# Role of Moringa oleifera on Green Synthesis of Metal/Metal Oxide Nanomaterials

Authors: Vikram Jadhav; Arun Bhagare; Ismat H. Ali; Akshay Dhayagude; Dnyaneshwar Lokhande; Jayraj Aher; Mohammed Jameel; Mycal Dutta
Journal: Journal of Nanomaterials
 (2022)

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## Abstract

Being an environmentally benign method biosynthesis of nanomaterial paying much more attention to researchers, it has many advantages over other routes, such as one pot, facile synthesis, and cost-effective; synthesized material can have good affinity due to surface modification and hence became a most attractive candidate for medicinal and biological applications. Moreover, biosynthesis creates a bridge of interdisciplinary research. Biosynthesis can be done by using bacteria, microbes, plant extracts, etc. In this study, we focus on the synthesis of some metal and metal oxide nanomaterials (M/MO NMs) by using an extract of parts from the Moringa oleifera plant. It is a natural source that can serve as a capping, stabilizing, and reducing/oxidizing agent due to the presence of some of the phytochemical parameters. Moreover, it is a rich source of antioxidants, including quercetin and chlorogenic acids, such as flavonoids, phenolics, astragalin, anthocyanins, cinnamates, and carotenoids, as well as a good source of carotene, iron, potassium, calcium, terpenes, quinines, saponins, alkaloids, proteins, tannins, and vitamin. These components produce smaller particles and give a compelling impact on the activities of M/MO NMs nanoparticles. Here, we discuss nanoparticles such as FeO, CuO, ZnO, NiO, MgO, Ag, and Au.


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## Body

## 1. Introduction

Nanotechnology is the most rapidly developing discipline in advanced material science research ([1] [2][3]. It will play a crucial role in several essential technologies due to advancements in organizing nanoscale structures into specified unique structures [4][5]) based on particular features such as size and distribution morphology ([6]; [7]). It is becoming more popular in the domestic and commercial fields [8]), including chemical science [9], physical science, biomedical sciences, drug delivery ([10] [11], photocatalysis, and optoelectronic devices [12]. [13]. For example, nanoscale Ge and Si quantum dots (>10 nm) could be produced in a controlled manner for innovative optoelectronic device applications such as electroluminescent devices [14] and ZnO-based nanomedicine for biomedical applications [15]. Nanoparticles are fascinating because of their unique surface area, which causes physical and chemical changes in their parameters compared to the original materials of the chemical compounds [16]; [17]). At the nanoscale, controlling the size and shape can thus be used to create and manufacture materials that give a variety of applications, including antimicrobial activities [18, 19], anticancer activities [20–22], antidiabetic activities [23], biosensing [24], catalysis [25], medication delivery, tumour hyperthermia, and agriculture sector [26] which are just a few of the applications for these particles [27]. Various techniques and methods have been documented for synthesizing M/MO NPs (Figure 1) like hydrothermal, sol-gel, chemical vapour deposition, gas-phase technique, microwave-assisted, microemulsion, electrochemical method, laser irradiation, and solvothermal method [28, 29]. The overview of some of the nanoparticles synthesis methods is shown in Figure 1.Figure 1
Overview of different types of nanoparticle synthesis methods.Chemical and physical method approaches are not as practical as biosynthesis processes. Due to the stabilizing and reducing agent nature, the biosynthetic technique involves the utilization of harmless materials, more cost-effective and environmentally friendly, as shown in Figure2, such as a biocompatible and benign extract from a plant [30]. Plant-mediated nanoparticles are simple to make, easily available, inexpensive, and readily scaled up. The presence of metabolites and phytochemicals in plant leaf extracts such as terpenoids, alkaloids, flavonoids, proteins, peptides, and tannins increased the biosynthetic manufacturing of nanoparticles [31, 32]. The extract’s inherent components determine the nanoparticles’ various shapes, sizes, and morphologies. The use of plant parts extracts in nanoparticle synthesis is commonly referred to as a green synthesis method approach [33]. The idea of nanoparticles may be linked to the mechanism of nanoparticle production in plants. Plant-mediated nanoparticles are being investigated as a possible next-generation disinfectant, with uses in clinical care, consumer items, and other industrial settings [34]. The antibacterial, antifungal, anticancer, anti-HIV, antidiabetic, high catalytic, and photochemical activity nanoparticles have also gotten much attention [35, 36].Figure 2
Advantages of green synthesis method.Several research groups have shown considerable interest in its unique qualities and discovered excellent uses in various fields. Researchers have devised several synthetic approaches for nanoparticle manufacturing, revealing a significant advantage to ecosystems and biodiversity via clean, harmless, and ecologically friendly processes, including bacteria, fungus, and plants [37]. However, several nanoparticle compositions have exhibited toxicity at the nanodimensions [38, 39]. Nanomaterials and green chemistry are collaborating to develop ecologically, or ecofriendly benign M/MO nanoparticles are utilizing plants, microbes, and other natural resources to solve toxicity problems [40].Parts of Moringa oleifera plants have been reported to various phytochemical parameters [41]; it is a good source of antioxidants, including quercetin and chlorogenic acids, such as flavonoids, phenolics, astragalin, anthocyanins, cinnamates, and carotenoids, as well as a rich source of carotene, Fe, K, Ca, terpenes, quinines, saponins, alkaloids, proteins, tannins, and vitamin C [42, 43]. As shown in Figure 3, the advantages of Moringa oleifera, thus improving the shelf life of fat-containing foods, act as a good metal-reducing, capping, and stabilizing agent [44–46]. The recent work of this review is Moringa oleifera plant leaf extracts utilized for the biosynthesis of FeO, NiO, MgO, CuO, ZnO, Ag, and Au nanoparticles since it has been acting as an environmentally ecofriendly process. Researchers and scientists have been drawn to this path to synthesize M/MO NPs using Moringa oleifeara leaf extract because of the readily available, safe use, and rich sources of diverse metabolites.Figure 3
Advantages of Moringa oleifera plant leaf extract.


## 2. Biosynthesis of Metal Nanoparticles

The Moringa oleifera plant synthesized M/MO NPs in many processes (Figure4). The method consists of three steps: primary treatment, biosynthesis, and characterization of nanomaterials. Moringa oleifera plant extract was utilized as a reducing/oxidizing, capping, and stabilizing agent in producing the M/MO NPs. According to the literature survey, some of the M/MO NPs, their synthesis, and comparative study have been discussed in Table 1.Figure 4
Green synthesis of M/MO NPs using MO leaves.Table 1
Summary of parameters and conditions for biosynthesized nanoparticles from Moringa oleifera plant.
NPsPrecursorMO extract conc. (g/ml)Reaction Temp./ TimeSize (nm)/MorphologyPhotocatalytic/biological activityReferencesFeO0.5 M FeCl310 g, capping agent100°C, 24 hrs15.01±6.03nm rod likeAntibacterial testAisida, S. O. et al. [47]FeO1.60g of FeCl3.6H2O2 g, reducing agent250°C, 15 hrs66±20nm agglomeration—[48]FeO0.5 M FeCl310 g/100ml,reductant100°C, 24 hrs76±2.0 nonuniform rod likePhotocatalytic and antibacterial activity[49]FeO0.15 M FeCl3 6H2O30g60°C26.2 nm, irregular spherical—Aisida, S. O. et al. [50]FeO0.01 M FeCl320 gm reductant500°C, 5 hrsBelow 5 nm (quantum dots)—[51]FeO0.1 M (Fe(NO3)3.9H2O60g/lit, Reductant50°CLess than 100nm, spherical agglomerated—[52]FeO0.5 M FeCl2.7H2OReducing power—45 nm irregular shapeAntioxidant and antibacterial activities[53]CuO0.01 M Cu(CH3COO)2.H2O5 gm400°C, 1 hr35-95 nm, quasispherical shapeAntifungal activity[54]CuOCuSO4 5H2O60g, natural reducing agent50°CLower to 100 nm aggregation—[55]CuO1 gm Cu(NO3)2·3H2O5 gm, reducing and stabilizing agent200°C for 1 hAverage size 45.30nm, cluster-likeBactericidal activity[56]CuO2 g/20 ml copper acetate tetrahydrate20 gm/100 ml, reducing and capping agent400°C for 2 hAverage size 12 nm aggregatesAntioxidant and anticancer activity[57]CuO3gm/10 ml copper (II) nitrate3 gm biocapping agent100°C, 1 h12 and 18 nm sphericalAntimicrobial activity[58]ZnO1 mM Zn(NO3)2·6H2O5 gm reducing agent60°C 20 min——Manokari, M., and Shekhawat, M. S. [59].ZnO(Zn(NO3)2 6H2O)30 gm, reducing agent500°C, 1 hr16 to 31.9 nm spherical shapeElectrochemical activity[60]ZnO2.1 g zinc acetate5 g, stabilizing and accelerating agents350°C, 5 hrs52 nm, sphericalPhotocatalytic and antibacterial activity[61]ZnO2 g, (Zn (NO3)2.6H2O)20 gm, stabilizing agent400°C for 2 hrs16– 20 nm spherical and agglomerated particlesAntimicrobial activity[62]ZnO1.5 g Zn(NO3)2.6H2O5 g (flowers, seeds, and leaves) chelating agent500°C, 2 hrs(13.2, 13.9, and 10.8 nm)Photocatalytic activity[63]NiO3 g/100 ml nickel nitrate hexahydrate9 gm/300 ml, chelating reduction/oxidizing agent500°C, 2 hrsAverage size17.80nm—[64]NiO1.82 g/100 ml, nickel nitrate2 gm/200 ml, reducing agent and capping agent500°C, 3 minAverage size 12 nm, spherical shapePhotocatalytic and antimicrobial activity[65]NiO0.1 mM Ni (NO3)220 g/100 ml acts as a fuel400°C, 9 hrs9.69 nm agglomerated spherical shapeCytotoxicity and antibacterial activity[66]MgO1 mM MgCl2.6H2O4 gm biocapping and bioreducing agent600°C60-100 nm spherical shapeAntioxidant and antibacterial activities[67]MgO1 mM MgCl2.6H2O4 gm reducing agent600°C for 5 hrs20-50 nm spherical shapeAntibacterial activity[68]MgO1 mM MgCl2.6H2O4 g green agent600°C for 5 hrs40–70 nm spherical shapeAntioxidant, antibacterial, and antifungal[69]MgOMgCl2.6H2O4gm/100 ml reducing agent and stabilizing agent600°C for 5 hrs40 to 100 nm cubic shape—[70]Ag1 mM AgNO320 gm reducing agent—46 nm spherical shape—[71]Ag1 mM AgNO310 g reducing agent—9-11 nm agglomeratedAntimicrobial activity[72]Ag1 mM AgNO320 g reducing agent—8 nm monodispersed spherical shapeAntimicrobial activity[73]Ag1 mM AgNO35 g (stem barks) reducing agent60°C40 nm spherical shapeAnticancer activity[74]Ag1 mM AgNO310 g reducing agent60–80°C, 20 min57 nm spherical shapeAntimicrobial activity[75]Ag0.001 M,0.01 M, and 0.1 M AgNO33, 5, and7 g reducing agent—15–25 nm disperse and semispherical shapesAntibacterial activity[76]Ag1 mM AgNO3Reducing agent37°C for 24 hoursUniform-sizedAntibacterial activity[77]Au1 mM (HAuCl43H2O, ACS reagent)20 g capping agent and reducing agent—100 nm triangular, hexagonal, and sphericalCatalytic activity and anticancer[78]Au0.0254 mmol/L HAuCl4, 3H2O43.6 mg/ml reducing and stabilizing agent30°C, 10 min20-60 nm spherical shape—[79]Au1 mM HAuCl4.3H2O20 g bioreduction—15.2 nm spherical, oval, and hexagonal shapeAntioxidant, antidiabetic, and anticancer activities[80]Au1 mM HAuCl45 gm reducingand capping agent—96 nmAnticancer activity[81]Au1 mM HAuCl4.3H2O5 g bioreduction—10–20 nm spherically shapedAnticancer activity[82]


### 2.1. Iron Oxide (FeO) NPs

Aisida et al. [47], in their research worked, synthesized a green and environmentally friendly approach for nanoparticles in which using an aqueous extract of the Moringa oleifera plant serves as a reductant and capping agent. MO leaf powder extract and FeCl3 solution were used to synthesize dark-brown-capped MO-FeO NPs. UV-Vis spectroscopy confirmed the noticeable color change from orange to dark brown (Figure 5), leading to FeO NPs. The rod-like morphologies of NPs were shown by SEM and TEM, with a 15 nm average particle size. In terms of antimicrobial activity, biosynthesized FeO NPs inhibited growth more effectively than chemical FeO NPs against antimicrobial. Additionally, smaller particles have a greater surface area and bioactivity, making them excellent antimicrobial agents against harmful microorganisms.Figure 5
Biosynthesis of FeO nanorods.Tovar et al. [48] almost have similar work as previous authors. Using the MO leaf extract and (Iron (III) chloride hexahydrate) for the synthesis of FeO NPs, in this process, the Moringa oleifera acted as a capping agent. The germination rate and development of corn seeds were studied using synthesized FeO NPs loaded with N, P, and K. Moringa, and chitosan had a favourable influence on corn plant speed germination parameters, with no adverse effects on seed germination.MO FeO NP possesses structural and superparamagnetic properties and suitable particle sizes for biomedical applications [47] performed two parts in which the Moringa oleifera (MO) leaves were dried at room temperature (RT) and sunlight (SL). MO acted as a capping agent; both solutions were gradually reduced from brown to dark black by adding FeCl3.6H2O solution. The FeO NPs obtained were characterized and the size of RT FeO and SL FeO NPs measured by SEM was 16 to 18 nm and 18 to 20 nm, respectively. XRD analysis showed a BCC lattice structure for RT, while SL exhibited a quasicrystalline structure.


### 2.2. Copper Oxide (CuO) NPs

The researchers [54] used MO leaf extract as a capping agent and copper acetate solution to synthesize nanocrystalline CuO powder (fine dark black). A simple green chemistry strategy made CuO NPs from Moringa oleifera leaf extract, and XRD, FE-SEM, EDX, FT-IR, UV-DRS, and PL were used to characterize. CuO NPs show good antifungal activity [56] used Moringa oleifera (MO) leaf extract for the synthesis of CuO microspheres. The color of the solution changed from bluish to dark green during stirring, indicating that the biological components included in the MO leaf extract converted Cu (NO3)23H2O to Cu2+ ions. The formation of monoclinic crystal-structured CuO was revealed by the XRD pattern, which confirms the conversion of Cu (NO3)23H2O to Cu2+ ions by phytochemicals contained in the MO leaf extract. As seen by SEM micrographs, it shows the cluster-like morphologies that mimic hierarchical CuO microspheres. In the FTIR spectrum, the asymmetric stretching deformation vibration bands correspond to Cu–O bonds, which imparted monoclinic unit crystal formation, and the synthesized NPs show better antibacterial activity.


### 2.3. Zinc Oxide (ZnO) NPs

Elumalai et al. [62] employed a straightforward and environmentally safe chemical route to synthesize zinc oxide nanoparticles (ZnO NPs) from Moringa oleifera leaf extract. UV–Vis, XRD, FESEM, EDX, FT–IR, and PL evaluated the ZnO NPs. The hexagonal wurtzite structure of NPs was found by the XRD investigation. The functional groups act as a stabilizing agent in the leaf extract for the ZnO NPs confirmed by FT–IR. The size (16–20 nm) and morphology (spherical and agglomerated) were characterized by FE-SEM. The typical absorption peak of Zn NPs was seen in UV–Vis absorption. Antimicrobial activity studies confirmed the presence of a maximum inhibition zone [64] biosynthesized NiO NP and ZnO NP using extracts of Moringa Oleifera leaves as an efficient chelating and oxidant/reductant of [Ni(H2O)6](NO3)2 and Zn(NO3)2.6H2O. XRD. Attenuated Total Reflection-FTIR, UV-Vis-NIR, and PL methods explore the NiO NP and ZnO NP structural and optical characteristics of these two semiconductors created in the same process. Pure cubic NiO-NPs and pure wurtzite ZnO-NPs with average crystallite sizes of 17.80 nm and 10.81 nm, respectively, were formed, according to the structural study. The diffuse reflectance investigation revealed that their band gaps were 4.28 eV and 3.35 eV, respectively.


### 2.4. Nickel Oxide (NiO) NPs

Ezhilarasi et al. [66] synthesized the nickel oxide nanoparticles (NiO-NPs) using the green method. It shows cytotoxicity and antibacterial activity. In this process, the color changed from dark brown to reddish ink, and after applying temperature, a light-yellow powder of NiO NPs was produced. The NiO NMps were single crystalline with a face-centred cubic phase and two strong PL at 305.46 nm and 410 nm. XRD and FTIR verified the formation of a pure NiO phase (average size 9.69 nm). HR-TEM confirmed the creation of nano and microstructures (agglomerated spherical shape). With different doses of NiO NPs generated from Moringa oleifera plant extract, the in vitro cytotoxicity and antibacterial activity were tested.


### 2.5. Magnesium Oxide (MgO) NPs

Fatiqin et al. [68] green synthesized magnesium oxide nanoparticles (MgO NPs) were achieved in this work by combining Moringa oleifera leaf extracts with a magnesium chloride solution. The produced MgO NPs vary from 20 to 50 nm (spherical shape). The absorption of MgO nanoparticles in the UV-Vis spectrum is at 280 nm. The inhibition zones showed the antibacterial activity of MgO NPs against S. aureus and E. coli. [69] used an aqueous extract of Moringa oleifera (MO) leaves as a green agent to produce nanosize MgO (MgO NPs) from MgCl2 solution. UV-Vis absorption was used to validate the formation of MgO NPs in this synthesis. XRD investigation validated the spherical crystal structure of MgO NPs. Using SEM, TEM, and particle size analyzer (PSA) data, the particle size of the synthesized MgO NPs was determined to be between 40 and 70 nm. The NPs showed excellent antibacterial and antifungal activity.


### 2.6. Silver (Ag) NPs

Moodley et al. [72] described silver nanoparticles (AgNPs) synthesized from Moringa oleifera leaf extracts and studied their antibacterial activities. UV–Vis spectrum analysis was used to establish the synthesis of AgNPs by reducing Ag + (AgNO3). A UV–Vis spectrometer was used to scan NP solutions and the control from 190 to 900 nm. Surface plasmon resonance at 450 nm and 440 nm verified the production of silver nanoparticles in both fresh and freeze-dried leaf samples. According to FTIR spectroscopic technique, flavonoids, terpenoids, and polysaccharides predominate and are useful for the reduction as well as capping agents during the synthesis of Ag NPs. According to the X-ray diffraction examination, shows 9 and 11 nm NPs size. The antimicrobial activity of Ag NPs was shown in both bacterial and fungal strains.Vasanth et al. [74], in their work, synthesized colloidal silver nanoparticles (AgNPs) from Moringa olifera (MO) stem bark extract. Morphology was studied using electron and atomic force microscopic imaging (40 nm, and pentagon-shaped). Human cervical cancer cells (HeLa) were used to analyze the effects of produced AgNPs, and cell morphology was assessed using 4,6-diamidino-2-phenylindole (DAPI) staining. The effectiveness of AgNPs was investigated using fluorescence-activated cell sorting (FACS), and it was discovered that they trigger death in HeLa cells via generating reactive oxygen species (ROS).


### 2.7. Gold (Au) NPs

Anand et al. [78] used 1 M chloroauric acid with Moringa oleifera (MO) aqueous flower extract for the AuNP synthesis. The UV-Vis spectrophotometer (200–800 nm) was used to describe the formation of the colloidal solution of Au NP. TEM was analyzed to particle size (100 nm) that was triangular, hexagonal, and irregular spherical. Primary analytical tests analyzed AuNP and functional group interaction in floral extract and FTIR, and the 1H-NMR technique was used to investigate capping agents. Catalytic reduction of nitrophenol and nitroaniline using Au NP, which were analyzed by UV-Vis, revealed a fast decrease in some minutes, suggesting industrial effluent degradation. Furthermore, AuNPs might have anticancer activities. [79] worked on an ecofriendly method to synthesize gold nanoparticles (AuNPs) by reducing chloroauric acid with Moringa oleifera leaf extract which acts as a reducing agent. The chloroauric acid solution was reduced and transformed to AuNPs in the size range of 20-60 nm (spherical shape) using leaf extract. The MO plant extract contains several phytochemicals that function as reducers and stabilizers. These are environmentally acceptable synthesizing stabilized gold nanoparticles suitable for various biological applications.


## 2.1. Iron Oxide (FeO) NPs

Aisida et al. [47], in their research worked, synthesized a green and environmentally friendly approach for nanoparticles in which using an aqueous extract of the Moringa oleifera plant serves as a reductant and capping agent. MO leaf powder extract and FeCl3 solution were used to synthesize dark-brown-capped MO-FeO NPs. UV-Vis spectroscopy confirmed the noticeable color change from orange to dark brown (Figure 5), leading to FeO NPs. The rod-like morphologies of NPs were shown by SEM and TEM, with a 15 nm average particle size. In terms of antimicrobial activity, biosynthesized FeO NPs inhibited growth more effectively than chemical FeO NPs against antimicrobial. Additionally, smaller particles have a greater surface area and bioactivity, making them excellent antimicrobial agents against harmful microorganisms.Figure 5
Biosynthesis of FeO nanorods.Tovar et al. [48] almost have similar work as previous authors. Using the MO leaf extract and (Iron (III) chloride hexahydrate) for the synthesis of FeO NPs, in this process, the Moringa oleifera acted as a capping agent. The germination rate and development of corn seeds were studied using synthesized FeO NPs loaded with N, P, and K. Moringa, and chitosan had a favourable influence on corn plant speed germination parameters, with no adverse effects on seed germination.MO FeO NP possesses structural and superparamagnetic properties and suitable particle sizes for biomedical applications [47] performed two parts in which the Moringa oleifera (MO) leaves were dried at room temperature (RT) and sunlight (SL). MO acted as a capping agent; both solutions were gradually reduced from brown to dark black by adding FeCl3.6H2O solution. The FeO NPs obtained were characterized and the size of RT FeO and SL FeO NPs measured by SEM was 16 to 18 nm and 18 to 20 nm, respectively. XRD analysis showed a BCC lattice structure for RT, while SL exhibited a quasicrystalline structure.


## 2.2. Copper Oxide (CuO) NPs

The researchers [54] used MO leaf extract as a capping agent and copper acetate solution to synthesize nanocrystalline CuO powder (fine dark black). A simple green chemistry strategy made CuO NPs from Moringa oleifera leaf extract, and XRD, FE-SEM, EDX, FT-IR, UV-DRS, and PL were used to characterize. CuO NPs show good antifungal activity [56] used Moringa oleifera (MO) leaf extract for the synthesis of CuO microspheres. The color of the solution changed from bluish to dark green during stirring, indicating that the biological components included in the MO leaf extract converted Cu (NO3)23H2O to Cu2+ ions. The formation of monoclinic crystal-structured CuO was revealed by the XRD pattern, which confirms the conversion of Cu (NO3)23H2O to Cu2+ ions by phytochemicals contained in the MO leaf extract. As seen by SEM micrographs, it shows the cluster-like morphologies that mimic hierarchical CuO microspheres. In the FTIR spectrum, the asymmetric stretching deformation vibration bands correspond to Cu–O bonds, which imparted monoclinic unit crystal formation, and the synthesized NPs show better antibacterial activity.


## 2.3. Zinc Oxide (ZnO) NPs

Elumalai et al. [62] employed a straightforward and environmentally safe chemical route to synthesize zinc oxide nanoparticles (ZnO NPs) from Moringa oleifera leaf extract. UV–Vis, XRD, FESEM, EDX, FT–IR, and PL evaluated the ZnO NPs. The hexagonal wurtzite structure of NPs was found by the XRD investigation. The functional groups act as a stabilizing agent in the leaf extract for the ZnO NPs confirmed by FT–IR. The size (16–20 nm) and morphology (spherical and agglomerated) were characterized by FE-SEM. The typical absorption peak of Zn NPs was seen in UV–Vis absorption. Antimicrobial activity studies confirmed the presence of a maximum inhibition zone [64] biosynthesized NiO NP and ZnO NP using extracts of Moringa Oleifera leaves as an efficient chelating and oxidant/reductant of [Ni(H2O)6](NO3)2 and Zn(NO3)2.6H2O. XRD. Attenuated Total Reflection-FTIR, UV-Vis-NIR, and PL methods explore the NiO NP and ZnO NP structural and optical characteristics of these two semiconductors created in the same process. Pure cubic NiO-NPs and pure wurtzite ZnO-NPs with average crystallite sizes of 17.80 nm and 10.81 nm, respectively, were formed, according to the structural study. The diffuse reflectance investigation revealed that their band gaps were 4.28 eV and 3.35 eV, respectively.


## 2.4. Nickel Oxide (NiO) NPs

Ezhilarasi et al. [66] synthesized the nickel oxide nanoparticles (NiO-NPs) using the green method. It shows cytotoxicity and antibacterial activity. In this process, the color changed from dark brown to reddish ink, and after applying temperature, a light-yellow powder of NiO NPs was produced. The NiO NMps were single crystalline with a face-centred cubic phase and two strong PL at 305.46 nm and 410 nm. XRD and FTIR verified the formation of a pure NiO phase (average size 9.69 nm). HR-TEM confirmed the creation of nano and microstructures (agglomerated spherical shape). With different doses of NiO NPs generated from Moringa oleifera plant extract, the in vitro cytotoxicity and antibacterial activity were tested.


## 2.5. Magnesium Oxide (MgO) NPs

Fatiqin et al. [68] green synthesized magnesium oxide nanoparticles (MgO NPs) were achieved in this work by combining Moringa oleifera leaf extracts with a magnesium chloride solution. The produced MgO NPs vary from 20 to 50 nm (spherical shape). The absorption of MgO nanoparticles in the UV-Vis spectrum is at 280 nm. The inhibition zones showed the antibacterial activity of MgO NPs against S. aureus and E. coli. [69] used an aqueous extract of Moringa oleifera (MO) leaves as a green agent to produce nanosize MgO (MgO NPs) from MgCl2 solution. UV-Vis absorption was used to validate the formation of MgO NPs in this synthesis. XRD investigation validated the spherical crystal structure of MgO NPs. Using SEM, TEM, and particle size analyzer (PSA) data, the particle size of the synthesized MgO NPs was determined to be between 40 and 70 nm. The NPs showed excellent antibacterial and antifungal activity.


## 2.6. Silver (Ag) NPs

Moodley et al. [72] described silver nanoparticles (AgNPs) synthesized from Moringa oleifera leaf extracts and studied their antibacterial activities. UV–Vis spectrum analysis was used to establish the synthesis of AgNPs by reducing Ag + (AgNO3). A UV–Vis spectrometer was used to scan NP solutions and the control from 190 to 900 nm. Surface plasmon resonance at 450 nm and 440 nm verified the production of silver nanoparticles in both fresh and freeze-dried leaf samples. According to FTIR spectroscopic technique, flavonoids, terpenoids, and polysaccharides predominate and are useful for the reduction as well as capping agents during the synthesis of Ag NPs. According to the X-ray diffraction examination, shows 9 and 11 nm NPs size. The antimicrobial activity of Ag NPs was shown in both bacterial and fungal strains.Vasanth et al. [74], in their work, synthesized colloidal silver nanoparticles (AgNPs) from Moringa olifera (MO) stem bark extract. Morphology was studied using electron and atomic force microscopic imaging (40 nm, and pentagon-shaped). Human cervical cancer cells (HeLa) were used to analyze the effects of produced AgNPs, and cell morphology was assessed using 4,6-diamidino-2-phenylindole (DAPI) staining. The effectiveness of AgNPs was investigated using fluorescence-activated cell sorting (FACS), and it was discovered that they trigger death in HeLa cells via generating reactive oxygen species (ROS).


## 2.7. Gold (Au) NPs

Anand et al. [78] used 1 M chloroauric acid with Moringa oleifera (MO) aqueous flower extract for the AuNP synthesis. The UV-Vis spectrophotometer (200–800 nm) was used to describe the formation of the colloidal solution of Au NP. TEM was analyzed to particle size (100 nm) that was triangular, hexagonal, and irregular spherical. Primary analytical tests analyzed AuNP and functional group interaction in floral extract and FTIR, and the 1H-NMR technique was used to investigate capping agents. Catalytic reduction of nitrophenol and nitroaniline using Au NP, which were analyzed by UV-Vis, revealed a fast decrease in some minutes, suggesting industrial effluent degradation. Furthermore, AuNPs might have anticancer activities. [79] worked on an ecofriendly method to synthesize gold nanoparticles (AuNPs) by reducing chloroauric acid with Moringa oleifera leaf extract which acts as a reducing agent. The chloroauric acid solution was reduced and transformed to AuNPs in the size range of 20-60 nm (spherical shape) using leaf extract. The MO plant extract contains several phytochemicals that function as reducers and stabilizers. These are environmentally acceptable synthesizing stabilized gold nanoparticles suitable for various biological applications.


## 3. Conclusion

This review summarised that Moringa oleifera plant leaves have active compounds that serve as capping, reducing, and stabilizing agents and produce biosynthesized M/MO NPs. Several approaches were gathered, and it was found that Moringa oleifera plant leaves can readily biosynthesize numerous types of M/MO nanoparticles. Biosynthesised ZnO and AgNPs outperform chemically produced NPs in terms of antibacterial characteristics. However, not all articles discuss the size of NPs resulting from the concentration of Moringa oleifera plant leaf extract or temperature changes. In general, the size of the nanoparticles was determined by manipulating the concentration of Moringa oleifera leaf extract and the temperature during biosynthesis.



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*Source: 2147393-2022-04-07.xml*