Hydrothermal preparation of Nickel oxide nanoparticles for photocatalytic removal of Congo red and antibacterial applications

Nickel oxide nanoparticles were successfully synthesized using a simple hydrothermal method and systematically characterized for photocatalytic and antibacterial applications. The UV–visible absorption spectrum revealed strong absorption in the ultraviolet region, and the optical band gap from the Tauc plot was estimated to be 3.4 eV, indicating semiconductor behaviour. FTIR analysis confirmed the formation of Ni–O interactive bonding from a characteristic vibration at 429 cm⁻¹ . The powder XRD patterns also showed well-defined diffraction peaks, which corresponds to the cubic phase of NiO. The morphology of NiO nanoparticles were seen in SEM images, which demonstrates the agglomerated porous nanoparticles and EDX analysis justifies the presence of Ni and O elements with high purity. XPS results revealed the oxidation states and bonding interactions of NiO nanoparticles. The photocatalytic activity of NiO nanoparticles toward Congo red dye exhibited 83.2% degradation within 60 min, following pseudo-first-order kinetics with a rate constant of 2.62 × 10⁻² min⁻¹ . The influence of pH 7 and catalyst dosage on the degradation efficiency was optimized. Scavenger studies exhibits that superoxide radicals and holes were the dominant reactive species. The photocatalyst retained good stability with minimal decrement in efficiency after five cycles. Antibacterial activity of NiO nanoparticles was tested against Staphylococcus aureus and Klebsiella pneumoniae , showed strong activity with inhibition zones of 11.5 mm and 18.4 mm (25 and 50 µg/mL) for S. aureus and 13.6 mm and 18.8 mm for K. pneumoniae . These results demonstrates that NiO nanoparticles exhibit efficient photocatalytic degradation and promising antibacterial activity for environmental remediation applications.