Microstructural investigation and magnetic studies on sonochemically synthesized Ni-substituted copper zinc ferrite nanoparticles for heterogeneous green catalytic click chemistry and dye degradation

Abstract

Cu_0.5Ni_0.3Zn_0.2Fe₂O₄ nanoparticles were synthesized via a sonochemical method and annealed at 600 °C to achieve a pure crystalline spinel phase. Rietveld refinement of the X-ray diffraction (XRD) pattern confirmed the phase purity, crystallite size and cationic distribution. FESEM and HRTEM images revealed that the nanocrystals are highly agglomerated due to strong magnetic interactions among the nanoparticles. EDAX was employed to confirm the elemental composition of the synthesized Cu_0.5Ni_0.3Zn_0.2Fe₂O₄ nanoferrite. HRTEM analysis also ruled out the presence of any impurity phases. Fourier-transform infrared spectroscopy (FTIR) revealed characteristic metal–oxygen stretching vibrations at the tetrahedral lattice sites, while UV-vis spectroscopy showed a direct optical band gap of 2.23 eV. Magnetic measurements demonstrated near-saturation in the M–H loops in the low-field region (∼2000 Oe), indicating strong ferromagnetic behavior due to the presence of divalent Ni²⁺ ions in the spinel lattice. Photocatalytic studies using rhodamine-B dye under visible light irradiation showed that the degradation efficiency of CuFe₂O₄ (55%) increased to 78% with combined Zn and Ni doping. Kinetic analysis showed that a pseudo-second-order model was followed with a correlation coefficient of R² = 0.995. The catalyst also exhibited good recyclability, retaining photocatalytic activity over three consecutive cycles. Cu_0.5Ni_0.3Zn_0.2Fe₂O₄ nanoparticles served as an efficient heterogeneous catalyst for three-component Huisgen 1,3-dipolar CuAAC “click” reactions in aqueous media. The catalyst's stability, reusability, and ease of magnetic separation highlight its green chemistry potential. These multifunctional nanoparticles show great promise as visible-light-active photocatalysts and sustainable catalysts for organic transformations, contributing to key Sustainable Development Goals (SDGs).