Magnetic rod-like MIL-88B(Fe)/CoFe2O4 metal–organic framework decorated with Bi2O2CO3 nanoparticles for efficient catalytic reduction of toxic nitrophenols

Abstract

In this study, ternary magnetic rod-like nanocomposites of Bi₂O₂CO₃/MIL-88B(Fe)/CoFe₂O₄ were successfully synthesized using a straightforward hydrothermal method. The process involved the integration of different amounts of bismuth subcarbonate (Bi₂O₂CO₃) nanoparticles with an iron-based rod-like metal–organic framework (MIL-88B(Fe)) and magnetic CoFe₂O₄ nanoparticles. A range of analytical techniques, including Fourier transform Infrared (FT-IR) spectroscopy, X-ray diffraction (XRD), Raman spectroscopy, energy dispersive X-ray spectroscopy (EDX), field emission scanning electron microscopy (FE-SEM), vibration sample magnetometry (VSM), Brunauer–Emmett–Teller analysis, and zeta potential measurements were employed to examine the structural characteristics, composition, crystallinity, morphology, magnetic properties, surface area, and surface charge of the resulting nanocomposite. The nanocomposite demonstrated significant catalytic activity in the reduction of nitroaromatic compounds specifically 4-nitrophenol (4-NP), 2-nitrophenol (2-NP), 4-nitroaniline (4-NA), and 2-nitroaniline (2-NA) in aqueous solutions, utilizing sodium borohydride (NaBH₄) as a reducing agent at room temperature. Notably, rapid reduction rates were observed under the selected conditions, with 4-NP being reduced in 14 minutes (k_app = 0.162 min⁻¹), 2-NP in 25 minutes (k_app = 0.105 min⁻¹), 4-NA in 8 minutes (k_app = 0.405 min⁻¹), and 2-NA in 10 minutes (k_app = 0.272 min⁻¹). Additionally, the Bi₂O₂CO₃/MIL-88B(Fe)/CoFe₂O₄ catalyst could be readily separated from the reaction mixture using an external magnetic field and was found to be recyclable up to four times without a notable decrease in catalytic performance. Even after four uses, the catalyst retained its stability, original structure, crystalline nature, and morphology.