Progress toward Room-Temperature Synthesis and Functionalization of Iron-Oxide Nanoparticles

Abstract

Novel magnetic nanohybrids composed of nanomaghemite covered by organic molecules were successfully synthesized at room temperature with different functionalization agents (sodium polystyrene sulfonate, oxalic acid, and cetyltrimethylammonium bromide) in low and high concentrations. Structural, vibrational, morphological, electron energy-loss spectroscopy, magnetic, and Mössbauer characterizations unraveled the presence of mainly cubic inverse spinel maghemite (γ-Fe2O3), whilst X-ray diffraction and 57Fe Mössbauer spectroscopy showed that most samples contain a minor amount of goethite phase (α-FeOOH). Raman analysis at different laser power revealed a threshold value of 0.83 mW for all samples, for which the γ-Fe2O3 to α-Fe2O3 phase transition was observed. Imaging microscopy revealed controlled-size morphologies of nanoparticles, with sizes in the range from 8 to 12 nm. Organic functionalization of the magnetic nanoparticles was demonstrated by vibrational and thermogravimetric measurements. For some samples, Raman, magnetic, and Mössbauer measurements suggested an even more complex core-shell-like configuration, with a thin shell containing magnetite (Fe3O4) covering the γ-Fe2O3 surface, thus causing an increase in the saturation magnetization of approximately 11% against nanomaghemite. Field cooling hysteresis curves at 5 K did not evidence an exchange bias effect, confirming that the goethite phase is not directly interacting magnetically with the functionalized maghemite nanoparticles. These magnetic nanohybrids may be suitable for applications in effluent remediation and biomedicine.

In Situ and after Synthesis of Magnetic Nanoarchitectures Grown onto Zeolite Type 5A/CTAB Frameworks and Their Ecotoxicological Properties

“…Moreover, all the samples (see zoomed region in Figure 6c), present a very small coercivity field (around 50 Oe) at RT, suggesting that at least parts of the samples are in a superparamagnetic regime in close agreement with functionalized iron oxide nanostructures found in the literature. 41 At 5 K (Figure 6d), all the samples showed an FI character, as would be expected for the cubic spinel structure of the γ-Fe 2 O 3 , also highlighted by Mossbauer spectroscopy. All the M s values estimated from LAS in Figure 6e,f are below the bulk values for the Fe 3 O 4 (92 emu/g) and γ-Fe 2 O 3 (60−80 emu/g).…”

“…However, it is important to mention that the M(H) loops for the NPD2 and NPD3 samples do not reach the saturation regime. Moreover, all the samples (see zoomed region in Figure c), present a very small coercivity field (around 50 Oe) at RT, suggesting that at least parts of the samples are in a superparamagnetic regime in close agreement with functionalized iron oxide nanostructures found in the literature . At 5 K (Figure d), all the samples showed an FI character, as would be expected for the cubic spinel structure of the γ-Fe 2 O 3 , also highlighted by Mössbauer spectroscopy.…”

“…In addition, the maximum M s value recorded at 5 K for the samples are different, being larger for the NPD4 sample with 80.7 emu g –1 . This value suggests a stabilization of a Fe 3 O 4 phase due to its functionalization with CTAB during its growth, which can be associated with a γ-Fe 2 O 3 @Fe 3 O 4 core–shell structure under a CTAB layer . It highlights the advantage of the application of organic functionalizing agents as an initial medium in the co-precipitation synthesis method to avoid total oxidation; meanwhile, the formation of undesirable secondary Fe oxide phases (in situ) in the presence of inorganic zeolite reduces the M s values.…”

“…This value suggests a stabilization of a Fe 3 O 4 phase due to its functionalization with CTAB during its growth, which can be associated with a γ-Fe 2 O 3 @Fe 3 O 4 core− shell structure under a CTAB layer. 41 It highlights the advantage of the application of organic functionalizing agents as an initial medium in the co-precipitation synthesis method to avoid total oxidation; meanwhile, the formation of undesirable secondary Fe oxide phases (in situ) in the presence of inorganic zeolite reduces the M s values. The second highest M s value corresponds to the NPD1 sample, presumably due to the larger bare γ-Fe 2 O 3 NPs contribution, in comparison with the other samples.…”

Surface Adsorption Mechanism between Lead(II,IV) and Nanomaghemite Studied on Polluted Water Samples Collected from the Peruvian Rivers Mantaro and Cumbaza

“…Previous studies have shown that the threshold value depends strongly on the size of the NPs and also the functionalized agent. The latter may give thermal stability to the iron oxide NP sample, i.e., the γ α transition will occur at higher temperatures [ 23 , 24 , 25 , 26 ]. Hence, two protocols given in the experimental sections were performed to correctly analyze the RG1 sample.…”