Mechanics, Materials Science & Engineering, April 2017 – ISSN 2412-5954
Structural, Optical, Morphological and Elemental Analysis on Sol-gel Synthesis of Ni Doped TiO2 Nanocrystallites4 T. Sakthivel1, K. Jagannathan1,a 1 – Department of Physics, SRM University, Vadapalani campus, Chennai-600026, Tamilnadu, India a – kjagan81@gmail.com DOI 10.2412/mmse.80.76.610 provided by Seo4U.link
Keywords: TiO2 nanoparticle, sol-gel synthesis, band gap tuning, photoanode.
ABSTRACT. Pure and Ni doped titanium dioxide nanoparticles were successfully synthesized by sol-gel method and characterized usingXRD, UV-Visible, FTIR, FESEM and EDS techniques. XRD pattern confirms the formation of tetragonal TiO2. The absorbance spectra of pure and Ni doped TiO2 showed absorption spectrum at ultra-violet region due to electronic transition between bonding and anti-bonding orbital (π-π•). Bandgap energy of Ni doped TiO2 decreased to 2.5 eV when compared to pure TiO2 (3.39 eV). FESEM study reveals agglomerated spherical shaped morphology. The functional groups of the prepared samples were identified using FTIR spectroscopy and the elemental analysis was further supported with EDS analysis.
Introduction. TiO2 is the promising material as semiconductor having high photochemical stability, non-toxicity, high surface area and low cost. TiO2 is used in many applications such as pigments, adsorbents, photo catalytic, sensors, Photovoltaic devices. [1-2]TiO2 exhibit three main phases namely anatase, rutile and brookite [3]. Among them anatase phase is formed at a lower temperature with a band gap of 3.0-3.2 eV, whereas for the rutile it is 3.0 eV[4]. Also, it has proven itself as one of the promising material to replace the toxic and expensive other metal oxides like CdO, SnO2, In2O3 and etc., for opto-electronic applications. Among others, TiO2 is a superior one in opto-electronic applications, especially in conducting electrodes of dye-sensitized solar cells (DSSC). But the limitation towards using metal oxides is absorption spectrum in UV region [5]. Different dopants are used in TiO2 for the absorption of visible light, such as transition metal ion doping (Fe, Co, Ni, Cu, Zn and Zr) has been found to be efficient dopants for improved photostability and bandgap tuning[6]. Experimental Procedure Preparation of TiO2 Nanoparticles.The TiO2 nanoparticles were obtained from 5 ml of titanium (IV) isopropoxide (TTIP) dissolved in 5 ml of ethanol with 20 ml of distilled water added to the above solution. The mixed solution was vigorously stirred for 1 hr in order to form a gel. The gel was dried at 75 °C for 5 hr to remove the water and organic materials. Then, the dried gel was sintered at 450°C for 2 hr in high temperature muffle furnace. Finally the pureTiO2 nanoparticles were obtained by solgel method. Preparation of nickel doped TiO2 nano particles.The nickel doped TiO2 nano particles were obtained from titanium (IV) isopropoxide (TTIP) and iso-propanol as the starting material. 5 ml of TTIP was added drop wise to 45 ml of iso-propanol for the TiO2 formation. The solution was vigorously stirred for 45 min to form sols. 5% nickel nitrate was mixed drop by drop to the above
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Mechanics, Materials Science & Engineering, April 2017 – ISSN 2412-5954
solution with constant stirring for 1 hr to form the gel. After that a similar procedure explained above was followed to obtain Ni/TiO2 nano particles by sol-gel method. Results and Discussions Structural analysis: X-ray diffraction The Fig.1 shows the XRD pattern of pure and nickel doped TiO2 nanoparticles prepared by sol gel method. The peaks in the diffraction patterns corresponds to anatase phase of TiO2 nanoparticles, the lattice parameters have been calculated and it was found to be a = b=3.7898 Å and c= 9.5148 Å. The obtained lattice parameter values are matched with previous literatures and diffraction pattern was in good agreement with JCPDS files # 21-1272 [7]. The dominant (101) peak shows that the anatase phase was formed in the synthesized materials. Intensity of diffraction peaks in Ni doped TiO2 is low and a slight broadness occurred in diffraction peaks of Ni/TiO2 nanoparticles is due to nickel content.
Fig. 1. XRD pattern of TiO2 and Ni/TiO2 nanoparticles. The crystallite size of the pure and nickel doped TiO2 nanoparticles are found to be 10 nm. Crystallite size (D) of these samples are estimated by applying the Scherrer’s equation. Optical studies: UV-Visible spectroscopy. The Fig. 2 (a) shows the optical absorption spectrum of TiO2 and Ni/TiO2 with an absorption maximum at 312 nm and 337 nm respectively. The absorption edges of Ni doped nanoparticles were shifted to the lower energy region (red shift) compared to pure TiO2. The Fig.2 (b) shows the estimated optical band gap energy of prepared nanoparticles using Tauc plot and band gap values are found to be 3.39 eV and 2.5 eV for pure and Ni doped TiO2 respectively. The reduction in band gap energy of Ni/TiO2 is due to the presence of Ni metal ion which induces metastable states in pure TiO2 for band gap tuning.
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Mechanics, Materials Science & Engineering, April 2017 – ISSN 2412-5954
b)
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Fig. 2. (a) optical absorption spectra of TiO2 and Ni/TiO2 nano particles. (b) Tauc plot of TiO2 and Ni/TiO2 nano particles. Elemental analysis: FTIR
Fig. 3. FTIR Spectrum of TiO2 and Ni/TiO2 nanoparticles. The FTIR spectrum of Pure and nickel doped TiO2 nanoparticles are shown in Fig. 3. The broadband spectrum occurs at 510-780 cm-1 corresponds to metal oxides (TiO2 nanoparticles). It is attributed to the Ti-O bending vibration and shows the formation of metal oxide bonding in the prepared sample. Whereas, the characteristic peaks at 1619 cm-1 and 3962 cm-1 are associated with the O-H bending vibration of the water molecules absorbed on TiO2 surfaces in pure TiO2 and Ni doped TiO2. The peaks obtained at 3360 cm-1 is due to stretching vibration of O-H groups in the prepared samples. Morphological analysis: FESEM The morphology of synthesized material is spherical shaped nanoparticles combined with flake shaped morphology with agglomeration in pure TiO2 are shown in Fig. 4. But Ni doped TiO2 nanoparticles exhibit non-uniform distribution compared with those of pure TiO2 and this result suggest that Ni doping can suppress the TiO2 particle growth, as is shown in Fig. 4.
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Mechanics, Materials Science & Engineering, April 2017 – ISSN 2412-5954
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Fig. 4. FESEM Images of pure TiO2 and Ni/TiO2 nanoparticles. EDS Analysis. From the Fig. 5. EDS spectrum doping of Ni into TiO2 is confirmed according to the relative atomic and weight percentage of Ni. It is clear from Ni element is present in the doped TiO2 samples and Ni2+ ions are incorporated in Ti4+ lattice sites.
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a) Fig. 5. EDAX Spectra for pure TiO2 and Ni/TiO2 nanoparticles.
Summary. In summary TiO2 and Ni/TiO2 nanoparticles were prepared by simple sol-gel method. The XRD analysis confirms the formation of anatase TiO2 nano particles. The doping of Ni into TiO2 lattice shifts the position of its fundamental absorption edge toward the longer wavelength and reduces its band gap energy, so that it can absorb energy from visible light photons. The existences of functional groups were identified by FTIR analysis. The FESEM analysis shows the mixed morphology of both spherical and flake like morphology with rough surfaces in the prepared samples. Hence the prepared sample with reduced bandgap energy of Ni doped TiO2 may be useful in photoanode application of DSSC. Acknowledgement: The authors convey their gratitude to the management of SRM University for their motivation and support. References [1] Siti Nur Fadhilah Zainudin, Masturah Markom, Huda Abdullah, structural behavior of ni-doped TiO2 Nanoparticles and Its photovoltaic performance on dye-sensitized solar Cell (DSSC), Advanced Materials Research Vol. 879 (2014) pp 199-205, doi:10.4028/www.scientific.net/AMR.879.199 [2] R. Elilarassi, G. Chandrasekaran, Synthesis, Structural and optical characterization of Ni-doped ZnO nanoparticles, J. Mater Sci: Mater Electron (2011) 22:751–756, DOI 10.1007/s10854-0100206- 8
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