Wood Fiber/Iron Salicylate Composite for Organic Dye Removal in Water Purification: Adsorption and Visible Light-Assisted Degradation

Abstract Cost-effective, nature-based advanced materials offer highly promising platforms for sustainable removal of recalcitrant dyes in water treatment technologies. In the present work, wood fibers (WFs) act as renewable support, providing essential anchoring functionalities, structural robustness, and chromophore units on the lignocellulose surface. The covalent immobilization of iron salicylate—a bio-derivable catalyst characterized by strong Fe(III) coordination and high oxidative stability—was achieved under ecofriendly microwave heating conditions, yielding iron loadings of 0.5 at %. The WF-[Fe(Sal)] material showed remarkable trade-off between catalytic activity and stability throughout photocatalytic dye degradation, in the presence of visible light and H2O2. Cationic dyes, rhodamine B (RB) and methylene blue (MB), were removed through a synergistic mechanism of adsorption and catalytic degradation, while the removal of the anionic dye, indigo carmine, was primarily driven by oxidative degradation. Under optimal conditions, cationic dye removal efficiencies as high as 97% for RB and 89% for MB within 150 min were achieved in the presence of H2O2 vs 82% for RB and MB in the absence of H2O2. As for the anionic dye indigo carmine, 93% removal was obtained in the presence of H2O2 vs 8% in the absence of H2O2. Furthermore, the catalytic material maintained its structural and chemical integrity over five cycles, with no detectable iron leaching.