytic activity of magnetically reusable spinel ZnFe2O4 nanocatalysts.
J Supercond Novel Magn, 30 (2017), pp. 2631-2640
S. Asiri, M. Sertkol, H. Güngüneş, Md. Amir, A. Manikandan, İ. Ercan, et al.
The temperature effect on magnetic properties of NiFe2O4 nanoparticles.
J Inorg Organomet Polym Mater, 28 (2018), pp. 1587-1597
A. Silambarasu, A. Manikandan, K. Balakrishnan, S.K. Jaganathan, E. Manikandan, J.S. Aanand.
Comparative study of structural, morphological, magneto-optical and photo-catalytic properties of magnetically reusable spinel MnFe2O4 nano-catalysts.
J Nanosci Nanotechnol, 18 (2018), pp. 3523-3531
L. Li, C. Liu, H. Zhang, P. Liang, N. Mitsuzaki, Z. Chen.
Synergistic effect of Ti(OBu)4 and annealing regime on the structure, morphology and photoelectrochemical response of α-Fe2O3 photoanode.
Electrochim Acta, 281 (2018), pp. 246-256
S. Saritas, M. Kundakci, O. Coban, S. Tuzemen, M. Yildirim.
Ni:Fe2O3, Mg:Fe2O3 and Fe2O3 thin films gas sensor application.
Physica B: Condens Matter, 541 (2018), pp. 14-18
P. Li, Z. He, C. Luo, Y. Xiao, Y. Wang, J. Hu, et al.
α-Fe2O3@dopamine core–shell nanocomposites and their highly enhanced photoacoustic performance.
Appl Surf Sci, 466 (2019), pp. 185-192
G. Rahmana, O.S. Joo.
Facile preparation of nanostructured α-Fe2O3 thin films with enhanced photoelectrochemical watersplitting activity.
J Mater Chem A, 1 (2013), pp. 5554-5561
K.M. Batoo, G. Kumar, Y. Yang, Y. Al-Douri, M. Singh, R.B. Jotania, et al.
Structural, morphological and electrical properties of Cd2+ doped MgFe2−xO4 ferrite nanoparticles.
J Alloys Compd, 726 (2017), pp. 179-186
K. Gherab, Y. Al-Douri, C.H. Voon, U. Hashim, M. Ameri, A. Bouhemadou.
Aluminium nanoparticles size effect on the optical and structural properties of ZnO nanostructure synthesized by spin-coating technique.
Results Phys, 7 (2017), pp. 1190-1197
Y. Al-Douri, M. Ameri, A. Bouhemadou, R. Khenata.
Annealing temperature effect on structural, optical, morphological and electrical properties of CdS/Si(100) nanostructure.
Microsyst Technol, 22 (2016), pp. 2529-2541
J. Lin, X. Zhang, L. Zhou, S. Li, G. Qin.
Pt-doped α-Fe2O3 photoanodes prepared by a magnetron sputtering method for photoelectrochemical water splitting.
Mater Res Bull, 91 (2017), pp. 214-219
U. Khan, A. Akbar, H. Yousaf, S. Riaz, S. Naseem.
Ferromagnetic properties of Al-doped Fe2O3 thin films by sol–gel.
Mater Today: Proc, 2 (2015), pp. 5415-5420
C. Liu, Y. Wang, P. Zhao, W. Li, Q. Wang, P. Sun, et al.
Porous α-Fe2O3 microflowers: synthesis, structure, and enhanced acetone sensing performances.
J Colloid Interface Sci, 505 (2017), pp. 1039-1046
Z. Liu, R. Yu, Y. Dong, W. Li, B. Lv.
The adsorption behavior and mechanism of Cr(VI) on 3D hierarchical α-Fe2O3 structures exposed by (001) and non-(001) planes.
Chem Eng J, 309 (2017), pp. 815-823
S. Shuang, Z. Xie, Z. Zhang.
Enhanced photocatalytic properties of CdS nanoparticles decorated α-Fe2O3 nanopillar arrays under visible light.
J Colloid Interface Sci, 494 (2017), pp. 107-113
S. Ibraheam, Y. Al-Douri, A.H. Azman.
Characterization and analysis of wheat-like CdS nanostructure under temperature effect for solar cells applications.
Optik, 127 (2016), pp. 8907-8915
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