The antioxidant and photocatalytic activity of Artemisia stelleriana-based silver nanoparticles (AS-AgNPs) was investigated in this study. Microscopic, X-ray diffraction and spectroscopic studies were used to characterize the synthesized AS-AgNPs. UV–visible spectrophotometric examination revealed a peak at 425 nm. The phytocompounds involved in the transformation of silver ions into AS-AgNPs were confirmed using Fourier-transform infrared spectroscopy analysis. The crystalline nature of the AS-AgNPs was verified using the X-ray powder diffraction technique. Spherical-shaped AS-AgNPs with a size of 22.7 nm were proved using field emission scanning electron microscopy. The AS-AgNPs were top-notch photocatalysts for the degradation of Reactive Blue-222A (RB-222A) and Reactive Blue-220 (RB-220) dyes. After 80 min of UV light exposure, AS-AgNPs degraded RB-222A and RB-220 dyes by 94.6 and 90.8%, respectively. The phytotoxicity investigation in Vigna radiata and Artemia salina indicated that the hazardous dye can be degraded into innocuous chemicals by AS-AgNPs. The results suggest that AS-AgNPs are an excellent antioxidant and photocatalyst for the degradation of synthetic dyes.
Silver nanoparticles (AgNPs) were synthesized using Artemisia stelleriana leaves.
Spherical-shaped AgNPs with 22.7 nm size were detected.
Degradations of Reactive Blue-220 and Reactive Blue-222A dyes were validated owing to the photocatalytic activity of AgNPs.
Low toxicity was observed during the toxicity analysis of the degraded dye.
AgNPs also showed significant antioxidant potential.
The pharmacological values of plants are the reason for their utilization in treating various infections or diseases from the former age (Sofowora et al. 2013). Plants are utilized in multiple fields due to their excellent properties (Prabhu & Poulose 2012). Green synthesis is a part of nanotechnology where plants are widely used as reducing, capping and stabilizing agents (Hussain et al. 2016). The plant extract which contains numerous phytochemical compounds can reduce the metal ions to metal/metal oxide nanoparticles (NPs) (Kumar et al. 2021). Utilization of plant extract in NP synthesis is an alternative to chemical and physical synthesis (Beyene et al. 2017). Plant extract-based NP synthesis is pollution-free, non-toxic, more sustainable and eco-friendlier (Ying et al. 2022). One to a hundred nanosized particles have promising activities like antioxidant, antimicrobial, anticancer, antidiabetic, cytotoxic, anthelminthic, and photocatalytic activities.
Silver nanoparticles (AgNPs) have been reported for different medical properties, so it is used as an alternative medicine for numerous health conditions (Danish et al. 2022). It is also reported for other applications like biosensing and photocatalytic activities. AgNPs can remove or degrade the dyes utilized in different industries (Prasher & Sharma 2023). The distinct size, shape, and surface characteristics of AgNPs are responsible for their degrading activity. The precise catalytic mechanism of AgNPs in different reactions can vary, although it frequently entails reactant molecule adsorption on the nanoparticle surface, followed by processes for electron transfer (Levard et al. 2012).
Artemisia stelleriana is an aromatic herb commonly known to be old women, dusty miller and beach wormwood due to its physical appearance. The plant contains compounds like flavonoids, alkaloids, monoterpenes, sesquiterpenes, vitamins, minerals and other compounds, so it has high medicinal importance. The A. stelleriana leaves were utilized in treating peptic ulcers and hair loss. It was also reported that the leaf extract of A. stelleriana has good antioxidant activity (Mayuri et al. 2022). A. stelleriana belongs to the Asteraceae family and has been already reported for synthesizing ZnO NPs which has great photocatalytic activities (Puthukulangara Jaison & Kadanthottu Sebastian 2023).
The present study deals with the green synthesis of AgNPs from the leaf extract of A. stelleriana. Green-synthesized NPs were characterized using UV–Visible spectrophotometry (UV–Vis), X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), energy-dispersive X-ray spectroscopy (EDX), and field emission scanning electron microscopy (FESEM) and their photocatalytic and antioxidant activities. We also attempted to study the toxicity of degraded dyes using Vigna radiata and Artemia salina lethality assay.
MATERIALS AND METHODS
Plant extract preparation
Healthy leaves of A. stelleriana were weighed (10 g) and cleaned with sterile distilled water and were refluxed up to 30 min at 60 °C with 50 ml sterile distilled water and cooled. The extract was filtered using No. 1 Whatman filter paper, and the filtrate was used for the synthesis of AgNPs.
Synthesis of AS-AgNPs
The reduction of silver nitrate was confirmed after the solution mixture changed to brownish black when 50 ml of the A. stelleriana extract was added to 400 ml of silver nitrate solution (0.01 M) and made up the volume to 500 ml using sterile distilled water. Then, the mixture was stirred for 2 h at room temperature. The synthesized AgNPs were separated and purified using centrifugation (at 10,000 rpm for 10 min) (Ravichandran et al. 2019).
Characterization of AS-AgNPs
The reduction of silver ions to NPs in the extract was verified by a UV–Vis spectrophotometer (300–800 nm) (Shimadzu UV-1800ENG240V UV Spectrophotometer). The surface morphology of the synthesized AS-AgNPs was confirmed by FESEM (ZEISS Sigma HV). The elemental composition and percentage were validated by EDX analysis. The functional groups that helped in the transformation of ions to NPs were studied using FTIR (QATR-S Spectrophotometer) at a resolution of 2 cm−1 and scanning range of 500–4,000 cm−1. The crystalline nature and size of the NPs were identified using XRD analysis (Rigaku MiniFlex X-ray Diffractometer).
Similar to photocatalytic degradation, scavenging studies were determined. Along with the catalyst, 0.01 mmol of isopropyl alcohol (IPA), 0.1 mmol of ascorbic acid (AA), and 0.01 mmol of ethylenediaminetetraacetic acid (EDTA) were added to the dye to scavenge hydroxyl radicals (OH−), superoxide radicals (O2−) and holes (h+), respectively.
The degradation efficiency of AS-AgNPs and treated dye phytotoxicity reduction were determined using the V. radiata toxicity test and A. salina lethality assay. V. radiata toxicity test was performed as the previously reported method with minor changes (Dharshini et al. 2023; Puthukulangara Jaison & Kadanthottu Sebastian 2023). The V. radiata seeds were allowed to germinate in a Petri dish and subjected to untreated and treated dye solutions, respectively. After 7 days of treatment, the plant's root and shoot length toxicity were evaluated. A. salina (Brine shrimp) lethality assay was studied using an already described protocol with minor modifications (Bilal et al. 2016). In test tubes, the hatched nauplii (10 each) were exposed to untreated and treated dye solutions for 24 h and then the mortality rate (MR) was evaluated by counting the dead nauplii under a binocular microscope.
In-vitro antioxidant assay
RESULTS AND DISCUSSION
Synthesis and UV–Vis spectral analysis
Fourier-transform infrared spectroscopy (FTIR)
The FTIR spectrum helps to confirm the functional groups involved in the stabilization and reduction of Ag ions to NPs. The FTIR spectrum of A. stelleriana extract and synthesized AS-AgNPs was noticed from the range between 500 and 4,000 cm−1. The figure shows the FTIR spectral analysis of the leaf powder of A. stelleriana (Figure 1(b)) and AS-AgNPs (Figure 1(c)). The FTIR spectrum of A. stelleriana leaf powder exhibited multiple peaks at 3,325.67, 2,923.25, 2,853.64, 1,607.23, 1,417.98, 1,315.74, 1,243.96, 1,026.43 and 519.60 cm−1. The peaks at 3,325.67 and 2,923.25 cm−1 (O–H stretching), 2,853.64 cm−1 (N–H stretching), 1,607.23 cm−1 (C = C stretching), 1,417.98 and 1,315.74 cm−1 (O–H bending), 1,243.96 cm−1 (C–O stretching), 1,026.43 cm−1 (CO–O–CO stretching) and 519.60 cm−1 (C–Br stretching) may be associated with tannins, flavonoids, alkaloids, resins, saponins and phenolic compounds present in the A. stelleriana extract (Mousavi et al. 2018). The biosynthesized AS-AgNPs showed bands at 2,118.41 cm−1 (C ≡ C stretching), 1,905.23 cm−1 (C = C = C stretching), 1,504.99 cm−1 (N–O stretching) 1,365.77 cm−1 (O–H bending) and 1,017.73 cm−1 (C–F stretching). The metal-oxygen bond is ascribed to the peaks at 506.55 cm−1, confirming the synthesis of AS-AgNPs. The reduction in O–H bands and the appearance of carboxyl groups after AS-AgNPs formation could be symptomatic of redox reactions between Ag ions and biomolecules. The electron in the carbonyl group can be a reason for the transformation of Ag ions to AS-AgNPs (Laouini et al. 2021).
X-ray diffraction (XRD)
Field emission scanning electron microscopy (FESEM) and energy-dispersive X-ray spectroscopy (EDX)
It is possible that under UV light, electrons will get excited from the valence band to the conduction band which leads to the formation of photogenerated species, i.e., a positive hole in the valance band and conduction electrons in the conduction band. These photogenerated species help in the degradation of RB-220 and RB-222A dyes by developing highly reactive radicles. By interacting with water molecules, the positive holes create the hydroxyl group and hydrogen ion, which are then transformed into hydroxyl radicals. Meanwhile, the dissolved oxygen interacts with the water molecule to create the hydroxyl radical. In photocatalytic degradation, these photogenerated radicals, i.e., hydroxyl radicals and holes, play a crucial role (Shaikh et al. 2020; Bhatt & Patel 2021).
Reusability of AS-AgNPs
Brine shrimp (Artemia salina) is a model organism for toxicity studies that are true representative of aquatic life. The brine shrimp lethality test was done to know the ability to kill brine shrimp nauplii hatched in the laboratory within a certain period. After one day, it was noticed that all the brine shrimp remained alive in the artificial seawater, and in potassium permanganate solution, all nauplii were dead. It was also observed that the MR was lower in the treated effluents in comparison with the untreated effluents. When compared with all the treated samples, the maximum MR was noticed in RB-222A dye and the least mortality was observed in RB-220 dye (Figure 8(b)). The current investigation proved that Ag/Ag2ONPs synthesized from the A. stelleriana degraded the toxic compounds from textile dyes. ZnO NPs synthesized for A. stelleriana also displayed similar effects nullifying the effects of toxic dyes through brine shrimp assay and V. radiata tests (Puthukulangara Jaison & Kadanthottu Sebastian 2023).
The A. stelleriana leaf extract-mediated AS-AgNPs were synthesized and characterized using spectroscopic and microscopic analyses. The protocol adopted here is a cost-effective, simple, non-toxic and pollution-free method. Spherical-shaped Ag/Ag2ONPs with an average size of 22.7 nm were synthesized. The radical scavenging activity was observed at 600 μg/ml of AS-AgNPs. Under UV light irradiation, the synthesized NPs showed the degradation of toxic industrial dyes, RB-220 and RB-222A. The toxicity study conducted in V. radiata and A. salina also revealed that the Ag/Ag2ONPs synthesized from A. stellariana successfully reduced the toxicity of the textile dyes. The limitation of this study was that the complete recovery of NPs was not possible. The study can be further extended by developing nanomembranes or nanocapsules using AS-AgNPs, which can be utilized in the degradation of hazardous textile dyes. Future research on the production of nanomembranes or nanocapsules and their applications in both environmental and biomedical fields can be guided by the findings of this study.
DATA AVAILABILITY STATEMENT
All relevant data are included in the paper or its Supplementary Information.
CONFLICT OF INTEREST
The authors declare there is no conflict.