tHighly stable and magnetically recoverable MFe2O4(M = Zn, Co, Mn) spinel ferrite nanoparticles; synthe-sized using sol gel-hydrothermal technology via utilizing polyvinyl alcohol surfactant, were proposed asheterogeneous catalysts for the reduction of nitroarenes. The morphological characteristics, structuralexploration, surface, optical, vibrational and magnetic properties were performed using powder X-raydiffraction, high-resolution transmission electron microscopy, energy dispersive X-ray, N2sorptiome-try, diffused UV–vis reflectance spectroscopy, FTIR, point of zero charge, vibrating sample magnetometer(VSM) and thermokinetic analysis via TGA technique. The results showed that MnFe2O4exhibited the bestperformance in the reduction of 4-nitrophenol (4-NP), 2,4,6 tri-nitrophenol (2,4,6-NP) and 4-nitroaniline(4-NA) and revealed 100% conversion into the corresponding amino derivatives in 270 sec with rateconstant equal 0.01061 s−1, 0.01134 s−1and 0.01355 s−1, respectively. The superiority of the catalyticreduction of MnFe2O4was due to increasing the pore radius and pore volume (6.75 nm, 0.227 cm3/g) val-ues compared to other nanoferrites. The synthesized nanoferrites indicate independence of the activityon crystallite sizes due to the insignificant margin of change (from 6 to10 nm). Conversely, decreasing theactivity of ZnFe2O4was due to increasing the Zn2+ions size that induces an increase in lattice parametervalues and thus increases the long-range electron transfer between Fe2+–Fe3+ions. The MnFe2O4cat-alyst that presented the highest saturation magnetization (135 emu/g) indicated the highest reductionpotential for 4-NA comparatively in the presence of NaBH4and the reduction reaction followed pseudofirst-order kinetics. Increasing the reduction performance of 4-NA compared to other nitroaromatics onMnFe2O4was explained based on the formed intermediates, their reactivities, hydrophobicity and topoint of zero charges. It has been explored that the reduction efficacy of 4-NP was enhanced on MnFe2O4with the addition of ammonium oxalate and benzoquinone where it was inferior following the additionof tertiary-butyl alcohol. More important correlations concerning the effect of octahedral sites, residualorganics, heat of activation (Ea) and activation free energy (G*) values; determined while the removalof citrate/PVA moieties, on nitroarenes reduction rates were well scrutinized and discussed. |
