Effect of hydrothermal temperature on the structural, morphological, optical properties and photocatalytic performances of cobalt sulfide nanomaterials

The powders of cobalt sulfide were successfully synthesized using hydrothermal technique at various temperatures (180, 200 and 220 °C). X-ray diffraction revealed that the resulting samples are the hexagonal CoS, and the cubic Co9S8. Fourier transform infrared further verified the cobalt sulfide formation, showing Co-S band vibrations at 600 cm-1 across all samples. Scanning electron microscopy unveiled diverse hierarchical morphologies with notable porosity. Energy-dispersive X-ray microanalysis revealed the purity of samples, showing no traces of impurities. Electrochemical impedance spectroscopy showed a charge transfer phenomenon in the high-frequency range. The optical band gap energies (Eg) were determined using the Tauc model, yielding 1.95 eV for CoS and 2.81 eV for Co9S8. The photocatalytic efficiency of cobalt sulfides for dye degradation was assessed employing methylene blue as a model colorant through photocatalytic technology. This study underscores all samples as efficient and stable photocatalysts, especially the CoS-Co9S8 mixture phases.