2.3.2. Reagents

All chemicals were of analytical grade. The chemical reagents used included phosphoric acid (H3PO4, 85.0%, Fischer scientific, Loughborough, UK), potassium dichromate (K2Cr2O7, 99.0%, Merck, Darmstadt, Germany), boric acid (H3BO3, 99.5%, LOBA Chemie, Mumbai, India), hydrochloric acid (HCl, 37.0%, Fischer scientific, Loughborough, UK), nitric acid (HNO3, 70.0%, sodium hydroxide (NaOH, 99.0%, Merck, Darmstadt, Germany), and ammonia solution (NH3, 35.0%, Fischer scientific, Loughborough, UK).

### 2.3.3. Instruments and Characterization Techniques

The following instruments were used through this work: a furnace, the drying oven (Fisher Scientific Equipment, American provisioner of scientific instruments, Waltham, MA, USA), digital electronic balance (PCE-BSK 310, PCE Instruments, Southampton, UK), and DIW system (Millipore, Darmstadt, Germany) were used. The pH measurements of the samples were achieved using a pH meter (AD110, ADWA, Szeged, Hungary). Fourier transform infrared spectroscopy (FT-IR) (Thermo Fisher Scientific, Oxford, UK), an orbital shaker instrument (Thermo Fisher Scientific, Waltham, MA, USA), a COD digestor instrument (auto time-controlled, MAC, Udaipur, India), a BOD5 incubator (Airco, Mumbai, India), UV– Vis spectrophotometers (PG Instruments, Lutterworth, UK), an incubator (Thermo Fisher Scientific, Oxford, UK), a portable multiparameter water-quality measurement (HORIBA company, Irvine, CA, USA), and a Kjeldahl digestion instrument (ESEL, India) were used.

Samples of raw bone waste materials were analyzed by a scanning electron microscope (SEM) model (Quanta 250 FEG—field emission gun—attached with accelerating voltage 30 kV (FEI Company, Eindhoven, Netherlands) [18].

### *2.4. Batch Experiments Fe/NPs*

The treatment wastewater experiments were carried out in 1L treated by Fe/NPs optimized by varying the dose (0.1, 0.3, 0.4, and 0.5 g/L agitated 30 min) and contact time (0, 15, 30, 45, and 60 min agitated with 0.4 g). All experiments were carried out in a jar test at 100 rpm. The same set of the experiment was repeated three times. All experiments were conducted at room temperature. The residual concentration of pollutants in the filtrate was detected using the EPA method. The removal efficiency (R%) was calculated from the Equation (1) [9,19,20]:

$$\text{R\%} = \frac{\text{C}\_0 - \text{C}\_\text{e}}{\text{C}\_0} \times 100 \tag{1}$$

where R% is the removal efficiency, C0 is the initial concentration (mg/L), and Ce is the concentration after adsorption (mg/L).

### **3. Results and Discussion**

*3.1. Characterization*

3.1.1. UV–Vis Spectral Analysis of Fe/NPs

Fe/NPs formations were confirmed by the color change that immediately occurred after the addition of the plant extract iron solution and the adjusted pH. The dark color was a result of surface plasmon excitation vibrations in the Fe/NPs [11]. The absorption peaks were at 215, 210, 257, and 210 nm for onion, potato peels, tea waste, and moringa, respectively. This indicates the presence of Fe/NPs [2]. Figure 2 shows the UV–visible absorption spectrum of Fe/NPs synthesized using each extract waste residue. The formation of Fe/NPs is known to take place through complexation of Fe salts followed by the capping of Fe with phenolic compounds [11].

**Figure 2.** UV–Vis absorption spectrum of onion, potato peels, tea waste, and moringa magnetite nanoparticles.

### 3.1.2. Appearance of Synthesized Fe/NPs

The appearance of the black color of the Fe/NPs solution indicates the formation of Fe/NPs with the increasing time; this is shown in Figure 3. The color changes arise due to the excitation of the surface plasma resonance phenomenon typically of Fe/NPs [2]. The nanoparticles' formation was confirmed by the color immediately converted from transparent brown to black in a few seconds, demonstrating the synthesis of iron nanoparticles [11].

6 of

**Figure 3.** Onion, potato peels, tea waste, and moringa magnetite nanoparticles.

#### 3.1.3. XRD Pattern Analysis of Fe/NPs

The XRD was obtained to investigate the presence of nanoparticles on moringa, potato, onion, and tea surface. The XRD pattern of the synthesized adsorbent was in the angle range of 2θ, applying Cu kα radiation (*λ* = 1.5 Å). The XRD technique was used to identify the structure of the prepared iron nanoparticles and is depicted in Figure 4.

**Figure 4.** The XRD pattern of (**a**) moringa, (**b**) tea waste, (**c**) potato peels, and (**d**) onion magnetite nanoparticles.

The characteristic nanoparticle peak occurred at approximately 2θ = (10◦ – 60◦). The analysis of the spectrum XRD technique was used for particle-size analysis of Fe/NPs; the XRD pattern shows that the peaks the nanoparticle were 44◦, 35◦, 35–32◦, and 30–35–44◦ for moringa, potato, onion, and tea, respectively. This resulted in no clear reflection peak in potato and onion due to the other crystalline phase, which might be present as impurity. Thus, the nanoparticles essentially consisted of a binary mixture of the two spinel magnetic iron oxides, magnetite-Fe2O3 and solid elements [1,6]. In this pattern, the peak at the angle of 32, 30, 35, and 44◦ confirmed the presence of Fe2O3 particles in the adsorbent structure. Generally, the XRD analysis confirmed that the Fe2O3 particles were successfully coated on the moringa, potato, onion, and tea surface [11].

### 3.1.4. Energy Dispersive X-ray Analysis

EDX analysis was then performed on the surface of the Fe/NPs, as shown in Figure 5; the EDX results of onion, potato peels, tea waste, and moringa magnetite nanoparticles reveals the elemental composition of the prepared nanoparticles. The EDX profile shows intense peak signals of iron with a K α peak at 6.5 keV, 6.2 keV, 0.9 keV, and 0.7 keV. Other signals observed include that of oxygen and carbon; the presence of C and O peaks were related to polyphenols or any other C and O containing a compound in the natural materials' extract. The existence of elemental iron and oxygen demonstrate that the nanoparticles were essentially present in oxide form [11]. The percent of detected elements were carbon (C) 12%, iron (Fe) 52%, and oxygen (O) 28%. These results indicate the extract of moringa leaves and potato peels were more highly efficiency than onion and tea for the formation of magnetite iron nanoparticles. Very similar results were reported for Fe nanoparticles prepared with the other leaf [11].

**Figure 5.** The EDX pattern of (**a**) moringa, (**b**) onion, (**c**) tea waste and (**d**) potato peels magnetite nanoparticles.

#### 3.1.5. The FT-IR Spectra of Fe/NPs

The FT-IR measurements were carried out to identify the possible bio-molecules responsible for the reduction of ferrous chloride and capping of the reduced Fe/NPs. The FT-IR spectra of Fe/NPs after preparation by the green synthesis method from onion, potato peels, tea waste, and moringa extracts are shown in Figure 6. All of the above peaks which can be detected in the spectrum of synthesized Fe/NPs were subjected to FT-IR that showed various bands; the O-H stretching at approximately 3400 cm<sup>−</sup><sup>1</sup> showed the presence of hydroxyl groups from the polyols such as flavones, terpenoids, and polysaccharides present in the various extracts. The decrease in intensity of band O-H stretching in onion and potato might be due to the interaction of nanoparticles. The bands at 1645 cm<sup>−</sup><sup>1</sup> and 1041 cm<sup>−</sup><sup>1</sup> denote the presence of organic material in the sample, majorly contributed by onion, potato peels, tea waste, and moringa iron magnetite particles (Fe/NPs). These bands confirmed the presence of compounds such as flavonoids and terpenoids and, hence, may

be held responsible for the efficient capping and stabilization of the obtained magnetite nanoparticles [11].

**Figure 6.** FT-IR spectrum of (**a**) moringa, (**b**) tea waste, (**c**) potato peels and (**d**) onion magnetite nanoparticles.

3.1.6. XRF Analysis of Banana, Orange, and Pomegranate

The XRF pattern of iron oxide nanoparticle prepared from onion, potato peels, tea waste, and moringa are shown in Table 2. The results show the Fe2O3 composite in onion, potato peels, tea waste, and moringa Fe/NPs. The percent of magnetite nanoparticles (Fe2O3) from onion, potato peels, tea waste, and moringa were 67.3%, 53.92%, 40.86%, and 46.86%, respectively. The Fe2O3 percent in magnetite nanoparticles was onion > potato peels > moringa > tea waste.

**Table 2.** The XRF of onion, potato peels, tea waste, and moringa magnetite nanoparticles.


3.1.7. Yield of Iron Oxide Nanoparticles

The iron oxide nanoparticles were dried at 50 ◦C until the magnetite nanoparticles were completely dry. The weight of magnetite nanoparticles related to the type of extract used in the synthesis of nanoparticles. Table 3 shows that the weight of the magnetite nanoparticles for moringa, potato, onion, and tea were 38.235, 19.116, 19.116, and 12.899, respectively.

**Table 3.** Yield of onion, potato peels, tea waste, and moringa magnetite nanoparticles.


### *3.2. Effect of Contact Time*

Figure 7 illustrates the effect of contact time on the efficiency of magnetite nanoparticles for the removal of pollutants from grey wastewater, The following condition were applied: 0.1 g/L solution of the adsorbent, optimal pH (pH = 7.5 ± 0.1), and the contact time of (0–60) min, as indicated in Table 4; the removal efficiencies were increased sharply up to equilibrium at 45 min and then slightly increased after 45 min until 60 min. The sharp increase in the removal efficiency may be due to the existence of enormous vacant active sites in the surface. However, by raising the contact time, the availability of pollutants to the active sites on the adsorbent surface was limited [21], which makes the adsorption efficiency reduce. In a similar study, this phenomenon was investigated using different adsorbents [1]. Iron nanoparticles were used for removing pollutants from wastewater, due to the interaction between the compounds and the functional groups at the surface of the absorbent. The functional groups served to define the effectiveness, selectivity, capacity, and reusability of an absorbent. Furthermore, in the case of high iron oxide loading at the surface, the higher the rate of reduction in the nitrate and ammonium ion [22]. The results showed that the optimum time for metal removal by magnetic nanoparticles was obtained in 45 min [1,23].

**Figure 7.** Effect of contact time on removal efficiency of iron magnetite nanoparticles at agitation speed 200 rpm, dose 0.1 g/L, and 20 ± 5 ◦C. (**a**) 15, (**b**) 30, (**c**) 45, and (**d**) 60 min, iron magnetite nanoparticles such as (FeNPs/moringa, FeNPs/potato, FeNPs/onion and FeNPs/tea).



Notes: 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.

### *3.3. Effect of Adsorbent Dosage*

The effect of amount (0.1–0.5 g/L) of magnetic nanoparticles (Fe/NPs) on the removal of pollutants from wastewater such as chemical oxygen demand, biological oxygen

demand, total suspended solid, turbidity, ammonia, Kjeldahl nitrogen, total nitrogen, phosphate, and nitrate were studied in samples before and after treatment. The dosage of nanoparticles affected its ability to sorbent contaminants. As shown in Figure 8, when the magnetic particles' dosage increased, the removal efficiency increased, as shown in Table 5. Usually, the reduction of pollutant concentration with the increased dose of iron nanoparticles is a surface function. It may be assumed that the availability of active sites on the nanocomposite increases at higher doses [8,23].

**Figure 8.** Effect of different doses on efficiency of iron magnetite nanoparticles (agitation speed 200 rpm, time 45 min, and 20 ± 5◦C). (**a**) 0.1, (**b**) 0.3, (**c**) 0.4, and (**d**) 0.5 g.



Notes: 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.

The effect of different amounts of Fe/NPs on the adsorption capacity and efficiency under the optimal condition (pH = 7.4, t = 45 min and 200 rpm) is illustrated in Figure 8. It can be observed that, with an increase in the adsorbent dosage from 0.1 to 0.5 g/L, the removal efficiencies at optimum dose (0.4), for onion, potato, moringa, and tea, were from 88.39, 88.39, 88.39, 88.39, 22.86, 52,81, 22.86, 27.94 and 96.66%, 81.25, 81.25, 81.25, 81.25, 24.57, 44.68, 27.98, and 81.06%, 87.85, 87.85, 87.85, 87.85, 30.17, 55.46, 34.45, and 88.93%, 82.5, 82.5, 82.5, 82.5, 24.91, 31.87, 26.09, and 97.06% of COD, BOD, TSS, turbidity, ammonia, TKN, TN, phosphate, and nitrate, respectively. The rise in the adsorption efficiency was related to the increase in the availability of active sites on the adsorbents which can give rise to the adsorption of pollutants. Jung et al. reported that, with an increase in the dosage of various adsorbents, the pollutants' removal was enhanced. However, a decrease in the adsorption capacity with an increase in the adsorbent dosage was probably due to the instauration of the active sites on the adsorbent surface during the adsorption process. This phenomenon

can also be due to the aggregation resulting from high adsorbate concentrations, leading to the decrease in the active surface area of the adsorbent [1,23].
