Ganeshraja Ayyakannu Sundaram
Mössbauer spectroscopy is based on the Mössbauer effect discovered by Rudolf Mössbauer [1]. The discovery was honored by the Nobel Prize in 1961. Mössbauer spectroscopy effect is the recoilless (also called: recoil-free) nuclear resonance emission/absorption of γ-rays. In the case of a nuclear transition, the de-excited nucleus is normally recoiled by the momentum of the γ-photon emitted, which makes its resonance absorption impossible by another ground-state nucleus of the same types. In solids, however, recoilless photons can be emitted (and reabsorbed by another ground-state nucleus) with some probability. The basic principles of Mössbauer spectroscopy presented in below video (see in online). Mössbauer spectroscopy has found numerous applications in physics, chemistry and biology. This spectroscopic technique continues to make significant contributions, such as 2004/5’s analysis of soil on the surface of Mars [2], with spectra collected in situ. In this merit, I carried out some of the works on 119Sn and 57Fe Mössbauer spectroscopy investigations of Sn and Fe containing titania nanoparticles, respectively, in Mössbauer Effect Data Center, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian, China [3-8].
Figure 1 57Fe Mössbauer spectra of different concentration of iron presented titania (S1-S5) samples at room temperature [3].
Herein, I give an interesting 57Fe Mössbauer spectroscopy report on iron grafted and doped titania nanoparticles. 57Fe Mössbauer spectroscopy measurements were used in determining the chemical state of iron in as-prepared samples. As shown in Figure 1, the spectral peaks of different concentration of iron presented titania (S1-S5) samples could be fitted by the simple addition of spectra for iron oxide coupled and doped TiO2 in equal proportion [3]. It is noteworthy that the quadrupole splitting (QS) and isomer shift (IS) for the surface-coupled and bulk-doped iron oxide are different. The doublets were assigned to Fe3+ states and showed IS = 0.35-0.38 mms-1 and QS = 0.50-0.61 mms-1 for iron oxide doped TiO2, whereas IS = 0.33-0.36 mms-1 and QS = 0.94-1.08 mms-1 for iron oxide surface coupled TiO2, indicates surface iron oxide having a larger structural degree of freedom as compared to that of doped iron oxide. It may be due to the formation of higher symmetric state, and oxygen vacancies or structural defects [9]. The peak area of bulk doped and coupled iron sites are 18.4-45.7% and 54.3-81.6% for different concentration of iron present in titania (S1-S5) samples. It concluded that bulk doped iron sites are smaller than surface coupled iron sites. Alternatively, the value of isomer shift for the superparamagnetic doublet is around 0.34 mm s-1 with larger QS values of the sample with particle diameter of less than 10 nm, which is larger than those of the amorphous samples [10]. This confirms that the nanoparticles begin to show superparamagnetic behavior in the case of hematite. The superparamagnetic behavior [11] of these nanoparticles leads to a complete lack of magnetic hyperfine splitting of the spectrum and represents in quadrupole doublet with IS of ~0.34 mm s-1 and a QS of ~0.99 mm s-1 [12]. These results confirm that bulk doped Fe3+ ions are substitutionally introduced into TiO2 crystal at Ti4+ sites and superparamagnetic Fe2O3 nanocrystals are in coupled state with titania surface matrix.
References
[1] R.L. Mössbauer, Z. Physik 151 (1958) 124-143.
[2] G. Klingelhofer, http://akguetlich.chemie.unimainz.de/klingelhoefer/rahmen/
eframrows.htm (see also http://athena.cornell.edu/ the_mission/ins_moss.html).
[3] A.S. Ganeshraja, K. Rajkumar, K. Zhu, X. Li, S. Thirumurugan, W. Xu, J. Zhang, M.
Yang, K. Anbalagan, J. Wang, RSC Adv. 6 (2016) 72791–72802.
[4] A.S. Ganeshraja, S. Thirumurugan, K. Rajkumar, K. Zhu, Y. Wang, K. Anbalagan, J.
Wang, RSC Adv. 6 (2016) 409-421.
[5] A. S. Ganeshraja, K. Nomura, J. Wang, Hyperfine Interact. 237 (2016) 139 (1-8).
[6] A.S. Ganeshraja, M. Yang, K. Nomura, S. Maniarasu, G. Veerappan, T. Liu, J. Wang, J.
Phys. Chem. C 121 (2017) 6662−6673.
[7] A.S. Ganeshraja, K. Zhu, K. Nomura, J. Wang, Appl. Surf. Sci. 441 (2018) 678–687.
[8] A. S. Ganeshraja, J. Wang, Mössbauer Effect Reference and Data Journal, 41(1) (2018)
1-34.
[9] M. Liu, X. Qiu, M. Miyauchi, K. J. Am. Chem. Soc., 135 (2013) 10064−10072.
[10] T.K. Kundu, M. Mukherjee, D. Chakravorty, T. P. Sinha: J. Mater. Sci., 33 (1998)
1759−1763.
[11] A.F. Lehlooh, S.H. Mahmood, J. Magnet. Magnet. Mater., 151 (1995) 163−166.
[12] M. Grigorova, H.J. Blythe, V. Blaskov, V. Rusanov, V. Petkov, V. Masheva, D. Nihtianova,
L. M. Martinez, J. S. Munoz, M. Mikhov, J. Magnet. Magnet. Mater., 183 (1998)
163−172.
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Department of Chemistry, National College (Autonomous),
Tiruchirapalli 620 001, Tamil Nadu, India
e-mail: drganeshraja13@gmail.com
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