**1. Introduction**

Recently, there has been a grea<sup>t</sup> development in the use of nanotechnology in many applications such as medical and environmental fields, which have made many people, believe that this technology can improve their current standard of living [1,2]. The nanoparticles are characterized by many characteristic approaches, such as shape and size, which allow these particles to be used in many life applications including water treatment [2]. The particles are called nanomaterials at particles sizes ranging from 1 to 100 nm [3]. The nanoparticles are characterized by a large surface area, which distinguishes them from the other bulk materials with the same composition, which made this technology improve properties and features such as catalytic activity, electrical conductivity, hardness, and

**Citation:** Ahmed, H.M.; El-khateeb, M.A.; Sobhy, N.A.; Hefny, M.M.; Abdel-Haleem, F.M. Green Synthesis of Magnetite Nanoparticles Using Waste Natural Materials and Its Application for Wastewater Treatment. *Environ. Sci. Proc.* **2023**, *25*, 99. https://doi.org/10.3390/ ECWS-7-14181

Academic Editor: Carmen Teodosiu

Published: 14 March 2023

**Copyright:** © 2023 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

antimicrobial [3]. The nanoparticles are used in water treatment due to these particles having a large functional surface area capable of binding, absorbing, and carrying other compounds [2]. Among the nanoparticles that are widely used in water treatment, such as iron particles with magnetic properties, these particles are characterized by unique properties such as surface area; these properties of Fe/NPs make them applicable in various areas, such as catalysis, magnetic storage media, biosensors, magnetic resonance, and wastewater treatment [2,4].

The preparation of raw materials is carried out by various methods including physical, chemical, enzymatic, and biological. Physical methods are divided into the grinding of large particles, thermal evaporation, plasma arcing, spray pyrolysis, spray deposition, and layerby-layer growth. Chemical methods are divided into the sol–gel method, electrophoresis, chemical vapor deposition, chemical solution deposition, and hydrolysis. The biological method, which uses a one-step biological extraction method, is environmentally friendly, as it uses environmentally friendly materials such as plant materials, bacteria, fungi, microalgae, and is called the green synthesis method [3,5].

Green synthesis uses plants and microorganism; the synthesis of nanoparticles is an environmentally friendly, economically viable method for large-scale production and a cost-effective method without any harmful and expensive chemicals. The green synthesis of nanoparticles is produced by the biological method in order to overcome the problems with more efficiency than physical and chemical methods due to the length of time and the multiplicity of steps during the preparation process [6]. The green synthesis method depends on the mechanism of the bio-reduction of nanoparticles due to many bio-molecules (vitamins, amino acids, proteins, phenolic acids, and alkaloids) in plant and microorganisms. Phenolic acids are powerful antioxidants, possessing hydroxyl and carboxyl groups that are able to bind metals. The active hydrogen may be responsible for the reduction of metal ions in the formation of nanoparticles [2–4,7].

Iron nanoparticles are prepared from plant extracts such as fruit and vegetable extracts. Iron nanomaterials are considered effective materials in water treatment because of their magnetic properties. Iron particles are found in the forms of Fe2O3 and Fe3O4 [3,8,9].

Iron nanoparticles have recently gained grea<sup>t</sup> research interest in environmental applications since they offer high surface reactivity due to the high surface area. Environmental applications of iron nanoparticles include the detection and elimination of pollutants in wastewater treatment. The application of iron nanoparticles in the environment offers advantages such as improved performance, lower energy consumption, and reduction in residual waste. Iron nanoparticles are one of the most researched and efficient nanoparticles for the removal of pollutants from wastewater [10,11].

The prepared nanoparticles are characterized to know the extent of their formation through many methods such as scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), and visible and ultraviolet spectroscopy [3,12–14].

In this study, the preparation of iron nanoparticles (Fe/NPs) was based on the green synthesis method, where extracts of different natural materials such as moringa leaves, potato peels, tea waste, and onion peels used for the synthesis of iron nanoparticles (Fe/NPs). The iron nanoparticles were characterized using different techniques such as X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), and visible and ultraviolet spectroscopy (UV spectrum). The particle size, magnetic properties, and morphology of Fe/NPs depended on the conditions of the materials used, such as the extract of onion peels, potato peels, tea waste, and moringa leaves; the obtained nanoparticles had different particle sizes, morphologies, yields, and magnetic properties. These Fe/NPs were used in wastewater treatment; the different parameters were applied to determine the efficiency of iron nanoparticles, such as contact time (0–60) min and dose (0.1–0.5) g/L, using this technology after the sedimentation stage of raw wastewater.

### **2. Materials and Methods**

#### *2.1. Preparation of the Extracts of Waste Natural Materials and Iron Nanoparticles*

This work aims to prepare iron nanoparticles from extracted waste natural materials (WNMs), as shown in Figure 1. The magnetic iron nanoparticles were synthesized using a mixture of FeCl3·6H2O and FeCl2·4H2O, aided with onion, potato, tea, and moringa extracts. These materials were obtained from the local markets, Giza, Egypt. They were prepared by washing onion peels, potato peels, tea waste, and moringa leaves several times using tap water to remove any dust, and then they were rinsed and dried at room temperature. The onion peels, potato peels, and moringa leaves were cut into small pieces. Then, approximately 50 g of every waste extract was weighed and boiled in 500 ml of tap water for 30 min. The filtrate of the extract was kept at 4 ◦C in the refrigerator [4,15]. The magnetite nanoparticles were prepared from the extracts by adding 5 ml of extract to a bottle of iron solution with the simultaneous drop-wise addition of NaOH (I N) solution (this process was carried out at 80 ◦C, and the solution was mixed at 1000 rpm for 2 h) [16]. The synthesis of nanoparticles was observed by the changing color of the solution from orange to black; the formation of Fe/NP was confirmed by the appearance of a black precipitate [15]. Fe/NPs were separated by centrifugation at 1000 rpm/min, collected, and dried in a dry oven at 50 ◦C for 48 h [11].

**Figure 1.** Schematic diagram of onion, potato, tea, and moringa residues in production of iron nanoparticles.

### *2.2. Characterization of the Synthesized Fe/NPs*

The prepared magnetite nanoparticle (Fe/NPs) compounds were characterized using several instruments. For example, a UV–visible spectrophotometer (T-70 spectrophotometer at the Housing and Building Research Center, Chemistry Lab) was used for the analysis of synthesized Fe/NPs periodically as a function of time in the wavelengths ranging from 190–340 nm with a resolution of 0.5 nm. Crystallographic study of Fe/NPs was carried out using X-ray diffraction (XRD 6100, Shimadzu, Tokyo, Japan) with CuK α radiation from 40 kV/30 mA using the 2θ range of 20–70◦. Chemical functional group identification on Fe/NPs was determined using FT-IR (FT-IR 8400S, Shimadzu, Tokyo, Japan) in the spectral range of 400–4000 cm<sup>−</sup><sup>1</sup> and elemental analysis was carried out in the Na-U channel using EDX (EDX 720, Shimadzu, Tokyo, Japan).

### *2.3. Characteristics of Raw Wastewater*

#### 2.3.1. Sample Sites and Analysis of Raw Samples

The grey water (collected from the Orasqualia station for wastewater treatment), characteristics indicated that such wastewater was relatively strong, as exhibited by the ammonia, COD, BOD, TDS, EC, pH, PO4, TP, TN, TKN, NH3, NO3, TSS, and phosphate. The characteristics of grey water are shown in Table 1 compared with the Egyptian Environmental Association Affair (EEAA) [17]. The COD and BOD were 560 and 302 mg/L, respectively. The PO4, TP, TN, TKN, NH3, and NO3, were 3.3, 0.66, 33.6, 28.2, 13.2, and 5.4. The pH, EC, TSS, and TDS were 7.2, 1099, 330, and 611 mg/L; turbidity was 89.5 NTU. ORP was −19.7 mV, respectively.



Notes: \* Average for three samples, TDS is total dissolved solid, TSS is total suspended solid, COD is chemical oxygen demand, BOD is biological oxygen demand, NH3 is ammonia, NO3 is nitrate, TKN is total Kjeldahl nitrogen, TN is total nitrogen, TP is total phosphorus, and PO4 is phosphate. ORP is oxidation reduction potential.
