Sustainable photocatalytic detoxification of organic azo dyes using nickel manganite spinel nanoparticles

Abstract

This study presents a sustainable and efficient approach for wastewater remediation using pristine NiMn<inf>2</inf>O<inf>4</inf> (NMO) spinel nanoparticles (NPs) as a photocatalyst to degrade toxic industrial dyes. Unlike conventional methods, the NMO NPs based system operates without requiring Fenton reagents (e.g., H<inf>2</inf>O<inf>2</inf>) or pH adjustments, offering a cost-effective, scalable, and environmentally friendly solution. The NMO NPs were synthesized via a simple co-precipitation route and exhibit a tetragonal crystalline structure, with an average particle size of ~100 nm, high surface area (~3.32 m2/g), and a visible-light-responsive bandgap of 1.75 eV. Under Xenon (Xe) lamp irradiation, these NMO NPs demonstrated exceptional photocatalytic degradation efficiency, achieving over 93 % removal of both cationic dyes (Crystal Violet (CV) and Malachite Green (MG)) and anionic dyes (Acid Fuchsin (AF) and Rose Bengal (RB)) within 180 min. The apparent rate constants for CV and MG degradation were calculated to be 0.013 and 0.014 min−1, respectively. Radical scavenging experiments indicated that hydroxyl (·OH−) and superoxide (·O2−) radicals played dominant roles in the degradation mechanism. Furthermore, LC-MS analysis revealed the stepwise degradation pathway of MG, involving demethylation, hydroxylation, oxidation, and deamination, leading to harmless by-products. This work establishes pristine NMO as a promising, reagent-free photocatalyst for real-world dye contaminated water treatment applications. © 2025 Elsevier B.V., All rights reserved.