Influence of Floral Extract Phytochemistry on the Structural and Optical Properties of Green-Synthesized Iron Oxide Nanoparticles

Nanomaterials have become indispensable in modern scientific and technological domains due to the exceptional properties that distinguish them from their bulk counterparts. Defined by dimensions typically below 100 nanometers, these materials display enhanced surface-area-to-volume ratios, which directly contribute to superior chemical reactivity, improved catalytic behavior, size-dependent optical features, and the emergence of quantum confinement effects. These attributes have significantly advanced their use in various sectors, including environmental remediation, medical diagnostics, targeted drug delivery, sensors, and energy conversion and storage systems [1, 2].

Among the various classes of nanomaterials, iron oxide nanoparticles (Fe₂O₃ NPs) have attracted particular attention owing to their low toxicity, environmental stability, magnetic responsiveness, and biocompatibility. Their utility spans a broad spectrum of applications such as water purification, magnetic hyperthermia, lithium-ion batteries, and biosensing platforms. The ability to tailor their morphology, crystallinity, and surface chemistry at the nanoscale makes them highly versatile for integration into functional devices [3, 4].

In recent years, the focus has shifted toward green synthesis methods, which utilize biological entities such as plant extracts as reducing and capping agents to replace hazardous chemicals typically used in traditional physical or chemical nanoparticle production. This eco-friendly synthesis approach aligns with the 12 principles of green chemistry and offers a sustainable, low-cost alternative that minimizes environmental impact while ensuring nanoparticle stability and uniformity [5].

In this context, the present study employs floral extracts from Rosa damascena (Damask rose), Rosa chinensis (China rose), and Moringa oleifera as bio-reductants and stabilizers for the synthesis of Fe₂O₃ nanoparticles. These botanical sources are known to contain diverse phytochemicals, including flavonoids, polyphenols, terpenoids, and alkaloids that facilitate the reduction of ferric ions (Fe³⁺) and control the growth of nanoparticles in aqueous solution. The selection of these specific plants was motivated by their high content of bioactive compounds, long-standing use in traditional medicine, broad ecological availability, and proven biocompatibility. Moreover, their comparative analysis under identical synthesis conditions enables the evaluation of how variations in phytochemical composition affect the nucleation and stabilization of nanoparticles [6, 7].

The underlying mechanisms by which plant-derived phytochemicals facilitate nanoparticle formation primarily involve redox and capping processes. Compounds such as polyphenols, flavonoids, terpenoids, and saponins can donate electrons to ferric ions, reducing them to Fe₂O₃ nuclei while undergoing oxidation themselves. For example, phenolic hydroxyl groups may oxidize to quinones as they reduce Fe⁺³ to Fe⁺² or Fe₃O₄. Simultaneously, these phytochemicals adsorb onto the nanoparticle surfaces, forming a protective organic layer that inhibits agglomeration and allows for better control over particle size and shape. This dual functionality reduction and stabilization is fundamental to the green synthesis strategy and underscores its value as a safer, scalable, and environmentally conscious alternative to conventional methods [8, 9].

While various biological systems, such as algae and fungi, have been employed in green nanoparticle synthesis due to their enzymatic or polysaccharide-based reducing capabilities, these methods often require sterile cultivation conditions, longer synthesis durations, and more complex handling. In contrast, floral extracts provide a simpler, more accessible alternative that leverages naturally abundant phytochemicals for rapid and effective nanoparticle formation [10, 11]. This study thus highlights the comparative advantage of flower-based synthesis in terms of operational ease, sustainability, and phytochemical diversity.

By exploring these natural extracts for nanoparticle synthesis, this work contributes not only to the advancement of green nanotechnology but also offers insights into the design of scalable, biocompatible methods that leverage abundant plant-based resources. The novelty of this study lies in its comparative evaluation of three distinct floral systems and their effectiveness in modulating nanoparticle characteristics under standardized parameters.

3.1 X-ray diffraction analysis

Figure 2 shows the XRD analysis of the crystalline structure of the iron oxide nanoparticles synthesized using green methods. The diffraction patterns for all three samples showed characteristic peaks indicating a crystalline structure with varying degrees of crystallinity. The major diffraction peaks were observed at 2θ values of approximately 30°, 33.35°, 35.5°, 43°, 53.5°, 57°, and 62.6°, corresponding to the 220, 311, 311, 400, 422, 511, and 440 crystal planes, respectively. These peaks are consistent with the standard diffraction patterns of magnetite (Fe₃O₄) and maghemite (γ-Fe₂O₃) phases, indicating successful formation of iron oxide nanoparticles through thermal decomposition of ferric chloride at 300–400℃ [12].

Figure 2. The X-ray diffraction (XRD) of the prepared compounds

Although all samples exhibited similar peak positions, indicating the formation of comparable iron oxide phases, variations in peak intensity and width were observed. These differences reflect variations in crystallite size, purity, and degree of structural order among the samples, which are directly influenced by the type and composition of the plant extract used during synthesis.

Sample 1, prepared using Rosa damascena extract, showed the sharpest and most intense peaks, suggesting a higher degree of crystallinity and purity. This can be attributed to the high concentration of bioactive compounds such as phenolic acids, flavonoids, and anthocyanins, which are known to act as strong reducing and stabilizing agents during nanoparticle synthesis [13]. These compounds promote controlled nucleation and growth of iron oxide nanoparticles, resulting in well-ordered crystalline structures [14].

Sample 2, synthesized using Moringa oleifera extract, displayed slightly broader and less intense peaks, indicating lower crystallinity compared to Sample 1. Moringa is rich in proteins, amino acids, and polysaccharides, which also possess reducing capabilities, but may lead to less uniform nucleation and stabilization compared to polyphenol-rich extracts [15].

Sample 3, derived from Rosa chinensis extract, showed the weakest and broadest peaks, pointing to reduced crystallinity and less ordered structures. This may be due to the lower antioxidant content and higher fiber composition in the plant matrix, which limit the efficiency of reduction and stabilization processes during nanoparticle formation [16].

In addition to the qualitative observations, a comparative analysis of the full width at half maximum (FWHM) values of the most intense diffraction peaks was conducted to quantitatively assess the crystallinity of the synthesized nanoparticles. Sample 1 (Rosa damascena) exhibited the narrowest FWHM values, confirming the presence of well-crystallized particles with minimal lattice strain. In contrast, Samples 2 and 3 showed broader peaks, indicative of smaller crystallite sizes and higher defect densities. This trend supports the earlier qualitative interpretation, suggesting that the phytochemical composition of each extract significantly influences the nucleation rate, growth kinetics, and final crystal quality of the iron oxide nanoparticles.

The observed differences in crystallinity and peak sharpness among the three samples may be directly attributed to the nature and concentration of plant-specific phytochemicals involved in the synthesis process. For instance, Rosa damascena contains a high abundance of phenolic compounds and flavonoids, which not only facilitate efficient reduction of Fe³⁺ ions but also promote uniform nucleation and limit structural defects, leading to higher phase purity. In contrast, the relatively broader peaks in Moringa oleifera and Rosa chinensis samples suggest less ordered crystalline phases, potentially due to less effective capping or slower reduction kinetics caused by proteins or fibrous components.

These findings reinforce the idea that phytochemical diversity and concentration in plant extracts play a crucial role not only in initiating nanoparticle formation but also in determining the structural integrity and phase quality of the final product.

3.2 Field Emission Scanning Electron Microscopy analysis

Figure 3 presents the FESEM images of iron oxide nanoparticles synthesized using Rosa damascena, Moringa oleifera, and Rosa chinensis extracts. The images reveal that the particles generally exhibit a quasi-spherical morphology with varying degrees of surface roughness and aggregation. Notably, significant agglomeration is observed in all three samples, which is commonly attributed to the intrinsic magnetic interactions and high surface energy of iron oxide nanoparticles.

Figure 3. Field Emission Scanning Electron Microscopy (FESEM) of the prepared compounds

Sample 1 (Rosa damascena) displayed the formation of unique nanotube-like structures with diameters reaching approximately 70.3 nm. This suggests a directional growth behavior potentially induced by specific phytochemicals such as flavonoids and anthocyanins present in the extract. Sample 2 (Moringa oleifera) exhibited a dense assembly of larger spherical particles with average sizes around 100.1 nm, whereas Sample 3 (Rosa chinensis) showed smaller, more irregular particles averaging 26.8 nm in diameter.

The differences in particle size and morphology across the samples can be directly correlated with the composition of the plant extracts used in the green synthesis. Polyphenol-rich extracts (e.g., Rosa damascena) appear to support more controlled nucleation and growth, while protein- or fiber-dominant extracts (e.g., Moringa and Rosa chinensis) may lead to less uniform stabilization.

Although the green synthesis route effectively produced nanoscale structures, the presence of pronounced agglomeration remains a notable limitation. No surfactants or dispersion techniques were applied in the current synthesis, which may have allowed for secondary clustering. To address this in future work, the incorporation of biocompatible surfactants (such as PVP or CTAB) or the application of ultrasonication could be considered to improve dispersion and reduce aggregation while maintaining green chemistry principles.

3.3 Atomic Force Microscopy analysis

Figure 4 shows the AFM of the samples, revealing fine details of the distribution and height of nanoparticles on the sample surface.

Figure 4. Atomic Force Microscopy (AFM) of the prepared compounds

AFM images showed that the samples synthesized via green methods exhibited significant variation in particle size and distribution, along with a relatively rough and irregular surface. This variation is attributed to the interaction of natural organic compounds present in the plant extracts used during the synthesis process, which directly influences the final surface morphology of the nanoparticles [17-19].

3.4 Ultraviolet–Visible spectroscopy analysis

Ultraviolet–Visible (UV–Vis) spectroscopy was employed to investigate the optical properties of the synthesized iron oxide nanoparticles. The measurements were conducted in the spectral range of 200–800 nm to identify the characteristic absorption behavior of the samples prepared using different plant extracts (Figure 5).

Figure 5. Ultraviolet–Visible (UV–Vis) of the prepared compounds

All three samples exhibited distinct absorption bands within the 200–500 nm range. Prominent peaks were observed at approximately 270–280 nm and 360–370 nm, along with a weaker absorption band around 420 nm. These bands are primarily attributed to Ligand-to-Metal Charge Transfer (LMCT) transitions from oxygen ligands to Fe³⁺ ions, as well as d–d electronic transitions within the iron ions themselves [20]. Similar absorption features have been consistently reported in the literature for iron oxide nanoparticles synthesized via green methods [21].

Notably, Sample 3, synthesized using Rosa chinensis (Chinese rose) extract, demonstrated the highest absorbance intensity across the measured range. This suggests enhanced stabilization of the nanoparticles, likely due to the presence of phenolic compounds and flavonoids in the extract. These biomolecules serve not only as reducing agents but also as effective capping agents, preventing nanoparticle agglomeration and promoting the formation of smaller, more monodisperse particles with higher optical activity [22].

These findings underscore the significant role of the phytochemical composition of the plant extract in modulating the optical and structural characteristics of the resulting nanoparticles.