Causonis trifolia- based green synthesis of multifunctional silver nanoparticles for dual sensing of mercury and ferric ions, photocatalysis, and biomedical applications

Abstract

Health and environmental concerns are often raised by the development of antibiotic resistance and water contamination from various aquatic contaminants, including antibiotic residues, dyes, and heavy metal ions. This paper outlines a facile, affordable, and eco-friendly way to address these issues by green synthesis of silver nanoparticles (CT@AgNPs) under sunlight irradiation using Causonis trifolia leaf extract (CTLE), known for its medicinal properties. The greenly synthesized CT@AgNPs exhibited antioxidant, antibacterial, and photocatalytic properties and were an effective nanoprobe for the selective detection of Fe³⁺ and Hg²⁺ in water. CT@AgNPs were thoroughly examined using several sophisticated analytical methods, including FTIR, UV-vis spectroscopy, Scanning electron microscopy (SEM), Powder X-ray diffraction (PXRD), Energy dispersive X-ray (EDX), and Zeta potential (ZP). FTIR demonstrated the effective functionalization of CT@AgNPs with the polar leaf extract of Causonis trifolia. The optical properties of CT@AgNPs in solution were monitored using UV-vis spectrophotometric analysis. The synthesis of spherical shaped CT@AgNPs with a face-centered cubic geometry and a 12.7 nm average crystallite size was assessed by SEM and XRD, respectively. CT@AgNPs showed a potent antibacterial activity against Gram-positive bacteria (L. monocytogenes and S. epidermidis) and Gram-negative bacterial strains (P. aeruginosa and B. bronchiseptica). CT@AgNPs showed high sensitivity for colorimetric detection of Hg²⁺ and Fe³⁺ with a limit of detection of 1.04 μM and 47.57 μM, respectively in spiked water samples, highlighting their potential for use in environmental monitoring applications. CT@AgNPs showed remarkable antioxidant ability, assessed by DPPH, TFC, and TPC assays. On exposure to sunlight, CT@AgNPs also showed good photocatalytic capability by degradation of methyl orange (79%) and crystal violet (77%) with rate constant values of 0.0157 min^-1, and 0.0150 min^-1, respectively. This work demonstrates the potential of green route-synthesized AgNPs as efficient and sustainable materials for biomedical and environmental applications.

Fig. 1. Schematic representation of CTLE and the biogenic synthesis of CT@AgNPs.

Fig. 2. (a) UV vis. spectrum of CT@AgNPs indicated by solid line and UV vis. Spectrum of Causonis trifolia extract indicated by dotted line, (b) band gap energy calculaions of CT@AgNPs using Tauc plot, (c) FTIR spectra of pure leave extract CTLE (black line) and CT@AgNPs (red line), respectively, and (d) PXRD analysis of greenly synthesized CT@AgNPs.

Fig. 3. (a) SEM image of CT@AgNPs, (b) EDX analysis of CT@AgNPs, (c) ZP analysis of CT@AgNPs.

Fig. 4. (a) UV-vis spectra of CT@AgNPs along with various heavy metal ions, (b) bar graph for change in absorbance, and (c) photographic illustration of interaction of CT@AgNPs with different heavy metal ions.

Fig. 5. (a) UV-vis spectra of CT@AgNPs with various dilutions of Hg²⁺ ions, (b) determination of LOD using calibration curve between change in absorbance and concentration, and (c) photographic illustration of colorimetric sensing of Hg²⁺ ions with naked eye using CT@AgNPs.

Fig. 6. (a) UV-vis spectra of CT@AgNPs with varying concentrations of Fe³⁺ ions, (b) LOD determination using a calibration curve between change in absorbance and concentration, and (c) colorimetric assay of Fe³⁺ ions with the naked eye using CT@AgNPs.

Fig. 7. (a) Bar graph of inhibition zones of CT@AgNPs, standard antibiotic erythromycin, and CTLE, (b) DPPH assay of CT@AgNPs compared with standard antioxidant (ascorbic acid), (c) TFC assay of CT@AgNPs along with quercetin, (d) TPC assay of CT@AgNPs compared with gallic acid.

Fig. 8. (a) Absorbance sectrum of methyl orange dye after regular intervals of time, (b) absorbance sectrum of crystal violet dye after regular intervals of time, (c) dye degradation (%) versus time graph for methyl orange and crystal violet dyes (d) reaction kinetics plot of degradation of methyl orange and crystal violet dyes.

Fig. 9. (a) Effect of dye concentration on degradation efficiency, (b) effect of catalyst dose, (c) effect of pH, (d) effect of radical scavengers on degradation efficiency.