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Indian Institute of Science

1. Chalasani, Rajesh. Functionalized Nanostructures : Iron Oxide Nanocrystals and Exfoliated Inorganic Nanosheets.

Degree: PhD, Faculty of Science, 2018, Indian Institute of Science

This thesis consists of two parts. The first part deals with the magnetic properties of Fe3O4 nanocrystals and their possible application in water remediation. The second part is on the delamination of layered materials and the preparation of new layered hybrids from the delaminated sheets. In recent years, nanoscale magnetic particles have attracted considerable attention because of their potential applications in industry, medicine and environmental remediation. The most commonly studied magnetic nanoparticles are metals, bimetals and metal oxides. Of these, magnetite, Fe3O4, nanoparticles have been the most intensively investigated as they are, non-toxic, stable and easy to synthesize. Magnetic properties of nanoparticles such as the saturation magnetization, coercivity and blocking temperature are influenced both by size and shape. Below a critical size magnetic particles can become single domain and above a critical temperature (T B , the blocking temperature) thermal fluctuations can induce random flipping of magnetic moments resulting in loss of magnetic order. At temperatures above the blocking temperature the particles are superparamagnetic. Magnetic nanocrystals of similar dimensions but with different shapes show variation in magnetic properties especially in the value of the blocking temperature, because of differences in the surface anisotropy contribution. The properties of magnetic nanoparticles are briefly reviewed in Chapter 1. The objective of the present study was to synthesize Fe3O4 nanocrystals of different morphologies, to understand the difference in magnetic properties associated with shape and to explore the possibility of using Fe3O4 nanocrystals in water remediation. In the present study, oleate capped magnetite (Fe3O4) nanocrystals of spherical and cubic morphologies of comparable dimensions (∼10nm) have been synthesized by thermal decomposition of FeOOH in high-boiling octadecene solvent (Chapter 2). The nanocrystals were characterized by XRD, TEM and XPS spectroscopy. The nanoparticles of different morphologies exhibit very different blocking temperatures. Cubic nanocrystals have a higher blocking temperature (T B = 190 K) as compared to spheres (T B = 142 K). From the shift in the hysteresis loop it is demonstrated that the higher blocking temperature is a consequence of exchange bias or exchange anisotropy that manifests when a ferromagnetic material is in physical contact with an antiferromagnetic material. In nanoparticles, the presence of an exchange bias field leads to higher blocking temperatures T B because of the magnetic exchange coupling induced at the interface between the ferromagnet and antiferromagnet. It is shown that in these iron oxide nanocrystals the exchange bias field originates from trace amounts of the antiferromagnet wustite, FeO, present along with the ferrimagnetic Fe3O4 phase. It is also shown that the higher FeO content in nanocrystals of cubic morphology is responsible for the larger exchange bias fields that in turn lead to a higher blocking temperature.… Advisors/Committee Members: Vasudevan, S (advisor).

Subjects/Keywords: Nanostructures; Iron Oxide Nanocrystals; Exfoliated Inorgnaic Nanosheets; Iron Oxide Nanocrystals; Magnetic Nanocrystals; Magnetic Nanoparticles; Magnetic Iron Oxide Nanocrystals; Magnetic Nanoparticles; Surfactant Intercalation; Layered Materials - Delamination; [email protected]; Inorganic Nanosheets; Layered Double Hydroxide; Oleate Capped Magnetite Nanocrystals; Nanotechnology

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APA (6th Edition):

Chalasani, R. (2018). Functionalized Nanostructures : Iron Oxide Nanocrystals and Exfoliated Inorganic Nanosheets. (Doctoral Dissertation). Indian Institute of Science. Retrieved from http://etd.iisc.ac.in/handle/2005/3463

Chicago Manual of Style (16th Edition):

Chalasani, Rajesh. “Functionalized Nanostructures : Iron Oxide Nanocrystals and Exfoliated Inorganic Nanosheets.” 2018. Doctoral Dissertation, Indian Institute of Science. Accessed January 16, 2021. http://etd.iisc.ac.in/handle/2005/3463.

MLA Handbook (7th Edition):

Chalasani, Rajesh. “Functionalized Nanostructures : Iron Oxide Nanocrystals and Exfoliated Inorganic Nanosheets.” 2018. Web. 16 Jan 2021.

Vancouver:

Chalasani R. Functionalized Nanostructures : Iron Oxide Nanocrystals and Exfoliated Inorganic Nanosheets. [Internet] [Doctoral dissertation]. Indian Institute of Science; 2018. [cited 2021 Jan 16]. Available from: http://etd.iisc.ac.in/handle/2005/3463.

Council of Science Editors:

Chalasani R. Functionalized Nanostructures : Iron Oxide Nanocrystals and Exfoliated Inorganic Nanosheets. [Doctoral Dissertation]. Indian Institute of Science; 2018. Available from: http://etd.iisc.ac.in/handle/2005/3463

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