Binary metal oxide nanocomposites have attracted significant attention as efficient photocatalysts due to their enhanced charge separation and synergistic interfacial interactions. In this study, a NiO/Cr₂O₃ binary metal oxide nanocomposite was successfully fabricated using a simple and cost-effective chemical synthesis route and systematically characterized for its photocatalytic degradation of methylene blue (MB) under light irradiation. Structural and phase analysis using X-ray diffraction confirmed the coexistence of crystalline NiO and Cr₂O₃ phases without the formation of secondary impurities. Morphological investigations by electron microscopy revealed a nanoscale heterostructured architecture with improved surface contact between the constituent oxides. Optical studies demonstrated enhanced visible-light absorption and a reduced effective band gap for the nanocomposite compared to pristine NiO and Cr₂O₃, facilitating efficient photo-induced charge carrier generation. The photocatalytic performance of the NiO/Cr₂O₃ nanocomposite exhibited significantly higher degradation efficiency of methylene blue than the individual metal oxides, attributed to improved charge transfer across the heterojunction and suppressed electron–hole recombination. The NiO/Cr₂O₃ nanocomposite demonstrated superior photocatalytic activity compared to individual oxides, achieving over 92% degradation of MB within 120 minutes. Kinetic analysis followed pseudo-first-order reaction behavior, confirming the superior catalytic activity of the binary system. The enhanced photocatalytic mechanism was further elucidated through reactive species involvement, highlighting the dominant role of hydroxyl and superoxide radicals. These results demonstrate that the NiO/Cr₂O₃ nanocomposite is a promising visible-light-driven photocatalyst for the treatment of organic dye pollutants in wastewater.

Keywords: NiO/Cr₂O₃ Nanocomposite; Photocatalysis; Methylene Blue; Wastewater Treatment;