Table 1 determined the phytochemicals analysis of B. pinnatum (aqueous extract). The steroids, alkaloids, flavonoids, tannins, saponins, and reducing sugar were found in B. pinnatum leaf extract. Terpenoids and Glycosides were absent in the extract. Kavit et al., (2013) reported the medicinally active phytoconstituents like tannins, alkaloids, terpenoids, steroids, and saponins in the leaves of Phyllanthus fraternus.
CHARACTERIZATION OF SiNPs
UV-Visible absorbance spectroscopy is broadly being utilized as a technique to determine the optical properties of nanosized particles. The result obtained from the analysis of UV-Visible spectroscopy of the sample is presented in Figure 2. The SiNPs formation was confirmed by the peak occurrence in the range between 230 to 300 nm in UV spectra because of the Surface Plasmon Resonance nature of silica nanoparticles in the reaction medium. The optical feature is similar to earlier report (Djangang et al., 2015) and indicated to Si-O-Si bond approving the existence of silica nanoparticles. Babu et al., (2018) were analysis the optical properties of Cynodon dactylon assisted silica nanoparticles using the UV-Visible spectroscopy and obtained the peak at wavelength at 350 nm in UV spectra.
The nature of biogenic SiNPs was evaluated from the X-Ray Diffraction pattern. The most substantial peaks at 2theta values of 22.01 correspond to the amorphous nature of SiNPs and are shown in Figure 3.The average size of the SiNPs was calculated by Debye-Scherrer's formula. The size of the B. pinnatum leaf extract mediated SiNPs is 24 nm. Mohd et al., (2017) carried out the XRD analysis to find out the crystalline nature and size of the sugarcane bagassemediated nanomaterials. The XRD was used to confirm the formation of amorphous silica nanoparticles from palm kernel shell ash by the modified sol–gel extraction method (Imoisili et al., 2020).
The elemental composition and purity of B. pinnatum leaf extract mediated SiNPs were determined by the EDAX analysis. Figure 4 shows the EDAX spectrum for phyto-genic mediated SiNPs. The atomic percentages of carbon (21.68%), oxygen (50.95%), and silica (27.37%) were present in green synthesized SiNPs. The carbon was derived from plant extract. The SiNPs were synthesized by Dubey et al., (2021), and they assessed the level of its composition. They reported the presence of silica and oxygen with no other impurities.
The shape or morphology of the synthesized SiNPs was determined by the SEM analysis. The microscopic images of B. pinnatum leaf extract mediated SiNPs are presented in Figure 5 and clearly show the distribution and spherical shape of the SiNPs. The synthesized silica nanoparticles were spherical in shape and agglomerated because of existence of biomolecules from B. pinnatum leaf extract. Adebisi et al., (2020) reported the production of biogenic SiNPs using maize stalk and determined its morphology using the SEM analysis. It is worthy to note that the outcome of SEM analysis is compared to Zamani et al., (2020), and spherical shaped silica nanoparticles have been produced using the extract of Saccharomyces cerevisiae confirmed by SEM analysis.
FT-IR spectra of plant extract and SiNPs are shown in Figures 6 a and b. The peaks such as 3348, 2970, 2885, 1921, 1658, 1442, 1087, 879, 671, and 555 cm-1 are in Figure 4 a and correspond to the hydroxyl, amide, and carboxyl functional groups. The spectrum of SiNPs shows the peaks such as 2978, 2893, 1589, 1396, 1143, 1072, 956, 678, and 555 cm-1. Agreeing to result of FT-IR (Figure 4a) it was detected that the chemical bond of silicon and oxygen in the biogenic silica nanoparticles. The peaks of 1072, 956, 678, and 555 cm-1 are referring to the Si-O-Si bonds. The intense peaks of 2978, 2893, 1589, 1396, 1143 cm-1 were corresponding to C–H stretching, hydroxyl, amide, and carboxyl functional groups which were derived from B. pinnatum leaf extract. FT-IR study was determined the functional groups of capping, reducing, and stabilizing agents from B. pinnatum leaf extract to form the nanomaterials. Anuar et al., (2020) were found the functional groups or chemical groups, namely Si-O-Si, CH2, -OH, and Si-OH form the FT-IR spectrum of coconut husk ash mediated silica nanomaterials.
Zeta potential analysis is a traditional method to determine the stability of the nanomaterials. The SiNPs from B. pinnatum show negative charges and the zeta potential value of -32.4 mV (Figure 7). The high value of zeta potential refers to the stability of the suspension due to the increased force of electrostatic repulsion between the particles. The low zeta potential value indicates the aggregation of the nanomaterials (Wang et al., 2010). The SiNPs with antibacterial properties were produced by Joni et al., (2020). In addition, they reported the zeta potential value of −24.69 mV for the SiNPs.
Thermal stability of synthesized SiNPs was performed to determine the weight loss of green synthesize SiNPs at different temperatures (the range between 30 to 1000°C) (Figure 8 a & b). It was obtained that, mass of the SiNPs decreased in two stages on different temperature range of 30°C - 800°C. At first stage, 53.8% of mass loss was acquired at a temperature of 250°C because of evaporation of water molecules on surface of silica nanoparticles. In the second stage, about 7.6% of mass loss was obtained at the temperature ranges from 300 – 800°C due to the vaporization of the remaining residue of the phyto-compounds. The mass reduction of bio-synthesized silica nanomaterials was assessed by the exothermic peak in the DTA curve. The similar results were reported by Maroušek et al., (2022) and Sankareswaran et al., (2022).
SEED GERMINATION ASSAY
Different concentrations (5, 10, 15, and 20 μg/mL) of SiNPs were used in the present investigation. The maximum level (100%) of seed germination was achieved on 5 μg/mL SiNPs treated treatment, and meanwhile, the minimum level (40%) of seed germination was observed on 20 μg/mL of SiNPs treated treatment. The increased shoot length of 4.3 cm was observed on the treatment of 5 μg/mL SiNPs, and decreased shoot length of 1.8 cm was achieved with a concentration of 20 μg/mL of SiNPs. The highest root length (1.0 cm) was observed on T2 treatment (5 μg/mL of SiNPs), and the lowest root length (0. 2 cm) was recorded on T4 treatment (20 μg/mL of SiNPs) (Table 2). Results showed that SiNPs have a significant effect on seed germination, the length of the shoot, and the root. Roohizadeh et al., (2015) observed that SiNPs improved the seed germination on Vicia faba.