Eco-friendly synthesis of NiO nanostructured photocatalyst for different environmental/wastewater treatment applications

In the present work, we report the synthesis of nickel oxide (NiO) nanoparticles (NPs) using a simple, low-cost, and eco-friendly sol-gel/auto combustion technique. Each sample was synthesized using different fuels, namely citric acid, thiourea, and glycine, respectively. The structural and morphological properties of the NiO nanoparticles were characterized using X-ray diffraction (XRD) and Field Emission Scanning Electron Microscope (FESEM), while their optical properties were analyzed via Diffuse Reflectance Spectroscopy (DRS). The electro/photocatalytic activity of the synthesized NiO samples was evaluated in the visible region using Methylene Blue (MB) dye as a model organic pollutant. Hence, among the tested samples, NiO, synthesized with thiourea as the fuel (2-NiO), exhibited the highest degradation rate (97.6 %) and the best electrocatalytic performance, with a rate constant of 0.15 min⁻¹. Additionally, 2-NiO demonstrated superior electrocatalytic activity, excellent recyclability, and operational stability. Scavenger tests confirmed the effective generation of superoxide and hydroxyl radicals, highlighting the potential of 2-NiO for environmental remediation. These results suggest that thiourea is the most effective fuel for NiO synthesis, and 2-NiO is a promising candidate for wastewater treatment applications.