## 2 Structure, Synthesis, and Properties of Bimetallic CuFe Nanoparticles
### Synthesis and Properties
#### 2.2.2 Chemical Reduction
The nanoparticles were found to be spherical with diameter ranging from 15 to 20 nm and containing FeCu\({}_{4}\) and CuFe\({}_{2}\)O\({}_{4}\) phases. The same procedure was used by [PERSON] et al. [49] for the synthesis of CuFe nanoparticles with different amounts of Cu, 0.1, and 0.5 in the samples. Structural, crystallographic, magnetic properties were studied (Figure 6). A low amount of Cu in the particles (Fe\({}_{0.9}\)Cu\({}_{0.1}\)) favors the core@shell structure while higher amount of Cu (Fe\({}_{0.5}\)Cu\({}_{0.5}\)) prefers the segregated (Janus) structure. The authors found CuFe alloy phase accompanied by Fe\({}_{3}\)O\({}_{4}\) phase in the case of Fe\({}_{0.9}\)Cu\({}_{0.1}\), and CuO\({}_{2}\) phase in the case of Fe\({}_{0.5}\)Cu\({}_{0.5}\). The magnetic properties are associated with composition changes and with the increasing the Cu concentration, the coercivity decreases, going from 626 Oe for Fe\({}_{0.9}\)Cu\({}_{0.1}\) to 53 Oe for Fe\({}_{0.5}\)Cu\({}_{0.5}\). Synthesis of CuFe alloy NPs fully covered by graphene layers via high temperature pyrolysis is possible [50]. Using a copper phthalocyanine based precursor and an iron acetylacetonate led to CuFe nanoalloy in which most of the Fe atoms were surrounded by Cu atoms (Figure 7). The main phase of the particles obtained is the CuFe alloy, but a small amount of iron carbide (Fe\({}_{3}\)C) phase is also observed. CuFe nanoparticles have also been produced by synthesizing the nZVI using the reduction of ferric chloride (FeCl\({}_{3}\)6H\({}_{2}\)O) by NaBH\({}_{4}\) followed by planting Cu onto the surface of nZVI by redox reaction occurring between the Cu\({}^{2+}\) and nZVI [51; 52; 53; 54]. Synthesis of bimetallic FeCu nanoparticles with different Cu to Fe ratio of 1:20, 1:10, 1:6.7, and 1:5 (_w/w_) and average size of 45 nm, 59 nm, 72 nm, and 85 nm, respectively, was reported [52]. [PERSON] et al. [53] proposed method for the synthesis of Fe@Cu core@shell structures with uniform shape and an average diameter of less than 20 nm using monodispersed carboxymethyl cellulose (CMC) as stabilizer (Figure 8). At this point, it should be emphasized that the properties, and in particular the magnetic properties of the synthesized materials, depend not only on the size, shape, structure, but most of all on the composition of the synthesized materials. The presence of iron oxides in nanoparticles influences its magnetic properties and can change saturation  
Figure 6: XRD results of (a) nZVI (nano-scale zero valent iron particles), (b) Fe\({}_{0.9}\)Cu\({}_{0.1}\), (c) Fe\({}_{0.5}\)Cu\({}_{0.5}\), and (d) Cu NPs. Symbols: (\(\bullet\)) nZVI, (\(\blacktriangle\)) Cu\({}^{0}\), (\(\blacksquare\)) cuprite, (\(\blacktriangledown\)) tenorite, and (\(\blacktriangle\)) magnetite. Magnetic hysteresis of the nZVI, Fe\({}_{0.9}\)Cu\({}_{0.1}\), Fe\({}_{0.5}\)Cu\({}_{0.5}\), and Cu particles at room temperature. Reprinted from [49]. Copyright 2018, with permission from Elsevier. magnetization, coercivity, blocking temperature, and relaxation time, and thus may limit their use [55]. Figure 8: (**a**) Transmission electron microscopy (TEM) images of as-prepared carboxymethyl cellulose (CMC)-stabilized Fe@Cu nanoparticles, inset is TEM image of an individual nanoparticle. (**b**) Size distribution of CMC-stabilized Fe@Cu nanoparticles. (**c**) The formation process of CMC-stabilized Fe@Cu nanoparticles. Reprinted from [53], Copyright 2011, with permission from Elsevier. Figure 7: Structural and elemental analysis of the CuFe alloy. (**a**) High-angle annular dark field/STEM image of CuFe alloy nanoparticles and EDS elemental mapping of (**b**) Cu and (**d**) Fe in the same area. (**e**) EDS intensity profiles of yellow line in (**a**). Reproduced with permission from ref. [50]. Copyright 2015 American Chemical Society.