Cobalt oxide nanoparticles (Co₃O₄-Nps) have many applications and now a days the green methods of synthesis of these NPs are preferred over other methods because of associated benefits. In this study, Co₃O₄-Nps were synthesized by using leaves extract of Populus ciliata (safaida) and cobalt nitrate hexa hydrate as a source of cobalt. The synthesized NPs were analyzed by different techniques such as fourier transform spectroscopy (FTIR), x-ray diffraction (XRD), transmission electron microscopy (TEM) and scanning electron microscopy (SEM). Antibacterial activities of the synthesized Co₃O₄-Nps were evaluated against gram negative and gram positive bacteria and found active against Escherichia coli (E. coli), Klebseilla pneumonia (K. pneumonia), Bacillus subtillus (B.subtillus) and Bacillus lichenifermia (B. lichenifermia). The activity results were analyzed statistically by one-way ANOVA, with ‘Dunnett’s Multiple Comparison Test’. The maximum mean activity (21.8 ± 0.7) was found for B. subtilis and minimum mean activity (14.0 ± 0.6) was observed for E. coli.

The tin dioxide nanoparticles (SnO₂ NPs) were fabricated via eco-friendly process using Daphne mucronata (D. mucronata) leaves extract as capping and reducing agent. The N₂ adsorption/desorption experiment was performed to determine the surface area by Brunauer–Emmett–Teller (BET) method and S_BET was found to be 147 m² g⁻¹. The crystalline nature and lattice parameter was studied by x-ray diffraction (XRD) and calculated crystallite size is 15.63 nm. The surface morphology was examined by scanning electron microscopy (SEM) and the estimated average particle size is 64 nm. The percentage composition and purity of the SnO₂ NPs was determined by energy dispersive x-ray (EDX). The raman active modes were identified by using raman spectroscopy while functional groups upon the surface were studied by using fourier transform infrared (FTIR) spectroscopy. The photocatalytic performance of SnO₂ NPs was examined against Rhodamine 6G (R6G) and 99.70% rhodamine 6G (R6G) were degraded in 390 min with the degradation rate of 0.0148 per min. The SnO₂ NPs were screened against the selected microorganisms and the order of antimicrobial activity is given as; Gram negative bacteria (GNB) > Gram positive bacteria (GPB) > fungi.

The cobalt oxide nanoparticles (Co₃O₄ NPs) were synthesized via the green method using Piper nigrum (P. nigrum) leaves extract and were calcined at different temperatures. The crystalline nature was studied through x-ray diffractometer (XRD). With increasing calcination, the amorphous phase transitioned to the crystalline phase. Diffuse reflectance spectroscopy (DRS) was used to observe UV-Visible light absorbance phenomenon, and Tauc’s plot was used to calculate the band gap energy, which was found to decrease with calcination. Scanning electron microscopy (SEM) was used to analyze the surface morphology, and Fourier transform infrared (FTIR) spectroscopy was used to classify the surface functional groups. The antibacterial efficacy of the Co₃O₄ NPs was examined against Gram-positive bacteria (GPB) and Gram-negative bacteria (GNB), whereas its antioxidant potential was explored against ABTS free radicals. Antibacterial and antioxidant potentials of Co₃O₄ NPs were found to decrease with increasing calcination.

The aim of this study was to explore the antibacterial and antioxidant efficacy of nickel oxide nanoparticles (NiO NPs). The Raphanus sativus (R. sativus) extract mediated NiO NPs were calcined at 100, 300, 600 and 900 ℃ in a muffle furnace for 3 h. The increased intensity of diffraction bands in the X-ray diffraction (XRD) spectrum suggest that the degree of crystallinity increases with increasing calcination temperature. The desired elements was depicted in the energy dispersive X-rays (EDX) spectrum confirm the purity of the NiO Sample. The variation in surface morphology and increase in the particles size from 12.78 to 51.42nm was determined from the transmission electron microscope (TEM) micrographs. The shift toward higher wavelength was observed in the diffuse reflectance spectroscopy (DRS) spectra with increasing calcination temperature, results into a clear decrease in band gap from 3.12 to 2.86 eV. The presence of hydroxyl group along with other organic moieties were confirm through Fourier transform infrared (FTIR) spectroscopy analysis. The biological potential of the calcined NiO NPs was examined during the antibacterial and antioxidant experiments. The antibacterial effect of NiO NPs was studied using the agar well diffusion process, and the ABTS free radical scavenging potential of NiO NPs was also assessed. The activity of NiO NPs calcined at 100 °C is greater than that of those calcined at higher temperatures.

The Tin dioxide nanoparticles (SnO₂ NPs) were synthesized by modified microemulsion method and were screened for antibacterial and antioxidant applications. The crystalline nature was explored by using x-ray diffraction (XRD) analysis and the calculated crystallite size is 24.68 nm. The morphology was examined by scanning and transmission electron microscopies (SEM and TEM) and particles based on TEM image is 79.10 nm. The elemental analysis was performed by energy dispersive x-ray (EDX) and only desired elements was detected. The optical activity was investigated using diffuse reflectance spectroscopy (DRS) and band gap derived via Tauc plot is 2.82 eV. The surface functional moiety was detected by Fourier transform infrared spectroscopy (FTIR). The agar well diffusion technique was manipulated to screen the SnO₂ NPs against selected bacteria whereas DPPH free radical scavenging activity was also performed. The activity of both samples was noticed to increase with increasing the amount of samples in the experiment. The SnO₂ NPs with IC₅₀ value of 1.50 g was found more active than the ascorbic acid with IC₅₀ of 2.42 g.