Introduction

Nanotechnology has been a game-changer in multiple scientific arenas by allowing for the precise alteration of materials at an incredibly small scale. This has led to new capabilities and enhancements in various applications. Silver nanoparticles (AgNPs) are particularly noteworthy for their distinct features, such as superior electrical conductivity and resistance to microbial growth [1]. Their synthesis has become a focal point of research, especially given their applicability in healthcare, electronics, and eco-sciences [2,3,4].

Conventional techniques for creating AgNPs often require the use of toxic substances and are energy-intensive. In response to the growing focus on sustainability, researchers are investigating more environmentally friendly methods for nanoparticle production. One such innovative approach involves leveraging plant-based extracts as reducing agents. These natural extracts contain organic compounds that can serve multiple roles in the nanoparticle formation process, including reduction and stabilization. This method not only speeds up the production process but is also cost-effective and less harmful to the environment [5, 6].

Among a variety of plants studied for this purpose, P. palaestina, indigenous to the Eastern Mediterranean, has shown considerable promise. Also classified scientifically as Pistacia terebinthus, this versatile plant can either be a tree or a shrub and is commonly found in specific Mediterranean ecosystems. It is prevalent in elevated and hilly landscapes across a range of Middle Eastern countries and nearby islands. In Arabic dialects, the fruit of this plant is often called “Butom,” and it holds various roles in local traditions [7,8,9].

The leaves of P. palaestina have a history of use in traditional medicine, offering a range of health benefits. Various techniques, from cold pressing to steam distillation, are used to extract the beneficial compounds from the leaves [10]. These natural extracts have attracted attention for their potential medicinal properties, including their ability to act as antioxidants and anti-inflammatory agents [11, 12]. Chemical analysis has revealed that the plant is rich in a variety of bioactive compounds, such as flavonoids and fatty acids, which are thought to contribute to its therapeutic effects [13].

The surface-enhanced resonance of AgNPs is another aspect that makes them particularly intriguing. This phenomenon refers to the significant enhancement of electromagnetic fields around the nanoparticle surface. When AgNPs are exposed to light, the conduction electrons on the nanoparticle surface undergo collective oscillations, known as localized surface plasmon resonance (LSPR). This resonance leads to a substantial increase in the intensity of light near the particle surface, enhancing various optical properties. This unique characteristic of AgNPs has led to their widespread use in fields like sensing, imaging, and photothermal therapy. In biosensing, AgNPs enhance the detection of biomolecules, allowing for highly sensitive and specific diagnostic techniques, crucial in disease detection and management [8]. In spectroscopy, particularly in surface-enhanced Raman scattering (SERS), these nanoparticles significantly increase the Raman signals of molecules, enabling the detection of trace amounts of substances. This feature is invaluable in environmental monitoring, food safety analysis, and forensic science [14, 15].

Despite the numerous advantages, the green synthesis of silver nanoparticles and their applications in surface-enhanced resonance face challenges. Controlling the size and shape of nanoparticles during synthesis, understanding the long-term environmental impact, and ensuring scalability and reproducibility are some ongoing research areas. Future advancements in these domains are expected to address these challenges, leading to more refined and sustainable nanoparticle synthesis methods and broadening the scope of their applications in technology and medicine [16, 17].

In this work, we have employed P. palaestina leaf extract as a novel reducing agent to fabricate Ag nanoparticles of diverse diameters. The variation in these diameters is directly influenced by the concentration of silver nitrate introduced during the synthesis process. To understand and validate the structural and optical properties of these differently sized Ag nanoparticles, we used techniques such as SPM, XRD, Raman, UV–visible absorption, and photoluminescence spectroscopy for comprehensive characterization.

Materials and Methods

Leaves from the P. palaestina plant was harvested at the Al-Arroub Agricultural Station in Hebron, (West Bank, Palestine) during the summer of 2023. Silver nitrate (AgNO3) was used in the experiments, with distilled water serving as the solvent. Figure 1 shows the flowchart of the preparation process of leaf extract and synthesis of Ag nanoparticles. The collected samples were dried in a shaded area and subsequently ground into a fine powder using a grinding machine. Following this, 35 mg of the powdered sample was boiled in 350 mL of deionized water for half an hour. After filtration through Whatman paper and a 0.1-µm membrane, the solution turned a light-yellow color and was stored in the refrigerator at 4 °C for further analysis and used in synthesis.

Fig. 1
figure 1

Flowchart of the preparation process of leaf extract and synthesis of Ag nanoparticles

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To produce silver nanoparticles of varying diameters, we prepared aqueous solutions of AgNO3 at different concentrations: 1.18 mM, 3.5 mM, 5.88 mM, and 8.24 mM, using deionized water. Subsequently, 50 mL of P. palaestina leaf extract was added dropwise to each 50-mL AgNO3 solution. The mixture was subsequently warmed in a heating mantle, maintaining a temperature range of 80 to 84 °C for 2 h, while being stirred continuously. The emergence of a brownish-yellow to black color signified the successful formation of silver nanoparticles. To separate and purify the synthesized nanoparticles, the solution was centrifuged at 10,000 rpm for 10 min. This centrifugation step was repeated five times to ensure the retrieval of pure silver nanoparticles.

The size and morphology of Ag nanoparticles were assessed using scanning probe microscopy (SPM-9700HT, Shimadzu, Japan). The measurement parameters included a scanning speed of 0.5 Hz and a resolution of 256 × 256 pixels. The spatial resolution of the device was determined to be 0.2 nm. The X-ray diffraction analysis was conducted using (Bruker D2 PHASER, Bruker, Billerica, MA, USA) with Cu kα radiation (30 kV and 10 mA). Raman spectroscopy was performed using a confocal Raman microscopy system Witec Alpha 300R (Ulm, Germany) with an excitation wavelength of 532 nm and laser power of 75 mW. The UV-vis absorption spectra of the samples were measured on a UV-2600i (Shimadzu, Tokyo, Japan) spectrophotometer. The photoluminescence spectra were measured using RF-6000 spectrofluorometer (Shimadzu, Tokyo, Japan). The Shimadzu Lab solution software was used for data acquisition.

Results and Discussion

Morphology and Structure of Ag Nanoparticles

The shape and height of the Ag nanoparticles were assessed using scanning probe microscopy (SPM) topography images, captured in a non-contact dynamic mode. The AFM tip employed for this was a super sharp silicon (SSS-NCH) from Nanoworld, featuring a force constant of 42 N/m, a resonance frequency of 320 kHz, and a tip radius of 2 nm. Figure 2a–d illustrates the atomic force microscopy (AFM) topographic representation of silver nanoparticles on a mica substrate at various concentration molarities (1.18, 3.5, 5.88, and 8.24 mM). The images clearly depict the spherical morphology of the nanoparticles. Height analysis, as illustrated in Fig. 2e–g, indicates that the observed heights of these nanoparticles range from 3 to 27 nm. In Fig. 2k–n, a particle size distribution histogram for the silver nanoparticles is presented, utilizing data extracted from Fig. 2a–d that encompasses approximately 1700 nanoparticles in the image. Analysis using particle measurement software reveals that the average diameters of these nanoparticles are approximately 10 nm, 7 nm, 4 nm, and 2 nm for different concentration molarities (1.18, 3.5, 5.88, and 8.24 mM), respectively. This outcome leads to the conclusion that as the concentration of AgNO3 increases, the size of Ag nanoparticles decreases. This trend is clearly depicted in Fig. 3 where the concentration of silver nitrate (AgNO3) significantly influences the characteristics of the produced silver nanoparticles. The pattern observed can be interpreted using the principles of nucleation and growth. Higher AgNO3 concentrations accelerate the nucleation process, leading to the formation of many tiny clusters. These clusters serve as the foundational units for the nanoparticles. This dynamic interaction between the precursor concentration and the nucleation process accounts for the decrease in nanoparticle size as the AgNO3 concentration increases [2, 18].

Fig. 2
figure 2

a–d Atomic force microscopy (AFM) topography images of Ag nanoparticles on a mica substrate at different concentrations (1.18, 3.5, 5.88, and 8.24 mM), scan sizes: 4 μm × 4 μm, 3 μm × 3 μm, 2 μm × 2 μm, and 2 μm × 2 μm, respectively. e–h Line profiles for nanoparticles identified in the image (a–d). i–l Particle size distribution histogram

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Fig. 3
figure 3

The influence of AgNO3 concentration on the diameter of Ag nanoparticles

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Figure 4 displays the X-ray diffraction (XRD) patterns for the Ag nanoparticles for different concentration molarities (1.18, 3.5, 5.88, and 8.24 mM), verifying their face-centered cubic lattice structure. All the Ag nanoparticles display consistent diffraction profiles, featuring distinct peaks at 2θ angles of 38.5°, 44.5°, 65.0°, 77.5°, and 82.0°. These peaks correspond to the (111), (200), (220), (311), and (222) crystallographic planes of face-centered cubic crystals, respectively. The data obtained is in well agreement with the literature report of JCPDS-File No. 04-0783 [19, 20].

Fig. 4
figure 4

X-ray diffraction pattern of the silver nanoparticles for different concentration molarities (1.18, 3.5, 5.88, and 8.24 mM) deposited on a glass substrate

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Raman Spectroscopy of Ag Nanoparticles

Surface enhanced Raman spectroscopy (SERS) is a well-known and extensively researched technique for characterizing metal nanoparticles. To determine the possible functional groups of capping agents involved in the stability of silver nanoparticles [21], Raman spectrum of the Ag nanoparticles was recorded as shown in Fig. 5. It consists of vibrational modes at 248, 360, 482, 585, 652, 1098, 1347, and 1580 \({\text{cm}}^{-1}\). The P. palaestina leaf extract contained several organic constituents such as carboxylic and hydroxyl groups. In Raman spectra, the peak at 248 \({\text{cm}}^{-1}\), which is identified and attributed specifically to the stretching vibrations found in the silver-nitrogen (Ag–N) bond [22]. The vibrational mode observed at the peak position of 360 \({\text{cm}}^{-1}\) is attributed to the in-plane bending of the C–C-Cl bond [23]. The skeletal deformation of C-N–C is observed around 482 \({\text{cm}}^{-1}\) [24]. The features at 585 \({\text{cm}}^{-1}\) assigned to skeletal deformation of C-S-C. The other band at 652 \({\text{cm}}^{-1}\) was related to stretching S − C. The peak 1098 \({\text{cm}}^{-1}\) belongs to in-plane C − C − H bend and C − C − S bend [25]. The peak at 1347 \({\text{cm}}^{-1}\) is linked to bending (CH2) and bending (C − O − H) and the symmetric in plane C − C ring stretching is observed at around 1580 \({\text{cm}}^{-1}\) [26, 27]. Thus, from the preferential enhancement of these Raman bands, it can be concluded that the carboxylate groups of the P. palaestina are involved in the capping of the silver nanoparticles [21].

Fig. 5
figure 5

Raman spectrum and deconvolution results of silver nanoparticle deposited on glass substrate

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Absorption and Photoluminescent of P. palaestina Leaf Extract

Figure 6 illustrates the absorption characteristics of P. palaestina leaf extract, as measured by a UV–vis spectrophotometer. The absorption spectrum of P. palaestina is distinguished by prominent bands with several peaks occurring at wavelengths of 225, 267, 355, and 670 nm. The initial two peaks, at 225 nm and 267 nm, are likely due to the presence of phenolic compounds such as quinic acid, gallic acid, trigalloylglucose acid, and tetragalloylquinic acid in the leaf extract [13]. These compounds are known to serve as coating agents and play a crucial role in the reduction process during the synthesis of silver nanoparticles. The absorption peak observed at 355 nm is linked to glycerol, which plays a crucial role as a stabilizer in the synthesis of silver nanoparticles [28, 29]. Additionally, the inset of Fig. 6 highlights an absorption peak at 670 nm, suggesting the presence of chlorophyll [30, 31].

Fig. 6
figure 6

UV–Vis spectrum of the aqueous extract leaves of the P. palaestina at wavelength 200 to 800 nm

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The photoluminescence spectra of P. palaestina, depicted in Fig. 7, were observed at various excitation wavelengths, revealing distinctive features that can be attributed to specific compounds present in the sample. The spectrum suggests that tocopherols and phenols are responsible for the shorter wavelength band observed in the total fluorescence spectra. Upon exciting the solution extract from P. palaestina with a 200-nm wavelength, two prominent emission peaks are observed. The first peak, located at 248 nm, is associated with phenol compounds. The second peak, found at a position of 365 nm, corresponds to the presence of glycerol in the extract. Furthermore, when the extract is excited at a wavelength of 270 nm, both the phenolic and glycerol compounds exhibit a broad and red-shifted emission peak at 325 nm, along with a distinct shoulder at 395 nm [32], as depicted in Fig. 7b. The fluorescence analysis of P. palaestina leaf extract leverages the presence of naturally occurring fluorescent components, including phenolic compounds, tocopherols, pheophytins, and their oxidation products. These compounds demonstrate comparable UV-absorption and fluorescence characteristics, as indicated [33].

Fig. 7
figure 7

Emission spectrum of P.Palaestina leaf extract with a λex = 200 nm. b λex = 270 nm. c) λex = 420 nm. d P. palaestina leaf extract under UV light

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Figure 7c displays a prominent long-wavelength band in the spectra of P. palaestina. When excited at a wavelength of 420 nm, this band exhibits emission in the range of 600 to 750 nm. Within this spectrum, two distinct peaks are apparent: a pronounced peak at 680 nm and a broader peak around 730 nm. These peaks are indicative of the presence of chlorophyll and pheophytin, respectively. These findings align with the research reported by Musa [31], which details the distinct spectral properties typical of these compounds. The leaf extract of P. palaestina displays intense luminescence, attributed to the presence of chlorophyll. To investigate this, a UV lamp with a wavelength of 365 nm and a power of 15 W was employed. As depicted in Fig. 7d, under UV light, the leaf extract of P. palaestina exhibits a distinct pink and orange luminosity.

Absorption and Photoluminescent of Ag Nanoparticles

Silver nanoparticles (AgNPs) exhibit exceptional optical properties, including absorption and photoluminescence, which are influenced by their size, shape, and surrounding medium. The hallmark of these properties is surface plasmon resonance (SPR), which results in a strong absorption band in the visible spectrum, giving AgNPs distinct colors. AgNPs can also exhibit photoluminescence by absorbing and re-emitting light at longer wavelengths, although this effect is typically more subtle compared to other materials [34]. Figure 8 illustrates the UV–visible absorption spectra of silver nanoparticles (AgNPs) at different silver ion concentrations: 1.18, 3.5, 5.88, and 8.24 mM. Silver features free electrons on its surface, and the observed surface plasmon resonance (SPR) absorption band is formed by the synchronous resonance of these electrons with the electromagnetic wave of the incoming light. This UV–vis spectroscopy analysis is crucial for monitoring the reduction process from Ag+ to Ag0. The appearance of peaks in the spectra signifies the SPR characteristics of AgNPs [35].

Fig. 8
figure 8

UV–visible absorption spectra of silver nanoparticles for different concentration molarities (1.18, 3.5, 5.88, and 8.24 mM)

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Each sample’s spectrum predominantly shows a single absorption peak. The SPR bands were found within the 395 to 398 nm range, consistent with typical properties of silver nanoparticles. Variations in the SPR band, attributed to aggregated and different-sized nanoparticles, were observed, as highlighted by Bamsaoud et al. [36].

Furthermore, the position of the SPR band in UV–Vis spectra is affected by several factors: particle size, shape, dynamics of charge transfer between the nanoparticles and the medium, their interaction with the medium, and the local refractive index [37]. Photoluminescence serves as a key technique in determining the optical characteristics of silver nanoparticles as photonic materials. Investigations included recording fluorescence emission at various concentrations under two excitation wavelengths: 210 nm and 250 nm as shown in Fig. 9a, b. This analysis revealed multiple emission peaks in fluorescence, spanning a range of 300 to 800 nm. Notably, each excitation wavelength produced distinct, intense peaks which were consistent across all concentrations tested. The fluorescence of these nanoparticles varied with the excitation wavelength. A notable observation was a sharp peak at 365 nm, a shoulder peak at 395 nm, and broader peaks at 470, 640, 700, and 740 nm. Peaks at 365 and 470 nm were aligned with surface plasmon resonance seen in UV–visible spectroscopy, suggesting that fluorescence mainly arises from single-electron transitions between specific energy states [38]. Excitation at the shorter wavelength of 210 nm resulted in a pronounced emission peak at 365 nm, alongside weaker and broader peaks at 395, 470, 640, and 740 nm. Conversely, excitation at the longer wavelength of 250 nm reduced the intensity of the 365 nm peak while enhancing and broadening other resonance peaks at 475 and 700 nm. This variance in excitation and emission is attributed to the presence of both small and large nanoparticles, as well as aggregated nanoparticles [39, 40]. As the excitation wavelength increases, the emission peak’s intensity diminishes, and the 365-nm peak experiences a slight red shift. The red shift observed in the fluorescence spectrum occurs because electrons are energized to energy levels that are lower when exposed to longer excitation wavelengths. Consequently, their relaxation also happens at these extended wavelengths [41]. Furthermore, as the excitation wavelength lengthens, it may deviate from the nanoparticles’ optimal resonance conditions. This deviation can result in a diminished light absorption efficiency, which in turn causes a decrease in the intensity of the emission. Additionally, quantum confinement in nanoparticles plays a significant role, especially as the particle size nears the exciton Bohr radius. In such quantum confined states, the electronic properties of the nanoparticles differ from those in bulk materials, influencing the absorption and emission spectra. The interaction between the increased excitation wavelength and this quantum-confined states can cause alterations in the emission spectrum, manifesting as shifts in its characteristics [42, 43].

Fig. 9
figure 9

Photoluminescence spectra of silver nanoparticles of various concentrations AgNO3 at different excitation wavelengths: a 210 nm and b 250 nm

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Conclusion

This research successfully establishes a cost-effective, environmentally friendly method for synthesizing AgNPs using native P. palaestina leaf extract, offering a sustainable alternative to conventional chemical methods. The resultant nanoparticles were spherical and varied in size from 2 to 27 nm, with a notable correlation between the concentration of silver nitrate (AgNO3) and nanoparticle size—higher AgNO3 concentrations resulted in smaller nanoparticles. Scanning probe microscopy (SPM) effectively analyzed their height and morphology, while X-ray diffraction (XRD) analysis confirmed their crystalline nature. The study’s investigation into various properties of the Ag nanoparticles, using techniques like Raman spectroscopy, UV-visible absorption, and photoluminescence (PL), yielded significant findings. Raman spectroscopy identified prominent peaks at 585 cm−1 and 1580 cm−1, indicating specific molecular vibrations. The UV-visible spectrophotometry analysis observed a surface plasmon resonance (SPR) band between 395 and 398 nm, which is characteristic of Ag nanoparticles. The photoluminescence properties varied with the excitation wavelength, showing distinct peaks at 365 nm, a shoulder peak at 395 nm, and broader peaks at 470 and 690 nm. These variations in photoluminescence are indicative of the diverse electronic environments within the nanoparticles. Additionally, the optical analyses of the P. palaestina leaf extract revealed the presence of significant bioactive compounds such as polyphenols, glycerol, and chlorophylls. These compounds likely contribute to the effective reduction and stabilization of the Ag nanoparticles. This study not only advances the understanding of green synthesis of nanoparticles but also highlights the potential of using natural extracts in nanotechnology, opening avenues for environmentally friendly and sustainable synthesis methods. The ability to tune these optical properties by altering the size, shape, and dielectric environment of the nanoparticles adds to their versatility and appeal in scientific and industrial applications. Therefore, future research could explore further optimization of synthesis parameters to fine-tune nanoparticle properties for specific applications, as well as investigate the broader implications of using green synthesis methods in various fields.