Green synthesis of nanoparticles has received a lot of attention from scientists globally because it is eco-friendly, relatively rapid, and a cost-effective method. This work presents a method for the green synthesis of nickel oxide nanoparticles (NiO-NPs) using leaf extracts of Populus ciliata as a reducing and stabilising agent. The synthesised NiO-NPs were characterised by ultraviolet-visible spectroscopy, Fourier transform infrared spectroscopy, powder X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. It was found that the synthesised NiO-NPs shapes varied, were highly crystalline, and had a face-centred cubic geometry. The calculated crystallite size of the synthesised nanoparticles was 44 nm. Moreover, the antibacterial activity of the synthesised NiO-NPs was also conducted against Gram-positive bacteria (Bacillus subtilis, Bacillus licheniformis) and Gram-negative bacteria (Escherichia coli and Klebsiella pneumoniae). Bacillus subtillus showed a maximum inhibition zone of 28.1±1.6 mm, whereas Klebsiella pneumonia showed a minimum inhibition zone of 9.2±0.5 mm. It was also found that the antibacterial activity increased with an increase in the concentration of NiO-NPs.

Abstract The research article is based on biodiesel synthesis by the transesterification of waste cooking oil with methanol in the presence of heterogeneous catalysts prepared from different marble. Eight samples of marble were successfully converted into potential catalysts by calcination. The thermal treatment of waste marbles at 300oC-1000oC converted the metal carbonates (CaCO3) to metal oxides (CaO). The calcined marble was analyzed by chemical tests, flame atomic absorption spectroscopy (FAAS), Fourier transform infrared spectroscopy (FT-IR), and X-ray diffraction studies (XRD). The presence of CaO in these catalysts made them highly reactive for biodiesel synthesis. The basicity and percentage of calcium in marble catalysts were calculated to know their basic strength. The transesterification was performed by fast stirring using waste cooking oil, methanol and nine different types of marble catalysts for 5 min at five different conditions, i.e., room temperature, hot plate stirring, solar ordinary irradiations, solar concentrated reflected irradiations and solar concentrated refracted irradiations. The solid catalysts were easily separated from the product for re-use. All marble catalysts were found to be active and basic except one namely silver pun (I). The production of biodiesel was confirmed by ASTM standards, TLC examination and by gas chromatography (GC).