Visible-light induced fenton reaction by Mooihoekite (Cu₉Fe₉S₁₆) nanoparticles for rhodamine B dye degradation

In the present work, Mooihoekite (Cu₉Fe₉S₁₆) nanoparticles were synthesized by the one-pot synthesis method (CFS), and annealed at 150 °C (CFS150) and 300 °C (CFS300) for 4 h. Structural analysis shows the particles were tetragonal crystal structures, with the planes matching with standard data for Cu₉Fe₉S₁₆. The average crystallite size increased from 23 to 33 nm with increase in the annealing temperature from 0 ˚C to 300 °C. The flake-like structure is observed for Cu₉Fe₉S₁₆ annealed at 300 °C. From the optical data, the transitions are found to be directly allowed, with the band gap value of 2.29 to 2.20 eV when the annealing temperature increased from 0 to 300 °C. The particles' refractive index and optical dielectric constant were also studied using three different methods that are consistent with each other. The improved specific surface area with annealing temperature is reflected in the BET analysis and the calculated specific surface area for the samples CFS, CFS 150 and CFS 300 were 12.97, 19.02, and 22.31 m²/g respectively. The annealing at 300 °C also improved the pore size approximately 8 times, which improved dye degradation efficiency. The synthesized particles acted as a photo Fenton reagent for degrading rhodamine B dye. The results showed a degradation efficiency of 91.53% for rhodamine B dye with particles annealed at 300 °C when illuminated at AM 1.5 conditions with 250 W LED light. The results indicate that the change in morphology of Cu₉Fe₉S₁₆ nanoparticles with annealing temperature resulted in enhancing the specific surface area, which improves the photo Fenton dye degradation of rhodamine B dye.