Silver nanoparticles were prepared through an environmental friendly and cost-effective plant-mediated technique, using crude extracts of Welsh onion plant. The synthesized nanoparticles were characterized using UV-vis spectrophotometer, powdered X-ray diffractometer (p-XRD), Fourier transform infra-red (FTIR) spectrophotometer, and transmission electron microscope (TEM). Silver nanoparticles of different sizes and morphologies were obtained by varying some synthesis parameters such as concentrations of AgNO3 (1, 2 and 5 mM) and ratio of the volume of the plant extract to AgNO3 (1:5 and 1:10) at constant reaction temperature of 80 °C. The difference in the reaction conditions showed significant effects on silver nanoparticles obtained. The surface plasmon resonance (SPR) varied with change in concentration of AgNO3 and the ratio of the AgNO3 to the plant extracts. The lowest SPR appeared around 412 nm (2 mM; 1:10), while the largest was achieved around 427 nm (5 mM; 1:10). FTIR results revealed the presence of different characteristic functional groups responsible for the bioreduction of silver ions in Welsh onion extract. Transmission electron microscopy (TEM) showed that the lowest average particle size of the silver nanoparticles was 3.74 nm (2 mM; 1:10), while the highest was 15.72 nm (1 mM; 1:5). Monodispersed spherical shaped nanoparticles were obtained from the 2 mM concentration of the AgNO3, while particles with some degree of agglomeration were obtained from 1 and 5 mM concentration. The p-XRD studies revealed face centred cubic structures. The nanoparticles obtained from 1 and 5 mM (1:5) gave moderate photo-catalytic potentials in the degradation of methyl red dye. However, the photocatalytic property increased with increase in the concentration of the precursor salt (AgNO3) from 1 to 5 mM. Gram positive Staphylococcus aureus and Bacillus cereus and Gram negative Klebsiela pneumonia and Escherichia coli bacteria strains were susceptible to the silver nanoparticles (2 mM). The nanoparticles were most active against E. coli with a minimum inhibitory concentration (MIC) below 0.05 mg/mL. The silver nanoparticles could become potential compounds in the future antibiotic research.

The green synthesis of silver nanoparticles using Cyamopsis tetragonoloba plant extract, and their photocatalytic and antibacterial properties is reported. Three precursor concentrations of 1 mM, 2 mM and 5 mM were used, and at two different ratios of 1:5 and 1:10 plant extract to the precursor. The formation of the nanoparticles was followed by the periodic study of surface plasmon resonance using the UV-visible spectroscopy, which revealed the formation of nanoparticles with regular bands after 45 min. of reaction. Fourier transform infrared spectroscopy was used to study the functional groups present in the plant biomolecules which aided the reduction and stabilization of the nanoparticles. Transmission electron microscopy analysis and X-ray diffraction pattern showed the particle sizes and crystalline structures, while the zeta potential values indicated the stability of the nanoparticles. The 5 mM concentration gave the largest particle sizes of about 12.90 nm and the most stable particles. The photocatalytic properties of the particles studied using Methyl red showed a low efficiency of 17.85% degradation achieved under 2 h. The antibacterial potency of the nanoparticles was screened against some Gram-negative and Gram-positive bacteria. The results showed that the nanoparticles have good antibacterial activities.