**2. Green synthesis of hybrid magnetic-semiconductor oxides nanomaterials**

The synthesis method plays a vital role in guiding the application of MNPs. Because this stage determines the basic properties such as particle size, size distribution, morphology, stability, and even surface properties of the MNPs. There are several different methods for synthesizing MNPs, which have been discussed in detail in many papers [2–4]. It can be observed that the common techniques used for synthesizing MNPs include coprecipitation, thermal decomposition, sonochemical, microemulsion, chemical vapor deposition, etc. In addition to these methods, a new and compatible approach to materials synthesis is using agents of natural origin such as plant extracts, bacteria, and fungi instead of chemical agents. The critical role of natural agents is as stabilizers by complexing with metal ions. Intriguingly, the natural agent-metal ion complex system reacts with the hydroxyl group in solution, forming a metal oxide instead of a metal hydroxide. This hypothesis seems plausible since metal oxides are formed at low temperatures, not by high-temperature metal hydroxide decomposition. In addition, natural agents act as capping agents, avoiding the agglomeration of nanoparticles. This approach aims to take advantage of available, renewable, natural agents and limit dependence on chemical agents to move towards a "greener" and more environmentally friendly world. Accordingly, the process of synthesizing MNPs is also done in the simplest way. It makes even more sense in environmental applications to use a "green" approach to clean the environment instead of potentially hazardous methods.

Plant extracts were the most common among the natural agents used to synthesize MNPs.

Mangosteen peel is a natural product widely used in the synthesis of nanoparticles. They are rich in phenolic compounds, flavonoids, and terpenoids. Phenolic

#### *Hybrid Magnetic-Semiconductor Oxides Nanomaterial: Green Synthesis and Environmental… DOI: http://dx.doi.org/10.5772/intechopen.107031*

compounds are all potent antioxidants, while flavonoids, benzophenones, and anthocyanins are thought to be closely involved in reducing metal cations to nanoparticles [5, 6]. Yusefi et al. [7] synthesized Fe3O4 from mangosteen peel extract, with extract concentrations varying from 0.1, 2, 5, and 10 wt.%. The results show that the obtained ferromagnetic iron oxide nanoparticles have an average size of 13.42 nm. The saturation magnetization values varied from 49.80 emu/g to 69.42 emu/g as the extract concentration increased from 0 to 10 wt.%. Nanoparticles have high stability and a long storage time. In another publication by this group of scientists, they demonstrated that the extract of *Garcinia Mangostana* fruit peel could be used as a bio-stabilizer and capping agent to enhance physicochemical properties and stability of Fe3O4 nanofluid [8].

The peel of pomegranate (*Punica granatum L.*) is generally of no value in consumption but has been found to be highly medicinal. Several studies indicated that they contain many valuable bioactive compounds, such as polyphenols, flavonoids, proanthocyanidins, and hydrolyzable tannins [9–11]. In addition to the anti-cancer, anti-fungal, and inflammatory activities, the antioxidant activity is quite intense, which is attributed to polyphenols compounds such as punicalagin and ellagic acid. Thanks to that, it attracted many scientists' attention to synthesizing nanomaterials [12–14]. Yusefi et al. [15] synthesized magnetic iron oxide nano using Punica Granatum Fruit Peel Extract. The biologically active substances in the extract act as stabilizers, forming complexes with metal ions (Fe2+, Fe3+). This was further confirmed when the results confirmed that a significant number of organic compounds were present in the ferromagnetic oxide mixture. The organic matter content increased gradually with the concentration of extract used. In contrast, magnetism (magnetic saturation) shows in the opposite direction. Another work has also been carried out with similar results [16].

*Lathyrus sativus* is a well-known plant that contains alkaloids, carotenoids, flavonoids, starch, carbohydrates, essential oil, leguminvicilin, legumelin, vitamin C, oleoresin, gum resin, tannins, terpenes, phenols, riboflavin, beta-carotene, proteins, and amino acids, which act as capping, reducing and stabilizing agents [17, 18]. Thanks to this unique feature, many research groups have used L. sativus shell extract to synthesize magnetite nanoparticles [19, 20].

Potatoes are mainly composed of carbohydrates, mostly starch. These macromolecules with hydroxyl groups are expected to facilitate metal complexation. Sharma et al. [21] used potato extract to synthesize ferromagnetic nanoparticles with the assistance of ultrasonication which facilitated quick and easy complexation.
