Ag-NiFe₂O₄ over Mesoporous Silica for Efficient 4-Nitrophenol Reduction: Nanocatalyst Development, Kinetics Studies and Reaction Optimization

An innovative magnetic ternary catalyst, silver-doped nickel ferrite integrated into the nanoreactor mesoporous silica (Ag-NiFe₂O₄/meso-SiO₂), has been synthesized, offering a promise in the catalytic transformation of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP). This design synergistically combines the exceptional catalytic activity of ∼3 nm silver nanoparticles (AgNPs) with the structural advantages of ordered mesoporous silica (meso-SiO₂), effectively stabilizing the nanoparticles and preventing agglomeration. The incorporation of a magnetic NiFe₂O₄ not only enhances reusability but also facilitates efficient magnetic recovery, addressing key challenges in catalyst reusability. Comprehensive characterization using XRD, FTIR spectroscopy, UV-vis DRS spectroscopy, XPS, FESEM, HRTEM, and VSM analyses confirms the material's structural integrity, mesoporosity, and robust magnetic properties. BET-BJH suface area-porosity analysis reveals a 262.18 m²/g surface area for meso-SiO₂, with pore size in the range of 7.13 nm, which can accommodate both AgNPs (3 nm) and NiFe₂O₄ (∼15-18 nm) enabling reaction inside the channels and thereby meso-SiO₂ acting as a nanoreactor for conversion of 4-NP. Employing a Box-Behnken design under response surface methodology, the catalyst achieved optimal reduction conditions; i.e., 0.2 mmol/L 4-NP, 5.3 mg catalyst, 49.1 mg NaBH₄, and a reaction time of 12 minutes. The Ag-NiFe₂O₄/meso-SiO₂ system demonstrated first order kinetics with exceptional catalytic efficiency, operational stability over five repeated cycles, and rapid magnetic separation, showcasing its potential as a model platform for sustainable nanocatalysis. This study pioneers the integration of noble-metal nanoparticles with magnetic materials inside the mesoporous nanoreactors, setting new dimensions of advanced catalytic systems in green and efficient chemical processes.