A sustainable approach using green synthetic magnetic iron oxide nanoparticles for Cu2+ and Ni2+ removal and dye adsorption from wastewater

Abstract Water scarcity is an escalating global issue, with industrial water consumption contributing significantly to the problem. As a result, an effective water treatment is essential to ensure clean water availability. Conventional treatment methods, such as chemical precipitation and ion exchange, are effective but often costly and energy-intensive. Alternatively, the microbial synthesis of magnetic iron oxide nanoparticles (MIONPs) offers a green, sustainable approach. Biologically synthesized MIONPs have broad applications in environmental engineering, medicine, and material science. In this study, MIONPs were synthesized using Bacillus sp. RAS02, a bacterium isolated from the industrial wastewater of Alshafae Company for Leather Tanning Manufacture. Characterization confirmed the nanoparticles consist primarily of magnetite (Fe₃O₄), with 93.56% iron oxide content. The MIONPs were spherical, with particle sizes ranging from 5.77 to 21.05 nm, and showed an absorption band at 459.06 cm⁻ 1 , indicating the presence of Fe–O bonds. Magnetic saturation was measured at 49.29 emu/g. Optimization of MIONP synthesis using a 2ⁿ factorial experimental design revealed that cell biomass, metal concentration, and reaction time significantly influence nanoparticle formation. These MIONPs demonstrated strong potential for wastewater treatment due to their biocompatibility, low toxicity, and effectiveness in heavy metal ion removal. Cu 2 ⁺ was removed by 76.64% at pH 2.5 and 96.74% at pH 6, while Ni 2 ⁺ was removed by 70.59% and 94.89%, respectively. Additionally, the MIONPs achieved 80% decolorization of methylene blue dye in approximately five hours, indicating their utility in treating dye-contaminated wastewater.