Marine alga-mediated facile green synthesis, antibacterial and enhanced catalytic activity of highly stable superparamagnetic NiO nanostructure

A facile ecofriendly green synthesis method for highly stable nickel oxide nanoparticles have been developed using aqueous extract of a marine edible alga, Ulva sp.. The formation of nanoparticles was confirmed by a distinct broad band at 314 nm in the UV-Vis spectrum. The optical band gap of the NiO nanoparticles is estimated to be similar to 3.54 eV. The occurrence of nu(Ni-O) band at 612 cm(-1) in the FT-IR spectrum confirmed the formation of the NiO. The XRD profile suggested a fcc lattice structure with average nanoparticles size of 12.29 nm. The microstrain and the dislocation density values calculated from the Williamson-Hall (W-H) plot suggested a defect rich NiO nanostructures, which was also corroborated by Raman spectroscopy. The NiO NPs exhibited superparamagnetic behavior. The HR-TEM analysis revealed predominantly spherical and quasi-spheroidal NiO NPs with size in the range of 5-20 nm. Retrievable and reusable the as-prepared nanoparticles served as efficient catalyst for almost complete and faster reduction of 4-nitrophenol at low catalyst concentration. Further, the biogenically accessed NiO nanoparticles showed pronounced antimicrobial activity.