Precisely engineered magnetically retrievable hierarchical 3-D ZnO nanoflowers/graphene oxide/Fe3O4/Co nanocomposites for the visible light driven photocatalytic degradation of methylene blue.

The design of efficient, visible light driven, and recyclable photocatalysts is highly desirable for sustainable wastewater treatment. In this study, a rationally designed magnetically retrievable hierarchical three-dimensional (3D) ZnO nanoflower photocatalyst anchored on cobalt-decorated magnetic graphene oxide was successfully prepared and subsequently applied for the degradation of the carcinogenic and neurotoxic cationic dye-methylene blue under visible light irradiation. The distinctive flower-like ZnO structure offered a large surface area and abundant active sites, and graphene oxide worked as an efficient electron acceptor, effectively inhibiting electron-hole recombination and allowing the band gap of ZnO to be tuned to the visible region. The addition of cobalt further promoted photocatalytic activity by enhancing charge transfer, while magnetic nanoparticles enabled easy and environmentally friendly catalyst recovery. Photocatalytic degradation in a custom photoreactor achieved rapid, efficient degradation with strong recyclability across multiple cycles. Detailed structural, morphological and spectroscopic analyses confirm the successful synthesis of the hierarchical nanocomposite and reveal the synergistic effects underlying its superior performance. Compared with previously reported ZnO based photocatalysts, the hierarchical 3-D ZnO nanoflowers/graphene oxide/Fe3O4/Co nanocomposites reported in this work demonstrated improved activity and recyclability which clearly indicates its potential as a sustainable and efficient photocatalyst for the treatment of dye-polluted wastewater.