Green Synthesis of ZnO and Co ₃ O ₄ Nanoparticles Using Giant Calotrope Leaf Extract for Antimicrobial Applications

Abstract Antimicrobial infectious diseases have been a fatal problem worldwide. In the present finding, “Giant Calotrope” leaf extract mediated zinc and cobalt oxide nanoparticles (ZnO and Co 3 O 4 NPs) were synthesized within the ratios of precursor salt to leaf extract as 1:1 (50:50), 1:2 (50:100, and 1:3 (50:150) mL using 0.5 M of precursor salts. The NPs were characterized using thermal gravimetry coupled with differential thermal analysis (TGA/DTA), X‐ray diffraction (XRD), scanning electron microscopy with energy dispersive spectroscopy (SEM‐EDS), Fourier transform infrared (FTIR) spectroscopy, transmission electron microscopy with high‐resolution transmission electron microscopy (TEM‐HRTEM), selected area electron diffraction (SAED), and ultraviolet‐visible (UV–vis) spectroscopy. TGA/DTA showed that both ZnO and Co 3 O 4 NPs were stable beginning from 500 °C to 800 °C and XRD data proves the size of ZnO and Co 3 O 4 NPs to be 29.40, 25.86, 37.01, 22.5, 14.0, and 23.3 nm for the 1:1, 1:2, and 1:3 ratios, respectively. SEM coupled with TEM‐HRTEM, SAED confirms the spherical shape of Co 3 O 4 and ZnO NPs. FTIR shows the presence of saturated and unsaturated biomolecules in the leaf of a giant calotrope. The bandgap energy of ZnO NPs was 3.46, 3.49, and 3.44 eV, and for the Co 3 O 4 NPs, 4.60, 4.80, and 4.44 eV for the 1:1, 1:2, and 1:3 ratios, respectively. The antimicrobial applications of ZnO and Co 3 O 4 NPs were investigated against Streptococcus pyogenes , Escherichia coli , and Fusarime oxysporum . Among the 1:1, 1:2, and 1:3 ratios of ZnO and Co 3 O 4 NPs , the 1:2 provides 11, 13, 10.5, and 11 mm zones of inhibition against S. pyogenes and E. coli , respectively. Similarly, the 1:2 ratios of ZnO and Co 3 O 4 NPs showed 11 and 17 mm inhibition zones against F. oxysporum .