One-Pot biogenic synthesis of mesoporous Nickel Ferrite for sustainable degradation of bromothymol blue Dye

Abstract In this study, biogenic nickel ferrite (NiFe 2 O 4 ) nanoparticles were successfully synthesized using Costus speciosus extract via a green, eco-friendly method without the need for hazardous chemical reagents. This synthesis leveraged the phytochemical content of the extract as a natural reducing and stabilizing agent. The resulting NiFe 2 O 4 was calcined at 800 °C to enhance its crystallinity, structural integrity, and functionalty performance. Structural and morphological characteristic of the sample was confirmed through x-ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive x-ray spectroscopy (EDX). Fourier-transform infrared spectroscopy (FTIR) verified the formation of the spinel ferrite structure, while Brunauer–Emmett–Teller (BET) analysis revealed a mesoporous texture with a surface area of 19.7 m 2 g −1 and an average pore diameter of 18.92 nm. Vibrating sample magnetometry (VSM) demonstrated the ferrimagnetic nature of NiFe 2 O 4 , with a saturation magnetization of 42.78 emu g −1 . Optical analysis determined a direct bandgap energy of 1.68 eV and a positive surface charge (+5.57 mV), favoring photocatalytic activity. Photocatalytic experiments showed efficient bromothymol blue (BTB) degradation under visible light, achieving 94% removal within 30 min at pH 8.0. The kinetics followed a pseudo-first-order model with a rate constant of 0.084 min −1 . These results highlight the potential of green-synthesized NiFe 2 O 4 as a highly efficient, magnetically recoverable photocatalyst for sustainable environmental remediation applications. For reference, metallic nickel nanoparticles (NiNPs) were synthesized under similar green conditions using the same plant extract; however, they were not used for photocatalytic testing. Instead, NiNPs were characterized by XRD, SEM, and EDX to enable direct comparison with the NiFe 2 O 4 phase and to highlight the synthetic versatility of the plant-mediated route.