Shell-mediated control of surface chemistry of highly stoichiometric magnetite nanoparticles

Abstract

<p>Magnetite nanostructures gradually oxidize under environmental conditions. Here we demonstrate that a Zn-ferrite epitaxial coating protects magnetite cores from oxidation and provides a core/shell system with enhanced magnetic properties.</p>

Differentiating Nanomaghemite and Nanomagnetite and Discussing Their Importance in Arsenic and Lead Removal from Contaminated Effluents: A Critical Review

“…Taking results from the literature, it can be indirectly inferred that Mössbauer spectroscopy has often been implemented in Fe-oxide NPs with sizes bigger than 10 nm [ 8 , 11 ]. As an example, da Costa et al [ 12 ] studied the magnetic properties of nano-Fe 3 O 4 and nano-γ-Fe 2 O 3 prepared by wet chemical methods and, using integral low-energy electron Mössbauer spectroscopy (ILEEMS), they were able to differentiate between both nano-Fe-oxides with grain sizes of 15 nm (Fe-oxide NPs with sizes smaller than this value were not reported).…”

“…Even in functionalized samples prepared by co-precipitation, a fast oxidation may also occur. Some examples are given in [ 3 , 4 , 8 , 9 , 30 , 43 , 55 , 56 , 57 ] for inorganic and organic coatings.…”

“…Bulk magnetite (Fe 3 O 4 ) and maghemite (γ-Fe 2 O 3 ) are common iron-oxides (Fe-oxides) found in nature as minerals and in the corrosion industry [ 1 , 2 ]. However, with the appearance of nanotechnology and advances in new routes of synthesis (including physical, chemical, and biosynthesis), many researchers have tried to prepare either pure ˈnanomagnetiteˈ (nano-Fe 3 O 4 ) or nanomaghemite (nano-γ-Fe 2 O 3 ) or a mixture of these phases forming the core–shell-like nanosystems [ 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 ]. Moreover, it should be emphasized that these materials can exist in a ferrofluid form, magnetic nanopowders, solid magnetic matrices, core–shell-like structures, and magnetic colloid solutions.…”

“…However, in a nanoscale regime, the results may suggest that it is hard to compare different nano-Fe 3 O 4 or nano-γ-Fe 2 O 3 when they are prepared from different routes. For instance, the three main issues found in nano-oxide systems are (i) the fast conversion from nano-Fe 3 O 4 to nano-γ-Fe 2 O 3 , (ii) the different optical, thermal, magnetic, electronic, mechanical, textural, colloidal, surface, and adsorptive properties due to different Fe-oxide growth mechanisms [ 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 ], and (iii) the problem related to a critical size of the nanoparticles (NPs), i.e., below a certain critical radius (~10 nm), these two Fe-oxide phases are rather difficult to differentiate even from the perspective of different conventional techniques, such as powder X-ray diffraction (pXRD), zero-field Mössbauer spectroscopy (MS), X-ray photoelectron spectroscopy (XPS), and Vibrating Sample Magnetometry (VSM) measurements, often yielding a bad interpretation and characterization of the correct Fe-oxide phase presented in the sample. According to the literature, many scientific works agree that this critical radius is located ca.…”

“…According to the literature, many scientific works agree that this critical radius is located ca. 10 nm [ 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 ]. Below this critical size, nanoparticle (NP) surface magnetic effects are huge and considerable, giving rise to coexisted competitive magnetic effects.…”