Correlating pH-controlled green synthesis of NiO nanoparticles with their magnetic properties and catalytic performance

Nickel oxide nanoparticles (NiO) were prepared through environmentally friendly methods, using Nigella sativa seed extract as a stabilizing agent and different pH for the working solutions (pH=7, 9 and 11, respectively). In a second step, these NiO NPs were characterized with various and complementary techniques, as X-ray diffraction (XRD), Fourier transfer infrared spectroscopy (FTIR), Brunauer-Emmett-Teller method (BET), scanning electron microscopy (SEM) with EDS profiles, and a vibrating sample magnetometer (VSM). XRD patterns confirmed the one and only formation of NiO, as revealed by the Rietveld refinement procedure. The use of Williamson equation showed a significant variation in structural and microstructural parameters. Fourier transfer infrared spectroscopy (FTIR) analysis revealed vibration modes specific to Ni-O nanomaterials at 470 cm-1. On the other hand, magnetic investigations highlighted the fact that NiO, obtained in a solution with a pH equal to 9,called NiO-9, has the highest Ms and Mr values, of the order of 1.524 and 0.084 emu/g respectively, thus improving its ferromagnetic performance. Moreover, in the presence of NaBH4 and with the aim to reduce 4-nitrophenol to 4-aminophenol, in the case of water treatment, it appeared that the total time for the catalytic activity of NiO-9 was the lowest, i.e., 30 min. Moreover, NiO-9 was characterized by the faster rate constant, namely 0.29 min-1, which could be linked to intrinsic properties of this material (microstrain, electroactive sites and generated carrier charges).