Green and Chemical Synthesis of Silver Nanoparticles: A Comparative Study for Optical, Morphological, Structural, and Antibacterial Activities

Two different methods (chemical and biological) are used to synthesize silver nanoparticles in this study. Silver nitrate was reduced using NaOH in a chemical method, while in a biological approach, Ag ions were reduced with an aqueous leaf extract of Tridax procumbens. Both types of synthesized nanoparticles were characterized using FT-IR, UV-Visible, XRD, PL, DLS, ZE, and SEM with EDAX. The X-ray diffraction (XRD) patterns established the incidence of a crystalline face centred cubic (FCC) structure in both nanoparticles samples. The average nanoparticles sizes were 29 nm for the chemically produced nanoparticles and 18 nm for the biologically synthesized ones. SEM analysis revealed a spherical shape for both types of nanoparticles, with average sizes of 36 nm for the chemically produced and 25 nm for the biologically synthesized nanoparticles. The surface plasmon resonance (SPR) peaks were observed at 384 nm for the chemically synthesized nanoparticles and at 424 nm for the biologically synthesized ones. FT-IR analysis indicated that O-H, C=O, and C-O-C functional groups were involved in the formation of Ag nanoparticles, with a zeta potential of -27.83 eV, exhibited long-term stability and resistance to agglomeration compared to the chemically synthesized nanoparticles, which had a zeta potential of -9.46 eV. Photoluminescence (PL) analysis demonstrated an enhanced visible spectrum for the nanoparticles. Additionally, the antibacterial activity tests showed that the biosynthesized Ag nanoparticles were more effective than the chemically synthesized ones. This enhanced activity was attributed to the protein capping and the mode of entry into bacterial cells, making the biosynthesized nanoparticles more potent. The study concluded that biosynthesized Ag nanoparticles exhibit a smaller crystalline size, better morphology, and more significant antimicrobial activity compared to their chemically synthesized counterparts.