Stepwise surface-functionalized magnetic Fe3O4@SA@PANI@ZnO nanocomposite: An enhanced photocatalyst for the degradation of methyl orange dye

Abstract

Effective removal of synthetic dye pollutants from wastewater is vital for safeguarding aquatic ecosystems and public health. Among these pollutants, methyl orange (MO), a widely used anionic azo dye, is of particular concern owing to of its high chemical stability, toxicity, and resistance to conventional treatment methods. Developing efficient, reusable, and environmentally friendly photocatalysts for dye degradation remains a critical challenge in wastewater treatment research. In this study, a novel, stepwise-functionalized magnetic nanocomposite (Fe₃O₄@SA@PANI@ZnO), was synthesized via a simple co-precipitation approach. The design comprised a Fe₃O₄ magnetic core for easy recovery, sequential functionalization with salicylic acid (SA) for improved surface anchoring, grafting with conductive polyaniline (PANI) to enhance charge transfer, and deposition of ZnO nanoparticles to provide active photocatalytic sites. Structural, morphological, and chemical properties of the composite were systematically characterized using advanced analytical techniques. Photocatalytic activity was evaluated by monitoring MO degradation under ultraviolet (UV) irradiation. The Fe₃O₄@SA@PANI@ZnO nanocomposite achieved nearly complete discoloration and significant mineralization, exhibiting a degradation efficiency of 98 % and a reaction rate constant of 0.146 min⁻¹. These values significantly outperformed those of Fe₃O₄, Fe₃O₄@SA, and Fe₃O₄@SA@PANI. Moreover, the nanocomposite retained excellent catalytic activity over five reuse cycles, highlighting its stability, recyclability, and promise for sustainable wastewater treatment applications.