Optimum Green Synthesis, Characterization, and Antibacterial Activity of Silver Nanoparticles Prepared from an Extract of Aloe fleurentinorum

Te synthesis of metal nanoparticles through the use of plant extract is a process that is not only simple but also inexpensive, quick, and favorable to the environment. As a result, it is utilized in a wide variety of felds. When synthesizing silver nanoparticles (AgNPs), several diferent kinds of plant extracts were utilized. Te manufacture of silver nanoparticles was carried out in this study using an environmentally friendly technique. Te aqueous extract of the Aloe feurentinorum plant was utilized as a stabilizing and reducing agent. To determine the optimal conditions for the synthesis of silver nanoparticles, it was necessary to investigate the impact of several parameters on the process. Tese parameters included the reactant volume ratio, pH values, temperature, and reaction time. To get crystallite and stable silver nanoparticles, an aqueous solution of AgNO 3 (0.01M) was added to an aqueous extract of Aloe feurentinorum plant at a temperature of 60 degrees Celsius and a pH of 8. Te mixture was then stirred with a magnetic stirrer for ninety minutes (90 minutes). Using a variety of methods (UV-vis spectrophotometer, FTIR, XRD, SEM, EDX, and XPS), several approaches were utilized to investigate and describe the green-produced AgNPs. Trough the use of the SEM method, it was demonstrated that the morphology of AgNPs is tetrahedral. It was determined using X-ray difraction that the size of crystalline AgNPs was 26.7nm. AgNPs that have been optimally synthesized have antibacterial properties that are both signifcant and efective against various bacterial species that have been tested at varying doses.


Introduction
Nanotechnology is an intriguing discipline that investigates the development and manipulation of nanomaterials, which are very small particles that range in size from one nanometer to one hundred nanometers [1,2].Tese particles have many promising applications in various sectors, such as health [3], agriculture [4], cosmetics [5], food [6], optics [7,8], cancer therapy [9], catalysis [10,11], and more.Metal oxide nanoparticles (MNPs) that are manufactured utilizing environmentally acceptable technologies are gaining interest because they are energy-efcient, safe, cost-efective, and environmentally friendly [12,13].Compared to their bulk material, MNPs exhibit notably diferent features in terms of morphology, surface chemistry, physical characteristics, and optical properties [14,15].
Nanomaterial researchers have paid particular attention to AgNPs among other MNPs because of their unique characteristics and multifunctionality.Manufacturing fabrication of numerous devices, optical sensors, electrical conductors, catalysts, and medication administration are some of the most remarkable inherent qualities [15,16].In addition, lotions, sunscreen products, and ointments are made using AgNPs [17,18].Te AgNPs have also shown signifcant antimicrobial potential [19,20].Tere are three main ways that NPs are often made: chemically, physically, and by green synthesis [21,22].Physical nanomaterial production techniques need heating and pressurized environments, as well as costly machinery.Serious environmental and human health risks are associated with using various hazardous solvents, expensive metal salts, stabilizers, and reductants in the chemical synthesis of AgNPs [23,24].Tese limitations restrict the usefulness of physicochemical approaches to nanoparticle manufacturing.
Terefore, a simple, cost-efective, eco-friendly, and fast approach is needed.Te environmentally friendly routeassisted manufacture of MNPs has garnered much interest owing to the fact that it is risk-free.Green production may be a good alternative to several physicochemical procedures because of their safety, cheap cost, low toxicity, and repeatability.Additionally, green production makes producing AgNPs on a large scale easier.Many research papers have described the creation of silver nanoparticles (AgNPs) from plants using various plant parts as natural resources.Tese plant parts include leaves, peels, roots, stems, seeds, and fruit.Plant extracts include many phytochemicals, including polyphenols, proteins, enzymes, amino acids, vitamins, polysaccharides, aldehydes, and ketones.Tese phytochemicals can decrease metal ions and stable nanoparticles to the appropriate shapes and sizes.Te number of solventbased research studies that have been published up to this point on the environmentally friendly manufacturing, characterization, and bio-potential of AgNPs is limited [25].
Phytochemical or plant-based synthesis of nanoparticles using diferent plant extracts as reducing agents and stabilizing agents instead of chemical or high radiation beams [22] because they contain carbohydrates, proteins, fats, and secondary metabolites such as favonoids, terpenoids, alkaloids, and polyphenols [26].Te extracts could be used from diferent plant parts, such as leaves, roots, bark, fruits, seeds, stems, fowers, and oil [27].Yemen is a rich country for medical exceptive plants and herbs.Still, most current research focuses on chemical and pharmaceutical studies, and only some researchers use these plants for nanoparticle synthesis.
Aloe is a monocotyledon plant genus from the Liliaceae family [28,29].Aloe L. genus includes more than 600 subspecies and varieties [30].It is widespread in Asia but only in Southwest Arabia, Socotra, and India [29].Aloes have boat-shaped and succulent leaves [31].From the previous research, Aloes have cytotoxic properties, so it was used as an antibacterial [32].Te Aloe L. genus in Yemen is presented by 20 species, including Aloe feurentinorum Lavranos and Newton [29,33].Aloe feurentinorum is characterized by stemless armed leaves, rosulate, and lanceolate at the apex surface, which is dark green, very thick, fresh, rough, and without teeth (Figure 1).Aloe feurentinorum occurs on the eastern rain-shadowed slopes of Yemen mountains and Asir region "Saudi Arabia" [29].Previous studies about Aloe feurentinorum focused on phytochemical screening (Scheme 1) and antimicrobial activities.Moreover, many researchers have used the green method of Aloe vera species to synthesize nanoparticles.Tis work aims to study the physical and biological characteristics of AgNPs synthesized by an ecofriendly route using an aqueous extract of the Aloe feurentinorum plant grown in Yemen.

Materials and Methods
2.1.Materials.Te Aloe feurentinorum plant was collected from Sana'a in Yemen, silver nitrate (United Kingdom), ammonia solution, absolute ethanol, and deionized water from a science college laboratory.

Characterization and Measurement
Techniques.Te synthesis's pH values were adjusted using a METROHM pH meter.Te optimal conditions of nanoparticle synthesis were observed and checked by a SPECTROD200 (Analytik Jena) An ultraviolet and visible double-beam spectrophotometer was used with a wavelength range from 300 to 700 nm.Te molecules, present as a capping reduction agent for nanoparticles, were characterized using (FTIR) Fourier transform infrared, which was used from a 4000 to 400 cm −1 range of wavenumber.Te AgNPs structure and crystalline properties were studied using XD-2 (Shimadzu ED-720) powder X-ray difractometer at a voltage of 36 kV and a current of 20 mA using CuK (α) radiation in the range of 5 °< 2θ < 75 °a wavelength of 1.54056 A °at 1 °min −1 scanning rate.Te morphology of the AgNPs was observed by QUANTA FEC 250 SEM.Te X-ray Photoelectron Spectroscopy (XPS) analyses were applied using a K-ALPHA (Termo Fisher Scientifc, Waltham, MA, USA) with monochromatic X-ray K-alpha radiation −10 to 1350 eV spot size 400 μm at pressure 10 −9 mbar with full-spectrum pass energy 200 eV and narrow-spectrum 50 eV.

Te Aloe feurentinorum Plant Extract Preparation.
Te Aloe feurentinorum leaves (AFL) were collected from Dr Hassan Ebrahim Garden, Sana'a, Yemen, during the summertime of 2022.Te plant (AFL) underwent multiple washes utilizing distilled water.Ten, dried at room temperature for three days away from sunlight, the plant was ground to a fne powder.Ten, 5 g of (AFL) powder was immersed in 100 mL deionized water and stirred for 30 min utilizing a magnetic stirrer.At 60 °C, the extract was cooled at room temperature and fltered.

Green Synthesis of Silver Nanoparticles (AgNPs).
A 0.01 M of silver nitrate (0.17 gm of AgNO 3 in 100 mL deionized water) was prepared, and aqueous AFL extract was added to AgNO 3 solution with diferent conditions as the volume ratio of reactant, pH value, and the reaction temperature to get the optimal conditions for synthesis nanoparticles.(2) Te Optimal pH Value.After selecting the optimal volume ratio, 4 solutions were prepared (G 5 , G 6 , G 7 , G 8 ) by changing the pH values of the reaction by adding diluted NH 3 solution at pH 5.7, 7, 8, and 9.
(4) Te Optimal Reaction Time.One sample was prepared using the optimal conditions by mixing the optimal volume ratio (1 : 1), at the optimal pH value (pH � 8), and the optimal temperature (60 °C) with continuous stirring until 2 h.

Antibacterial Activity Studies.
To investigate the biological activity of AgNPs produced using Aloe feurentinorum leaf extract, the antibacterial activities of AgNPs were studied against diferent bacterial types using the agar difusion technique.Te studies were against 2 types of Gram-positive bacteria (Staphylococcus Aureus and Bacillus Subtilis) and 2 types of Gram-negative bacteria (Escherichia Coli and Salmonella Typhi).Te AgNPs efect on bacteria was tested with a 100% solution as a synthesized AgNPs at the optimal conditions as a stock solution, and three different dilutions from the stock (75%, 50%, 25%), and they were labeled as G 100 , G 75 , G 50 , G 25 .After inoculating the bacterial cells on Petri dishes, the holes were made in the bacterial dishes and flled with diferent concentrations of synthesized AgNPs.Ten, the dishes were incubated at 37 °C for a full one-day duration.Te antibacterial activities of AgNPs samples were determined by measuring the inhibition zones around the samples.International Journal of Chemical Engineering semiconductor's absorption threshold determines the minimum amount of photon energy required to generate photoelectrons and holes.By using the absorption spectra of the optimal conditions, the band gap in Figure S5 (at supplementary materials) was determined for synthesized AgNPs using Tauc's equation ((ɑɦʋ) 2 � k(ɦʋ − E g )), as shown in Figure S5 (at supplementary materials).

Fourier Transform Infrared Characterization.
Te method used to show the structure and function groups presented in materials is the Fourier transform infrared spectra.FTIR was shown in Figure S6 (at supplementary materials) for Aloe feurentinorum leaf extract and the synthesized AgNPs.It shows a broad stretching vibration band of OH for AFL extract at 3250 cm −1 , which decays in intensity of AgNPs IR spectra.Tat indicates this bond is used in the reduction process for silver ions to AgNPs [34].Likewise, the stretching vibration band of the C�O group at 1520 cm −1 and the curvature vibration band of the OH group at 1440 cm −1 are utilized in the synthesis of AgNPs as a reducing, capping, and stabilizing agent.

X-Ray Difraction
where D is the average particle size, K is a constant (0.94), λ is the wavelength of the x-ray (1.5406A °), β is the full width at half maximum of the peak (rad) (FWHM), and θ is the position of the difraction peak.Te microstrain is determined utilizing equation ( 2).Te microstrain and crystalline size values are displayed in Table 1.
Te (a � b � c) are the lattice parameters for the synthesized AgNPs, which have a face-centered cubic (FCC) crystallinity, were determined using equation (3), and from these values, the volume was calculated by equation (4).
where (h, k, l) are the Miller indices and d is the plane spacing determined through Bragg's equation (5).
Te lattice parameters (a, b, and c) (Table 2) are practically indistinguishable from those announced in the (JCPDS no.87-0719) card for AgNPs.
A dislocation is an imperfection in a crystal related to the lattice existing in various crystal pieces.Te dislocation density can be determined utilizing equation (6).Te values of dislocation density are displayed in Table 2.
From the XRD pattern, the porosity of the synthesized samples was determined.Te percentage of porosity was determined and tabulated in Table 2, as indicated by equation ( 7) [35], where ρ x is the theoretical density and ρ is the determined density from X-ray data utilizing the equation formula (8).
Z is the number of chemical units in one crystal unit cell � 4, M is the molecular weight (107.87 g/mole), N is Avogadro's number, and V is the volume.

Energy Spectrum Component
Analysis.X-ray energy dispersive spectrometry.Te elements were analyzed using energy-dispersive X-ray spectrometry (EDX).EDX images of Ag-NPs are displayed in Figure 3, revealing peaks corresponding to elements such as Ag, O, N, C, and others present in the plant.Tis verifes the utilization of the Aloe feurentinorum plant as a reducing agent in producing silver nanoparticles.Table 3 exhibits the elemental analysis of the synthesized silver nanoparticles by X-ray energy dispersive spectrometry.

Scanning Electron Microscopy (SEM).
Te conducted SEM images of the silver nanoparticles (AgNPs) demonstrated their synthesis as tetrahedral particles, as seen in Figure 4. Te plant known as Aloe feurentinorum has signifcant promise in silver nanoparticle synthesis.Using higher-density scanning electron microscopy (SEM) techniques facilitated the identifcation of silver nanoparticles exhibiting a tetrahedral shape, as visually depicted in Fig- ure 4. Te utilization of Aloe feurentinorum plant extract in synthesizing silver nanoparticles resulted in the successful formation of silver nanostructures, as evidenced by the scanning electron microscopy (SEM) image.

XPS Analysis.
Te XPS assessment was carried out to analyze the structure of the silver nanoclusters as well as their chemical makeup (Figure 5).Te fndings demonstrate two distinct peaks, 367.37 eV (Ag 3d5/2) and 373.52 eV (Ag International Journal of Chemical Engineering 3d3/2).In addition, the fact that the binding energy of Ag 3d5/2 is in the middle of the range for Ag (0) and Ag(I), which is between 366.42 and 374.26 eV, indicates that Ag (0) is present [1].Te fact that the peaks moved to inferior binding energies demonstrates that the chemical behavior of the surface Ag atoms changed.Tis change in chemical nature might be attributed to a combination of Ag (0) and Ag (I), as seen by the shift in the peaks.Te structure of tryptophan is similar to that of the skeleton of an amino acid, and its functional groups include carboxyl and amino groups.4 for the 4 diferent bacterial strains, which indicate diferent efects by variation AgNP concentration.Te higher inhibition zones were observed on Escherichia ColiGramnegative bacteria, which has a greater inhibition zone for AgNPs at diferent concentrations (16−18 mm), maybe because of the bacterial cell wall thickness.Gram-positive bacteria have a peptidoglycan thick layer cell wall, which makes them more resistant than Gram-negative species [36,37].AgNPs may be synthesized by combining several organic chemicals found in the Aloe plant extract with AgNO 3 .Tese components include saponin, tannin,  6 International Journal of Chemical Engineering terpenoids, and favonoids.Green synthesis incorporates these organic molecules shown in Figure 6.As a consequence of the accumulation of these nanocrystals at the cell membrane, the membrane's permeability is increased, ultimately leading to the cell's death [28].In general, it was observed that the inhibitory activity increased by increasing the concentration of AgNPs.

Conclusion
Successfully green synthesized AgNPs using Aloe feurentinorum plant extract were carried out in our research work.UV-vis analysis determined the optimal conditions (V/V ratio, pH, T, and reaction time) for the green synthesized AgNPs.Te capping and reducing agents present in the AFL BioSource were identifed by FTIR and XPS techniques.Te average size of the particles was determined to be 26.8 nm using XRD analysis.SEM images showed the tetrahedral morphology of the synthesized AgNPs.In this work, the antimicrobial activity studies for these synthesized AgNPs revealed a stronger and more promising efect for the Gram-negative bacteria than the Gram-positive bacteria, especially for Escherichia Coli species.International Journal of Chemical Engineering

3. 1 .
Ultraviolet-Visible Spectroscopy Characterization 3.1.1.Te Volume Ratio of Reactant Efect.Te comparison of the UV-vis absorption spectrum of the extract in FigureS1(at supplementary materials) with the spectra of the green synthesized silver nanoparticles verifed the AgNPs formation at a constant volume of AFL (10 ml).It monitored the formation of AgNPs after diferent volumes of AgNO 3 (0.01 M) from 10 ml to 40 ml.Te absorbance peaks indicate that increasing AgNO 3 volume from 10 ml to 40 ml causes a decrease in AgNPs formation.Tat means the sample G1, which had the reactants' 1 : 1 volume ratio, had the highest absorption.So, the optimal volume ratio determined for the green synthesized AgNPs is G1.3.1.2.Te pH Value Efect.Studying the efect of pH on the formation of Ag-NPs by changing the pH values from 5.7 to 9 is shown in FigureS2(at supplementary materials).Te UV-vis absorbance peak decreased, then increased, then decreased, and the absorbance peaks shifted to a blue wavelength (425 nm).Tis indicates the decrease of AgNP diameter.So, the optimal pH value for the green synthesized AgNPs is G7 at pH � 8.3.1.3.Te Temperature of the Reaction.Te silver nanoparticles' UV-visible spectra synthesized at various temperatures are shown in FigureS3(at supplementary materials).It shows that the absorbance peak increases and then decreases.Te maximum absorbance of sample G11 is at temperature 60 °C.Tat indicates the optimal reaction temperature at this value.3.1.4.Te Reaction Time.As shown in FigureS4(at supplementary materials), the absorbance range gradually increased as the reaction time increased and the color intensity increased with the incubation duration.Tis indicates an increase in the formation of AgNPs with increasing color intensity with time.3.1.5.Band Gap Energy Determination. Te semiconductor gap refers to the spatial separation between the valence and conductance bands, which are devoid of electrons.Te

Table 3 :
Elemental analysis of the as-synthesized AgNPs.

Table 4 :
Te antibacterial activities of the synthesized AgNPs.