Optical properties of cerium oxide (CeO2) nanoparticles synthesized by hydroxide mediated method Mawlood Maajal Ali, Hadeel Salih Mahdi, Azra Parveen, and Ameer Azam
Citation: AIP Conference Proceedings 1953, 030044 (2018); doi: 10.1063/1.5032379 View online: https://doi.org/10.1063/1.5032379 View Table of Contents: http://aip.scitation.org/toc/apc/1953/1 Published by the American Institute of Physics
Optical Properties of Cerium Oxide (CeO2) Nanoparticles Synthesized by Hydroxide Mediated Method Mawlood Maajal Ali, Hadeel Salih Mahdi, Azra Parveen a) and Ameer Azam Department of Applied Physics, Z.H. College of Engineering & Technology, Aligarh Muslim University, Aligarh202002, India a) Email; [email protected]
Abstract: The nanoparticles of cerium oxide have been successfully synthesized by hydroxide mediated method, using cerium nitrate and sodium hydroxide as precursors. The microstructural properties were analyzed by X- ray diffraction technique (XRD). The X-ray diffraction results show that the cerium oxide nanoparticles were in cubic structure. The optical absorption spectra of cerium oxide were recorded by UV-VIS spectrophotometer in the range of 320 to 600 nm and photoluminescence spectra in the range of 400-540 nm and have been presented. The energy band gap was determined by Tauc relationship. The crystallite size was determined from Debye–Scherer equation and came out to be 6.4 nm. Keywords: XRD, Optical Properties, FTIR PACS: 61.05.cp; 78.67; 33.20.Ea.
INTRODUCTION Nanotechnology advances the possibility to create and manage materials at the nanometre scale. In recent years, considerable efforts have been done towards the development of new synthetic methods for preparation of nano structure cerium oxides due to their potential advantages in several applications, such as a catalyst, an electrolyte material of solid oxide fuel cells, diesel fuel additive, a material of high refractive index, an insulating layer on silicon substrates, gas sensors and more recently biomedicine [1–5]. Cerium oxide (CeO2) also known as nano ceria is an excellent semiconducting material with broad band gap energy of 3.19 eV which makes them good candidate for catalytic applications . There are many studies that describe the biological effects of nano ceria. It has been clearly established that cerium oxide nanoparticles, different to other metal oxide nanoparticles, not exhibit cytotoxic effects, but also confer protection against numerous cellular damages, such as radiological insults which promote the production of free radicals [7, 8]. Several methods have been used to synthesize cerium oxide nanoparticles . In this paper, the cerium oxide nanoparticles were successfully synthesized by hydroxide mediated method. The properties of the prepared materials were characterized by X-ray diffraction (XRD) analysis, Fourier transformed infrared (FT-IR) spectra, UV-analysis and PL Spectroscopic techniques
MATERIALS AND METHOD Cerium Oxide is synthesized by hydroxide mediated method. An aqueous solutions of 0.1M of cerium nitrate and 0.1M of NaOH were prepared separately with double distilled water. The solution of NaOH was added dropwise to the solution of cerium nitrate and stirred using magnetic stirrer for 4 h at room temperature. After the addition of NaOH solution, a precipitate with pinkish color was obtained. The obtained precipitate was washed with double distilled water and ethanol and then further subjected to centrifugation at 6000 rpm for 20 min. This process was repeated for 4 times. The obtained sample was then dried at 70 0C for 2 h in the oven and then annealed at 240 0C for 10 h to obtain the final pinkish color cerium oxide nano powder.
2nd International Conference on Condensed Matter and Applied Physics (ICC 2017) AIP Conf. Proc. 1953, 030044-1–030044-4; https://doi.org/10.1063/1.5032379 Published by AIP Publishing. 978-0-7354-1648-2/$30.00
RESULTS AND DISCUSSION Structure Analysis The XRD pattern of cerium oxide nano powder shown in Fig.1 was characterized by X-ray diffraction (XRD) in the 2q range of 200–700 (Rigaku Miniflex II) using Cu Kα radiations (λ = 1.54A˚) operated at a voltage of 30 kV and current of 15 mA. The diffracted peaks found at diffraction angles 2q of 28.270, 32.780, 47.050, 55.940, 59.070 and 69.090 corresponds to the (111), (200),(220),(311),(222) and (400) peak with cubic phase. The powder patterns are in good agreement with the standard JCPDS card no. (JCPDS-34-0394) .The spectra clearly depicts that there are no extra impurity peaks present. The crystallite size of cerium oxide nano powders was determined from Debye– Scherer equation  and came out to be 6.4 nm.
FIGURE 1. XRD patterns of cerium oxide
Optical Properties The optical properties of cerium oxide nanoparticles were studied by UV-visible absorption spectroscopy (Perkin Elmer Spectrophotometer) in the range of 320−600 nm and are shown in Fig. 2(a). Absorbance peak was observed around at 349 nm for the prepared cerium oxide nanoparticles. The absorbance usually depends on numerous factors such as band gap, oxygen deficiency, grain size, impurity centers, lattice strain and surface roughness .
FIGURE 2(a). Absorbance spectra of cerium oxide nanoparticles
The optical band gap of the nano powder was calculated by the Tauc relationship  as shown in Fig. 2(b) and came out to be 3.1 eV.
FIGURE 2(b). Band gap of cerium oxide nanoparticles
FTIR Spectroscopy FTIR spectra of cerium oxide nanoparticles were recorded by the Perkin-Elmer in the range of 400−4000 cm−1 and shown in Fig.3 which recognize the chemical bonds as well as functional groups in the compound.The large peak at 3472 cm-1 is due to the O−H group displays the stretching vibration of the absorbed water on the surface of the cerium oxide nanoparticles . The absorption peak around 1385 cm-1 is due to the N-O stretching band. The absorption peaks around 1055 and 852 cm-1 corresponds to the stretching and bending vibrations of the intercalated C–O species in the precursor. The functional group of C=C was observed at peak 1510 cm-1.The peak at 560 cm-1 is attributed to the O-Ce-O stretching mode of vibration .
FIGUR 3. FTIR spectra of cerium oxide nanoparticles
Photoluminescence Spectra (PL) The fluorescence spectra of the cerium oxide were recorded at room temperature by Fluorescence spectrophotometer (F-4600) with the excitation wavelength of 330 nm and shown in Fig.4. Photoinduced fluorescence spectrum is very useful technique for investigating energy levels. The violet emission peak at 477 nm due to the radiating defects is related to the interface traps existing at the grain boundaries . The bluish green emission at 508 nm may also attribute to the surface defects, and a few authors reported that these peaks are related to the dislocations or oxygen defects .
FIGURE 4. PL spectra of cerium oxide nanoparticles
CONCLUSIONS We have successfully synthesized cerium oxide nanoparticles by hydroxide mediated method. The confirmation of nanoparticles structure of cerium oxide was completed through XRD data which shows the presence of all the main peaks. The sharp peaks in FTIR spectrum determined the existence of Ce-O stretching mode. The optical band gap energy was calculated from Tauc relationship and came out to be 3.1 eV for cerium oxide. The intensity of PL band is observed to decrease with increasing calcination temperature due to the increase in particle size.
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