Abstract
Controlled synthesis of anisotropic iron oxide nanoparticles is a challenge in the field of nanomaterial research that requires an extreme attention to detail. In particular, following up a previous work showcasing the synthesis of magnetite nanorods (NRs) using a two-step approach that made use of polyethylenenemine (PEI) as a capping ligand to synthesize intermediate β-FeOOH NRs, we studied the effect and influence of the capping ligand on the formation of β-FeOOH NRs. By comparing the results reported in the literature with those we obtained from syntheses performed (1) in the absence of PEI or (2) by using PEIs with different molecular weight, we showed how the choice of different PEIs determines the aspect ratio and the structural stability of the β-FeOOH NRs and how this affects the final products. For this purpose, a combination of XRD, HRTEM, and direct current superconducting quantum interference device (DC SQUID) magnetometry was used to identify the phases formed in the final products and study their morphostructural features and related magnetic behavior.
Highlights
Magnetite (Fe3 O4 ) magnetic nanoparticles (NPs) are still widely recognized as an interesting material, despite having been the long-lasting subject of many studies, due to their versatility in terms of application in many diverse fields, ranging from catalysis [1] and magnetic information storage [2] and extending to medical and theranostic applications such as magnetic resonance imaging (MRI) [3], drug delivery [4], and magnetic hyperthermia [5]
Since PEI is a well-established and widely known capping agent, used to control the shape and size of many different nanosized systems [26,27], we studied and compared the different outcomes obtained by heating treatment of the β-FeOOH NPs that had been achieved by reaction processes performed (1) in the absence of PEI; (2) by addition of a low weight-average molecular weight PEI (800 g/mol); or (3) a PEI of high weight-average molecular weight (25,000 g/mol)
The addition of PEI determined the synthesis of shorter nanorods; in particular, the length of the nanorods changed from 31.7 nm to 38.7 nm depending on the molecular weight of the polymer used in the synthesis (800 g/mol and 25,000 g/mol, respectively), while their diameter was kept constant in both samples
Summary
Magnetite (Fe3 O4 ) magnetic nanoparticles (NPs) are still widely recognized as an interesting material, despite having been the long-lasting subject of many studies, due to their versatility in terms of application in many diverse fields, ranging from catalysis [1] and magnetic information storage [2] and extending to medical and theranostic applications such as magnetic resonance imaging (MRI) [3], drug delivery [4], and magnetic hyperthermia [5]. Β-FeOOH, whose natural formation is due to the corrosion of iron in chloride-containing environments, is an antiferromagnetic oxy-hydroxide material [14], usually synthesized by hydrolysis of FeCl3 ·6H2 O with typical shapes of nanospindles and nanorods due to its crystallographic features [15,16]. If these shapes could be maintained during reduction, considering that in such a process the crystal defects and porosity of the structure could increase systematically, magnetite with different morphologies would be gained
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