Catalytic reduction of 4-nitrophenol by means of nanostructured polymeric Schiff base complexes

Polymeric Schiff base ligands were synthesized using 2-hydroxybenzaldehyde (L²), 4-hydroxy-3-methoxybenzaldehyde (L⁴), and 5-aminoisophthalic acid. The nanostructured complexes were then synthesized using Ni²⁺, Cu²⁺, and Mn³⁺. The ligands and complexes thus synthesized were characterized using Fourier-transform infrared spectroscopy, X-ray diffraction, thermogravimetric analysis (TGA), and field-emission scanning electron microscopy. The thermal stability of the complexes was confirmed using TGA. The synthesized complexes were used as catalysts in the reduction of 4-nitrophenol (4-NP) to 4-aminophenol in an aqueous phase in the presence of sodium borohydride. In this work, the catalytic reactivity of nanostructured complexes was compared using the rate constant (k) of the reaction. The reaction time for the reduction of 4-NP was 5–14 min for different complexes. The catalytic system based on Ni²⁺/2-hydroxybenzaldehyde was the most active and displayed reusability in the reduction of 4-NP.