Facile Hydrothermal Synthesis of ZnSe/NiFe2O4 Nanocomposite: Kinetic and Mechanistic Insights into Methylene Blue Degradation

Abstract

This work demonstrates the fabrication of a novel composite ZnSe/NiFe₂O₄ through a facile hydrothermal route, followed by its application as a photocatalyst for the efficient sunlight-assisted degradation of Methylene Blue (MB) dye. SEM analysis of the composite revealed considerable particle agglomeration, while TEM analysis indicated rectangular and cubic nanoparticles with an average size of 17.5 nm, and the corresponding SAED pattern confirmed the polycrystalline structure of the composite. EDX analysis verified the presence of all the elements within the ZnSe/NiFe₂O₄ composite, which was further confirmed by the XPS studies. Tauc plot analysis revealed a direct band gap of 1.69 eV for the composite. Further, VSM analysis revaled that the ZnSe/NiFe₂O₄ nanocomposite exhibits a saturation magnetization (Ms) of 12.63 emu g^− 1, a coercive field (Hc) of 141.99 Oe, and a remanent magnetization (Mr) of 2.44 emu g^− 1. Additionally, it was found that the modification of the band gap and reduction in charge recombination result in the enhanced visible-light activity of the ZnSe/NiFe₂O₄ composite (reduced PL emission and increased MB dye degradation efficiency of 93% as compared to the pure ZnSe which showed 54.6% of degradation efficiency). Also, the composite has a good magnetic recoverability and operational stability with 87% of degradation efficiency remaining after four reuse cycles, showing a low level of deactivation and good structural integrity. The improved photocatalytic performance, the high efficiency of charge separation, magnetic separation, and long-term reusability of the ZnSe/NiFe₂O₄ system are the features that demonstrate the high practical importance and novelty of ZnSe/NiFe₂O₄ in contrast to traditional single-component photocatalysts. Further, kinetic studies revealed that the degradation followed pseudo-first-order kinetics with a rate constant of 0.02053 min^− 1. The underlying photocatalytic mechanism was also investigated through VB-XPS analysis, Tauc plot analysis, and scavenger studies. Additionally, LC-MS analysis confirmed that the ZnSe/NiFe₂O₄ composite effectively degrades the MB dye rather than simple decolorization.