pH independent adsorption: Reusable zinc-ferrite nanospheres for the selective recovery of dyes from binary mixtures

Efficient separation of colorant pollutants is a formidable challenge, prompting research into innovative materials. We developed zinc-ferrite nanoparticles via the Microwave-Assisted Solvothermal Technique (MAST), exploiting judicious solvent compositions to enhance Lewis's acidity. Upscaling to gram batches yielded nanoparticles with a higher specific surface area (149 m²g⁻¹). These nanoparticles demonstrated selective separation of dyes from binary mixtures, including Orange-G (OG), Fluorescein-Sodium (FSS), and Methyl-Orange (MO), with their high sorption rate fitting to the pseudo-second-order kinetic model. Langmuir isotherm for OG and MO were observed with respective adsorption capacity (q_m) of 94.12 mg/g, 104.28 mg/g, whereas FSS more likely matched Sips isotherm with q_m = 124.31 mg/g at natural pH in room temperature (27 °C). Desorption, reliant on solution pH and OH⁻ ions, enabled efficient regeneration and multiple reuses without significant efficiency loss over five reuse cycles. Remarkably, selective separation was independent of surface charge and remained effective across a wide pH range and in the presence of common anions, namely I⁻, NO³⁻, C₂H₃O₂⁻ routinely encountered in dye effluents. This ecologically safe, scalable adsorbent offers a promising solution for expensive dye recovery.