The Use of Deep Eutectic Solvents for the Synthesis of Iron Oxides Nanoparticles: A Driving Force for Materials Properties

Abstract

In this study, we explored the use of Deep Eutectic Solvents (DESs) as a green and sustainable alternative for the synthesis of Iron Oxide Nanoparticles (IONs). Six different binary mixtures of Hydrogen Bond Acceptors (HBAs) and Donors (HBDs) were prepared and thoroughly characterized to investigate how their components and physicochemical properties influence the structure, morphology, and magnetic properties of the resulting IONs. In addition, the role of DESs was assessed using ATR-MIR spectroscopy, providing insights into HBA-HBD interactions with iron precursors. The study highlights the critical role of DES constituents, particularly the interactions between HBAs and HBDs, in directing nanoparticle size, structure, and morphology. Indeed, our results demonstrate that the choice of DES significantly impacts the crystalline phase of iron oxide nanoparticles, yielding either magnetite (Fe₃O₄) or hematite (α-Fe₂O₃). These findings established a robust framework for leveraging DES in nanomaterial synthesis, paving the way for more environmentally friendly approaches in diverse industrial and scientific applications.

Keywords: Deep Eutectic Solvents; Hematite; IONs; Magnetite; Structural oriented synthesis.

Figure 1

Behavior of density (a), molar conductivity (b), and viscosity (c), of the five studied DESs between 50°C and 90°C: ChCl:GA (3:1) (), ChCl:TEG (1:3) (), ChCl:U (1:2) (), GC:TEG (1:2) (), and GC:U (1:2) ().

Figure 2

Walden plot of ChCl:GA (3:1) (), ChCl:TEG (1:3) (), ChCl:U (1:2) (), GC:TEG (1:3) (), and GC:U (1:2)ChCl:GA (3:1) (); the black straight line is referred to a 0.1 M solution of KCl.

Figure 3

SEM images collected simultaneously in transmission (left side of each insert) and with backscattered electrons (right side of each insert) of samples ION‐1 (highlighted in blue) and ION‐2 (highlighted in red). In Parts a–c samples are displayed with a 50 kx magnification; in Parts b–d the same samples are displayed with a 150 kx magnification.

Figure 4

PXRD patterns of IONs samples reported according to their crystal structure: magnetite (part a) and hematite (part b).

Figure 5

Part (a): AGM curves of the whole series of IONs samples. Part (b): magnification of the magnetization curves relative to samples ION‐2 (red dash) and ION‐3 (black dots).

Figure 6

Part (a): ATR‐MIR spectra (normalized with respect to the 1060 cm⁻¹ peak of TEG) of GC:TEG (1:2) alone (), in interaction with FeCl₂∙4H₂O (), and in interaction with FeCl₃∙6H₂O (). Part (b): ATR‐MIR spectra (normalized with respect to the 1060 cm⁻¹ peak of TEG) of ChCl:TEG (1:3) alone (∙), in interaction with FeCl₂∙4H₂O (), and in interaction with FeCl₃∙6H₂O (). Dotted curves are referred to DES components, namely TEG (), GC (), and ChCl (). Full spectra are reported in Figure S6.