Bandgap engineering of Tb-doped CoNiFe2O4-rGO composites for photocatalytic dye degradation

Abstract

This study developed a magnetically recoverable, solar-driven photocatalyst for methylene blue (MB) dye mineralization. Three materials were synthesized: cobalt-nickel ferrite (CNFO), terbium-doped CNFO (Tb-CNFO), and a reduced graphene oxide composite (Tb-CNFO@rGO), using wet-chemical and ultrasonication methods. Structural, optical, compositional, and photocatalytic properties were evaluated. X-ray diffraction confirmed a cubic spinel phase with crystallite sizes of 16, 22, and 19 nm for CNFO, Tb-CNFO, and Tb-CNFO@rGO, respectively. Tauc plot analysis indicated bandgap reductions from 2.98 eV (CNFO) to 2.28 eV (Tb-CNFO) and 1.53 eV (Tb-CNFO@rGO). UV-Vis spectroscopy showed enhanced visible-light absorption for Tb-CNFO@rGO. EPR analysis identified hydroxyl (·OH) and superoxide (O 2 − ) radicals as dominant species. Tb-CNFO@rGO exhibited superior photocatalytic activity, with a rate constant of 0.030 min −1 , significantly higher than CNFO and Tb-CNFO, and retained 85.6% activity after five cycles via facile magnetic separation. These results demonstrate Tb-CNFO@rGO as an efficient, reusable photocatalyst for solar-driven dye wastewater treatment.