Efficient preparation of Fe3O4@BH4− and Ag@BH4− NPs with antioxidant activity by a homogenous and recyclable TAIm[BH4] reductive ionic liquid: selective reduction of 4-nitrophenol to 4-aminophenol

An efficient and mild protocol was developed for the reduction of 4-nitrophenol to the 4-aminophenol in the presence of recyclable silver (Ag@BH₄⁻ NPs) and magnetite nanoparticles (Fe₃O₄@BH₄⁻ MNPs). The NPs were characterized by TEM, HRTEM, UV–Vis, TGA, VSM, XRD, EDX, XPS, and DLS analyses. The reduction was conducted in the absence of any external reducing agent like NaBH₄ underwent ultrasound irradiation at 60 °C for 2 h. Also, in the presence of TAIm[BH₄] ionic liquid, the reduction was performed under normal conditions (no need to ultrasound irradiation) and gave quantitative yield for 4-aminophenol at room temperature. TAIm[BH₄] ionic liquid (density = 1.42 g/cm⁻³, viscosity = 1165 cP), as a new reducing agent was applied for the efficient preparation of Ag@BH₄⁻ NPs and Fe₃O₄@BH₄⁻ MNPs, with a mean diameter and zeta potential of 26 nm, 16 nm, and – 40 mV and – 55 mV, respectively. It was suggested that TAIm[BH₄] ionic liquid plays the role of a capping agent in addition to reducing capability in order to metal NPs preparation, which improves the dispersion stability of the NPs with a negatively charged zeta potential resulted in the decreased agglomeration of NPs. The NPs as well as TAIm[BH₄] ionic liquid showed high antioxidant activity evaluated by DPPH assay, which the total DPPH quenching was observed at 180 μg/mL. Also, TAIm[BH₄] IL showed a 70% inhibitory effect at a concentration of 200 μg/mL. The Ag@BH₄⁻ and Fe₃O₄@BH₄⁻ NPs follows first-order kinetics for the reduction of 4-NP with the reaction rate of (6.75 × 10^–3 s⁻¹) and (5.6 × 10^–3 s⁻¹), respectively. A reasonable mechanism was suggested based on the observation and literature review. A new approach to synthesis of reductive Ag and Fe3O4 NPs with high antioxidant activity was introduced by TAIm[BH4] reductive ionic liquid for the efficient reduction of 4-NP to 4-AP. [ABSTRACT FROM AUTHOR]